what metals are in stainless steel?

All stainless steel must contain chromium, with a minimum content of 10.5% (some standards require more than 13%).

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I. Core Elements

Chromium (Cr)

Content: All stainless steel must contain chromium, with a minimum content of 10.5% (some standards require more than 13%).

Function: Forms a dense Cr₂O₃ oxide film with oxygen to prevent further corrosion; Increase the electrode potential of ferrite and enhance its corrosion resistance. The higher the chromium content, the stronger the oxidation resistance and acid resistance (for example, ferritic stainless steel can contain up to 30% chromium).

Nickel (Ni)

Content: Austenitic stainless steel contains approximately 8% to 12% nickel (such as 304 and 316 steels).

Function: Stabilize the austenite structure, enhance toughness, weldability and resistance to electrochemical corrosion. Nickel can also improve high-temperature performance, but it is costly. In some steel grades, manganese and nitrogen are used as substitutes.

Ii. Auxiliary alloying elements

Molybdenum (Mo)

It enhances the corrosion resistance to chlorides and reducing media (such as sulfuric acid and hydrochloric acid), which is commonly found in acid-resistant steels like 316.

Titanium (Ti) and niobium (Nb)

Strong carbide-forming elements, preferently combine with carbon, prevent chromium carbide precipitation at the grain boundaries from causing chromium depletion (intergranular corrosion), and are often used in welded stainless steels (such as 321 and 347 steels).

Manganese (Mn) and nitrogen (N

As a substitute for nickel, austenitic stainless steels used to reduce costs (such as the 200 series) stabilize the austenite structure by expanding the γ zone.

Copper (Cu)

To enhance corrosion resistance in non-oxidizing acids such as sulfuric acid and phosphoric acid, some steel grades are used in chemical equipment.

Iii. Other Elements

Carbon (C) : The content is usually less than 0.08% (low-carbon steel such as 304L), and high-carbon steel (such as martensitic stainless steel 3Cr13) is used in scenarios with high hardness requirements, but it will reduce corrosion resistance.

Silicon (Si), aluminium (Al) : Enhances oxidation resistance and is used in high-temperature environments (such as gas turbine components).

Tungsten (W), cobalt (Co) : They are used in special stainless steels to enhance high-temperature strength and wear resistance.

Iv. Typical Stainless Steel Types and Composition Differences

Typical application scenarios of the main components of the type (excluding iron)

Austenitic stainless steel Cr (18% - 20%), Ni (8% - 10%), Mo (optional) for food equipment and chemical pipelines

Ferritic stainless steel Cr (15% - 30%), a small amount of Mo, Ti, nitric acid resistant equipment, architectural decoration

Martensitic stainless steel Cr (12% - 18%), C (0.1% - 1.2%) cutting tools, steam turbine blades

Duplex stainless steel Cr (22% - 25%), Ni (4% - 7%), Mo (3%), Marine engineering, petrochemical reaction towers

Sum up

The metallic composition of stainless steel is centered on chromium, with elements such as nickel, molybdenum and titanium adjusted according to performance requirements. For instance, austenitic stainless steel relies on nickel to maintain structural stability, while ferritic stainless steel achieves corrosion resistance through a high chromium content. In special environments, elements such as tungsten and cobalt may be added to meet extreme performance requirements.