An austempered ductile iron alloy with a mixed austenitic-bainitic structure is made by a method which enables the iron to withstand high cyclical stresses while having a high resistance to abrasion. Articles such as automobile roller-follower camshafts that are made from the iron alloy may have portions thereof selectively austempered to reduce the overall cost and time required to manufacture the article.
A bainite forming process for treating a steel material reduces the time required for a complete thermal treatment as well as the cycle time for the thermal treatment device without necessitating any special means for handling the steel material. The steel material is heated to a temperature higher than the austenitic transformation point, and temporarily quenched to an intermediate point temperature higher than the martensitic transformation point. Then, the temperature of the steel material is again raised towards the range corresponding to bainitic transformation to form a bainitic structure. The reheating is discontinued before the temperature corresponding to the austenitic transformation point is reached, and the steel material is then quenched. In the heating steps, only the portion to be treated by the bainite forming process is locally irradiated with a high-density energy beam.
A new class of ductile iron is formed by the hot isostatic pressing of a ductile iron casting, followed by austempering of the ductile iron casting. Hot isostatic pressing can be carried out at a pressure in the range of 10,000 to 17,000 psi at a temperature above 1600.degree. F., and usually in the range of 1850.degree. F. to 2050.degree. F. Austempering of the material is carried out by heating to the austenitizing temperature (about 1500.degree. F. to 1800.degree. F.), maintaining the austenitizing temperature for a suitable time period, and rapidly cooling to an austempering temperature (about 400.degree. F. to 750.degree. F.) to form ausferrite within the sample.
A method of producing a cam shaft or a similar member that has a core pipe upon which are secured, via expansion of the core pipe, components that are spaced from one another and have a precribed position on the core pipe, with the expansion of the core pipe being effected by introducing a hydraulic fluid into the core pipe. The surface of the components that are secured on the core pipe and are made of a ductile spheroidal graphite iron or sintered material, are subjected to a mechanical abrasion and are melted via a controlled laser beam in such a way as to first slightly reduce the adhesive pressure betewwn the components and the core pipe as a consequence of the melting of the surface layer, and subsequently, after hardening of the melted layer and due to temperature equalization in the components and the core pipe, to increase the adhesive pressure to a higher value. The melting results in a ledeburitic structure having an adequate depth.
The invention relates to a method of producing a grinding roll in which a roll tire made from a highly wear-resistant bainitic cast material is applied to the basic roll body. In order to create a roll tire with particularly high reliability against fractures and with relatively high wear resistance and compression strength, the roll tire is produced from a ductile bainitic spheroidal graphite cast material having a breaking elongation of approximately 0.1 to 2.5% and a compression strength of approximately 1,000 to 1,800 Mpa.
A cast iron component, eg a camshaft, has a wear-resistant layer formed on at least one surface portion thereof, said layer being rich in primary carbides. The cast iron surrounding the carbides and in the remainder of the component has a structure which is substantially ausferritic. A method of manufacturing a component is also claimed.
