Grain Refining Annealing

You do grain refinement annealing to make the structure finer and more uniform after heavy forming or heat treatment. The material is deliberately heated to a temperature below the austenitizing limit and then slowly cooled. This makes the grain smaller, the material tougher, and you avoid stresses. If you don't hit the temperature cleanly, the structure can become coarse again or distort – so better to work controlled in the furnace than to hold the torch on it.