Influence of Deep Cryogenic Treatment on Microstructural Evolution and Transformation Kinetics Simulation by Finite Element Method of Low‐Carbon High‐Alloy Martensitic‐Bearing Steel

Abstract

Nowadays, deep cryogenic treatment (DCT) is taken as a promising technique for improving the performance of steel. This article is focused on the influence of different heat treatment processes involving DCT on the microstructural evolution of a high Cr-Co-Mo high-temperature-bearing steel. Moreover, a multiphysical field coupling numerical model is built to investigate the martensitic transformation kinetics during DCT. The results show that DCT significantly improves the hardness and promotes the transformation of retained austenite to martensite at low temperatures. DCT not only refines the retained austenite as thin-film morphology but also increases the precipitation of carbides and induces the carbides more homogenous distribution. This indicates that DCT promoted the segregation of carbon atoms and reduced the carbon content of martensite. The finite element model simulation shows that the retained austenite transformation is still incomplete, and the simulation results agree well with the experimental data by X-Ray diffraction and transmission electron microscope analysis. This implies that the finite element simulation can better reflect and verify the experimental results.

Cryogenic Treatment of Martensitic Steels: Microstructural Fundamentals and Implications for Mechanical Properties and Wear and Corrosion Performance

“…For instance, it was found that CT at −196 • C (following sequence A) reduced the RA from 26 vol.% to one tenth of this value in the case of the steel with 0.15% C, 14% Cr, 13% Co, 2.4% Ni, and 4.8% Mo [69]. Similar results were also obtained through cryogenic treatment of X30CrMoN15 1 steel [71], an experimental steel with 0.17% C, 15% Cr, 11% Co, 3.3% Mo, 2.5% Ni, and 2% W [321], or AISI 440C steel [16], both treated via sequence A. Repeated CT cycles may further decrease the RA, but only to a very limited extent [17].…”

“…The hardness of 0.15% C-14% Cr-13% Co-4.8% Mo-2.4% Ni steel austenitised at 1020 • C increased by 7 HRC by subjecting it to CT at −196 • C for 2 or 10 h (following sequence A) [69,70]. Very consistent results were obtained by cryogenic treatments of 0.17% C, 15% Cr, 11% Co, 3.3% Mo, 2.5% Ni, and 2% W steel at −196 • C for 20 h [321]. Cryogenic treatment at −196 • C for 10 h increased the hardness by 12 HRC after hardening from 1050 • C, indicating that the given CT effectively reduced the RA [69].…”

“…Figure 24 provides clear evidence of retained austenite reduction due to the application of CT. Another consequence of CT application is the accelerated precipitation rate of carbides during tempering. This phenomenon was experimentally proven for different steels like those containing 0.15% C, 14% Cr, 13% Co, 2.4% Ni, and 4.8% Mo [69,70], or 0.17% C, 15% Cr, 11% Co, 3.3% Mo, 2.5% Ni, and 2% W [321], or AISI 440C [16]. Also, overall microstructural refinement, see the example in Figure 25, is a typical feature of cryogenically treated martensitic stainless steels.…”