Sharing China-Made with Global Customers
Sharing China-Made with Global Customers
Effect of heat after welding of welded pipe
Post welding heat is a measure to heat or preserve the welding area after the welding groove is filled.
Post heat treatment can reduce the cooling rate of the joint after weld crystallization, make the diffused hydrogen escape from the weld, and prevent the delayed crack of high-strength steel.
For high strength steel with limited preheating and interpass temperature, preheating + post heating process can be adopted, which can not only prevent cracking, but also reduce welding residual stress.
The combination of post heating and preheating can reduce the preheating temperature and ensure the welding quality.
"Post heating specification" includes post heating temperature, holding time, etc. the composition, strength and structural stiffness of materials shall be considered. The practice shows that:
1. For carbon manganese steel with low strength, such as 16MnR, if post heating is adopted, the temperature can reach 150 ℃ ~ 200 ℃;
2. For 18mnmonb steel, the cold crack prevention shall not be lower than 180 ℃, and the reheat crack can be prevented above 220 ℃. If 180 ℃ preheating + 180 ℃ x2h post heating is adopted, the reheat crack will not appear.
However, the higher the post heating temperature is, the better. For some steels, the higher the post heating temperature will lead to embrittlement. For example, for Low Alloy High-Strength Quenched and tempered steel 14mnnonbb, cold cracks can be avoided by preheating at 200 ℃, and reheat cracks can be prevented only by preheating to 270 ℃. Reheat cracks can be avoided by preheating at 200 ℃ and post heating at 250 ℃ x2h. 350 ℃ ~ 500 ℃ is the brittle zone and the plasticity decreases, If heated within this temperature range, reheat cracks will appear, so the post heating temperature shall not exceed 270 ℃.
English
Español
