Suggested Preheat Temperatures for Welding Structural Steel Materials has welding processes, material thickness, and minimum preheat temperatures in the Row or X axis. In the Column or Y axis are 18 structuralsteel materials, from ASTM A36 to API 5L Gr. X42, to Cl.2 to ASTM A517. When you need to know quickly, nothing beats the convenience of a chart. Desk size 11 x 17 wall size 22 x 28. Laminated twotone.