Alloy structural steel(GB 3077-88)
Alloy structural steel is a kind of steel alloy used in a variety of structural applications. It is composed of a combination of metal elements, including manganese, tungsten, vanadium, molybdenum, nickel, and chromium, which increase hardness and durability while maintaining an optimum balance of strength and ductility. The resulting metal is strong, durable, and corrosion resistant.
GB3077-88 is a Chinese national standard governing the quality of alloy structural steel. The standard is meant for rolled steel for general engineering and structural applications, as compared to specialized steels for specific applications such as tool steels and die steels. The grade is divided into 3 subgroups — Carbon steel, alloy steel and special steel — based on their chemical composition.
Carbon steel, or carbon-manganese steel, is a strong, malleable steel that offers the highest strength-to-weight ratio among all steels. This makes it ideal for general engineering and structural applications and, due to its malleability, it is also easy to shape and weld. Alloy steel, which can contain up to 1% nickel and up to 0.6% molybdenum, is a stronger, but less malleable steel and can offer better resistance to wear and corrosion. Special steel, which can contain up to 1% molybdenum, offers the highest strength ratio and is the most resistant to wear.
The grade under GB 3077-88 follows the following parameters:
Tensile Strength – Quoted in MPa, it determines how much force is needed to break a material.
Yield Strength – Quoted in MPa, it determines the stress needed to cause a structure or object to bend or deform.
Elongation – Quoted in percent, it determines the degree to which a material can extend before meeting rupture.
Impact Strength – Quoted in joules per cubic centimeter, it determines the amount of energy delivered by an impact source.
Coefficient of Thermal Expansion – Quoted in mu m/m/°C, it determines how much a material will expand and contract during temperature changes.
Fatigue Strength – Quoted in MPa, it determines how many times a material may be subjected to an external force before fracturing.
Hardness – Quoted in Brinell, Vickers, or Rockwell, it determines how resistant the material is to surface indentation.
Vertical Expansion – Quoted in mm/m, it determines the amount of upward expansion due to maximum weight load.
Heat Treatability – Quoted in degree, it determines how well the material may be treated with heat.
Weldability – Quoted in magnitude, it determines the ease with which a material can be welded.
The grade under GB 3077-88 also covers specific testing methods, including ultrasonic test and dimensional test.
In conclusion, alloy structural steel offers the best balance of strength, ductility, and corrosion resistance, making it an ideal choice for structural and other general engineering applications. The grade under GB 3077-88 is probably the most commonly used and provides a combination of properties that are suitable for a variety of applications.
