Stainless Steels

An Introduction

Stainless Steels are famed for their corrosion resistance properties. To qualify as a Stainless Steel, the alloy must contain a minimum of 12% Chromium to ensure a passive layer of Chromium Oxide - the source, in addition to Nickel, of Stainless Steel's corrosion resistance. They are divided into three sepearate sub-categories, which you may find listed below, designated by their microstructures and alloying components. Their breadth of usage is breath taking: from the everyday of a kitchen splash back guard or polished bathroom surface, to pipes used in the massively corrosive chemical industry, Stainless Steel is more than just the material your cutlery is made from.

Ferritic Stainless Steel

Composition

0.01-0.20 Carbon, 11%-30% chromium,  along with other alloying elements, such as molybdenum, aluminium and titanium.

Common Shapes

Ferritic Stainless Steels are commonly available in

  • Sheets and Plates

  • Welded & Seamless Tubes and Pipes 

  • Structural profiles

  • Wire

  • Rods

  • Bars

  • Fittings

(Not all alloys or tempers available in all shapes)

Characteristics

  • Ferro-magnetic

  • Usually kept as-is, not heat treated or work hardened

  • Good ductility

  • Good formability

  • Resistance to localised corrosion, pitting, and stress-corrosion cracking

Uses

  • 409 is commonly used in automotive exhausts

  • Food handling equipment

  • Automotive trim

  • Heat exchangers

  • Marine applications

  • Piping for corrosive media

Weldability

Welding of Ferritic Stainless Steels is not generally recommended due to grain coarsening, leading to embrittling intermetallic phases when subjected to the higher temperatures used in welding. If they are to be welded, post-joining annealing is a must. 

Machinability

New grades of Ferritic Stainless Steels have been developed to make them more amenable to machining. 430F is one such, if not the leader, in free machining Ferritic Stainless Steels

Commonly Used Alloys (SAE)

405 | 409 | 429 | 430 | 434 | 436 | 439 | 442

444 | 446

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Austenitic Stainless Steel

Composition

0.03-0.25 Carbon, 2.0-10.0 Manganese, 1.00-3.0 Silicon, 16-26 Chromium, 1-37.0 Nickel.

Common Shapes

Austenitic Stainless Steels are commonly available in

  • Sheets and Plates

  • Welded & Seamless Tubes and Pipes 

  • Structural profiles

  • Rods

  • Bars

  • Shapes

  • Castings

(Not all alloys or tempers available in all shapes)

Characteristics

  • Non-magnetic

  • Non-heat-treatable

  • Over 70% of Stainless Steels produced are Austenitic.

  • Resistant to brittleness at low temperatures

  • Strength of 205-275 MPa

  • Good high temperature strength and corrosion resistance

  • Excellent cryogenic properties

Uses

  • Cookware

  • Cutlery

  • Kitchen equipment (304 & 306)

  • Medical instruments

  • Structural and Architectural applications

Weldability

Austenitic Stainless Steels are the most weldable of all Stainless Steels. Alloy 310 is the most weldable of Austenitic Stainless Steels. 

Machinability

Austenitic Stainless Steels are easily machined, formed and pressed into shape, due to their good ductility. Alloy 303 is the free-machining alloy of the range.

Commonly Used Alloys (SAE)

201 | 202 | 205 | 301 | 302 | 303 | 304 | 305 308 | 309 | 310 | 314 | 316 | 317 | 321 | 330 347 | 348

Martensitic Stainless Steel

Composition

 11-17% Chromium, less than 0.4% Nickel and up to 1.2% Carbon

Common Shapes

Martensitic Stainless Steels are commonly available in

  • Sheets and Plates

  • Welded & Seamless Tubes and Pipes 

  • Shapes

  • Wire

  • Rods

  • Bars

  • Fittings

(Not all alloys or tempers available in all shapes)

Characteristics

  • Ferro-magnetic

  • Heat treatable up to 1900 Mpa yield strength

  • Addition of Chromium and Molybdenum may be added to increase corrosion resistance and mechanical properties respectively.

Uses

  • Steam turbines

  • Jet engines

  • Super heating used in power plants

  • Cutlery

  • Gears

  • Medical instruments

Weldability

Welding is not the best option for joining Martensitic stainless steels. They are commonly joined via connecting flanged fittings.

Machinability

Martensitic Stainless Steels have the best machining properties of all the Stainless Steels.

Commonly Used Alloys (SAE)

403 | 410 | 414 | 416 | 416Se | 420 | 420F  422 | 431 | 440A | 440B 440C

Integ Metals // Materials // Steel // Stainless Steel
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