Effect of Niobiumizing Temperature and Time on Microstructure andProperties of Niobiumizing Layer on GCr15 Steel Surface

Niobiumizing layer was prepared on surface of GCr15 steel for pin shaft by solid powder packing method at different temperatures (910, 930, 950, 970℃) for different holding times (1, 2, 4, 5, 6 h). The effect of niobiumizing temperature and time on micromorphology, phase composition, microhardness, wear resistance and corrosion resistance of the niobiumizing layer was investigated. The results show that the niobiumizing layer prepared under different conditions was closely combined with the matrix. The niobiumizing layer was composed of NbC and α-Fe. With increasing niobiumizing temperature or niobiumizing time, the amount of NbC phase increased, the α-Fe phase disappeared gradually, and the thickness and microhardness of the niobiumizing layer increased. When the niobiumizing temperature was 950℃ and the niobiumizing time was 2 h, the self-corrosion potential of the niobiumizing layer was the largest and the self-corrosion current density was the smallest, indicating the corrosion resistance was the best. Considering the thickness, corrosion resistance and wear resistance comprehensively, the optimal niobiumizing process was niobiumizing temperature of 950℃ and niobiumizing time of 5 h. The niobiumizing layer prepared under this condition had relatively good corrosion resistance and small fluctuation of friction coefficients, and the average friction coefficient was only 0.22.