Book Description

The hardness of several brasses was investigated as a function of grain size. It follows the relation, H = H sub O + k sub H l to the minus 1/2 power, which is derivable from other relations between hardness and yield strength, on the one hand, and, yield strength and grain size, based on the Hall-Petch relation, on the other hand. This hardness-grain size relationship was experimentally verified for a wide range in grain diameters. Brinell hardness and Rockwell B hardness measurements were made for grain diameters varying from 350 microns to 5.5 microns. Diamond pyramid hardness (DPH) values were also measured. Various loads ranging from 10 gms to 1000 gms were used to obtain DPH values as a function of the grain size and the size of the indentation. A transition in hardness associated with a change in single grain behaviour as compared with true polycrystalline behaviour occurred for a critical (d/l) ratio of the order of unity. The transition in hardness seems to be similar to that reported by Armstrong for tension testing when a few grains are contained in the specimen cross-section. (Author).