What is the weldability of Q345B steel plate?

Due to the application of thermal cycling during welding, welding can significantly change the original microstructure of the welded area and the mechanical properties of the Q345B steel plate. The main problems when welding are cold cracks and loss of toughness of welded joints. In the following, weldability will be broadly defined as the sensitivity of the plate to these problems.
Cold cracks occur near the weld fusion line (FL) after welding, where Q345B steel is rapidly cooled from a temperature close to the melting point and is quench hardened. Cold cracks are caused by the interaction of the locally hardened microstructure (martensite) of the parent metal and the diffusible hydrogen caused by the welding material and the atmosphere.

The mechanism of cracking is considered to be a typical hysteretic fracture. Steels with high carbon content and high alloy content have higher crack sensitivity because of their high hardenability, which shows high hardness near their welding melting line. Reducing the crack sensitivity can be solved by using a low content of chemical components to reduce the degree of hardening, and reducing the hydrogen content by preheating the welded joints and welding materials. However, from the perspective of the actual process, it is not desirable to use preheating because it will reduce the welding work efficiency in actual work. From this point of view, our priority should be to reduce the chemical composition to the lowest possible level.

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