RT Journal Article
SR Electronic
A1 Bublíková, Dagmar
A1 Jirková, Hana
A1 Stehlík, Adam
A1 Jeníček, Štěpán
T1 Effect of Temperature and Deformation on the Stability of Retained Austenite in Closed-die Forgings from High-strength Martensitic Manganese-silicon Steels
JF Manufacturing Technology Journal
YR 2023
VO 23
IS 3
SP 269
OP 275
DO 10.21062/mft.2023.030
UL https://journalmt.com/artkey/mft-202303-0001.php
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.