Alloy steel is a kind of steel made mainly by adding or changing alloy elements in ordinary carbon steel to obtain desirable mechanical properties, physical properties or special preformance. It is widely used in a variety of industrial fields such as manufacturing automotive and aerospace components.
The common series of alloy steels are designated by four-digit numbers followed by a letter indicating their application. The first two digits identify the alloy and the last two digits are used to refer to the specific heat treatment and chemical composition. The letter of the four-digit number serves two purposes, one to indicate the metallurgical behavior and the other to indicate the type of formulation used to make the steel. A capital letter usually stands for heat-treatable steels and indicates that the letter “T” (Treated) is attached at the end of the four-digit number. Lower-case letters usually stand for non-heat-treatable steels and indicates that the letter “R” (Received) is attached at the end of the four-digit number.
The four-digit number in the alloy steel designation system is mainly composed of two parts. The first part consists of two digits used to indicate the type of steel and the second part consists of two digits used to identify the specific chemical composition or heat-treatment condition.
The first two digits in the alloy steel designation indicate the type of steel. Steels with lower numbers are generally lower alloy grades, while steels with higher numbers are generally higher alloy grades. For example, 1050 steel is an ordinary carbon steel, while 5140 steel is a low alloy steel and 5160 steel is a high alloy steel.
The last two digits in the alloy steel designation indicate the specific chemical composition or heat-treatment condition. Firstly, the second part ends in zero to indicate that the alloy is not heat treated. For example, 1040 steel is an unalloyed steel with a carbon content of 0.40%. Where the last two digits have non-zero number, this indicates that the steel has some form of heat treatment and the particular treatment can be determined based on the place in the table. For example, 4140 steel is treated in an annealing process, 5140 steel is treated in a normalizing process and 5160 steel is treated in a quenching and tempering process.
In summary, alloy steel numbers are usually composed of four digits. The first two digits indicate the type of steel and the last two digits indicate the specific chemical composition and heat-treatment condition. This information can be further broken down into the application, metallurgical behaviour and formulation type. Knowing the alloy steel number can help you find the correct material for your applications and enables you to get the best performance out of the material that you choose.
