APFR/2- Austenitic Stainless Steel

Valbruna Grade

APFR/2

Description of material

APFR/2 is a Cr- Ni –N austenitic stainless steel designed for elevated temperature applications whose Nitrogen content warrants a high mechanical strength and hot corrosion resistance.

Applications

Exhaust valves for gasoline and diesel internal combustion engines where a high temperature strength and corrosion resistance to combustion products are needed.

Corrosion resistance

APFR/2 has a good resistance to oxidation and corrosion to combustion products that form inside the engine. When solution treated, this grade offers a stable austenitic structure.

Cold working

APFR/2 has a fair ductility in the annealed condition. Its machinability is approximately comparable to the standard austenitics with a high Nitrogen content and, therefore, it could be only improved with a right choice of cutting fluids, tools and machining parameters.

Weldability

In solid state joining such as Friction Welding, APFR/2 provides a quality bond line. When friction welded with a stem of alloy or martensitic steel, a stress relieving or tempering of the valve must be done in order to soften the martensitic structure of HAZ and bond line.

Hot working

APFR/2 has a good hot plasticity and is suitable for processing by hot extrusion or by upsetting with electric resistance heating. However, overheating must be always avoided. The choice of hot working temperature and process parameters must always evaluate both the strain rate and the consequent increasing of temperature that is reached after hot deformation. High strain rates and temperature at the top end of the range during the extrusion and forging process, could generate internal bursts of stems of valves. The same care must be carried out for electrical upsetting process in order to maintain the right geometry of the bulb and to avoid hot cracks and internal shortness of the head valve. A low or medium temperature range of hot working is recommended.

Heat treatment

Heat treatments don’t increase the mechanical properties of APFR/2 and only full annealing or stress relieving can be done.

Designations