Effect of Trace Element on Microstructure and Fracture Toughness of Weld Metal

Abstract

The microstructure and fracture toughness of weld metal under Ti-free and Ti-containing different fluxes were investigated in this study. It was found that the trace element Ti of flux in submerged arc welding produced significant influence on the fracture toughness. The addition of 60 ppm Ti induced the sharp increase in J 0.2 value from 232.78 to 364.08 kJ/m 2 . Microstructure characterization revealed that a large number of oxide inclusions prompted the nucleation of acicular ferrites and refined grains, which improved the fracture toughness of Ti-containing weld metal greatly. Moreover, the crack propagation path was more tortuous and bifurcated due to the small amount of carbide precipitations along grain boundaries and blocky martensite-austenite islands for Ti-containing weld metal. Meanwhile, the large-angle grain boundaries caused crack deflection and increased the resistance of crack propagation compared to Ti-free weld metal.

Effect of the Cooling Rate of Thermal Simulation on the Microstructure and Mechanical Properties of Low-Carbon Bainite Steel by Laser-Arc Hybrid Welding

“…With the precipitation of ferrite, the generated LB and M-A constituents enriched many elements near the grain boundary, resulting in the formation of a mixed structure. During the gradual decrease in the grain size, the content of M-A constituents increased, which were mainly distributed near the grain boundary [22], thereby negatively affecting the plasticity of the material and further reducing the elongation. The content of AF and the M-A constituents affected the toughness of the steel [23], but it was obvious that the M-A constituents played a leading role as shown in Figure 8, i.e., that the stress between 6 s and 8 s did not follow the tendency as well as the point 't 8/5 = 8 s' in Figure 9.…”

“…Accounting for the short time of t 8/5 , the cooling rate exceeded the critical cooling rate of martensite and inhibited the diffusion of carbon atoms. The iron lattice was rearranged in a tangential transformation mode, from FCC γ-Fe to BCC α-Fe, and most of the carbon atoms were retained in α-Fe to form a supersaturated solid solution with LM retained at room temperature [22]. When t 8/5 was 6-18 s, the cooling time increased between 800 and 500 • C, and the diffusion of carbon could not be completely suppressed.…”