V157M- Precipitation Hardening

Valbruna Grade

V157M

Description of material

V157M is a Cr-Ni-Al-Mo semi-austenitic precipitation hardening stainless steel with moderate corrosion resistance and a high strength obtained by different kinds of heat treatments. The behavior of this grade during heat treatment is the same of AV177AL. Some little variations of chemical balance of Ni % and Mo% doesn’t substantially influence its corrosion performance. This grade has a soft austenitic structure with values of strength close to 300 series. A high increase of the mechanical properties as Rp, Rm and HB is obtained by the transformation of Austenite to Martensite by cryogenic treatment (cond.R), by conditioning close to room temperature (cond.T) and by heavy cold deforming (cond. C). All these treatments must be followed by a hardening (cond. RH, TH and CH) heat treatment at a specific temperature able to minimize the distortions of pieces.

Applications

Stainless steel springs or devices where high Rm, HB and resistance corrosion better than 400 martensitic series are required.

Melting practices

Argon Oxygen Decarburization

Corrosion resistance

The structure and chemical composition of V157M shows the same corrosion resistance of austenitic 300 series steels, but better than the martensitic 400 series. Depending on environments and final use, attentive evaluations should be done in terms of H-embrittlement and stress corrosion cracking. The Molybdenum content helps against pitting corrosion.

Cold working

V157M can be cold drawn and cold headed in the annealed condition, but it’s important to know that this grade has a very high cold working hardening factor due to a rapid formation of a Martensite structure.

Machinability

Machining is the same of austenitic 302 or 304 in the annealed condition, but it is very difficult after hardening due to the higher hardness of Martensite.

Weldability

V157M is weldable by the typical inert gas processes, because these methods have a protective effect on the weld steel avoiding the loss of Aluminum. Normally, neither preheating nor post-welding heat treatments are necessary. FZ and HAZ have mechanical properties close to the base steel in the annealed condition. Obviously, a solution annealing followed by conditioning and precipitation hardening is mandatory to obtain high strength of the weld.

Hot working

V157M could have a certain amount of Ferrite in its austenitic structure, mainly in large sections or ingots. This situation should be well considered in order to avoid cracks primed by ferrite during hot deforming or forging.

Designations