论文部分内容阅读
Although cold treatments have been used to reduce the retained austenite in the cases of carburised steel for many years,there is little data on deep cold temperatures be- low -70℃or treatment times longer than an hour or two.This study set out to determine the effects of such deep cold treatments at temperatures -150℃for 24 h. The study investigated the effects of deep cold on the microstrncture,hardness profile, residual stress and internal oxidation on two typical carburising steels,16MnCr5 and 21NiCrMo2.The study found that for both 16MnCr5 and 21NiCrMo2 carburised toαcase depth of approximately 0.8 mm,the longer and colder the deep cold treatment, the more the austenite retained in the case was converted to martensite and the harder it became.After low temperature tempering,the hardness difference was smaller,but still significant.In both steels,the case appeared more refined and homogeneous after deep cold treatment.Deep cold treatment had a negligible effect on the core properties of either steel.
Although cold treatments have been used to reduce the retained austenite in the cases of carburised steel for many years, there is little data on deep cold temperatures be-low -70 ° C or treatment times longer than an hour or two. This study set out to determine the effects of such deep cold treatments at temperatures -150 ° C for 24 h. The study investigated the effects of deep cold on the microstrncture, hardness profile, residual stress and internal oxidation on two typical carburizing steels, 16 MnCr5 and 21 NiCrMo2. The study found that for both 16MnCr5 and 21NiCrMo2 carburised to αcase depth of approximately 0.8 mm, the longer and colder the deep cold treatment, the more the austenite retained in the case was converted to martensite and the harder it became. After low temperature tempering, the hardness difference was smaller, but still significant.In both steels, the case had more refined and homogeneous after deep cold treatment. Deep cold treatment had a negligible effect on the core pro perties of either steel.