The Optimization of Process Parameters and Microstructural Characterization of Fiber Laser Welded Dissimilar HSLA and MART Steel Joints

Abstract

Nowadays, environmental impact, safety and fuel efficiency are fundamental issues for the automotive industry. These objectives are met by using a combination of different types of steels in the auto bodies. Therefore, it is important to have an understanding of how dissimilar materials behave when they are welded. This paper presents the process parameters' optimization procedure of fiber laser welded dissimilar high strength low alloy (HSLA) and martensitic steel (MART) steel using a Taguchi approach. The influence of laser power, welding speed and focal position on the mechanical and microstructural properties of the joints was determined. The optimum parameters for the maximum tensile load-minimum heat input were predicted, and the individual significance of parameters on the response was evaluated by ANOVA results. The optimum levels of the process parameters were defined. Furthermore, microstructural examination and microhardness measurements of the selected welds were conducted. The samples of the dissimilar joints showed a remarkable microstructural change from nearly fully martensitic in the weld bead to the unchanged microstructure in the base metals. The heat affected zone (HAZ) region of joints was divided into five subzones. The fusion zone resulted in an important hardness increase, but the formation of a soft zone in the HAZ region.

The Influence of Laser Welding on the Mechanical Properties of Dual Phase and Trip Steels

“…Similar results have been reached by other authors [5][6][7][18][19][20]28,29], although they used specimens with transverse laser weld and dissimilar materials were joined. lower values of deformation properties-uniform extension Ag approx.…”

“…In the transition zone between the base metal and heat affected zone, microhardness has not declined markedly, i.e., any substantial soft zone hasn't been found for each material. Otherwise, other researchers identified soft zones when thicker materials with high power were welded [5][6][7]20].…”

“…Results of microstructural changes received when similar materials were welded comply with [5][6][7]20]: the fusion zone of dual phase steel consisted of fully martensitic structure; the fusion zone of high strength low alloyed steel consisted of ferrite, bainite and martensite; and the fusion zone of multi-phase steel consisted of martensite with laths oriented randomly. In the heat affected zone of the weld joints ( Figure 13), a mixed martensite-ferrite structure occurs.…”

“…The study is focused on the measurement of strength and deformation properties for base material and laser welded by a solid-state fiber laser. Many authors have investigated the influence of laser welding on the tensile properties on specimens with transverse weld [5,6,[18][19][20]. Thus, the research was focused on the specimens with longitudinal butt laser weld, as it is used for tailored TWBs.…”

“…In the case of high-strength low-alloy (HSLA) steels, the increase of the ferritic matrix strength is achieved especially by microalloying elements Ti, V, and Nb, which increase strength by grain size control, precipitation hardening, or substitution hardening of structure [4,5]. Dual phase steels consist of a ferritic matrix with 5% to 30% martensite content.…”