Everything You Need To Know About Stainless Steel

Stainless Steel Fabrication

The casting of stainless steel involves molten metal being poured into a cast cavity, to which it conforms and the cast retains the cavity shape when cooled. Rolling of stainless steel sees the raw billets pass through a series of precise pinch rollers, to reduce their thickness and shape the steel into sheets or other forms. This process can be performed hot or cold, to produce a variety of final materials of diverse strengths and crystalline structures.
The forging of stainless steel requires it to be heated and then shaped by hammering or pressing it into the desired form. Machining stainless steel enables it to be cut and shaped using various machines, such as lathes and mills.

316L stainless steel pipe

Stainless Steel Composition:

Stainless steel primarily consists of iron (Fe), chromium (Cr), and varying amounts of other elements such as nickel (Ni), manganese (Mn), molybdenum (Mo), and sometimes nitrogen (N). Chromium is the essential element that gives stainless steel its corrosion-resistant properties by forming a thin, invisible oxide layer on the surface, known as the passive layer.

Stainless Steel Types:

1. Austenitic Stainless Steel
Austenitic stainless steel is the most common classification, offering high corrosion resistance, ductility, and toughness. It is alloyed with a minimum of 16% chromium and 6% nickel, with other metals/non-metals such as manganese, nitrogen, and sometimes molybdenum. These steels can handle salt exposure, although some brown staining is possible.

2. Martensitic Stainless Steel
This type of stainless steel is generally stronger and harder but suffers lower corrosion resistance. They contain 12–18% chromium and may also include nickel or molybdenum.

3. Ferritic Stainless Steel
Ferritic stainless steels can have a broad range of chromium content (10.5–27%) and use higher carbon content steels than austenitic types. This group is less ductile and tougher, but still has good corrosion resistance and is often used for automotive applications. These steels react less well to salt and are not generally used in marine environments.

4. Duplex Stainless Steel
Duplex stainless steels combine austenitic and ferritic stainless steels, with a carefully tuned proportion of both types of crystalline structure. They offer higher strength combined with great corrosion resistance and are often used in chemical processing and oil and gas applications.

5. Precipitation-Hardening Stainless Steel
Precipitation-hardening stainless steel is achieved by the formation of small particles, precipitated within the material, that increase its strength and hardness by inducing lattice stress. This can commonly deliver 3–4 times the strength of basic austenitic stainless steel.

Stainless Steel Grades:

Stainless steel grades are classified based on their chemical composition and properties, with common grades including 304 (austenitic), 316 (austenitic with higher corrosion resistance), 430 (ferritic), and 410 (martensitic), among others.
Each grade is designed to meet specific requirements for corrosion resistance, strength, and temperature resistance, depending on the intended application.

Table 1: Austenitic Stainless Steel

SAE	201	202	205	254	301	302	302B	303	303Se	304	304L
UNS equivalent	S20100	S20200	S20500	S31254	S30100	S30200	S30215	S30300	S30323	S30400	S30403
SAE	304Cu	304N	305	308	309	309S	310	310S	314	316	316L
UNS equivalent	S30430	S30451	S30500	S30800	S30900	S30908	S31000	S31008	S31400	S31600	S31603
SAE	316F	316N	317	317L	321	329	330	347	348	384	-
UNS equivalent	S31620	S31651	S31700	S31703	S32100	S32900	N08330	S34700	S34800	S38400	-

Table 2: Ferritic Stainless Steel

SAE	405	409	429	430	430F	430FSe	434	436	442	446
UNS equivalent	S40500	S40900	S42900	S43000	S43020	S43023	S43400	S43600	S44200	S44600

Stainless Steel Properties:

Generally highly resistant to corrosion.
Strong and durable-resistant to bending, cracking, and breaking.
Non-porous and non-reactive-easy to clean and autoclave.
Can achieve a range of quality finishes.
Can withstand high temperatures without degrading.
Suitable for use at cryogenic temperatures.
Sustainable materials, in that they are 100% recyclable without loss or degradation.

Table 3: Physical Properties of Stainless Steel

Property	Value/Notes
Density	7.75 x 103 to 8.05 x 103 kg/m3
Ductility	Typical annealed austenitic stainless steel delivers 70% elongation at break
Malleability	Highly malleable when annealed, some grades work harden very quickly and lose malleability
Tensile strength (general grades)	500–750 MPa
Yield strength (general grades)	500–650 MPa
Tensile strength (precipitation hardened)	850–1,700 MPa
Yield strength (precipitation hardened)	520–1,500 MPa
Melting point	1,370–1,420 °C
Thermal conductivity is poor (typical)	15 W/(mK)
Electrical conductivity is poor (typical)	1.33 m/Ωmm²
Magnetic permeability – austenitics (HIGHLY variable by grade and work hardening)	1.003 to 1.005 when measured at magnetizing forces of 200 oersteds (16k A/m)
Magnetic permeability – ferritics (HIGHLY variable by grade and work hardening)	Up to 6.0 for annealed 304 grade, when measured at magnetizing forces of 200 oersteds (16k A/m)

Stainless Steel Forms:

Stainless Steel Pipes, Tubes, Fittings, Flanges, Forgings, Fasteners, Plates, Sheets, Strips, Coils, Bars, Round Rods, Etc.

What Is the Color of Stainless Steel?

Stainless steels are naturally a uniform silver in color, although various companies offer proprietary "stainless coloring" processes that are analogous to anodizing. A range of bronze to golden colors can be achieved by heating stainless steel in an oven to around 700 °C in an oxygen atmosphere. This will result in the formation of iron oxides in the surface film, which will stain with shades of yellow, gold, and brown depending on temperature and time. Stainless steel will also develop hues of blue when heated to 250 °C in air, also by an oxidation process.

Stainless Steel: Composition, Types, Grades, Properties