Low interpass temperature can also cause welding defects, primarily significantly increasing the risk of hydrogen-induced cracking and cold cracking, and affecting dehydrogenation. For low-hydrogen basic electrodes like J507, precise temperature control is crucial; both excessively low and high temperatures are undesirable.
Main Risks of Low Interpass Temperature
|
Risk Type |
Specific Impact |
Description |
|
Increased Risk of Cold Cracks (Delayed Cracks) |
Cracks appear in the weld during cooling or some time after welding. |
Low temperatures make it difficult for hydrogen to diffuse and escape; residual stress and hydrogen embrittlement can easily lead to brittle fracture. |
|
Formation of Hardened Structure |
High-hardness martensite structure forms in the heat-affected zone of the base metal. |
Plasticity and toughness decrease, joint brittleness increases, especially in high-strength steels. |
|
Poor Dehydrogenation |
Hydrogen atoms cannot effectively escape from the weld after welding. |
Prolonged hydrogen residence time significantly increases the probability of hydrogen-induced porosity and delayed cracking. |
|
Decreased Arc Stability |
Difficulty in arc ignition, unstable and unfocused arc. |
Affects penetration and weld formation, leading to defects such as incomplete fusion and slag inclusions. |
Safety Control Recommendations:
Minimum Allowable Interpass Temperature: Generally not lower than 80℃; in cold environments or when welding thick plates, it is recommended to maintain 100–150℃.
Preheating Measures: Use an electric heater or flame heating to preheat the weld area to ensure uniform temperature.
Temperature Verification: Use an infrared thermometer to check the temperature before each weld pass to ensure it is within the process requirements range.
Drying Process: J507 welding electrodes must be dried at 350–400℃ for 1 hour to control hydrogen content from the source.
Safety Warning: Excessively low interpass temperature combined with damp welding electrodes can easily trigger fatal delayed cracks, which can lead to structural component fracture in severe cases.
