Chromium, chemical symbol Cr, atomic number 24, belongs to group VIB in the periodic table. The name of the element is derived from the Greek word meaning 'color', because all chromium compounds have color. Chromium is a steel-gray metal and is the hardest metal in nature. Chromium is the 17th most abundant element in the earth's crust at 0.01%. Natural chromium in its free state is extremely rare and is found mainly in chrome lead ore.

Chromium (Cr)

1, chromium can improve the strength and hardness of steel.

2, chromium can improve the high temperature mechanical properties of steel.

3, so that the steel has good corrosion resistance and oxidation resistance.

4, reduce the critical cooling rate of steel, improve the hardenability of steel.

5, to prevent graphitization Disadvantages: ① chromium is a significant increase in the brittle transition temperature of steel; ② chromium can promote the tempering of steel brittleness.

The effect of chromium on steel organization chromium is a carbide-forming element. In metallic materials, it can generate metal compounds such as Cr3C with carbon, and this metal compound has high strength and hardness. When it is diffusely distributed in a granular form on the metal matrix, it can greatly improve the strength, toughness, and wear resistance of the material.2 Chromium hinders the growth of austenitic grains In addition to manganese, all alloying elements can hinder the growth of austenitic grains during heating. In the material, it is formed with carbon the presence of carbides Cr3C, when the temperature of heating is not too high, this undissolved carbide can hinder the growth of austenite grains.

Influence of chromium on steel organization

Chromium is a carbide-forming element. In metallic materials, it can generate metal compounds such as Cr3C with carbon, which has high strength and hardness. When it is diffusely distributed in granular form on the metal matrix, it can greatly improve the strength, toughness, and wear resistance of the material.

Chromium hinders austenite grain growth

All alloying elements except manganese impede the growth of austenitic grains during heating. In the material, it is formed with the presence of carbon carbide Cr3C, when the heating temperature is not too high, this undissolved carbide can hinder the growth of austenite grain. This makes it easy to obtain fine austenite grains, thus obtaining a fine organization after cooling. We know that fine grains have higher strength, better plasticity and toughness than coarse grains.

Chromium improves hardenability

Materials are quenched with the purpose of obtaining more martensitic organization. In chromium-containing alloys, when quenched, chromium shifts the C-curve (austenitic isothermal transformation curve) to the right and a double C-curve occurs. This reduces the minimum cooling rate for obtaining martensitic organization, which is then easier to obtain, thus reducing the amount of residual austenite. In the tempering will be able to obtain more tempering organization, and this tempering organization performance is excellent is what we need.

Chromium improves the tempering stability of steel

When tempering, chromium slows down the diffusion of iron and carbon atoms, thus making the quenched steel tempering martensite is not easy to decompose, and slows down the formation and aggregation of carbon. Tempered at the same temperature, the strength and hardness of alloy steel than the same carbon content of carbon steel for high. Conversely, when tempered to the same hardness, alloy steel due to high tempering temperature, tempering time is long, and has a high plasticity, toughness, and its internal stress is small.

The role of chromium in stainless steel

Chromium is the most basic alloying element in stainless steel, and its content is generally above 13%. Its main role is to improve the corrosion resistance of steel. In the oxidizing medium, there is to make the steel surface to form a layer of solid and dense chromium oxide, so that the steel is protected. Chromium dissolved in steel can significantly improve the electrode potential of steel, reducing the formation of electrochemical corrosion due to different electrode potential. Chromium can also cooperate with nickel, can form a single-phase austenitic organization and give the steel good corrosion resistance, good toughness and strength. This shows that the role of chromium in stainless steel is particularly important. In summary, the role of chromium in metal materials is very important. We fully realize this, reasonable chromium applied to a variety of materials, the performance of the material can play a good role in improving.