Effect of Tempering Temperature on the Corrosion Resistance of New 9CrMoCoB Steel
In order to study the effect of tempering temperature on the corrosion resistance of heat-resistant steel containing B,and compare the effect of precipitation of B-containing carbide on the corrosion resistance,the 9CrMoCoB heat-resistant steel was isothermally quenched at 950 ℃ and normalized with air cooling at 1 100 ℃,and the tempering temperatures were selected at 680 ℃,700 ℃,720 ℃,740 ℃ and 760 ℃,respectively,and cooled in furnace after held for 2 h.Electrochemical tests were carried out on the heat-resistant steels using AC impedance and potentiodynamic polarization curve technologies to observe the influences of different tempering temperatures on the size and quantity of precipitated phases in the heat-resistant steels,and compare their influences on the corrosion resistance of heat-resistant steel.Meanwhile,the influences of B-carbides and B-carbides formed after isothermally quenching and 1 100 ℃ normalizing respectively on the corrosion resistance of heat-resistant steel were studied.The results show that the size of precipitated phase increases with the increase of tempering temperature.The sizes of B-containing carbides after tempering are smaller than that of non-B-carbides.With the increase of tempering temperature,the corrosion resistance increases first and then decreases.The corrosion resistance is best when the tempering temperature is 720 ℃.Compared with no B carbides,the corrosion resistance of heat resistant steel after 950 ℃ isothermally quenching is better.
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