- Email: [email protected]
Relationship of microstructure transformation and hardening behavior of type 17-4 PH stainless steel
Materials
Journal of University of Science and Technology Beijing Volume 13, Number 3, June 2006, Page 235
Relationship of microstructure transformation and hardening behavior of type 17-4 PH stainless steel Jun Wing”, Hong Zou2’,Cong Li”,Ruling Zuo3’,Shaoyu Qiu’’, and Baoluo Shen” I ) School of Materials Science and Engineering, Sichuan University, Chengdu 6 10064, China 2) National Key Laboratory for Nuclear Fuel and Materials, Nuclear Power Institute of China, P.O. Box 436, Chengdu 610041, China
3) School of Materials Science and Engineering, Chongqing University, Chongqing 400044. China (Received 2005-01-12)
Abstract: The relationship between the microstructure transformation of type 17-4 PH stainless steel and the aging hardening behavior was investigated. The results showed that, when 17-4 PH stainless steel aging at 595°C the bulk hardness of samples attains its peak value (42.5 HRC) for about 20 min, and then decreases at all time. TEM revealed the microstructure corresponding with peak hardness is that the fine spheroid-shape copper with the fcc crystal structure and the fiber-shape secondary carbide M,,C, precipitated from the lath martensite matrix. Both precipitations of copper and M&, are the reasons for strengthening of the alloy at this temperature. With the extension of holding time at this temperature, the copper and secondary carbide grow and lose the coherent relationship with the matrix, so the bulk hardness of samples decreases. Key words: 17-4 PH stainless steel; H1 100 condition; precipitation; copper; secondary carbide
[This work was financially supported (N0.51481080104ZS8501).]
by the
Key
Nuclear Fuel
1. Introduction The 17-4 PH (precipitation hardening) stainless steel is a martensite stainless steel containing approximately 3wt% Cu and is strengthened by the precipitation of highly dispersed copper particles in the martensite matrix [I-41. This alloy is more common than any other type of precipitation hardened stainless steels due to its excellent mechanical properties and excellent corrosion resistance [5-91. The condition of H900 (peak-aged condition) and HI 100 (over-aged condition) of this precipitationhardenable stainless steel are usually used conditions, but recently, some researchers found the alloy in H900 condition has more embrittlement tendency in some important working conditions [ 10-121. Now type 17-4 PH martensite stainless steel in the over H1 100 condition has been used in light water reactors (LWRs) and pressurized water reactors (PWRs) for components requiring a combination of high wear resistance, high strength, and good corrosion resistance [ 131.
and
Nuclear Materials
h b o r a t o t y of
Most researchers focused on evolution of the precipitation of copper [3, 7-8, 14-16], few are awareness of other precipitates in this alloy in HI 100 condition. And the relationship of the mechanical properties of 17-4 PH stainless steel in H1100 condition with the microstructure and its revolution is not clear. The study of detailed microstructure in 17-4 PH stainless steel after solution treatment and aging has assumed great significance due to the treatment influence on the mechanical properties. The aim of the present work is to investigate the phase transformation and the aging hardening behavior of this stainless steel at various stages of aging and to try to give an insight of the relationship of hardening behavior with microstructure of the alloy.
2. Material and experimental procedures The chemical composition of the 17-4 PH stainless steel is given in Table 1.
Table 1. Composition of the type 17-4 PH stainless steel C
Cr
Ni
cu
Nb
Si
Mn
P
S
0.04
16.39
4.32
3.4
0.36
0.6
0.3
0.023
0.013
Corresponding author: Jun Wang, E-mail: [email protected]
China
Fe Bal.
236
The initial material as-delivered for test specimens, which was sheet metal hot rolled to 20 mm in an L-T (longitudinal-transverse) orientation, was made in Changcheng Special Steel Corporation (Sichuan, China) and subsequently cut into specimens with the dimension of 10 mmxlO mmx55 mm. Heat treatment comprised two steps: ( 1 ) Solution treatment for 30 min at 1O4O0C, and then oil quench;
(2) Aging for various time at 595°C (Fahrenheit 1 100) and then air cool. The bulk hardness was measured using a Rockwell hardness meter with a load of 1.47 kN. Discs for transmission electron microscopy were prepared by standard techniques and thin foils produced using a twin-jet electropolisher. These samples were examined in a Philips Tecnai 20HR-TEM (high resolution transmission electron microscopy) equipped with EDX (energy dispersive X-ray analyzer). Philip X'Pert X-ray diffraction instrument was used to identify the
J. Univ. Sci. TechnoL Beijing, VoL13,No.3, Jun 2006 microstructure of this type alloy too.
3. Results and discussion 3.1. Solution treated microstructure The Martensite transformation start (M,)of the stainless steel is around 105°C [3]. Hence, the microstructures of martensite could be obtained easily in 174 PH stainless steel. The transmission electron micrograph with a low magnification, as shown in Fig. 1, was obtained from the solution-treated specimen, the corresponding microstructure is composed basically of lath martensite. The martensite laths have a high dislocation density, and micro-twins (arrowed) could often be observed in the martensite laths. The finding of micro-twins is accordant with those reported by C.S. Chiou [3] and Habibi-Bajguirani [ 161. The existence of twin-related laths was interpreted as a result of the accommodation of the strain created by the adjacent laths [ 161.
Fig. 1. TEM micrographs (a) showing twins (arrowed) in lath martensite formed in 17-4 PH stainless steel and its diffraction electron pattern (b) showing the presence of only one set of diffraction spots.
According to the Fe-Cu phase diagram, the solubility of Cu atoms increase to 7wt% at 1040°C [3]. It is therefore suggested that the matrix phase of 17-4 PH stainless steel is supersaturated with Cu after the solution treatment at 1040°C. But failure to detect copper precipitates in martensite laths after solution treatment indicates that the martensite phase is supersaturated with Cu in the solution-treated condition.
3.2. Hardening behavior Since the strength of 17-4 PH stainless steel is enhanced by the formation of copper precipitates, it is very important to understand the kinetics of precipitation. The hardness measurements as a function of holding time at 595°C are plotted in Fig. 2. It can be elicited that the alloy which being treated at this tem-
perature has obvious precipitation hardening behavior, the hardness at first increased acutely, from HRC 32.5 to HRC 42.5 in only 20 min, and the maximum value occurs at about 20 min, then it is markedly decreased from HRC 42.5 to HRC 38.5. From approximately 60 to 300 min, a slight decrease of bulk hardness was observed.
3.3. Relationship between phase transformation with hardening behavior As mentioned above, the microstructure of the solution treated sample, which has supersaturated copper after oil quench, even in air quench, is unsteady. When aging at the elevated temperature, copper gets more energy and precipitates from the matrix. The Xray diffraction profiles of the type 17-4PH stainless steel under different conditions are shown in Fig. 3. It
J. Wung et al., Relationship of microstructuretransformationand.. .
is obvious that the precipitate of copper after aging at 595°C is more than that of solution treatment samples.
237
nm. This is consistent with the outcome of C.S. Chiou [31. The orientation relationship between martensite
5(bcc) and copper (fcc) can be described as follows:
44 42 40-
T
. 38-
v1 m
2 r2
-u
3634-
32
30
1
c 0
50
100 150 200 Aging timc / min
250
300
This relation suggests that a NishiyamaWassermann relationship and K-S relationship, are obeyed. The result is consilient with that reported elsewhere [3,16]. This crystallographic orientation is expected, simply because copper crystals can replace austenite crystals, based on their same fcc lattice with unit cells of extremely similar size [3].
Fig. 2. Aging hardening behavior of 17-4PH stainless steel at 595OC.
4000
lb’
{llO)M
vi
c
5 3000-
. .2.2000 0
Vl
‘I
I
28 /
( 0 )
Fig. 3. X-ray diffraction profiles of different conditions of 17-4PH stainless steel: (a) solution treated; (b) solution treated+59S°Cx4 h.
Aging the solution-treated specimen at 595°C for 20 min brings about an age-hardening peak. A TEM bright field image of the specimen aged in this condition is presented in Fig. 4. The lath martensite matrix still exhibits a very high density of dislocations. There are few strain strings caused by copper precipitates in the dislocations of martensite. Fig. 4 gives the clear contrast corresponding to fine precipitates in this stage. The precipitates were identified as having an fcc structure and had been well-bonded with the matrix. The SADP (selected -area electron diffraction pattern) taken from the regions of the copper precipitate and martensite matrix are also shown in Fig. 4. The copper precipitate is of a sphericity shape, with a radius of less than 20
Fig. 4. Transmission electron micrograph (a) and corresponding diffraction pattern (b) for illustrating the copper precipitates (arrowed) obtained from the H1100-treated specimen.
In different areas of the same condition sample, TEM reveals that there is another fine fiber-shaped phase precipitate and the associate SADP identifies the new phase is the secondary carbide MZ3C6(Fig. 5). And there is one coplanar relationship, which is between the matrix and M24Z6. It indicates that the M& formation mechanism is that precipitate from the martensite matrix. The orientation relationship between martensite (bcc) and carbide (fcc) can be described as follows: (101)rnartmd/(51 l ) c x ~ e ,11 1 llmarten\d41491carbide.
238
Habibi-Bajguirani also found the secondary carbide, M&, precipitated in 15-5 PH, a similar precipitation-hardening stainless steel, in the condition of aging
J. Univ. Sci. Technol. Beging, Vo1.13, No.3, Jun 2006 at 500°C and the secondary carbide have a cube-cube orientation with the matrix [16].
Fig. 5. Transmission electron micrographs and corresponding diffraction pattern for illustrating the secondary carbide precipitates (arrowed)obtained from the H1100-treatedspecimen.
At the condition of aging at 595"C, the precipitation of certain morphology copper, which has the coherent relationship with the matrix, and M,,C6 strengthen the alloy, enhance the bulk hardness by the dispersion hardening effect [l-3,13-161, so the alloy attains the peak bulk hardness at 595°C for 20 min. Furthermore, with the extension of holding time at
this temperature, the microstructure of the alloy has some change (Fig. 6). When copper precipitate grows from the fcc structure to a critical dimension, the precipitate loses the coherent relationship with the matrix [3,14-161, which does not have the precipitation hardening effect only more.
Fig. 6. Transmission electron micrograph (a) and corresponding diffraction pattern (b) for illustrating the microstructure obtained from the H1100-treated specimen.
In additional, the precipitation of the secondary carbide M23C6,decreases the carbon content of the matrix further, which lessens the strength of the martensite matrix. So the bulk hardness of the alloy at 595°C after the time of peak value (about 20 min) decreases at all time.
4. Conclusions (1) When 17-4PH stainless steel aging at 595°C for about 20 min, the bulk hardness of the sample attains its peak value (HRC 42.5), and then decreases at all time. (2) After aged at 595°C there precipitates the fine spheroid-shape copper, with the fcc crystal structure and has the K-S relationship with martensite. Synchronously, the fiber-shape secondary carbide Mz3C6
precipitate from the martensite matrix. (3) The precipitation copper and M2$6 are the reasons for strengthening of the alloy at this temperature.
References U.K. Viswanathan, P.K.K. Nayar, and R. Krishnan, Kinetics of precipitation in 17-4PH stainless steel, Mater. Sci. Technol., 5(1989), p.346. Y. Meyzaud and R. Cozar, Design of aging-resistant martensitic stainless steels for pressurized water reactors, [in] Proceedings of Topical Conference on Ferritic Alloys for Use in Nuclear Energy Technologies, Snowbird, Utah, 1984. C.N. Hsiao, C.S. Chiou, and J.R. Yong, Aging reactions in a 17-4 PH stainless steel, Mater. Chem. Phys., 74(2002), p.134. B. Yrieix and M. Guttmann, Aging between 300 and 450 of wrought martensitic 13-17 wt.% Cr stainless steel, Ma-
J. Wung et uZ., Relationship of microstructure transformation and.. . ter. Sci. Technol., 9( 1993), p. 125. [5] M. Murayama, Y. Katayama, and K. Hono, Microstructural evolution in a 17-4 PH stainless steel after aging at 400"C, Met. Mater. Trans. A, 30A(1999), p.345. [6] F. Christien, R.Le Gall, and G. Saindrenan, Influence of stress on intergranular brittlement of a martensite stainless steel, D i f i s . Dej Date Pt A , 216-217(2003), p.275. [7] J.J. Shiao, C.H. Tsai, J.J. Kai, et al., Aging embrittlement and lattice image analysis in a Fe-Cr-Ni duplex stainless steel aged at 400"C, J. Nucl. Mater., 217(1994), p.269. [8] F. Danoix and P. Auger, Atom probe studies of the Fe-Cr system and stainless steels aged at intermediate temperature: a review, Mater. Charact., 44(2000), p.177. [9] F. Christien, R.Le Gall, and G. Saindrenan, Phosphorus grain boundary segregation in steel 17-4PH, Scripta Mater., 2003, No.48, p.11. [lo] K.C. Hsu and C.K. Lin, High-temperature fatigue crack growth behavior of 17-4 PH stainless steels, Metall. Mazer. Trans. A , 35A(2004), p.3018. [ I 11 W.C. Chiang, C.C. Pu,B.L. Yu, et al., Hydrogen suscepti-
239
bility of 17-4 PH stainless steel, Mater. Lett., 57(2003), p.2485. [ 121 C. Fahir Arisoy, Gokhan Basman, and M. Kelami Sesen, Failure of a 17-4 PH stainless steel sailboat propeller shaft, Eng. Failure Anal., 10( 2003), p.711. [I31 H. Xu and S. Fyfitch, Aging embrittlement modeling of Type 17-4PH at LWR temperatures, [in] 10th International Conference on Environmental Degradation of Materials in Nuclear Power System-water Reactor, lake Tahoe, NV, 2001, p.57. [ 141 K. Stiller, M. Hattestrand, and F. Danoix, Precipitation in 9Ni-12Cr-2Cu maraging steels, Acta Mater., 46( l998), p.6063. [ 151 K. Stiller, F. Danoix, and M. Hattestrand, Mo precipitation in a 12Cr-9Ni-4Mo-2Cu maraging steel, Mater. Sci. Eng. A , 250(1998), p.22. [I61 H.R. Habibi Bajguirani, The effect of ageing upon the microstructure and mechanical properties of type 15-5 PH stainless steel, Mater. Sci. Eng. A, 338(2002), p.142.
Journal of University of Science and Technology Beijing Volume 13, Number 3, June 2006, Page 235
Relationship of microstructure transformation and hardening behavior of type 17-4 PH stainless steel Jun Wing”, Hong Zou2’,Cong Li”,Ruling Zuo3’,Shaoyu Qiu’’, and Baoluo Shen” I ) School of Materials Science and Engineering, Sichuan University, Chengdu 6 10064, China 2) National Key Laboratory for Nuclear Fuel and Materials, Nuclear Power Institute of China, P.O. Box 436, Chengdu 610041, China
3) School of Materials Science and Engineering, Chongqing University, Chongqing 400044. China (Received 2005-01-12)
Abstract: The relationship between the microstructure transformation of type 17-4 PH stainless steel and the aging hardening behavior was investigated. The results showed that, when 17-4 PH stainless steel aging at 595°C the bulk hardness of samples attains its peak value (42.5 HRC) for about 20 min, and then decreases at all time. TEM revealed the microstructure corresponding with peak hardness is that the fine spheroid-shape copper with the fcc crystal structure and the fiber-shape secondary carbide M,,C, precipitated from the lath martensite matrix. Both precipitations of copper and M&, are the reasons for strengthening of the alloy at this temperature. With the extension of holding time at this temperature, the copper and secondary carbide grow and lose the coherent relationship with the matrix, so the bulk hardness of samples decreases. Key words: 17-4 PH stainless steel; H1 100 condition; precipitation; copper; secondary carbide
[This work was financially supported (N0.51481080104ZS8501).]
by the
Key
Nuclear Fuel
1. Introduction The 17-4 PH (precipitation hardening) stainless steel is a martensite stainless steel containing approximately 3wt% Cu and is strengthened by the precipitation of highly dispersed copper particles in the martensite matrix [I-41. This alloy is more common than any other type of precipitation hardened stainless steels due to its excellent mechanical properties and excellent corrosion resistance [5-91. The condition of H900 (peak-aged condition) and HI 100 (over-aged condition) of this precipitationhardenable stainless steel are usually used conditions, but recently, some researchers found the alloy in H900 condition has more embrittlement tendency in some important working conditions [ 10-121. Now type 17-4 PH martensite stainless steel in the over H1 100 condition has been used in light water reactors (LWRs) and pressurized water reactors (PWRs) for components requiring a combination of high wear resistance, high strength, and good corrosion resistance [ 131.
and
Nuclear Materials
h b o r a t o t y of
Most researchers focused on evolution of the precipitation of copper [3, 7-8, 14-16], few are awareness of other precipitates in this alloy in HI 100 condition. And the relationship of the mechanical properties of 17-4 PH stainless steel in H1100 condition with the microstructure and its revolution is not clear. The study of detailed microstructure in 17-4 PH stainless steel after solution treatment and aging has assumed great significance due to the treatment influence on the mechanical properties. The aim of the present work is to investigate the phase transformation and the aging hardening behavior of this stainless steel at various stages of aging and to try to give an insight of the relationship of hardening behavior with microstructure of the alloy.
2. Material and experimental procedures The chemical composition of the 17-4 PH stainless steel is given in Table 1.
Table 1. Composition of the type 17-4 PH stainless steel C
Cr
Ni
cu
Nb
Si
Mn
P
S
0.04
16.39
4.32
3.4
0.36
0.6
0.3
0.023
0.013
Corresponding author: Jun Wang, E-mail: [email protected]
China
Fe Bal.
236
The initial material as-delivered for test specimens, which was sheet metal hot rolled to 20 mm in an L-T (longitudinal-transverse) orientation, was made in Changcheng Special Steel Corporation (Sichuan, China) and subsequently cut into specimens with the dimension of 10 mmxlO mmx55 mm. Heat treatment comprised two steps: ( 1 ) Solution treatment for 30 min at 1O4O0C, and then oil quench;
(2) Aging for various time at 595°C (Fahrenheit 1 100) and then air cool. The bulk hardness was measured using a Rockwell hardness meter with a load of 1.47 kN. Discs for transmission electron microscopy were prepared by standard techniques and thin foils produced using a twin-jet electropolisher. These samples were examined in a Philips Tecnai 20HR-TEM (high resolution transmission electron microscopy) equipped with EDX (energy dispersive X-ray analyzer). Philip X'Pert X-ray diffraction instrument was used to identify the
J. Univ. Sci. TechnoL Beijing, VoL13,No.3, Jun 2006 microstructure of this type alloy too.
3. Results and discussion 3.1. Solution treated microstructure The Martensite transformation start (M,)of the stainless steel is around 105°C [3]. Hence, the microstructures of martensite could be obtained easily in 174 PH stainless steel. The transmission electron micrograph with a low magnification, as shown in Fig. 1, was obtained from the solution-treated specimen, the corresponding microstructure is composed basically of lath martensite. The martensite laths have a high dislocation density, and micro-twins (arrowed) could often be observed in the martensite laths. The finding of micro-twins is accordant with those reported by C.S. Chiou [3] and Habibi-Bajguirani [ 161. The existence of twin-related laths was interpreted as a result of the accommodation of the strain created by the adjacent laths [ 161.
Fig. 1. TEM micrographs (a) showing twins (arrowed) in lath martensite formed in 17-4 PH stainless steel and its diffraction electron pattern (b) showing the presence of only one set of diffraction spots.
According to the Fe-Cu phase diagram, the solubility of Cu atoms increase to 7wt% at 1040°C [3]. It is therefore suggested that the matrix phase of 17-4 PH stainless steel is supersaturated with Cu after the solution treatment at 1040°C. But failure to detect copper precipitates in martensite laths after solution treatment indicates that the martensite phase is supersaturated with Cu in the solution-treated condition.
3.2. Hardening behavior Since the strength of 17-4 PH stainless steel is enhanced by the formation of copper precipitates, it is very important to understand the kinetics of precipitation. The hardness measurements as a function of holding time at 595°C are plotted in Fig. 2. It can be elicited that the alloy which being treated at this tem-
perature has obvious precipitation hardening behavior, the hardness at first increased acutely, from HRC 32.5 to HRC 42.5 in only 20 min, and the maximum value occurs at about 20 min, then it is markedly decreased from HRC 42.5 to HRC 38.5. From approximately 60 to 300 min, a slight decrease of bulk hardness was observed.
3.3. Relationship between phase transformation with hardening behavior As mentioned above, the microstructure of the solution treated sample, which has supersaturated copper after oil quench, even in air quench, is unsteady. When aging at the elevated temperature, copper gets more energy and precipitates from the matrix. The Xray diffraction profiles of the type 17-4PH stainless steel under different conditions are shown in Fig. 3. It
J. Wung et al., Relationship of microstructuretransformationand.. .
is obvious that the precipitate of copper after aging at 595°C is more than that of solution treatment samples.
237
nm. This is consistent with the outcome of C.S. Chiou [31. The orientation relationship between martensite
5(bcc) and copper (fcc) can be described as follows:
44 42 40-
T
. 38-
v1 m
2 r2
-u
3634-
32
30
1
c 0
50
100 150 200 Aging timc / min
250
300
This relation suggests that a NishiyamaWassermann relationship and K-S relationship, are obeyed. The result is consilient with that reported elsewhere [3,16]. This crystallographic orientation is expected, simply because copper crystals can replace austenite crystals, based on their same fcc lattice with unit cells of extremely similar size [3].
Fig. 2. Aging hardening behavior of 17-4PH stainless steel at 595OC.
4000
lb’
{llO)M
vi
c
5 3000-
. .2.2000 0
Vl
‘I
I
28 /
( 0 )
Fig. 3. X-ray diffraction profiles of different conditions of 17-4PH stainless steel: (a) solution treated; (b) solution treated+59S°Cx4 h.
Aging the solution-treated specimen at 595°C for 20 min brings about an age-hardening peak. A TEM bright field image of the specimen aged in this condition is presented in Fig. 4. The lath martensite matrix still exhibits a very high density of dislocations. There are few strain strings caused by copper precipitates in the dislocations of martensite. Fig. 4 gives the clear contrast corresponding to fine precipitates in this stage. The precipitates were identified as having an fcc structure and had been well-bonded with the matrix. The SADP (selected -area electron diffraction pattern) taken from the regions of the copper precipitate and martensite matrix are also shown in Fig. 4. The copper precipitate is of a sphericity shape, with a radius of less than 20
Fig. 4. Transmission electron micrograph (a) and corresponding diffraction pattern (b) for illustrating the copper precipitates (arrowed) obtained from the H1100-treated specimen.
In different areas of the same condition sample, TEM reveals that there is another fine fiber-shaped phase precipitate and the associate SADP identifies the new phase is the secondary carbide MZ3C6(Fig. 5). And there is one coplanar relationship, which is between the matrix and M24Z6. It indicates that the M& formation mechanism is that precipitate from the martensite matrix. The orientation relationship between martensite (bcc) and carbide (fcc) can be described as follows: (101)rnartmd/(51 l ) c x ~ e ,11 1 llmarten\d41491carbide.
238
Habibi-Bajguirani also found the secondary carbide, M&, precipitated in 15-5 PH, a similar precipitation-hardening stainless steel, in the condition of aging
J. Univ. Sci. Technol. Beging, Vo1.13, No.3, Jun 2006 at 500°C and the secondary carbide have a cube-cube orientation with the matrix [16].
Fig. 5. Transmission electron micrographs and corresponding diffraction pattern for illustrating the secondary carbide precipitates (arrowed)obtained from the H1100-treatedspecimen.
At the condition of aging at 595"C, the precipitation of certain morphology copper, which has the coherent relationship with the matrix, and M,,C6 strengthen the alloy, enhance the bulk hardness by the dispersion hardening effect [l-3,13-161, so the alloy attains the peak bulk hardness at 595°C for 20 min. Furthermore, with the extension of holding time at
this temperature, the microstructure of the alloy has some change (Fig. 6). When copper precipitate grows from the fcc structure to a critical dimension, the precipitate loses the coherent relationship with the matrix [3,14-161, which does not have the precipitation hardening effect only more.
Fig. 6. Transmission electron micrograph (a) and corresponding diffraction pattern (b) for illustrating the microstructure obtained from the H1100-treated specimen.
In additional, the precipitation of the secondary carbide M23C6,decreases the carbon content of the matrix further, which lessens the strength of the martensite matrix. So the bulk hardness of the alloy at 595°C after the time of peak value (about 20 min) decreases at all time.
4. Conclusions (1) When 17-4PH stainless steel aging at 595°C for about 20 min, the bulk hardness of the sample attains its peak value (HRC 42.5), and then decreases at all time. (2) After aged at 595°C there precipitates the fine spheroid-shape copper, with the fcc crystal structure and has the K-S relationship with martensite. Synchronously, the fiber-shape secondary carbide Mz3C6
precipitate from the martensite matrix. (3) The precipitation copper and M2$6 are the reasons for strengthening of the alloy at this temperature.
References U.K. Viswanathan, P.K.K. Nayar, and R. Krishnan, Kinetics of precipitation in 17-4PH stainless steel, Mater. Sci. Technol., 5(1989), p.346. Y. Meyzaud and R. Cozar, Design of aging-resistant martensitic stainless steels for pressurized water reactors, [in] Proceedings of Topical Conference on Ferritic Alloys for Use in Nuclear Energy Technologies, Snowbird, Utah, 1984. C.N. Hsiao, C.S. Chiou, and J.R. Yong, Aging reactions in a 17-4 PH stainless steel, Mater. Chem. Phys., 74(2002), p.134. B. Yrieix and M. Guttmann, Aging between 300 and 450 of wrought martensitic 13-17 wt.% Cr stainless steel, Ma-
J. Wung et uZ., Relationship of microstructure transformation and.. . ter. Sci. Technol., 9( 1993), p. 125. [5] M. Murayama, Y. Katayama, and K. Hono, Microstructural evolution in a 17-4 PH stainless steel after aging at 400"C, Met. Mater. Trans. A, 30A(1999), p.345. [6] F. Christien, R.Le Gall, and G. Saindrenan, Influence of stress on intergranular brittlement of a martensite stainless steel, D i f i s . Dej Date Pt A , 216-217(2003), p.275. [7] J.J. Shiao, C.H. Tsai, J.J. Kai, et al., Aging embrittlement and lattice image analysis in a Fe-Cr-Ni duplex stainless steel aged at 400"C, J. Nucl. Mater., 217(1994), p.269. [8] F. Danoix and P. Auger, Atom probe studies of the Fe-Cr system and stainless steels aged at intermediate temperature: a review, Mater. Charact., 44(2000), p.177. [9] F. Christien, R.Le Gall, and G. Saindrenan, Phosphorus grain boundary segregation in steel 17-4PH, Scripta Mater., 2003, No.48, p.11. [lo] K.C. Hsu and C.K. Lin, High-temperature fatigue crack growth behavior of 17-4 PH stainless steels, Metall. Mazer. Trans. A , 35A(2004), p.3018. [ I 11 W.C. Chiang, C.C. Pu,B.L. Yu, et al., Hydrogen suscepti-
239
bility of 17-4 PH stainless steel, Mater. Lett., 57(2003), p.2485. [ 121 C. Fahir Arisoy, Gokhan Basman, and M. Kelami Sesen, Failure of a 17-4 PH stainless steel sailboat propeller shaft, Eng. Failure Anal., 10( 2003), p.711. [I31 H. Xu and S. Fyfitch, Aging embrittlement modeling of Type 17-4PH at LWR temperatures, [in] 10th International Conference on Environmental Degradation of Materials in Nuclear Power System-water Reactor, lake Tahoe, NV, 2001, p.57. [ 141 K. Stiller, M. Hattestrand, and F. Danoix, Precipitation in 9Ni-12Cr-2Cu maraging steels, Acta Mater., 46( l998), p.6063. [ 151 K. Stiller, F. Danoix, and M. Hattestrand, Mo precipitation in a 12Cr-9Ni-4Mo-2Cu maraging steel, Mater. Sci. Eng. A , 250(1998), p.22. [I61 H.R. Habibi Bajguirani, The effect of ageing upon the microstructure and mechanical properties of type 15-5 PH stainless steel, Mater. Sci. Eng. A, 338(2002), p.142.