17-4PH析出硬化型不鏽鋼兼具高強度與耐蝕性，但傳統析出硬化熱處理雖可獲得高硬度，卻常因延展性與韌性不足而不利冷鍛成型與抗衝擊需求。因此本研究以冷鍛加工為導向，將目標硬度設定為HRC 28~32作為軟韌化成效判斷依據，並建立一項可兼顧加工性與實際應用之熱處理方法。
研究首先在第一部分比較傳統析出硬化熱處理條件之組織與性質差異，結果顯示低溫時效雖可使抗拉強度達1364 MPa，但延展性僅2.1 %，呈現明顯脆化，不適合作為冷鍛加工應用材料。考量17-4PH不鏽鋼冷鍛加工之硬度需求與應用特性仍需要改善。本研究在第二部分提出兩階段軟韌化 (Soft-Tough)熱處理，並以第二階段持溫時間作為主要調控參數，使硬度能穩定落在可調控區間，其中ST12在性質與熱處理成本間具較佳平衡，雖強度較低，但可維持約26 %之延展性，且衝擊能量顯著提升，展現軟韌化效果，因此選為後續評估高溫熱循環及拉伸疲勞之代表條件。
接著研究在第三部分針對高溫熱循環評估顯示，ST12經冷熱交替循環後硬度與強度逐步回升且仍保有良好塑性緩衝，其衝擊值在3000與6000次循環後仍維持軟韌材之高水準，顯示ST12軟韌材在反覆熱脹冷縮環境下仍具高溫穩定性，且ST12-C6000整體機械性質表現最佳，為後續拉伸疲勞測試提供良好的機械基礎。
研究第四部分是對17-4PH不鏽鋼進行拉伸疲勞試驗，分析原材、ST12軟韌材及經高溫熱循環後材料在疲勞耐受性上的差異。常溫拉伸疲勞結果顯示，熱循環可提升ST12軟韌材之疲勞壽命，並伴隨硬度回升以延緩裂縫擴展。高溫拉伸疲勞則呈現明顯溫度效應，在450 ℃與600 ℃下循環壽命可達百萬次循環，且硬度仍維持在HRC 27左右；但於750 ℃時壽命驟降至2351次循環、硬度降至HRC 24，並伴隨沃斯田體訊號增加與析出物過時效及粗化等組織軟化趨勢。說明ST12軟韌材若用於高溫循環荷重環境，其應用溫度應控制在600度左右，降低壽命劇烈衰退情形。
研究第五部分則為應用端性能評估，比較軟韌處理對抗氫脆特性及材料耐腐蝕特性影響。首先以集氫試驗評估抗氫脆能力，結果指出當集氫時間延長後，軟韌材出現延展性下降的現象，但降伏強度與抗拉強度僅有輕微變化，且其延展性之氫脆指數低於原材。此外，軟韌材集氫後衝擊值仍可達到超過260 J/ cm2之高水準，顯示軟韌材相較於原材具較佳抗氫脆能力。在耐蝕性方面，極化曲線結果顯示軟韌化可降低腐蝕速率。然而，隨集氫時間增加，腐蝕電流密度與腐蝕速率皆有上升趨勢，表示氫作用會加速腐蝕反應。整體而言，軟韌化處理不僅可降低材料對氫脆的敏感性，使其抗氫脆特性優於原材，同時亦能改善耐蝕表現。
綜合而言，本研究所建立兩階段軟韌化熱處理可使17-4PH不鏽鋼滿足冷鍛所需硬度，兼顧延展性、衝擊韌性，並在高溫熱循環與拉伸疲勞環境下展現具體的性質穩定與破斷機制趨勢，同時軟韌化熱處理對氫氣環境下氫脆與含氯環境下局部腐蝕問題也發揮正面影響，說明本研究可作為17-4PH不鏽鋼應用端熱處理設計之參考，並為材料之高溫特性、疲勞壽命、耐腐蝕及氫脆特性提供實證數據與理論基礎。

This study is oriented toward cold forging applications, with a target hardness of HRC 28~32 used to evaluate the effectiveness of the soft-tough treatment. Based on this requirement, a soft-tough heat treatment process was established to balance processability and practical application performance. Subsequently, high-temperature thermal cycles, tensile fatigue tests, hydrogen embrittlement tests, and corrosion tests were conducted to systematically evaluate the microstructure, mechanical properties, high-temperature resistance, hydrogen embrittlement resistance, and corrosion resistance of the materials.
The results showed that conventional solution-aging treatment produced high tensile strength but caused severe embrittlement and poor cold-forging suitability. In contrast, the ST12 soft-tough treatment improved ductility, impact toughness, and thermal cycling stability. Thermal-cycled ST12, especially ST12-C6000, enhanced fatigue life, while ST12 maintained million-cycle fatigue life at 450~600 °C. The soft-tough treatment also improved hydrogen embrittlement resistance and corrosion resistance.
The results of this study can serve as a reference for the heat treatment and soft-tough design of 17-4PH stainless steel. This approach helps the material meet cold forging requirements while maintaining application reliability and provides useful reference data for the metallurgical design and hydrogen embrittlement resistance of high-strength structural components.

[1] Olsson, C. O., Landolt, D. (2003). Passive films on stainless steels chemistry, structure and growth. Electrochimica acta, 48(9), 1093-1104.
[2] Davis, J. R. (Ed.). (1994). Stainless steels. ASM international.
[3] Lo, K. H., Shek, C. H., Lai, J. K. L. (2009). Recent developments in stainless steels. Materials Science and Engineering: R: Reports, 65(4-6), 39-104.
[4] Pan, L., Kwok, C. T., Niu, B., Huang, X., Cao, Y., Zou, X., Yi, J. (2023). Enhancement in hardness and corrosion resistance of directed energy deposited 17–4 PH martensitic stainless steel via heat treatment. Journal of Materials Research and Technology, 23, 1296-1311.
[5] Altan, T., Ngaile, G., Shen, G. (Eds.). (2004). Cold and hot forging: fundamentals and applications (Vol. 1). ASM international.
[6] Manson, S. S. (1966). Thermal stress and low-cycle fatigue. Thermal stress and low-cycle fatigue. by Manson, 55425.
[7] Suresh, S. (1998). Fatigue of materials. Cambridge university press.
[8] Oriani, R. A. (1970). The diffusion and trapping of hydrogen in steel. Acta metallurgica, 18(1), 147-157.
[9] Frankel, G. S. (1998). Pitting corrosion of metals: a review of the critical factors. Journal of the Electrochemical society, 145(6), 2186-2198.
[10] Tuthill, A. H., Covert, R. A. (2000). Stainless steels: an introduction to their metallurgy and corrosion resistance. Dairy Food Environ San, 20, 506-517.
[11] Lai, J. K. L., Shek, C. H., Lo, K. H. (Eds.). (2012). Stainless steels: An introduction and their recent developments. Bentham Science Publishers.
[12] Dutta, S. (2018). Different types and new applications of stainless steel. Stainless steel, 62(5), 86-91.
[13] Sun, H., Li, D., Diao, Y., He, Y., Yan, L., Pang, X., Gao, K. (2022). Nanoscale Cu particle evolution and its impact on the mechanical properties and strengthening mechanism in precipitation-hardening stainless steel. Materials Characterization, 188, 111885.
[14] Wang, Z., Li, H., Shen, Q., Liu, W., Wang, Z. (2018). Nano-precipitates evolution and their effects on mechanical properties of 17-4 precipitation-hardening stainless steel. Acta Materialia, 156, 158-171.
[15] Babakoohi Ashrafi, A. A., Mohammadi, H., Habibolla Zade, A. (2016). Evaluation of precipitation hardening heat treatment of ph 17-7 stainless steel spring. Iranian Journal of Materials Science & Engineering, 13(2).
[16] Tian, J. L., Wang, W., Yan, W., Jiang, Z. H., Shan, Y. Y., Yang, K. (2017). Microstructure characteristics of segregation zone in 17-4PH stainless steel piston rod. Journal of Iron and Steel Research International, 24(7), 718-723.
[17] Schönbauer, B. M., Yanase, K., Endo, M. (2016). VHCF properties and fatigue limit prediction of precipitation hardened 17-4PH stainless steel. International Journal of Fatigue, 88, 205-216.
[18] Leksycki, K., Kaczmarek-Pawelska, A. (2024). Surface topography and corrosion resistance of AISI 630 stainless steel after finish turning under different cooling methods. Journal of Manufacturing Processes, 124, 1249-1258.
[19] Ping, L. I., ZHANG, X. Z. (2006). Effect of aging temperature on erosion-corrosion behavior of 17-4PH stainless steels in dilute sulphuric acid slurry. Journal of Iron and Steel Research, International, 13(5), 73-78.
[20] Wang, J., Zou, H., Li, C., Qiu, S. Y., Shen, B. L. (2006). The effect of microstructural evolution on hardening behavior of type 17-4PH stainless steel in long-term aging at 350 ℃. Materials Characterization, 57(4-5), 274-280.
[21] Rack, H. J., Kalish, D. (1974). The strength, fracture toughness, and low cycle fatigue behavior of 17-4 PH stainless steel. Metallurgical Transactions, 5(7), 1595-1605.
[22] Christien, F., Telling, M. T. F., Knight, K. S. (2013). Neutron diffraction in situ monitoring of the dislocation density during martensitic transformation in a stainless steel. Scripta Materialia, 68(7), 506-509.
[23] Morris Jr, J. W. (2011). On the ductile-brittle transition in lath martensitic steel. ISIJ international, 51(10), 1569-1575.
[24] Villa, M.; Grumsen, F.B.; Niessen, F.; Dahmen, T.; Cao, L.; Reich, M.; Kessler, O.; Huang, X.; Somers, M.A. Aging 17-4 PH martensitic stainless steel prior to hardening: Effects on martensitic transformation, microstructure and properties. Materialia 2023, 32, 101882.
[25] Wang, J., Zou, H., Li, C., Zuo, R., Qiu, S., Shen, B. (2006). Relationship of microstructure transformation and hardening behavior of type 17-4 PH stainless steel. Journal of University of Science and Technology Beijing, Mineral, Metallurgy, Material, 13(3), 235-239.
[26] Hsiao, C. N., Chiou, C. S., Yang, J. R. (2002). Aging reactions in a 17-4 PH stainless steel. Materials Chemistry and Physics, 74(2), 134-142.
[27] Mirzadeh, H., Najafizadeh, A. (2009). Aging kinetics of 17-4 PH stainless steel. Materials chemistry and physics, 116(1), 119-124.
[28] Murayama, M., Hono, K., Katayama, Y. (1999). Microstructural evolution in a 17-4 PH stainless steel after aging at 400 ℃. Metallurgical and Materials Transactions A, 30(2), 345-353.
[29] Yeli, G., Auger, M. A., Wilford, K., Smith, G. D., Bagot, P. A., Moody, M. P. (2017). Sequential nucleation of phases in a 17-4PH steel: Microstructural characterisation and mechanical properties. Acta Materialia, 125, 38-49.
[30] Wu, J. H., Lin, C. K. (2003). Influence of high temperature exposure on the mechanical behavior and microstructure of 17-4 PH stainless steel. Journal of materials science, 38(5), 965-971.
[31] Viswanathan, U. K., Banerjee, S., Krishnan, R. (1988). Effects of aging on the microstructure of 17-4 PH stainless steel. Materials Science and Engineering: A, 104, 181-189.
[32] Maki, T., Tsuzaki, K., Tamura, I. (1980). The morphology of microstructure composed of lath martensites in steels. Transactions of the Iron and Steel Institute of Japan, 20(4), 207-214.
[33] Morito, S., Huang, X., Furuhara, T., Maki, T., Hansen, N. (2006). The morphology and crystallography of lath martensite in alloy steels. Acta materialia, 54(19), 5323-5331.
[34] Yang, Y., Zhang, X., Fan, L., Xu, C. (2020, April). Mechanical properties of steel gun barrel processed by cold radial forging with stepped mandrel under different forgingratios. In Journal of Physics: Conference Series (Vol. 1507, No. 4, p. 042004). IOP Publishing.
[35] Chung, C. Y., Tzeng, Y. C. (2019). Effects of aging treatment on the precipitation behavior of ε-Cu phase and mechanical properties of metal injection molding 17-4PH stainless steel. Materials Letters, 237, 228-231.
[36] Bhambroo, R., Roychowdhury, S., Kain, V., Raja, V. S. (2013). Effect of reverted austenite on mechanical properties of precipitation hardenable 17-4 stainlesssteel. Materials Science and Engineering: A, 568, 127-133.
[37] Jones, J., Vafadar, A., Hashemi, R. (2023). A Review of the Mechanical Properties of 17-4PH Stainless Steel Produced by Bound Powder Extrusion. Journal of Manufacturing and Materials Processing, 7(5), 162.
[38] Nasiri, Z., Ghaemifar, S., Naghizadeh, M., Mirzadeh, H. (2021). Thermal mechanisms of grain refinement in steels: a review. Metals and Materials International, 27(7), 2078-2094.
[39] Huang, Y. T., Yen, Y. W., Hung, F. Y. (2025). A Study on Thermally Fatigued Phase Transformation and Bending Fracture Mechanisms of 310S Stainless Steel. Materials, 18(11), 2654.
[40] Li, J. S., Cheng, G. J., Yen, H. W., Wu, L. T., Yang, Y. L., Wu, R. T., Wang, S. H. (2019). Thermal cycling induced stress–assisted sigma phase formation in super duplex stainless steel. Materials & Design, 182, 108003.
[41] Hsu, C. A., Chiu, P. H., Chang, H. Y., Wang, S. H., Tsao, T. C., Yang, J. R., Lee, Y. T. (2023). Innovation in thermal cycling aging compared to isothermal aging for precipitation hardening stainless steel. Journal of Materials Research and Technology, 27, 4552-4561.
[42] Macek, W., Robak, G., Żak, K., Branco, R. (2022). Fracture surface topography investigation and fatigue life assessment of notched austenitic steel specimens. Engineering Failure Analysis, 135, 106121.
[43] Yan, S., Wang, Z., Li, T., Chen, Z., Du, X., Liu, Y., Wang, S. (2023). In situ characterization of 17-4PH stainless steel by small-angle neutron scattering. Materials, 16(16), 5583.
[44] Christien, F., Telling, M. T. F., Knight, K. S. (2013). A comparison of dilatometry and in-situ neutron diffraction in tracking bulk phase transformations in a martensitic stainless steel. Materials characterization, 82, 50-57.
[45] Li, X., Ma, X., Zhang, J., Akiyama, E., Wang, Y., Song, X. (2020). Review of hydrogen embrittlement in metals: hydrogen diffusion, hydrogen characterization, hydrogen embrittlement mechanism and prevention. Acta Metallurgica Sinica, 33(6), 759-773.
[46] Schutz, P., Martin, F., Auzoux, Q., Adem, J., Rauch, E. F., Wouters, Y., Latu-Romain, L. (2022). Hydrogen transport in 17− 4 PH stainless steel: Influence of the metallurgical state on hydrogen diffusion and trapping. Materials Characterization, 192, 112239.
[47] Tavakoli Shoushtari, M. R. (2010). Effect of ageing heat treatment on corrosion behavior of 17-4 PH stainless steel in 3.5% NaCl. International Journal of Iron & Steel Society of Iran, 7(1), 33-36.
[48] Kareem, M. Q., Mikó, T., Gergely, G., Gácsi, Z. (2023). A review on the production of 17-4PH parts using press and sinter technology. Science Progress, 106(1).
[49] Sarkar, S., Mukherjee, S., Kumar, C. S., Nath, A. K. (2020). Effects of heat treatment on microstructure, mechanical and corrosion properties of 15-5 PH stainless steel parts built by selective laser melting process. journal of manufacturing processes, 50, 279-294.
[50] Stoudt, M. R., Ricker, R. E., Lass, E. A., Levine, L. E. (2017). Influence of postbuild microstructure on the electrochemical behavior of additively manufactured 17-4 PH stainless steel. JOM, 69(3), 506-515.
[51] Garcia-Cabezon, C., Hernández, C. G., Castro-Sastre, M. A., Fernandez-Abia, A. I., Rodriguez-Mendez, M. L., Martin-Pedrosa, F. (2023). Heat treatments of 17-4 PH SS processed by SLM to improve its strength and biocompatibility in biomedical applications. journal of materials research and technology, 26, 3524-3543.
[52] Volume, A. H. (1987). 12: Fractography. ASM International, 517.
[53] Misra, R. D. K., Prasad, C. Y., Balasubramanian, T. V., Rao, P. R. (1987). On variation of impact toughness in 17-4 precipitation hardened stainless steel. Scripta metallurgica, 21(8), 1067-1070.
[54] Krauss, G. (2017). Tempering of lath martensite in low and medium carbon steels: assessment and challenges. steel research international, 88(10), 1700038.
[55] Schutz, P., Latu-Romain, L., Martin, F., Auzoux, Q., Adem, J., Wouters, Y., Menut, D. (2023). Onto the role of copper precipitates and reverted austenite on hydrogen embrittlement in 17-4 PH stainless steel. Materials Characterization, 202, 113044.
[56] Wang, Z., Fang, X., Li, H., Liu, W. (2017). Atom probe tomographic characterization of nanoscale Cu-rich precipitates in 17-4 precipitate hardened stainless steel tempered at different temperatures. Microscopy and Microanalysis, 23(2), 340-349.
[57] Niu, M. C., Yang, K., Luan, J. H., Wang, W., Jiao, Z. B. (2022). Cu-assisted austenite reversion and enhanced TRIP effect in maraging stainless steels. Journal of Materials Science & Technology, 104, 52-58.
[58] Hull, D. (1999). Fractography: observing, measuring and interpreting fracture surface topography. Cambridge University Press.
[59] Zhou, T., Neding, B., Lin, S., Tseng, J. C., Hedström, P. (2021). Cu precipitation-mediated formation of reverted austenite during ageing of a 15–5 PH stainless steel. Scripta Materialia, 202, 114007.
[60] Yeddu, H. K., Shaw, B. A., Somers, M. A. (2017). Effect of thermal cycling on martensitic transformation and mechanical strengthening of stainless steels–A phase-field study. Materials Science and Engineering: A, 690, 1-5.
[61] Nemat-Nasser, S., Guo, W. G. (2003). Thermomechanical response of DH-36 structural steel over a wide range of strain rates and temperatures. Mechanics of materials, 35(11), 1023-1047.
[62] Humphreys, F. J., Hatherly, M. (2012). Recrystallization and related annealing phenomena. elsevier.
[63] Totten, G. E. (Ed.). (2002). Handbook of residual stress and deformation of steel. ASM international.
[64] Murakami, Y. (2019). Metal fatigue: effects of small defects and nonmetallic inclusions. Academic Press.
[65] Zhang, H., Li, C., Shi, Y., Yao, G., Zhang, Y. (2022). Fatigue and tensile deformation behaviors of laser powder bed fused 304L austenitic stainless steel. Materials Science and Engineering: A, 849, 143503.
[66] Schijve, J. (2001). Fatigue of structures and materials. Dordrecht: Springer Netherlands.
[67] Huang, R., Zhao, H., Sun, Y., Lin, D., Tang, Z., Chen, B., Tan, C. (2024). Additive manufacturing of 17-4PH stainless steel: Effect of heat treatment on microstructure evolution and strengthening behavior. Materials Science and Engineering: A, 908, 146770.
[68] Zhao, Z., Wang, H., Huo, P., Bai, P., Du, W., Li, X., Zhang, W. (2022). Effect of solution temperature on the microstructure and properties of 17-4PH high-strength steel samples formed by selective laser melting. Metals, 12(3), 425.
[69] ASTM G102-23; Standard Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements. ASTM International: West Conshohocken, PA, USA, 2023.