Abstract
Transformation Induced Plasticity (TRIP) steels with silicon–manganese (Si–Mn) as the main element have attracted a lot of attention and great interest from steel companies due to their low price, high strength, and high plasticity. Retained austenite is of primary importance as the source of high strength and high plasticity in Si–Mn TRIP steels. In this work, the cold rolled sheets of Si–Mn low carbon steel were treated with TRIP and Dual Phase (DP) treatment respectively. Then, the microstructure and composition of the Si–Mn low carbon steel were observed and tested. The static tensile test of TRIP steel and DP steel was carried out by a CMT5305 electronic universal testing machine. The self-built true stress–strain curve model of TRIP steel was verified. The simulation results were in good agreement with the experimental results. In addition, the phase transformation energy of retained austenite and the work borne by austenite in the sample during static stretching were calculated. The work done by austenite was 14.5 J, which was negligible compared with the total work of 217.8 J. The phase transformation energy absorption of retained austenite in the sample was 9.12 J. The role of retained austenite in TRIP steel is the absorption of excess energy at the key place where the fracture will occur, thereby increasing the elongation, so that the ferrite and bainite in the TRIP steel can absorb energy for a longer time and withstand more energy.
Highlights
As early as the 1940s, scholars paid attention to the influence of stress on phase transformation in steel
In 1967, Zackay et al [5] found the effect of stress-induced phase transformation promoted retained austenite to martensite in high alloy chromium–nickel–molybdenum steel
In the past two decades [6,7,8,9,10,11], Transformation Induced Plasticity (TRIP) steels with silicon–manganese as the main element have attracted a lot of attention and great interest from steel companies due to the steel’s low price, high strength, and high plasticity
Summary
As early as the 1940s, scholars paid attention to the influence of stress on phase transformation in steel. The residual austenite which is stable at room temperature is transformed into martensite after being stressed, the transformed martensite increases the strength of the material, and the transient phase change induces plastic growth. Initial yield strengths, hardening coefficients, and hardening exponents of four phases were obtained They did not consider the influence of chemical composition on relevant parameters and the energy absorption of retained austenite during phase transformation. The present work establishes the stress–strain models of ferrite, martensite, bainite, and austenite respectively, and develops a stress–strain model for TRIP steel using the rule of mixtures. In this way, the energy absorption of residual austenite during phase transformation can be calculated. The energy of martensitic transformation after retained austenite is stressed can be mathematically analyzed
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