heat treatment process

Control process of heat treatment technology for welded components

To ensure the performance and quality of welded components, improve the plasticity of weld metal, eliminate or reduce welding residual stress, and prevent cracking, it is necessary to perform heat treatment on welded components when necessary. According to the sequence of heat treatment and welding processes, the heat treatment of welded components is often divided into three types: preheating treatment, post heat treatment, and post weld heat treatment.

1、 Preheating treatment is required before heat treatment, which means heating the structural components as a whole or locally before welding. The purpose is to slow down the temperature gradient and cooling rate during the heating of the welded joint, appropriately extend the cooling time of the welded joint from 800 ° C to 500 ° C, in order to facilitate the escape of hydrogen from the weld, reduce the formation of hardened structure, and prevent the occurrence of cold cracks.

2、 Secondly, after the welding is stopped, the post heat treatment immediately heats the workpiece or welding area with a preheating device and maintains it for a certain period of time. The purpose is to fully release hydrogen from the weld metal and prevent the formation of cracks. In practical applications, the effect of post heat treatment on preventing crack formation is more significant for low-alloy steels with higher strength grades and welded components with larger thickness. Choosing a reasonable post heat treatment temperature can reduce the preheating temperature to a certain extent, or even eliminate preheating.

3、 After welding the components, perform overall or partial heat treatment on them. Its purpose is to improve the microstructure and properties of metals, reduce welding residual stress, soften the quenched microstructure of the welding heat affected zone, enhance the toughness of welded joints, and improve the geometric stability of the structure. According to the different purposes of post weld heat treatment, it can be divided into stress removal heat treatment, post weld annealing, normalizing, quenching, low-temperature stress removal, etc.

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