Abstract
Laboratory heating experiments with a varied holding time of GCr15 bearing steels at 1498 K were performed to study the transformation of inclusions in solid GCr15 bearing steels during high temperature diffusion processes. Heating experiments at 1573 and 1648 K were also carried out to study the effect of these heating temperatures. Experimental results showed that inclusions transformed from Al2O3-CaO-(MgO) to Al2O3-CaS-(MgO-CaO) when the heat treatment was in the range of 1498 to 1648 K due to reactions between Al and S in the steel matrix and CaO in the inclusions. This is in good agreement with thermodynamic calculations. Moreover, the size of the inclusions hardly changed after heat treatment. The transformation rate of the inclusions depended strongly on both the heating temperature and the size of the inclusions. Kinetic analyses on the transformation of inclusions during heat treatment were performed based on a simplified analytical model. The mass transfer coefficients of CaO and CaS in inclusions were calculated, which ranged from 0.73 × 10−10 to 4.48 × 10−10 m/s.
Highlights
Bearing steels are widely applied in machinery manufacturing, railway transportation, automobile manufacturing, national defense industries, and other fields [1]
It is well known that the mass fraction, composition, size, morphology, and distribution of non-metallic inclusions have an important influence on the rolling contact fatigue (RCF) life of bearing steels [2,3,4,5]
The reaction between Al and S in the steel matrix and CaO in the inclusions dominated the transformation at 1498 K, while the reaction between S in the steel matrix and
Summary
Bearing steels are widely applied in machinery manufacturing, railway transportation, automobile manufacturing, national defense industries, and other fields [1]. It was reported that MnO-SiO2 oxide inclusions in Type 304 stainless steels may transform to MnO-Cr2 O3 during heat treatment in the range of 1273 to 1623 K [25,26,27] The contents of Mn, Si, and Cr in the steel had a strong influence on the transformation [28,29]. Yang et al investigated the transformation of inclusions in pipeline steels during solidification and cooling [33]. For a high temperature diffusion process highcarbide carbonas chromium bearing steels to reduce the segregation of bloom and precipitation of ribbonoftype well as aliquation carbide, reduce segregation of bloom and precipitation of ribbon type carbide as in well as aliquation. Transformation inclusions in Al-killed GCr15 bearing steelsKduring high temperature diffusion the processes has rarelyofbeen studied.
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