Effect of Intercritical Quenching on Reversed Austenite Formation and Cryogenic Toughness in QLT-Processed 9% Ni Steel

An intercritical quenching process is introduced between conventional water quenching and tempering to 25Mn2Si2Cr bainitic steel. The study suggests that the quenching–intercritical quenching–tempering (Q–IQ–T) process effectively improves mechanical properties compared with conventional air cooling and tempering (Q–T). When the intercritical austenitizing temperature is 860 °C, as‐treated steel's tensile strength, yield strength, impact energy (U‐notch) is 1453 MPa, 1141 MPa, and 99 J cm−2, respectively, which is enhancement of 5.4%, 3.2%, and 20.7% compared with the conventional Q–T process. The increase of toughness is achieved without compromising strength. The improvement of toughness arises from refinement of grain size and microstructure.

Section: Introductionmentioning

confidence: 99%

Effect of Intercritical Austenitizing Temperature during Quenching–Intercritical Quenching–Tempering Process on Toughness of 25Mn2Si2Cr Bainitic Steel

Tan

Zhang

et al. 2019

“…Finally, the contribution of other phenomena to the DSC signal in this temperature range besides precipitation reactions shall be addressed. The transformation of retained austenite or the precipitation of reverted austenite can cause a significant DSC signal. Therefore, the austenite contents of the solution‐annealed starting material and a specimen aged to 600 °C were checked by XRD.…”

Section: Introductionmentioning

confidence: 99%

Early Stages of Cu Precipitation in 15-5 PH Maraging Steel Revisited − Part I: Experimental Analysis

Primig

Stechauner

Kozeschnik³

2016

Even though Cu precipitation during isothermal aging of binary Fe-Cu alloys and of Cu-alloyed maraging steel has been carefully studied in the past, no detailed investigations of the early stages of Cu clustering upon continuous aging have been carried out so far. During continuous aging with a heating rate around 15 K min À1 of as-quenched 15-5 PH maraging steel in a differential scanning calorimeter (DSC), two exothermal reactions are observed, one at approximately 300 8C and the other one around 500 8C. These DSC signals are attributed to the nucleation and growth of Fe-rich Cu clusters in the lower temperature range, followed by Cu-enrichment of these clusters and seamless transformation into bcc-Cu precipitates at higher temperatures. Part I of this investigation focuses on the experimental characterization of the mechanisms governing these reactions in a comprehensive manner, where the authors first present the results of this analysis based on dilatometry, differential scanning calorimetry, hardness testing, and 3D atom probe tomography. The latter method is capable of detecting early clusters, which are not yet accessible by transmission electron microscopy. In the companion paper, part II, thermo-kinetic simulations are presented, which support the interpretation of the observed reactions and substantially aid in understanding the underlying mechanisms.

“…As a soft phase within the martensite matrix, reversed austenite has an important effect on the ductility of steels, such as maraging steel, TRIP steel, and 9% Ni steel 9. Many studies on the reversed austenite phase of high strength maraging and martensitic stainless steels have been carried out 10.…”

Section: Introductionmentioning

confidence: 99%

Formation of Reversed Austenite in High Temperature Tempering Process and its Effect on Mechanical Properties of Cr15 Super Martensitic Stainless Steel Alloyed with Copper

Jiang

et al. 2012

Formation mechanism of the reversed austenite of Cr15 super martensitic stainless steel (SMSS) alloyed with copper after high temperature tempering was investigated by means of thermo-calc software, transmission electron microscope (TEM), and X-ray diffraction (XRD). The mechanical properties of the SMSS were also tested. The experimental results show that the reversed austenite with low dislocation density is formed at high temperature tempering processing. The transformation of the martensite to reversed austenite is a diffused phase transformation, and the growth of the reversed austenite is closely related to the diffusion process of Ni. The bulk reversed austenite with large amount of stacking faults is formed with the increase of the tempering temperature. The volume fraction of reversed austenite increases at first and then decreases with increasing tempering temperature, and the maximum amount of the reversed austenite is obtained at 6508C. The reversed austenite is unstable at the tempering temperature above 6508C and the martensitic phase transformation will occur at the following cooling process. The mechanical properties of Cr15 super martensitic stainless steel are significantly influenced by the volume fraction of reversed austenite.