Influence of Austenitization Parameters on the Precipitation Sequence and the Chemical Homogenization of Austenite in a High-Performance Fe–Ni–Cr–Al–Ti–Mo Stainless Maraging Steel

Abstract

MLX19 stainless maraging steel grade exhibits a mechanical strength/fracture toughness balance within the required range for landing gear applications. However, the microstructure after the heat treatment still needs to be precisely controlled to obtain a better repeatability of the mechanical properties. This work shows that austenitizing is a critical stage. The influence of austenitization treatment parameters on the microstructure obtained after quenching was thus precisely quantified. It was first revealed that, after a standard austenitization at 850 °C and for specific heating rates and holding times, undissolved b-NiAl precipitates, reaching sizes up to 500 nm, still remain in the as-quenched state, in addition to a high retained austenite fraction. It was also found that large amounts of retained austenite are the result of local heterogeneities in the chemical composition of the austenitic phase prior to quenching, while the undissolved precipitates change the overall chemical composition of the austenitic matrix. New austenitization conditions were thus proposed, leading to a better homogeneity of the chemical composition of the martensitic matrix after quenching.

Near-Net Shape Manufacture of Ultra-High Strength Maraging Steel Using Flow Forming and Inertia Friction Welding: Experimental and Microstructural Characterization

“…The chemical composition of some of these precipitates (marked as 1 and 2) is presented in Table 3. The precipitates were found to be enriched with nickel, titanium and aluminium elements, and according to a previous study conducted on MLX ® 19 steel by Rocchi et al [28], these are η-Ni3(Ti, Al) precipitates. According to the previous studies [1,[23][24][25], the martensite in this zone is expected to experiences peak temperatures inbetween 590 -730 °C, resulting in the formation of reverted austenite and fine precipitates.…”

The Effect of Selective Laser Melting Fabrication Parameters on the Tensile Strength of an Aged New Maraging Steel Alloy with 8% Cr, Reduced Ni Content (7%), and No Co or Mo

“…The amount of this austenite formed during ageing increases with higher ageing temperatures and longer ageing times [2,16]. The formation of reverse austenite is due to the matrix being enriched with elements that stabilise austenite [17], such as those resulting from the partial dissolution of Ni 3 (Ti, Mo) and the formation of Fe 2 Mo [18]. The surrounding matrix is enriched in Ni, which leads to partial reversion of the austenite [19].…”