Effect of aluminum on microstructure and heat treatment of steel

① Aluminum has a strong affinity with oxygen and nitrogen, and is a deoxidizing nitrogen agent in steelmaking.

② Aluminum strongly reduces the austenitic phase region in steel.

③ The affinity of aluminum and carbon is small, and the carbides of aluminum do not appear in steel. Aluminum strongly promotes the graphitization of carbon, and the addition of chromium, titanium, vanadium, niobium and other strongly magnetized forming elements can inhibit the graphitization of aluminum.

④ Aluminum refines the essential grains of steel and increases the coarsening temperature of steel grains. However, when the content of aluminum in steel exceeds a certain value, austenite grains are easy to grow and coarsening.

⑤ Aluminum increases the transformation temperature of steel martensite and reduces the residual austenite content after quenching, which is opposite to other alloying elements except cobalt.