Abstract The laser welded joint of 2000MPa cold rolled annealed hot pressed steel (PHS) is easy to break during cold rolling. In this paper, the laser welding method is used to butt weld four kinds of PHS2000 with a thickness of 3.5mm. The four kinds of PHS2000 steel are added with elements of 0% Nb, 0.04% Nb, 0.06% Nb + Cr and 0.08% Nb + Cr. The microstructure of the four kinds of welded joints is compared and analyzed. The mechanical properties of the four kinds of joints are compared through hardness test and tensile test. The results show that after adding 0.04% Nb, residual austenite appears in the weld zone and fully quenched zone, the width of columnar crystal decreases, the average hardness of the weld zone decreases from 595HV to 408HV, and the tensile strength increases from 608MPa to more than 800MPa. For chromium containing steel, the increase of niobium content can reduce the size of columnar crystal in weld zone.

Microstructural evolution, interfacial reaction and fracture during vacuum brazing of 50Mo-50Re alloys using amorphous alloy Fe-5.6Si-2.6B(wt%) were investigated. A binary intermetallic compound, σ(Mo2Re3) formed as parallel contiguous layers in the diffusion zone. In addition, Fe from the braze alloy, in combination with dissolved Mo from the substrate, formed two layers of binary compounds µ-Mo6Fe7 and λ-MoFe2, adjacent to diffusion zone. The unreacted Fe-based filler metal solidified as α-Fe solid solution. Fracture analysis showed that the mode of failure was mainly transgranular cleavage with partly intergranular and the fracture located on the interface of 50Mo-50Re alloy and the central area of brazing seam.

Three dimensional (3D) printing technology has been widely used in metal manufacturing industry. This study focused on the vacuum brazing of 3D printed Inconel 718 superalloy with BNi-2 amorphous filler metal. Interfacial microstructure and element distribution revealed excellent wettability and spreadability of the filler metal as well as favorable brazability of the base material. Brazed joint could be divided into two distinct zones: isothermally solidified zone (ISZ) consisting of γ-Ni solid solution and diffusion-affected zone (DAZ) consisting of a large amount of precipitates besides γ-Ni solid solution. Microhardness reached peak values in DAZ. Although borides filled the gaps of base material’s grains to restrict grain boundary sliding and restrain the expansion of gaps, but its high hardness and brittleness would cause DAZ turn into weaker region when external loads were very large. The complete diffusion of B indicated the completion of isothermally solidified process. Precipitate CrB2 with high hardness and brittleness was the key point of reducing the joint strength. Shear strength of the brazed joint was up to 802 MPa, and fracture morphology presented a mixed ductile-brittle fracture.