METHOD FOR ANNEALING STAINLESS STEEL WITHOUT OCCURRENCE OF SURFACE ROUGHENING

PROBLEM TO BE SOLVED: To stably obtain a stainless steel free from surface roughening by previously determining the min. oxidation power to obviate the occurrence of the surface roughening and executing annealing in an atmosphere contg. gaseous nitrogen while controlling the compsn. and dew point of the gas in such a manner that the oxidation power higher than this oxidation power is attained. SOLUTION: The annealing conditions are previously empirically determined in such a manner that the surface roughening by nitriding does not arise at all in the stainless steel. The oxidation power expressed by Gibbs free energy ΔG is previously calculated from the determined annealing conditions. The annealing conditions with the actual machine are then so controlled that the oxidation power ΔG determined from the annealing conditions with the actual annealing equipment is kept smaller than the oxidation power ΔG at all times. At this time, the annealing temp. is relatively little in the degree of freedom in change and, therefore, the control of the dew point and the control of the components (the concn. of hydrogen in the case of the gaseous mixture composed of the hydrogen and nitrogen) of the atmosphere gas are preferably executed. As a result, the nitriding of the surface of the stainless steel at the time of the annealing is prevented with good accuracy.