Effect of groove shapes on mechanical properties of welded joints of ASTM4130 steel

The 30 mm thick ASTM4130 steel pipe was fabricated by gas tungsten arc welding and shielded metal arc welding under quenched and tempered conditions. Whereafier, the mechanical properties of welded joints of both V groove and combination double V groove were measured, while the microstructure feature and fracture morphology of both welded joints were investigated. Moreover, the effect of groove shapes on the properties of welded joints was explored. The results show that the welding efficiency of the combination double V groove joint is as two times as that of the V groove joint. But the hardness and toughness of the heat-affected zone （HAZ） with combination double V groove can not satisfy the requirements. Also, the coarse grain heat-affected zone （CGHAZ） of the cap layer is mainly composed of granular bainite, tempered martensite and a small amount of carbon-free bainite, and the fractured swface of the fusion line is entirely dominated by the quasi-cleavage mode. That the mechanical properties of the combination double V groove are lower than that of the V groove lie in the penetration ratio, welding heat input, and the areas and distribution feature of brittle zones. The combination double V groove is not suitable for the fabricating of ASTM4130 steel.

Effect of weld faying part groove shape on reduction of inner flash in steel pipe joints fabricated by friction welding

The groove shape of the weld faying part was investigated to obtain an ideal pipe frictiowelded joint that had a fracture in the base metal and no inner flash of it.The steel pipe had inner and outer diameters of 8.0 mm and 13.5 mm,respectively,and the weld faying surface was of a basic flat shape(butt)type.Moreover,stepped and tapered groove shapes were prepared.Pipe groove shapes were welded with a friction speed of 27.5 s_1 and a friction load of 2.79 kN.Joining phenomena during the welding process were observed,and the tensile strength of joints was evaluated.The joints,that fabricated with flat or step groove shapes,made with a friction time at which the friction torque reached the initial peak did not have the tensile strength of the base metal nor a fracture in the base metal.However,the joints fabricated with a friction time that reached past the initial peak had a large flash,and they contained a fracture in the base metal.In contrast,when joints were made with a gently tapered groove shape with a friction time reaching the time of the initial peak,they achieved a fracture in the base metal,despite having an extremely small inner flash.Therefore,the shape at the weld faying part was capable of reducing the flash exhausted from the weld interface.

Effect of core bar inserted into weld faying part to obtain an ideal pipe joint with non-generating inner flash via friction welding

In this study,the effect of core bar inserted into weld faying part to obtain an ideal pipe joint with non-generating inner flash via friction welding is described.A steel pipe with inner and outer diameters corresponding to 8.0 mm and 13.5 mm was used,and the weld faying surface was machined to a groove shape of a flat(butt)type.The core bar of various materials was inserted in the weld faying part of the pipes,and those pipes were welded with a friction speed of 27.5 s−1 and friction pressure of 30 MPa.The core bars did not decrease inner flash when joints were fabricated with a core bar of some metallic materials with melting points below that of steel;thus,they were melted during the welding process.The joint with an alumina core bar did not decrease inner flash and was crushed by generating an inner flash.However,a commercially pure tungsten(CP-W)core bar was successfully achieved for decreasing the inner flash.Additionally,all joints with a CP-W core bar did not exhibit the tensile strength of the base metal and a fracture in the base metal,when they were fabricated during the same time,the friction torque reached the initial peak.The joint exhibited a fracture in the base metal when it was fabricated with a CP-W core bar and a taper groove shape that was proposed in the previous study.Furthermore,the core bars were easily removed from the joints;thus the joint with almost no inner flash was successfully obtained.To reduce the inner flash of pipe joints,they should be fabricated with a CP-W core bar inserted into the weld faying part with a taper groove shape.