Benefits from using cold drawn F55 / UNS S32760 material

Broder Metals Group Ltd is a steel and copper alloy distributor carrying a wide range of cobalt alloy, nickel alloy, aluminium bronze and copper alloys, and stainless steels for the value and pump industry. One of our in-demand alloys is F55 (UNS S32760), but it seems that one of the secrets of the industry is the mechanical property improvement obtained by cold drawing F55.

F55 (UNS S32760) is a super duplex stainless steel with a roughly equal split of austenite and ferrite microstructure, which provides a high mechanical strength along with good ductility. Corrosion resistance properties are excellent in a variety of environments: this material provides high resistance to pitting, crevice corrosion resistance, stress corrosion cracking, corrosion fatigue and erosion.

It performs very well in chloride stress-corrosion situations and is good for sulphide stress corrosion resistance. It also has low thermal expansion and higher heat conductivity than austenitic only steels, while weldability and workability is good.

Most people in the industry will be aware of the benefits from using F55 (UNS S32760) material in ball, needle, gate and butterfly valves, grade actuators, gearboxes, and other applications such as in heat exchangers, desalination plants, and utility and industrial systems to name just a few.

Material supplied in the A (annealed) Condition provides a minimum of 550 MPa 0.2% Yield Strength with a minimum 750 MPa Ultimate Tensile Strength. Hardness is a maximum 290 HBW (31 HRC), which conforms to the requirements of NACE MR0175.

What may be less well known is the benefits obtained from deliberate application defined amounts of cold work to convert Condition A material to Condition S (Strained). Obviously, the chemistry-induced benefits of corrosion resistance remain, but mechanical performance is enhanced with an increase in Yield Strength (minimum of 550 MPa increased to a minimum of 720 MPa) and Ultimate Tensile Strength (minimum of 750 MPa increased to 860 MPa minimum). Hardness increases to a maximum of 335 HBW (36 HRC), while there is a slight trade-off in elongation which drops from a minimum of 25% to a minimum of 16% (measured across 50 mm or 4D).

However, a property often looked for in Cold Drawn F55 is not covered by ASTM A276 Condition S, but one or both designations of FG (Fastener Grade) or FLT (Fastener Low Temperature).

Added to the Condition S properties above are Charpy Impact test properties at low temperatures: at -46oC a minimum of 35 Joules (single) and 40 Joules (average), while at a temperature of -1010C results of greater than 20 Joules (single) and 27 Joules (average) are obtained.

This toughness adds a new dimension to the uses that super duplex grades can be used for, and while the FG / FLT designation obviously applied to fasteners being used in cryogenic or other low operating environments, Broder Metals Group are seeing increasing requests for material to be supplied cold drawn that was previously only asked for in Condition A.

We obviously carry a full range of sizes in Condition A sizes and can convert to Condition S with low temperature Charpy Impact test properties, to suit our customerís requirement, very quickly.

Tel: 0114 232 9240

Spring 2020 // Issue 52
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