Tuesday 23 September 2008

type stainless stels1

Types of Stainless Steels:

In addition to chromium, nickel, molybdenum, titanium, niobium and other elements may also be added to stainless steels in varying quantities to produce a range of stainless steel grades, each with different properties. There are a number of grades to chose from, but all stainless steels can be divided into five basic categories:

Image79Austenitic

Image79Ferritic

Image79Martensitic

Image79Duplex

Image79Precipitation hardening

These are named according to the microstructure inherent in each steel group (a function of the primary alloying elements). Austenitic and ferritic grades account for approximately 95% of stainless steel applications.

Image79Austenitic Stainless Steels:

When nickel is added to stainless steel in sufficient amounts the crystal structure changes to "austenite". The basic composition of austenitic stainless steels is 18% chromium and 8% nickel. Austenitic grades are the most commonly used stainless steels accounting for more than 70% of production (type 304 is the most commonly specified grade by far).

Basic properties of Austenitic Steels:

Image79excellent corrosion resistance in organic acid, industrial and marine environments.

Image79excellent weldability (all processes)

Image79excellent formability, fabricability and ductility

Image79excellent cleanability, and hygiene characteristics

Image79good high and excellent low temperature properties (high toughness at all temperatures)

Image79non magnetic (if annealed)

Image79hardenable by cold work only (These alloys are not hardenable by heat treatment)

Common uses of Austenitic Steels:

Image79computer floppy disk shutters (304)

Image79computer keyboard key springs (301)

Image79kitchen sinks (304D)

Image79food processing equipment

Image79architectural applications

Image79chemical plant and equipment

302

304

316

Carbon

0.15% max..

0.08% max

0.08% max

Chromium

17.00 to 19.00%

18.00 to 20.00%

16.00 to 18.00%

Manganese

2.0% max

2.0% max.

2.0% max.

Silicon

1.0% max.

1.0% max.

1.0% max.

Nickel

8.00 to 10.00%

8.00 to 10.50%

10.00 to 14.00%

Molybdenum

----

----

2.00 to 3.00%

Table 1. Chemical Composition of Austenitic steels

302

304

316

Tensile strength (Ksi)

90 -185

84-185

84-185

Yield strength (Ksi)

40-140

42-140

42-140

Elongation in 2 inches (Annealed)

50 %

55 %

50 %

Modulus of elasticity (psi)

28 x 10 6

28 x 10 6

28 x 10 6

Hardness (Annealed)

RB 75 - RB90

RB 75 - RB90

RB 75 - RB90

Hardness (Cold work)

RC 25 - RC39

RC 25 - RC39

RC 25 - RC39

Table 2. Mechanical properties of Austenitic Stainless steels

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