Microstructure, Mechanical Properties and Welding of Low Carbon, Medium Manganese TWIP/TRIP Steel

Pavel Podany,Christopher Reardon,Martina Koukolikova,Radek Prochazka,Ales Franc

doi:10.3390/met8040263

Pavel Podany, Christopher Reardon + Show 3 more

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https://doi.org/10.3390/met8040263

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Abstract

Manganese twinning induced plasticity (TWIP) steels are attractive materials for the automotive industry thanks to their combination of strength and excellent toughness. This article deals with basic microstructural and mechanical properties of sheet metal of two heats of low-carbon medium-manganese steel with different aluminium levels. Microstructure observation was carried out using optical and scanning electron microscopy. Electron backscatter diffraction (EBSD) and X-ray diffraction were used for phase analysis. In an experiment that focused on the weldability of both materials, sheet metals were laser-welded using various laser power settings, with and without shielding gas. Various combinations of joints between materials of the two heats and sheet metal conditions were tested (work-hardened upon cold rolling + annealed). Mechanical properties of the weld joints were determined using miniature tensile testing and conventional hardness measurement. The strengths of miniature specimens of the weld metal were very close to the strength of the base material.

Highlights

Steels with Mn, Si, and Al in fairly high concentrations show high plasticity and strength when deformed thanks to the mechanical twinning (TWIP steels) or to martensitic transformation induced by deformation (TRansformation Induced Plastisity–TRIP steels) [1,2,3,4]
For stacking fault energy (SFE) with values that are greater than 18 mJ/m2, the twinning induced plasticity (TWIP) effect has a tendency to occur, for lower values, the TRIP effect is leading, with an α0 martensite phase being formed for SFE values that are below 12 mJ/m2
In steels with an Mn content below 15%, the TRIP effect takes over, while for an Mn content that is higher than 25%, the TWIP effect is leading

Summary

Introduction

Steels with Mn, Si, and Al in fairly high concentrations show high plasticity and strength when deformed thanks to the mechanical twinning (TWIP steels) or to martensitic transformation induced by deformation (TRansformation Induced Plastisity–TRIP steels) [1,2,3,4]. An important factor determining the type of deformation mechanism in these types of steels is their stacking fault energy (SFE). For SFE with values that are greater than 18 mJ/m2 , the TWIP effect has a tendency to occur, for lower values, the TRIP effect is leading, with an α0 martensite phase being formed for SFE values that are below 12 mJ/m2. In steels with an Mn content (wt %) below 15%, the TRIP effect takes over, while for an Mn content that is higher than 25%, the TWIP effect is leading. It means that in an Mn content in the range

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