Effect of soaking time on deep cryogenic treatment of Nimonic-90 alloy

Abstract

The current experimental work on Nimonic-90 alloy presents the behaviour of hardness as a result of microstructural change occurring after deep cryogenic treatment. The results of the microstructure alterations at sub-zero temperature showed an effective change in hardness. Compared to the hardness value corresponding to a 36-h soaking period, the 24-h soaking period's hardness value was lower. One of the main factors contributing to the enhancement in Nimonic-90's hardness was the phase change and grain size reduction during the soaking period. Nimonic-90's hardness behaviour was largely controlled by tempering following deep cryogenic treatment. The maximum and minimum hardness values were corresponding to 100 °C and 200 °C, respectively. At the soaking period of 36 h, tempering temperature of 100 °C and tempering time of 1 h, and the hardness of Nimonic-90 came as 443.36 HV. With more tempering cycles and higher tempering temperatures, a corresponding decline in hardness value was observed. The sample that was subjected to a tempering temperature of 200 °C, a soaking time of 24 h, and three tempering had the lowest value of hardness out of all the deep cryogenically treated samples. According to the findings, the maximum hardness was 1.56 times the hardness of untreated sample.