Analysis of the Reasons for Performance Fluctuations in 20CrMnTi High Strength and Tough Pipe Materials

Abstract Regarding the issue of mechanical property fluctuations in 20CrMnTi high-frequency resistance welded pipes, optical microscopy and X-ray diffraction were used to analyze the microstructure of the matrix, inner and outer surfaces, and straight weld joints of samples with normal and fluctuating properties, as well as to determine the residual austenite content. The reasons for performance fluctuations were elucidated, improvement measures were proposed, and mechanical properties were measured through tensile testing. The results indicate that the microstructure of the 20CrMnTi finished pipe is composed of martensite, ferrite, and residual austenite. The presence of excessive decarburization bands throughout the entire wall thickness at the straight weld seam is the main reason for the fluctuation of the mechanical properties of the pipe. By adjusting the process parameters during high-frequency resistance welding and using anti decarburization coating, the residual decarburization strip can be significantly reduced, and even the central part can be completely eliminated. The overall mechanical properties can be stabilized, meeting the conditions of yield strength (R p0.2 ) above 780 MPa, tensile strength (R m ) above 1000 MPa, elongation at break (A 50 ) not less than 7.5 %.