ASTM, DIN, GB Steel Grade Comparison: How to Choose the Right Steel

Steel is one of the most versatile materials in the world; composed primarily of iron and carbon, the addition of carbon enhances its hardness. Given its widespread use across industries such as construction, furniture manufacturing, and automotive parts, it is essential to classify steel to distinguish the properties—such as strength and corrosion resistance—of different grades.

In my interactions with clients, they often present material designations based on American (ASTM), German (DIN), or European (EN) standards and ask if I can supply them; I then offer the corresponding Chinese National Standard (GB) materials. However, this sometimes leads to concerns among clients regarding whether the GB-standard steel I provide will meet their specific requirements. Therefore, I would like to use this article to explain the differences between various steel grades.

What Are Steel Grades?

A steel grade is a standardized identification system used to define the composition, mechanical properties, and performance requirements of a specific type of steel. Different steel grades are created by adjusting the chemical composition of iron-based materials, mainly through controlling the amount of carbon and adding alloying elements such as chromium, nickel, molybdenum, manganese, and silicon.

Steel material grades vary between countries and regions because each industrial system has developed its own standards for defining and classifying materials. The United States, Germany, China, Japan, and other regions have established their own steel designation systems based on their manufacturing history, industrial requirements, and application standards.

For example, the same type of steel may have different designations under different standards. American standards commonly use ASTM, AISI, or SAE designations, Germany and Europe use DIN and EN standards, while China uses GB/T standards. 

The purpose of these different steel grade systems is to help engineers and manufacturers clearly identify material performance requirements. Although some steel grades from different countries may be considered equivalent, they are not always completely identical. When selecting alternative materials for manufacturing, factors such as chemical composition, mechanical properties, heat treatment conditions, and final application requirements should always be considered.

Standard	Management & Developing Organizations	Typical Naming Format	Primary Measurement Units	Main Affected and Application Fields
ANSI / ASTM / ASME / SAE (USA)	Decentralized private associations coordinated by ANSI (ASTM, ASME, etc.)	ASTM A36 ASME B16.5 1/2"-13 UNC	Imperial (inches)	North America, global petrochemical, aerospace, pressure vessels
DIN (Germany)	DIN (German Institute for Standardization)	DIN 933 DIN EN ISO 4017	Metric (mm,)	Europe, global precision machinery, automotive industry
GB / GB/T (China)	SAC (Standardization Administration of China)	GB 7251 (mandatory) GB/T 700-2006 (recommended)	Metric (mm)	China, Belt and Road projects, export manufacturing
ISO (International Organization for Standardization)	ISO (Geneva, Switzerland)	ISO 9001 ISO 4017 ISO 2768	Metric (mm)	Global international trade and technical exchange
EN (European Norm)	CEN / CENELEC / ETSI	EN 10204 3.1 EN 10025	Metric (mm)	EU/EEA, CE‑marked markets
JIS (Japanese Industrial Standards)	JISC (Japanese Industrial Standards Committee)	JIS G3101 (e.g., SS400) JIS B1180	Metric (mm)	Japan, East/Southeast Asia, electronics/semiconductors, automotive supply chain

How Different Countries Name Steel Grades?

Different countries use different naming systems for steel grades. Some standards classify steel based on chemical composition, while others classify materials according to mechanical properties such as yield strength or tensile strength. Understanding these naming rules helps engineers quickly identify equivalent materials when manufacturing custom parts in China.

ASTM / AISI Steel Grades (USA)

American steel grades usually use numbers to indicate chemical composition, especially carbon content and alloy elements.

Steel Grade	Naming Rule	Example
AISI 1020	"10" indicates plain carbon steel, "20" indicates approximately 0.20% carbon	Low carbon steel
AISI 4140	"41" indicates chromium-molybdenum alloy steel, "40" indicates approximately 0.40% carbon	Alloy structural steel

For AISI grades, the number mainly provides information about the material composition.

EN / DIN Steel Grades (Europe)

European grades of steel usually combine letters and numbers to describe material type, strength level, or chemical composition.

Steel Grade	Naming Rule	Example
S235JR	"S" means structural steel, "235" represents minimum yield strength (235 MPa)	Similar to Q235
C45	"C" means carbon steel, "45" represents approximately 0.45% carbon	Similar to 45 Steel

EN standards often focus on both chemical composition and mechanical performance requirements.

JIS Steel Grades (Japan)

Japanese JIS grades use letters and numbers to indicate steel type and strength or carbon content.

Steel Grade	Naming Rule	Example
S45C	"S" means steel, "45" represents approximately 0.45% carbon, "C" means carbon steel	Similar to 45 Steel
SS400	"SS" means structural steel, "400" represents minimum tensile strength (400 MPa)	Similar to Q235

Some JIS grades are composition-based, while others, such as SS400, are classified mainly by mechanical properties.

GB Steel Grades (China)

Chinese GB standards use different naming methods depending on the steel category. Some grades are based on chemical composition, while others are based on strength levels.

Steel Grade	Naming Rule	Example
Q235	"Q" represents yield strength, "235" represents minimum yield strength (235 MPa)	Structural steel
45 Steel	"45" represents approximately 0.45% carbon content	Medium carbon steel
40Cr	"40" represents approximately 0.40% carbon, "Cr" indicates chromium alloy steel	Alloy steel

GB standards include both structural steels (Q235/Q355) and engineering steels (20 Steel, 45 Steel, 40Cr, 42CrMo), which are widely used in Chinese manufacturing.

Common Steel Grade Equivalents for CNC Machining

When manufacturing custom parts in China, many customers provide material requirements based on ASTM, AISI, DIN, EN, or JIS standards. Chinese manufacturers usually select corresponding GB/T materials according to chemical composition, mechanical properties, and application requirements.

The following section introduces commonly used Chinese steel grades and their international equivalents.

Q235 Steel (GB/T 700) 

Q235 is one of the most widely used carbon structural steels in China. Unlike traditional carbon steels such as 20 Steel and 45 Steel, Q235 is classified mainly according to its minimum yield strength, rather than carbon content. The letter “Q” represents the yield strength, while “235” indicates a minimum yield strength of approximately 235 MPa.

Q235 contains relatively low carbon content, providing excellent weldability, ductility, and cost efficiency. It is commonly used for structural components, welded frames, brackets, machine bases, steel structures, and general fabrication parts.

Typical chemical composition:

Element	Q235 (GB/T 700)	ASTM A36	EN S235JR	JIS SS400
Carbon (C)	≤0.20%	≤0.26%	≤0.22%	≤0.17%
Silicon (Si)	≤0.35%	≤0.40%	≤0.55%	≤0.50%
Manganese (Mn)	≤1.40%	≤1.20%	≤1.60%	≤1.40%
Phosphorus (P)	≤0.045%	≤0.040%	≤0.035%	≤0.050%
Sulfur (S)	≤0.045%	≤0.050%	≤0.035%	≤0.050%

Common equivalent steel grades:

• ASTM A36 (USA) ASTM A36 has a similar application range to Q235. The main difference is the chemical composition: Q235 has a carbon content of ≤0.20%, while A36 allows up to approximately 0.26% carbon and higher manganese content (up to 1.20%). The higher carbon and manganese content can provide slightly higher strength, but may slightly reduce weldability compared with Q235.

• EN S235JR (Europe) S235JR is one of the closest substitutes for Q235 steel. Both grades have similar carbon content (≤0.20%) and yield strength (235 MPa). While the phosphorus and sulfur content in S235JR is typically ≤0.035% compared to a maximum of ≤0.045% for Q235, S235JR offers slightly better toughness, though the difference is minimal.

• JIS SS400 (Japan) SS400 is often compared with Q235 because both are commonly used low carbon structural steels. SS400 typically has a lower carbon content (≤0.17%) compared with Q235 (≤0.20%), which provides slightly better weldability and formability. However, Q235 generally has a clearly defined yield strength requirement (≥235 MPa), while SS400 is mainly classified by tensile strength (≥400 MPa), resulting in some differences in mechanical performance. For CNC machining, SS400 may offer slightly better machinability due to its lower carbon content, while Q235 can provide more predictable load-bearing performance due to its defined yield strength requirement.

Q355 Steel (GB/T 1591)

Q355 is a type of low-alloy, high-strength structural steel within the Chinese steel material grades. Its naming convention is similar to that of Q235 and is based on yield strength; the "355" indicates a minimum yield strength of approximately 355 MPa. Compared to Q235, Q355 offers higher strength and superior load-bearing capacity, enabling engineers to reduce material thickness while maintaining structural performance.

Typical chemical composition:

Element	Q355 (GB/T 1591)	ASTM A572 Grade 50	EN S355JR	JIS SM490A
Carbon (C)	≤0.20%	≤0.23%	≤0.24%	≤0.20%
Silicon (Si)	≤0.55%	≤0.40%	≤0.55%	≤0.55%
Manganese (Mn)	≤1.60%	≤1.35%	≤1.60%	≤1.65%
Phosphorus (P)	≤0.030%	≤0.030%	≤0.035%	≤0.035%
Sulfur (S)	≤0.030%	≤0.030%	≤0.035%	≤0.035%

Common equivalent steel grades:

• ASTM A572 Grade 50 (USA) ASTM A572 Grade 50 is often considered comparable to Q355 because both provide similar yield strength levels. However, A572 Grade 50 achieves its strength through alloying elements such as vanadium or columbium, while Q355 uses a different alloy design. For structural applications, mechanical properties should be verified before substitution.

• EN S355JR (Europe) S355JR is the closest European equivalent to Q355. Both materials have a minimum yield strength around 355 MPa. The main differences are related to chemical composition limits, impact testing requirements, and material delivery conditions.

• JIS SM490 (Japan) SM490 is a structural steel commonly used in Japanese industrial applications. It provides similar strength levels but may have different requirements for weldability and toughness.

20 Steel (GB/T 699) 

20 Steel is one of the most commonly used low carbon steels in China. It contains approximately 0.17–0.24% carbon, providing a good balance between strength, ductility, machinability, and weldability.

Compared with structural steels such as Q235, 20 Steel focuses more on chemical composition control and is commonly used for mechanical components requiring machining rather than large welded structures.

Typical chemical composition:

Element	20 Steel (GB/T 699)	AISI 1020	DIN C22	JIS S20C
Carbon (C)	0.17–0.24%	0.18–0.23%	0.17–0.24%	0.18–0.23%
Silicon (Si)	0.17–0.37%	≤0.35%	≤0.40%	≤0.35%
Manganese (Mn)	0.35–0.65%	0.30–0.60%	0.40–0.70%	0.30–0.60%
Phosphorus (P)	≤0.035%	≤0.040%	≤0.035%	≤0.030%
Sulfur (S)	≤0.035%	≤0.050%	≤0.035%	≤0.035%

Common equivalent steel grades:

• AISI 1020 (USA) AISI 1020 is one of the closest equivalents to 20 Steel. Both have similar carbon content and provide similar machinability and mechanical performance. The main difference is that AISI 1020 follows ASTM/SAE specifications, which may have different requirements for material testing and chemical composition control.

• DIN C22 / EN C22 (Europe) C22 has a very similar carbon content range to 20 Steel and is widely used for mechanical components. Differences mainly exist in sulfur, phosphorus control, and delivery conditions required by European standards.

• JIS S20C (Japan) S20C is commonly considered equivalent to 20 Steel. It provides similar strength and machining characteristics, but inspection standards and mechanical property requirements may vary.

45 Steel (GB/T 699)

45 Steel is one of the most widely used medium carbon steels in China. With a carbon content of approximately 0.42–0.50%, it provides higher strength, hardness, and wear resistance compared with low carbon steels.

It is commonly selected for mechanical parts requiring higher load capacity and better wear resistance.

Typical chemical composition:

Element	45 Steel (GB/T 699)	AISI 1045	DIN C45E	JIS S45C
Carbon (C)	0.42–0.50%	0.43–0.50%	0.42–0.50%	0.42–0.48%
Silicon (Si)	0.17–0.37%	≤0.40%	≤0.40%	≤0.35%
Manganese (Mn)	0.50–0.80%	0.60–0.90%	0.50–0.80%	0.60–0.90%
Phosphorus (P)	≤0.035%	≤0.040%	≤0.035%	≤0.030%
Sulfur (S)	≤0.035%	≤0.050%	≤0.035%	≤0.035%

Common equivalent steel grades:

• AISI 1045 (USA) AISI 1045 has similar carbon content and mechanical properties to 45 Steel. Both are widely used for shafts and mechanical components. Differences may exist in material supply conditions, hardness requirements, and mechanical testing standards.

• DIN C45 / EN C45E (Europe) C45 is one of the closest equivalents to 45 Steel. Both provide similar strength and machinability. C45E may have tighter chemical composition control, making it more suitable for precision mechanical applications.

• JIS S45C (Japan) S45C is widely used in Japanese machinery applications and is commonly considered equivalent to 45 Steel. However, heat treatment conditions should be reviewed because final mechanical properties depend strongly on processing.

40Cr Steel (GB/T 3077)

40Cr is one of the most commonly used alloy structural steels in China. Compared with carbon steels such as 45 Steel, 40Cr contains chromium (Cr) as the main alloying element, which significantly improves its hardenability, strength, and wear resistance.

Chromium plays an important role in improving the performance of 40Cr. It increases the steel's ability to form martensite during quenching, allowing the material to achieve higher hardness and strength after heat treatment. Chromium also improves wear resistance and reduces deformation under high loads, making 40Cr suitable for mechanical components that require better fatigue resistance and durability.

In addition to chromium, 40Cr contains manganese (Mn) and silicon (Si), which further improve the steel's strength and toughness. After processes such as quenching and tempering, 40Cr can achieve a good balance between hardness, strength, and impact resistance.

Typical chemical composition:

Element	40Cr (GB/T 3077)	AISI 5140	DIN 41Cr4	JIS SCr440
Carbon (C)	0.37–0.44%	0.38–0.43%	0.38–0.45%	0.38–0.43%
Silicon (Si)	0.17–0.37%	0.15–0.35%	≤0.40%	≤0.35%
Manganese (Mn)	0.50–0.80%	0.70–0.90%	0.60–0.90%	0.60–0.90%
Chromium (Cr)	0.80–1.10%	0.70–0.90%	0.90–1.20%	0.90–1.20%
Phosphorus (P)	≤0.035%	≤0.035%	≤0.035%	≤0.030%
Sulfur (S)	≤0.035%	≤0.040%	≤0.035%	≤0.030%

Common equivalent steel grades:

• AISI 5140 (USA) AISI 5140 is one of the closest equivalents to 40Cr. Both materials contain approximately 0.40% carbon and around 1.0% chromium, providing similar strength and wear resistance after heat treatment. The main difference is that AISI 5140 typically has slightly higher chromium content control (Cr: approximately 0.70–0.90%) and different hardenability requirements under SAE standards. For large-section parts requiring uniform hardness after quenching, the hardenability specification should be confirmed before substitution.

• DIN 41Cr4 / EN 41Cr4 (Europe) 41Cr4 has a very similar chemical composition to 40Cr, with carbon content around 0.38–0.45% and chromium content around 0.90–1.20%. Compared with 40Cr, EN 41Cr4 usually has tighter control of phosphorus and sulfur impurities, which can improve toughness, fatigue resistance, and material consistency. It is often preferred for precision mechanical components where stable mechanical properties are required after heat treatment.

• JIS SCr440 (Japan) SCr440 has a similar alloy composition to 40Cr, with carbon content around 0.38–0.43% and chromium content around 0.90–1.20%. The main difference is that JIS standards focus more on chemical composition and mechanical properties after heat treatment, while GB 40Cr is commonly selected based on general alloy structural steel requirements. In practical applications, the final hardness and strength depend mainly on the quenching and tempering process, so heat treatment conditions should be matched when replacing SCr440 with 40Cr.

42CrMo Steel (GB/T 3077)

42CrMo is a high-strength alloy steel containing chromium and molybdenum. Compared with 40Cr, it provides higher strength, toughness, and fatigue resistance.

Due to its excellent mechanical properties after heat treatment, 42CrMo is widely used for high-load and safety-critical components.

Typical chemical composition:

Element	42CrMo (GB/T 3077)	AISI 4140	DIN 42CrMo4	JIS SCM440
Carbon (C)	0.38–0.45%	0.38–0.43%	0.38–0.45%	0.38–0.43%
Silicon (Si)	0.17–0.37%	0.15–0.35%	≤0.40%	≤0.35%
Manganese (Mn)	0.50–0.80%	0.75–1.00%	0.60–0.90%	0.60–0.90%
Chromium (Cr)	0.90–1.20%	0.80–1.10%	0.90–1.20%	0.90–1.20%
Molybdenum (Mo)	0.15–0.25%	0.15–0.25%	0.15–0.30%	0.15–0.30%
Phosphorus (P)	≤0.035%	≤0.035%	≤0.025%	≤0.030%
Sulfur (S)	≤0.035%	≤0.040%	≤0.035%	≤0.030%

Common equivalent steel grades:

• AISI 4140 (USA) AISI 4140 is one of the most widely recognized equivalents to 42CrMo. Both are chromium-molybdenum alloy steels with similar strength and heat treatment capabilities. However, differences may exist in chemical composition ranges and hardenability requirements.

• DIN 42CrMo4 / EN 1.7225 (Europe) 42CrMo4 is one of the closest international equivalents to Chinese 42CrMo. Both materials are widely used for high-strength mechanical components. European standards may have stricter requirements for impact toughness and material quality classification.

• JIS SCM440 (Japan) SCM440 is commonly used as an equivalent material in Japan and has similar alloy composition. However, heat treatment specifications and hardness requirements should be reviewed before replacement.

How to Select the Right Steel Grade for CNC Machining in China?

To conclude, when selecting steel based on material grades for custom manufacturing, I believe the following factors should be comprehensively considered:

1. Chemical Composition: Elements such as carbon, chromium, nickel, and molybdenum directly influence the material's strength, hardness, and corrosion resistance.
2. Mechanical Property Requirements: Consider metrics such as yield strength, tensile strength, hardness, and fatigue resistance based on the final application.
3. Manufacturing Processes: Processes such as CNC machining, welding, forming, and heat treatment may impose specific requirements on material properties.
4.  Certification Requirements: For critical components, verify whether material certificates (such as MTC, EN 10204 3.1, or relevant ASTM documentation) are required.

By understanding the relationships between different steel grade systems, my clients can select the right materials with greater confidence when working with the LVMA CNC team, thereby avoiding risks associated with improper material substitution. If you are also unsure about material selection, please feel free to contact LVMA CNC; we will help you choose the optimal material.