Evaluation of finite element simulation of water quenched cracking for medium carbon alloy steels using acoustic emission technique

Quenching is an important technology for enhancing strength of steels. It is the development tendency of heat treatment to replace both polluted oil quenching and polymer aqueous solution quenching with clean water quenching. However, the problem of easy cracking of medium carbon alloy steels quenched in water has long been a concern for many researchers. Although the finite element simulation (FES) can be used to predict tensile transient stress concentration that may lead cracking during quenching, there has been a lack of experiments to confirm the time of cracking during water quenching. And this problem which has long puzzled us has recently been solved, that is, the occurrence time of quenching cracking can be detected by acoustic emission (AE) technology used k-means clustering method to process AE signals. The results indicate that the cracking time of water quenching for a AISI 4140 medium carbon alloy steel cylinder sample is 11–15 s, which is well consistent with 9–13 s predicted by FES. Moreover, FES reveals that the quenching cracking is caused by the tangential tensile stress in the surface layer, and it is also confirmed by the macroscopical observation. Besides, the FES shows that the tensile stress value leading to water-quenching cracking is far lower than yield strength, which reveals that quenching cracking is a brittle failure under low stress state. The study indicates the high accuracy of our FES, which provides a new path for the process design to avoid water quenching cracking.