Austenitic steel – definition and properties
The designation austenitic steel is attributed to the word AUSTENITE, which was named after Sir William Chandler Roberts-Austen (1843-1902). Austenitic steel is a steel with more than 8% nickel content and has a cubically surface-centred crystal structure. Along with ferrous and martensitic steels, it belongs to the group of stainless steels and exhibits a particularly good combination of mechanical properties in connection with corrosion stability. Due to these properties, austenitic steels are widely used in all areas where high demands are placed on corrosion stability. The group of austenitic steels, for example, includes the materials 1.4301 (X5CrNi18-10, AISI 304), 1.4401 (X5CrNiMo17-12-2, AISI 316), 1.4404 (X2CrNiMo17-12-2, AISI 316L), 1.4571 (X6CrNiMoTi17-12-2, AISI 316 Ti).
Properties of austenitic steel
The group of austenitic stainless steels has the advantage of high resistance against aggressive environmental conditions, particularly corrosion attacks. The austenitic microstructure and the high shapeability associated with it result in outstanding toughness properties, even at low application temperatures. The good toughness results in poor machinability of the material.
Austenitic steel with a high nickel component has the following properties
- Increased corrosion stability as opposed to low-nickel chromium steel (particularly stress-crack corrosion)
- Austenitic steel is largely non-magnetic (not ferromagnetic)
- Low yield strength (200–300 N/mm²) • High tensile strength (700–1300 N/mm²)
- High heat expansion coefficient (16.0 × 10−6 K−1 for the material 1.4301)
- Density 1.4301 (V2A, AISI 304): 7.9 g/cm3, 1.4401 (V4A, AISI 316L): 8.0 g/cm3
- Cannot be hardened by conventional heat-treatment processes
- Easily weldable
Stainless steel has properties which are highly demanded in industry, medical and dental technology, automotive construction, the construction industry and the chemical industry. Its comparatively low hardness and tendency toward cold welding are limiting factors for many applications in question. These drawbacks can be eliminated with the BORINOX® process for stainless steel hardening.
How can the curing of stainless steel improve the properties of austenitic steel?
The positive properties of steels containing nickel can be improved by the BORINOX® process without worsening the corrosion resistance. An advantage which conventional curing processes typically cannot provide. This process can be used, for example, to increase the surface hardness of an untreated steel from 200 HV to more than 1300 HV. Despite the clear increase in the surface hardness, the BORINOX® process does not negatively affect the corrosion resistance. The tremendous increase in the surface hardness also effectively prevents abrasive wear, cavitation wear and the cold welding of stainless steel pairings. The resulting diffusion layer is dark and does not tend to flake, as is typically the case with coatings using PVD processes, chrome-plating, nickel-plating and thermal spraying.