Abstract
COD tests were conducted on JIS-SM41B, -SM50B and -SM58Q steel plates in order to examine the effect of strain-aging on embrittlement of these steels. Hot straining embrittlement phenomenon was also studied on weld joints of cold worked steel plates. Finally the bending radius allowable in cold working of structual steels was examined on the basis of COD test results.
The main results obtained are as follows:
(1) Strain-aging strongly affects the brittle fracture behavior and shifts the COD transition curve toward the higher temperature range. Fibrous crack initiation at the crack tip and its slow growth, on the other hand, are not strongly affected by strain-aging if the prestrain is limited up to 10%.
(2) The amount of the shift of COD transition curve toward the higher temperature range due to strain-aging is in good accordance with the prediction based on the Tetelman's critical fracture stress theory.
(3) The COD value at the hot straining embrittled zone near the weld joint of cold worked steel plate is nearly equal to that of the steel plate which is strained and then aged at 250°C for one hour.
(4) The critical bending radius allowable in cold working can be calculated using the COD test results, and it is 4.57.3 times as large as the plate thickness.
