I. Effect of aluminum on microstructures and heat treatment of steel
(1) Aluminum has a strong affinity with oxygen and nitrogen, and is a deoxidizing nitrogen determinant in steelmaking.
(2) Aluminum strongly reduces the austenite phase zone in steel.
(3) The affinity between aluminium and carbon is small, and there is generally no aluminium carbide in steel. Aluminum strongly promotes the graphitization of carbon, and the graphitization of aluminium can be inhibited by adding chromium, titanium, vanadium and niobium.
(4) Aluminum refines the intrinsic grains of steel and increases the temperature of grain coarsening. However, when the content of Al in steel exceeds a certain value, the austenite grains tend to grow and coarsen.
(5) Aluminum increases martensite transformation temperature of steel and decreases retained austenite content after quenching, which is contrary to other alloying elements except cobalt.
II. Effect of Aluminum on Mechanical Properties of Steel
(1) Aluminum reduces the sensitivity of steel to notches, decreases or eliminates the aging phenomenon of steel, especially decreases the ductile-brittle transition temperature of steel, and improves the toughness of steel at low temperature.
(2) Aluminum has greater solid solution strengthening effect, and high aluminium steel has higher specific strength. The high temperature strength and endurance strength of ferritic Fe-Al alloys are higher than Cr13 steel, but their room temperature plasticity and toughness are low, and cold deformation processing is difficult.
(3) The comprehensive properties of austenitic Fe-Al-Mn steel are better.
III. EFFECT OF ALUMINIUM ON THE PHYSICAL, CHEMICAL AND TECHNOLOGICAL PROPERTIES OF STEEL
(1) The addition of aluminium to ferrochromium alloy can reduce the temperature coefficient of resistance and can be used as electrothermal alloy material.
(2) Aluminum and silicon play similar roles in reducing core loss of transformer steel.
(3) When the aluminium content reaches a certain value, passivation occurs on the surface of steel, which makes the steel corrosion resistant in oxidizing acid and improves the corrosion resistance to hydrogen sulfide. Aluminum is harmful to the corrosion resistance of steel in chlorine and chloride atmosphere.
(4) Aluminum nitride layer is formed on the surface of steel containing aluminium after nitriding, which can improve hardness, fatigue strength and wear resistance.
(5)The oxidation resistance of steel can be significantly improved by adding aluminium as alloying element. Aluminizing or Aluminizing on the surface of steel can improve its oxidation resistance and corrosion resistance, and can be used to manufacture solar water heaters, etc.
(6)Aluminum has adverse effects on hot working performance, weldability and cutting performance.
IV. Application of Aluminum in Steel
(1) Aluminum plays a major role in deoxidation and grain size control in general steels.
(2) As one of the main alloying elements, aluminium is widely used in special alloys, including nitrided steel, stainless acid-resistant steel, heat-resistant non-skin steel, electrothermal alloys, hard and soft magnetic alloys, etc