Influence of micro-alloying elements and deep cryogenic treatment on microstructure and mechanical properties of S5 cold work shock resisting tool steel

The tempering process is applied in marine 10Ni5CrMoV steel to study microstructure, and mechanical properties by multi‐scale characterizations, strain hardening behavior, and cryogenic toughening mechanism are further investigated. As the tempering temperature increases from 590 to 630 °C, the dislocation density decreases by up to 25% and the austenite volume fraction decreases by up to 35%. Additionally, the morphology of austenite changes from strip to bulk, which weakened the pinning effect on the laths, leading to a coarsened martensite and an increase in the equivalent grain size. Based on the modified Crussard–Jaoul analysis, the specimens at different tempering temperatures exhibit a single‐stage strain hardening behavior during plastic deformation. The increase in strength is attributed to the continuous transformation‐induced plasticity effect and the increasing dislocation density. Furthermore, high austenite volume fraction and the proportion of grain boundary misorientation above 45° promote the release of stress concentration and hinder the propagation of cracks. This results in an increase in the ductile–brittle transition temperature (DBTT) of the specimens from −105 to −135 °C. At a tempering temperature of 610 °C, the specimen demonstrates an outstanding balance between yield strength (868 MPa) and cryogenic toughness (DBTT of −135 °C).

Study on Strain Hardening and Cryogenic Toughness of Marine 10Ni5CrMoV Steel during Tempering

Zou,

Dong,

Jiang

et al. 2024

Effects of Cryogenic Rolling on the Microstructure Evolution and Mechanical Properties of Low‐Density Fe‐28Mn‐8Al‐1C Steel

Xiong,

Luan,

Zha

et al. 2024

This study undertakes a systematic investigation into the influence of cryogenic rolling (CR) deformation on the microstructure evolution and mechanical properties of low‐density Fe‐28Mn‐8Al‐1C steel. The results reveal that the microstructure undergoes a series of transformations, from equiaxed austenite grains to elongated grains with strain bands, twinning, dislocation entanglements, and dislocation cells. The texture evolves from brass to copper with increasing deformation. Besides, the mechanical properties exhibit a direct correlation with the extent of deformation, as evidenced by the notable increase in ultimate tensile strength, yield strength, and microhardness from 882 to 1861, 505 to 1791 MPa, and 284 to 578 HV, respectively. However, elongation decreases from 64% to 6.6%, indicative of the strength‐ductility trade‐off. The aforementioned findings provide insight into the potential for manipulating the microstructure evolution and mechanical properties of low‐density steels utilizing CR.

Response Surface Method Optimization of Hard Machining with Cryogenically Treated Cutting Tools: Surface Roughness, Cutting Force, Tool Wear, Rietveld Analysis, and Metallurgical Properties

Kara,

Takmaz,

Erkan

et al. 2024

The study consists of two stages: machinability tests and metallographic examinations. In the first stage of the study, response surface methodology (RSM) optimization was performed for the main‐cutting‐force (Fc) and average surface roughness (Ra) values obtained as a result of turning tests. In the second stage, the wear performance of cutting tool tips with and without deep cryogenic treatment was explained with the support of SEM images, EDX, XRD, and microhardness analyses. As a result of ANOVA analysis, it was found that the most effective parameter on Fc was the feed rate, with 78.89%. As a result of RSM‐optimization, the lowest Fc value was found to be 339.99 N. The most effective parameter on Ra was found to be the feed rate at 69.38%. In terms of tool life, 15% and 11% improvements were achieved in uncoated and coated carbide cutting tools, respectively. As a result of Rieltveld's analysis, it was determined that cryogenic treatment increased the carbide percentages in the tools. As a result of microhardness measurements, it was observed that the hardness of uncoated and coated carbide tools increased by 4.6% and 5.15%, respectively, after cryogenic treatment.