Alloy structure steels (GB 3077-88)
Overview
Alloy structure steels refer to the type of alloy steel which has been developed for the purpose of the restructure of steel objects in the engineering industry. Specifically, GB 3077-88 refers to the alloy structure steel used in such structures as machinery, boilers and vehicles. The alloy generally consists of Iron as the base material and other alloying elements such as Carbon, Silicon, Molybdenum, Chromium, and Vanadium. These elements are added to the steel in order to increase its strength, durability, and corrosion resistance. In the methods for designating these steels, which is established according to the more general and widely used ISO nomenclature system, there are several points worth noting.
Designation System
The designations of alloy structure steels according to the GB/T standards can be divided into several parts as follows:
1. Steel Type.
The beginning of a steel code usually defines the type of steel in question. For example, China uses ‘45’ to designate carbon steels and ‘20’ for alloy steels.
2. Chemical Composition of the Steel.
The specific elements and their amounts within the steel are represented at the start of the code. For example, 45# means steel with 0.45% carbon content.
3. Mechanical Properties of Steel.
The mechanical properties of an alloy steel, such as its tensile strength, yield strength, and elongation rate, are represented immediately after the chemical composition.
4. Treatment Condition Designation.
The treatment condition of a steel variety indicates the type of temperature and time manipulation to which a steel had been subjected to in order to achieve its desired strength. These are represented by ‘C’, ‘M’, or ‘T’, which indicate cold caused treatment, medium caused treatment or tempering, or hot treated condition, respectively.
Exemplary Alloy Structure Steel
The most common type of alloy structure steel is 45#, or 45# steel. It is a medium-carbon structural steel with a carbon content of 0.45%, a phosphorus content of less than 0.035%, a sulphur content of less than 0.035%, and a silicon content of less than 0.30%. It also contains manganese, chromium, and nickel as alloying elements. Depending on what type of product requires the steel, it can be produced in either a hot-rolled, or cold-rolled condition. The mechanical properties of 45# steel produced in a hot-rolled condition consists of a maximum tensile strength of 650 Mpa, a yield strength of 415 Mpa, and an elongation of 28%. The mechanical properties of 45# steel produced in a cold-rolled condition consists of a maximum tensile strength of 620_760 Mpa, a yield point of 355 Mpa, and an elongation of 19%.
Conclusion
To conclude, alloy structure steels (GB 3077-88) are a category of alloy steels which are specifically developed for use in the engineering industry. They are typically composed of iron and other alloying elements in order to provide them with greater strength, durability, and corrosion resistance. Designations of the steels are made according to the Chinese GB/T standards, which comprises of four main parts. The main alloy structure steel is 45# steel, which has a maximum tensile strength of 650 Mpa in a hot-rolled condition, and a maximum tensile strength of 620-760 Mpa in a cold-rolled condition.
