Study on microstructure and properties of laser cladding B-containing martensitic stainless steel coating on front ring of nuclear main pump
B-containing martensitic stainless steel coatings were prepared on front ring of nuclear main pump by high speed laser cladding(EHLA)and gravity powder feeding laser cladding.The optical microscopy,scanning electron microscopy and transmission electron microscopy were employed to study the microstructure of the mar-tensitic stainless steel coating.The micro hardness of the coating was measured using micro hardness tester.The results showed that the δ-Fe phase precipitated from the liquid during the early stage.When the temperature re-duced to 1 220℃,the δ-Fe transformed into bulk austenite.The residual B-rich liquid transformed into eutectic phase,including Cr2B layer and austenite layer.When the temperature reached the martensitic starting tempera-ture,the bulk austenite became the martensitic.Finally,the microstructure of the coating was martensite and eu-tectic phase.The EHLA coating exhibited a larger temperature gradient and a larger growth rate.The two aspects contributed to a finer microstructure.The dendrite space was only approximately 3 μm.The hardness of the EH-LA coating reached approximately 650 HV which was higher than the 650 HV of gravity powder feeding laser cladding layer.It should be ascribed to the finer microstructure and higher dislocation density in the EHLA coat-ing.
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