Chart method to determine necessary preheat in steel welding

A chart method determining preheat temperatures is reviewed with focus on the effect of carbon equivalency and weld metal diffusible hydrogen. The validity of some of the preheat methods is compared with that of the chart method on the basis of cold cracking experimental results. Consequently, a number of carbon equivalents have been proposed. Among them, CEN carbon equivalent is considered a preferable index in assessing the cold cracking susceptibility of steels. The effect of weld metal diffusible hydrogen on the cold cracking susceptibility is found to be not linear but logarithmic. It is, however, difficult to determine preheat temperatures in steel welding. This is because cold cracking is influenced by many factors. Hence, a chart method is considered a reliable choice for a wide variety of welding conditions.