Application of the Unconventional Thermomechanical Treatment on Low-Alloyed High-Strength Steel

Co-authors JIRKOVÁ Hana, MIKMEKOVÁ Šárka, MAŠEK Bohuslav

The demands are increasing on material properties, lowering the mass of components, and lowering production costs are all strong drivers for the development of low-alloyed steels with high strength, which are low cost owing to their low content of alloying elements. Modern advanced low-alloyed steels processed in unconventional ways of heat or thermomechanical treatment can reach substantially better mechanical properties when compared to conventional treatments. Experiments were carried out to test several strategies of thermomechanical treatment of a newly designed low-alloyed high-strength steel 42SiCr with about 0,4% C and 2% Si. The aim of the experiment was to develop and optimize a new type of heat treatment based on the Q-P process (Quenching - Partitioning) which should be capable of achieving strengths of up to 2000 MPa with ductility of 10%. During the optimization process, the main focus was on the influence of various intensities of incremental deformations and the speed of cooling on the development of the structure. By modelling the treatment, a microstructure was obtained formed of a martensite matrix, bainit and finely diffused retained austenite. The influence of the technological process parameters on the structure development was analyzed using several microscopic methods and the resulting mechanical properties were measured by means of tensile test. The volume fraction of the retained austenite was established by X-ray diffraction phase analysis.