Study On Welding Technology Of Anti - Large Deformation X70 Pipeline Steel

With modern long-distance pipeline involves more natural disasters such as earthquakes, mudslides and landslides. For pipeline steel not only has high tenacity, but also have the large deformation ability, in this context to high-deformation of pipeline steel development and application has caused the great attention of the scholars at home and abroad. In this paper, in order to high-deformationX70pipeline steel as the research object, for X70deformation to sustain strong toughness of pipeline steel under different welding process and welding joint organization and mechanical properties were studied. The main results of the study are as follows:The high-deformation of X70pipeline steel matrix organization of polygonal ferrite+bainite duplex organization, ferrite is about45%, bainite content of about55%, ductile to brittle transition temperature form-100℃to-120℃, better impact toughness at low temperature. Continuous cooling transformation results show that Precipitation of bainite need at higher cooling rate range (about10℃/s), and the bainite formation range is narrow. When the welding heat input control in the15-20kJ/cm, cooling after welding speed control in20℃/s can hold ferrite+bainite bipolar organization, and get a good strong toughness match at the same time.Use gas metal arc welding (GMAW)and manual arc welding, combine gas metal arc welding with flux-cored wire semi-automatic welding (SMAW+FCAW)filler covering to high-deformation X70pipeline steel welding experiment, the girth weld under two kinds of welding technology welding joint organization, mechanical properties and resistance to HIC performance results indicate that:(1) Under the GMAW welding process, the weld metal organization is acicular ferrite+a small amount of quasi p ainly polygonal ferrite+bainite organization..(2) Two kinds of welding process of the welding joint has the high tenacity and uniform elongation, lower and showed higher strain hardening exponent, the welding joint has excellent resistance to deformation ability, meet the performance requirements to high-deformation of pipeline steel. olygonal ferrite; SMAW+FCAW welding process of weld metal organization m(3)0℃CTOD test showed that compared with the SMWA+FCAW welding process, using GMAW process of welding the high-deformation X70pipeline steel has good fracture toughness of weld metal and heat affected zone, and CTOD of weld metal and heat affected zone is0.4498mm and0.8688mm respectively, SMAW+FCAW process of weld metal CTOD value of0.4049mm, HAZ of CTOD value of0.1322mm, under the two kinds of welding process of CTOD values meet the requirement of API standard1104.(4) The high-deformation X70pipeline steel CSR=0.627%, CLR=13.225%, CTR=4.188%, Comply with the requirement of API standard; GMAW process of welding joints CSR=2.597%, CLR=26.871%, CTR=37.567%; MAW+FCAW process of welded joint CSR=1.15%, CLR=36.93%, CTR=6.92%, more than the API standard requirement. GMAW process of welded joint crack sensitive rate is bigger, show high HTC sensitivity.