초록 ▼

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

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.

대표청구항 ▼

A process for making a through hardened, compressively surface stressed nodular iron gear capable of withstanding applied tooth root tensile stress excursions of at least about 60,000 psi without fatigue failure, said process comprising the sequential steps of: casting a gear blank from nodular iron

A process for making a through hardened, compressively surface stressed nodular iron gear capable of withstanding applied tooth root tensile stress excursions of at least about 60,000 psi without fatigue failure, said process comprising the sequential steps of: casting a gear blank from nodular iron; annealing the blank to yield a substantially homogeneous matrix microstructure upon cooling; cooling the blank to room temperature; machining teeth into the blank; heating the machined casting in a nonoxidizing atmosphere to a temperature of about 1600°F. to about 1700°F. to austenitize the matrix and dissolve sufficient uncombined carbon to provide an austenitic phase comprising about 0.7% to about 1.1% dissolved carbon; quenching the casting to an isothermal transformation temperature of above about 425°F. and below about 650°F. and at such a rate as to avoid the nose of the time-temperature transformation curve of the nodular iron so as to preclude the formation of significant amounts of pearlite, feathery bainite or martensite prior to and during subsequent isothermal transformation at said quenching temperature; maintaining the casting at said isothermal transformation temperature for a time sufficient to convert said austenitic phase to at least 50% acicular bainite; cooling said casting from said isothermal transformation temperature to room temperature; and shot peening the surface of the gear at the roots of the gear\s teeth to impart to said surface a residual compressive stress of at least about 40,000 psi and provide a residual compressive stress of about 10,000 psi at a depth of about 0.006 inch to about 0.015 inch beneath the surface. A through hardened, high stress gear capable of withstanding occasional applied tooth root tensile stress excursions of at least about 60,000 psi, said gear comprising a base portion and a plurality of teeth integral with and extending from said base portion, said teeth each comprising a central core and a skin cold worked by impingement on said core at least at the tooth\s root where it joins the base, said base, core and skin comprising nodular iron the matrix of which comprises at least about 50% by weight non-feathery acicular bainite having a dissolved carbon content of about 0.7% to about 1.1% by weight and a Vickers hardness between about 577 and 720, and said skin having a residual compressive stress of at least about 40,000 psi at its surface and about 10,000 psi at a depth between about 0.006 inch and 0.015 inch below said surface.