PT  - JOURNAL ARTICLE
AU  - Bublíková, Dagmar
AU  - Jirková, Hana
AU  - Stehlík, Adam
AU  - Jeníček, Štěpán
TI  - Effect of Temperature and Deformation on the Stability of Retained Austenite in Closed-die Forgings from High-strength Martensitic Manganese-silicon Steels
DP  - 2023 Jul 5
TA  - Manufacturing Technology Journal
PG  - 269--275
VI  - 23
IP  - 3
AID - 10.21062/mft.2023.030
IS  - 12132489
AB  - In advanced steels, retained austenite is an important phase in the final microstructure, which provides a favourable combination of strength and ductility. Advanced methods capable of achieving this include the Q-P process (Quenching and Partitioning). By this means, strength of around 2000 MPa and elongation of 10-15 % can be obtained. The main factors that determine whether retained austenite remains stable in the mar-tensitic matrix include its morphology, particle size and distribution. A closed-die forging was made from an experimental steel containing 0.42 % C, 2.45 % Mn, 2.09 % Si, 1.34 % Cr and 0.56 % Ni and Q-P processed. Based on previous data measured in a real-world process, two basic heat treatment sequences were created and tested on a thermomechanical simulator. The two sequences differed in the cooling rates. Upon heat treatment, a martensitic microstructure with a retained austenite content of 13-17 % was obtained. The ul-timate strength was in the range of 2100-2200 MPa with elongations A5mm 8-15 %. Austenite stability was tested by bringing the material to various temperatures (200, 300, 400, -18, -196 °C) and by cold forming at various strain rates (10-3, 10-1, 10 s-1). The volume fraction of carbon in austenite was calculated from the lattice parameters determined by X-ray diffraction.