Influence of Heat-Treatment on Enhancement of Yield Strength and Hardness by Ti-V-Nb Alloying in High-Manganese Austenitic Steel

Abstract

To deal with the problem of poor yield strength and hardness in the initial use of high-manganese austenitic steel, we investigated the alloying design, microstructure, precipitates, mechanical properties, and comprehensive strengthening mechanism of high-manganese austenitic steel through two novel heat-treatment processes, namely continuous heating process (CHP) and segmented heat preservation process (SHPP). In this work, austenitic Fe-0.9C-17Mn-0.8Si-2.0Cr-0.3Ni-0.5Cu-0.7Mo steels alloyed with Ti, V, and Nb were designed. The grain size of SHPP steels was smaller than that of CHP steels due to the smaller size of precipitates. The results of mechanical experiments showed that the yield strength and impact toughness of SHPP steel were obviously higher than those of CHP steel, but the Brinell hardness of CHP steel was higher than that of SHPP steel. The higher Brinell hardness and poorer impact toughness of CHP steel were mainly due to the larger-sized precipitates. Finally, solid-solution strengthening played the most effective role of increasing the yield and tensile strengths of the two steels.

Effect of Aging Treatment on Precipitates and Intrinsic Mechanical Behavior of Austenitic Matrix in Ti–V–Nb‐Alloyed High‐Manganese Steel

“…As shown in Figure 3b, the precipitation temperature of MC carbides is ≈1350 °C in the experimental steel, which is higher than the formation temperature of austenite. Thus, as the higher temperatures accelerate the diffusion of alloying elements and carbon atoms, some large‐sized MC carbides containing multiple alloying elements will be formed in situ during the solidification of steel, such as (Ti, V, Nb)C, (Nb, V)C, and (Ti, Nb)C. [ 4 ] In addition, the microstructure of tested steel is mostly composed of austenite at 1100 °C. Figure 3b shows the engineering stress–strain curves and tensile test data of the casting specimen, as well as the 1050S, 1100S, 1150S, and 1200S test steels.…”

“…Zhou et al reported that a sufficient amount of Gmicrometer/submicrometer precipitated particles was distributed in cast Ti–V–Nb‐alloyed high‐Mn steel, and the micrometer particles were mostly composed of C, and Nb, with a small V and Ti content, whereas the submicrometer precipitates were mostly composed of vanadium carbides. [ 4,5 ] According to Yong, [ 23 ] VC has the largest solubility product in austenite compared with TiC and NbC, thereby TiC and NbC can precipitate during solidification, whereas large amounts of fine VC particles tend to precipitate at lower temperatures. Therefore, we speculated that the decreased average size and density of the precipitates observed in the experimental steels during the solid‐solution treatment processing were mainly related to the solution of VC.…”

“…As they had precipitated in a lower temperature range, the slower diffusion rate of the alloying elements inhibited their coarsening. [ 4,5 ] It is well known that these finely distributed precipitates can effectively improve the yield strength of steels. [ 16,27,28 ]…”

“…However, the poor hardness and wear resistance before work hardening limit the extensive use of high‐Mn austenitic steel. [ 1–8 ] With respect to mining applications, there have been numerous studies based on Ti–V–Nb alloying techniques aimed at improving the prior hardness and wear performance of high‐Mn steels while maintaining their superior toughness and ductility through precipitation strengthening; [ 9 ] micrometer and/or nanosized precipitates, such as titanium carbide, niobium carbide, and vanadium carbides (VC and V 2 C), are formed in these steels after solid‐solution processing and aging at an adequate temperature. [ 10–17 ] These carbide particles have a remarkable effect on the microstructure and mechanical behaviors of high‐manganese austenitic steels.…”

Optimization of Mechanical Properties of High-Manganese Steel for LNG Storage Tanks: A Comprehensive Review of Alloying Element Effects

“…In the production of medium and thick plates from high-manganese steel for storage tanks, a combination of hot rolling and subsequent heat treatment is commonly employed to control the resulting microstructure and properties (as shown in Figure 1). Upon undergoing hot processing, alloying elements display unique action mechanisms within high-manganese austenitic steels at low temperatures [26,27]. Reproduced with permission from ref.…”