What is Steel ?
In life, we often encounter Steel and Iron two words, Iron typically refers to unprocessed raw material, carbon content greater than 2.11%, low hardness but brittle, such as pig iron, cast iron. Steel is a processed material widely used across industries, the carbon content of 0.02% -2.11% between the better toughness and strength, including three categories of carbon steel, alloy steel,special performance steels(Stainless steel).
Steel -Carbon Steel
Carbon steel is a steel with iron and carbon as its main components, and is one of the most common types of steel with high strength, good processability and excellent cost performance.
According to the carbon content, carbon steel can be divided into three categories to suit different applications. The higher the carbon content, the greater the hardness and strength, but the plasticity is reduced and the fatigue life is shortened.
| Type | Carbon Content | Characteristics | Applications |
|---|---|---|---|
| Low Carbon Steel（Mild Steel） | ≤ 0.25% | Low strength, good ductility and toughness, easy welding and cold work | Rebars, pipelines, cold-rolled steel sheets |
| Medium Carbon Steel | 0.25%-0.6% | Higher strength and hardness but lower toughness, suitable for heat treatment | Mechanical parts, shafts, gears |
| High Carbon Steel | 0.6%-2.11% | High hardness, excellent wear resistance, but brittle and hard to weld | Tools, springs, cutting implements |
You can find the corresponding grade numbers for the three types of carbon steel in the table below.
| Type | Standard | Grade | Carbon Content |
|---|---|---|---|
| Low Carbon Steel | China (GB) | Q195, Q215, Q235, Q275 | ≤ 0.25% |
| USA (ASTM) | A36, A283 | 0.26%-0.29% | |
| Europe (EN) | S235JR, S235J0, S275JR | ≤ 0.26% | |
| Medium Carbon Steel | China (GB) | 45, 50, 60 | 0.25%-0.6% |
| USA (ASTM) | A1050, A1045 | 0.50%-0.60% | |
| Europe (EN) | C45, C50E, C60E | 0.50%-0.60% | |
| High Carbon Steel | China (GB) | T8, T10, 65Mn, 70 | 0.6%-2.11% |
| USA (ASTM) | A1095, A1080 | 0.90%-1.05% | |
| Europe (EN) | C60E, C70E, C80 | 0.60%-1.00% |
Carbon Steel is divided according to quality
According to the different content of sulfur (S) and phosphorus (P), carbon steel can be divided into the following major composition grades:
- Ordinary carbon steel (S ≤ 0.055%, P ≤ 0.045%)
- High-quality carbon steel (S ≤ 0.040%, P ≤ 0.040%)
- High quality carbon steel (S ≤ 0.030%, P ≤ 0.035%)
Sulfur(S) can lead to steel “thermal embrittlement”, that is, at high temperatures the brittleness of steel increases, reducing its plasticity and toughness. This phenomenon is particularly obvious in the welding process, the welded steel is prone to cracks, affecting the safety of the structure.
Phosphorus(P) causes “cold embrittlement” of steel, i.e. a significant increase in the brittleness of steel at low temperatures, leading to a reduction in impact toughness at low temperatures. On the contrary, phosphorus can improve the machinability of steel to a certain extent, which reflects the two sides of the analysis of things, the advantages and disadvantages can be transformed into each other according to the actual situation.At Safewellfab, we specialize in analyzing material properties to deliver customized solutions that meet specific application requirements.
In China usually carbon steel generally choose Q235B. which according to the mechanical properties and chemical composition is divided into Q195, Q215, Q235, Q225, Q275 (the number indicates the minimum yield strength Mpa), the individual steel grades according to the quality level of ABCD four levels.
D is the best, AB level steel according to the degree of deoxidation sub boiling steel (F), semi-sedated steel (B), C level for the sedated steel (Z), D level for the special sedated steel (TZ), low alloy steel is generally sedated steel, so the steel grades do not indicate the way of deoxidation.
Safewellfab is leveling Q235b Steel Coils
Steel-Alloy Steel
The steel formed by adding one or more alloying elements to carbon steel is called alloy steel, and its properties can be significantly optimized by adjusting the type and content of alloying elements.
| Element | Purpose |
|---|---|
| Chromium (Cr) | Enhances hardness, wear resistance, and corrosion resistance; widely used in stainless steel. |
| Nickel (Ni) | Improves strength and toughness, enhances corrosion resistance, particularly suitable for low-temperature environments. |
| Molybdenum (Mo) | Enhances high-temperature performance, reduces brittleness, and improves creep resistance. |
| Manganese (Mn) | Increases strength and hardness, improves hardenability and wear resistance. |
| Silicon (Si) | Improves strength, elastic limit, and oxidation resistance; commonly used in spring steel and electrical steel. |
| Vanadium (V) | Enhances impact resistance and wear resistance, refines grain structure, and improves strength. |
| Titanium (Ti) | Improves corrosion resistance, refines grain structure, prevents grain boundary precipitation, and enhances weldability. |
For example, the more widely used grade Q345 in China, and the A572 Grade 50 in the U.S., improves strength, toughness, and tensile properties through the addition of appropriate amounts of manganese and silicon, while maintaining good weldability and workability.
Alloy steels according to elemental content
- Low-alloyed steel (total alloying elements < 5%)
- Medium-alloyed steels (total alloying elements 5-8%)
- High alloy steels (total alloying elements > 8%)
- Engineering structural steels: usually low and medium carbon steels, including low alloy high-strength steels, such as Q355, Q460, etc.
Tool steels, structural steels and special performance steels
- Tool steel usually refers to the steel used in the manufacture of tools, molds, cutting tools, etc., requiring high hardness, high wear resistance, impact resistance and good thermal stability
- Structural steel is used for building and engineering structures of steel, with good mechanical properties, plasticity and welding properties
- Special performance steel with special physical and chemical properties, stainless steel, heat-resistant steel, wear-resistant steel, etc.
The previously mentioned alloy steels and carbon steels both can be used as tool steels and structural steels, which is a flexible choice.
Examples of structural steel: 35CrMo (alloy steel), Q235 (ordinary carbon steel)
Examples of tool steels: high-speed steel (HSS), T1 (tungsten steel)
Steel Names Explained in China
1.General structural steels are designated using the pinyin letter “Q”, which represents the yield point. The designation is then formed by combining the yield strength value (MPa), the quality grade specified in Table 1 (A, B, C, D, E), and the deoxidation method symbols (F, b, Z, TZ) in sequence. For example, the designations for carbon structural steel are: Q235AF, Q235BZ; and for low-alloy high-strength structural steel: Q345C, Q345D.
Among these, Q235 and Q345 are the most typical engineering steels, widely produced, used in large volumes, and applicable across various fields. These two grades are commonly found in almost all countries worldwide.
2.In the designation of carbon structural steel, the symbols for killed steel (“Z”) and special killed steel (“TZ”) can be omitted. For instance, Q235 steel with quality grades C and D should be designated as Q235CZ and Q235DTZ, but they can be simplified to Q235C and Q235D. For low-alloy high-strength structural steel, while killed and special killed steels exist, the deoxidation method symbols are not added at the end of the designation.
3.The designation for alloy structural steel consists of Arabic numerals and chemical element symbols. The first two digits indicate the average carbon content in hundredths of a percent (ten-thousandths), while the subsequent element symbols denote the alloying elements in the steel. The numbers following the element symbols represent their respective percentages. If an alloy element content is less than 1.5%, the percentage is not indicated. However, if the average content exceeds 1.5%, 2.5%, or 3.5%, it is marked with numbers such as 2, 3, or 4, respectively.
For example:
- 40Cr indicates an alloy structural steel with an average carbon content of 0.40% and a chromium content of less than 1.5%.
- If it is a high-quality steel grade, the letter “A” is added to the designation, such as 23CrNi3A.
Alloy structural steels encompass a wide variety of types with significant differences in properties, resulting in diverse application areas.
To see more naming conventions for steel grades, you can visit this webpage：https://mp.weixin.qq.com/s/dCFXyNMwqt0bieQ3qR9bZg
