What is a weld crack? It is the most common serious defect in weldments. Under the joint action of welding stress and other brittleness factors, the bonding force of metal atoms in the local area of the welded joint is destroyed and a new interface is formed. In welding technology, we should avoid welding cracks.
Hot cracks of welding cracks:
Hot cracks are generated under high temperature, from the solidification temperature to the temperature above A3, so they are called hot cracks, also called high temperature cracks. How to prevent hot cracks? As the generation of hot cracks is related to stress factors, the prevention methods should also start from two aspects of material selection and welding process.
Cold cracks of welding cracks:
Cold cracks are generated during or after welding, at a lower temperature, around the martensite transformation temperature (i.e. Ms point) of steel, or at a temperature range below 300~200 ℃ (or T ＜ 0.5Tm, Tm is the melting point temperature expressed in absolute temperature), so they are called cold cracks.
Reheat cracks of welding cracks:
Reheat cracks refer to the welded joints of some low-alloy high-strength steels and heat-resistant steels containing vanadium, chromium, molybdenum, boron and other alloy elements. During the heating process (such as stress relief annealing, multi-layer and multipass welding, and high-temperature work), cracks that occur in the coarse grain zone of the heat affected zone and crack along the original austenite grain boundary are also called stress relief annealing cracks (SR cracks).
There are many reasons for welding cracks, but no matter what the reason, as long as the prevention methods are mastered, the accidents of cracks during welding can be greatly reduced.
Post time: Sep-20-2022