Evaluation of the plastic deformation behavior of modified 100Cr6 steels with increased fractions of retained austenite using cyclic indentation tests

Abstract

In highly loaded components, such as roller bearings, early failures may occur due to microstructural defects. Thus, a higher defect tolerance of the material can improve the fatigue lifetime. To produce steels with high defect tolerance, innovative alloying concepts, and a sound knowledge of the influence of heat treatment parameters on the resultant mechanical properties is indispensable. Consequently, two bearing steels based on 100Cr6 with different silicon contents were investigated to achieve relatively high retained austenite (RA) fractions, which are assumed to increase the defect tolerance at cyclic loading. To understand the relation between bainitic heat treatment and mechanical characteristics, the resultant RA fractions, Vickers hardness, microhardness, and cyclic hardening exponent CHT eII, which correlates to defect tolerance of metallic materials, were determined for differently heat-treated conditions. Based on the statistical design of experiments and measurements obtained with X-ray diffraction and cyclic indentation testing, regression calculations were conducted. Pertaining to the results of the regression analyses, the heat treatment parameterizations of these steels were specifically determined for certain desired property combinations within the boundaries investigated. Therefore, the temperatures used in the austenitizing and bainitizing procedures have shown the highest influence on the mechanical characteristics and the RA fraction of both steels.

Influence of the Inherited Structure Induced by Al and Si Alloying on Microstructure Evolution and Mechanical Properties of 100Cr6 Steels

“…The cementite particles of 1.5Si–100Cr6 steel are significantly larger than those observed in the localized carbides region of 1.5Al–100Cr6 steel, while the retained austenite appears relatively finer in 1.5Si–100Cr6 steel. However, both variants show an apparently similar amount of retained austenite, being 22% in the 1.5Si–100Cr6 steel [ 18 ] and 24% in the 1.5Al–100Cr6 steel. Note that the amounts of retained austenite were determined by XRD and thus represent a more or less integral value of the retained austenite content.…”

“…In addition, the solution‐treated microstructure was characterized after quenching from austenitization temperature. Note that the heat treatment parameters were chosen based on a parameter analysis, which is described in detail for 1.5Si–100Cr6 in another study [ 18 ] and was performed analogously for 1.5Al–100Cr6. To produce the fatigue and tensile specimens, the heat treatment, which was done at IWT Bremen, was performed in a salt bath, as these specimens had a significantly bigger volume.…”

Effect of Different Microstructures on Surface Residual Stress of Induction-Hardened Bearing Steel

“…Without taking into account the difference in alloy content, carbon steel with a carbon content higher than 0.7 wt.% will obtain its martensite structure after quenching, and is usually accompanied by retained austenite. During use, if this retained austenite is subjected to mechanical or thermal stress, it will easily transform into martensite [8,9], resulting in changes in shape and size (distortion). This will indirectly lead to the premature failure of other parts and cause unnecessary external losses [34].…”

“…The impact of retained austenite on wear resistance in bearings has been investigated by Rivero [6], Roy [7], Šmel , ova [8] and Ostermayer [9] et al The results of these studies show that the ductility of the retained austenite causes the surface hardness to be less than expected, resulting in the fatigue life of the parts to become reduced. In addition, the retained austenite belongs to a metastable phase and is easily transformed into martensite by external environmental factors, such as temperature and load, which affects the stability of subsequent use and may lead to poor fatigue life.…”