Question:We are considering doing induction tempering on a cast iron (class 30) piece that had just been hardened. We would like to finish ways on certain machines by milling them at 35-40RC. From a metallurgical point of view, do you think this can be done and get a reasonable and consistent heat-treated condition to a depth of 0.150’’ (3.8 mm)?

Dan H:There is an ongoing debate about the effectiveness of induction tempering as opposed to conventional (furnace or oven) tempering. In this case, however, induction tempering of class-30 (gray) cast iron is routinely done in the industry, oftentimes after dunk quenching in polymer (due to the part mass). The material typically quenches out in the range of 55 HRC, and a 750ºF (400ºC) temper will reduce the hardness to about 45–50 HRC. You can use Tempil® paint or a thermal temperature measurement instrument to determine the proper power settings to achieve the tempering temperature.