Method for producing cast iron gear

A method for producing cast iron gears comprising the steps of:

• heating a blank composed of cast iron and having a teeth forming part adapted to be formed into a teeth part of said cast iron gears to such a temperature that at least said teeth forming part is at least austenitized;
• and
• hot rolling said teeth forming part of said blank by pressing projecting teeth of a rolling machine against said teeth forming part which is in a hot state and within an austenitized range, while cooling said blank, thereby generating said teeth part in said teeth forming part of said blank,
• wherein, after said heating step, said blank is cooled from 1000.degree. to 600.degree. C. at a rate of not less than 25.degree. C/s., and then cooled from 600.degree. to 400.degree. C. at a rate of not less than 10.degree. C/s., whereby said teeth part has one of a martensite-based structure and a mixed structure of martensite and fine pearlite.

A method for producing cast iron gears comprising the steps of:

• heating a blank composed of cast iron and having a teeth forming part adapted to be formed into a teeth part of said cast iron gears to such a temperature that at least said teeth forming part is at least austenitized;
• and
• hot rolling said teeth forming part of said blank by pressing projecting teeth of a rolling machine against said teeth forming part which is in a hot state and within an austenitized range, while cooling said blank, thereby generating said teeth part in said teeth forming part of said blank,
• wherein, after said heating step, said blank is cooled by one of a first cooling process and a second cooling process, said first cooling process comprising cooling from 1000.degree. to 600.degree. C. at a rate of not less than 25.degree. C./s., and then cooling from 600.degree. to 400.degree. C. at a rate of not less than 1.degree. C./s. and less than 10.degree. C./s., and said second cooling process comprising cooling from 1000.degree. to 600.degree. C. at a rate of not less than 1.degree. C./s. and less than 25.degree. C./s., whereby said teeth part has one of a fine pearlite-based structure and a mixed structure of ferrite and pearlite.