Comparison of steels in mechanical engineering with other standards such as JIS and AISI

There are different designation systems for the properties of steel. The underlying standards form the basis for the classification and designation of steel grades using material numbers. In this article we compare the steel grades classified according to DIN/EN/ISO with their respective counterparts in JIS (Japanese Industrial Standard).

What is steel?

According to DIN EN 10020 Part 1, steel is defined as a material that consists predominantly of iron and has a maximum carbon content of 2%. Compounds of iron and carbon with a carbon content higher than 2% are cast irons. The mass fraction of iron is larger than that of any other element. Due to the iron ore used in its production, steel always contains a corresponding amount of silicon and manganese.

Steel can be divided into three main grades according to its chemical composition:

• Unalloyed steels: consist of iron and carbon, as well as small quantities of other elements below defined limits.
• Stainless steels (also called rust-proof steels): mass fraction of at least 10.5% chromium and a maximum of 1.2% carbon
• Alloyed steels: Contains at least one alloying element in addition to iron and carbon. Alloying elements change the properties of steel. Alloyed steels are not stainless steels.

The classification of steel types is further divided according to quality classes.

There are tables for the different steel quality classes.

Different types of steel and properties of steel

The composition of steel determines its properties. Carbon as the main component influences, for example, hardness and strength. A higher carbon content generally leads to an increased hardness, but also to a reduced ductility (toughness). Other alloying elements for steel alloys can be:

• Chrome (Cr): Chrome increases the corrosion resistance of steel and is often found in stainless steels. It also helps increase strength at higher temperatures.
• Manganese (Mn): Manganese is used to improve the strength and hardness of steel as well as for desulfurization and deoxidation during steel production.
• Nickel (Ni): Nickel increases toughness, impact strength and stability to low temperatures. It is a commonly used alloying element in stainless steels and alloy steels.
• Molybdenum (Mo): Molybdenum improves the strength and resistance to stress corrosion cracking and high temperature properties of steel. It is found in many alloyed steels.
• Vanadium (V): Vanadium increases the strength, hardness and wear resistance of steel. It is often used in tool steels and high-strength steels.
• Copper (Cu): Copper can increase the corrosion resistance and electrical conductivity of steel.
• Silicon (Si): Silicon contributes to deoxidation and increases the strength of steel. It is common in structural steels.
• Titanium (Ti): Titanium increases the strength of steel.
• Aluminum (Al): Aluminum can increase corrosion resistance and strength.

The following table shows an overview of common steel grades in the various standardized notations. The character □ is a placeholder in the designation.

Explanation for the steel designation

The designation of steels is not uniform. In general, however, one can assume that the DIN standards such as DIN EN 10027-1 (according to material number consisting of code letters and numbers) and DIN EN 10027-2 (according to chemical composition), derive general principles.

Material short name

The DIN lists requirements for the material short names and divides them into two groups. For Group 1, the designation depends on the utilization and mechanical properties of the steel. For Group 2, the designation depends on the chemical composition of the steel. This designation makes sense when the individual alloying elements provide information about certain properties such as corrosion resistance or when they are to undergo heat-treatment. The short name in Group 1 consists of at least one main symbol and the minimum yield strength in megapascals, e.g. S235, where S stands for steels in steel construction. Additional symbols may be added depending on the property and use, e.g. S235J2.

An example of a name according to chemical composition in Group 2 would be 42CrMo4. The percentage content of the element in the steel composition is indicated. For example, C45 for a steel with a carbon content of about 0.45%.

The steel designation according to JIS standards are composed in a similar way. The designation usually consists of one letter indicating the steel group or type, followed by one number containing specific information about the steel grade (chemical or mechanical properties). SS400, for example, stands for an unalloyed structural steel (SS = Structured Steel).

Material number of steel

Material numbers are assigned by the Steel Institute VDEh. The designation consists of the following parameters: X.YYZZ(AA). The following applies:

• X = main group
• Y = grade number (steel group)
• Z = counting number
• A = extended counting number

According to European standards, the material number for steel always begins with 1., e.g. 1.7033 for chromium alloyed quenched and tempered steel.

Selection of the steel group number

This material number serves the purpose of uniquely identifying materials and documenting specific material properties. The material number for steel can be found in tables.

Comparison of standardization

Steel grades are subject to different standards. The standards serve to ensure the quality, properties and utilization of steel in various industries and applications. The following list contains the standards of various institutes and committees:

• JIS: Japanese Industry Standard from the Japanese Industrial Standards Committee.
• ISO: International Standard from the International Organization for Standardization.
• AISI: American Standard from the American Iron and Steel Institute (AISI).
• DIN: German Industrial Standard from the German Institute for Standardization (Deutsches Institut für Normung, DIN).
• EN: European standards from one of the European Committees for Standardization (CEN, CENELEC, ETSI)
• BS: British Standard from the British Standards Institute (BSI).