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Stainless steel - What is it ? |
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When stainless steels were first developed about 70 years ago and from that time on very quickly conquered all technical areas as well as all everyday-life areas, nobody would have imagined the multitude of their uses and applications. These are mainly due to the excellent features of stainless steels and to the fact that these features can be adjusted to fit certain needs through the application of particular alloy additions (see table)
In general we distinguish between ferritic and austenitic stainless steels. Ferritic stainless steels normally contain an alloy addition of about 12 - 18% Chromium, while austenitic stainless steels contain in addition to a Chromium alloy of around 18% also a Nickel content of at least 8%. Other major alloy additions that may be used are Molybdenum, Manganese, Silicon, Tungsten, Vanadium, Cobalt, Titanium, or Niob.
Depending on the application of the material, desired chemical and physical material characteristics can be achieved through these alloy additions, especially:
- resistance to heat,
- resistance to cold,
- good possibilities for distortion,
- high strength or particularly
- resistance to corrosion.
| kind of steel | C | Cr | Ni | | martensitic | 0,07% - 0,1% | 12% - 18% | - | | ferritic | abt. 0,07% | 13% - 17% | - | | austenitic | <= 0,07% | >= 18% | >= 8% | | austenitic-ferritic | <= 0,07% | >= 18% | >= 8% | | kind of steel | corrosion
resistance | strenght | weldability | | martensitic | inferior to good | high | none to good | | ferritic | good to very good | inferior | inferior to good | | austenitic | very good | high | good to very good | | austenitic-ferritic | very good | very high | inferior to good | Table: features of different kinds of steel
We will consider mainly austenitic stainless steels, since only these steels have the necessary resistance to rust in water supply systems. These austenitic stainless steels are also known under names such as V2A, V4A, Nirosta and similar trade designations.
For the stainless steels that can be applied in water supply systems due to their rust resistance the ease of processing plays of course also a role. Through this additional criterium, the spectrum of used materials is narrowed even further, so that we can limit ourselves to the following materials:
- Material-No. 1.4301 - X 5 CrNi 18 10
- Material-No. 1.4541 - X 6 CrNiTi 18 10
- Material-No. 1.4306 - X 2 CrNi 18 11
- Material-No. 1.4307 - X 2 CrNi 18 9
- Material-No. 1.4571 - X 6 Cr Ni Mo Ti 17 12 2
- Material-No. 1.4404 - X 2 Cr Ni Mo 17 12 2
- Material-No. 1.4435 - X 2 Cr Ni Mo 18 14 3
- Material-No. 1.4462 - X 2 Cr Ni Mo N 22 5 3
Stainless steels of these different material grades are available as tins of various thicknesses with various surface quality, as rod materials (round-, square angle-, flat-steel), as pipes as well as various custom profiles which are normally only produced according to clients´ demands.
In order to avoid structural changes due to material pollutions it is self-evident that particular care is necessary during the melting of stainless steels. For this reason one generally starts with nearly carbon-free iron to which the different, exactly measured alloy components are added in an electronic oven.
The work in the electronic oven proceeds under vacuum conditions in order to avoid the diffusion of polluting air particals into the melt. |
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HUBER - WHERE QUALITY AND SERVICE SPRING TO MIND
Huber Technology UK, Units C and D Brunel Park
Bumpers Farm, Chippenham Wiltshire SN14 6NQ
Phone +44 1249 765000, Fax +44 1249 449076, E-mail: rotamat@huber.co.uk |
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