MICROSTRUCTURE AND MECHANICAL PROPERTY OF LASER WELDED JOINT FOR HYPOEUTECTOID U-Nb ALLOY
LI Yubin(), WANG Wei, HE Jianjun, ZHANG Zhiqiang, ZHANG Tongyan
China Academy of Engineering physics, Mianyang 621900
Cite this article:
LI Yubin, WANG Wei, HE Jianjun, ZHANG Zhiqiang, ZHANG Tongyan. MICROSTRUCTURE AND MECHANICAL PROPERTY OF LASER WELDED JOINT FOR HYPOEUTECTOID U-Nb ALLOY. Acta Metall Sin, 2014, 50(3): 379-386.
The microstructures and mechanical properties of hypoeutectoid U-Nb alloy laser welded joint were investigated by optical microscopy (OM), X-ray diffractometer (XRD), transmission electron microscopy (TEM), split hopkinson pressure bar (SHPB) and other analysis apparatus. The results show that the microstructure of hypoeutectoid U-Nb alloy base metal is α-U+γ-U lamellar pearlite under isothermal heat treatment, while the laser welding seam is composed of α' lath martensite for pre-heated or α' twin martensite for no pre-heated with orthogonal crystal structure. The quasi-static tensile strength of welded joint (about 400 MPa) is much less than base metal and microstructures of weld, for the main reason of incomplete penetration weld and low fracture toughness. Between dynamic impact loading for base and welded joint, the strain rate of welded joint is lower than base metal, and the yield strength of welded joint is higher. Also, the compressive stress-strain curves indicated that the flow stresses for welded joint increased with the increase of strain rate and the obvious effect of strain rate hardening has been observed. At strain rate of 2000 s-1, selected plastic deformation taking place in welded joint is due to the tremendous difference mechanic properties between weld seam and base metal, and the adiabatic shear band(ASB) only appears in the rest of welded joint.