Microstructure and properties of 1Cr12Ni2WMoVNb (GX-8) steel bored barrels with and without QPQ treatment

Abstract

Bored barrels are one of the primary parts of small arms. In order to enhance the service life of bored barrels, specimens of 1Cr12Ni2WMoVNb (GX-8) steel bored barrels were treated by QPQ salt bath at temperatures 530°C for 1–4h, followed by the same post-oxidation process with heating temperature of 440°C for 1h. QPQ nitrided layers were formed on the surface of GX-8 steel after QPQ salt bath and the optimized treatment time was determined to be 1h. Specimens with and without QPQ-1h were studied by micro-hardness test, SEM, wear resistance test, Tafel polarization curves, salt spray corrosion and ball firing. Layers formed during QPQ-1h contains a mixture of magnetite (Fe3O4), Fe1-XO, CrN, ε phase, γ′-Fe4N and α-Fe phases. This layer leads to significant improvement in wear resistance as a result of remained Fe3O4 film, while the fine distribution of nitride precipitates introduces high hardness and large residual microstresses. The formation of thick Fe3O4 film results in an improvement in the corrosion resistance of steel. After the breakdown of Fe3O4 film, the absence of chromium in solid solute by precipitation of chromium nitrides and carbides leads to significant decreases in corrosion resistant. The QPQ-1h process results almost one times increases in the lifetime of bored barrels, as a result of wear resistance improvement after QPQ treatment.