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Hot Deformation Behaviors of S31042 Austenitic Heat-Resistant Steel
Available online at w.sciencedirect.com --I/
*:2ScienceDirect JOURNAL OF IRON AND STEEL RESEARCH, INTERNATIONAL. 2011, 18(10): 54-58, 79
Hot Deformation Behaviors of S31042 Austenitic Heat-Resistant Steel WANG Jing-zhong”‘
,
LIU Zheng-dong’
,
CHENG Shi-chang’
,
BAO Han-sheng’
2. School of Metallurgy and (1. Central Iron and Steel Research Institute, Beijing 100081, China; Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, Shaanxi, China) Abstract: The hot deformation behavior of S31042 austenitic heat-resistant steel was investigated over the temperature range of 900- 1200 ‘C and strain rate range of 0. 01 - 10 s-l using hot compression tests and the corresponding flow curves were obtained. The hot deformation activation energy of the test steel is 625 kJ/mol. The hot deformation equation and the relationship between the peak stresses, deformation temperature and strain rate were set up. The Zener-Hollomon parameter under various conditions was determined. The relation between the Zener-Hollomon parameter and the microstructure evolution of test steel was discussed. With the decrease of Zener-Hollomon parameter, the microstructure of test steel transforms from deformation instability to dynamic recovery, partial dynamic recrystallization, full dynamic recrystallization with equiaxial structure, and finally to full dynamic recrystallization with mixed crystal structure. The deformation condition can be adjusted easily by utilizing the Zener-Hollomon parameter to obtain equiaxial microstructure. Key words: S31042 steel; hot deformation behavior; Zener-Hollomon parameter; microstructure
T h e ultra-supercritical ( USC ) power plants with increased steam parameter evidently improve the efficiency of coal-fired generator set, which reduces fuel consumption and the emissions of environmentally damaging gases“’. Therefore, the construction of USC power plants is under developing in China currently[’’. Owing to the increase in steam parameter, the elevated temperature properties of the materials to build components of USC power plants must be improved greatly. However, commercial 5331042 steel needed for constructing USC power plants in China, which was widely used as superheater and reheater for the boilers, is dependent on importation, influencing construction period, and the material cost is very high. For this reason, the domestic production of S31042 steel tube is urgently required. S31042 steel with good long-term strength at elevated temperature and high temperature steam oxidation resistance belongs to one of the multi-compositestrengthened austenitic heat-resistant steelsC3’. Because of large amount of alloying elements, the
hot deformation behavior will be the important issue during the seamless tube production. There is no report on hot deformation behavior of S31042 steel. LiteratureC4’had reported the hot deformation behavior of S30432 which also belongs to austenitic heat-resistant steel, but the difference in chemical composition between S31042 steel and S30432 steel is obvious, leading to the hot deformation results of S30432 steel not to be applied in S31042 steel. Therefore, investigating the quantitative relationship between flow stresses, deformation temperature and strain rate is of importance. The mechanical behaviors of S31042 steel during hot deformation were investigated using hot compression methods with Gleeble-3500 thermal-mechanical simulator. The experimental data were scientifically processed and the hot deformation equation, activation energy and the relationship between peak stress, deformation temperatures and strain rates of S31042 steel were obtained. The final microstructure of steel deformed under different conditions was analyzed corresponding to the change in
Foundation Item: Item Sponsored by National Science and Technology Support Plan of China (2007BAE51B02) E-mail: wzjxjd2003@yahoo. corn. cn; Received Date: September 25, 2010 Biography: WANG Jing-zhong(l974-), Male, Doctor:
Issue 10
55
Hot Deformation Behaviors of S31042 Austenitic Heat-Resistant Steel
polishing and electrolytic etching by 40% of nitric acid solution, the microstructure was observed by using optical microscope.
Zener-Hollomon parameter.
1 Experimental Procedure The test steel was smelted by a vacuum induction furnace and vacuum casted, forging into bar of 15 mm in diameter. The chemical composition (mass percent, %) of test steel is: C 0. 060, Cr 24. 20, Ni 20. 50, N 0.26, Nb 0.42, Mn 1.55, and Si 0.40. The size of specimen for hot compression is $8 mmX 15 mm. T h e hot compression experiment was carried out on Gleeble-3500 thermal-mechanical simulator. Prior to hot compression, all of the specimens were preheated to 1270 "Cand held for 180 s to ensure the specimens having same microstructure before deformation and cooled at 10 C / s to corresponding hot compression temperature. In order to have uniformity in temperature inside and outside of specimen, on cooling to the corresponding hot compression temperature, all the specimens must be held for 60 s before deformation. The hot compression experiment carried out over the temperature range from 900 to 1ZOO "Cand strain range from 0.01 s-l to 10 s-'. On reaching 1. 2 of true strain [E=ln(H/h), here H is initial height of the specimens before hot compression, and h is the final height of specimens after hot compression], specimen was cooled by water immediately. After cutting longitudinally, grinding and
100
2
Results and Discussion
Flow stress curves of S31042 steel The flow curves of S31042 steel deformed at different temperatures and strain rates for the total true strain of 1. 2 were obtained as shown in Fig. 1. It can be seen that with increase in the deformation temperature or decrease in deformation strain rate, the peak stress on the various flow stress curves decreases. When the deformation temperature is lower and the strain rate is higher, the flow curves belong to the type of dynamic recovery, for example, the flow curves obtained at temperature of 9 0 0 and 1000 "Cand strain rate of 1 and 10 s-'. For the deformation at 1200 'C, evident characteristics of full dynamic recrystallization, the appearance of static stress, can be found in these flow curves over the strain rate range from 0.01 to 10 s - l , as shown in Fig. 1 ( a ) to ( d ) . At the same deformation temperature, the flow stress of every curve decreases with the decrease in stain rate. Similarly, at the same strain rate, the flow stress of every curve also decreases with the increase in deformation temperature. Based on the further treatment of the results in
2. 1
7-I 1 100
l OOo
1200
B2 400
e
300 200
100
0
0.2
0.6
1.0
1.4
I
0.2
0
0.6
1.0
True strain (a) 0.01 s - l i
(b) 0.1 s-l;
(c)
1 s-l;
(d) 10 s-'.
Fig. 1 Flow curves of S31042 steel under different deformation conditions
1.
*
56
-
Fig. 1 , the peak strain E~ and peak stress up obtained from the flow curves are listed in Table 1. From Table 1, it can be seen evidently that at the same deformation temperature, the up will increase with the rise in strain rate, and meanwhile, corresponding peak true strain also increases. But in the case of equal strain rate, E , and up will gradually increase with the deformation temperature decrease. The appearance of maximal peak stress is at deformation temperature of 900 ‘Cand strain rate of 10 s-’ , and the minimal peak stress appears on the flow curve of 1ZOO *Cand 0.01 s-l. Table 1
EP
tion with the measured results of the flow curves in Fig. 1, the relationship curves between nominal peak stress and strain rate as well as deformation temperature can be obtained (in Fig. 2 and Fig. 3) in hot deformation process of the test steel. When the deformation temperature is a constant, taking partial derivative of the both sides of Eqn. ( 2 ) to strain rate, it can be obtained as
(3) When the strain rate is constant, taking partial derivative for both sides of Eqn. (2) to 1/T, it can be obtained as
Peak stress upand peak strain at different deformation conditions of test steel Deformation
a,/MPa
Vol. 18
Journal of Iron and Steel Research, International
Strain rate/s-’
temperature/%
0.01
0.1
1
10
900
308
365
380
430. 5
1000
174
219
293
333
1100
81
133
182
235
1200
51
70
124
157
900
0. 21
0. 30
0. 41
0. 46
1000
0. 19
0. 28
0. 40
0. 44
1100
0. 12
0. 23
0. 38
0. 43
1200
0. 18
0. 22
0. 29
0. 40
(4) According to Eqn. (2) and Eqn. (4) and the regressed analysis results from Fig. 2 and Fig. 3 , it can be obtained Q= 625 kJ/mol, n = 6. 713, and A = 6. 6 1 X l o ” . Consequently, under the deformation conditions over a temperature range of 900 - 1ZOO “C, the hot deformation equation of S31042 steel can be expressed as Eqn. (5). ;=6. 60X101’[sinh(0. 0 0 5 5 6 2 ~ , ) ] ~ ’X~ ’ ~ expl 1.5
2 . 2 Establishment of the hot deformation equation of S31042 steel According to Ref. [5] to Ref. [7], the relationship among the flow stress u , the deformation temperature T and the strain rate E. could be expressed by a typical hyperbolic sine function as follows: ;=A[ sinh(au)lnexp( -Q / R T ) (1) where, A , a and n are material constants which are independent of deformation temperature; Q is the hot deformation activation energy; R is the gas constant; T is Kelvin temperature; and u is the static stress, or peak stress, or the stress for a given strain. In this work, the peak stress is taken, and sinh(a 0,) is defined as the nominal peak stress. The value of a is calculated as 0. 005 562, according to Ref. [S]. After taking natural logarithms of both sides of Eqn. ( 1) and rearranging, it is obtained as l n [ s i n h ( a a ) ] = l ~ / n f Q / ( n R T ) - lnA/n (2) It can be seen from Eqn. (2) that when the deformation rate (or temperature) is constant, there is a linear relation between natural logarithm of the nominal peak stress and the natural logarithm of deformation rate (or the reciprocal of deformation temperature). On the basis of Eqn. (2) and in combina-
Is”
-
I
r\
rj
--?I
(5)
-
0.5 0 -
g -0.5 -1.5
-
-5
Fig. 2
-3
-1
In &
0
1
3
Relationship between peak stress and strain rate for S31042 steel
1.5 -
0.1 A 1
-1.5
v 10 6.6
7.0
7.4
7.8
IM)Om-‘
8.2
8.6
T
Fig. 3
Relationship between peak stress and deformation temperature for S31042 steel
' 57
Hot Deformation Behaviors of S31042 Austenitic Heat-Resistant Steel
Issue 10
2 . 3 Zener-Hollomon parameter and its relationship to the peak stress Zener-Hollomon parameter ( 2 parameter) , which was known as temperature modified strain rate, was widely used to characterize the combined effect of strain rate and temperature on the deformation process, especially on the deformation r e s i s t a n ~ e ~ as ~ - shown ' ~ ~ in the following equations. (6) Z=;exp(Q/RT) Substituting the Q value into Eqn. ( 6 1 , it can be obtained as Table 2
Z=Eexp(625 OOO/RT) (7) According to the deformation conditions and Eqn. ( 7 ) , the value of 2 parameter corresponding to different deformations can be confirmed and listed in Table 2 , and then the relation expression between In2 and a,[see Eqn. ( 8 ) ] as well as the fitted curves as Fig. 4 can be obtained by means of integrating the test results in Fig. 1. Obviously, in the present work, there exists a linear relation between I n 2 and a,, and the correlation coefficient is about 0. 991. g,=20. 0 4 l G f l 4 5 7 631. 706/T-901. 9 1 (8)
Zener-Hollomon parameter corresponding to different deformation conditions
Deformation temperature/%
Zener-Hollomon parameter 1 s-1
10 s-1
900
6. 80 X loz5
6. 8 0 X loz6
6. 80 X lo2'
6. 8 0 X 10''
1000
4 . 4 3 ~1023
4.43
x 1025 6. 00 X loz3
4. 43 x 1 0 2 6
6. 00 X loz1
x 1024 6. OOX 10"
4.43
1100 1200
1. 4 6 X l o z o
1.46 X loz1
1. 46 X 10"
1 . 4 6 1023 ~
0.01
s-1
0.1
s-1
6. 00 X loz4
1.0
450 350
g
0
-
w
250
M
b
-1.0
150 50
______~-~
45 Fig. 4
50
55
In2
60
65
70
Relationship between 2 parameter and peak stress for S31042 steel
2 . 4 Relationship between the hot deformation behavior of S31042 steel and Zener-Hollomon parameter Using the data listed in Table 2 , the relationship curves between the deformation temperatures, logarithm of strain rate and logarithm of Zener-Hollomon parameters are drawn as shown in Fig. 5. From Fig. 5 it can be seen that the Zener-Hollomon parameter increases apparently with the drop in deformation temperature and rise in strain rate. According to the microstructure obtained via different deformation conditions, the relationship map between deformation temperature, strain rate and Zener-Hollomon parameter can be devided roughly into different zones to characterize the state of the microstructure during hot processing under different deformation conditions with the same true strain t o 1.2. Accompanying t h e Zener-Hollomon parameter
-2.0
Fig. 5
900
1 000
1 100 Temperattwe/'T:
1 200
Zener-Hollomon parameter of S31042 steel under different conditions
decrease, the microstructure of materials deformed under different deformation conditions transforms from flow instability and dynamic recovery to partial dynamic recrystallization, full dynamic recrystallization with equiaxial grain, and finally to full dynamic recrystallization but with mixed crystal structure. When the strain is given, the relationship between the microstructure and Zener-Hollomon parameter can be determined using hot compression test. Based on Eqn. ( 7 ) and Fig. 5 , when the strain is preset, whatever change the deformation temperature and strain rate are, so long as the Zener-Hollomon parameter is known, the final microstructure can be conjectured after hot working. In other words, so long as the Zener-Hollomon parameter is identical, even though the deformation temperature or strain rate is different, the same microstructure
58
Journal of Iron and Steel Research, International
can be obtained. Associating with the microstructure and Zener-Hollomon parameter make it convenient for adjusting the hot working processes, but report on using this method in practice was not seen in technical literature up to now. T h e authors' research group believes that this method will be utilized in production practice in the near future. It was shown in Fig. 5 that when Zener-Hollomon parameter is above l o z 5 , the microstructure is flow instability and dynamic recovery, and its typical feature is shown in Fig. 6 ( a ) and (b). When 2 is in the range of ZenerHollomon parameter from 3. 16 X loz3 to 3. 16 X loz5, the deformation state of test steel is at
Vol. 18
partial dynamic recrystallization and its typical microstructures are shown in Fig. 6 (c) and (d) of which Zener-Hollomon parameters are 6 X l o z 3 and 6 X l o z 4 , respectively. When the Zener-Hollomon parameter is in the range of 3.16 X 10'' to 3.16 X l o z 3 , the deformation state of test steel is at full dynamic recrystallization and its typical microstructures with fine equiaxial crystal are shown in Fig. 6 ( e ) and ( f ). However, when the Zener Hollomon parameter is below 3. 16 X l o z 2 , the typical microstructure of test steel is mixed crystal as shown in Fig. 6 ( g ) corresponding to Zener Hollomon parameter of 6.00 X loz1. Based on the analysis above, it is evident that for
( a ) 1000 % , 1 s - ' , 2=4. 4 3 X l O Z 5 , flow instability; (b) 1000 C , 0. 1 s - l , dynamic recovery, 2=4. 43X102'; (c) 1100 C , 1 s - I , 2=6. OOX l o z 3 , partial dynamic recrystallization; ( d ) 1100 'C , 10 s - l , Z=6. OOX l o z 4 , partial dynamic recrystallization; (e) 1100 'C , 0. 1 sC1, 2=6. OOX l o z z , full dynamic recrystallization with fine grains; ( f ) 1200 C , 10 s - l , 2 = 1 . 4 6 X loz3; ( g ) 1100 C , 0.01 s - l , Z=6. OOX loz1, mixed crystal.
Fig. 6
Typical microstructure of s31042 steel deformed under different conditions (s=l. 2)
S31042 steel, the flow stress increases with increasing Zener-Hollomon parameter. T h e lower the Zener-Hollomon parameter, the larger the extent of flow softening, the more easily the dynamic recrystallization may occur, and the bigger the dynamic recrystallization grain size is. T o obtain good microstructure for S31042 steel, it is necessary to avoid processing at zone of Zener-Hollomon parameter which is below 3. 1 6 X lo" or above 3. 1 6 X loz3.
3 Conclusions 1) The hot deformation average activation energy is 625 kJ/mol of S31042 steel in the deformation condition range of this test. T h e hot deformation equation is established as € = 6 . 60X1019[sinh(0. 0 0 5 5 6 2 ~ ~ , ) X ]~.~~~
I?-
expl
2 ) For S31042 steel, the quantitative relation between the peak stress, the deformation temperature
and the strain rate can be described as a,=20. 041&+1457 631.706/T-901.91 3) For S31042 steel deformed under the condition of temperature of 900 to 1200 "C , strain rate of 0.01 to 10 s-' and e of 1 . 2 , with the decrease in deformation temperature and the increase in strain rate, the Zener-Hollomon parameter increases and the typical microstructure transforms from mixed crystal t o fine equiaxial crystallization, partial dynamic recrystallization, finally to dynamic recovery and flow instability. T o improve the hot deformation microstructure of S31042 steel, it is necessary to avoid the higher Zener-Hollomon parameter zone above 3. 16 X loz3 and the lower Zener-Hollomon parameter zone below 3. 16 X 10" when hot deformation was carried out. 4 ) Associating with the microstructure and Zener-Hollomon parameter will make it convenient for adjusting the hot working processes t o obtain expected final microstructure of S31042 steel. (Continued on Page 79)
Issu e 10
E ffect of Heat I n p u t on G a s Metal A r c Welded A us te nitic Sta inle s s Ste e l
and Forests, Government o f India for .providing financial support to curry out this investigation through a research and development project, No. 19/2005-CT. T h e authors also wish to thank Maila m India L i m i t e d , Pondicherry , f o r providing the welding consumables to carry out this research.
Hygiene Association Journal, 1995, 5 6 ( 2 ) : 128. Hilton D E , Plumridge P N. Particulate Fume Generation During GMAW and GTAW [J]. Welding and Metal Fabrication, 1991(12): 555. Ma J , Apps R L. MIG Transfer Discovery of Importance to Industry [J]. Welding and Metal Fabrication, 1982(9): 307. Gray C N , Hewitt P J , Dare R M. New Approach Would Help Control Weld Fumes at Source: Part 1 [J]. Welding and Metal Fabrication, 1982(9): 318. Gray C N , Hewitt P J , Hicks R. The Effeet of Oxygen on the Rate of Fume Formation in Metal Inert Gas Welding Arcs [C]/ Weld Pool Chemistry and Metallurgy. London: The Welding Institute, 1980: 167. The European Union. European Directive 86/642/CEE Regarding the Worker’s Protection Against Risks of Exposure to Chemical, Physical and Biological Agents During Work Activities [S]. Brussels: The European Union, 1986. American Welding Society. AWS/ANSI F1. 2 Laboratory Methods for Measuring Fume Generation Rates and Total Fume Emission of Welding and Allied Processes [S]. Miami: American Welding Society, 1992. Castner H R. Fume Generation Rates for Stainless Steel, Nickel and Aluminum Alloys [J]. Welding Journal, 1996(12): 393s. Jenkins N T, Eagar T W. Chemical Analysis of Welding Fume Particles [J]. Welding Journal, 2005, 84(Supplement) : 87s. Peter J Hewitt, Andrew D Workman. Health Consideration in Metal Arc Welding [J]. Australasian Welding Journal, 1997, 42(2): 23.
References :
c11 c21
C3l
C41 C5l
C6l c71
79 *
Voitkevich V. Welding Fumes-Formation, Properties and Biological Effects [MI. Nashville: Abington Publishing, 1995. Pires I , Quintino L, Miranda R M. Analysis of the Influence of Shielding Gas mixtures on the Gas Metal Arc Welding Metal Transfer Modes and Fume Formation Rate [J]. Materials and Design, 2007, 28: 1623. Pires I, Quintino L, Miranda R M, et al. Fumes Emission During Gas Metal Arc Welding [J]. Toxicological and Environmental Chemistry, 2006, 8 8 ( 3 ) : 385. IIW. Statement on Manganese [MI. Villepinte: International Institute of Welding, 2005. Gray C N, Hewitt P J , Dare P R M. New Approach Would Help Control Weld Fumes at Source: Part 2 [J]. Welding and Metal Fabrication, 1982, (10): 393. Heile R F, Hill D C. Particulate Fume Generation in Arc Welding Processes [J]. Welding Journal, 1975, 54(7): 201s. Hewett P. T h e Particle Size Distribution, Density, and Specific Surface Area of Welding Fumes From SMAW and GMAW Mild and Stainless Steel Consumables [J]. American Industrial
(Continued From Page 58) C5l
References :
c11
C2l
c31
c41
C61 Fujio Abe. Precipitate Design for Creep Strengthening of 9% Cr Tempered Martensitic Steel for Ultra-Supercritical Power Plants [J]. Science and Technology of Advanced Materials, 2008, 9(1): 1. ZHU Ping, ZHAO Jian-cang, CHAI Xiao-yan, et al. Research on the Matching of Super 304H Austenitic Stainless Steel Welding Material and the Connector Performance [J]. Electrical Equipment, 2007, 8(4): 43 (in Chinese). Semba H , Igarashi M, Yamadera Y, et al. Report of the 123rd Committee on Heat-Resisting Materials and Alloys [J]. JSPS, 2003, 44(3): 119. TAN Shu-ping. Effect of Composition and Processing on Properties and Strengthening Mechanism of S30432 Steel [D]. Harbin: Harbin Institute of Technology, 2009.
c71 [81
[9l
[lo1
Sellars C M , Tegart W J McG. On the Mechanism of Hot D e formation [J]. Acta Metallurgical, 1966, 1 4 ( 9 ) : 1136. Jonas J J , Sellars C M, Tegart W J McC. Strength and Structure Under Hot-Working Conditions [J]. Metal Reviews, 1969, 14(130): 1. Sellars C M , Tegart W J McG. Hot Workability [J]. International Metallurgical Reviews, 1972, 17(158): l. LU Yun-hai, F U Rui-dong, QIU Liang, et al. Deformation Behavior of Nitrogen Strengthened High Manganese Austenitic Steel [J]. Transactions of Materials and Heat Treatment, 2007, 28(2): 69 (in Chinese). Zener C, Hollomon J H. Effect of Strain Rate Upon the Plastic of Steel [J]. J Appl Phys, 1944, 15(1): 22. Medina S F , Hernandez C A. General Expression of ZenerHollomon Parameter as a Function of the Chemical Composition of Low Alloy and Microalloy Steels [J]. Acta Mater, 1996, 44(1): 137.
*:2ScienceDirect JOURNAL OF IRON AND STEEL RESEARCH, INTERNATIONAL. 2011, 18(10): 54-58, 79
Hot Deformation Behaviors of S31042 Austenitic Heat-Resistant Steel WANG Jing-zhong”‘
,
LIU Zheng-dong’
,
CHENG Shi-chang’
,
BAO Han-sheng’
2. School of Metallurgy and (1. Central Iron and Steel Research Institute, Beijing 100081, China; Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, Shaanxi, China) Abstract: The hot deformation behavior of S31042 austenitic heat-resistant steel was investigated over the temperature range of 900- 1200 ‘C and strain rate range of 0. 01 - 10 s-l using hot compression tests and the corresponding flow curves were obtained. The hot deformation activation energy of the test steel is 625 kJ/mol. The hot deformation equation and the relationship between the peak stresses, deformation temperature and strain rate were set up. The Zener-Hollomon parameter under various conditions was determined. The relation between the Zener-Hollomon parameter and the microstructure evolution of test steel was discussed. With the decrease of Zener-Hollomon parameter, the microstructure of test steel transforms from deformation instability to dynamic recovery, partial dynamic recrystallization, full dynamic recrystallization with equiaxial structure, and finally to full dynamic recrystallization with mixed crystal structure. The deformation condition can be adjusted easily by utilizing the Zener-Hollomon parameter to obtain equiaxial microstructure. Key words: S31042 steel; hot deformation behavior; Zener-Hollomon parameter; microstructure
T h e ultra-supercritical ( USC ) power plants with increased steam parameter evidently improve the efficiency of coal-fired generator set, which reduces fuel consumption and the emissions of environmentally damaging gases“’. Therefore, the construction of USC power plants is under developing in China currently[’’. Owing to the increase in steam parameter, the elevated temperature properties of the materials to build components of USC power plants must be improved greatly. However, commercial 5331042 steel needed for constructing USC power plants in China, which was widely used as superheater and reheater for the boilers, is dependent on importation, influencing construction period, and the material cost is very high. For this reason, the domestic production of S31042 steel tube is urgently required. S31042 steel with good long-term strength at elevated temperature and high temperature steam oxidation resistance belongs to one of the multi-compositestrengthened austenitic heat-resistant steelsC3’. Because of large amount of alloying elements, the
hot deformation behavior will be the important issue during the seamless tube production. There is no report on hot deformation behavior of S31042 steel. LiteratureC4’had reported the hot deformation behavior of S30432 which also belongs to austenitic heat-resistant steel, but the difference in chemical composition between S31042 steel and S30432 steel is obvious, leading to the hot deformation results of S30432 steel not to be applied in S31042 steel. Therefore, investigating the quantitative relationship between flow stresses, deformation temperature and strain rate is of importance. The mechanical behaviors of S31042 steel during hot deformation were investigated using hot compression methods with Gleeble-3500 thermal-mechanical simulator. The experimental data were scientifically processed and the hot deformation equation, activation energy and the relationship between peak stress, deformation temperatures and strain rates of S31042 steel were obtained. The final microstructure of steel deformed under different conditions was analyzed corresponding to the change in
Foundation Item: Item Sponsored by National Science and Technology Support Plan of China (2007BAE51B02) E-mail: wzjxjd2003@yahoo. corn. cn; Received Date: September 25, 2010 Biography: WANG Jing-zhong(l974-), Male, Doctor:
Issue 10
55
Hot Deformation Behaviors of S31042 Austenitic Heat-Resistant Steel
polishing and electrolytic etching by 40% of nitric acid solution, the microstructure was observed by using optical microscope.
Zener-Hollomon parameter.
1 Experimental Procedure The test steel was smelted by a vacuum induction furnace and vacuum casted, forging into bar of 15 mm in diameter. The chemical composition (mass percent, %) of test steel is: C 0. 060, Cr 24. 20, Ni 20. 50, N 0.26, Nb 0.42, Mn 1.55, and Si 0.40. The size of specimen for hot compression is $8 mmX 15 mm. T h e hot compression experiment was carried out on Gleeble-3500 thermal-mechanical simulator. Prior to hot compression, all of the specimens were preheated to 1270 "Cand held for 180 s to ensure the specimens having same microstructure before deformation and cooled at 10 C / s to corresponding hot compression temperature. In order to have uniformity in temperature inside and outside of specimen, on cooling to the corresponding hot compression temperature, all the specimens must be held for 60 s before deformation. The hot compression experiment carried out over the temperature range from 900 to 1ZOO "Cand strain range from 0.01 s-l to 10 s-'. On reaching 1. 2 of true strain [E=ln(H/h), here H is initial height of the specimens before hot compression, and h is the final height of specimens after hot compression], specimen was cooled by water immediately. After cutting longitudinally, grinding and
100
2
Results and Discussion
Flow stress curves of S31042 steel The flow curves of S31042 steel deformed at different temperatures and strain rates for the total true strain of 1. 2 were obtained as shown in Fig. 1. It can be seen that with increase in the deformation temperature or decrease in deformation strain rate, the peak stress on the various flow stress curves decreases. When the deformation temperature is lower and the strain rate is higher, the flow curves belong to the type of dynamic recovery, for example, the flow curves obtained at temperature of 9 0 0 and 1000 "Cand strain rate of 1 and 10 s-'. For the deformation at 1200 'C, evident characteristics of full dynamic recrystallization, the appearance of static stress, can be found in these flow curves over the strain rate range from 0.01 to 10 s - l , as shown in Fig. 1 ( a ) to ( d ) . At the same deformation temperature, the flow stress of every curve decreases with the decrease in stain rate. Similarly, at the same strain rate, the flow stress of every curve also decreases with the increase in deformation temperature. Based on the further treatment of the results in
2. 1
7-I 1 100
l OOo
1200
B2 400
e
300 200
100
0
0.2
0.6
1.0
1.4
I
0.2
0
0.6
1.0
True strain (a) 0.01 s - l i
(b) 0.1 s-l;
(c)
1 s-l;
(d) 10 s-'.
Fig. 1 Flow curves of S31042 steel under different deformation conditions
1.
*
56
-
Fig. 1 , the peak strain E~ and peak stress up obtained from the flow curves are listed in Table 1. From Table 1, it can be seen evidently that at the same deformation temperature, the up will increase with the rise in strain rate, and meanwhile, corresponding peak true strain also increases. But in the case of equal strain rate, E , and up will gradually increase with the deformation temperature decrease. The appearance of maximal peak stress is at deformation temperature of 900 ‘Cand strain rate of 10 s-’ , and the minimal peak stress appears on the flow curve of 1ZOO *Cand 0.01 s-l. Table 1
EP
tion with the measured results of the flow curves in Fig. 1, the relationship curves between nominal peak stress and strain rate as well as deformation temperature can be obtained (in Fig. 2 and Fig. 3) in hot deformation process of the test steel. When the deformation temperature is a constant, taking partial derivative of the both sides of Eqn. ( 2 ) to strain rate, it can be obtained as
(3) When the strain rate is constant, taking partial derivative for both sides of Eqn. (2) to 1/T, it can be obtained as
Peak stress upand peak strain at different deformation conditions of test steel Deformation
a,/MPa
Vol. 18
Journal of Iron and Steel Research, International
Strain rate/s-’
temperature/%
0.01
0.1
1
10
900
308
365
380
430. 5
1000
174
219
293
333
1100
81
133
182
235
1200
51
70
124
157
900
0. 21
0. 30
0. 41
0. 46
1000
0. 19
0. 28
0. 40
0. 44
1100
0. 12
0. 23
0. 38
0. 43
1200
0. 18
0. 22
0. 29
0. 40
(4) According to Eqn. (2) and Eqn. (4) and the regressed analysis results from Fig. 2 and Fig. 3 , it can be obtained Q= 625 kJ/mol, n = 6. 713, and A = 6. 6 1 X l o ” . Consequently, under the deformation conditions over a temperature range of 900 - 1ZOO “C, the hot deformation equation of S31042 steel can be expressed as Eqn. (5). ;=6. 60X101’[sinh(0. 0 0 5 5 6 2 ~ , ) ] ~ ’X~ ’ ~ expl 1.5
2 . 2 Establishment of the hot deformation equation of S31042 steel According to Ref. [5] to Ref. [7], the relationship among the flow stress u , the deformation temperature T and the strain rate E. could be expressed by a typical hyperbolic sine function as follows: ;=A[ sinh(au)lnexp( -Q / R T ) (1) where, A , a and n are material constants which are independent of deformation temperature; Q is the hot deformation activation energy; R is the gas constant; T is Kelvin temperature; and u is the static stress, or peak stress, or the stress for a given strain. In this work, the peak stress is taken, and sinh(a 0,) is defined as the nominal peak stress. The value of a is calculated as 0. 005 562, according to Ref. [S]. After taking natural logarithms of both sides of Eqn. ( 1) and rearranging, it is obtained as l n [ s i n h ( a a ) ] = l ~ / n f Q / ( n R T ) - lnA/n (2) It can be seen from Eqn. (2) that when the deformation rate (or temperature) is constant, there is a linear relation between natural logarithm of the nominal peak stress and the natural logarithm of deformation rate (or the reciprocal of deformation temperature). On the basis of Eqn. (2) and in combina-
Is”
-
I
r\
rj
--?I
(5)
-
0.5 0 -
g -0.5 -1.5
-
-5
Fig. 2
-3
-1
In &
0
1
3
Relationship between peak stress and strain rate for S31042 steel
1.5 -
0.1 A 1
-1.5
v 10 6.6
7.0
7.4
7.8
IM)Om-‘
8.2
8.6
T
Fig. 3
Relationship between peak stress and deformation temperature for S31042 steel
' 57
Hot Deformation Behaviors of S31042 Austenitic Heat-Resistant Steel
Issue 10
2 . 3 Zener-Hollomon parameter and its relationship to the peak stress Zener-Hollomon parameter ( 2 parameter) , which was known as temperature modified strain rate, was widely used to characterize the combined effect of strain rate and temperature on the deformation process, especially on the deformation r e s i s t a n ~ e ~ as ~ - shown ' ~ ~ in the following equations. (6) Z=;exp(Q/RT) Substituting the Q value into Eqn. ( 6 1 , it can be obtained as Table 2
Z=Eexp(625 OOO/RT) (7) According to the deformation conditions and Eqn. ( 7 ) , the value of 2 parameter corresponding to different deformations can be confirmed and listed in Table 2 , and then the relation expression between In2 and a,[see Eqn. ( 8 ) ] as well as the fitted curves as Fig. 4 can be obtained by means of integrating the test results in Fig. 1. Obviously, in the present work, there exists a linear relation between I n 2 and a,, and the correlation coefficient is about 0. 991. g,=20. 0 4 l G f l 4 5 7 631. 706/T-901. 9 1 (8)
Zener-Hollomon parameter corresponding to different deformation conditions
Deformation temperature/%
Zener-Hollomon parameter 1 s-1
10 s-1
900
6. 80 X loz5
6. 8 0 X loz6
6. 80 X lo2'
6. 8 0 X 10''
1000
4 . 4 3 ~1023
4.43
x 1025 6. 00 X loz3
4. 43 x 1 0 2 6
6. 00 X loz1
x 1024 6. OOX 10"
4.43
1100 1200
1. 4 6 X l o z o
1.46 X loz1
1. 46 X 10"
1 . 4 6 1023 ~
0.01
s-1
0.1
s-1
6. 00 X loz4
1.0
450 350
g
0
-
w
250
M
b
-1.0
150 50
______~-~
45 Fig. 4
50
55
In2
60
65
70
Relationship between 2 parameter and peak stress for S31042 steel
2 . 4 Relationship between the hot deformation behavior of S31042 steel and Zener-Hollomon parameter Using the data listed in Table 2 , the relationship curves between the deformation temperatures, logarithm of strain rate and logarithm of Zener-Hollomon parameters are drawn as shown in Fig. 5. From Fig. 5 it can be seen that the Zener-Hollomon parameter increases apparently with the drop in deformation temperature and rise in strain rate. According to the microstructure obtained via different deformation conditions, the relationship map between deformation temperature, strain rate and Zener-Hollomon parameter can be devided roughly into different zones to characterize the state of the microstructure during hot processing under different deformation conditions with the same true strain t o 1.2. Accompanying t h e Zener-Hollomon parameter
-2.0
Fig. 5
900
1 000
1 100 Temperattwe/'T:
1 200
Zener-Hollomon parameter of S31042 steel under different conditions
decrease, the microstructure of materials deformed under different deformation conditions transforms from flow instability and dynamic recovery to partial dynamic recrystallization, full dynamic recrystallization with equiaxial grain, and finally to full dynamic recrystallization but with mixed crystal structure. When the strain is given, the relationship between the microstructure and Zener-Hollomon parameter can be determined using hot compression test. Based on Eqn. ( 7 ) and Fig. 5 , when the strain is preset, whatever change the deformation temperature and strain rate are, so long as the Zener-Hollomon parameter is known, the final microstructure can be conjectured after hot working. In other words, so long as the Zener-Hollomon parameter is identical, even though the deformation temperature or strain rate is different, the same microstructure
58
Journal of Iron and Steel Research, International
can be obtained. Associating with the microstructure and Zener-Hollomon parameter make it convenient for adjusting the hot working processes, but report on using this method in practice was not seen in technical literature up to now. T h e authors' research group believes that this method will be utilized in production practice in the near future. It was shown in Fig. 5 that when Zener-Hollomon parameter is above l o z 5 , the microstructure is flow instability and dynamic recovery, and its typical feature is shown in Fig. 6 ( a ) and (b). When 2 is in the range of ZenerHollomon parameter from 3. 16 X loz3 to 3. 16 X loz5, the deformation state of test steel is at
Vol. 18
partial dynamic recrystallization and its typical microstructures are shown in Fig. 6 (c) and (d) of which Zener-Hollomon parameters are 6 X l o z 3 and 6 X l o z 4 , respectively. When the Zener-Hollomon parameter is in the range of 3.16 X 10'' to 3.16 X l o z 3 , the deformation state of test steel is at full dynamic recrystallization and its typical microstructures with fine equiaxial crystal are shown in Fig. 6 ( e ) and ( f ). However, when the Zener Hollomon parameter is below 3. 16 X l o z 2 , the typical microstructure of test steel is mixed crystal as shown in Fig. 6 ( g ) corresponding to Zener Hollomon parameter of 6.00 X loz1. Based on the analysis above, it is evident that for
( a ) 1000 % , 1 s - ' , 2=4. 4 3 X l O Z 5 , flow instability; (b) 1000 C , 0. 1 s - l , dynamic recovery, 2=4. 43X102'; (c) 1100 C , 1 s - I , 2=6. OOX l o z 3 , partial dynamic recrystallization; ( d ) 1100 'C , 10 s - l , Z=6. OOX l o z 4 , partial dynamic recrystallization; (e) 1100 'C , 0. 1 sC1, 2=6. OOX l o z z , full dynamic recrystallization with fine grains; ( f ) 1200 C , 10 s - l , 2 = 1 . 4 6 X loz3; ( g ) 1100 C , 0.01 s - l , Z=6. OOX loz1, mixed crystal.
Fig. 6
Typical microstructure of s31042 steel deformed under different conditions (s=l. 2)
S31042 steel, the flow stress increases with increasing Zener-Hollomon parameter. T h e lower the Zener-Hollomon parameter, the larger the extent of flow softening, the more easily the dynamic recrystallization may occur, and the bigger the dynamic recrystallization grain size is. T o obtain good microstructure for S31042 steel, it is necessary to avoid processing at zone of Zener-Hollomon parameter which is below 3. 1 6 X lo" or above 3. 1 6 X loz3.
3 Conclusions 1) The hot deformation average activation energy is 625 kJ/mol of S31042 steel in the deformation condition range of this test. T h e hot deformation equation is established as € = 6 . 60X1019[sinh(0. 0 0 5 5 6 2 ~ ~ , ) X ]~.~~~
I?-
expl
2 ) For S31042 steel, the quantitative relation between the peak stress, the deformation temperature
and the strain rate can be described as a,=20. 041&+1457 631.706/T-901.91 3) For S31042 steel deformed under the condition of temperature of 900 to 1200 "C , strain rate of 0.01 to 10 s-' and e of 1 . 2 , with the decrease in deformation temperature and the increase in strain rate, the Zener-Hollomon parameter increases and the typical microstructure transforms from mixed crystal t o fine equiaxial crystallization, partial dynamic recrystallization, finally to dynamic recovery and flow instability. T o improve the hot deformation microstructure of S31042 steel, it is necessary to avoid the higher Zener-Hollomon parameter zone above 3. 16 X loz3 and the lower Zener-Hollomon parameter zone below 3. 16 X 10" when hot deformation was carried out. 4 ) Associating with the microstructure and Zener-Hollomon parameter will make it convenient for adjusting the hot working processes t o obtain expected final microstructure of S31042 steel. (Continued on Page 79)
Issu e 10
E ffect of Heat I n p u t on G a s Metal A r c Welded A us te nitic Sta inle s s Ste e l
and Forests, Government o f India for .providing financial support to curry out this investigation through a research and development project, No. 19/2005-CT. T h e authors also wish to thank Maila m India L i m i t e d , Pondicherry , f o r providing the welding consumables to carry out this research.
Hygiene Association Journal, 1995, 5 6 ( 2 ) : 128. Hilton D E , Plumridge P N. Particulate Fume Generation During GMAW and GTAW [J]. Welding and Metal Fabrication, 1991(12): 555. Ma J , Apps R L. MIG Transfer Discovery of Importance to Industry [J]. Welding and Metal Fabrication, 1982(9): 307. Gray C N , Hewitt P J , Dare R M. New Approach Would Help Control Weld Fumes at Source: Part 1 [J]. Welding and Metal Fabrication, 1982(9): 318. Gray C N , Hewitt P J , Hicks R. The Effeet of Oxygen on the Rate of Fume Formation in Metal Inert Gas Welding Arcs [C]/ Weld Pool Chemistry and Metallurgy. London: The Welding Institute, 1980: 167. The European Union. European Directive 86/642/CEE Regarding the Worker’s Protection Against Risks of Exposure to Chemical, Physical and Biological Agents During Work Activities [S]. Brussels: The European Union, 1986. American Welding Society. AWS/ANSI F1. 2 Laboratory Methods for Measuring Fume Generation Rates and Total Fume Emission of Welding and Allied Processes [S]. Miami: American Welding Society, 1992. Castner H R. Fume Generation Rates for Stainless Steel, Nickel and Aluminum Alloys [J]. Welding Journal, 1996(12): 393s. Jenkins N T, Eagar T W. Chemical Analysis of Welding Fume Particles [J]. Welding Journal, 2005, 84(Supplement) : 87s. Peter J Hewitt, Andrew D Workman. Health Consideration in Metal Arc Welding [J]. Australasian Welding Journal, 1997, 42(2): 23.
References :
c11 c21
C3l
C41 C5l
C6l c71
79 *
Voitkevich V. Welding Fumes-Formation, Properties and Biological Effects [MI. Nashville: Abington Publishing, 1995. Pires I , Quintino L, Miranda R M. Analysis of the Influence of Shielding Gas mixtures on the Gas Metal Arc Welding Metal Transfer Modes and Fume Formation Rate [J]. Materials and Design, 2007, 28: 1623. Pires I, Quintino L, Miranda R M, et al. Fumes Emission During Gas Metal Arc Welding [J]. Toxicological and Environmental Chemistry, 2006, 8 8 ( 3 ) : 385. IIW. Statement on Manganese [MI. Villepinte: International Institute of Welding, 2005. Gray C N, Hewitt P J , Dare P R M. New Approach Would Help Control Weld Fumes at Source: Part 2 [J]. Welding and Metal Fabrication, 1982, (10): 393. Heile R F, Hill D C. Particulate Fume Generation in Arc Welding Processes [J]. Welding Journal, 1975, 54(7): 201s. Hewett P. T h e Particle Size Distribution, Density, and Specific Surface Area of Welding Fumes From SMAW and GMAW Mild and Stainless Steel Consumables [J]. American Industrial
(Continued From Page 58) C5l
References :
c11
C2l
c31
c41
C61 Fujio Abe. Precipitate Design for Creep Strengthening of 9% Cr Tempered Martensitic Steel for Ultra-Supercritical Power Plants [J]. Science and Technology of Advanced Materials, 2008, 9(1): 1. ZHU Ping, ZHAO Jian-cang, CHAI Xiao-yan, et al. Research on the Matching of Super 304H Austenitic Stainless Steel Welding Material and the Connector Performance [J]. Electrical Equipment, 2007, 8(4): 43 (in Chinese). Semba H , Igarashi M, Yamadera Y, et al. Report of the 123rd Committee on Heat-Resisting Materials and Alloys [J]. JSPS, 2003, 44(3): 119. TAN Shu-ping. Effect of Composition and Processing on Properties and Strengthening Mechanism of S30432 Steel [D]. Harbin: Harbin Institute of Technology, 2009.
c71 [81
[9l
[lo1
Sellars C M , Tegart W J McG. On the Mechanism of Hot D e formation [J]. Acta Metallurgical, 1966, 1 4 ( 9 ) : 1136. Jonas J J , Sellars C M, Tegart W J McC. Strength and Structure Under Hot-Working Conditions [J]. Metal Reviews, 1969, 14(130): 1. Sellars C M , Tegart W J McG. Hot Workability [J]. International Metallurgical Reviews, 1972, 17(158): l. LU Yun-hai, F U Rui-dong, QIU Liang, et al. Deformation Behavior of Nitrogen Strengthened High Manganese Austenitic Steel [J]. Transactions of Materials and Heat Treatment, 2007, 28(2): 69 (in Chinese). Zener C, Hollomon J H. Effect of Strain Rate Upon the Plastic of Steel [J]. J Appl Phys, 1944, 15(1): 22. Medina S F , Hernandez C A. General Expression of ZenerHollomon Parameter as a Function of the Chemical Composition of Low Alloy and Microalloy Steels [J]. Acta Mater, 1996, 44(1): 137.