Selected Metals - 3: 300 Series Stainless Steels
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
Stainless steel was invented by Englishman Harry Brearley in 1913. While attempting to find a more wear resistant steel he alloyed it with a larger than normal quantity of chromium and found the result to be highly resistant to the acid etching pen that he used to mark his specimens (chromium had been used as an alloy in steels for a few years but in only very small quantities). As is often the case with invention, serendipity brings forth something new and unexpected. In this instance a stainless steel was invented while attempting to find a more wear resistant steel..

Over the years many alloys have been mixed into stainless steel however the most common alloying elements are chromium and nickel. Therefore carbon and chromium/nickel percentages give the best profile of this steel.

S300xx (AISI/SAE 300) series are austenitic steels that provide the best corrosion resistance of all the stainless steels. However they will not heat treat like carbon steels and this limits them in strength. 300 series is easy to segregate from other steels because it is non-magnetic.

Following are a few 300 series stainless steels familiar to most machinists (note how carbon, chromium, and nickel effect the properties of the steel).

S30300 (AISI/SAE 303)

  • Carbon 0.15%
  • Chromium 17 to 19%
  • Nickel 8 to 10%
  • Other alloys manganese, sulphur, phosphorus, silicon, zirconium, molybdenum
  • Machinability excellent
  • Hadenability none
  • Weldability not recommended
  • Applications nearly everything
  • Comments one of the most popular easier machining stainless steels.  Available in all sizes and forms.

S30400 (AISI/SAE 304)

  • Carbon 0.18% max
  • Chromium 18 to 20%
  • Nickel 8 to 12%
  • Other alloys manganese, sulphur, phosphorus, silicon
  • Machinability slow speeds heavy feeds, use chip breaker, will work harden
  • Hadenability none
  • Weldability fusion welding and resistance welding
  • Applications nearly everything
  • Comments This is the oldest and most widely used austenitic stainless steel. It possesses an excellent combination of strength, corrosion resistance and machinability. All sizes and forms are available.

S31600 (AISI/SAE 316)

  • Carbon 0.08%
  • Chromium 16 to 18%
  • Nickel 10 to 14%
  • Other alloys manganese, sulphur, phosphorus, silicon, molybdenum
  • Machinability slow speeds heavy feeds, use chip breaker, will work harden
  • Hadenability none
  • Weldability fusion and resistance - no
  • Applications marine hardware
  • Comments best corrosion resistance of the three, widely available.
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label: stainles steel, aisa, sae, aluminum, copper, tool steel, history of metal,