Grades of Stainless Steel and Their Properties

How and why is stainless steel graded?In general, while stainless steel can resist many types of corrosion, all grades are likely to be corroded by chlorides, with those grades which are high in chromium, molybdenum and nickel exhibiting the most resistance. Similarly, while some steel is entirely non-magnetic, other types retain their magnetic attraction.Properties and uses of 200 series 200 series stainless steel is non magnetic, and made up of approximately 17% chromium, 4% nickel and 7% manganese. Less common than the 300 series grade, to which it is most similar, it is most often used for knives and cooking utensils. It retains strength at high temperatures, and is less prone to attack from corrosion than the 300 series. Once corrosion has begun, however, it often breaks down rapidly. While it can withstand immersion in environments such as seawater, it cannot do so indefinitely, with some corrosion beginning within months.Properies and uses of 300 series 300 series stainless steel is also non magnetic, and makes up over 70% of total stainless steel production. As such it can be found in use across a range of applications, including domestic architecture and construction of planes, trains and automobiles. Consisting of approximately 18% chromium and 8% nickel, it is also often used in kitchen utensils and catering equipment, and is similar in its corrosion resisting properties to the 200 series. If used in environments without high chloride content, it is extremely proficient at resisting corrosion, but where chloride levels are high, performance will rapidly decline.Properties and uses of 400 series Unlike the 200 and 300 series, 400 series stainless steel is magnetic. Containing approximately 11% chromium and 1% manganese, this series responds well to hardening through heat, but has poor resistance to corrosion. Unless protected, 400 series is not practical for any kind of seawater application. It is most commonly used in applications which require heat resistance, such as exhaust pipes, heat exchangers, combustion burners and so on. It should not be used in low temperature environments, as its strength drops rapidly in this situation.Properties and uses of 600 series In a similar fashion to the 400 series, 600 series stainless steel can be heat treated to extremely high strength levels (leading to the common reference to this series as 'precipitation hardening'), exhibiting tensile strength of up to double the 300 series. It also retains its magnetism. Vulnerable to chloride environments, 600 series is also vulnerable to stress cracking when corroded. Most 600 series can only remain in seawater without corrosion for a few days. Similarly to the 400 series, this type should not be used in low temperatures.