Controlled Cooling as an Alternative to Normalizing/Iso-annealing Heat Treatment of Case Carburizing Grade Steel Forgings

Case carburizing grade steel forgings are often normalized or iso-annealed to improve machinability. The aim here is to get a uniform ferrite-pearlite microstructure and controlled, uniform hardness. The conventional method is to cool the forgings to room temperature & then reheat to Austenizing temperature. Since during forging material is above austenitizing temperature, controlled slow cooling after trimming can give similar results.

In this work, the effect of forging temperature and cooling rate on microstructure is studied. Further the effect of on machinability and distortion behaviour during case carburizing is studied. It was observed that the controlled cooled gear blanks had coarse grain size resulting in superior machinability, and no change was observed in the distortion behaviour of the gears during carburizing.

The final aim of the work was to use forge heat for normalising, saving energy consumption. This also makes the process Greener without compromising the quality of the parts.