Abstract
In the present study, the evolution of microstructure in laser-welded joints of ferrite-based dual-phase Fe-Al-Mn-C steel sheets was analyzed and its effect on the mechanical properties of the joints was investigated. Laser welding was performed using different powers and welding speeds to attain different heat inputs. Electron backscatter diffraction (EBSD) examinations and hardness measurements were used to characterize the microstructure of the welds. The tensile properties were found to depend on the heat input, but joint strength exceeding that of the base metal (BM) were obtained at low heat inputs. However, the fracture location shifted from the base metal to the heat-affected zone (HAZ) as the heat input was increased. The HAZ consisted of a mixture of austenite, ferrite and martensite, and its width increased with increasing the heat input. It was supposed that the incompatibility between the ferrite, austenite and martensite phases led to early void formation and fracturing of the phase interfaces in the wide HAZ.
Highlights
Diverse types of high-strength and high-performance steels have been proposed with the aim of reducing the weight of automobile bodies
To allow for a comparison of the strengths of the samples before and after welding, the strength of the base metal (BM) is indicated in Figure 1a by a dotted line
The strengths of the specimens subjected to heat inputs of less than 22.5 kJ/m were similar to that of the BM
Summary
Diverse types of high-strength and high-performance steels have been proposed with the aim of reducing the weight of automobile bodies. Highly deformable high-strength steels such as transformation-induced-plasticity (TRIP) steels and twinning-induced-plasticity (TWIP) steels have been developed [1,2,3,4,5,6,7,8]. A ferrite-based lightweight steel, namely, Fe-Al-Mn-C steel, which exhibits transformation-induced hardening during deformation, was announced [9,10,11,12]. Ferrite-based lightweight steel contains the alloying elements Mn, Al, and C. These elements expand the lattice of the steel while reducing its density by virtue of their low atomic masses [6].
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