Imperfections in welds Commonly used steels are considered to be readily welded. However, these materials can be at risk from the following types of imperfection: porosity ; solidification cracking ; hydrogen cracking ; reheat cracking . Other fabrication imperfections are lamellar tearing and liquation cracking but using modern steels and consumables, these types of defects are less likely to arise. In discussing the main causes of imperfections, guidance is given on procedure and welder techniques for reducing the risk in arc welding. Porosity Porosity is formed by entrapment of discrete pockets of gas in the solidifying weld pool. The gas may originate from poor gas shielding, surface contaminants such as rust or grease, or insufficient deoxidants in the parent metal (autogenous weld), electrode or filler wire. A particularly severe form of porosity is 'wormholes', caused by gross surface contamination or welding with damp electrodes. The presence of mang...
Weldability of steel groups PD CEN ISO/TR 15608:2005 identifies a number of steels groups which have similar metallurgical and welding characteristics. The main risks in welding these groups are: Group 1. Low carbon unalloyed steels, no specific processing requirements, specified minimum yield strength R eH ≤ 460N/mm 2 . For thin section, unalloyed materials, these are normally readily weldable. However, when welding thicker sections with a flux process, there is a risk of HAZ hydrogen cracking, which will need increased hydrogen control of the consumables or the use of preheat. Group 2. Thermomechanically treated fine grain steels and cast steels with a specified miniumum yield strength R eH > 360N/mm 2 . For a given strength level, a thermomechanically processed ( TMCP ) steel will have a lower alloy content than a normalised steel, and thus will be more readily weldable with regard to avoidance of HAZ hydrogen cracking and the achievement of maximum hardness ...