Strain Rate, Temperature, and Grain Size Dependence of the Lower Yield Stress of Polycrystalline Iron

Abstract

Syn op sisThe strain rate, temperature , and grain size dependence of the lower yield stress ~r /Jolycrystalline iron containing 0.002 to 0.05 wt % carbon has been investigated by cOIn/Jression tests at temjJeratures ranging from 77° to 573°K and over strain rates ranging from 3.3 X 10-5 to 4 X 10 3 sec-I.The strain rate and tem/Jerature dejJendence of the lower yield stress is independent of grain size and carbon content. The rela tion between the eifective stress and the activation volume agrees /1;ell u 'ith the various results obtainedfrom the tests at low strain rates for var..ving temperatures. From these results it is concluded that the diformation of iron over the strain rates and temperatures tested is controlled by the single thermally activated process, which is /Jresumed to be the overcoming of the Peierls-.Nabarro barrier by the moving dislocations.The e.!feet of grain siz e on twinning and the effect of SO/l1te interstitial atoms on k y in the Petch equation are discussed.