Excessive interlayer temperature will cause coarse grains in the heat affected zone, which will reduce the weld strength and low temperature impact toughness. If it is lower than the preheating temperature, cracks may occur during welding. Therefore, it is stipulated that the temperature between lanes shall not be lower than the preheating temperature, and the maximum temperature shall not be higher than a certain limit. For austenitic stainless steel, too high interlayer temperature will lead to overheating at the weld and produce black weld bead. For ordinary carbon steel, the interlayer temperature is required to be lower than 250℃, and for ordinary austenitic stainless steel, it is required to be lower than 150℃ (some even lower than 100℃ and generally lower than 120℃).