JIRKOVÁ Hana UWB in Pilsen

Influence of Chromium and Manganese on Mechanical Properties of Low Alloyed High Strength Steels with Retained Austenite Processed by Modern Methods of Thermomechanical Treatment

Co-authors KLOKAN Martin, KUČEROVÁ Ludmila, MAŠEK Bohuslav

New procedures of heat treatment make it possible to obtain a combination of very good tensile strength and great ductility for low alloyed high strength steels. Three treatments utilizing the metastable austenite component for improving steel formability have been developed for their unconventional processing. These are the intercritical annealing typical for TRIP steels, the long term low temperature bainite annealing and the Q-P process. In the experimental program the intercritical annealing and the Q-P process were tested on two low alloyed steels with carbon content of about 0.2 %, chromium content between 0.09% and 0.79% and manganese content in the interval from 0.6% to 1.5 %. The influence of various cooling rates on the structure development and mechanical properties was examined for both types of treatment. Additionally the impact of different quenching temperatures in the Q-P process was also investigated. The influence of chromium on the morphology of the hardening phase was analysed metallographically. Multiphase structures with various amounts of ferrite, bainite, retained austenite and MA constituent were achieved on the experimental specimens. The tensile strength after the Q-P process exceeded 830 MPa with ductility above 30%.