Effect of cooling rate after finish rolling on heredity in microstructure and mechanical properties of 60Si2MnA spring steel

¹ State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, P.R. China
e-mail: 13401162963@163.com
² Henan Jiyuan Iron and Steel Group Co., Ltd, Henan Jiyuan 459000, P.R. China

Received: 19 November 2015
Accepted: 7 April 2016

Abstract

The hot-rolled 60Si2MnA spring steels were obtained by different cooling rates after finish rolling through dynamic thermal simulation test, and followed by some quenching-tempering treatment. The relationship among the condition of proeutectoid ferrite precipitation, microstructures and mechanical properties of hot-rolled spring steel, and heredity in microstructure and mechanical properties during heat treatment was investigated comprehensively. Results showed that as the cooling rate increased from 0.5 °C/s to 5 °C/s, the bulk content of proeutectoid ferrite decreased from 24% to 2%, pearlitic colony size and interlamellar spacing also decreased, the reciprocal of them both followed a linear relationship with the reciprocal of proeutectoid ferrite content. So the microstructure became finer and more uniform, the tensile strength and percentage of area reduction of hot-rolled spring steel both increased. During heat treatment, the average grain size and standard deviation of its normal distribution both depended linearly on the content of proeutectoid ferrite. Therefore, the austenite grain, quenched microstructure and tempered troostite all also became finer and more uniform. Finally, the tensile strength and percentage of area reduction of spring steel after heat treatment also increased, and the tensile fracture of spring steel transformed from the intergranular fracture to the cleavage and dimple fracture.