In a process for improving the strength characteristics of a wire composed of an austenitic metal alloy selected from the group consisting of stainless steel alloys of the AISI 200 and 300 series and non-stainless steel alloys containing iron, manganese, chromium, and carbon, comprising the following steps: (a) deforming the wire at a strain of at least about 10 percent and at a temperataure in the range of about Md minus 50.degree. C. to about Md plus 50.degree. C., (b) cooling the wire to a temperature no higher than about minus 75.degree. C.; and (c) drawing the cooled wire whereby the cross-sectional area of the wire is reduced by a certain percentage and the wire has a martensite phase of at least about 50 percent by volume and an austenite phase of at least about 10 percent by volume, the improvement comprising carrying to the drawing of step (c) by drawing the wire through two dies placed in series in such a manner that the cross-sectional area of the wire is reduced by the first die by a percentage in the range of about 8 to about 15 percent and the cross-sectional area of the reduced wire is further reduced by the second die by a percentage in the range of about 8 to about 15 percent based on the area of the wire exiting the first die.
A method for making a fastener having a head and a shank from wire or rod consisting essentially of AISI 200 or 300 series stainless steel comprising the following steps: (a) cooling the wire or rod to a temperature of less than about minus 75.degree. C.; (b) drawing the cold wire or rod through a die at a strain sufficient to provide a tensile strength for the wire or rod in the range of about 75 ksi to about 160 ksi, the strain and the die size being such that the area of the wire or rod will be reduced by at least about 3 percent; and (c) dividing the wire or rod into slugs and cold heading each slug to provide the fastener.
A process and apparatus is provided for forming spring wire into coils. A take-up block with a peripheral surface receives convolutions of wire as it is rotated. At least one pinch roll confines convolutions of the spring wire to the peripheral surface. The shape of the peripheral surface of the block and the circumferential surface of the pinch roll combine to define a gap for urging the convolutions of spring wire to migrate upward. At least one rotatable wire receiving basket is mounted adjacent the take-up block, and further drive means are provided for rotating the at least one wire receiving basket. In a preferred form, stationary guide loops are utilized to keep the spring wire moving in a predetermined trajectory from the take-up block to the rotating wire receiving basket. Again in a preferred embodiment, there are two wire receiving baskets, both rotated at a predetermined and adjustable speed, and the wire is wrapped into a coil firstly on one of the wire receiving baskets, and then on the other of the wire receiving basket. While each wire receiving basket is being filled, the coil of wire in the other can be removed.
A clutch disc spring for a land vehicle, such as an over-the-road truck or an automobile, which has an increased life. The spring, formed of ferrous material, is cooled by vaporizing low temperature nitrogen to slowly, cryogenically cool the spring to a temperature of about -300 degrees Fahrenheit and maintain the spring at that temperature for several hours. The cryogenic treatment converts retained austenite within the spring to martensite, thereby improving the mechanical properties of the spring. The spring is then tempered to temper the newly formed martensite, further improving the mechanical properties of the spring. These improved mechanical properties include better wear resistance, strength and resistance to fatigue.
