The direct hardening alloy steels is part of engineering steels courses. The engineering steels is part of the steel applications set of courses. In this course, a definition of direct hardening alloy steels and the different alloy elements. Then, the Jominy test will be studied and using this test you will characterise the effect of tempering on direct hardening. After that the parameter showed in a certificate will be explained. Finally, applications, process of manufacturing and selection of steel for low hardenability will be explained.