Thermomechanical methods for improving the fatigue characteristi

Details Thermomechanical methods for improving the fatigue characteristi Thermomechanical methods for improving the fatigue characteristi

1991-11-08

1994-02-08

Dean, R.

Metal treatment

Process of modifying or maintaining internal physical...

Heating or cooling of solid metal

148598, 148599, 148645, 148648, 148650, C21D 806

Patent

active

052845346

ABSTRACT:
A thermomechanical method for improving the fatigue characteristics of a metallic material (for example carbon steel and low alloy steel) takes advantage of the materials' plastic flow characteristics to improve external and internal surface conditions. The material is heated to a temperature in the range of about 0.3 to 0.45 its homologous temperature, e.g., from about 200 degrees C to about the Young's Modulus Transition Temperature of said material. While the temperature of the material is in this range, force is applied to the material to produce in at least the region of said material to be treated a tensile stress level greater than the yield point of said material at the temperature, and thereby to produce limited plastic elongation in the region. The material is then cooled under stress, the stress being maintained above the instantaneous yield point of the material during at least part of the cooling process. As a result of this process, the shape of existing stress raisers (e.g., radii at the base of cracks and flaws) are changed in ways which lower stress concentration factors in the material.

REFERENCES:
patent: 4544610 (1985-10-01), Okamoto et al.
patent: 4915900 (1990-04-01), Nomura et al.

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