Stainless Steel

Stainless Steel is usually involved when we talk about metallic materials, stainless steel plays an important role in the metal world, and has wide applications, this is because it possesses unique characteristic and properties to meet the requirement, whether you are an engineer, producer, or user, you should learn more about this material, in the article, let us show you to a comprehensive understanding of STAINLESS STEEL.

What is stainless steel?

Stainless steel is iron alloys with a minimum of 10.5% chromium content, which is a essential element to form a passive film on the surface to avoid rusting, usually containing 10 to 30 percent chromium with low carbon content, other alloying elements are added to enhance it structure and properties, The main elements include as following:

  • Nickel
  • Chromium
  • Manganese
  • Molybdenum
  • Silicon
  • Titanium
  • Copper
  • Carbon
  • Nitrogen

Addition of different chemical elements can enable to impact and alter stainless steel characteristics, such as formability, ductility and cryogenic toughness properties, and improve performance in strength and corrosion resistance.

Reading more stainless steel chemical composition.

How Stainless Steel is made

Stainless steel has a long history, manufacturing technology is varied to get high quality material, and reduce cost.

According to grades and raw material to use different refine technologies, main raw material include scrap, iron melt, Chromium ore, Nickel ore alloy and so on。

Different grades have different raw material with proper temperature, firstly, melting relative material into furnace to form molten and fluid mixture, secondly, reducing carbon content to proper composition improve steel properties, as we discuss above, AOD and VOD are for removing carbon content process, thirdly, balancing relative alloys with exact temperature finally create stainless steel.

Stainless steel classifications and grades

Stainless steels are classified several families, Austenitic stainless steelFerritic stainless steelMartensitic Stainless SteelDuplex stainless steel and Precipitation-hardening stainless steel, there are more than 100 grades of stainless steel, each of them has unique chemical composition and properties.

Stainless Steel Classifications

Nickel and Chromium chemical composition percentage in Austenitic, Ferritic, Martensitic, Duplex and Precipitation-hardening steels。

Austenitic stainless steels (Fe-Cr-Mn and Fe-Cr-Ni)

Austenitic stainless steels are the largest group and have the most used alloys, which contain 16 to 26 percent chromium and up to 35 percent nickel content, common Austenitic Stainless Steels are listed below。

  • 201
  • 202
  • 205
  • 904L (super Austenitic)
  • 254SMO (super Austenitic)

304 is a typical 18-8 Chromium Nickel grade, as well as basic grade of Austenitic stainless steels, 304L is low carbon content 304, 316L is low carbon and addition of molybdenum element grade.

304 – Basic grade

310S30815 – Increasing high temperature resistance

316317904L6Mo – Increasing corrosion resistance

316L

304L321 – Weld stabilized grades

308L347 – Welding corrosion grades

303 – Free machining grade

302HQ – Low work hardening rate for cold heading

Austenitic steel grades have good comprehensive performance, good weldability and formability and excellent corrosion resistance, altering and improving the performance after adding different alloy elements such as molybdenum, titanium, copper。

They are non-magnetic in the solution-annealed condition, not hardenable by heat treatment.

Ferritic stainless steels (Fe-Cr)

Ferritic stainless steels contain chromium content of 10.5-18%, adding chromium element improve the corrosion resistance, toughness and weldability, ferritic grades are magnetic due to their ferritic microstructure, because of their low carbon content (less than 0.2 percent), they are not hardenable by heat treatment, they have bad mechanical properties and process performance compared to Austenitic stainless steels.

430 – Basic grade

444 – Higher corrosion resisting weldable grade

409Cr12 – Utility grades with increasing toughness

430F澳门凯发娱乐 – Free machining grade

Common grades in Ferritic stainless steels group include 430, 409, 439, 436, 441, 444。

Martensitic Stainless Steels (Fe-Cr-C)

Martensitic stainless steels can be improved mechanical properties by heat treatment, chromium alloy is key element containing 12–14% content, which is lower than that of Ferritic stainless steels,

Generally, they also contain 0.1 to 1 percent carbon, 0.2 to 1 percent molybdenum and, less than 2percent nickel, they have high carbon content.

澳门凯发娱乐Tt is also magnetic.

410 – Basic grade

420 – Higher hardness grade

431 – Higher corrosion resistant and toughness grade

440A, 440B, 440C – Increasing hardness after heat treatment

Common Martensitic Stainless Steel grades have 403, 410, 410S, 414, 414L, 416, 418, 420, 422, 431, 440 and 500 series.

Duplex stainless steels (Fe-Cr-Ni-(Mo)-N)

Duplex stainless steels are combined of Ferrite and Austenite structure, usually contain 21 to 27 percent chromium, 1.35 to 8 percent nickel, 0.05 to 3 percent copper, and 0.05 to 5 percent molybdenum.

Duplex grades have Ferrite and Austenite stainless steels benefits, high strength and toughness, excellent corrosion resistance and good weldability they are magnetic.

Common duplex grades have 2101, 2304, 2205 and 2507.

Precipitation-hardening stainless steels (Fe-Cr-Ni (Mo-Cu-Al-Nb)- N)

This group grades contain both chromium and nickel, with a high tensile strength. Matrix for the Austenitic or Martensitic crystal structure

Commonly used grade is PH 17-4, also known as 630 grade, with 17% of chromium, 4% of nickel, 4% of copper and 0。3% of niobium。

澳门凯发娱乐Precipitation hardening stainless steel adding strengthening elements of different composition and percentage, the process of precipitation in different composition and percentage of carbide, nitride, carbon nitride and intermetallic compounds, a kind of high strength stainless steel can increase the strength of the steel and maintain sufficient toughness。

Stainless steel alloys are also designated by 200 series, 300 series, 400 series, 500 series, 600 series and Nickel grades

Stainless Steel Properties

Corrosion Resistance

Stainless steel has good corrosion resistance, that is the biggest difference between it and carbon steel.

澳门凯发娱乐Chromium element existed and other addition of alloys increase corrosion resistance, These elements react with oxygen from water and air to form a very thin, stable film on the surface to prevent rust and corrosion.

Here are main corrosion attacks:

  • Pitting corrosion (approx 23%)
  • Intergranular corrosion (approx 9%)
  • Stress corrosion cracking (approx 49%)
  • Crevice corrosion
  • General corrosion

Increasing Chromium content and Molybdenum content can improve corrosion resistance, in general, Austenitic Stainless Steels is better than Ferritic Stainless Steels, Duplex Stainless Steels perform best, in the different environment, such as air, sea water, acid, high temperature condition, thus selecting right stainless steel grade is very important to use in these conditions。

Thought stainless steels have excellent corrosion resistance, and not easy to rust, unfortunately, the corrosion may be occur under certain condition, such as strong acid, strong alkali, strong oxidizing solution, that will result in rust and stain.

Physical Properties

Stainless steel physical properties include thermal properties, electromagnetic properties and other properties.

  • Modulus of Elasticity
  • Thermal Expansion
  • Thermal Conductivity
  • Density
  • Magnetic Conductivity
  • Melting Point
  • Specific heat
Materials Modulus of Elasticity Gpa Thermal Expansion Coefficient 10-6 °K-1 Thermal Conductivity W m-1 °K-1 Ferro Magnetism Density Kg/dm³
Cr-Ni Austenitics2101815No7.8
Cr-Mn Austenitics2101715No7.8
Cr Ferritics2201123Yes7.7
Cr-Ni (Mo)-N Duplex2101415Intermediate7.8
Cr-C Martensitics2151130Yes7.7

Mechanical Properties

  • Yield Strength (MPa)
  • Ultimate Tensile Strength (MPa)
  • Elongation (%)
  • Young’s Modulus (MPa)
  • Impact resistance
  • Fire Resistance
  • Creep resistance
  • Fatigue resistance
  • Properties at cryogenic temperatures
  • Properties at elevated temperatures
Common Name UNS No. Yield Strength
MPa (ksi)
Tensile Strength
MPa (ksi)
Elongation(%) Hardness, Max
Brinell Rockwell B
201 S20100 260
(38)
515
(75)
40 95
304 S30400 205
(30)
515
(75)
40 217 95
304L S30403 170
(25)
515
(75)
40 201 92
316 S31600 205
(30)
515
(75)
40 183 88
321 S32100 205
(30)
515
(75)
40 217 95
347 S34700 205
(30)
515
(75)
40 201 92
309S S30908 205
(30)
515
(75)
40 217 95
310S S31008 205
(30)
515
(75)
40 217 95
316L S31603 170
(25)
515
(75)
40 217 95
317L S31703 205
(30)
515
(75)
35 217 95
317LMN S31726 240
(35)
550
(80)
40 223 96
904L N08904 220
(31)
490
(71)
35 90
S31254 310
(45)
655
(95)
35 223 96
N08367 310
(45)
655
(95)
30 241
409 S40910
S40920
S40930
170
(25)
380
(55)
20 179 88
405 S40500 170
(25)
415
(60)
20 179 88
430 S43000 205
(30)
450
(65)
22
>.050” thick
183 89
434 S43400 240
(35)
450
(65)
22 89
436 S43600 240
(35)
450
(65)
22 89
439 S43035 205
(30)
415
(60)
22 183 89
444 S44400 205
(30)
415
(60)
20 217 96
26-3-3 S44660 450
(65)
585
(85)
18 241 100
S44735 415
(60)
550
(80)
18 255 25 HRC
410 S41000

Annealed

205
(30)
450
(65)
20 217 96
420 S42035

Annealed

690
(100) maximum
15 217 96
2304 S32304 400
(58)
600
(87)
25 290 32 HRC
2205 S31803 450
(65)
620
(90)
25 293 31 HRC
2205 S32205 450
(65)
655
(95)
25 293 31 HRC
2507 S32750 550
(80)
795
(116)
15 310 32 HRC
S32760 550
(80)
750
(108)
25 270

Stainless Steel finishes

There is a oxide film on at the surface to protect surface to avoid damaging and rusting, various finishes can be provided. Mill finishes and mechanical polish are common surface finishes, typical finishes are listed below

NO.1Hot rolled, annealed, pickled, dull non reflective finish
NO.2DCold rolled, annealed, pickled, smooth non reflective finish
NO.2BCold rolled, annealed, pickled, smooth reflective finish, the most wide used finish
BASmooth, bright, reflective finish by annealing in the controlled atmosphere furnace
NO.3non reflective finish, light polishing using grinding belt, 100 – 120 grit
NO.4Reflective dull polishing, brushed finish, using 120 – 320 grit belt after light grinding
NO.6Cold rolled, dull satin finish by tampico brushing a No.4 finish
NO.7High reflective finish, by a finely ground surface, 320 grit is buffed
NO.8High reflective, bright polishing, smooth surface, mirror finish
TRCold worked to obtain a specified properties

Stainless Steel Forms

Stainless steel has high strength and excellent corrosion resistance, and it is easy to weld and clean, safe and durable material, with various surface finishes for option, it can be recycled and reused.

Stainless steel is a ideal material to design and fabricate in flat and long products, such as platesheetstripbarwirepipetube.

These shapes are likely formed by Hot Rolling or Cold Rolling process, other process many be required depending on requirement and applications.

Stainless Steel applications

Industrial Applications

Chemical Processing, Pharmceutical and Petrochemical Industries, stainless steels are used for these corrosive and high temperature environments, including stainless steel equipment and parts.

Structure

Architecture, building and construction

Food and Beverage

Stainless steel is ideal material use in food and beverage industries because of safe and easy to clean features, not only in the process, also in storage.

Automotive

It is used for car body structure, exhaust system and other parts, high strength and perfect appearance.

Jewelry

Stainless steel have bright surface, even mirror surface, after concern processing, it can be finished for decorative use, like Jewelry, ring, watch etc.

3D printing

Stainless steels are ideal material to resist corrosion, and keep good mechanical properties, 316L type is a common grade to use in 3D print industries.