Microstructure and properties of heat treated 1Cr17Ni4MoB steel fabricated by laser melting deposition

A 1Cr17Ni4MoB steel was fabricated on the 40CriNiMoA surface by laser melting deposition (LMD), and then underwent heat treatment. The microstructure evolution and properties of laser deposited 1Cr1 7Ni4MoB steel and that underannealing temperatures of 500 degrees C, 700 degrees C, 900 degrees C for 1 h were characterized, especially their interface properties. The strength mechanism of laser deposited steel was analyzed. The results show that the microstructure of deposition is comprised of martensite dendrite, interdendritic carbon-boride (M2B) and retained austenite. The overlap of layer reduces cracks and coarsening equiaxed grains are observed between layers for the epitaxial grown from unmelted dendrite. The microhardness of deposition reaches up to approximately 600 HV, which is attributed to martensitic transformation, solution strengthening, carbon-boride and fine dendrites. With the increase of annealing temperature, martensite decomposes into ferrite and precipitated (Fe,Cr)23(C)6 along martensite lath, resulting in the decrease of microhardness. Meanwhile, lamellar eutectic borides go through fusing and spherification. The appearance of retained austenite was explained by carbon partitioning. Composition analysis shows that carbon segregate in plane grain and C-depletion area was observed in substrate. The increase of annealing temperature facilitates carbon diffusion from substrate, and carbon content exceeds deposition with the annealing temperature of over 700 degrees C. (C) 2018 Published by Elsevier Ltd.