Influence of Production Method on the Properties of Dual Phase Steel Tubes

Dual phase steel tubes can be produced by a variety of methods. In the present study, comparisons between dual phase steel tubes produced directly from a dual phase steel sheet and tubes produced using a new method are made. The conventional method is to process dual phase sheet steel through a tube making operation with electrical resistance welding. In the new processing method, a ferrite/pearlite sheet steel is formed into a tube, which is then normalized, induction heated to an intercritical temperature, quenched, and tempered, producing a dual phase microstructure. Tubes produced directly from a dual phase steel sheet have variations in microstructure and mechanical properties between the weld region and nonweld region material; whereas, tubes that have been produced from ferrite/pearlite steel sheet and treated to create a dual phase microstructure following the tube forming operation show little or no variation between the weld and nonweld regions. Dual phase tubes produced by the new method appear to have three main advantages over tubes produced in the traditional manner: (1) microstructural uniformity between the weld and nonweld material, (2) mechanical property uniformity between the weld and nonweld material, and (3) compressive rather than tensile residual stress components on the outer surface of the tubes.