15 Apr,2024
Tip：Preventive Measures for Hot Cracks
1) Control harmful impurity elements such as C, S, and P; transfer elements such as Mn, Ti, and Zr through welding materials to overcome the adverse effects of S.
2) Alkaline welding rods or fluxes should be used for important welding structures because they have strong desulfurization capabilities.
3) Adding grain-refining elements to the weld metal or base metal (selected materials) can improve crack resistance and corrosion resistance.
4), control weld shape
Surface cladding and butt welds with shallower penetration have better crack resistance, while butt welds and fillet welds with larger penetration have poorer crack resistance because the shrinkage stress of the latter two welds is basically perpendicular to the accumulation of impurities. The crystallographic interface has a greater tendency of hot cracking.
5) If the cooling rate is too fast, the strain rate of the weld metal will increase (the plastic deformation of the material cannot keep up), and cracks will easily occur. For this reason, slow cooling measures should be adopted, and preheating can slow down the cooling rate. In addition, slow cooling cannot be achieved by increasing the welding heat input, because excessive welding heat input will cause grain growth and increase the tendency of segregation, which is counterproductive.
6) Reduce the stiffness and restraint of joints. Specific measures include reducing the structural thickness in design, rationally arranging welds, and rationally arranging assembly and welding sequences.
7) For thick plate welding, multi-layer welding can be used. The tendency of cracks is less severe than that of single-layer welding, but attention should be paid to controlling the penetration depth of each layer. In addition, avoiding stress concentration at welded joints (such as stress concentration caused by defects such as misaligned edges, meat bites, incomplete welding, etc.) is also an effective way to reduce the tendency of cracks.
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