Abstract
The effect of austenitizing temperature and aging treatment on the microstructure and mechanical properties of two new cold-rolled automotive steel plates (20Mn2Cr and 20Mn2CrNb) was investigated by using isothermal heat treatment, optical microscope, scanning electron microscope, microhardness tester, and tensile testing machine. The results show that as the austenitizing temperature increased, the original austenite grain sizes of both steels increased. The original austenite grain size of 20Mn2CrNb was smaller than that of 20Mn2Cr. The microhardness of 20Mn2CrNb gradually decreased with increasing aging temperature, while the hardness of 20Mn2Cr varied irregularly. The mechanical properties of 20Mn2Cr were better than those of 20Mn2CrNb under the same heat-treatment process. The effect of heat treatment on microstructure and mechanical properties was related to the martensite content, dislocation density, and precipitation of second-phase particles.
Highlights
The development of automotive steel products with high-strength plasticity is one of the main ways to produce lightweight parts, and is of great significance for energy saving and environmental protection [1,2,3,4,5,6,7,8]
There has been a large amount of domestic and international research and development work on high-strength plasticity automotive steel. It has developed into the third generation, with the main forms being nano-bainite steel, delta transformation-induced plasticity (δ-TRIP) steel, medium manganese steel, quench and partitioning (Q&P) steel, etc. [9,10,11,12,13,14,15]
Nano-bainitic steel is subjected to a low-temperature bainite phase transition region (125–300 ◦ C)
Summary
The development of automotive steel products with high-strength plasticity is one of the main ways to produce lightweight parts, and is of great significance for energy saving and environmental protection [1,2,3,4,5,6,7,8]. Our research group proposed the design of high-strength plastification steel (PRM) from the interaction of second-phase particles (precipitation) and dislocations (zero- and one-dimensional) and microstructure submicron (two-dimensional) and multiphase (three-dimensional) refinement, breaking through the technical bottleneck of the single mechanism of residual austenite plastification. Based on this idea, new low-alloy steels for flexible applications with high strength plasticity for automobiles were designed and developed, and preliminary cold-rolled steel sheets and hot-formed parts with relatively good mechanical properties were obtained [21,22,23]. Nb on the microstructure and mechanical properties were studied to provide theoretical guidance for obtaining better properties
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