The Effect of Heat Treatment Process on the Hardenability of Gear Steel 20CrMnTiH Containing B

This article systematically investigates the effects of different heat treatment processes on the hardenability of 20CrMnTiH gear steel with w［B］ content of 0.0018% and 0.0051%. By theoretically calculating the solubility product in the Ti-Al-B-N system， it was confirmed that boron in the hot-rolled bars used in the experiment exists in the effective form. The study compared the microstructure and end quenching hardness curves of hot-rolled state， spheroidized annealed state at two different temperatures （600 ℃ and 650 ℃）， and normalized state. The results indicate that the heat treatment process significantly affects the hardenability of steel， and the order of performance is： normalized state>hot-rolled state>spheroidized annealed state （600 ℃）>spheroidized annealed state （650 ℃）. It is analyzed that this difference is mainly due to the solid solution behavior of boron in cementite. During high temperature spheroidizing annealing process， more boron atoms dissolve into cementite， and in the subsequent austenitization process， this part of boron is difficult to fully dissolve back to the austenite grain boundaries in a short time to play its role in improving hardenability， resulting in a decrease in hardenability. This study clarifies that solid solution boron in cementite is a key factor affecting the hardenability of boron containing gear steel after heat treatment， providing important basis for optimizing the heat treatment process to fully utilize the performance advantages of boron steel.