THE YIELDING OF STEEL STUDIED BY ULTRASONICS.
YALE UNIV NEW HAVEN CONN KLINE GEOLOGY LAB
Pagination or Media Count:
Changes in the ultrasonic attenuation in steel specimens have been observed during tensile tests. Samples of AISI 1020, 1045, and 1095 steel quenched and tempered to a spheroidized condition have been used. Both attenuation and microstrain measurements fail to reveal pre-yield dislocation motion in the as-tempered specimens. Upon reapplication of the load to samples in the strain-aged condition there is a large pre-yield attenuation increase but no observable microstrain up to 90 of the flow stress. These and other observed changes can be related to changes in the free dislocation density and the mean dislocation segment length. The results show that the increase in flow stress in the strain-aged condition is caused by increased frictional stresses rather than by dislocation pinning. Strain aging is found to proceed through three distinct stages. The second of these follows the t to the 23 power law and is characterized by an activation energy of 20 kcalmole. Author
- Properties of Metals and Alloys