The effect of (y->a') phase transformation on microstructure and properties of austenitic Cr-Ni steels

Abstract

The paper presents the results of the investigations concerning the effect of (γ→α’) phase transformation on microstructure, magnetic and mechanical properties of austenitic stainless steel grade X5CrNi18-10. Design/methodology/approach: Light microscope examinations, microhardness measurements and static tensile tests were performed in order to reveal microstructure and changes in mechanical properties. The magnetic properties: relative magnetic permeability μ (Maxwell-Wien bridge) and coercive force Hc (permalloy probe) were measured at room temperature. The analysis of the phase composition was carried out on the basis of X-ray investigations. In the qualitative X-ray analysis the comparative method was applied. Findings: : It was found that the plastic deformation in cold rolling within the range 10-70% of investigated austenitic Cr-Ni steel induced in its structure a phase transformation of paramagnetic austenite into ferromagnetic martensite. Research limitations/implications: The results of the X-ray quantitative analysis allowed to determine the proportional part of martensite phases α` in the structure of investigated steel in the examined range of cold plastic deformation. Practical implications: A wide range of practical applications of austenitic X5CrNi18-10 steel sheets is warranted by both their high corrosion resistance and high plastic properties, especially in the supersaturated state. Besides, a strong correlation was found between the magnetic properties and the (γ→ α’) phase transformation. Originality/value: In the course of deformation, the volume fraction of martensite increased at the expense of the amount of austenite resulting in the hardening of the material. In general, a gradual increase of the yield strength results from the strain hardening of the austenite structure and formation of strain-induced martensite.