Regular Article

Effect of proeutectoid carbide on heredity in microstructure-mechanical properties and fatigue life of GCr15 bearing steel

¹ The State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China
² Henan Jiyuan Iron and Steel Group Co., Ltd, Henan, Jiyuan 459000, China

^⁎ e-mail: 15239718910@126.com

Received: 6 September 2016
Accepted: 19 January 2017

Abstract

The hot-rolled GCr15 bearing steels were obtained by different cooling rates before pearlite transformation temperature through dynamic thermal simulation test, and followed by some spheroidizing annealing and quenching-tempering treatment. The relationship between the condition of proeutectoid carbide precipitation, microstructure-mechanical properties of hot-rolled bearing steel, heredity in microstructure-mechanical properties and fatigue life after heat treatment was investigated comprehensively. Results showed that as the cooling rate decreased from 100 °C/s to 0.5 °C/s, the proeutectoid carbide thickness and continuity both linearly increased from 0.04 µm and 0.05 to 0.72 µm and 0.93. The morphology of proeutectoid carbide changed from the small and dispersed strips to the thick and big networks. The tensile strength and percentage of area reduction of hot-rolled bearing steel both decreased. During heat treatment, the thick and big carbide networks could not be eliminated. The carbide precipitations by spontaneous nucleation in spherical form and non-spontaneous nucleation with the undissolved carbide strips as cores during spheroidizing annealing process were observed by high-temperature confocal laser scanning microscopy. The thickness and inhomogeneity of carbide in annealed and tempered microstructures both increased gradually. Finally, the strength and plasticity of heat-treated bearing steel still decreased, the fatigue life decreased by 91%. The tensile fracture changed from the quasi-cleavage fracture to the intergranular and quasi-cleavage fracture.