Stainless steel, as its name suggests, is more resistant to corrosion than plain carbon or low alloy steels.
Picture 3.3 Harry Brearley.
Stainless steel was discovered by accident in 1913 by a Sheffield chemist called Harry Brearley. He was trying to solve the problem of rapid wear of the inside of rifle barrels and decided to try out a steel containing a high proportion of chromium. Routine analysis of steel at that time involved dissolving it in acid. The high chromium steel, however, would not dissolve and also stayed shiny when left around in the laboratory. Brearley immediately realised the potential his steel had for making cutlery that would not rust. Progress by accidental discovery in this way in not uncommon in science. Sometimes it is referred to as serendipity.
Picture 3.4 Checking steel turbine blades.
Stainless steel has a high resistance to corrosion and retains its strength at high temperatures. These properties make it ideal for making turbine blades for use in the power generation industry. The blades have to operate in widely varying conditions ranging from high pressure, super heated steam at 580°C to a lower pressure environment where condensation can be a problem.
The corrosion resistance and ease with which it can be sterilised make stainless steel the first choice material for surgical instruments.
Picture 3.5 Stainless steel cutlery stays nice and shiny throughout its life.
Stainless steel - aesthetic appeal
In addition to being resistant to corrosion, stainless steel is aesthetically pleasing. It is chosen by architects because of its durable bright clean surface and its ability to reflect subtle changes in the light that falls on it. Stainless steel has been used to clad the outside of prestigious buildings and to form a major component of modern bridges.
The composition of stainless steel
The key to the corrosion resistance of stainless steel is its chromium content. Other elements such as copper, aluminium, nickel and molybdenum help steel resist corrosion but their effect is limited if chromium is not present.
Steels that contain below 4% chromium are called alloy steels. It is only steel with more than 4% chromium that is called stainless steel.
For extra protection, for example against the hostile environment of sulphurcontaining flue gases, steel containing over 12% chromium is used.