EFFECT OF BORON CONTENT ON HIGH-TEMPERATURE OXIDATION RESISTANCE OF B-BEARING HIGH-SPEED STEEL

Abstract

The oxidation behavior of B-bearing high-speed steel was studied at 923[Formula: see text]K. The results showed that the as-cast microstructure of 1.0 wt.%B high-speed steel was composed of pearlite + ferrite + M7(C, B)3 + M2(B, C). When the boron content increased, the microstructure gradually changed into martensite + retained austenite + netlike M2(B, C) + M[Formula: see text](C, B)6 + M7(C, B)3. The cyclic oxidation of B-bearing high-speed steel at K followed parabolic rule. The unit area mass gain of 1 wt.%B high-speed steel was 4.2 g/m2 after 923 K/250 h oxidation, and the unit area mass gain of 3 wt.%B high-speed steel was only 3.5 g/m2. The oxidation of boron element formed B2O3, which was mainly enriched at the interface of the oxide film/matrix. B2O3 flowed in the oxide film at high temperature and was easy to fill the defect. B2O3 was easy to form B2O3-SiO2 borosilicate with SiO2. The more boron content was, the more favorable it was to form B2O3-SiO2 borosilicate oxide layer rich in B2O3 and the more favorable it was to spread in the oxide film, so that the oxidation resistance of B-bearing high-speed steel could be remarkably improved.