High stress nodular iron gears and method of making same

Details High stress nodular iron gears and method of making same High stress nodular iron gears and method of making same

1979-03-06

1980-09-16

Rutledge, L. DeWayne

Metal treatment

Compositions

Heat treating

148 35, 148 39, 148139, 148141, C21D 500, C22C 3700

Patent

active

042227933

ABSTRACT:
High stress, acicular bainitic, nodular iron gears having residual compressive stresses at the surface of the teeth's roots of at least about 40,000 psi and a subsurface residual compressive stress of about 10,000 psi at a depth between about 0.006 inch and 0.015 inch beneath the surface. Method for making gears including: casting nodular iron blank; heating blank to ferritize its microstructure prior to cutting teeth into the blank; heating it in a nonoxidizing environment to an austenitic phase dissolved-carbon-content of about 0.7% to about 1.1%; rapidly quenching the austenitized casting to an acicular-bainite-forming isothermal transformation temperature; isothermally transforming the austenite at that temperature to at least 50% acicular bainite before cooling; and shot peening at least the roots of the teeth to impart the residual compressive stresses thereto.

REFERENCES:
patent: 2796373 (1957-06-01), Berg
patent: 3414442 (1968-12-01), Greenwood et al.
patent: 3784416 (1974-01-01), Davies
patent: 3860457 (1975-01-01), Vourinen
Angus, H. T., "Physical and Engineering Properties of Cast Iron", British Cast Iron Research Association, Alvechurch, Birmingham, England, 1960.
Almen, J. O., "Peened Surfaces Improve Endurance of Machine Parts", Metals Progress, Feb., 1943, pp. 209-215, 270.
Metals Handbook, 1948 Edition, ASM, pp. 248-250.
"Shot Peening", 3rd Ed., 1947, American Wheelabrator & Equip. Corp., pp. 165-167.

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