Differences Between Carbon Steel and Stainless Steel

Carbon Steel

It mainly refers to steel whose mechanical properties depend on the carbon content in the steel and generally does not contain a large amount of alloying elements, sometimes also called mild carbon steel or plain carbon steel.

Also known as plain carbon steel, carbon steel is an iron-carbon alloy with a carbon content (WC) of less than 2%.

In addition to carbon, carbon steel generally contains small amounts of silicon, manganese, sulfur and phosphorus.

According to the application, carbon steel can be divided into three categories: carbon structural steel, carbon tool steel and free-cutting structural steel. Carbon structural steel can be further divided into two types: construction structural steel and machine manufacturing structural steel.

According to the smelting method, it can be classified into open-hearth steel, converter steel and electric furnace steel.

According to the deoxidation method, it can be divided into rimmed steel (F), killed steel (Z), semi-killed steel (b) and special killed steel (TZ).

According to the carbon content, carbon steel can be categorized into low carbon steel (WC ≤ 0.25%), medium carbon steel (WC 0.25%-0.6%) and high carbon steel (WC > 0.6%).

According to the phosphorus and sulfur content, plain carbon steel can be divided into ordinary plain carbon steel (with relatively high phosphorus and sulfur), high-quality carbon steel (with relatively low phosphorus and sulfur), high-grade high-quality carbon steel (with lower phosphorus and sulfur) and ultra-high-quality carbon steel.

Generally, the higher the carbon content in carbon steel, the greater its hardness and the higher its strength, but the lower its ductility.

Stainless Steel

Stainless and acid-resistant steel is referred to as stainless steel for short, which consists of two major parts: stainless steel and acid-resistant steel. In short, steel that can resist atmospheric corrosion is called stainless steel, while steel that can resist chemical medium corrosion is called acid-resistant steel. Stainless steel is a high alloy steel with more than 60% iron as the matrix, added with chromium, nickel, molybdenum and other alloying elements.

When the chromium content in the steel exceeds 12%, the steel is not easy to corrode and rust in air and dilute nitric acid. The reason is that chromium can form a very dense chromium oxide film on the steel surface, which effectively protects the steel from corrosion. The chromium content in stainless steel generally exceeds 14%, but stainless steel is not absolutely rust-proof. In coastal areas or some places with serious air pollution, when the chloride ion content in the air is high, some rust spots may appear on the surface of stainless steel exposed to the atmosphere, but these rust spots are only limited to the surface and will not erode the internal matrix of stainless steel.

Generally speaking, steel with a chromium content (Wcr) greater than 12% has the characteristics of stainless steel. According to the microstructure after heat treatment, stainless steel can be further divided into five major categories: ferritic stainless steel, martensitic stainless steel, austenitic stainless steel, austenitic-ferritic stainless steel and precipitation hardening stainless steel.

Stainless steel is usually classified by matrix structure into the following types:

1. Ferritic stainless steel: containing 12% to 30% chromium. Its corrosion resistance, toughness and weldability improve with the increase of chromium content, and its chloride stress corrosion resistance is better than other types of stainless steel.

2. Austenitic stainless steel: containing more than 18% chromium, as well as about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. It has comprehensive performance and can resist corrosion by various media.

3. Austenitic-ferritic duplex stainless steel: combining the advantages of austenitic and ferritic stainless steel, and having superplasticity.

4. Martensitic stainless steel: featuring high strength, but relatively poor ductility and weldability.