Development of Direct Annealing Treatments After Hot Working in Alloyed Steels

摘要

In the analyzed 40CrMo steel it has been observed that the application of direct annealing after hot working requires considering the following factors: 1. The austenite transformation during cooling is not homogeneous, with important banded zones where transformation takes place at longer times. This characteristic, probably due to segregations, can affect notably the final hardness of the steel and lead to inadequate predictions if conventional CCT curves are considered. 2. The influence of the cooling cycle parameters has been analyzed. The temperature at the entrance of the tunnel notably affects the final hardness, promoting the formation of hard phases if high temperatures are selected. 3. For the analyzed conditions, the transformation is not complete at the exit of the tunnel. In consequence, this transformation is completed during the following air cooling part of the cycle. A time reduction of this part, followed by a rapid cooling, can lead to a significant increase in the hardness of the steel due to the formation of hard phases in the remaining untransformed regions of the steel.