Larson–Miller relation

The Larson-Miller relationship describes materials science contexts such as creep, fracture predictions and the decrease of the hardness of hardened steel parts as a function of time and temperature.

P = T (C ln t)

P is the Larson-Miller parameter, such as adjusting to the hardness when starting depending on the time t ( h) and the temperature T ( K). The experimentally determined material constant C is for iron, nickel and cobalt-based materials at 20 The temperature therefore has a much stronger influence on the decrease in hardness than the time.

The Larson-Miller relationship can be used to save time and energy saving during the heat treatment in hardening shops. Example: Hardened steel parts from C45 ( carbon steel without Sondercarbidbildner ) with an initial hardness of 61 HRC is just a start of 4 hours at 190 ° C, the nominal hardness of 53 HRC. Instead, the rise time can be shortened to 1.5 hours at a temperature of 210 ° C to achieve the same hardness value.

The formula was drawn up by FR Larson and James Miller in the 1950s because of experimental investigations of creep and fracture processes for life prediction of turbine blades in jet engines.