Microstructure evolution of fibre laser welded TRIP and HSLA steel sheets with different thicknesses

Abstract

The microstructure of fibre laser welded joint of TRIP 690T and HSLA LAD340 steel sheets with different thicknesses was evaluated. The microstructure in the fusion zone was built of martensite, lower bainite and a small portion of upper bainite. Martensite and lower bainite created in both the coarse-grained and fine-grained heat affected zones (HAZs) near 690T steel, but some portion of ferrite was also identified in the fine-grained HAZ near 690T steel. Acicular ferrite, upper bainite, and equiaxed ferrite were observed in both the coarsegrained and fine-grained HAZs near LAD340 steel, but lower bainite was occasionally found in the coarse-grained HAZ near LAD340 steel. Creation of hard microconstituents caused an increase in microhardness values in the fusion zone and both HAZs compared to the base metals. The highest microhardness of 457 HV0.1 was measured in the coarse-grained HAZ near 690T steel with martensitic and lower bainitic microstructure.

Microstructure and tensile properties of the different thickness ASSAPH440 high strength steel/DC52D+ZF45 galvanized cold rolled sheet dissimilar metal welding joint by CO2 laser welding for automobile manufacturing

“…They found that the microstructure of the weld zone is martensite, and the microstructure is the mixture of martensite, bainite and ferrite on both sides of HAZ, which also has observed in this paper (show in figures 8-10). Sevc [32] has investigated the fiber laser welded TRIP/HLSA sheets with different thicknesses, they found that the highest microhardness is at the HAZ of TRIP steel side, while in this study, the higher microhardness is at the weld center, which also agrees with our research result (show in figure 11). Rahul [18] has investigated on the effect of power and velocity of laser beam welding on tensile strength of the TRIP steel butt weld joint, and Shu [33] has also studied the effect of process parameters on the tensile strength of the laser welded joint of HC550/DP780 high strength steel with different thicknesses.…”

Microstructure and mechanical properties of fibre laser welded joints of CP780 and TRIP690 steel

“…The ferrite portion increased with the distance from the weld centre and with a decrease in the maximal temperature achieved during the welding cycle in the inter-critical temperature interval. The smallest value of 214 HV 0.1 in the HAZ of TRIP690 steel was in the vicinity of TRIP690 steel BM and represented the softening region of sub-critical HAZ [27]. From the information above, it is obvious that significant differences can be found when describing the microstructure in HAZs of CP and TRIP steel grades.…”

“…Acicular cementite, massive ferrite, layered pearlite, and granular bainite were mainly observed in the joint [19]. In the work [27], TRIP690 and 340LAD steel were fibre laser welded. The microstructure in the coarse-grained HAZ of TRIP690 steel was built mainly of martensite and lower bainite with a maximal hardness of 457 HV 0.1 .…”

“…From the information above, it is obvious that significant differences can be found when describing the microstructure in HAZs of CP and TRIP steel grades. Some authors claim fully martensitic microstructure in the coarse-grained upper-critical HAZs [12,17,19], but others observed more complex microconstituents [10,11,19,27]. Some authors observed the softening regions in the sub-critical HAZs [2,11,13,27]; others didn't identify them [17].…”

Effects of magnetic field and post-weld heat treatment on microstructure and properties of laser welded joints of 22MnB5-TRIP590 steel

“…The microstructure and properties of laser-welded TRIP steel joints have previously been studied [5][6][7][8][9]. For instance, P. VEC [10] found that the weld zone structure of the laser-welded joint of TRIP690T steel is martensite, lower bainite, and a small amount of upper bainite. Furthermore, the fine grain zone near TRIP690T steel is martensite, lower bainite, and ferrite.…”