EFFECT OF SURFACE CONDITION ON THE EXHAUSTION OF DUCTILITY BY COLD OR HOT STRAINING.
Progress rept. no. 7,
BROWN UNIV PROVIDENCE R I
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The compressive prestrain exhaustion limit needed to cause brittle behavior in subsequent tension was found to be much higher in ABS-B steel bars with surfaces machined by about 0.030 in. before straining than with as-rolled surfaces, even more so when the surfaces were machined after straining. Removal of the strained surface caused a small increase of exhaustion limit even when the surfaces had been machined before prestraining. In all cases the increase was larger for bars prestrained at 550F than at 70F. The surface effect was found stronger than in earlier tests with an ABS-C steel. In addition the microhardness was found to rise gradually in a 0.030 in. layer adjacent to the surface and to reach a peak at the surface itself in all as-rolled or as-strained surfaces. The surface damage from an unfavorable rolling history permits an easier surface embrittlement by hot straining in a region of strain concentration close to a weld and creates a dangerous trigger of brittle fracture, as is indicated by service fractures starting at such regions. A study of the rolling and straining history causing such weak regions could help their prevention. Author
- Properties of Metals and Alloys