Abstract
Third-generation advanced high-strength steels (AHSS) containing metastable retained austenite are being developed for the structural components of vehicles to reduce vehicle weight and improve crash performance. The goal of this work was to compare the effect of temperature on austenite stability and tensile mechanical properties of two steels, a quenched and partitioned (Q&P) steel with a martensite and retained austenite microstructure, and a medium manganese transformation-induced plasticity (TRIP) steel with a ferrite and retained austenite microstructure. Quasi-static tensile tests were performed at temperatures between −10 and 85 °C for the Q&P steel (0.28C-2.56Mn-1.56Si in wt.%), and between −10 and 115 °C for the medium manganese TRIP steel (0.14C-7.14Mn-0.23Si in wt.%). X-ray diffraction measurements as a function of strain were performed from interrupted tensile tests at all test temperatures. For the medium manganese TRIP steel, austenite stability increased significantly, serrated flow behavior changed, and tensile strength and elongation changed significantly with increasing temperature. For the Q&P steel, flow stress was mostly insensitive to temperature, uniform elongation decreased with increasing temperature, and austenite stability increased with increasing temperature. The Olson–Cohen model for the austenite-to-martensite transformation as a function of strain showed good agreement for the medium manganese TRIP steel data and fit most of the Q&P steel data above 1% strain.
Highlights
Advanced high-strength steels (AHSS) are being incorporated into vehicles for weight reduction and improved crash performance [1,2,3]
With some of the more recently introduced third-generation AHSS, there are new issues encountered in automotive manufacturing and service, e.g., the wide variation in tensile behavior with respect to temperature and negative strain-rate sensitivity of medium manganese transformation-induced plasticity (TRIP) steel [4]
The goal of this study is to gain a better understanding of temperature effects on tensile behavior and austenite stability of two types of third-generation AHSS
Summary
Advanced high-strength steels (AHSS) are being incorporated into vehicles for weight reduction and improved crash performance [1,2,3]. With some of the more recently introduced third-generation AHSS, there are new issues encountered in automotive manufacturing and service, e.g., the wide variation in tensile behavior with respect to temperature and negative strain-rate sensitivity of medium manganese transformation-induced plasticity (TRIP) steel [4]. Under forming operations and crash conditions, steel components are subjected to deformation at a wide range of strain rates (0.01–1000 s−1 ), and adiabatic heating can occur at higher rates [6,7]. Adiabatic heating during high strain rate deformation may increase austenite stability and impact mechanical behavior [9,10,11]. The effect of temperature on flow stress in the range of −40 to 100 ◦ C is an important performance metric for sheet steels considered for use in vehicles [4]
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