Effect of cyclic cryogenic treatment on the properties and structure of 40CrNiMoA steel

Abstract

In this work, the effect of different treatment processes on properties and structure of 40CrNiMoA steel after temperature cycling experiments were studied. Different treatment processes contained that heat treatment (HT), cryogenic treatment before tempering (CT-1) and cryogenic treatment after tempering (CT-2). After that, some samples of the different treatment processes were done by temperature cycling experiments, which was cooled from room temperature to −190°C for 4 hours, then heated from −190°C to 125°C for 4 hours, at last cooled to the room temperature. The temperature cycling experiments were repeated fifteen times. The rate of cooling and heating was 4°C/min. Both the quenching and tempering were done in a vacuum furnace. All the cryogenic treatments and temperature cycling experiments of fifteen times were done in a program-controlled cryogenic container. The results show that, the strength and plasticity achieve the optimal matching, when 40CrNiMoA steel was done by cryogenic treatment after tempering (CT-2). At the same time the microstructure of the steel is homogeneous, and the performance gets more stable after temperature cycling experiments. The performance of 40CrNiMoA has not deteriorative phenomenon after temperature cycling experiments. Therefore, compared to the heat treatment (HT) and cryogenic treatment before tempering (CT-1), the cryogenic treatment after tempering(CT-2) can improve the comprehensive performance of 40CrNiMoA steel. It also can increase the attended performance and working life in the formidable natural condition.