Influence of Quenching Process on the Microstructure Evolution and Hardness of A514CrQ Rack Steel

Abstract

The influence of quenching process on the microstructure evolution and hardness of A514CrQ rack steel has been investigated in this paper. The results showed that granular bainite + a small amount of lath martensite can be obtained after water quenching at 790 ℃/30 min. After 820 ℃-950 ℃/30 min water quenching， full lath martensite was obtained， and with the increase of quenching temperature， the width of martensite block increased， and hence the hardness gradually decreased. The 820 ℃ was identified as the optimal quenching temperature. When the holding time was 1 min-5 min， granular bainite +lath martensite was obtained by water quenching at 820 ℃， and the hardness of the specimen was much lower. When the holding time was 10 min-70 min， full lath martensite was obtained after water quenching at 820 ℃， the martensite block width increased with the increasing holding time， and hence the hardness gradually decreased and tended to be flat. Then the optimal holding time was identified as 10 min. After 820 ℃/10 min air quenching or oil quenching， granular bainite + lath martensite/bainite was obtained， and the content of martensite/bainite after oil quenching was higher. This leads to the lowest hardness of air quenching， the center of oil quenching， and the largest hardness of water quenching. In the process of double cycle quenching process， the final microstructure was determined by the secondary quenching medium， and the martensite/bainite lath can be refined more effectively by using water as the primary quenching medium. After 820 ℃/10 min water quenching + 820 ℃/10 min water quenching， the martensitic block width was the smallest and the hardness was the highest. Thus， this double water quenching process can serve as the preferred quenching process for rack steels.

Keywords

• a514crq rack steel； quenching process； microstructure evolution； hardness