About Stainless Steel
Advantages of Stainless Steel / Chemical & physical properties / Uses

CHEMICAL & PHYSICAL PROPERTIES

There are three basic classes of stainless steels, so designated for the metallurgical conditions of the steels :

Class I : Martensitic - Heat treatable, Straight Chromium

This class is so named for the man, Martens, who first examined metals microscopically. It is referred to as, “martensitic” because of its acicular or needle like microstructure in the hardened condition. Its chief alloying agent is chromium, found in amounts from 11.5 to 18.0%. It contains from 0.08 to 1.10% carbon. It is magnetic and responds excellently to heat treating, producing a hard and strong stainless steel.

Class II : Ferritic - Non - Heat treatable. Straight Chromium

This class name is derived from the latin word “ferum” meaning iron. It is so named because its micro-structure is very similar to that of low-carbon iron. It also utilizes chromium as its chief alloying agent, being found in amounts from 14.0 to 27.0%. It has a very low carbon content of 0.8 to 2.0%. Due to its high chromium and low carbon content, ferritic alloys do not generally harden in high temperatures. It is magnetic alloy, and is soft and ductile.

Class III : Austenitic - Non- Heat treatable, Chromium- Nickel

The austenitic class derivesits name from Roberts-Austen who first observed its characteristics banded grain structure. its chief alloys are: chromium, found in amounts from 16.0 to 26.0% and an appreciable nickel content from 6.0 to 22.0%.

This alloy cannot be heat treated, but responds excellently to cold working. It is generally non-magnetic. In the annealed condition, this alloy is tough, strong, and extremely ductile. Austenite itself is soft and tough and remains ductile even at extreme low temperatures.

Extra- low-Carbon (ELC) Grades

These alloys contain only approximately .03% carbon which is low enough to permit elimination of carbide precipitation during welding. These graded are not generally recommended for high-temperature utilization.

American Iron & Steel Institute (AISI)
Designation System

200’s - Chromium - Nickel - Manganese Stainless Steel
This series is austenitic, non - heat treatable and non-magnetic.

300’s - Chromium - Nickel Stainless Steel
This series is austenitic, non - heat treatable and non-magnetic.

400’s - Chromium Stainless Steel
This series is martensitic, heat treatable and magnetic. It also includes types which are ferritic, non-heat treatable, and magnetic.

“L” at the end of the series number indicates low-carbon content ( Not exceeding .03%) Example: 304L

“F” at the end of the series number indicates the addition of a “free-machining” element. (Example:440F)

“S” at the end of 309 or 310 type indicate carbon not exceeding .08%

“Ti ” at the end of the series number denotes addition of titanium. ( Example : 316 Ti)

Chemical Composition
Type	Chrome	Nickel	Carbon	Magnesium	Silicon	Molybdenum	Titanium	Nitrogen
201	16-18%	3.5-5.5%	.15 max	5.5-7.5%	1% max			.25 max
301	16-18%	6-8%	.15 max	2% max	1% max
302	17-19%	8-10%	.15 max	2% max	1% max
304 / 304l	18-20%	8-10.5%	.08 max	2% max	.75% max
316 / 316l	16-18%	10-14%	.08 max	2% max	.75% max	2-3%
409	10.5-11.75%		.08 max	1% max	1% max		6 x C min; .75 max
410	11.5-13.5%		.15 max	1% max	1% max
430	16-18%		.12 max	1% max	1% max

Mechanical Properties
Type	Yield (min)	Tensile (min)	Elongation (min)	Hardness (max)
201	38,000	95,000	40%	95 (Rb)
301	30,000	90,000	40%	95 (Rb)
302	30,000	75,000	40%	92 (Rb)
304 / 304l	30,000	75,000	40%	92 (Rb)
316 / 316l	30,000	75,000	40%	95 (Rb)
409	30,000	55,000	20%	80 (Rb)
410	30,000	65,000	20%	95 (Rb)
430	30,000	65,000	22%	88 (Rb)