FV520B is a martensitic precipitation hardening stainless steel. It is similar to the more common PH grade 17-4PH. It combines moderate corrosion resistance with high strength and moderate toughness.
Approximate Composition – 14% Cr, 5%Ni, 1.5% Mo, 1.5% Cu, 0.05% C plus Nb (Exact composition ranges vary between EN and ASTM standards. UNS S45000 is a near equivalent).
This grade combines the following characteristics:
- Moderate corrosion resistance, better than standard martensitic grades. Can be better than 17-4 PH depending on environment
- Controlled balance of mechanical properties by ageing (precipitation hardening)
- High 0.2% proof strength from 720 MPa minimum to 1030 MPa minimum dependent on heat treatment condition
- Moderate toughness – 40 Joules minimum in lowest heat treatment condition even at moderately low sub-zero temperatures –70°C
- Weldable with matching consumables
- Difficult to machine
FV 520B, like 17-4 PH, develops its high strength from the precipitation of copper particles in its martensitic matrix. The supply of this grade is complicated by the mismatch between the “traditional” heat treatment conditions and those laid down in the EN standard. For example, age hardening at 450°C has long been considered to give the maximum strength in this grade. Yet, no such heat treatment is recognised in EN 10088-3. The aerospace standards S143/144/145 are closer to established heat treatments. The combination of high strength and good corrosion resistance finds uses in:
Pump shafts, impellers, fasteners, fans, valves, hydraulic equipment, turbine blades, aerospace, nuclear transport flask, medical devices.