In this study, the microstructure and mechanical properties of API-X42 steel-free API-B steel couplings have been investigated. The bonding of these two metals was performed by the arc welding process of coated metal in three welding streams of 85, 100 and 115 amps. A microscope, scanning electron microscope and X-ray diffraction analysis were used to investigate the microstructure and characterization of base metals and weld metals. Mechanical properties of bonding were investigated using impact, tensile, micro hardness and failure failure tests. The evaluations showed that by increasing the incoming heat during the ferritic welding of the microstructure, the amount of cooling was decreased by 50%, and the amount of Widgetman Stretched ferrite, multi-ferrite, and ferrite ferrite increased. Also, by increasing the incoming heat, the size of the grains increased in the metal and, in particular, HAZ increased. Increasing grain size at the base of base metal is due to the shortage of nitride alloy elements and Nb and Ti carbide. The semi-quantitative EDS analysis of the bubbles in the weld metal showed that these entrails contain a large amount of Mn and Ti, which is necessary for the formation of phytonutrients in the microstructure. The results of micro-tachometric test showed that the welding metal at all the average input temperatures has a higher hardness than the other regions and the hardness of the weld center to the base metals has decreased. According to the results of the longitudinal tensile test, it was found that the welding metal at all incoming temperatures had the highest yield strength and tensile strength compared to other regions due to the formation of needle ferrite in the boiling metal. The cross-sectional tensile test results showed that in the welding process, a deflection amplitude of 85 A occurs from base metal B, but due to the increase in the heat input due to the size increase of the grains in the region affected by the fracture heat, this region occurred at the base of the base metal B. The impact test results showed that the welding metal at all input energy points had a greater impact than other regions. By increasing the inlet temperature, a sharp drop in the impact energy of the heat affected region on both sides of the base metal, so that in the welding current of 115 amperes, the impact energy of HAZ is less than that of base metals. According to the failure diagrams of the tofence, it was found that the welding metal had a resistance to cracking resistance of 85 amps in the cracking region more than other regions due to the formation of needle ferrite. key words Pipeline, welding, inlet heat, microstructure, mechanical properties