What Role Do C, Si, Mn, And P Play in U Steel Material List?

What role do C, Si, Mn, and P play in u steel material list?

The content of more or less of an element will cause changes in material properties and uses, so we have compiled this piece of knowledge for your reference:

1. C element

The C element is the main alloying element in steel materials. C exists in the form of interstitial solid solution or carbide in steel materials.

Generally, according to the C element content, steel can be divided into low carbon steel (C content less than 0.25%), medium carbon steel (C content 0.25%-0.6%), and high carbon steel (C content greater than 0.6%). When the C content is less than or equal to 100ppm, it can generally be subdivided into ultra-low carbon steel.

Generally speaking, in steel, the higher the C content, the higher the strength and hardness of the steel, but the plasticity and toughness will also decrease; conversely, the lower the C content, the higher the plasticity and toughness of the steel, and its strength. , the hardness will also decrease accordingly.

The C element is an austenite stabilizing element. Steel types with structural strengthening usually have higher carbon content, such as DP steel, TRIP steel, CP steel, QP steel, etc.

Steel grades for deep drawing and ultra-deep drawing purposes are usually produced with ultra-low carbon components.

2. Si element

Si mainly exists as a reducing agent and deoxidizer in the steelmaking process. When the content is greater than 0.5%, it can be considered to be added as an alloying element, which can significantly improve the yield strength and yield ratio of the steel. When Si exceeds 3%, it will significantly reduce the steel's yield strength. It improves the plasticity and toughness of steel and increases the ductile-brittle transition temperature of steel.

When the Si content is high, red iron scale will easily appear on the surface of the hot-rolled strip, making it difficult to clean with subsequent pickling. And higher Si content will improve the corrosion resistance of steel and reduce the coating performance of steel.

3. Mn element

Mn is infinitely miscible with Fe and mainly exists in the form of substitutional solid solution in steel materials. It is one of the main strengthening elements in steel materials. Adding Mn can improve the strength and hardness of steel, and improving the "hardenability" of steel is one of the important strengthening elements in high-strength steel.

Mn can form high-melting-point MnS with S in steel smelting, thereby weakening and destroying the adverse effects of S.

4. S element

Generally speaking, S is a harmful element in steel. Steel with a high sulfur content is prone to brittle when subjected to pressure processing at high temperatures, which is usually called thermal embrittlement.

The higher the sulfur content, the more serious the hot embrittlement phenomenon, so the sulfur content in steel must be controlled. General high-grade high-quality steel: S＜0.02%-0.03%; high-quality steel: S＜0.03%-0.045%; ordinary steel: S＜0.055%-0.7% or less.

Sulfur can reduce the strength of steel, so it is beneficial to the cutting of steel, but it is rarely used except for easy-cut steel.

4. P element

P element is generally a harmful element in steel. P can significantly reduce the plasticity and toughness of steel, especially at low temperatures.

At the same time, P is the element with the strongest effect in strengthening ferrite. Therefore, some steel types use the method of adding a small amount of P to improve the strength of the material. The combined use of P and copper further improves the atmospheric corrosion resistance of steel.

Common brands using P as strengthening element are B170P1, HC180Y, B180P2, etc.

5. Al element

Generally speaking, Al is a beneficial element in steel materials and is mainly used as a deoxidizer. At present, most low-carbon steel products use Al as a deoxidizer.

As a strong oxidant, Al can generate highly finely divided and ultra-microscopic oxides, which can prevent the grain growth of steel when it is heated and refine the grains.

As an alloying element, it contributes to the nitriding of steel, thereby improving the thermal stability of steel. AlN itself has high stability when heated.

Generally, the Al content in low carbon steel is 0.02-0.1%.

6. Nb, Ti, V elements

Nb, Ti, and V in steel mainly refine the grains by forming fine and dispersed carbides. At the same time, the carbides will strongly hinder dislocation slip when the steel is deformed, thereby greatly improving the yield strength of the material.

Generally, micro-alloying elements such as Nb, Ti, and V are added to low-alloy high-strength steel. The characteristics of this type of steel are that it can obtain higher yield under low carbon equivalent, high yield-to-strength ratio, relatively stable forming, small rebound, and average hole expansion rate. High, but formability is average.

7. Cr, Mo elements that improve hardenability

Cr is a medium carbide-forming element. Among all various carbides, chromium carbide is the smallest. It can be evenly distributed in the steel volume, so it has high strength, hardness, yield point and high wear resistance. Because it can refine the structure and evenly distribute it, it has good plasticity and toughness.

The addition of Mo element can refine the grains and improve the tempering stability of martensite. Combined with Cr and Ni, it can greatly improve the hardenability and toughness.