Carbonitriding method, machinery component fabrication method, and machinery component

摘要

A carbonitriding method that can improve the nitrogen permeating rate to render the carbonitriding process effective includes an atmosphere control step, and a heating pattern control step. The atmosphere control step includes an undecomposed NH3 partial pressure control step, and a CO/CO2 partial pressure control step. The undecomposed NH3 partial pressure control step and the CO/CO2 partial pressure control step are carried out in the atmosphere control step such that ac* defined by the following equation (1) is at least 0.88 and not more than 1.27, and α defined by equation (2) is at least 0.012 and not more than 0.020, where PN is the undecomposed ammonia partial pressure and PH is the hydrogen partial pressure in the heat treatment furnace, wherein;ac*=(Pco)2⁢K×Pco2(1)PCO: partial pressure of carbon monoxide (atm), PCO2: partial pressure of carbon dioxide (atm)K: equilibrium constant at +CO2 2CO;α=PN0.006×(PH)32×(1.877-1.055×ac*)100.(2)

主权项

1. A carbonitriding method for carbonitriding a workpiece formed of steel that contains at least 0.8 mass % of carbon by heating in an atmosphere including ammonia, carbon monoxide, carbon dioxide, and hydrogen, the method comprising:
an atmosphere control step of controlling an atmosphere in a heat treatment furnace, and a heating pattern control step of controlling a temperature history applied to said workpiece in said heat treatment furnace, wherein said atmosphere control step comprises
an undecomposed NH3 partial pressure control step of controlling a partial pressure of undecomposed ammonia in said heat treatment furnace, anda CO/CO2 partial pressure control step of controlling the partial pressure of at least one of carbon monoxide and carbon dioxide in said heat treatment furnace, and said undecomposed NH3 partial pressure control step and said CO/CO2 partial pressure control step are carried out in said atmosphere control step such that ac* defined by a following equation (1) is at least 0.88 and not more than 1.27, and α defined by equation (2) is at least 0.012 and not more than 0.020, where PN is the undecomposed ammonia partial pressure and PH is the hydrogen partial pressure in said heat treatment furnace, whereinac*=(Pco)2K×Pco2(1)PCO: partial pressure of carbon monoxide (atm), PCO2: partial pressure of carbon dioxide (atm)K: equilibrium constant at ±CO22COα=PN0.006×(PH)32×(1.877-1.055×ac*)100.(2)