Page 237 - Mechanical Engineer's Data Handbook

ENGINEERING MATERIALS 225

6.4 Stainless steels

6.4. I Types of stainless steel can be heat treated to improve properties and can be
made with a wide range of properties. They are used
Stainless steels comprise a wide range of iron alloys for cutlery.
containing more than 10% chromium. They are
classified as austenitic, ferritic and martensitic. 6.4.1 Selection of stainless steels

Austinitic stainless steels The applications of the different stainless steels are
listed below.
A standard composition is l8%Cr, 8%Ni (18/8 steel).
These steels have high resistance to corrosion, good Austenitic
weldability, high toughness, especially at low tempera-
ture, and excellent ductility. They may be hardened by Window and aoor frames. Roofing and guttering.
cold working and are non-magnetic. Special proper- Chemical plant and tanks. Domestic hot water piping.
ties are produced by the addition of molybdenum, Spoons, forks, knife handles. Kitchen utensils. Wash-
cadmium, manganese, tungsten and columbium. ing machines. Hospital equipment. Car hub caps, rim
embellishers and bumpers. Wheel spokes. Welding
rods and electrodes. Wire ropes. Yacht fittings, masts
Ferritic stainless steels and marine fittings. Nuts, bolts, screws, rivets, locking
wire, split pins. Shafts. Coil and leafsprings.
The chromium content is normally 16-20% with
corrosion resistance better than martensitic but in- Ferritic
ferior to austenitic steels. They are used for presswork
because of their high ductility, but are subject to brittle Mouldings and trim for cars, furniture, television sets,
failure at low temperature. They have moderate gas and electric cookers, refrigerators, etc. Coinage.
strength and limited weldability and are hardenable by Spoons and forks. Domestic iron soles. Vehicle si-
heat treatment. The low carbon content makes them lencers. Driving mirror frames. Fasteners. Parts to
suitable for forming without cracking. They are mag- resist atmospheric corrosion. Heat-resistant parts, e.g.
netic and have low coefficients of thermal expansion. oil-burner sleeves and parts working up to 800 "C.

Martensitic stainless steels Martensitic

The chromium content is 12-18% and the nickel Structural components. Tools. High temperature tur-
content is 1-3%. These steels are the least corrosion bine parts. Flat and coil springs. Scales, rulers, knives,
resistant of all. They are unsuitable for welding or cold spatulas. Kitchen tools and appliances where high
forming. They have moderate machineability and are strength and hardness are required with moderate
used where high resistance to tempering at high corrosion resistance. Surgical and dental instruments.
temperature is important, e.g. for turbine blades. They Record player spindles. Fasteners.