Features of stainless steel
Stainless steel is extremely resistant to corrosion compared to other steels. However, it can be eroded or rusted under certain environments and usages so it is important to use it correctly. Stainless steel is a type of alloy and is normally steel with added chrome or nickel. One property of stainless steel is that the chrome reacts with the oxygen in the air and creates a passive film on the surface making it difficult to rust. Further, it is good for mechanical work since it has higher tensile strength and is better at stretching than steel. Therefore, it does not need plating or coating and is used in many products including outdoors and humid areas, and in machinery that handles pharmaceuticals.
Varieties of stainless steel
Categorization by chemical composition Chrome type stainless steel and chrome/nickel stainless steel
Stainless steel is mostly made up of steel and the main components are chrome and nickel. Chrome stainless steel contains only chrome and chrome/nickel stainless steel contains both chrome and nickel. Representative examples are: 13 chrome stainless steel containing 13% chrome, 18 chrome stainless steel containing 18% chrome, and 18 chrome 8 nickel, which is generally used for SUS304. As well as chrome and nickel, impurities such as carbon, phosphorous and sulfur, and additives such as molybdenum, copper, niobium and titanium greatly affect the features of the stainless steel. A variety of products can be made.
Categorization according to metallography martensite, ferrite, austenite
Stainless steel can be categorized by metallographic structure as well as chemical components. The organization of metals differs according to the structure of their crystals. These are fixed by the components and temperature and the typical varieties of metallographic structure are martensite, ferrite and austenite. Martensite is a rapidly cooled version of austenite, leaving deformations in the crystals and making it hard. Chrome stainless steel can have either martensite structure of ferrite structure. Chrome/nickel stainless steal is generally austenite and is called austenite stainless steel.

Main examples of stainless steel
Category	Steel type	General organization
Austenite	SUS 201	17Cr-4.5Ni-6Mn-N
	SUS202	18Cr-5Ni-8Mn-N
	SUS301	17Cr-7Ni
	SUS302	18Cr-8Ni-0.1C
	SUS303	18Cr-8Ni-High S
	SUS304	18Cr-8Ni
	SUS304L	18Cr-9Ni-Low C
	SUS316	18Cr-12Ni-2.5Mo
	SUS316L	18Cr-12Ni-2.5Mo-Low C
Ferrite	SUS430	18Cr
	SUS444	19Cr-2Mo-Ti,Nb,Zr-extremely low(C,N)
Martensite	SUS410	13Cr

 

 

There are many varieties of stainless steel surface finishing. Hot rolling is called No.1 and cold rolling is called No.2D. Thin rolling to increase the brilliance is No.2B. The D stands for dull, the B for bright. Grinding is divided according to the roughness of the grinding belt. The larger the count of the grinding belt, the finer the finish.

Main surface finishes of steel
Name	Finishing type	Finishing method
No,1	Silver-white matte	After hot rolling, heat treated, pickled or treatment based on this
No,2D	Dull grey frosted finish (dull finish)	After cold rolling, heat treated, pickled or gently cold-rolled with a frosted roller
No,2B	Smoother than 2D with slight brilliance	Cold-rolled 2D finish to give the right level of brilliance with a light roller
BA	Finish close to the brilliance of a mirror	After cold rolling, bright heat treatment, and light cold-roll to increase the brilliance
No,3	Brilliant and slightly rough finish	100-120 Abrasive grain grinding belt applied to No.2D or No. 2B finish
NO,4	Brilliant and fine	150-180 Abrasive grain grinding belt applied to No.2D
#400	Brilliance close to BA	No.2B finish ground by a 400 buffer
HL （Hairline）	Finish with long continuous grinding	Appropriate grain grinding belt applied long and continuously like a hair across the finish (normally 150-240 abrasive grain)