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:
Austenitic
Ferritic
Martensitic
Duplex
Precipitation 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.
Austenitic 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:
excellent corrosion resistance in organic acid, industrial and marine environments.
excellent weldability (all processes)
excellent formability, fabricability and ductility
excellent cleanability, and hygiene characteristics
good high and excellent low temperature properties (high toughness at all temperatures)
non magnetic (if annealed)
hardenable by cold work only (These alloys are not hardenable by heat treatment)
Common uses of Austenitic Steels:
computer floppy disk shutters (304)
computer keyboard key springs (301)
kitchen sinks (304D)
food processing equipment
architectural applications
chemical 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
No comments:
Post a Comment