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The effect of (γ → α') phase transformation on microstructure and properties of austenitic Cr-Ni steels

Kurc A., Stokłosa Z.

Archives of Materials Science and Engineering

2010

Vol. 41, nr 2

85-94

Purpose: 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.

The influence of the martensite α’ phase occurring in the structure of cold rolled austenitic Cr-Ni steel on its mechanical properties

Kurc A., Kalinowska-Ozgowicz E.

Archives of Materials Science and Engineering

2009

Vol. 37, nr 1

21-28

Purpose: In this paper the mechanical properties and structure of cold rolled austenitic stainless steel X5CrNi18-8 with a draft of 17%-78% were presented. Design/methodology/approach: The main methods used for these researches were the static tensile test, microhardness and metallographic observations by optical microscopy. The tested samples have also been analyzed fractographically. The amount of martensite α’ in the obtained microstructures was investigated with X-ray diffraction patterns. The scope of this study was to achieve the correlations between the mechanical and structural properties of cold rolled stainless steel. Findings: Results showed increasing the mechanical properties (Rm, Rp0.2, HV) and decreasing the plasticity (A) with the increasing degree of draft during cold rolling of investigated austenitic stainless steel. Research limitations/implications: In future examinations there is a need to broadening the methodology about the magnetic properties investigations which in the more precise way permit to define the quantity of the martensite α’ phase in the structure of steel X5CrNi18-10 and describe its morphology. Practical implications: A wide range of practical applications of austenitic X5CrNi18-8 steel sheets is warranted by both their high corrosion resistance and high plastic properties, especially in the supersaturated state. Originality/value: The analytic dependence of the yield point (Rp0.2) of the investigated steel on the draft degree in cold rolling has been confirmed.