welding-alloys.com 6 Welding procedure Preheating is key to ensure high-quality welds and reduce the risk of cracking. The need for preheating depends on factors such as base metal composition, base material thickness, the specific cobalt grade, and the number of weld layers. Cobalt based alloys have lower ductility than other materials, making them more prone to cracking during welding, especially when welded onto base materials like lowalloy or stainless steels. These metals have different coefficients of thermal expansion, which can lead to thermal stresses during the heating and cooling cycles of welding. The resulting difference in expansion rates can cause cracking in the weld deposit. Proper preheating helps reduce thermal gradients, minimising residual stresses and the potential for cracking. This ensures a sound, defect-free weld when working with cobalt based alloys and dissimilar base metals. Product Base metal grade < 0.3% carbon steels 0.3-0.5% carbon steels Up to 3% total alloy steels 3-10% total alloy steels Martensitic high alloy steels e.g. 12% Cr Ferritic high alloy steels e.g. 17% Cr Austenitic high alloy steels e.g. 316 Nickel alloys STELLOY 25 100 150 150 200 200 100 100 100 STELLOY 21 100 150 150 200 200 100 100 100 STELLOY 6 BC 150 200 200 250 300 100 100 100 STELLOY 6 200 250 250 250 300 150 150 150 STELLOY 6 HC 200 250 250 300 300 200 150 150 STELLOY 12 275 300 300 300 300 250 200 200 STELLOY 1 350 350 350 350 350 350 250 250 Recommended preheating temperature (°C) - single layer, welded on different base metals Base metal composition Number of weld layers Preheating temperature Base metal thickness Specific Cobalt grade
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