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Effect of austenitizing temperature on the mechanical properties of high-strength maraging steel
Materials Science & Engineering A 587 (2013) 209–212
Contents lists available at ScienceDirect
Materials Science & Engineering A journal homepage: www.elsevier.com/locate/msea
Effect of austenitizing temperature on the mechanical properties of high-strength maraging steel H. Hou, L. Qi, Y.H. Zhao n School of Materials Science and Engineering, North University of China, Taiyuan 030051, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 12 April 2013 Received in revised form 24 August 2013 Accepted 29 August 2013 Available online 5 September 2013
This paper investigates the effect of austenitizing temperature on mechanical properties of X00CrNiCoMo9-9-5-3 corrosion resistant maraging steel. The results show that solution treatment recrystallization temperature of this experimental steel is 850 1C. After a solution treatment below 850 1C, the experimental steel will change to form austenite via the non-dispersive phase transition from α′ to γ, which inherits the forging structure high density defects. Then the experimental steel can cool to form high strength martensitic steel. Moreover, high hardness austenite increases the resistance to phase transition in the cooling process and increases the content of retained austenite, thus guaranteeing excellent low temperature toughness of maraging steel. & 2013 Published by Elsevier B.V.
Keywords: Austenitizing temperature Low temperature solution treatment Mechanical properties Maraging steel
1. Introduction High-strength maraging steel has good corrosion resistance, and can be used in adverse environments such as corrosive atmosphere and so on without any surface protection. So it has good development trend. In order to improve the strength and toughness of maraging steel many scholars have researched its strengthening and toughening mechanism, but the current researches are mainly about the relationship between precipitates and alloying [1,2]. Maraging steel can be improved by solution and aging treatment, and to a great extent the solution treatment process can determine the effective grain size and strengthening by aging. So it is necessary to study the effect of solution treatment process on the microstructure [3,4]. Solution treatment temperature of martensite stainless steel is usually higher. Spiridonov has studied the effect of heat treatment on the microstructure and mechanical properties of maraging steel, and it is concluded that martensite stainless steel can obtain high strength and toughness ratio only when the temperature is above 950 1C [5]. But high solution temperature can lead to austenite grain growth, which produces unfavorable effects on mechanical properties [6]. Liu has found that the Cr–Co–Ni–Mo maraging stainless steel austenitizing at 1050 1C can optimize its tensile mechanical properties [7]. However, so far, no paper has systematically studied the effect
n
Corresponding author. Tel.: þ 86 15035172958; fax: þ 86 3513557519. E-mail addresses: [email protected], [email protected], [email protected] (Y.H. Zhao). 0921-5093/$ - see front matter & 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.msea.2013.08.070
of austenitizing temperature on strength and toughness of Cr–Co–Ni–Mo maraging stainless steel [8]. Therefore, the aim of the work is to study the mechanical properties of a corrosion resistant maraging steel (X00CrNiCoMo99-5-3) with different solution treatment temperatures. The results showed that the strength of a low solution treatment temperature specimen was obviously higher than those at other temperatures. For example, the impact energy of specimen with solid solution treated at 750 1C is six times more than that of 1000 1C. By a solution treatment at lower temperature, such maraging steel can not only save energy, but also guarantee excellent strength and toughness ratio, so it is very meaningful to research it further.
2. Material and experimental procedures The chemical constituents of the test steel are shown in Table 1. Through vacuum induction furnace smelting þvacuum selfconsuming re-melting (the mass of melted steel was 25 kg), the test steel raw materials were made into ingots. Then they were forged (end forging temperature is 850 1C) into a 40 40 mm2 rod. With a Formastor-D full-automatic phase change measuring instrument, the As and Af temperatures were measured as 620 1C and 690 1C, respectively. Metallographic samples and billets were cut out along the length of the forged rod. The specimen billets were treated by solid solution at 750, 800, 850, 900, 950 and 1000 1C , and kept warm for 1 h followed by water cooling. Then the aging treatment was carried out at 500 1C for 2 h. Afterwards the specimen billets were processed into standard tensile specimens and U-notch impact specimens. The tensile
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H. Hou et al. / Materials Science & Engineering A 587 (2013) 209–212
temperature impact fracture morphologies of solution treatment specimens at 750 1C and 1000 1C. From the picture it can be seen that the fracture mode of higher solution temperature material at low temperature is mainly brittle fracture, and only in a local area there exists ductile tearing. Therefore, with solution temperature decreasing, ductile tearing area proportion gradually increases [11]. The low temperature impact fracture of solution specimen at 1000 1C is not only flat but also with no plastic deformation, the energy consumption of unstable crack extension is low, low temperature impact absorbing energy is only 10 J and the fracture mechanism exhibits quasicleavage fracture. The low temperature impact fracture of solution specimen at 750 1C is mainly dimple fracture. When the solution specimens undergo plastic deformation, applied external force makes the dislocation movement gather in inclusions place, and accumulated elastic strain energy makes the interface between inclusions and matrix interface form microvoids. These microvoids are interconnected to form the morphology of dimple fractures. The spherical inclusions at the bottom of the dimple were sulfide inclusions by EDS analysis. Small sleek inclusions slow down stress focus, reduce crack propagation, and increase tenacity [12].
specimens were 5 mm in diameter and 65 mm in length. The dimension of U-notch impact specimens was 10 10 55 mm3. The room temperature tensile properties were determined by an MTS-810 tensile testing machine. The U-notch impact absorbing energies were measured by a JBN300 impact testing machine at room temperature (20 1C) and liquid nitrogen temperature ( 196 1C). The microstructures of metallographic samples were examined and analyzed by an OLYMPUS Gx51 Metalloscope. Fracture morphology of impact specimens was analyzed by S-4300 SEM. The phase compositions of metallographic samples were measured by a PHILIPS APD-10 X. According to the data collected from the diffraction instrument, austenite volume fraction was determined [9].
3. Results and discussion 3.1. Effect of solution temperature on mechanical properties As shown in Fig. 1, specimen elongation percentage and reduction of area increase as the temperature rises to the maximum of 15% and 68%, respectively. Room temperature impact energy has a certain dispersion, but the change of solution temperature has no significant effect on it [10]. It is noteworthy that with solution temperature rising from 750 1C to 1000 1C, the material's tensile strength drops from 1380 MPa to 1200 MPa, yield strength drops from 1353 MPa to 1123 MPa, and low temperature ( 196 1C) impact absorbing energy drops from 60 J to 10 J. It is obvious that low temperature solution treatment can improve the comprehensive mechanical properties of the test steel; therefore, the operational reliability of the component at low temperature can be assured.
3.3. Effect of solution treatment temperature on microstructure The original forging state specimens without heating treatment were observed by a metalloscope. It was found that deformation austenite grains existed in the original organization, which indicated that the dynamic recrystallization of material was incomplete in forging processes, and deformation state and lots of microdefects were still in grains. Specimens at low solution temperature for 1 h still inherit forging state organization; as shown in Fig. 3(a), grain boundaries present zigzag shape, near which tiny recrystallization grains appear. The phenomenon indicates that at lower solution temperature, the X00Cr NiCoMo9-9-5-3 steel changes to form austenite via the nondispersive phase transition from α′ to γ [13], which retains a large number of dislocation defects of forging state martensite and makes it stable in hardening state. This indicates that when the solution temperature rises to 900 1C, austenite is formed by recrystallization, and the grains present equiaxial shape [14]. As shown in Fig. 3(b), at a temperature above 950 1C the recrystallization austenite grains grow up gradually and present obvious equiaxial shape. When the solution treatment temperature further rises, the test steel still changes to form austenite via the nondispersive phase transition from α′ to γ. But at the moment, the
3.2. Low temperature impact on fracture morphology As mentioned above, after solution treatment at different temperatures, low temperature impact toughness of the experimental steel shows large differences. Fig. 2 indicates the low Table 1 Chemical compositions of the test steel. C
Cr
Ni
Co
Mo
Al
Si
Mn
P
S
0.0024
8.94
9.35
4.94
2.57
0.018
0.29
0.26
0.0054
0.0039
160
100
1400
140
1200 80
120
tensile strength yield strength
600
40
elongation after fracture
400
100
Aku2 /J
60
800
A, Z /%
Rp0.2, Rm /MPa
1000
80 60 the room temperature
reduction of area
40
liquid nitrogen impact
20 200
20
0
0 750
800
850
900
950
Solution temperature /
1000
0 750
800
850
900
950
Solution temperature /
Fig. 1. Effect of solution temperature on mechanical properties.
1000
H. Hou et al. / Materials Science & Engineering A 587 (2013) 209–212
211
Fig. 2. SEM fractography of impact fracture at low temperature ( 196 1C).
Fig. 3. Microstructure after different solution temperature treatments. (a and b) Grain morphology at 750 1C, 1000 1C 200 . (c and d) Metallographic morphology at 750 1C, 1000 1C 1000 .
organization will proceed with the recovery, grain boundary migration and recrystallization [13,15], and the reserved defects disappear, thus reducing the strength of steel. Fig. 3(c) shows that at low solution treatment temperature martensite organization is fine. But when the solution treatment temperature was raised, martensite organization coarsened seriously, as shown in Fig. 3(d). Fine martensite lath size not only enhances strength and toughness of the material directly, but also makes strengthening phase that precipitated in aging process distribute more uniformly [16], thus improving comprehensive mechanical properties of the test steel. 3.4. Effect of solution treatment temperature on the retained austenite content Fig. 4 shows the analysis results of the amount of retained austenite in the specimens before and after aging treatment. Using the contrast method for calculation, the amount of retained
austenite in the specimens at 750 1C is 7.39%, but it is only 0.49% at 1000 1C. This indicates that with solution temperature rising, retained austenite content reduces quickly. This is because at 750 1C austenite inherits higher defect density of forging state organization and increases the resistance to martensitic transformation during cooling, thus enhancing the amount of retained austenite. However, with solution treatment temperature rising, the defects in austenite begin to recover and increase the ability of martensitic transformation during cooling, thus reducing the amount of austenite. So the amount of retained austenite at 1000 1C is 1/15 that of 750 1C. Besides, Fig. 4 also shows that above 900 1C, eventual retained austenite content in organization is maintained at about 0.5%. This is due to the fact that austenite is formed by recovery and recrystallization, and the phase transformation from γ to α′ is complete. Compared with solution treatment specimens, after aging treatment, the amount of retained austenite is higher. This is because some reverted austenites are formed during aging treatment.
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H. Hou et al. / Materials Science & Engineering A 587 (2013) 209–212
(2) The high hardened degree austenites in the test steel are formed through a low temperature solution treatment, which increase the phase transformation resistance to γ-α′ during cooling and a large amount of retained austenite ensures a test steel with good low temperature toughness.
Volume fraction of retained austenite /%
10
8
6
the specimens without aging
Acknowledgments
the specimens with aging 4
This research was sponsored by the Project supported by FANEDD (No. 20101420120005), the Shanxi Provincial Foundation for Returned Scholars China (No. 2010-78), the National Natural Science Foundation of China (No. 50975263), and the Special Program for International S&T Cooperation of the Ministry of Science and Technology, China (No. 2011DFA50520).
2
0
References 750
800
850
900
950
1000
Solution temperature / Fig. 4. Effect of solution treatment on the retained austenite volume fraction.
Other reports pointed out that retained austenite existing in the martensitic matrix can guarantee larger low temperature ( 196 1C) impact toughness [17,18]. Moreover, in this experiment, the impact energy of specimen with solid solution treated at 750 1C is six times more than that of 1000 1C. This is because austenite ductile phase existing in low solution treatment temperature specimen can passivate crack tip and ease the stress concentration, thus guaranteeing excellent toughness of the matrix [19]. 4. Conclusions (1) X00CrNiCoMo9-9-5-3 corrosion resistant maraging steel during low temperature solution treatment via the non-dispersive phase transition from α′ to γ to form the austenite inherited the higher defects density of the forging state; hardened degree of martensite is higher followed by cooling, making the test steel stronger.
[1] E.U. Lee, R. Goswami, M. Jones, et al., Metall. Mater. Trans. A 42 (2011) 415–423. [2] X.Q. Li, Y.P. Song, Foundry Technol. 32 (2011) 95–96. [3] Z.L. Xie, Z.Y. Liu, J. Chen, R. Xu, G.D. Wang, J. Iron Steel Res. 23 (2011) 37–41. [4] Y. Lu, J.H. Wang, J. Su, Z.Y. Yang, G. Xie, Special Steel 32 (2011) 60–63. [5] V.B. Spiridonov, V.S. Fridman, Met. Sci. Heat Treat. 7 (1975) 589–594. [6] S.G. Chernyavskaya, V.S. Fridman, S.I. Krasnikova, A.V. Drobot, A.F. Lednyanskii, Met. Sci. Heat Treat. 3 (1978) 241–242. [7] K. Liu, Y.Y. Shan, Z.Y. Yang, J. Mater. Sci. Technol. 22 (2006) 769–774. [8] W. Wang, L.X. Li, Z.Y. Yang, H. Hou, Y.L. Ding, Foundry Technol. 33 (2012) 405–407. [9] A. Mahmudi, S.H. Nedjad, M.M.J. Behnam, Int. J. Miner. Metall. Mater. 18 (2011) 557–561. [10] Q. Zhang, M.J. Wang, L.W. Zhang, D.B. Yu, Y.T. Yang, J. Wu, Trans. Mater. Heat Treat. 25 (2004) 30–34. [11] B. Paul, S. Bruno, HTM Haerterei-Tech. Mitt. 33 (1978) 1–12. [12] C. Lang, J.I. Teindl, Prot. Met. 9 (1973) 139–142. [13] V.D. Sadovskii, G.N. Bogacheva, V.M. Umova, Met. Sci. Heat Treat. 11 (1969) 258–259. [14] V.M. Schastlivtsev, A.I. Uvarov, Y.I. Anufrieva, I.L. Yakovleva, M.S. Khadyev, A.A. Kruglov, Fiz. Met. Metalloved 8 (1991) 183–190. [15] S.S. Ryzhak, L.N. Belyakov, Ya.M. Potak, G.G. Solov'eva, L.M. Pevzner, V.V. Sachkov, O.K. Revyakin, Met. Sci. Heat Treat. 14 (1972) 150–155. [16] V.P. ll'ina, V.A. Troitskaya, Met. Sci. Heat Treat. 42 (2000) 53–56. [17] N.A. Sorokina, N.A. Pavlenko, N.V. Andrushova, Met. Sci. Heat Treat. 32 (1990) 598–602. [18] V.L. Nikol'skaya, L.M. Pevzner, N.G. Orekhov, Met. Sci. Heat Treat. 17 (1975) 763–767. [19] K.R. Chen, J.X. Li, J.Z. Wu, Iron Steel 20 (1985) 24–30.
Contents lists available at ScienceDirect
Materials Science & Engineering A journal homepage: www.elsevier.com/locate/msea
Effect of austenitizing temperature on the mechanical properties of high-strength maraging steel H. Hou, L. Qi, Y.H. Zhao n School of Materials Science and Engineering, North University of China, Taiyuan 030051, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 12 April 2013 Received in revised form 24 August 2013 Accepted 29 August 2013 Available online 5 September 2013
This paper investigates the effect of austenitizing temperature on mechanical properties of X00CrNiCoMo9-9-5-3 corrosion resistant maraging steel. The results show that solution treatment recrystallization temperature of this experimental steel is 850 1C. After a solution treatment below 850 1C, the experimental steel will change to form austenite via the non-dispersive phase transition from α′ to γ, which inherits the forging structure high density defects. Then the experimental steel can cool to form high strength martensitic steel. Moreover, high hardness austenite increases the resistance to phase transition in the cooling process and increases the content of retained austenite, thus guaranteeing excellent low temperature toughness of maraging steel. & 2013 Published by Elsevier B.V.
Keywords: Austenitizing temperature Low temperature solution treatment Mechanical properties Maraging steel
1. Introduction High-strength maraging steel has good corrosion resistance, and can be used in adverse environments such as corrosive atmosphere and so on without any surface protection. So it has good development trend. In order to improve the strength and toughness of maraging steel many scholars have researched its strengthening and toughening mechanism, but the current researches are mainly about the relationship between precipitates and alloying [1,2]. Maraging steel can be improved by solution and aging treatment, and to a great extent the solution treatment process can determine the effective grain size and strengthening by aging. So it is necessary to study the effect of solution treatment process on the microstructure [3,4]. Solution treatment temperature of martensite stainless steel is usually higher. Spiridonov has studied the effect of heat treatment on the microstructure and mechanical properties of maraging steel, and it is concluded that martensite stainless steel can obtain high strength and toughness ratio only when the temperature is above 950 1C [5]. But high solution temperature can lead to austenite grain growth, which produces unfavorable effects on mechanical properties [6]. Liu has found that the Cr–Co–Ni–Mo maraging stainless steel austenitizing at 1050 1C can optimize its tensile mechanical properties [7]. However, so far, no paper has systematically studied the effect
n
Corresponding author. Tel.: þ 86 15035172958; fax: þ 86 3513557519. E-mail addresses: [email protected], [email protected], [email protected] (Y.H. Zhao). 0921-5093/$ - see front matter & 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.msea.2013.08.070
of austenitizing temperature on strength and toughness of Cr–Co–Ni–Mo maraging stainless steel [8]. Therefore, the aim of the work is to study the mechanical properties of a corrosion resistant maraging steel (X00CrNiCoMo99-5-3) with different solution treatment temperatures. The results showed that the strength of a low solution treatment temperature specimen was obviously higher than those at other temperatures. For example, the impact energy of specimen with solid solution treated at 750 1C is six times more than that of 1000 1C. By a solution treatment at lower temperature, such maraging steel can not only save energy, but also guarantee excellent strength and toughness ratio, so it is very meaningful to research it further.
2. Material and experimental procedures The chemical constituents of the test steel are shown in Table 1. Through vacuum induction furnace smelting þvacuum selfconsuming re-melting (the mass of melted steel was 25 kg), the test steel raw materials were made into ingots. Then they were forged (end forging temperature is 850 1C) into a 40 40 mm2 rod. With a Formastor-D full-automatic phase change measuring instrument, the As and Af temperatures were measured as 620 1C and 690 1C, respectively. Metallographic samples and billets were cut out along the length of the forged rod. The specimen billets were treated by solid solution at 750, 800, 850, 900, 950 and 1000 1C , and kept warm for 1 h followed by water cooling. Then the aging treatment was carried out at 500 1C for 2 h. Afterwards the specimen billets were processed into standard tensile specimens and U-notch impact specimens. The tensile
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H. Hou et al. / Materials Science & Engineering A 587 (2013) 209–212
temperature impact fracture morphologies of solution treatment specimens at 750 1C and 1000 1C. From the picture it can be seen that the fracture mode of higher solution temperature material at low temperature is mainly brittle fracture, and only in a local area there exists ductile tearing. Therefore, with solution temperature decreasing, ductile tearing area proportion gradually increases [11]. The low temperature impact fracture of solution specimen at 1000 1C is not only flat but also with no plastic deformation, the energy consumption of unstable crack extension is low, low temperature impact absorbing energy is only 10 J and the fracture mechanism exhibits quasicleavage fracture. The low temperature impact fracture of solution specimen at 750 1C is mainly dimple fracture. When the solution specimens undergo plastic deformation, applied external force makes the dislocation movement gather in inclusions place, and accumulated elastic strain energy makes the interface between inclusions and matrix interface form microvoids. These microvoids are interconnected to form the morphology of dimple fractures. The spherical inclusions at the bottom of the dimple were sulfide inclusions by EDS analysis. Small sleek inclusions slow down stress focus, reduce crack propagation, and increase tenacity [12].
specimens were 5 mm in diameter and 65 mm in length. The dimension of U-notch impact specimens was 10 10 55 mm3. The room temperature tensile properties were determined by an MTS-810 tensile testing machine. The U-notch impact absorbing energies were measured by a JBN300 impact testing machine at room temperature (20 1C) and liquid nitrogen temperature ( 196 1C). The microstructures of metallographic samples were examined and analyzed by an OLYMPUS Gx51 Metalloscope. Fracture morphology of impact specimens was analyzed by S-4300 SEM. The phase compositions of metallographic samples were measured by a PHILIPS APD-10 X. According to the data collected from the diffraction instrument, austenite volume fraction was determined [9].
3. Results and discussion 3.1. Effect of solution temperature on mechanical properties As shown in Fig. 1, specimen elongation percentage and reduction of area increase as the temperature rises to the maximum of 15% and 68%, respectively. Room temperature impact energy has a certain dispersion, but the change of solution temperature has no significant effect on it [10]. It is noteworthy that with solution temperature rising from 750 1C to 1000 1C, the material's tensile strength drops from 1380 MPa to 1200 MPa, yield strength drops from 1353 MPa to 1123 MPa, and low temperature ( 196 1C) impact absorbing energy drops from 60 J to 10 J. It is obvious that low temperature solution treatment can improve the comprehensive mechanical properties of the test steel; therefore, the operational reliability of the component at low temperature can be assured.
3.3. Effect of solution treatment temperature on microstructure The original forging state specimens without heating treatment were observed by a metalloscope. It was found that deformation austenite grains existed in the original organization, which indicated that the dynamic recrystallization of material was incomplete in forging processes, and deformation state and lots of microdefects were still in grains. Specimens at low solution temperature for 1 h still inherit forging state organization; as shown in Fig. 3(a), grain boundaries present zigzag shape, near which tiny recrystallization grains appear. The phenomenon indicates that at lower solution temperature, the X00Cr NiCoMo9-9-5-3 steel changes to form austenite via the nondispersive phase transition from α′ to γ [13], which retains a large number of dislocation defects of forging state martensite and makes it stable in hardening state. This indicates that when the solution temperature rises to 900 1C, austenite is formed by recrystallization, and the grains present equiaxial shape [14]. As shown in Fig. 3(b), at a temperature above 950 1C the recrystallization austenite grains grow up gradually and present obvious equiaxial shape. When the solution treatment temperature further rises, the test steel still changes to form austenite via the nondispersive phase transition from α′ to γ. But at the moment, the
3.2. Low temperature impact on fracture morphology As mentioned above, after solution treatment at different temperatures, low temperature impact toughness of the experimental steel shows large differences. Fig. 2 indicates the low Table 1 Chemical compositions of the test steel. C
Cr
Ni
Co
Mo
Al
Si
Mn
P
S
0.0024
8.94
9.35
4.94
2.57
0.018
0.29
0.26
0.0054
0.0039
160
100
1400
140
1200 80
120
tensile strength yield strength
600
40
elongation after fracture
400
100
Aku2 /J
60
800
A, Z /%
Rp0.2, Rm /MPa
1000
80 60 the room temperature
reduction of area
40
liquid nitrogen impact
20 200
20
0
0 750
800
850
900
950
Solution temperature /
1000
0 750
800
850
900
950
Solution temperature /
Fig. 1. Effect of solution temperature on mechanical properties.
1000
H. Hou et al. / Materials Science & Engineering A 587 (2013) 209–212
211
Fig. 2. SEM fractography of impact fracture at low temperature ( 196 1C).
Fig. 3. Microstructure after different solution temperature treatments. (a and b) Grain morphology at 750 1C, 1000 1C 200 . (c and d) Metallographic morphology at 750 1C, 1000 1C 1000 .
organization will proceed with the recovery, grain boundary migration and recrystallization [13,15], and the reserved defects disappear, thus reducing the strength of steel. Fig. 3(c) shows that at low solution treatment temperature martensite organization is fine. But when the solution treatment temperature was raised, martensite organization coarsened seriously, as shown in Fig. 3(d). Fine martensite lath size not only enhances strength and toughness of the material directly, but also makes strengthening phase that precipitated in aging process distribute more uniformly [16], thus improving comprehensive mechanical properties of the test steel. 3.4. Effect of solution treatment temperature on the retained austenite content Fig. 4 shows the analysis results of the amount of retained austenite in the specimens before and after aging treatment. Using the contrast method for calculation, the amount of retained
austenite in the specimens at 750 1C is 7.39%, but it is only 0.49% at 1000 1C. This indicates that with solution temperature rising, retained austenite content reduces quickly. This is because at 750 1C austenite inherits higher defect density of forging state organization and increases the resistance to martensitic transformation during cooling, thus enhancing the amount of retained austenite. However, with solution treatment temperature rising, the defects in austenite begin to recover and increase the ability of martensitic transformation during cooling, thus reducing the amount of austenite. So the amount of retained austenite at 1000 1C is 1/15 that of 750 1C. Besides, Fig. 4 also shows that above 900 1C, eventual retained austenite content in organization is maintained at about 0.5%. This is due to the fact that austenite is formed by recovery and recrystallization, and the phase transformation from γ to α′ is complete. Compared with solution treatment specimens, after aging treatment, the amount of retained austenite is higher. This is because some reverted austenites are formed during aging treatment.
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H. Hou et al. / Materials Science & Engineering A 587 (2013) 209–212
(2) The high hardened degree austenites in the test steel are formed through a low temperature solution treatment, which increase the phase transformation resistance to γ-α′ during cooling and a large amount of retained austenite ensures a test steel with good low temperature toughness.
Volume fraction of retained austenite /%
10
8
6
the specimens without aging
Acknowledgments
the specimens with aging 4
This research was sponsored by the Project supported by FANEDD (No. 20101420120005), the Shanxi Provincial Foundation for Returned Scholars China (No. 2010-78), the National Natural Science Foundation of China (No. 50975263), and the Special Program for International S&T Cooperation of the Ministry of Science and Technology, China (No. 2011DFA50520).
2
0
References 750
800
850
900
950
1000
Solution temperature / Fig. 4. Effect of solution treatment on the retained austenite volume fraction.
Other reports pointed out that retained austenite existing in the martensitic matrix can guarantee larger low temperature ( 196 1C) impact toughness [17,18]. Moreover, in this experiment, the impact energy of specimen with solid solution treated at 750 1C is six times more than that of 1000 1C. This is because austenite ductile phase existing in low solution treatment temperature specimen can passivate crack tip and ease the stress concentration, thus guaranteeing excellent toughness of the matrix [19]. 4. Conclusions (1) X00CrNiCoMo9-9-5-3 corrosion resistant maraging steel during low temperature solution treatment via the non-dispersive phase transition from α′ to γ to form the austenite inherited the higher defects density of the forging state; hardened degree of martensite is higher followed by cooling, making the test steel stronger.
[1] E.U. Lee, R. Goswami, M. Jones, et al., Metall. Mater. Trans. A 42 (2011) 415–423. [2] X.Q. Li, Y.P. Song, Foundry Technol. 32 (2011) 95–96. [3] Z.L. Xie, Z.Y. Liu, J. Chen, R. Xu, G.D. Wang, J. Iron Steel Res. 23 (2011) 37–41. [4] Y. Lu, J.H. Wang, J. Su, Z.Y. Yang, G. Xie, Special Steel 32 (2011) 60–63. [5] V.B. Spiridonov, V.S. Fridman, Met. Sci. Heat Treat. 7 (1975) 589–594. [6] S.G. Chernyavskaya, V.S. Fridman, S.I. Krasnikova, A.V. Drobot, A.F. Lednyanskii, Met. Sci. Heat Treat. 3 (1978) 241–242. [7] K. Liu, Y.Y. Shan, Z.Y. Yang, J. Mater. Sci. Technol. 22 (2006) 769–774. [8] W. Wang, L.X. Li, Z.Y. Yang, H. Hou, Y.L. Ding, Foundry Technol. 33 (2012) 405–407. [9] A. Mahmudi, S.H. Nedjad, M.M.J. Behnam, Int. J. Miner. Metall. Mater. 18 (2011) 557–561. [10] Q. Zhang, M.J. Wang, L.W. Zhang, D.B. Yu, Y.T. Yang, J. Wu, Trans. Mater. Heat Treat. 25 (2004) 30–34. [11] B. Paul, S. Bruno, HTM Haerterei-Tech. Mitt. 33 (1978) 1–12. [12] C. Lang, J.I. Teindl, Prot. Met. 9 (1973) 139–142. [13] V.D. Sadovskii, G.N. Bogacheva, V.M. Umova, Met. Sci. Heat Treat. 11 (1969) 258–259. [14] V.M. Schastlivtsev, A.I. Uvarov, Y.I. Anufrieva, I.L. Yakovleva, M.S. Khadyev, A.A. Kruglov, Fiz. Met. Metalloved 8 (1991) 183–190. [15] S.S. Ryzhak, L.N. Belyakov, Ya.M. Potak, G.G. Solov'eva, L.M. Pevzner, V.V. Sachkov, O.K. Revyakin, Met. Sci. Heat Treat. 14 (1972) 150–155. [16] V.P. ll'ina, V.A. Troitskaya, Met. Sci. Heat Treat. 42 (2000) 53–56. [17] N.A. Sorokina, N.A. Pavlenko, N.V. Andrushova, Met. Sci. Heat Treat. 32 (1990) 598–602. [18] V.L. Nikol'skaya, L.M. Pevzner, N.G. Orekhov, Met. Sci. Heat Treat. 17 (1975) 763–767. [19] K.R. Chen, J.X. Li, J.Z. Wu, Iron Steel 20 (1985) 24–30.