Stainless Steel Grades - Cnc machining

Stainless Steel is the name given to a group of steel alloys which contain more than 12% Chromium, and is divided into the following stainless steel grades:

1. Austenitic Grades
2. Martensitic Grades
3. Ferritic Grades

Chromium is known for its high affinity to oxygen and forms a stable oxide film (known as a passive oxide layer) on the surface of the stainless steel. This layer forms instantaneously in normal atmospheres, is self healing and rebuilds itself once it has been removed. This film is the reason why stainless steel is such a high resistance to corrosion.

Austenitic Grades

This group of stainless steels contain:

• 17% - 25% Chromium
• 8% - 20% Nickel
• As well as a number of additional elements that help manufacturers achieve the required properties.

Fully annealed conditions of this grade deliver a range of physical and mechanical properties. Mechanical properties can further be enhanced through cold working techniques.

Welding of these stainless steel grades can be done, with the low carbon content resulting in fewer problems during welding than seen with the Martensitic and Ferritic grades. These stainless steels are also normally non-magnetic, however they will become slightly magnetic when cold working techniques have been used.

The Basis Austenitic Grades:

1. T302
2. T303
3. T304
4. T304L
5. T310S
6. T316
7. T316L
8. T321
9. T347

Martensitic Grades

These stainless steel grades contain:

• 12% - 14% Chromium
• 0.08% - 2.00% Carbon

Because of Martensitic Grades’ high carbon content, these stainless steels respond well to heat treatment, used for various mechanical strengths, such as hardness.

The high carbon content also means that extreme care is required during welding processes. Note that, when Martensitic Grades are heat treated, the results are a useful combination of mechanical properties and resistance to corrosion.

Martensitic Grades:

1. T409
2. T410
3. T420
4. T431

Ferritic Grades

Ferritic grades contain:

• A minimum of 17% Chromium
• 0.08% - 2.0% Carbon

An increased Chromium content leads to an increased resistance to corrosion at higher temperatures, but has a lack of mechanical properties as these grades cannot undergo heat treatment.

Magnetic, welding this group of stainless steels should be done with the utmost care.

Ferritic Grades:

1. T430