Sheffield, England born Harry Brearly discovered stainless steel in 1913. In an experiment, he found that steel’s corrosion
resistance increased when the chromium content is raised to 12 percent or more. He is seen as the person who laid the
foundation for the development of various stainless steel grades.
The development of stainless steel almost came to a complete standstill during the First World War. By the late 1920′s it
was found that two grades of stainless steel namely martensitic stainless steel and austenitic stainless steel were the most
versatile and useful. Martensic stainless steel has a chromium content of between 13 and 18 percent while austenitic
stainless steel contains 18 percent chromium and 8 percent nickel.
In today’s terms stainless steel is used as a generic term to describe corrosion resistant steel that has a minimum
chromium capacity of 10.5 percent. The chromium creates a passive and self renewing chromium oxide film around the
steel at atomic level and this prevents the iron from rusting.
The material we know as stainless steel (also commonly referred to as “Inox” or “Rostfrei”) is such a common feature of 21st century living that there can be few of us who have not seen or handled articles made from it. But how many of us really know what stainless steel is?
What is stainless steel?
‘Stainless’ is a term coined early in the development of these steels for cutlery applications. It was adopted as a generic name for these steels and now covers a wide range of steel types and grades for corrosion or oxidation resistant applications.
Stainless steels are iron alloys with a minimum of 10.5% chromium. Other alloying elements are added to enhance their structure and properties such as formability, strength and cryogenic toughness.
These include metals such as:
Non-metal additions are also made, the main ones being:
the main requirement for stainless steels is that they should be corrosion resistant for a specified application or environment. The selection of a particular “type” and “grade” of stainless steel must initially meet the corrosion resistance requirements. Additional mechanical or physical properties may also need to be considered to achieve the overall service performance requirements.
The History of Stainless Steel
A few corrosion-resistant iron artifacts survive from antiquity. A famous (and very large) example is the Iron Pillar of Delhi, erected by order of Kumara Gupta I around the year AD 400. However, unlike stainless steel, these artifacts owe their durability not to chromium, but to their high phosphorus content, which together with favorable local weather conditions promotes the formation of a solid protective passivation layer of iron oxides and phosphates, rather than the non-protective, cracked rust layer that develops on most ironwork.
The corrosion resistance of iron-chromium alloys was first recognized in 1821 by the French metallurgist Pierre Berthier, who noted their resistance against attack by some acids and suggested their use in cutlery. However, the metallurgists of the 19th century were unable to produce the combination of low carbon and high chromium found in most modern stainless steels, and the high-chromium alloys they could produce were too brittle to be of practical interest.
This situation changed in the late 1890s, when Hans Goldschmidt of Germany developed an aluminothermic (thermite) process for producing carbon-free chromium. In the years 19041911, several researchers, particularly Leon Guillet of France, prepared alloys that would today be considered stainless steel. In 1911, Philip Monnartz of Germany reported on the relationship between the chromium content and corrosion resistance of these alloys.
Harry Brearley of the Brown-Firth research laboratory in Sheffield, England is most commonly credited as the “inventor” of stainless
steel. In 1913, while seeking an erosion-resistant alloy for gun barrels, he discovered and subsequently industrialized a martensitic stainless steel alloy. However, similar industrial developments were taking place contemporaneously at the Krupp Iron Works in Germany, where Eduard Maurer and Benno Strauss were developing an austenitic alloy (21% chromium, 7% nickel), and in the United States, where Christian Dantsizen and Frederick Becket were industrializing ferritic stainless.