Characteristic Cooling Time t8/5
The t8/5 time describes the time interval during which the welded joint traverses the critical temperature range from 800 °C to 500 °C. It decisively determines the resulting microstructure and hardness within the heat-affected zone.
The t8/5 time is the cooling time of the weld from 800 to 500 degrees. In this range, it is determined which microstructure forms in the steel. If it cools too fast, the material becomes hard and brittle, and cracks can even occur. If it cools too slowly, the grain becomes coarse and toughness suffers. You can influence the cooling time via the heat input and the preheating temperature. Depending on the steel grade, you have to keep the time within a certain window, which you control via the welding parameters and the joint geometry.