Influence of Al on mechanical properties and carbides of quenched and tempered H11 steel

H11 steel with mass fraction of Al (0.77% and 0) was treated by different quenching and tempering processes, and the variation of hardness and impact energy were systematically investigated. Moreover, carbide extraction at annealed, 1060℃ quenched, 1060℃ quenched + 510℃ tempered, 1060℃ quenched + 560℃ tempered, and 1060℃ quenched + 600℃ tempered were conducted. Finally, the type and morphology of carbides were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The main conclusions are as follows:(1) Al can improve the impact toughness and tempering hardness of H11 steel; however, it reduces the hardness of quenching. (2) Al can promote the dissolution of carbides and the homogeneity of elements during the austenitizing process. (3) Al can prevent the precipitation and accumulation of carbides during the tempering process, which is more obvious under 560℃. (4) Al can prevent the accumulation of carbon and alloy elements, such that (Fe,Cr)₂C, MoC and Cr₇C₃ become more stable and suppresses the precipitation of (Fe,Cr)₃C, Mo₂C, and Cr₂₃C₆ during the tempering process.