Effects of cryogenic treatment on mechanical properties and microstructure of Fe-Cr-Mo-Ni-C-Co alloy

Abstract

Fe-Cr-Mo-Ni-C-Co alloy was quenched in liquid nitrogen and held for 24 h. Hardness tester, OM, XRD, SEM were used to investigate the mechanical properties and microstructures of the alloy. The results show that the hardness increases by 1–2 (HRC) and the compressive strength decreases slightly after cryogenic treatment. The increase in hardness is attributed to the transformation from austenite to martensite and the precipitation of the very tiny carbide η-Fe₂C. The decrease in compressive strength is caused by residual stress. The great amount of carbides, such as Cr₇C₃ and Fe₂MoC, in the alloy and the obvious difference in thermal expansion coefficient between these carbides and the matrix at the cryogenic temperatures lead to this residual stress. The microscopy of cryogenic martensite is different from that of the non-cryogenic martensite. The cryogenic martensite is long and fine; while the non-cryogenic martensite is short and coarse. There is obvious surface relief of the cryogenic martensite transformation. It is not orientational of this kind surface relief and the boundary of this surface relief is smooth and in a shape of butterfly. The surface relief in the non-cryogenic martensite is wide and arranged in parallel, and the boundary of surface relief is not smooth. These characteristics may imply different growth ways of the two kinds of martensite.

Keywords

Fe-Cr-Mo-Ni-C-Co alloy / powder metallurgy / microstructure / mechanical properties / cryogenic martensite

References

[1] LiangY.-t., YangQ.-rui.. Study on high nickel cast iron engine stigma seat [J]. Foundry Technology, 1997, 5(2): 53-55

[2] ZhuP.-l., YangJian.. A method of taking out valve insert [J]. Machinery Design & Manufacture, 2004, 3(5): 12-13

[3] KiyohikoN., ShinjiS., KagaoO., HiroshiS.. Fine-blanking performance of non-magnetic high manganese cryogenic steel and its application to superconducting dipole magnet [J]. Cryogenics, 1994, 34(Suppl): 477-480

[4] FredjB., HabibS.. Effects of the cryogenic cooling on the fatigue strength of the AISI 304 stainless steel ground components [J]. Cryogenics, 2006, 46(6): 439-448

[5] HanJ. K., KimY. G.. Low cycle fatigue behaviour of a cryogenic Fe-30Mn-5Al-0.1NB-0.3C steel [J]. Materials Science and Engineering A, 1987, 91(2): 73-79

[6] CollinsD. N., DormerJ.. Deep cryogenic treatment of a 2D cold-work tool steel [J]. Heat Treatment of Metals, 1997, 24(3): 71-74

[7] FuR.-d., ZhengY.-z., RenY.-bin.. Mechanical properties of 32Mn-7Cr-0.6Mo-0.3N austenitic steel for cryogenic applications [J]. Journal of Materials Engineering and Performance, 2001, 10(4): 456-459

[8] ZhuY.-z., YinZ.-m., ZengYu.. Effects of heat treatment on microstructure and mechanical properties of Fe-Co-Ni-Cr-Mo-C alloy [J]. Journal of Central South University of Technology, 2004, 11(3): 229-234

[9] ZhuY.-z., YinZ.-min.. The hot densification of a Fe-based sintered alloy Fe-Cr-Mo-Ni-Co-C [J]. Journal of Central South University: Science and Technology, 2006, 37(3): 456-460

[10] ErilN., HolmedalB., EvangelistaE.. Modelling grain boundary strengthening in ultra-fine grained aluminum alloys [J]. Materials Science and Engineering A, 2005, 410/411(25): 178-182

[11] XuL.-j., XingJ.-d., WeiS.-zhong.. Artificial neural network prediction of retained austenite content and impact toughness of high-vanadium high-speed steel (HVHSS) [J]. Materials Science and Engineering A, 2006, 433(1/2): 251-256

[12] LiX.-bing.. Influence of solid-solution treatment on mechanical properties of nickel-chromium-molybdenum alloy and analysis of its fracture [J]. Journal of Central South University of Technology: Natural Science, 2004, 35(4): 353-357

[13] GuoJ.-t., WangS.-h., XiongL.-y., WuD.-h., DengW., HuangY.-yang.. Influence of chemical composition and alloying elements on microdefects and electron density in Ni-Al alloys [J]. Transactions of Nonferrous Metals Society of China, 2002, 12(3): 370-374

[14] LuB., LiangYing.. The effect of quenching process on the structure and properties of the bimetal SAW [J]. Journal of Central South University of Technology: Natural Science, 1999, 30(1): 67-70

[15] PengK.-ding.. The diffusion of carbon in steel in cryogenic treatment [J]. Journal of Yunnan University: Natural Edition, 1996, 18(3): 231-234