Limiting grain size

Grain growth depends on heat management. If the material gets too hot or stays at temperature too long, the grains grow and the structure becomes coarse. This makes the part brittle and prone to cracking. So you have to keep the heat input under control and watch the cooling. With steel, it helps to monitor the interpass temperature and not continue welding too hot. If you stick to the structure parameters, the grain size stays within the allowed range and the component retains its toughness.