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What is Stainless Steel? All One Needs to Know About Stainless Steel


What is Stainless Steel?

Stainless steel is the generic name for a number of different steels used primarily for their resistance to corrosion. Stainless steels are produced by adding at least 11% chromium to steel to produce a thin passive protective layer of Cr2Q3, which promotes corrosion resistance. This is improved by further increasing the chromium content. 

What are the Types of Stainless Steel?

Four basic groups of stainless steel are available:

  1. Ferritic Stainless Steels: - This group contains between 16 and 30 per cent chromium, with a maximum of 0.1 per cent carbon. These materials can be welded with a preheat of 150°C and the use of the 25 per cent chromium and 20 per cent nickel core wire electrode. Sometimes combination welds are made, with the final layers being completed with electrodes of even higher chromium content (up to 30 per cent), in order to give the surface an extremely high resistance to corrosion. A post heat at 730°C should be performed immediately after welding to prevent brittleness.
  2. Martensitic Stainless Steels: - Martensitic grades contain similar amounts of chromium, but more carbon than ferritics and possibly other additions such as molybdenum to increase hardenability and strength. Can be heat treated. This group contains from 11.5 to 14 per cent chromium and from 0.2 to 0.4 per cent carbon. Such steels are difficult to weld because they can form the very hard martensitic structure regardless of the cooling rate. They are known as air-hardening steels. They can be welded by preheating to around 350°C and using a 25 per cent chromium and 20 per cent nickel flux coated electrode. A post-heat of 750°C usually ensures acceptable ductility.
  3. Austenitic Stainless Steels: - Austenitic grades contain between 17-25% Cr, 7-20% nickel and in some instances molybdenum. They are face-centred cubic in structure, nonmagnetic and can be formed and welded more easily than ferritics. Austenite (gamma) phase field is extended to room temperature. Most corrosion resistant.
  4. The Basic Austenitic Grades:
  • T302
  • T303
  • T304
  • T304L
  • T310S
  • T316
  • T316L
  • T321
  • T347
  1. Typical composition:

18% chromium, 8% nickel, 0.15% carbon.

Remainder: Fe (S. & P. kept below 0.045%), Ti or Nb.

 

  1. Effect of elements on properties:

The nickel is added to give toughness and may be increased to 11.5% to prevent work hardening (for rivets and fastenings). The chromium is added to give corrosion resistance. In addition titanium or niobium is often added to prevent inter-granular corrosion (weld decay) in the following proportions: Ti – 5 x C content, Nb = 10 x C content.

Approximate melting temperature

1420°C to 1395°C

Hardness

170 Hv (water quench from 1000°C)

Tensile strength

Approx. 620 N/mm²

Yield point

Approx. 280 N/mm²

Mass

7.92 g/cm³ at +20°C

Coefficient of linear expansion

0.02           °C

 

  1. How to identify:

This iron-based alloy has a characteristic silver lustre imparted to it by the amount of chromium and nickel. It is the chromium which combines with oxygen and rapidly forms a very thin oxide which is continuous and stable and impervious to further attack by the atmosphere. The thickness of this oxide film increases with the degree of polish to give a mirror finish. These steels give a dull red spark when touched on a grinding wheel.

  1. Corrosion:

The corrosion resistance is excellent in most environments but solutions of nitric, hydrofluoric and sulphuric acid will attack 18/8 stainless steel. These acid solutions are used to remove the oxide scale which result from strongly heating the material in air. The term used for this treatment is pickling.

Types of Corrosion:

  • Inter Crystalline Corrosion (Weld Decay) -
  • Pitting Corrosion
  • Stress Corrosion
  1. Duplex Stainless Steels: - Duplex stainless steels were developed to provide the strength of ferritics, but with improved corrosion resistance. They contain about 22% Cr, 5% Ni, and possibly molybdenum. Ferrite + Austenite
  2. Precipitation-Hardening (PH) Stainless Steels: – Ultra high strength due to precipitation hardening.

 

Applications of Stainless Steel

Stainless steels are used extensively in food and drink production and the chemical and energy industries; martensitics are used for cutlery and other cutting tool manufacture.

Properties of Stainless Steel

  • Aesthetic qualities: it can be polished to a satin or mirror finish;
  • "Dry corrosion" occurs to steel at higher temperatures where it oxidises or scales up. Stainless steel is far more resistant to this than ordinary carbon steel and grades such as 310 (25% chromium 20% nickel) were specifically developed for use at high temperatures;
  • Non-contamination of the liquids stainless comes into contact with, because there is no coating to break down and dissolve;
  • Weight savings; as thinner sections and more innovative design structures can be used, with cost savings on foundations and platform weights;
  • Many anti-corrosion coatings are fire hazards or the materials themselves have a low melting point.

 

Advantages of Stainless Steel

  • Does not react or influence other materials.
  • Used extensively in the food/catering divisions.
  • Used widely in the medical world. E.g. Plates and screws to repair bones.
  • Aesthetic Qualities: It can be polished to a satin or mirror finish.
  • Dry Corrosion: Stainless steel is far more resistant to this than ordinary carbon steel.
  • Grades such as 310 (25% chromium 20% nickel) were specifically developed for use at high temperatures.
  • Non-contamination: Because there is no coating to break down and dissolve there is no contamination of liquids that stainless steel comes in contact with.
  • Weight: As thinner sections and more innovative design structures can be used, giving cost savings on foundations and platform weights.

What are the Various Grades of Stainless Steel?

Austenitic Stainless Steels

301

High strength for roll formed structural components

304, 304L, 304H

Standard 18/8 grades

310, 310S, 310H

High temperature resistant grades

316, 316L, 316H

Improved resistance to pitting corrosion in chloride environments

321, 321H, 347

Stabilized grades for heavy section welding and high temperature applications

904L

High resistance to general corrosion, pitting and stress corrosion cracking

Ferritic Stainless Steels

409

Automotive exhaust grade – weld stabilized

430, 430F

Resistant to mildly corrosive environments

439

Resistant to mildly corrosive environments – weld stabilized

444

A ferritic alternative to grade 316 / 316L – weld stabilized

Duplex Stainless Steels

2101

Lean duplex – economical alternative to 304 and 316

2304

Duplex alternative to grade 316

2205

Standard duplex stainless steel - high resistance to pitting and stress corrosion

2507

Super duplex with very high resistance to pitting and stress corrosion

Martensitic Stainless Steels

410

Standard martensitic grade for low-duty hardened applications

416

Free-machining bar grade

420

Higher hardness martensitic grade for cutlery, cutting tools and dies

431

High hardness and toughness grade, primarily for shafting

440A, 440B, 440C

Very high hardness grades used in cutting tools

Precipitation Hardening Stainless Steel

630

(17-4PH) High strength shafting grade


What are the Maximum Operating Temperatures of Stainless Steel Grades?

Stainless steels have good strength and good resistance to corrosion and oxidation at elevated temperatures. Stainless steels are used at temperatures up to 1700° F for 304 and 316 and up to 2000 F for the high temperature stainless grade 309(S) and up to 2100° F for 310(S).

Influence of Alloying Elements on the Properties of Stainless Steel

 

Element

Effect on Stainless Steel

Chromium

Forms a passive film with oxygen that prevent the further diffusion of oxygen into the surface

 

Composition needs to contain at least 10.5% to be a stainless steel

Nickel

Increases ductility and toughness. Increase corrosion resistance to acids

 

Additon creates non-magnetic structure

Molybdenum

Increases pitting and crevice corrosin resistance. Increase resistance to chlorides

Copper

Increase corrosion resistance to sulfuric acid

Manganese

Substitute for nickel (200 series)

Titanium/Niobium

Ties up carbon and prevents inter-granular corrosion in welded zone of ferritic grades

Nitrogen

Increase strength and corrosion resistance in austenitic and duplex grades

Silicon

Improves resistance to high temperature scaling

Sulfur

Usually kept low excet for "free-machining" grades

Carbon

Usually kept low.  Used in martensitic grades to increase strength and hardness

 

Comparitive International Grades of Stainless Steel

British

French

German

Italian

Japanese

Swedish

USA

304S21

Z12CN17.08

1.431

X12CrNi 17 07

SUS301

14 23 31

301

304S31

 

 

 

SUS302

14 23 32

302

304S15304S16

Z8CN18.09

1.4301

X5CrNi 18 10

SUS301

14 23 33

304

304S11

Z2CN18.10

1.4306

X2CrNi 18 11

SUS304L

14 23 52

304L

305S19

Z8CN18.12

 

X8CrNi 18 12

SUS305

 

305

309S24

Z15CN24.13

 

X16CrNi 23 14

SUS309

 

309

310S24

Z12CN25.20

1.4845

Z22CrNi 25 20

SUS310S

14 23 61

310

315S16

 

 

 

 

14 23 40

 

316S31316S33

Z6CND17.11

1.44011.4436

X8CrNiMo 17 13

SUS316

14 23 4314 23 47

316

316S11316S13

Z2CND17.12

1.44041.4435

X2CrNiMo 17 12

SUS316L

14 23 5314 23 48

316L

317S12

Z2CND19.15

1.4435

X2CrNiMo 18 16

SUS317L

14 23 67

317L

317S16

 

1.4436

 

SUS317

14 23 66

317

320S31320S33

Z8CND17.12

1.45711.4573

 

 

14 23 50

 

321S31

Z6CNT18.12

1.4541

X6CrNiTi 18 11

SUS321

14 23 37

321

347S31

Z6CNNb18.11

1.4558

X6CrNiNb 18 11X8CrNiNb 18 11

SUS347

14 23 38

347

403S17

Z6C13

1.4

X6Cr13

SUS403

14 23 01

403

405S17

Z6CA13

1.4002

Z6CrA1 13

SUS405

 

405

409S19

 

1.4512

 

 

 

409

430S17

Z8C17

1.4016

X8Cr 17

SUS430

14 23 20

430

434S17

Z8CD17.01

1.4113

X8CrMo 17

SUS434

14 23 25

434

410S21

Z12C13

1.40061.4024

X12Cr 13

SUS410

13 23 02

410

410S45

Z30C13

 

 

 

 

 

 


 

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Established in 1975, the Metallica Metals Group has its operations spread across major cities in India. We are a pioneer in the stainless steel pipes, carbon steel pipes and alloy steel pipes manufacturing and processing industry. Our products are exported to over 70 countries across the world, while in India we have supplies to even the remote areas. With over 250 tons of sale in stainless steel and carbon steel pipes every day, Metallica has emerged as a prominent vendor for many buyers in India and Overseas.

We procure significant quantities of materials from Indian carbon steel pipe mills and overseas manufacturers of stainless steel pipes. Given our extensive network for sourcing the best quality goods at most competitive prices, we are a preferred seller of steel products for various turnkey projects in India and Worldwide.

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With a team of over 50 people dedicated for deliveries and response to our esteemed customers, we can offer the best service. At the same time, we are also committed to offer best quality products and most competitive prices to our customers. We are professional manufacturer and supplier of stainless steel seamless pipes, with exports all across the globe.

As one of the biggest supplier of A106 seamless steel pipes in India, Metallica carries inventory of over 15,000 tons in its warehouses in Mumbai, Maharashtra India. We sell our ASTM A106 seamless pipe products throughout India, and to international clients. We can supply our ASTM A106 seamless steel pipe products not only in industry-standard lengths and diameters, but also in custom length and diameters. Our range of carbon steel A106 seamless pipes encompasses size range from 1/4 NPS to 24 NPS in thickness upto SCH XXS.

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