Optimization of TMCP parameters to improve the mechanical properties of 201LN stainless steel for cryogenic applications

The study aims to optimise thermo-mechanically controlled processing (TMCP) parameters for 201LN stainless steel to achieve improved yield and tensile strengths, alongside excellent ductility, toughness, and fatigue properties. A 201LN alloy ingot (5.4 wt.% Ni and 7.0 wt.% Mn) was vacuum-cast and hot rolled into thick plates. Cylindrical samples were machined for uniaxial, two-step hot compression tests using a Gleeble simulator under six distinct TMCP schedules. The second step deformation was performed in the no-recrystallization regime at 850–1000 °C, followed by fast cooling to prevent precipitation and sensitization. Microstructural evolution was analysed using confocal laser scanning microscopy (CLSM) and Vickers hardness testing. Image analysis quantified grain size and distribution, revealing pancaked grain structures that contributed to dislocation or substructure strengthening. Hardness decreased with increasing second-step deformation temperature, with the highest values observed at 850 °C and 900 °C, showing increases of 55% and 45%, respectively, over the annealed condition. These findings demonstrate that TMCP enables tailored microstructures and properties in 201LN steel.