A quantitative assessment of the hardenability increase resulting from a superhardenability treatment

The superhardenability treatment, which consists of superheating steel melts to which fairly large aluminum additions have been made, has been studied in a wide range of low-alloy steels. By hardenability testing and dilatometry, it is shown that the treatment results in large and repeat-able hardenability increases due to a strong retardation of the ferrite/pearlite and bainite reactions. Superhardenability multiplying factors and equations which relate the ideal critical diameter of a superhardenable steel to its chemical content have been produced by using a combination of three hardenability tests. A mechanism for the superhardenability effect is proposed on the basis of the experimental finding that high austenitizing temperatures result in a loss of superhardenability.