Examples on Hall-Petch relations 1. We would like to produce a KCI ceramic part having a yield strength of 20 MN.m. Based on previous data, we know that a grain size of 5m gives a strength of 28 MN.m and that a grain size of 100 m gives a strength of 8 MN.m. What would the grain size required to produce a crystal having a strength of 20 MN.m? y = + kd 1/2 Given: oy = 28 MN.m and d = 5m oy = 8 MN.m and d = 100 m = constant 2. Suppose we count 64 grains per square millimetre in a photomicrograph taken at magnification x 10. What is the grain size index, GE? m = 2GE+ 3 Given: m = 64 grains/mm in magnification x 10. GE = ? m = Number of grains per square millimetre at magnification x I