Effect of air cooling time on temperature and microstructure uniformity of 960 MPa high strength steel by direct quenchingAuswirkung der Abkuhlzeit an Luft auf die Temperatur- und die Gefugegleichmassigkeit in hochfestem Stahl mit 960 MPa bei direktem Abschrecken

In order to improve the temperature and microstructure uniformity in the thickness direction of online-quenching 960 MPa high strength steel, the finite element software ADINA and the experiments have been used to analyze the effect of internal air cooling on temperature variation in the thickness direction during the online quenching process. The results showed that the interval air cooling could effectively improve the uniformity of temperature, microstructure and hardness in the direction of thickness of steel plate during the online quenching process. When air cooled for 3.2 s, the temperature difference between the surface and the core of the steel plate could be reduced by 90.13 %, and the cooling rate in the core could be reduced by about 85.20 % compared with continuous water cooling condition. The hardness difference between the surface and the core could reduce from 23 HV 5 to 5 HV 5. The internal air cooling process had an influence on the matensite lath morphology compared with continuous water cooling process. The microstructures with the different cooling conditions were martensite and the properties could still meet the requirements of 960 MPa high strength steel.

Automated summary

In this study, the effect of internal air cooling on the temperature variation in the thickness direction during the online quenching process of high strength steel was analyzed using finite element software and experiments. The results showed that the interval air cooling could effectively improve the uniformity of temperature, microstructure, and hardness in the direction of thickness of the steel plate.