Interlayer temperature issue

Carbon steel: <250°C, low-alloy steel: <300°C, stainless steel: <100°C. Wait. You can take a look at the welding engineer’s manual···

The interlayer temperature setting varies depending on the type of steel. The purpose is to control the input of heat input; if the interlayer temperature is too high, the molten pool remains at a high temperature for too long. If the t5/8 value is too large, grain growth becomes severe, resulting in excessively large grains in the weld and HAZ regions, which in turn reduces impact toughness. Therefore, it is necessary to control the layer temperature or bead temperature during welding. If the material requires preheating to prevent cold cracking, the layer temperature during welding should be maintained between the preheating temperature and the required interlayer temperature. 　　Grain size is related not only to temperature but also to alloying elements. Alloying elements serve two purposes: some can act as modifiers during the crystallization process in the melt, increasing the number of nucleation sites and thereby reducing grain size to refine the grains ； Some elements act as inoculants, restricting grain growth during the grain growth process and thereby refining the grains. 　Based on the above theory, the layer temperature control for carbon steel is more stringent, generally kept below 250 degrees, while it is higher for low-alloy steel, ranging from 300 to 350 degrees, depending on the specific type of steel. However, in the case of high-alloy steels, since one of the biggest problems with high-alloy welded joints is insufficient toughness, stricter control over specifications is required, and layer temperature control is also very strict, generally not exceeding 300 degrees. 　　In short, the definition of welding procedure specifications needs to be determined based on the product in question (including factors such as material and structure), and tests are certainly required for verification.

When welding carbon steel and low-alloy steel, there are generally no requirements regarding the interpass temperature of the weld seam. The interpass temperature of stainless steel welds should be kept below 150 degrees. However, if preheating is required, the temperature between layers should not be lower than the preheating temperature.