Effect of prior cold ring rolling on carbide dissolution during the austenitizing process of an M50 bearing steel

The influence of prior cold ring rolling (PCRR) on carbide dissolution during the austenitizing process of an M50 bearing steel was investigated by combining microstructural observations with kinetics analysis. The microstructural results show that the PCRR leads to a reduction in the volume fraction and the mean diameter of the undissolved carbides. The matrix of the as-quenched specimens after PCRR is enriched with more carbon and alloying elements than those without PCRR, which further confirms that the dissolution behavior of the alloy carbides is enhanced by PCRR during the austenitizing process. The kinetics of the transformation from ferrite to austenite (α → γ) without and with PCRR are determined by differential scanning calorimetry (DSC) upon heating. The austenite onset (Ac1) and end (Ac3) temperatures both decrease with as the thickness reduction from the PCRR increases. The activation energy for the α → γ transformation is calculated and shows a significant decline when the PCRR process is applied. In addition, the PCRR process results in a slight increase in the hardness regardless of the austenitizing temperature.

Effect of Cold Ring Rolling on the Wear Resistance of GCr15 Bearing Steel after Quenching and Tempering

In this work, the effects on dry wear behavior of cold ring rolling (CRR) of GCr15 bearing steel, after quenching and tempering (QT) heat treatment are investigated. The effects on steel microstructures and wear mechanisms of CRR with different austenitizing times are also discussed. The results show that, with a short austenitizing time of 10 min, CRR can increase the retained austenite content, decrease the undissolved carbide content and improve the hardness of the specimen, thus reducing ploughing and fatigue flaking, and decreasing the wear loss of the CRR specimen. With the longer austenitizing time of 20 min, the retained austenite content increases, the undissolved carbide content decreases, and the hardness increases significantly, both in specimens with and without CRR, so that ploughing, fatigue flaking, and wear loss can all be decreased. However, with an austenitizing time of less than 20 min, the effects of CRR on retained austenite content, undissolved carbide content, and hardness are not significant. Thus, CRR of less than 20 min cannot further improve wear morphology or decrease wear loss.

The Research on Diameter Growth of Deep Groove Ball Bearing Inner Ring in Cold Rolling Process

There is a close relationship between cold ring rolling product quality and ring diameter growth rate in cold rolling process, but the technological parameters are main factors in influencing ring diameter growth. The paper used both numerical simulation and experimental verification to study the effect of the core roller speed and wide-diameter ratio on increment of ring diameter in cold rolling process of deep groove ball bearing inner ring. It is found that the core roller has greater influence on diameter growth, and the faster the feeding speed of core roller is , the greater the increment of ring diameter is. Finally, it is verified that the agreement between numerical simulation and experiments is good.

Influence of the Intermediate Annealing on Deformation Ability of the Cold Rolled Ring

This paper studies the influence of the intermediate annealing on deformation ability of the cold rolled ring. The results show that: intermediate annealing can improve the ability of plastic deformation of the cold rolled ring, ring rupture occurred after 62.5% thickness reduction, on the other side the ring suffering intermediate annealing still be intact by rolling to upon 64.8% thickness reduction. The mechanism of the intermediate annealing improving deformation ability of cold rolled ring is explored by using optical microscopy, scanning electron microscopy, micro hardness tester and other materials characterization methods. It is found that after intermediate annealing, the amount of carbide particles significantly reduce and the hardness decrease. Meanwhile, dissolution of partial carbides occur during the cold ring rolling process, and with the increasing of the cold rolling deformation, the quantity of the dissolution of cementite in pearlite will increase, which resulting in the improvement of the deformability of the cold rolled ring.