Method for making a cone for a rock bit and product

A process for forming a tungsten carbide insert cone for a rock bit comprising the steps of:

• forming a cone blank from a steel containing about 0.40 to 0.75% carbon, the cone blank including a generally conical external surface, a generally cylindrical internal bearing cavity and a circumferentially extending ball bearing race in the bearing cavity;
• heating the cone blank to an austenitizing temperature and quenching the cone blank for producing a relatively higher core hardness in the cone blank;
• tempering the cone blank for reducing the core hardness of the cone blank;
• forming insert holes in the external surface of the cone blank for insertion of tungsten carbide inserts;
• placing an induction coil adjacent a portion of the ball race;
• rotating the cone about the induction coil for exposing the circumference of the ball race to energy from the induction coil for heating substantially only the ball race surface;
• and thereafter
• cooling the ball race surface sufficiently rapidly for selectively hardening the ball race surface to a hardness greater than the hardness of the core.

A process for forming a tungsten carbide insert cone for a rock bit comprising the steps of:

• forming a cone blank from a steel containing about 0.40 to 0.75% carbon, the cone blank including a generally conical external surface, a generally cylindrical internal bearing cavity and a circumferentially extending ball bearing race in the bearing cavity;
• heating the cone blank to an austenitizing temperature and quenching the cone blank for producing a relatively higher core hardness in the cone blank;
• tempering the cone blank for reducing the core hardness of the cone blank;
• forming insert holes in the external surface of the cone blank for insertion of tungsten carbide inserts;
• directing an electron beam against a portion of the ball race surface and rotating the cone blank for exposing the circumference of the ball race to the electron beam for heating the ball race surface above the austenitizing temperature of the steel;
• and
• cooling the ball race surface sufficiently rapidly for selectively hardening the ball race surface to a hardness greater than the core hardness of the cone.

A process for forming a tungsten carbide insert cone for a rock bit comprising the steps of:

• forming a cone blank from a steel containing about 0.40 to 0.75% carbon, the cone blank including a generally conical external surface, a generally cylindrical internal bearing cavity and a circumferentially extending ball bearing race in the bearing cavity;
• heating the cone blank to an austenitizing temperature and quenching the cone blank for producing a relatively higher core hardness in the cone blank;
• tempering the cone blank for reducing the core hardness of the cone blank;
• forming insert holes in the external surface of the cone blank for insertion of tungsten carbide insert;
• directing a high energy beam against a portion of the ball race surface and rotating the cone for exposing the circumference of the ball race to the high energy beam for heating a thin layer at the ball race surface above the austenitizing temperature of the steel;
• and
• cooling the ball race surface sufficiently rapidly for selectively hardening the ball race surface to a hardness greater than the core hardness of the cone.

A process for forming a tungsten carbide insert cone for a rock bit comprising the steps of:

• forming a cone blank for medium to high carbon hardenable steel, the cone blank including a generally conical external surface, a generally cylindrical internal bearing cavity, and a circumferentially extending ball bearing race in the bearing cavity;
• heating the cone blank to an austenitizing temperature and quenching the cone blank for producing a relatively higher core hardness;
• tempering the cone blank for reducing the core hardness;
• forming insert holes in the external surface of the cone blank for insertion of tungsten carbide inserts;
• and
• selectively heating and cooling substantially only the surface of the ball race for forming a surface layer in the ball race having a hardness greater than the core hardness of the cone after tempering.