The rapid cooling rate of the weld at low temperatures tends to increase the regional segregation of the weld crystallisation. Under stress, crystalline cracks appear in the centre of the weld.
The delayed effect of cold cracking increases. During the cooling process of the weld, the dissolution rate of free hydrogen decreases, the time for hydrogen to escape becomes shorter, and the cooling rate becomes faster, so the residual hydrogen content in the metal increases, which increases the tendency of cold cracking.
The possibility of brittle fracture at low temperatures increases.
The preheating effect becomes worse at low temperatures, the effect at low temperatures is not as good as at room temperature, and it is relatively difficult to maintain the temperature between the layers of the weld.
At low temperatures, the construction environment will be more complex and severe, prone to uncontrollable problems.
- Low temperature welding construction measures
1. Environment
The environment for low temperature welding is -15~0 degree Celsius, and the welding operation is stopped when it is lower than -15 degree Celsius.
Welding should be carried out at room temperature, when the environment does not reach, should be set up thermal insulation shed to ensure that the ambient temperature can meet the welding requirements.
When working in the wind and snow, the wind and snow protection device should be set up to protect the welding parts locally.
Strengthen the environmental observation, when the weather is bad, stop welding work in time to ensure the safety of personnel.
Try to choose the time of the day when the temperature is the highest to carry out welding work, in order to reduce the difficulty of welding work.
2. Welding material management
Check whether the welding wire is intact before use and take moisture-proof measures.
Strictly control the protective gas, the purity of protective gas is not less than 99.5%. Under the low temperature environment, check whether the gas cylinder mouth is blocked or frozen to ensure the smooth and stable use of protective gas.
