- Email: [email protected]
Aging Precipitation Behavior of 18Cr-16Mn-2Mo-1. 1N High Nitrogen Austenitic Stainless Steel and Its Influences on Mechanical Properties
Available online at www.sciencedirect.com
? ScienceDirect -r../
~_____
JOURNAL OF IRON AND STEEL RESEARCH, INTERNATIONAL. 2012, 19(8) : 43-51
Aging Precipitation Behavior of 18Cr-16Mn-2Mo-l.lN High Nitrogen Austenitic Stainless Steel and Its Influences on Mechanical Properties LI Hua-bing,
JIANG Zhou-hua,
FENG Hao,
MA Qi-feng, ZHAN Dong-ping
(School of Materials and Metallurgy, Northeastern University, Shenyang 110819. Liaoning, China)
Abstract: T h e solution-treated (ST) condition and aging precipitation behavior of 18Cr-16Mn-2Mo-1. 1N high nitrogen austenitic stainless steel ( HNS) were investigated by optical microscope ( O M ) , scanning electron microscope (SEM) , and transmission electron microscope (TEM). T h e results show that the ST condition of 18Cr-16Mn-ZMo1. 1N H N S with w N above 1% is identified as 1100 ‘C for 90 min, followed by water quenching to make sure the secondary phases completely dissolve into austenitic matrix and prevent the grains coarsening too much. Initial t i m e temperature-precipitation ( T T P ) curve of aged 18Cr-16Mn-2Mo-1. 1N H N S which starts with precipitation of 0. 05% in volume fraction is defined and the “nose” temperature of precipitation is found to be 850 ‘C with an incubation period of 1 min. Hexagonal intergranular and cellular CrZN with a = 0. 478 nm and c=O. 444 nm precipitates gradually increase in the isothermal aging treatment. The matrix nitrogen depletion due to the intergranular and a few cellular CrzN precipitates induces the decay of Vickers hardness, and the increment of cellular CrZN causes the increase in the values. Impact toughness presents a monotonic decrease and SEM morphologies show the leading brittle intergranular fracture. The ultimate tensile strength (U T S) , yield strength (YS) and elongation (El) deteriorate obviously. Stress concentration occurs when the matrix dislocations pile up at the interfaces of precipitation and matrix, and the interfacial dislocations may become precursors to the misfit dislocations, which can form small cleavage facets and accelerate the formation of cracks. Key words: solution-treated condition; aging precipitation behavior; time-temperature-precipitation curve; high nitrogen austenitic stainless steel ; mechanical property
T h e main properties of high nitrogen austenitic stainless steel ( H N S ) represent a combination of strength and corrosion resistance without more loss of Recent development in manufacturing H N S with high nitrogen content focuses mainly on the pressurized metallurgyC5]such as pressurized induction melting, pressurized plasma melting, pressurized electroslag remelting (PESR) , and arc slag remelting (ASRIC6’. T h e H N S with wN in excess of 1% can be obtained using the pressurized metallurgy technologies and some researches on the properties of the H N S have been carried out. T h e solution-treated ( S T ) condition of HNS with wN in excess of 1% needs systematical investigation according to the usual r e ~ e a r c h e s [ ~ -T~h~e. mechanical properties of HNS strongly depend on the wN as an
interstitial solution elementCg-’O1.Moreover, the ST H N S will show more thermal sensitivity in the heat processing such as hot rolling and welding with the increasing wN1”]. T h e austenitic matrix may decompose to form secondary phases which have been widely developed upon long-term exposures at about 900 cc12--141 Several researcher^"^-'^^ have studied
.
the aging precipitation behavior in H N S with wNbelow 1% and the mechanical properties of ST HNS. There are also some researches on the relationship between the aging precipitates and mechanical properties of 316LN and HNS with relatively lower wNc 19 - 201 . But the relationship between the aging precipitation behavior and mechanical properties of H N S needs further systematic investigation to understand the influencing mechanism especially that
Foundation Item: Item Sponsored by Key Program of National Science Foundation of China (50534010) ; Fundamental Research Funds for Central Universities of China (N100402015) Biography:LI Hua-bing(l978-1, Male, Associate Professor; E-mail: IihbBsmm. neu. edu. cn; Received Date: April 14, 2011
Journal of Iron and Steel Research, International
44
of the steel with nitrogen content above 1%. The 18Cr-16Mn-2Mo-1. 1N H N S has been successfully manufactured by a 25 kg pressurized induction furnace['''. The ST condition and aging precipitation behavior of 18Cr-16Mn-ZMc~l.1N HNS have been systematically investigated. Moreover, the influences of aging precipitates on the mechanical properties of 18Cr-16Mn-2Mel. 1 N HNS have been also illustrated.
1
VOl. 19
experiment were manufactured by a pressurized induction furnace under high purity nitrogen gas. They were supplied as plates with a thickness of 12 mm through the forging of a cast slab and subsequent hot rolling. Charpy V-notched (CVN) impact test specimens were prepared from the longest part of these quenched plates which is parallel to the rolling direction with a size of 10 mm X 10 mm X 55 'mm. T h e other hot rolled plates were extending t o 5 mm then cold rolled to 1.5 mm in thickness to prepare the tensile test specimens with a scale distance of 25 mm and a total distance of 115 mm. T h e specimens for microstructural characterization
Experimental Procedure
T h e chemical composition of current investigated material 18Cr-16Mn-2Mo-1. 1N H N S is given in Table 1. T h e ingots with wNabove 1% used in this
Table 1 Chemical composition of 1 8 C r 1 6 M r 2 M o - l . l N HNS
c 0.050
Cr
18.02
Mn 16. 10
Mo 1.96
Ni -
Si
P
0.03
0.014
were aged from 650 to 950 'C in range of 30 s to 60 min and the impact and tensile specimens were aged at 850 'C from 5 to 60 min then quenched in water. The samples for researching the microstructure were subjected to standard grinding and polishing techniques before electrolytic etching with 10% of oxalic acid ( in mass percent 1. Properly etched samples were examined on optical microscope ( O M , Carl Zeiss). The ImagePro Plus 5.0 (IPP 5.0) software for precise particle size calculation was used for statistically quantitative analysis of aging precipitation of the samples. T h e aging precipitation area percentage calculated by IPP5. 0 software was applied to replace the aging precipitation volume ratio. Three samples and lots of fields were counted for determining the initial TTP curve. T h e electronic microanalysis was carried out by scanning electron microscope (SEM, SSX-550) at 15 kV and transmission electron microscope (TEM, TECNCI G2 20) at 200 kV. Thin foils for T E M analysis were prepared by mechanical grinding down to 80 pm, and finished by a twin-jet electrolytic polishing technique using an electrolyte of 8 % of perchloric acid (in volume percent) in ethanol at -25 'C and 70 V. Vickers hardness ( H V ) was measured on hardness tester ( FM-700 1. CVN impact tests were performed on impact tester (JBW-500) and uniform tensile tests were carried out at a crosshead speed of 3 mm/min on an Instron testing machine at room temperature. T h e three samples were performed for testing the mechanical properties.
2 2. 1
(mass percent, A1
0.01
%)
0
N
Fe
0.003
1. 10
Balance
Results and Discussion Determination of ST condition
Fig. 1 ( a ) is the microstructure of hot rolled 18Cr-16Mn-2Mwl. 1N HNS without any other solution treatments. T h e secondary phases along the grain boundaries exist obviously. T o obtain the appropriate ST condition of 18Cr-16Mn-2Mo-1. 1N HNS with wNabove 1% , several ST tests with different conditions have been performed according to the usual rep o r t ~ [ ~ - " .The microstructures of ST specimens are presented in Fig. 1 (b> to (f). Several secondary phases still exist in Fig. 1 (b) and (el. The grain size is larger in Fig. 1 (d) and (f) than that in Fig. 1 (c). T h e main reason is that when wN exceeds 1% , the formation of the secondary phases in the cooling process after hot rolling will be accelerated obviously and is hardly dissolved into austenitic matrix during relatively lower temperature or shorter time solution treatment. Meanwhile, the grain will coarsen during relatively higher temperature or longer time solution treatment, which will influence the properties and application of materials. Therefore, the ST condition of 18Cr-16Mn-2Mwl. 1N HNS can be identified as 1100 'C for 90 min, followed by water quenching to make sure the secondary phases completely dissolve into austenitic matrix and prevent the grains coarsening too much. T h e ST specimens possess high strength and a certain toughness which are exhibited by the SEM morphologies of impact and tensile fracture as shown in Fig. 2. The fracture of ST
Issue 8
A g i n g Precipitation Behavior of 18Cr-16Mn-2Mo-1. 1N High Nitrogen Austenitic Stainless Steel
( a ) Un-solution-treated; ( d ) 1100 C X 1 2 0 min;
( b ) 1100 C X60 min; ( e l 1050 C X 9 0 min;
C X 9 0 min;
Microstructure of 18Crl6Mn-2Mo-1. 1N HNS under different ST conditions
Fig. 2
SEM morphologies of ST 18Cr16Mn-2Mo-1. 1N HNS at 1100 ‘c for 90 min
( b ) Tensile fracture.
specimens presents equiaxial dimples.
Aging precipitation behavior Initial TTP curve (Fig. 3 ) of aged 18Cr-16Mn2Mo-1. 1 N H N S which starts with precipitation of 0. 05% in volume fraction is defined and the “nose” temperature of precipitation is found to be 850 ‘C with an incubation period of 1 min by quantitative metallographic analysis with OM and IPP 5. 0 software. In previous research, the initial T T P curve of aged H N S which starts with precipitation of 0. 1% in volume fraction is usually defined. T h e initial TTP curves starting with precipitation of 0. 05% is more precise for determining the initial precipitation behavior than that of precipitation of 0. 1% due to the use of IPP 5 . 0 software as shown in Fig. 3. T h e
45
( f ) 1150 “CX90 min.
Fig. 1
( a ) Impact fracture;
2.2
( c ) 1100
-
1 000
$
900
-
2 E
800-
B
M
2
700
-
I
0.05%
BOO .0.1‘& 10’
Fig. 3
102
Aging time/s
lo:’
104
TTP curves of 18Cr16Mn-2Mo-l.lN HNS
microstructure of aged 18Cr-16Mn-2Mo-1. 1N H N S during isothermal aging at 850 “C is shown in Fig. 4. When the ST H N S is subjected to aging treatment for
Vol. 19
Journal of Iron and Steel Research, International
46
( b ) 1 rnin; ( c ) 5 mini (d) 10 mini ( e ) 30 min; (f) 60 rnin. Microstructure of 18Cr-16Mn-2Mo-1. 1N HNS aged at 850 'c for different aging time
(a) 0.5 min;
Fig. 4
0. 5 min, local grain boundaries become coarse by the formation of CrzN [Fig. 4 (a)]. T h e CrzN precipitates become more and coarser during the time at which the initial TTP curve starts with precipitation of 0. 05% in volume fraction [Fig. 4 (b)]. This is attributed to the long distance diffusion of solute N within the austenite matrix for a long timec2". The cellular CrzN just precipitates inward austenitic grains in aging treatment at 850 'C for 5 min [Fig. 4 (c)]. This phenomenon presents much faster than T H Lee's reports with the aging treatment at 900 'C for 1000 scS1, which can be attributed to the more wN above 1%. T h e growing up and increasing amount of cellular C r z N phase are observed with prolonging the aging time from 5 to 60 min [Fig. 4 (c) to (f)]. The CrzN precipitation content is determined by using OM and IPP 5.0 software as shown in Fig. 5. It can be seen that a monotonic increase in the volume fraction of precipitation occurs with prolonging the aging time at 850 "C. The SEM morphology and SEM energy dispersive spectrometer ( EDS) line profile of 18Cr16Mn-2Mo-1. 1N H N S are shown in Fig. 6. This result can qualitatively present that the precipitates with lamellar structure are rich in Cr and N while the adjacent matrix is depleted in Cr and N. T h e crystallographic structure of precipitates is identified by TEM and the selected area diffraction (SAD) patterns as shown in Fig. 7. T h e cellular CrzN precipitation which presents a lamellar structure has a hexagonal structure of a=O. 478 nm and c=O. 444 nm.
0
20 40 Aging timdmin
60
Fig. 5 Volume fraction of precipitation of 18Cr-16Mn2Mo-1. 1N HNS aged at 850 'c for different time
2 . 3 Influence of aging precipitation on mechanical properties Fig. 8 shows the effect of isothermal (850 'C)aging on the hardness values of 18Cr-16Mn-ZMel. 1N HNS. A pronounced increase in hardness is measured at 850 'C with the increase in aging time from 5 to 60 min. It is inferred that the presence, growth, and increased amount of cellular C r z N precipitates as revealed in Fig. 4 obtained after aging at 850 "C from 5 to 60 min cause the substantial increase in hardness. The reduction of hardness value from the ST specimen ( H V 313) to the aged one for 5 min is due to the matrix nitrogen depletion for the precipitation of intergranular and some cellular Cr2N precipitates. This result, in agreement with the previously published one, indicates that
Issue 8
Aging Precipitation Behavior of 18Cr-16Mn-2Mo-1. 1N High Nitrogen Austenitic Stainless Steel
47 *
10
5
0
6
2
10
14
(a) SEM morphology;
2
6
10
14
(b) SEM-EDS line
(c) SEM-EDS line profile of Cr element;
Fig. 6
0
Distancelpt
profile of cellular precipitation; (d) SEM-EDS line profile of N element.
SEM morphology and SEM-EDS line profile of 18Cr-16Mn-2Mwl. 1N HNS aged at 850 “c for 1 h
Fig. 7
(a) Bright field image: ( b ) SAD pattern of cellular CrzN. TEM analysis of 18C1-16Mn-2Mwl. 1N HNS aged at 850 “c for 1 h
the depletion by means of long distance diffusion of interstitial so1u t i on N element decreases the hardness of HNSCZZ1.Therefore, the cellular Cr, N is the main reason for influencing the hardness of 18Cr-16Mn2Mo-1. 1 N HNS. T h e essential effect will take place when the amount and size of cellular C r Z Narrive at a certain degree. Fig. 9 presents the plot of A,, at room tempera-
ture for 18Cr-16Mn-2Mo-1. 1 N H N S aged at 850 “C for different time. Comparing with the value of the ST specimen, the values of A,, present a monotonic decrease below 3 J with prolonging the aging time. T h e AKV of the specimen aged for 5 min is just lower than that of the ductile to brittle point of the ST specimen. It can be seen that a short time aging treatment just causes an obvious effect on the impact
Journal of Iron and Steel Research, International
48
0
Fig. 8
20 40 Aging timdmin
60
Vickers hardness of 18Crl6Mn-ZMch. 1N HNS aged at 850 “c for different time
250
150
6 p:
5(l
0 0
Fig. 9
20 40 Aginglime/min
60
Impact absorbed e n e m of 18Cr16Mn-ZMo-l.lN HNS aged at 850 “c for different time
properties of 18Cr-16Mn-2Mo-1. 1 N H N S at the precipitated sensitivity temperature. T h e formation of intergranular and cellular CrzN precipapitates is the reason for the occurrence of the extremely brittle behavior. T h e typical fracture appearances of impact tested 18Cr-16Mn-2Mo-l.lN HNS at room temperature are shown in. Fig. 10. Intergranular facets are the leading fracture mode with increasing the aging time at 850 %. T h e SEM morphologies of impact fracture are consistent with the CVN impact absorbed energy values, which are in agreement with the result in Ref. [20]. T h e fracture facets of the tested specimen aged for 5 min present the structure with tear ridge which shows the quasi-cleavage fracture. This is due to the nucleation and local growth of cellular CrzN. With increasing the aging time, the increment of the amount and size of cellular CrzN deteriorates the ability and strength of grain boundaries obviously so that the grain stripping cracks with a little deformation at room temperature. T h e leading brittle intergranular fracture at room temperature can be attributed to more precipi-
(a) 5 mini (b) 10 mini (c) 60 min. Fig. 10 SEM morphologies of fracture surfaces of 18C1-16Mn-ZMch. 1N HNS aged at 850
tates along grain boundaries and the cellular precipitates. T h e lamellar stripping structure is due to the formation of many small cleavage facets which nucleate along the precipitates. Fig. 11 shows the results of tensile tests at room temperature after the isothermal (850 %) aging treatment. T h e tensile results are in general agreement with the microstructure of aged 18Cr-16Mn-2Mo1. 1 N HNS. T h e microstructure of the aged specimens offers a gradual decay in the yield strength (YS) , ultimate tensile strength (UTS) and the elongation ( E l ) comparing with the non-aged specimen. T h e material exhibits brittleness. T h e amount of secondary phases is relevant to the mechanical properties, also the morphology is important to be noticedCz3’. For longer aging treatment from 5 to 60 mint the changed type, increased amount and grown size of
Vol. 19
c
for different time
secondary phases make the tendency of intergranular fracture more obvious and result in the deterioration of YS, U T S and El gradually. These results reveal that the cellular Cr2N can be considered as the main reason for the decrease in the tensile properties of this alloy. T h e result of YS presents different tendencies from previous report with relatively lower w [ N ] of 0. 77%c241. This is because of the cellular CrzN precipitated a t 850 ‘C for 5 min which makes more serious depletion of interstitial nitrogen atoms in austenitic matrix to increase the strength of materials. A series of SEM morphologies of tensile fracture surfaces after the isothermal (850 % > aging treatment are presented in Fig. 12. T h e intergranular fracture is the main fracture mode for the aged specimens. T h e increment of the amount and size of cellular CrzN deteriorates the ability and strength of
Issue 8
Aging Precipitation Behavior of 18Cr-16Mn-2Mo-1. 1N High Nitrogen Austenitic Stainless Steel 1 200
.YS UTS
0
Aging timdmin
Fig. 11 Variation of strength and elongation of 18C1-16Mn2Mo-1. 1N HNS at 850 “c for different aging time
*
49
*
grain boundaries. It makes the deformation along grain boundaries prior to the grain interior and the occurrence of whole grain stripping along the grain boundaries [Fig. 1 2 (a)]. With the prolongation of the aging time, the intergranular fracture and transgranular facets exist together which makes the further decrease of the strength and toughness [Fig. 1 2 (b)]. T h e cellular precipitates make many small cleavage facets nucleate along the precipitation intersection which can be seen clearly in Fig. 12 ( c > because of the difference on the main stress direction between tensile and impact test. Thin sections parallel to the
( a ) 5 mini ( b ) 10 min; ( c ) 60 min. Fig. 12 SEM morphologies of tensile fracture surfaces of 18Cr-16Mn-2Mwl. 1N HNS aged at 850 “c for different time
tensile direction are shown in the T E M morphologies of aged samples, which demonstrate the possible fracture mechanisms as shown in Fig. 13. Coherent intergranular and cellular Cr, N precipitates distributed on the grain boundaries and associated with the strain fields restrict the movement of dislocations and cause an intergranular fracture. With the coarsening of precipitation in this stage of aging treatment, this phenomenon becomes more significant. Stress concentration occurs when the matrix dislocations pile up at the interfaces of precipitation and matrix to push the leading dislocation. T h e interfacial dislocations shown in Fig. 13 may become pre-
( a ) 5 min;
cursors t o the misfit dislocations, which can form small cleavage In the present research, some phenomena can be found that the hardness values decrease from 0 to 5 min and then increase with prolonging the aging time. And the AKV,YS, UTS and the El all decrease with increment of intergranular and cellular CrzN for longer aging treatment. T h e relation among hardness, strength, toughness and plasticity is contrary t o the traditional concept. A number of experiments also are performed to test the new phenomenon, and the same result can be obtained. So the phenomenon is special for high nitrogen austenitic stainless steel with
( b ) 60 min.
Fig. 13 TEM morphologies of tensile fracture surfaces of 18Cr-16Mn-2Mwl. 1N HNS aged at 850 “c for different time
Journal of Iron and Steel Research, International
50
nitrogen content more than 1%. The special mechanical properties of high nitrogen austenitic stainless steel with aging treatment can be interpreted due to the effect of intergranular and cellular Cr2N. T h e intergranular and cellular C r z N is very prone to precipitate in the matrix and grain boundary as shown in Fig. 4 and Fig. 7, which deteriorates the ability and strength of grain boundaries and reduces the strength, toughness and plasticity of high nitrogen steels. The reduction of hardness value from 0 to 5 min is due to the matrix nitrogen depletion for relatively small number of the precipitation of intergranular and some cellular C r z N precipitates a s shown Fig. 4 ( a ) , ( b ) , and (c). With prolonging the aging time, a lot of cellular C r z N precipitates are the main cause for increasing the hardness of the steel than the matrix nitrogen depletion.
3
Conclusions
1) T h e solution-treated condition of 18Cr16Mn12Mo-1.1N H N S with wN above 1% is identified as 1100 ‘C for 90 min, followed by water quenching to ‘make sure the secondary phases completely dissolve into austenitic matrix and prevent the grains coarsening too much. 2 ) Initial time-temperature-precipitation curve of aged 18Cr-16Mn-2Mo-l.lN HNS which starts with precipitation of 0.05% in volume fraction is defined and the “nose” temperature of precipitation is found C with an incubation period of 1 min. to be 850 O Hexagonal intergranular and cellular CrZN with a = 0. 478 nm and c=O. 444 nm precipitates gradually increase in the isothermal aging treatment. 3) T h e matrix nitrogen depletion due to the intergranular and a few cellular CrzN precipitates induce the decay of Vickers hardness, and the increment of cellular CrzN causes the increase in the values. Impact toughness presents a monotonic decrease and SEM morphologies show the leading brittle intergranular fracture. T h e ultimate tensile strength, yield strength and elongation deteriorate obviously. Stress concentration occurs when the matrix dislocations pile up a t the interfaces of precipitation and matrix, and the interfacial dislocations may become precursors to the misfit dislocations, which can form small cleavage facets and accelerate the formation of cracks. References : [I]
Simmons J W. Overview: High-Nitrogen Alloying of Stainless Steels [J]. Mater Sci Eng, 1996, 207A(2): 159.
VOl. 19
Li H B, Jiang Z H , Zhang Z R, et al. Intergranular Corrosion Behavior of High Nitrogen Austenitic Stainless Steel [J]. Int J Miner Metall Mater. 2009, 16(6): 654. Li H B, Jiang Z H , Yang Y ,et al. Pitting Corrosion and Crevice Corrosion Behaviors of High Nitrogen Austenitic Stainless Steels [J]. Int J Miner Metall Mater, 2009, 16(5): 517. Li H B, Jiang Z H , Cao Y ,et al. Fabrication of High Nitrogen Austenitic Stainless Steels With Excellent Mechanical and Pitting Corrosion Properties [J]. Int J Miner Metall Mater, 2009, 16(4) : 387. Stein G , Huchlenbroich 1. Manufacturing and Application of High Nitrogen Steels [J]. Mater Manuf P m . 2004, 19(1): 7. Paton B E, Saenko V Y ,Pomarin Y M, et al. Arc Slag Reme lting for High Strength Steel and Various Alloys [J]. J Mater Sci, 2004, 39(24): 7269. SHI Feng, WANG Li-jun, CUI Weng-fang, et al. Precipitation Kinetics of CrzN in a High-Nitrogen Austenitic Stainless Steel [J]. J Iron Steel Res Int, 2008, 15(6): 72. Lee T H , Oh C S, Lee C G, et al. Precipitation Characteristics of the Second Phases in High-Nitrogen Austenitic 18Cr18Mn2Mo-0. 9N Steel During Isothermal Aging [J]. Met Mater Int, 20049 lO(3): 231. Speidel M 0. Properties and Applications of High Nitrogen Steels [C]//Proceeding of the 1st International High Nitrogen Steels. London: [s. n.]. 1989: 92. Katada Y ,Sagara M, Kobayashi Y. Fabrication of High Strength High Nitrogen Stainless Steel With Excellent Cor rosion Resistance and Its Mechanical Properties [J]. Mater Manuf Process, 2004. 19(1) : 19. Ogawa M, Hiraoka K, Katada Y. et al. Chromium Nitride Precipitation Behavior in Weld Heat-Affected Zone of High Nitrogen Stainless Steel [J]. ISIJ Int, 2002, 42(12): 1391. Lee T H , Kim S J , Jung Y C. Crystallographic Details of P r e cipitates in Fe22Cr21Ni-6MrAN) Superaustenitic Stainless Steels Aged at 900 C [J]. Metall Mater Trans, 2000, 31A (7) : 1713. Knutsen R D, Lang C L, Basson J A. Discontinuous Cellular Precipitation in a CrMn-N Steel With Niobium and Vanadium Additions [J]. Acta Mater, 2004, 52(8): 2407. Lee T H , Kim S J. Phase Identification in an Isothermally Aged Austenitic 22Cr21Ni-6Mo-N Stainless Steel [J]. Scripta Mater, 1998. 39(7): 951. Kikuchi M, Kajihara M, Choi S K. Cellular Precipitation Involving Both Substitutional and Interstitial Solutes: Cellular Precipitation of CrzN in C r N i Austenitic Steels [J]. Mater Sci Eng, 1991, 146A(1/2): 131. Santhi Srinivas N C, Pendase R. Gouthama. et al. Initial Stages of Discontinuous Precipitation in High Nitrogen Austenitic Stainless Steels [J]. Trans Indian Inst Met, 2002, 55(4): 247. LI Hua-bing, JIANG Zhou-hua, ZHANG Zu-rui, et al. Mechanical Properties of Nickel Free High Nitrogen Austenitic Stainless Steels [J]. J Iron Steel Res Int, 2007, 14 (Supplement 1) : 330. LI Hua-bing. JIANG Zhou-hua, ZHANG Zu-rui. et al. Effect of Grain Size on Mechanical Properties of Nickel-Free High Nitrogen Austenitic Stainless Steel [J]. J Iron Steel Res Int, 2007. 16(1): 58. Shankar P. Shaikh H , Sivakumar S, et al. Effect of Thermal Aging on the Room Temperature Tensile Properties of AISI Type 316LN Stainless Steel [J]. J Nuc Mater, 1999, 264(1): 29. Simmons J W, Covino B S, Hauk J A, et al. Effect of Nitride (CrzN) Precipitation on the Mechanical, Corrosion and Wear
Issue 8
[21]
[22]
[23]
Aging Precipitation Behavior of 18Cr-16Mn-2Mo-1. 1N High Nitrogen Austenitic Stainless Steel Properties of Austenitic Stainless Steels [J]. ISIJ Int, 1996, 36(7): 846. Li H B, Jiang Z H , Ma Q F , et al. Manufacturing High Nitrogen Austenitic Stainless Steels by Pressurized Induction Furnace [C]//Applied Mechanics and Materials, 2011, 5254: 1687. Santhi Srinivas N C , Kutumbarao V V. On the Discontinuous Precipitation of Crz N in Cr-Mn-N Austenitic Stainless Steels [J]. Scripta Mater, 1997, 37(3): 285. Storz 0, Ibach A , Pohl M. Morphology of r P h a s e and Its
[24]
[25]
51
Effects on the Mechanical Properties of Duplex Steels [C]// Proceedings of Duplex 2007 International Conference. Grado: Cs.n.1, 2007: 95. Jiang Z H , Zhang Z R , 1-i H B, et al. Microstructural Evolution and Mechanical Properties of Aging High Nitrogen Austenitic Stainless Steels [J]. Int J Miner Metall Mater, 2010, 17 ( 6 ) : 729. Maruyama K , Suzuki G , Kim H Y, et al. Saturation of Yield Stress and Embrittlement in Fine Lamellar TiAl Alloy [J]. Mater Sci Eng, 2002, 329A-331Ac6): 190.
? ScienceDirect -r../
~_____
JOURNAL OF IRON AND STEEL RESEARCH, INTERNATIONAL. 2012, 19(8) : 43-51
Aging Precipitation Behavior of 18Cr-16Mn-2Mo-l.lN High Nitrogen Austenitic Stainless Steel and Its Influences on Mechanical Properties LI Hua-bing,
JIANG Zhou-hua,
FENG Hao,
MA Qi-feng, ZHAN Dong-ping
(School of Materials and Metallurgy, Northeastern University, Shenyang 110819. Liaoning, China)
Abstract: T h e solution-treated (ST) condition and aging precipitation behavior of 18Cr-16Mn-2Mo-1. 1N high nitrogen austenitic stainless steel ( HNS) were investigated by optical microscope ( O M ) , scanning electron microscope (SEM) , and transmission electron microscope (TEM). T h e results show that the ST condition of 18Cr-16Mn-ZMo1. 1N H N S with w N above 1% is identified as 1100 ‘C for 90 min, followed by water quenching to make sure the secondary phases completely dissolve into austenitic matrix and prevent the grains coarsening too much. Initial t i m e temperature-precipitation ( T T P ) curve of aged 18Cr-16Mn-2Mo-1. 1N H N S which starts with precipitation of 0. 05% in volume fraction is defined and the “nose” temperature of precipitation is found to be 850 ‘C with an incubation period of 1 min. Hexagonal intergranular and cellular CrZN with a = 0. 478 nm and c=O. 444 nm precipitates gradually increase in the isothermal aging treatment. The matrix nitrogen depletion due to the intergranular and a few cellular CrzN precipitates induces the decay of Vickers hardness, and the increment of cellular CrZN causes the increase in the values. Impact toughness presents a monotonic decrease and SEM morphologies show the leading brittle intergranular fracture. The ultimate tensile strength (U T S) , yield strength (YS) and elongation (El) deteriorate obviously. Stress concentration occurs when the matrix dislocations pile up at the interfaces of precipitation and matrix, and the interfacial dislocations may become precursors to the misfit dislocations, which can form small cleavage facets and accelerate the formation of cracks. Key words: solution-treated condition; aging precipitation behavior; time-temperature-precipitation curve; high nitrogen austenitic stainless steel ; mechanical property
T h e main properties of high nitrogen austenitic stainless steel ( H N S ) represent a combination of strength and corrosion resistance without more loss of Recent development in manufacturing H N S with high nitrogen content focuses mainly on the pressurized metallurgyC5]such as pressurized induction melting, pressurized plasma melting, pressurized electroslag remelting (PESR) , and arc slag remelting (ASRIC6’. T h e H N S with wN in excess of 1% can be obtained using the pressurized metallurgy technologies and some researches on the properties of the H N S have been carried out. T h e solution-treated ( S T ) condition of HNS with wN in excess of 1% needs systematical investigation according to the usual r e ~ e a r c h e s [ ~ -T~h~e. mechanical properties of HNS strongly depend on the wN as an
interstitial solution elementCg-’O1.Moreover, the ST H N S will show more thermal sensitivity in the heat processing such as hot rolling and welding with the increasing wN1”]. T h e austenitic matrix may decompose to form secondary phases which have been widely developed upon long-term exposures at about 900 cc12--141 Several researcher^"^-'^^ have studied
.
the aging precipitation behavior in H N S with wNbelow 1% and the mechanical properties of ST HNS. There are also some researches on the relationship between the aging precipitates and mechanical properties of 316LN and HNS with relatively lower wNc 19 - 201 . But the relationship between the aging precipitation behavior and mechanical properties of H N S needs further systematic investigation to understand the influencing mechanism especially that
Foundation Item: Item Sponsored by Key Program of National Science Foundation of China (50534010) ; Fundamental Research Funds for Central Universities of China (N100402015) Biography:LI Hua-bing(l978-1, Male, Associate Professor; E-mail: IihbBsmm. neu. edu. cn; Received Date: April 14, 2011
Journal of Iron and Steel Research, International
44
of the steel with nitrogen content above 1%. The 18Cr-16Mn-2Mo-1. 1N H N S has been successfully manufactured by a 25 kg pressurized induction furnace['''. The ST condition and aging precipitation behavior of 18Cr-16Mn-ZMc~l.1N HNS have been systematically investigated. Moreover, the influences of aging precipitates on the mechanical properties of 18Cr-16Mn-2Mel. 1 N HNS have been also illustrated.
1
VOl. 19
experiment were manufactured by a pressurized induction furnace under high purity nitrogen gas. They were supplied as plates with a thickness of 12 mm through the forging of a cast slab and subsequent hot rolling. Charpy V-notched (CVN) impact test specimens were prepared from the longest part of these quenched plates which is parallel to the rolling direction with a size of 10 mm X 10 mm X 55 'mm. T h e other hot rolled plates were extending t o 5 mm then cold rolled to 1.5 mm in thickness to prepare the tensile test specimens with a scale distance of 25 mm and a total distance of 115 mm. T h e specimens for microstructural characterization
Experimental Procedure
T h e chemical composition of current investigated material 18Cr-16Mn-2Mo-1. 1N H N S is given in Table 1. T h e ingots with wNabove 1% used in this
Table 1 Chemical composition of 1 8 C r 1 6 M r 2 M o - l . l N HNS
c 0.050
Cr
18.02
Mn 16. 10
Mo 1.96
Ni -
Si
P
0.03
0.014
were aged from 650 to 950 'C in range of 30 s to 60 min and the impact and tensile specimens were aged at 850 'C from 5 to 60 min then quenched in water. The samples for researching the microstructure were subjected to standard grinding and polishing techniques before electrolytic etching with 10% of oxalic acid ( in mass percent 1. Properly etched samples were examined on optical microscope ( O M , Carl Zeiss). The ImagePro Plus 5.0 (IPP 5.0) software for precise particle size calculation was used for statistically quantitative analysis of aging precipitation of the samples. T h e aging precipitation area percentage calculated by IPP5. 0 software was applied to replace the aging precipitation volume ratio. Three samples and lots of fields were counted for determining the initial TTP curve. T h e electronic microanalysis was carried out by scanning electron microscope (SEM, SSX-550) at 15 kV and transmission electron microscope (TEM, TECNCI G2 20) at 200 kV. Thin foils for T E M analysis were prepared by mechanical grinding down to 80 pm, and finished by a twin-jet electrolytic polishing technique using an electrolyte of 8 % of perchloric acid (in volume percent) in ethanol at -25 'C and 70 V. Vickers hardness ( H V ) was measured on hardness tester ( FM-700 1. CVN impact tests were performed on impact tester (JBW-500) and uniform tensile tests were carried out at a crosshead speed of 3 mm/min on an Instron testing machine at room temperature. T h e three samples were performed for testing the mechanical properties.
2 2. 1
(mass percent, A1
0.01
%)
0
N
Fe
0.003
1. 10
Balance
Results and Discussion Determination of ST condition
Fig. 1 ( a ) is the microstructure of hot rolled 18Cr-16Mn-2Mwl. 1N HNS without any other solution treatments. T h e secondary phases along the grain boundaries exist obviously. T o obtain the appropriate ST condition of 18Cr-16Mn-2Mo-1. 1N HNS with wNabove 1% , several ST tests with different conditions have been performed according to the usual rep o r t ~ [ ~ - " .The microstructures of ST specimens are presented in Fig. 1 (b> to (f). Several secondary phases still exist in Fig. 1 (b) and (el. The grain size is larger in Fig. 1 (d) and (f) than that in Fig. 1 (c). T h e main reason is that when wN exceeds 1% , the formation of the secondary phases in the cooling process after hot rolling will be accelerated obviously and is hardly dissolved into austenitic matrix during relatively lower temperature or shorter time solution treatment. Meanwhile, the grain will coarsen during relatively higher temperature or longer time solution treatment, which will influence the properties and application of materials. Therefore, the ST condition of 18Cr-16Mn-2Mwl. 1N HNS can be identified as 1100 'C for 90 min, followed by water quenching to make sure the secondary phases completely dissolve into austenitic matrix and prevent the grains coarsening too much. T h e ST specimens possess high strength and a certain toughness which are exhibited by the SEM morphologies of impact and tensile fracture as shown in Fig. 2. The fracture of ST
Issue 8
A g i n g Precipitation Behavior of 18Cr-16Mn-2Mo-1. 1N High Nitrogen Austenitic Stainless Steel
( a ) Un-solution-treated; ( d ) 1100 C X 1 2 0 min;
( b ) 1100 C X60 min; ( e l 1050 C X 9 0 min;
C X 9 0 min;
Microstructure of 18Crl6Mn-2Mo-1. 1N HNS under different ST conditions
Fig. 2
SEM morphologies of ST 18Cr16Mn-2Mo-1. 1N HNS at 1100 ‘c for 90 min
( b ) Tensile fracture.
specimens presents equiaxial dimples.
Aging precipitation behavior Initial TTP curve (Fig. 3 ) of aged 18Cr-16Mn2Mo-1. 1 N H N S which starts with precipitation of 0. 05% in volume fraction is defined and the “nose” temperature of precipitation is found to be 850 ‘C with an incubation period of 1 min by quantitative metallographic analysis with OM and IPP 5. 0 software. In previous research, the initial T T P curve of aged H N S which starts with precipitation of 0. 1% in volume fraction is usually defined. T h e initial TTP curves starting with precipitation of 0. 05% is more precise for determining the initial precipitation behavior than that of precipitation of 0. 1% due to the use of IPP 5 . 0 software as shown in Fig. 3. T h e
45
( f ) 1150 “CX90 min.
Fig. 1
( a ) Impact fracture;
2.2
( c ) 1100
-
1 000
$
900
-
2 E
800-
B
M
2
700
-
I
0.05%
BOO .0.1‘& 10’
Fig. 3
102
Aging time/s
lo:’
104
TTP curves of 18Cr16Mn-2Mo-l.lN HNS
microstructure of aged 18Cr-16Mn-2Mo-1. 1N H N S during isothermal aging at 850 “C is shown in Fig. 4. When the ST H N S is subjected to aging treatment for
Vol. 19
Journal of Iron and Steel Research, International
46
( b ) 1 rnin; ( c ) 5 mini (d) 10 mini ( e ) 30 min; (f) 60 rnin. Microstructure of 18Cr-16Mn-2Mo-1. 1N HNS aged at 850 'c for different aging time
(a) 0.5 min;
Fig. 4
0. 5 min, local grain boundaries become coarse by the formation of CrzN [Fig. 4 (a)]. T h e CrzN precipitates become more and coarser during the time at which the initial TTP curve starts with precipitation of 0. 05% in volume fraction [Fig. 4 (b)]. This is attributed to the long distance diffusion of solute N within the austenite matrix for a long timec2". The cellular CrzN just precipitates inward austenitic grains in aging treatment at 850 'C for 5 min [Fig. 4 (c)]. This phenomenon presents much faster than T H Lee's reports with the aging treatment at 900 'C for 1000 scS1, which can be attributed to the more wN above 1%. T h e growing up and increasing amount of cellular C r z N phase are observed with prolonging the aging time from 5 to 60 min [Fig. 4 (c) to (f)]. The CrzN precipitation content is determined by using OM and IPP 5.0 software as shown in Fig. 5. It can be seen that a monotonic increase in the volume fraction of precipitation occurs with prolonging the aging time at 850 "C. The SEM morphology and SEM energy dispersive spectrometer ( EDS) line profile of 18Cr16Mn-2Mo-1. 1N H N S are shown in Fig. 6. This result can qualitatively present that the precipitates with lamellar structure are rich in Cr and N while the adjacent matrix is depleted in Cr and N. T h e crystallographic structure of precipitates is identified by TEM and the selected area diffraction (SAD) patterns as shown in Fig. 7. T h e cellular CrzN precipitation which presents a lamellar structure has a hexagonal structure of a=O. 478 nm and c=O. 444 nm.
0
20 40 Aging timdmin
60
Fig. 5 Volume fraction of precipitation of 18Cr-16Mn2Mo-1. 1N HNS aged at 850 'c for different time
2 . 3 Influence of aging precipitation on mechanical properties Fig. 8 shows the effect of isothermal (850 'C)aging on the hardness values of 18Cr-16Mn-ZMel. 1N HNS. A pronounced increase in hardness is measured at 850 'C with the increase in aging time from 5 to 60 min. It is inferred that the presence, growth, and increased amount of cellular C r z N precipitates as revealed in Fig. 4 obtained after aging at 850 "C from 5 to 60 min cause the substantial increase in hardness. The reduction of hardness value from the ST specimen ( H V 313) to the aged one for 5 min is due to the matrix nitrogen depletion for the precipitation of intergranular and some cellular Cr2N precipitates. This result, in agreement with the previously published one, indicates that
Issue 8
Aging Precipitation Behavior of 18Cr-16Mn-2Mo-1. 1N High Nitrogen Austenitic Stainless Steel
47 *
10
5
0
6
2
10
14
(a) SEM morphology;
2
6
10
14
(b) SEM-EDS line
(c) SEM-EDS line profile of Cr element;
Fig. 6
0
Distancelpt
profile of cellular precipitation; (d) SEM-EDS line profile of N element.
SEM morphology and SEM-EDS line profile of 18Cr-16Mn-2Mwl. 1N HNS aged at 850 “c for 1 h
Fig. 7
(a) Bright field image: ( b ) SAD pattern of cellular CrzN. TEM analysis of 18C1-16Mn-2Mwl. 1N HNS aged at 850 “c for 1 h
the depletion by means of long distance diffusion of interstitial so1u t i on N element decreases the hardness of HNSCZZ1.Therefore, the cellular Cr, N is the main reason for influencing the hardness of 18Cr-16Mn2Mo-1. 1 N HNS. T h e essential effect will take place when the amount and size of cellular C r Z Narrive at a certain degree. Fig. 9 presents the plot of A,, at room tempera-
ture for 18Cr-16Mn-2Mo-1. 1 N H N S aged at 850 “C for different time. Comparing with the value of the ST specimen, the values of A,, present a monotonic decrease below 3 J with prolonging the aging time. T h e AKV of the specimen aged for 5 min is just lower than that of the ductile to brittle point of the ST specimen. It can be seen that a short time aging treatment just causes an obvious effect on the impact
Journal of Iron and Steel Research, International
48
0
Fig. 8
20 40 Aging timdmin
60
Vickers hardness of 18Crl6Mn-ZMch. 1N HNS aged at 850 “c for different time
250
150
6 p:
5(l
0 0
Fig. 9
20 40 Aginglime/min
60
Impact absorbed e n e m of 18Cr16Mn-ZMo-l.lN HNS aged at 850 “c for different time
properties of 18Cr-16Mn-2Mo-1. 1 N H N S at the precipitated sensitivity temperature. T h e formation of intergranular and cellular CrzN precipapitates is the reason for the occurrence of the extremely brittle behavior. T h e typical fracture appearances of impact tested 18Cr-16Mn-2Mo-l.lN HNS at room temperature are shown in. Fig. 10. Intergranular facets are the leading fracture mode with increasing the aging time at 850 %. T h e SEM morphologies of impact fracture are consistent with the CVN impact absorbed energy values, which are in agreement with the result in Ref. [20]. T h e fracture facets of the tested specimen aged for 5 min present the structure with tear ridge which shows the quasi-cleavage fracture. This is due to the nucleation and local growth of cellular CrzN. With increasing the aging time, the increment of the amount and size of cellular CrzN deteriorates the ability and strength of grain boundaries obviously so that the grain stripping cracks with a little deformation at room temperature. T h e leading brittle intergranular fracture at room temperature can be attributed to more precipi-
(a) 5 mini (b) 10 mini (c) 60 min. Fig. 10 SEM morphologies of fracture surfaces of 18C1-16Mn-ZMch. 1N HNS aged at 850
tates along grain boundaries and the cellular precipitates. T h e lamellar stripping structure is due to the formation of many small cleavage facets which nucleate along the precipitates. Fig. 11 shows the results of tensile tests at room temperature after the isothermal (850 %) aging treatment. T h e tensile results are in general agreement with the microstructure of aged 18Cr-16Mn-2Mo1. 1 N HNS. T h e microstructure of the aged specimens offers a gradual decay in the yield strength (YS) , ultimate tensile strength (UTS) and the elongation ( E l ) comparing with the non-aged specimen. T h e material exhibits brittleness. T h e amount of secondary phases is relevant to the mechanical properties, also the morphology is important to be noticedCz3’. For longer aging treatment from 5 to 60 mint the changed type, increased amount and grown size of
Vol. 19
c
for different time
secondary phases make the tendency of intergranular fracture more obvious and result in the deterioration of YS, U T S and El gradually. These results reveal that the cellular Cr2N can be considered as the main reason for the decrease in the tensile properties of this alloy. T h e result of YS presents different tendencies from previous report with relatively lower w [ N ] of 0. 77%c241. This is because of the cellular CrzN precipitated a t 850 ‘C for 5 min which makes more serious depletion of interstitial nitrogen atoms in austenitic matrix to increase the strength of materials. A series of SEM morphologies of tensile fracture surfaces after the isothermal (850 % > aging treatment are presented in Fig. 12. T h e intergranular fracture is the main fracture mode for the aged specimens. T h e increment of the amount and size of cellular CrzN deteriorates the ability and strength of
Issue 8
Aging Precipitation Behavior of 18Cr-16Mn-2Mo-1. 1N High Nitrogen Austenitic Stainless Steel 1 200
.YS UTS
0
Aging timdmin
Fig. 11 Variation of strength and elongation of 18C1-16Mn2Mo-1. 1N HNS at 850 “c for different aging time
*
49
*
grain boundaries. It makes the deformation along grain boundaries prior to the grain interior and the occurrence of whole grain stripping along the grain boundaries [Fig. 1 2 (a)]. With the prolongation of the aging time, the intergranular fracture and transgranular facets exist together which makes the further decrease of the strength and toughness [Fig. 1 2 (b)]. T h e cellular precipitates make many small cleavage facets nucleate along the precipitation intersection which can be seen clearly in Fig. 12 ( c > because of the difference on the main stress direction between tensile and impact test. Thin sections parallel to the
( a ) 5 mini ( b ) 10 min; ( c ) 60 min. Fig. 12 SEM morphologies of tensile fracture surfaces of 18Cr-16Mn-2Mwl. 1N HNS aged at 850 “c for different time
tensile direction are shown in the T E M morphologies of aged samples, which demonstrate the possible fracture mechanisms as shown in Fig. 13. Coherent intergranular and cellular Cr, N precipitates distributed on the grain boundaries and associated with the strain fields restrict the movement of dislocations and cause an intergranular fracture. With the coarsening of precipitation in this stage of aging treatment, this phenomenon becomes more significant. Stress concentration occurs when the matrix dislocations pile up at the interfaces of precipitation and matrix to push the leading dislocation. T h e interfacial dislocations shown in Fig. 13 may become pre-
( a ) 5 min;
cursors t o the misfit dislocations, which can form small cleavage In the present research, some phenomena can be found that the hardness values decrease from 0 to 5 min and then increase with prolonging the aging time. And the AKV,YS, UTS and the El all decrease with increment of intergranular and cellular CrzN for longer aging treatment. T h e relation among hardness, strength, toughness and plasticity is contrary t o the traditional concept. A number of experiments also are performed to test the new phenomenon, and the same result can be obtained. So the phenomenon is special for high nitrogen austenitic stainless steel with
( b ) 60 min.
Fig. 13 TEM morphologies of tensile fracture surfaces of 18Cr-16Mn-2Mwl. 1N HNS aged at 850 “c for different time
Journal of Iron and Steel Research, International
50
nitrogen content more than 1%. The special mechanical properties of high nitrogen austenitic stainless steel with aging treatment can be interpreted due to the effect of intergranular and cellular Cr2N. T h e intergranular and cellular C r z N is very prone to precipitate in the matrix and grain boundary as shown in Fig. 4 and Fig. 7, which deteriorates the ability and strength of grain boundaries and reduces the strength, toughness and plasticity of high nitrogen steels. The reduction of hardness value from 0 to 5 min is due to the matrix nitrogen depletion for relatively small number of the precipitation of intergranular and some cellular C r z N precipitates a s shown Fig. 4 ( a ) , ( b ) , and (c). With prolonging the aging time, a lot of cellular C r z N precipitates are the main cause for increasing the hardness of the steel than the matrix nitrogen depletion.
3
Conclusions
1) T h e solution-treated condition of 18Cr16Mn12Mo-1.1N H N S with wN above 1% is identified as 1100 ‘C for 90 min, followed by water quenching to ‘make sure the secondary phases completely dissolve into austenitic matrix and prevent the grains coarsening too much. 2 ) Initial time-temperature-precipitation curve of aged 18Cr-16Mn-2Mo-l.lN HNS which starts with precipitation of 0.05% in volume fraction is defined and the “nose” temperature of precipitation is found C with an incubation period of 1 min. to be 850 O Hexagonal intergranular and cellular CrZN with a = 0. 478 nm and c=O. 444 nm precipitates gradually increase in the isothermal aging treatment. 3) T h e matrix nitrogen depletion due to the intergranular and a few cellular CrzN precipitates induce the decay of Vickers hardness, and the increment of cellular CrzN causes the increase in the values. Impact toughness presents a monotonic decrease and SEM morphologies show the leading brittle intergranular fracture. T h e ultimate tensile strength, yield strength and elongation deteriorate obviously. Stress concentration occurs when the matrix dislocations pile up a t the interfaces of precipitation and matrix, and the interfacial dislocations may become precursors to the misfit dislocations, which can form small cleavage facets and accelerate the formation of cracks. References : [I]
Simmons J W. Overview: High-Nitrogen Alloying of Stainless Steels [J]. Mater Sci Eng, 1996, 207A(2): 159.
VOl. 19
Li H B, Jiang Z H , Zhang Z R, et al. Intergranular Corrosion Behavior of High Nitrogen Austenitic Stainless Steel [J]. Int J Miner Metall Mater. 2009, 16(6): 654. Li H B, Jiang Z H , Yang Y ,et al. Pitting Corrosion and Crevice Corrosion Behaviors of High Nitrogen Austenitic Stainless Steels [J]. Int J Miner Metall Mater, 2009, 16(5): 517. Li H B, Jiang Z H , Cao Y ,et al. Fabrication of High Nitrogen Austenitic Stainless Steels With Excellent Mechanical and Pitting Corrosion Properties [J]. Int J Miner Metall Mater, 2009, 16(4) : 387. Stein G , Huchlenbroich 1. Manufacturing and Application of High Nitrogen Steels [J]. Mater Manuf P m . 2004, 19(1): 7. Paton B E, Saenko V Y ,Pomarin Y M, et al. Arc Slag Reme lting for High Strength Steel and Various Alloys [J]. J Mater Sci, 2004, 39(24): 7269. SHI Feng, WANG Li-jun, CUI Weng-fang, et al. Precipitation Kinetics of CrzN in a High-Nitrogen Austenitic Stainless Steel [J]. J Iron Steel Res Int, 2008, 15(6): 72. Lee T H , Oh C S, Lee C G, et al. Precipitation Characteristics of the Second Phases in High-Nitrogen Austenitic 18Cr18Mn2Mo-0. 9N Steel During Isothermal Aging [J]. Met Mater Int, 20049 lO(3): 231. Speidel M 0. Properties and Applications of High Nitrogen Steels [C]//Proceeding of the 1st International High Nitrogen Steels. London: [s. n.]. 1989: 92. Katada Y ,Sagara M, Kobayashi Y. Fabrication of High Strength High Nitrogen Stainless Steel With Excellent Cor rosion Resistance and Its Mechanical Properties [J]. Mater Manuf Process, 2004. 19(1) : 19. Ogawa M, Hiraoka K, Katada Y. et al. Chromium Nitride Precipitation Behavior in Weld Heat-Affected Zone of High Nitrogen Stainless Steel [J]. ISIJ Int, 2002, 42(12): 1391. Lee T H , Kim S J , Jung Y C. Crystallographic Details of P r e cipitates in Fe22Cr21Ni-6MrAN) Superaustenitic Stainless Steels Aged at 900 C [J]. Metall Mater Trans, 2000, 31A (7) : 1713. Knutsen R D, Lang C L, Basson J A. Discontinuous Cellular Precipitation in a CrMn-N Steel With Niobium and Vanadium Additions [J]. Acta Mater, 2004, 52(8): 2407. Lee T H , Kim S J. Phase Identification in an Isothermally Aged Austenitic 22Cr21Ni-6Mo-N Stainless Steel [J]. Scripta Mater, 1998. 39(7): 951. Kikuchi M, Kajihara M, Choi S K. Cellular Precipitation Involving Both Substitutional and Interstitial Solutes: Cellular Precipitation of CrzN in C r N i Austenitic Steels [J]. Mater Sci Eng, 1991, 146A(1/2): 131. Santhi Srinivas N C, Pendase R. Gouthama. et al. Initial Stages of Discontinuous Precipitation in High Nitrogen Austenitic Stainless Steels [J]. Trans Indian Inst Met, 2002, 55(4): 247. LI Hua-bing, JIANG Zhou-hua, ZHANG Zu-rui, et al. Mechanical Properties of Nickel Free High Nitrogen Austenitic Stainless Steels [J]. J Iron Steel Res Int, 2007, 14 (Supplement 1) : 330. LI Hua-bing. JIANG Zhou-hua, ZHANG Zu-rui. et al. Effect of Grain Size on Mechanical Properties of Nickel-Free High Nitrogen Austenitic Stainless Steel [J]. J Iron Steel Res Int, 2007. 16(1): 58. Shankar P. Shaikh H , Sivakumar S, et al. Effect of Thermal Aging on the Room Temperature Tensile Properties of AISI Type 316LN Stainless Steel [J]. J Nuc Mater, 1999, 264(1): 29. Simmons J W, Covino B S, Hauk J A, et al. Effect of Nitride (CrzN) Precipitation on the Mechanical, Corrosion and Wear
Issue 8
[21]
[22]
[23]
Aging Precipitation Behavior of 18Cr-16Mn-2Mo-1. 1N High Nitrogen Austenitic Stainless Steel Properties of Austenitic Stainless Steels [J]. ISIJ Int, 1996, 36(7): 846. Li H B, Jiang Z H , Ma Q F , et al. Manufacturing High Nitrogen Austenitic Stainless Steels by Pressurized Induction Furnace [C]//Applied Mechanics and Materials, 2011, 5254: 1687. Santhi Srinivas N C , Kutumbarao V V. On the Discontinuous Precipitation of Crz N in Cr-Mn-N Austenitic Stainless Steels [J]. Scripta Mater, 1997, 37(3): 285. Storz 0, Ibach A , Pohl M. Morphology of r P h a s e and Its
[24]
[25]
51
Effects on the Mechanical Properties of Duplex Steels [C]// Proceedings of Duplex 2007 International Conference. Grado: Cs.n.1, 2007: 95. Jiang Z H , Zhang Z R , 1-i H B, et al. Microstructural Evolution and Mechanical Properties of Aging High Nitrogen Austenitic Stainless Steels [J]. Int J Miner Metall Mater, 2010, 17 ( 6 ) : 729. Maruyama K , Suzuki G , Kim H Y, et al. Saturation of Yield Stress and Embrittlement in Fine Lamellar TiAl Alloy [J]. Mater Sci Eng, 2002, 329A-331Ac6): 190.