Failure mechanism of laser cladding repair of 30CrMnSiNi2A steel landing gear

Objective Failure mechanism of 30CrMnSiNi2A steel landing gear was studied by analyzing cracking phenomenon of Cr plating and hydrogenation treatment on the surface after laser cladding repair. Methods Appearance of failed parts, macrostructure and microstructure of fracture were observed by stereoscope, scanning electron microscope, energy dispersive spectrometer and metallographic structure analysis. In the meantime, hardness of matrix and cladding zone and hydrogen content of cladding zone were compared and detected. Results The result showed that cladding layer of outer cylinder had uniform shape and dense material. Microscopic edges of cross section near inner wall were very obvious, which was feathery under low magnification and characterized by cleavage fracture under high magnification. Cross section near outer wall under low magnification was granular, and that under high magnification was mainly characterized by intergranular fracture and supplemented by transgranular cleavage fracture, and typical chicken claw marks could be seen on the grain surface, and no obvious pollutants were found on the whole cross section. Radial hardness gradient of outer cylinder from inside to outside first decreased and then increased, and was gradually stabilized. Moreover, hydrogen content fluctuated greatly, reaching a maximum of 4×10⁻⁶. Conclusion Cracks in repair zone of outer cylinder were hydrogen-induced brittleness cracking, which were mainly related to high sensitivity of inner wall cladding zone to hydrogen embrittlement during electroplating process.