A part made from steel A has a surface hardness of 50 Rc and

A part made from steel. A has a surface hardness of 50 Rc and a hardness 3/8\" below the surface of 35 Rc. Would any of the other steels be both harder at the surface and softer 3/8\" below the surface if quenched in the same way? What would these hardness\'s be? What diameter round bar of steel A would have a surface hardness of 50 Rc if quenched in mildly agitated oil?

Solution

The observation that the hardness at the surface is more and that below the surface is less is expected for the quench test.

Jominy test relies on transformation of 100 % austenite to other phases after quenching. At the surface, rapid heat transfer causes Martensite to form, and at a distance below, where the thermal differential is not so large, other phases like pearlite ferrit etc my form which have lower hardness.

Whatever inital iron carbon alloy one starts with, after austenisation the same observation is made.

What diameter steel bar would have same hardness?   This is a function of the temperature not diameter. If same quench rate is used should have same result.