Abstract
Bainitic steels were the focus of this study. These steels have the potential to obtain a good combination of strength, ductility, and edge stretchability, which is a very desirable characteristic in the automotive industry. Cu precipitation potential was investigated during prolonged isothermal bainitization treatment. Precipitation strengthening and ductility were measured using a tensile test, and edge stretchability was measured using a hole expansion test. The microstructure was characterized by high-resolution scanning electron microscopy and an electron backscattered diffraction. Lower bainite was obtained by austenitization treatment and subsequent immersion into a salt bath at 400 °C. Cu precipitation occurred after 120 min of holding in the bath and enhanced the yield stress of the Cu-alloyed steel by 120 MPa as compared with a reference steel without Cu. The strengthening did not affect ductility and decreased the edge stretchability by 10%. Steels with different Mn contents were examined. It was found that the enhancement of Mn content from 1 to 2 wt.% did not boost Cu strengthening ability. This result showed that the presence of Mn did not cause an Mn-Cu precipitation strengthening synergy, observed previously during martensite tempering procedure.
Highlights
Materials 2021, 14, 1962. https://High strength steels are a group of materials that have received significant attention in the field of material research
The microstructure was characterized by high-resolution scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD)
Tensile testing revealed the influence of chemical composition and the duration of salt bath treatment on the mechanical properties (Table 2)
Summary
Materials 2021, 14, 1962. https://High strength steels are a group of materials that have received significant attention in the field of material research. Advancements in rolling technology have enabled the production of sheets with outstanding combinations of strength and ductility [1,2]. These sheet materials are extensively used, mainly in the automotive industry. Car developers relentlessly seek ways to save weight in their product, there is a need for better technological and better mechanical properties. Dual-phase, TRIP (transformation-induced plasticity), and complex phase steels have been developed and gradually introduced for industrial use. Their strength-ductility combination has exceeded conventional ferritic or martensitic steels
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