Welding Process about Low Carbon Steel and Low Alloy Steel

Welding Process about Low Carbon Steel and Low Alloy Steel

The welding of low carbon steel and low alloy steel belongs to the welding of dissimilar metal materials. The welded structure of dissimilar steel is not only economical and reasonable, but also saves valuable materials and improves the performance of the components. Welded structures made of dissimilar metals are increasingly used in modern machinery, chemicals, power, and mining. According to the metallographic structure, low carbon steel and low alloy steel belong to pearlitic steel, and these two kind of dissimilar steel welded structures are used in practice. Low carbon steel has excellent weldability and low steel cost. S355JR steel is a kind of low carbon steel. Glory Steel could offer S355JR steel as crane rail. Ordinary low-alloy steel is added small amount of alloying elements (mass fraction not exceeding 3%) based on carbon steel to make the microstructure of carbon steel change, so that this kind of steel has higher yield strength and better resilience. As the content of alloying elements in the steel increases, the strength of the low alloy steel gradually increases, the carbon content increases, the hardenability of the steel increases, and the weldability deteriorates.

Process measures such as welding preparation, welding preheating, welding process, and welding heat treatment of dissimilar steel welding shall be specified according to low alloy steel in which weldability is poor. Ordinary low alloy steel with 300MPa to 400 MPa, such as 09Mn2Si, S355JR steel and 16MnCu, have the same good gas cutting performance as low carbon steel. Since the hardened zone is very narrow, the hardened zone can be melted into the molten pool of the weld metal during the welding process, and the edge after the gas cutting can be directly welded without being machined. As the strength grade of the steel grade increases, the carbon content also increases, the hardenability is also large, and the gas cutting performance is relatively decreased. 15MnV steel with strength grade of 450MPa can not be preheated when the ambient temperature is not too low. The gas cutting is performed with oxyacetylene flame. After cutting, the cutting nozzle doesn’t need to be processed, and the welding can be directly applied. The weld metal will not be welded. The weld metal does not crack due to the gas cut of the weld bevel. For steel grades with strength grades exceeding 500 MPa, such as 18MnMoNb, 14MnMoV and 14MnMoVB, due to the high carbon content, the hardening tendency of the gas cutting edge is relatively large. Before gas cutting, if it is not annealed, the gas cutting is used to test the incision at the gas cutting edge. Cracks sometimes occur, and these cracks must be ground with a grinding wheel before they can be welded. Of course, such steel can be cut without preheating under low temperature annealing conditions, and microcracks are not generated. For steel with high strength grades and large thickness, if the welding groove is made by gas cutting, in order to prevent cracks, the same preheating specification as in welding can be used.

When ordinary low-alloy steel with different strength grades are welded to low-carbon steel, the weld metal and welded joints of dissimilar steels are generally required to have strength greater than the lowest strength of the steel to be welded. The plasticity and impact toughness value should not be lower than the steel grade with higher strength and poor plasticity and impact toughness or according to design requirements. Therefore, when these two types of steel are welded, the selected welding materials should also follow this principle, namely, the strength, plasticity and impact toughness values should not be lower than the lowest value of the material to be welded.

Through the analysis of the welding performance of ordinary low alloy steel low carbon steel, a reasonable welding process should be established, and the welding operation rules should be strictly observed, and the welded joint with excellent performance can be obtained. Effective control of cracks, pores and other defects can ensure the quality of welding. This has certain reference significance for welding the same type of dissimilar steel.