engleski

Microstructure and Mechanical Properties of Pipes Welded by High-Frequency Induction Welding

In this work the results of analysis of microstructure and mechanical properties of seam pipes made from low carbon steel St 37.2 grade after a high-frequency induction welding technique are shown. The seam pipes are produced by welding of the hot-rolled sheet (thickness of 3.8 mm) into the seam pipes &AElig ; 114.3x3.8 mm in industrial conditions. Microstructure at BM/HAZ interface is changing from the ferrite to the ferrite-pearlite. It was found that the hardness of weld metal is significantly higher (238 HV10) than the hardness of weld metal is significantly higher (146 HV10) than the hardness in the base material (146 HV10). The strenthening of weld metal is result of greater amount of the pearlite in the microstructure. After plastic deformation at rate of 84.6% the seam pipes &AElig ; 26.9x2.65 mm were obtained. By normalization of the pipes at 900oC the desirable mechanical properties were obtained with a homogenous ferrite microstructure. It was found that the ratio yield strength/tensile strength ratio of pipes after normalization is 0.73.

Steel ; pipes ; high-frequency induction welding ; mechanical properties ; microstructure

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