Heat treating a metallic workpiece in a fluidized bed

US5022934A · kind A · utility

Assignees

• Ewald Schwing · DE
• Horst Uhrner · DE

Inventors

• Ewald Schwing · Neukirchen-Vluyn, DE
• Peter Sommer · Copenhagen, DK
• Horst Uhrner · Issum, DE

Key dates

• Filing date: Jan 16, 1990
• Grant date: Jun 11, 1991
• Expiry date: Jan 16, 2010

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C23C8/32
• WIPO field: Materials, metallurgy
• WIPO sector: Chemistry

Abstract

A process for heat treating a metallic workpiece comprises the steps of first heating the metallic workpiece in a gas stream fluidized bed made from a plurality of refractory particles for 2 min to 10 min under an inert-gas atmosphere to a treatment temperature of from about 500.degree. to 650.degree. C. Then the heated workpiece is preoxidized with an oxidizing gas stream in the fluidized bed. Finally the heated workpiece is nitrocarburized by contacting it for between 0.5 h and 10 h in the fluidized bed with a gas mixture composed of nitrogen, ammonia, and a carbon-rich gas. The composition of the gas mixture is varied during the nitrocarburizing step from a starting composition of about 75% to 40% by volume of ammonia and from about 20% to 55% by volume nitrogen with the balance being propane or natural gas by reducing the ammonia partial volume in a series of steps at intervals from 10 min to 60 min and increasing the nitrogen partial volume component complementarily such that the partial volume component of the carbon-rich gas is kept constant during the carburization to an ending composition of from about 10% to 30% by volume ammonia. In this manner the workpiece surface is l…