Effect of Aluminum on the Structure and Mechanical Properties of Austenitic Steels

Abstract

The works on the structure and mechanical properties of aluminum-alloyed austenitic steels are analyzed. Aluminum in aging high-nitrogen Cr–Mn–Ni–V nonmagnetic steels is shown to decrease the strength due to a decrease in the amount of dispersed VN nitrides having precipitated during aging because of the formation of coarse AlN particles hard to dissolve on quenching heating. An additional increase in the strength of aging nonmagnetic Mn–Ni–V–C steels is reached by their alloying with aluminum, which does not form hard to dissolve compounds with carbon. A significant increase in the surface hardness and the wear resistance during nitriding is reached as a result of separate or complex alloying of Mn–Ni–V steels with chromium up to 3% and aluminum up to 1.2%, which increase the nitrided layer thickness. The best combination of the properties of the nitrided layer is achieved after nitriding these steels containing 2.5–3.5% V at 700°C (12 h) in a 80% N₂ + 20% HN₃ medium. In this case, the hardening of the core during aging is related to the precipitation of VC carbides, and that of the nitrided layer, to the formation of VN nitrides. A significant increase in the volume fraction of strengthening phases in manganese steels is reached by complex alloying with Al, Ni, Cu, and V in the amounts that provide the simultaneous precipitation of the VC carbide and NiAl intermetallics during aging. Nonmagnetic 50G17N10Yu4F2 steel with a combined carbide–intermetallic hardening is highly competitive in strength (σ_u > 1600 MPa, σ_0.2 > 1400 MPa) with high-strength 18Kh2N4VA ferromagnetic steels and significantly surpasses the well-known aging nonmagnetic high-nitrogen alloys.