This paper investigated the response of carburized 20CrNi2MoV steel to cryogenic treatment including microstructure and wear resistance. Two cryogenic treatment methods including cryogenic treatment at −80 °C (CT) and deep cryogenic treatment at −196 °C (DCT) as well as conventional heat treatment (CHT) were carried out after carburizing process. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractometry (XRD) were employed for microstructure characterization. The wear resistance was investigated by ball-on-disc sliding wear test on a multi-functional tribometer. The results show that the wear resistance of the experimental steel has been improved by 17% due to CT and by 25.5% due to DCT when compared to CHT. This significant improvement in wear resistance after cryogenic treatment is attributed to the microstructural changes including the finer martensitic structure, the reduction of retained austenite and the development of fine and more numerous carbides. Among these factors, the precipitation of fine carbides plays a more prominent role in enhancing wear resistance.

In order to control the size and distribution of carbides and improve the cold formability of 1.0C-1.5Cr bearing steel, the effects of annealing parameters during isothermal spheroidization were studied. Mean diameter of carbides (D), interparticle spacing of carbides (s), number of carbides per area (n), and carbides particle size distribution were measured. The cold formability was evaluated through hardness and fracture strain. The results show that when austenitizing time increases from 0.5 to 7 hours or austenitizing temperature increases from 1033 K to 1153 K (760 °C to 880 °C), the values of D and s both increase, and the value of n decreases. With the increasing of second annealing time from 0.5 to 2 hours or the increasing of second annealing temperature from 953 K to 993 K (680 °C to 720 °C), the values of D and s tend to increase and the value of n decreases. According to the measured values of D, s, and n, two models describing their relationships were proposed. In addition, the hardness decreases with the increasing of D. The fracture strain changes slightly at first and then decreases significantly when the value of D exceeds 0.36 μm.

The effects of the Y- and Ti-containing inclusions on the tensile and impact properties of reduced activation ferritic martensitic (RAFM) steels were evaluated. Four steels with different Y and Ti contents were produced via vacuum induction melting. The size and quantity of inclusions in the steels were analyzed using scanning electron microscopy, and the oxide particle formation mechanism was clarified. These inclusions helped to enhance the pinning effect of the austenite grain boundaries based on the Zener pinning force. The average prior austenite grain sizes, measured via the linear intercept method, were 12.34 (0 wt.% Ti), 9.35 (0.010 wt.% Ti), 10.22 (0.030 wt.% Ti), and 11.83 (0.050 wt.% Ti) μm for the four steels, in order of increasing Ti content, respectively. Transmission electron microscopy was conducted to observe the fine carbides. The strength and impact properties of the steel containing 0.010 wt.% Ti were improved, and the ductile-to-brittle-transition temperature was reduced to −70.5 °C. The tensile strength and impact toughness of the steel with 0.050 wt.% Ti were significantly reduced due to the coarsening of both the inclusions and grain size, as well as the precipitation of large TiN inclusions. The RAFM steel with approximately 0.015 wt.% Y and 0.010 wt.% Ti exhibited an optimized combination of microstructures, tensile properties, and impact properties among the four steels.