Effect of segregation on properties of S690 high strength seamless steel tube

The effect of segregation on the properties of S690 high strength seamless steel tube was analyzed by means of chemical composition analysis, tensile and impact properties test and metallographic examination. Then, the side bending, transverse tensile, weld impact test and metallographic examination of the welded seamless steel tube were carried out, and the influence of segregation on the welding procedure qualification of the seamless steel tube was analyzed. The results show that there was obvious carbide band segregation on the inner surface of S690 high strength seamless steel tube, which led to high carbon content and carbon equivalent. Segregation made the impact absorption energy of the seamless steel tube inner surface low; segregation caused the formation of coarse carbon-rich martensite+retained austenite and widmanstatten structure at the root fusion line, and granular bainite precipitated along the grain boundary, resulting in a decrease in impact toughness of the material.