For the welding of certain materials, in order to ensure the welding quality, in addition to the correct selection of welding methods and welding materials, a common feature of the welding process is to control the welding heat input.

      Different materials have different uses and requirements for welding heat input, such as:

      (1) When welding low-alloy high-strength steel, in order to prevent cold cracking, the minimum welding heat input should be limited; in order to ensure the impact performance of the joint, the upper limit of the welding heat input should be specified.

      (2) When welding low-temperature steels, in order to prevent the appearance of coarse ferrite or coarse martensite structure due to overheating of the weld, and to ensure the low-temperature impact performance of the joint, the welding heat input should be controlled to a small value.

      (3) When welding austenitic stainless steel, in order to prevent the burning of alloy elements, reduce welding stress, reduce the residence time of the molten pool in the sensitization temperature zone, and avoid intergranular corrosion, a smaller welding heat input should be used.

      (4) When welding heat-resistant and corrosion-resistant high-alloy steels, in order to reduce the combustion of alloy elements, avoid the formation of coarse-grained structure due to overheating of the molten pool, reduce high-temperature plasticity and fatigue strength, prevent hot cracks, and obtain better "equal strength" For joints, smaller welding heat input should be used.