1. Classification of alloy steels
Alloy steels are essentially carbon steels enhanced with additional alloying elements such as Si, Mn, W, V, Ti, Cr, Ni, Mo, etc.
These elements improve various properties of steel, such as strength, toughness, hardenability and weldability. Alloy steels are often categorized based on alloying element content.
Furthermore, alloy steels are specifically employed in different industries and are therefore also commonly classified according to their application.
Classification by league content
- Low alloy steel: Total alloy content less than 5%
- Medium alloy steel: Total alloy content between 5% to 10%
- High alloy steel: Total alloy content above 10%
Classification by use
- Alloy Structural Steel: Common low-alloy steel; carburizing alloy steel, quenched and tempered alloy steel, spring alloy steel; ball bearing steel.
- Alloy tool steel: Alloy cutting steel (including low alloy cutting steel, high speed steel); alloy mold steel (including cold work mold steel, hot work mold steel); steel gauge.
- Special Performance Steel: Stainless steel, heat-resistant steel, abrasion-resistant steel, etc.
2. Alloy steel numbering
1) High-strength, low-alloy structural steel
Your note is organized in the sequence of the Chinese Pinyin letter (Q) representing the yield point, yield limit value and quality grade symbol (A, B, C, D, E).
For example, Q390A means high-strength low-alloy structural steel with yield strength σs = 390N/mm2, quality grade A.
2) Alloy structural steel
Your note is made up of “two digits + element symbol + digit”.
The first two digits represent the ten thousandths of the average carbon content by mass in the steel, the element symbol indicates the alloying elements contained in the steel, and the number after the element symbol represents the hundredths of the average content of that element by mass. .
If the average mass fraction of the alloying element is less than 1.5%, only the element will be marked with no value. When the average mass fraction is ≥1.5%, ≥2.5%, ≥3.5%, etc., the numbers 2, 3, 4, etc., are marked after the alloying element accordingly.
For example, 40Cr, where the average mass fraction of carbon Wc=0.4%, and the average mass fraction of chromium WCr <1.5%. If it is high quality steel, “A” is added at the end of the grade, such as 38CrMoAlA steel, which is a high quality alloy structural steel.
3) Bearing steel
The letter “G” (the first Chinese Pinyin letter of the word “rolling”) is added before the note, and the number after indicates the thousandths of the chromium content by mass, while the carbon content is not indicated.
For example, GCr15 steel is a bearing steel with an average chromium mass fraction WCr = 1.5%.
If other alloying elements are present in chromium bearing steel, they will be expressed in the same way as general alloy structural steel. All bearing steels are high quality steels, but the grade does not end with “A”.
4) Alloy tool steel
The numbering method for this type of steel is similar to that for alloy structural steel, except that when Wc < 1%, a single digit is used to represent the thousandths of the mass carbon content. When the mass fraction of carbon is ≥1%, it is not indicated.
For example, in Cr12MoV steel, the average mass fraction of carbon is Wc = 1.45% ~ 1.70%, so it is not indicated; the average mass fraction of Cr is 12%, and the mass fractions of Mo and V are both less than 1.5%.
However, high-speed tool steels are exceptions, and the average carbon mass fraction is not indicated regardless of the quantity. Since both alloy tool steels and high-speed tool steels are high-quality steels, there is no need to mark “A” at the end of their grade.
5) Stainless steel and heat resistant steel
The number in front of the steel type indicates the thousandths of the mass fraction of carbon.
For example, in 3Cr13 steel, the average mass fraction Wc=0.3% and the average mass fraction WCr=13%. When the carbon mass fraction Wc≤0.03% and Wc≤0.08%, the prefixes “00” and “0” are used respectively, for example, steels 00Cr17Ni14Mo2, 0Cr19Ni9, etc.
3. Explanation of common alloy steels
1) Common low alloy steel
Q345
Applications: Mainly used for making bridges, ships, vehicles, boilers, pressure vessels, oil and gas pipelines, large steel structures, etc. It is used in hot-rolled and air-cooled state, the structure is fine-grained F+P, and it is no longer heat treated.
| Chemical composition% by weight | |||||
| W | Mn | Yes | V | No. | You |
| 0.18~0.20 | 1.0~1.6 | 0.55 | 0.02~0.15 | 0.015-0.06 | 0.02~0.2 |
Q345 includes the old steel grades 12MnV, 14MnNb, 16Mn, 18Nb, 16MnCu.
| Thickness mm | Mechanical properties | |||
| σ is MPa | σ b MPa | σ 5 % | A kv (20 ℃)J | |
| <16 | ≥ 345 | 470-630 | 21-22 | 34 |
| 16-35 | ≥ 325 | |||
| 35-50 | ≥ 295 | |||
Q420
Used in the normalized state, the structure is F+S. Q345 includes the former steel grades 15MnVN, 14MnVTiRE.
| Chemical composition% by weight | |||||||
| W | Mn | Yes | V | No. | You | Cr | No |
| ≤ 0.20 | 1.0~1.7 | 0.55 | 0.02~0.2 | 0.015-0.06 | 0.02~0.2 | ≤ 0.40 | ≤ 0.70 |
| Thickness mm | Mechanical properties | |||
| σ is MPa | σ b MPa | σ 5 % | A kv (20 ℃)J | |
| <16 | ≥ 420 | 520-680 | 18-19 GB/T159 |
3491-1994 |
| 16-35 | ≥ 400 | |||
| 35-50 | ≥ 380 | |||
2) Quenched and tempered alloy steel (low hardenability)
40cr
Applications: Used in the manufacture of various important parts in automobiles, tractors, machine tools and other machines, such as machine tool gears, main shafts, automobile engine crankshafts, connecting rods, screws, intake valves.
| Main chemical composition% by weight | W | 0.37-0.44 |
| Mn | 0.5-0.8 | |
| Yes | 0.17-0.37 | |
| Cr | 0.81-1.1 | |
| Mo | 0.07-0.12 | |
| Heat treated board size<25mm | extinguishing ℃ | 850 oil |
| quenching ℃ | 520 water oil | |
| Mechanical properties (≥) | σ b MPa | 980 |
| σ is MPa | 785 | |
| Heat treated board size<25mm | 9 | |
| ψ% | 45 | |
| A kv J. | 47 | |
| Annealed HB | 207 | |
3) Alloy spring steel
65Mn 60Mn2Si
Examples of applications for 65Mn 60Mn2Si steel: springs with a section ≤25mm, such as helical shock absorber springs in vehicles.
| Steel Grade | 65 minutes | 60Si2Mn | |
| Main components w% | W | 0.62-0.70 | 0.56-0.64 |
| Mn | 0.90-1.20 | 0.60-0.90 | |
| Yes | 0.17-0.37 | 1.50-2.00 | |
| Cr | ≤ 0.25 | ≤ 0.35 | |
| Heat treatment | extinguishing ℃ | 830 oil | 870 oil |
| Temperament | 540 | 480 | |
| Mechanical properties | σ is MPa | 800 | 1200 |
| σ b MPa | 1000 | 1300 | |
| δ 10 % | 8 | 5 | |
| ψ% | 30 | 25 | |
20 cr
Applications: It can manufacture gears in automobiles, tractors, camshafts in internal combustion engines, piston pins and other machine parts. It can withstand strong frictional wear, larger alternating loads, especially impact loads.
| Main chemical composition% by weight | W | 0.17-0.24 |
| Mn | 0.5-0.8 | |
| Yes | 0.20-0.40 | |
| Cr | 0.7-1.0 | |
| Heat treatment ℃ | Carbon | 930 |
| Preparation processing | 880 water and oil | |
| Tempera | 780-820 water and oil | |
| Temperament | 200 | |
| Mechanical properties (≥) | σ b MPa | 835 |
| σ is MPa | 540 | |
| δ 5 % | 10 | |
| ψ% | 4th | |
| A kv J. | 47 | |
| Blank size mm | <15 | |
4) Alloy carburizing steel (medium temperature):
20CrMnTi
| Main chemical composition% by weight | W | 0.17-0.24 |
| Mn | 0.8-1.10 | |
| Yes | 0.17-0.37 | |
| Cr | 1.0-1.3 | |
| Heat treatment ℃ | Carbon | 930 |
| Preparation processing | 880 water and oil | |
| Tempera | 770 water and oil | |
| Temperament | 200 | |
| Mechanical properties (≥) | σ b MPa | 1080 |
| σ is MPa | 850 | |
| δ 5 % | 10 | |
| ψ% | 45 | |
| A kv J. | 55 | |
| Blank size mm | <15 | |
5) Roller bearing steel:
GCr15:
Used to manufacture rolling elements (balls, rollers, needles) of bearings, inner and outer rings, etc. It can also be used to make precision gauges, cold punch dies, machine tool lead screws and other wear-resistant parts.
| Main chemical composition% by weight | W | 0.95-1.05 |
| Cr | 1.40~1.65 | |
| Yes | 0.15~0.35 | |
| Mn | 0.25~0.45 | |
| Heat Treatment Specification Performance | extinguishing ℃ | 820~840 |
| quenching ℃ | 150~160 | |
| HRC after tempering | 62~66 | |
| Main purpose | Ferrules with wall thickness <14mm and external diameter of 250mm. A steel ball with a diameter of 25-200 mm. A roll with a diameter of approximately 25mm. | |
6) Low alloy cutting tool steel:
9SiCr, CrWMn
| Steel Grade | 9SiCr | CrWMn | ||
| Chemical composition% by weight | W | 0.85-0.95 | 0.9-1.05 | |
| Mn | 0.3-0.6 | 0.8-1.1 | ||
| Yes | 1.2-1.6 | 0.15-0.35 | ||
| Cr | 0.95-1.25 | 0.9-1.2 W1.2-1.5 |
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| Heat treatment | Oil quenching | Quenching Temperature ℃ | ≥62 | |
| HRC hardness | 180-200 | 140-160 | ||
| Temperament | Quenching Temperature ℃ | 60-62 | 62-65 | |
| HRC hardness | Die, tap, drill, reamer, gear hob, cold stamping die, cold rolling roll | Complex and high-precision dies, broaches, gauges, stamping dies, etc. | ||
7) High Speed Steel:
W18Cr4V
| W | Mn | Yes | Cr | W | V | Manufacture of high-speed cutting tools, planers, drills, milling cutters, etc. |
| 0.7~0.8 | 0.1~0.4 | 0.2~0.4 | 3.8~4.4 | 17.5-19.0 | 1.0~1.4 |
8) Cold mold steel:
CR12:
Used to make various cold punch molds, cold head molds, cold extrusion molds and drawing molds, etc. For large cold molds made from Cr12 steel, there is minimal deformation in heat treatment, making them suitable for manufacturing complex and heavy molds.
| Chemical composition% by weight | ||||
| W | Yes | Mn | Cr | V |
| 2:00-2:30 | ≤ 0.40 | ≤ 0.40 | 11:50am-1:50pm | 0.15~0.30 |
| girdling | Oil quenching | Temperament | ||
| Temperature ℃ | HB hardness | Temperature ℃ | Temperature ℃ | HRC hardness |
| 870-900 | 207-255 | 950-1000 | 200-450 | 58-64 |
Usage example: cold stamping die, drawing die, stamping die, rolling die
9) Hot mold steel:
4Cr5MoSiV:
Its structure consists of tempered martensite, granular carbides and a small amount of residual austenite. To ensure hot hardness, multiple tempering is necessary.
| Chemical composition% by weight | |||||
| W | Yes | Mn | Cr | Mo | V |
| 0.32-0.42 | 0.80-1.20 | 0.40 | 4.50-5.50 | 1h00-1h50 | 0.30-0.50 |
| girdling | Oil quenching | Temperament | ||
| Temperature ℃ | HB hardness | Temperature ℃ | Temperature ℃ | HRC hardness |
| 840-900 | 209-229 | 1000-1025 | 540-650 | 40-54 |
Usage examples: hot die, die casting die, hot extrusion die, precision forging die
10) Steel Gauge
| Measure Tool | Steel Grade |
| Flat or card template | 10. 20 or 50, 55, 60, 60Mn, 65Mn |
| General meters and block meters | T10A, T12A, 9SiCr |
| High Precision Gauges and Block Gauges | Cr (cutting tool steel), CrMn, GCr15 |
| High-precision, complex-shaped gauges and block gauges | CrWMn (low deformation steel) |
| Corrosion resistant measuring tool | 4Cr13,9Cr18 (stainless steel) |
11) Stainless steel:
Stainless steel refers to types of steel with high resistance to corrosion in the atmosphere and in general environments.
| Steel Grade | Chemical composition% by weight | σb | σ0.2 | δ5 | ψ | Ak | Toughness | |
| W | Cr | MPa | MPa | % | % | J. | ||
| 1Ch13 Type M |
≤0.15 | 11.5-13.5 | ≥540 | ≥345 | ≥25 | ≥55 | ≥78 | ≥159 HB |
| Heat treatment: oil or water quenching of 9501000 ℃, rapid cooling and tempering of 700750 ℃; Objective: To produce parts that are resistant to weakly corrosive media and that can withstand impact loads, such as steam turbine blades, water pressure machine valves, structural structures, screws, nuts, etc. |
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| 9Cr18 Type M |
0.9-1.0 | 17-19 | ≥55 HRC | |||||
| Heat treatment: 1000-1050 ℃ oil quenching, 200-300 ℃ oil, air cooling and quenching; Usage: stainless steel mechanical cutting tool, cutting tool, surgical blade, high abrasion and corrosion resistance part |
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| 1Ch17 Type F |
≤0.12 | 16-18 | ≥450 | ≥205 | ≥22 | ≥50 | ≥183 HB | |
| Heat treatment 780°C ~ 850°C air cooling. Objective: Produce equipment for nitric acid factories, such as absorption towers, heat exchangers, acid tanks, transport pipes and equipment for food factories |
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Martensitic Stainless Steel:
1Cr13, 2Cr13, 3Cr13, 4Cr13, etc. All of them have sufficient corrosion resistance in oxidative media. Low carbon 1Cr13 and 2Cr13 steels have better corrosion resistance and good mechanical properties. As the carbon content increases, 3Cr13 and 4Cr13 steels increase strength and wear resistance, but reduce corrosion resistance.
Ferritic stainless steel:
1Ch17, 1Ch17Ti, etc. This type of steel has a chromium mass fraction of 17% ~ 30% and a carbon mass fraction of less than 0.15%. It has a single-phase ferrite structure and better corrosion resistance than Cr13 steel.
Austenitic Stainless Steel:
Type Cr18Ni9 (also known as type 18-8 stainless steel) is one of the most commonly used stainless steels. This type of austenitic stainless steel has a low carbon content (around 0.1%) and excellent corrosion resistance. Steel often includes additions of Ti (Titanium) or Nb (Niobium) to prevent intergranular corrosion.
This class of steel has lower strength and hardness and is non-magnetic. However, it offers superior plasticity, toughness and corrosion resistance compared to Cr13 type stainless steel. A solution treatment can further improve the corrosion resistance of this austenitic stainless steel.
