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Alloy Structure Steel

Overview

Alloy structure steel is used for mechanical parts and various engineering components, containing one or several alloying elements in specific amounts. It is a type of steel with excellent heat treatment properties. Due to its appropriate hardenability, after suitable metal heat treatment, the microstructure of alloy structural steel becomes uniform sorbite, bainite, or fine pearlite. Consequently, it possesses high tensile strength and yield ratio (generally around 0.85), high toughness and fatigue strength, and a low ductile-brittle transition temperature, making it suitable for manufacturing large cross-section machine parts.

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Characteristics

Alloy structural steel is a specialized steel known for its exceptional properties, making it a vital material in various industrial sectors. Below are the primary characteristics of alloy structural steel:

High Strength and Hardness:
Alloy structural steel offers superior strength and hardness, enabling it to withstand significant loads and pressures. This makes it an ideal choice for manufacturing high-strength parts and components.
Excellent Toughness and Ductility:
With outstanding toughness and ductility, alloy structural steel maintains its shape and performance under impact and vibration. This quality makes it suitable for producing parts that need to endure shocks and vibrations.
Superior Wear and Corrosion Resistance:
This steel exhibits excellent wear and corrosion resistance, allowing it to perform reliably in harsh working environments. It is especially suited for parts and components exposed to high temperatures, pressures, and speeds.
Good Weldability and Machinability:
Alloy structural steel is highly weldable and machinable, making it easy to manufacture and repair through various processes. This versatility is advantageous for producing complex shapes and structures.

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Production Process

Efficient Steelmaking Techniques for High-Quality Alloy Structural Steel:

Advanced Steelmaking Methods:To produce top-grade alloy structural steel, basic oxygen furnaces, open-hearth furnaces, and electric arc furnaces are utilized. Enhanced refining processes such as electroslag remelting and vacuum degassing further improve steel quality.

Precision Casting Techniques:Utilizing continuous casting or mold casting ensures uniform cooling or hot-forging/rolling of steel ingots, essential for high-quality steel production.

Uniform Heating and Forging/Rolling:Ensuring even temperature distribution and adequate holding time during heating helps eliminate segregation defects and ensures consistent deformation during forging and rolling. Rapid cooling above 600℃ for small sections, especially for carburizing steel with around 0.2% carbon, prevents banded structures. Large cross-section forgings require stress relief and white spot elimination measures.

Optimal Heat Treatment Procedures:Quenching to achieve a martensitic structure followed by tempering to form a sorbitic structure enhances the properties of quenched and tempered steel. Maintaining a proper concentration gradient during carburization avoids continuous network carbides at grain boundaries. For nitriding steel, pre-nitriding heat treatment ensures desired properties, followed by final precision machining. Post-nitriding, only the brittle thin “white layer” is ground off without further machining.

By implementing these advanced production processes, manufacturers can produce high-quality alloy structural steel suitable for a wide range of engineering applications.

Applications

Automotive Industry:

Crankshafts: Alloy structural steel is used in the manufacturing of crankshafts due to its high strength and fatigue resistance.

Gears: The material’s wear resistance and toughness make it ideal for gears that need to withstand high stress and friction.

Drive Shafts: Alloy structural steel’s ability to endure twisting and bending makes it suitable for drive shafts in vehicles.

Construction:

Structural Beams: The high tensile strength and durability of alloy structural steel make it perfect for structural beams in buildings and bridges.

Reinforcement Bars (Rebars): Used to reinforce concrete, alloy structural steel rebars provide enhanced strength and longevity to construction projects.

Aerospace Industry:

Landing Gear: Alloy structural steel’s combination of strength, toughness, and fatigue resistance is essential for landing gear components.

Aircraft Frames: The lightweight and high-strength properties of alloy structural steel are utilized in aircraft frames to ensure structural integrity while minimizing weight.

Machinery Manufacturing:

Tool Holders: In machining operations, tool holders made from alloy structural steel provide stability and durability.

Hydraulic Systems: Components such as cylinders and pistons benefit from the material’s high strength and wear resistance.

Oil and Gas Industry:

Drill Pipes: The demanding conditions of drilling require materials like alloy structural steel, which offers high strength and resistance to fatigue and corrosion.

Valve Components: The toughness and durability of alloy structural steel are crucial for valve components that operate under high pressure.

Railway Industry:

Rail Tracks: Alloy structural steel’s wear resistance and strength make it suitable for rail tracks, which must endure high loads and friction.

Train Wheels and Axles: These components benefit from the material’s toughness and resistance to fatigue.

Agricultural Equipment:

Plow Blades: The toughness and wear resistance of alloy structural steel make it ideal for plow blades that must withstand rough conditions.

Tractor Parts: Components such as axles and gears in tractors require the high strength and durability of alloy structural steel.

Common Sizes

Sheet and Plate:

Thickness: 0.5mm – 200mm

Width: 600mm – 2500mm

Length: 2000mm – 12000mm

Bar:

Diameter: φ16-190mm

Length 4-12m

Chemical Composition

Alloy Structure Steel
Grade (GB)	Chemical Composition (Mass Fraction) /%
Grade (GB)	C	Si	Mn	Cr	Mo	Ni	W	B	Al	Ti	V
20Mn2	0.17~0.24	0.17~0.37	1.40~1.80	_	_	_	_	_	_	_	_
30Mn2	0.27~ 0.34	0.17~0.37	1.40~ 1.80	_	_	_	_	_	_	_	_
35Mn2	0.32~0.39	0.17~0.37	1.40~1.80	_	_	_	_	_	_	_	_
40Mn2	0.37~ 0.44	0.17~0.37	1.40~1.80	_	_	_	_	_	_	_	_
45Mn2	0.42~0.49	0.17~0.37	1.40~1.80	_	_	_	_	_	_	_	_
50Mn2	0.47~ 0.55	0.17~0.37	1.40~1.80	_	_	_	_	_	_	_	_
20MnV	0.17~ 0.24	0.17~0.37	1.30~1.60	_	_	_	_	_	_	_	0.07~0.12
27SiMn	0.24~0.32	1.10~1.40	1.10~1.40	_	_	_	_	_	_	_	_
35SiMn	0.32~0.40	1.10~1.40	1.10~1.40	_	_	_	_	_	_	_	_
42SiMn	0.39~0.45	1.10~1.40	1.10~1.40	_	_	_	_	_	_	_	_
20SIMn2MoV	0.17~0.23	0.90~1.20	2.20~2.60	_	_	_	_	_	_	_	0.05~0.12
25SiMn2MoV	0.22~0.28	0.90~1.20	2.20~2.60	_	_	_	_	_	_	_	0.05~0.12
37SiMn2MoV	0.33~0.39	0.60~0.90	1.60~1.90	_	_	_	_	_	_	_	0.05~0.12
40B	0.37~ 0.44	0.17~0.37	0.60~0.90	_	_	_	_	0.0008~0.0035	_	_	_
45B	0.42~ 0.49	0.17~0.37	0.60~0.90	_	_	_	_	0.0008~0.0035	_	_	_
50B	0.47~0.55	0.17~0.37	0.60~0.90	_	_	_	_	0.0008~0.0035	_	_	_
25MnB	0.23~ 0.28	0.17~0.37	1.00~1.40	_	_	_	_	0.0008~0.0035	_	_	_
35MnB	0.32~ 0.38	0.17~0.37	1.00~1.40	_	_	_	_	0.0008~0.0035	_	_	_
40MnB	0.37~ 0.44	0.17~0.37	1.00~1.40	_	_	_	_	0.0008~0.0035	_	_	_
45MnB	0.42~ 0.49	0.17~0.37	1.00~1.40	_	_	_	_	0.0008~0.0035	_	_	_
20 MnMoB	0.16~ 0.22	0.17~0.37	0.90~1.20		0.20~0.30			0.0008~0.0035	_	_	_
15MnVB	0.12~ 0.18	0.17~0.37	1.20~1.60	_	_	_	_	0.0008~0.0035	_	_	0.07~0.12
20MnVB	0.17~ 0.23	0.17~0.37	1.20~1.60	_	_	_	_	0.0008~0.0035	_	_	0.07~0.12
40MnVB	0.37~ 0.44	0.17~0.37	1.10~1.40	_	_	_	_	0.0008~0.0035	_	_	0.05~0.10
20MnTiB	0.17~ 0.24	0.17~0.37	1.30~ 1.60	_	_	_	_	0.0008~0.0035	_	0.04~0.10	_
25MnTiBRE	0.22~ 0.28	0.20~ 0.45	1.30~ 1.60	_	_	_	_	0.0008~0.0035	_	0.04~0.10	_
15Cr	0.12~ 0.17	0.17~ 0.37	0.40~ 0.70	0.70~ 1.00	_	_	_	_	_	_	_
20Cr	0.18~ 0.24	0.17~ 0.37	0.50~ 0.80	0.70~ 1.00	_	_	_	_	_	_	_
30Cr	0.27~ 0.34	0.17~ 0.37	0.50~ 0.80	0.80~ 1.10	_	_	_	_	_	_	_
35Cr	0.32~ 0.39	0.17~ 0.37	0.50~ 0.80	0.80~ 1.10	_	_	_	_	_	_	_
40Cr	0.37~ 0.44	0.17~ 0.37	0.50~ 0.80	0.80~ 1.10	_	_	_	_	_	_	_
45Cr	0.42~ 0.49	0.17~ 0.37	0.50~ 0.80	0.80~ 1.10	_	_	_	_	_	_	_
50Cr	0.47~ 0.54	0.17~ 0.37	0.50~ 0.80	0.80~ 1.10	_	_	_	_	_	_	_
38CrSi	0.35~ 0.43	1.00~ 1.30	0.30~ 0.60	1.30~ 1.60	_	_	_	_	_	_	_
12CrMo	0.08~ 0.15	0.17~ 0.37	0.40~ 0.70	0.40~ 0.70	0.40~ 0.55	_	_	_	_	_	_
15CrMo	0.12~ 0.18	0.17~ 0.37	0.40 0.70	0.80~ 1.10	0.40~ 0.55	_	_	_	_	_	_
20CrMo	0.17~ 0.24	0.17~ 0.37	0.40~ 0.70	0.80~ 1.10	0.15~ 0.25	_	_	_	_	_	_
25CrMo	0.22- 0.29	0.17~ 0.37	0.60~ 0.90	0.90~ 1.20	0.15~ 0.30	_	_	_	_	_	_
30CrMo	0.26~ 0.33	0.17~ 0.37	0.40 0.70	0.80~ 1.10	0.15~ 0.25	_	_	_	_	_	_
35CrMo	0.32~ 0.40	0.17~ 0.37	0.40~ 0.70	0.80~ 1.10	0.15~ 0.25	_	_	_	_	_	_
42CrMo	0.38~ 0.45	0.17~ 0.37	0.50~ 0.80	0.90~ 1.20	0.15~ 0.25	_	_	_	_	_	_
50CrMo	0.46~ 0.54	0.17~ 0.37	0.50~ 0.80	0.90~ 1.20	0.15~ 0.30	_	_	_	_	_	_
12CrMoV	0.08~ 0.15	0.17~ 0.37	0.40~ 0.70	0.30~ 0.60	0.25~ 0.35	_	_	_	_	_	0.15~ 0.30
35CrMoY	0.30~ 0.38	0.17~ 0.37	0.40 0.70	1.00~ 1.30	0.20~ 0.30	_	_	_	_	_	0.10~ 0.20
12Cr1MoV	0.08~ 0.15	0.17~ 0.37	0.40~ 0.70	0.90~ 1.20	0.25~ 0.35	_	_	_	_	_	0.15~ 0.30
25Cr2MoV	0.22~ 0.29	0.17~ 0.37	0.40~0.70	1.50~ 1.80	0.25~ 0.35	_	_	_	_	_	0.15~ 0.30
25Cr2MolV	0.22~ 0.29	0.17~ 0.37	0.50~ 0.80	2.10~ 2.50	0.90~ 1.10	_	_	_	_	_	0.30~ 0.50
38CrMoAl	0.35~ 0.42	0.20~ 0.45	0.30~ 0.60	1.35~ 1.65	0.15~ 0.25	_	_	_	0.70~ 1.10	_	_
40CrV	0.37 0.44	0.17~ 0.37	0.50~ 0.80	0.80~ 1.10	_	_	_	_	_	_	0.10~ 0.20
50CrV	0.47~0.54	0.17~ 0.37	0.50~0.80	0.80~ 1.10	_	_	_	_	_	_	0.10~ 0.20
15CrMn	0.12~ 0.18	0.17~ 0.37	1.10~ 1.40	0.40~ 0.70	_	_	_	_	_	_	_
20CrMn	0.17~ 0.23	0.17~ 0.37	0.90~ 1.20	0.90~ 1.20	_	_	_	_	_	_	_
40CrMn	0.37 0.45	0.17 0.37	0.90~ 1.20	0.90~ 1.20	_	_	_	_	_	_	_
20CrMnSi	0.17 0.23	0.90~ 1.20	0.80~ 1.10	0.80~ 1.10	_	_	_	_	_	_	_
25CrMnSi	0.22~ 0.28	0.90~ 1.20	0.80~ 1.10	0.80~ 1.10	_	_	_	_	_	_	_
30CrMnSi	0.28~ 0.34	0.90~ 1.20	0.80~ 1.10	0.80~ 1.10	_	_	_	_	_	_	_
35CrMnSi	0.32~ 0.39	1.10~ 1.40	0.80 1.10	1.10~ 1.40	_	_	_	_	_	_	_
20CrMnMo	0.17~ 0.23	0.17~ 0.37	0.90 1.20	1.10~ 1.40	0.20~ 0.30	_	_	_	_	_	_
40CrMnMo	0.37~ 0.45	0.17~ 0.37	0.90~ 1.20	0.90≈ 1.20	0.20~ 0.30	_	_	_	_	_	_
20CrMnTi	0.17~ 0.23	0.17~ 0.37	0.80~ 1.10	1.00~ 1.30	_	_	_	_	_	0.04~ 0.10	_
30CrMnTi	0.24~ 0.32	0.17~ 0.37	0.80 1.10	1.00~ 1.30	_	_	_	_	_	0.04~ 0.10	_
20CrNi	0.17~ 0.23	0.17~ 0.37	0.40~ 0.70	0.45~ 0.75	_	1.00~ 1.40	_	_	_	_	_
40CrNi	0.37~ 0.44	0.17~ 0.37	0.50~ 0.80	0.45~ 0.75	_	1.00~ 1.40	_	_	_	_	_
45CrNi	0.42~ 0.49	0.17% 0.37	0.50 0.80	0.45~ 0.75	_	1.00~ 1.40	_	_	_	_	_
50CrNi	0.47~ 0.54	0.17m 0.37	0.50~ 0.80	0.45~ 0.75	_	1.00~ 1.40	_	_	_	_	_
12CrNi2	0.10~ 0.17	0.17 0.37	0.30~ 0.60	0.60~ 0.90	_	1.50~ 1.90	_	_	_	_	_
34CrNi2	0.30~ 0.37	0.17~ 0.37	0.60~ 0.90	0.80~ 1.10	_	1.20~ 1.60	_	_	_	_	_
12CrNi3	0.10~ 0.17	0.17 0.37	0.30~ 0.60	0.60~ 0.90	_	2.75~ 3.15	_	_	_	_	_
20CrNi3	0.17~ 0.24	0.17~ 0.37	0.30~ 0.60	0.60~ 0.90	_	2.75~ 3.15	_	_	_	_	_
30CrNi3	0.27~ 0.33	0.17~ 0.37	0.30~ 0.60	0.60~ 0.90	_	2.75~ 3.15	_	_	_	_	_
37CrNi3	0.34~ 0.41	0.17~ 0.37	0.30~ 0.60	1.20~ 1.60	_	3.00~ 3.50	_	_	_	_	_
12Cr2Ni4	0.10 0.16	0.17~ 0.37	0.30~ 0.60	1.25~ 1.65	_	3.25~ 3.65	_	_	_	_	_
20Cr2Ni4	0.17~ 0.23	0.17~ 0.37	0.30~ 0.60	1.25~ 1.65	_	3.25~ 3.65	_	_	_	_	_
15CrNiMo	0.13~ 0.18	0.17~ 0.37	0.70~ 0.90	0.45~ 0.65	0.45~ 0.60	0.70~ 1.00	_	_	_	_	_
20CrNiMo	0.17~ 0.23	0.17~ 0.37	0.60~ 0.95	0.40~ 0.70	0.20~ 0.30	0.35~ 0.75	_	_	_	_	_
30CrNiMo	0.28~ 0.33	0.17~ 0.37	0.70~ 0.90	0.70~ 1.00	0.25~ 0.45	0.50~ 0.80	_	_	_	_	_
30Cr2Ni2Mo	0.26~ 0.34	0.17~ 0.37	0.50~ 0.80	1.80~ 2.20	0.30~ 0,50	1.80~ 2.20	_	_	_	_	_
30Cr2Ni4Mo	0.26~ 0.33	0.17~ 0.37	0.50~ 0.80	1.20~ 1.50	0.30~ 0.60	3.30~ 4.30	_	_	_	_	_
34Cr2Ni2Mo	0.30~ 0.38	0.17~ 0.37	0.50~ 0.80	1.30~ 1.70	0.15~ 0.30	1.30~ 1.70	_	_	_	_	_
35Cr2Ni4Mo	0.32~ 0.39	0.17~ 0.37	0.50~ 0.80	1.60~ 2.00	0.25~ 0.45	3.60~ 4.10	_	_	_	_	_
40CrNiMo	0.37~ 0.44	0.17~ 0.37	0.50~ 0.80	0.60~ 0.90	0.15~ 0.25	1.25~ 1.65	_	_	_	_	_
40C-Ni2Mo	0.38~ 0.43	0.17~ 0.37	0.50~ 0.80	0.70~ 0.90	0.20~ 0.30	1.65~ 2.00	_	_	_	_	_
18CrMnNiMo	0.15~ 0.21	0.17~ 0.37	1.10~ 1.40	1.00~ 1.30	0.20~ 0.30	1.00~ 1.30	_	_	_	_	_
45CrNiMoV	0.42~ 0.49	0.17~ 0.37	0.50~ 0.80	0.80~ 1.10	0.20~ 0.30	1.30~ 1.80	_	_	_	_	0.10~0.20
18Cr2Ni4W	0.13~ 0.19	0.17~ 0.37	0.30~ 0.60	1.35~ 1.65	_	4.00~ 4.50	0.80~ 1.20	_	_	_	_
25Cr2Ni4W	0,21~ 0.28	0.17~ 0.37	0.30~ 0.60	1.35~ 1.65	_	4.00~ 4.50	0.80~ 1.20	_	_	_	_

Comparison Table of Steel Grades by Country

Alloy Structure Steel
NO.	GB	EN	ASTM	JIS
1	20Mn2		1524	SMn420
2	30Mn2		1330	SMn433
3	35Mn2	一	1335	SMn438
4	40Mn2		1340	SMn443
5	45Mn2		1345	SMn443
6	50Mn2		1552
7	20MnV
8	27SiMn
9	35SiMn	一
10	42SiMn
11	20SiMn2MoV		一
12	25SiMn2MoV
13	37SiMn2MoV
14	40B
15	45B
16	50B
17	25MnB	20MnB5
18	35MnB	30MnB5
19	40MnB	38MnB5
20	45MnB		—
21	20MnMoB
22	15MnVB		一
23	20MnVB		—
24	40MnVB
25	20MnTiB
26	25MnTiBRE
27	15Cr		5115	SCr415
28	20Cr		5120	SCr420
29	30Cr	一	5130	SCr430
30	35Cr	34Cr4	5135	SCr435
31	40Cr	41Cr4	5140	SCr440
32	45Cr	41Cr4	5145	SCr445
33	50Cr	—	5150	SCr445
34	38CrSi	—	—
35	12CrMo		—
36	15CrMo	—		SCM415
37	20CrMo	—	4120	SCM420
38	25CrMo	25CrMo4	4130	SCM430
39	30CrMo	34CrMo4	4130	SCM430
40	35CrMo	34CrMo4	4135	SCM435
41	42CrMo	42CrMo4	4140、4142	SCM440
42	50CrMo	50CrMo4	4150	SCM445
43	12CrMoV
44	35CrMoV
45	12CrlMoV	—		一
46	25Cr2MoV
47	25Cr2MolV
48	38CrMoAl			SACM645
49	40CrV
50	50CrV	51CrV4	6150
51	15CrMn			—
52	20CrMn
53	40CrMn			一
54	20CrMnSi	一
55	25CrMnSi
56	30CrMnS	—	一	—
57	35CrMnSi	一
58	20CrMnMo	—
59	40CrMnMo	42CrMo4	4140、4142	SCM440
60	20CrMaT
61	30CrMnTi
62	20CrNi
63	40CrNi			SNC236
64	45CrNi
65	50CrNi
66	12CrNi2			SNC415
67	34CrNi2	35NiCr6
68	12CrNi3			SNC815
69	20CrNi3	—	—
70	30CrNi3			SNC631
71	37CrNi3			SNC836
72	12Cr2Ni4
73	20Cr2Ni4		—
74	15CrNiMo	—	—	—
75	20CrNiMo		8.620	SNCM220
76	30CrNiMo
77	30Cr2Ni2Mo	30CrNiMo8	—	SNCM431
78	30Cr2Ni4 Mo	30NiCrMo16-6
79	34Cr2Ni2Mo	34CrNiMo6		—
80	35Cr2Ni4Mo	36NiCrMo16		—
81	40CrNiMo	39NiCrMo3		—
82	40CrNi2Mo		4340	SNCM439
83	18CrMnMiMo		—
84	45CrNiMoV	—	—
85	18Cr2Ni4W
86	25Cr2Ni4W

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