What is Stainless steel?


	Stainless steel is an alloy steel of Fe with over 11% of chromium. It has corrosion resistance by passive coat on the surface of the steel and lasts beautiful conditions longer.
	Corrosion resistance of stainless steel is improved as chromium content rate becomes higher and passive coat becomes better.

Fig.1 Classification of Stainless steel

To keep the properties such as corrosion resistance, mechanical property, workability and heat resistance, stainless steel is applied to a variety of field, e.g. tableware, kitchen tool, construction material, parts for machinery, medical appliances, chemical equipment and aircraft.

	Stainless steel does not always have advanced corrosion resistance under corrosive condition at all times. And depend on heat treatment, cold working and surface condition, the properties of stainless steel would be greatly different even same grade.
	Machining/working on stainless steel may have great difficulties comparing to ordinary grade of steel. Each grade of stainless steel has suitable machining/working and heat treatment by application.
	You need to carefully consider suitable properties of stainless steel according to the condition of application.

	Typical grade is SUS403, which is one of 13Cr series.
	As a property of martensitic stainless steel, it is hardened by rapid cooling or air cooling from high temperature. Wide range of hardness, strength, flatting and toughness are achieved by tempering at appropriate temperature.
	When it is heated in air, oxidation resistance is good. Strength is kept up to 500℃ and it can be applied for heat resistant condition.
	It has strong corrosion resistance to acid solution such as nitric acid at normal temperature.
	It is eroded by reducing solution such as Sulfric acid and hydrochloric acid. Corrosion resistance becomes lower if content of carbon, sulfur and phosphorus is higher.
	At welding, hardening crack has to be cared due to transformation distortion and hardenability.
	It has strong magnetic property under the condition of annealing, quenching and tempering.

	Typical grades are SUS430 of 17Cr series.
	Features of ferritic stainless steel are as follows; It is scarcely hardened by quenching from high temperature.
	In oxidizing solution and the air, corrosion resistance of the ferritic stainless steel is superior to that of 13 Cr.
	Grains are not able to be refined by heat treatment, attention should be paid not to be coarsened at high temperature.
	It is easy for cold working because most of areas are soft ferritic structure in any status. It shows magnetic property.

	Typical grade is SUS304, which is one of 18Cr-8Ni series.
	As a property of austenitic stainless steel, it is not be hardened by rapid cooling from high temperature, but it is able to be hardened by cold working.
	It has superior corrosion resistance so that it is applied to parts avoiding rust and chemical equipment.
	It has good oxidation resistance. It is used as heat resistant steel due to its high strength in high temperature.
	Grains are not able to be refined by heat treatment, attention should be paid not to be over heated.
	Most of stainless steel is non-magnetic after solution heat treatment of rapid cooling from high temperature, but it is hardened and slightly become magnetic by cold working.
	Superior corrosion resistance is achieved by solution heat treatment.
	In the case of SUS304, intergranular corrosion tends to be occurred by heating over 600℃. SUS304L and SUS316L are suitable for such application.
	We recommend using SUS321 and SUS347.

Typical grades are SUS329J1.

Features of duplex stainless steel are high strength and corrosion resistance by combination of austenitic and ferritic structures.

.It has superior properties of stress resistance, corrosion cracking, pitting corrosion resistance, and grain-boundary corrosion resistance.

Typical grades are SUS630 and SUS631.

Feature of precipitation hardening stainless steel is high hardness. It is achieved by age hardening after solution treatment.

Strength is the best of all stainless steel. Corrosion resistance is superior to martensitic and ferritic stainless steel, though it is inferior to austenitic.