Designation method of Chinese alloy structural steel

The designation system for Chinese alloy structural steels

The designation system for Chinese alloy structural steels commonly includes the symbol of the Chinese classification society (e.g. TJS), the steel grade symbol, the chemical composition and the mechanical properties, and other elements such as test methods or delivery states. The symbols are as follows:

Chinese classification society symbol: As for Chinese-made steel plates for shipyard, the designations must be given with Chinese classification society symbol TJS. This symbol stands for the Chinese Classification Society and it is a three digit code following the letter T.

Steel grade symbol: Generally, steel grade symbols include two parts: the first part is mainly composed of the chemical composition of the steel, indicating the major alloying elements; the second part indicates the required mechanical properties.

Chemical composition: The chemical composition of the steel indicates the proportions of the different metal elements in the steels. For alloy structural steels, the common elements are manganese, silicon, nickel and copper.

Mechanical properties: This indicates the mechanical properties of the alloy structural steel. Mechanical properties include tensile strength, yield strength, elongation, and hardness.

Test methods: This is mainly used to test the performance of the steel. Common test methods are tensile test, impact test, and Charpy V-notch test.

Delivery state: There are three delivery states for alloy structural steels: hot rolling, normalizing, and tempering.

The designations of alloy structural steels usually include elements such as the Chinese classification society symbol TJS, the steel grade symbol, the chemical composition, the mechanical properties, the test method, and the delivery state. By studying the designation system, the users can choose the correct steel quality according to their own engineering requirements.

Chinese alloy structural steel grade designations consist of a three digit number prefixed by a letter, whereby the letter denotes the quality, e.g. Q stands for quenched and tempered, and L denotes fine grain structure. The first number denotes the type of steel, e.g. 12 refers to a low alloy steel, 36 and 44 respectively to medium alloy steels and 55 to a high alloy steel. The second number and third number are related to the average carbon contents of these alloys (percent): the first digit is for 10s digit and the second digit is for the unit digit.

For example, Q345 is a low alloy structural steel with an average carbon content of 0.34%, and its symbol gi 1144 denotes its grade; Q stands for quenched and tempered steel and the last two digits refer to its carbon content (34). The letter A or B may be added to denote the crude steel, HW added for hot-rolled steel, Q is added for quenched and tempered steel and S, P, or G is added for cold deformed steels, the third letter N means not heat treated, T means heat treated normalizing and Q means quenched and tempered.

Therefore, Q345A is a low alloy structural steel with an average carbon content of 0.34%, which is not heat treated specified; while Q345B is a low alloy structural steel with an average carbon content of 0.34%, and is heat treated by normalizing.

Alloy structural steel grades are universally used in the construction of bridges, boilers, ships and other large structures. Furthermore, alloy steels are used for many components in various industries, such as machinery, vehicles and tools.