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Low-alloy steel welding rods are widely used for welding mild steel and low-alloy steel or for deposition on mild steel to form a heat resistive, corrosion-resistant or abrasion-resistant protective overlay. The chemical composition of low alloy steel welding rods should conform to the standards set forth in GB/T 5118-1995.
GB/T 5118-1995, the standard governing the chemical composition of the wires, first defines the wire products – low alloy steel welding rods – and their purpose. Low alloy steel welding rods are composed primarily of iron, with a variety of additional elements of varying concentrations. These additional elements provide increased strength, corrosion resistance, and heat-resistance when inserted into the iron matrix by welding. These additional elements must be present in the wire in the exact concentrations mandated by the standard in order for the welding rods to provide the desired properties. Excessive or insufficient amounts of the additional elements can impair the welding rod’s performance.
The standard provides a list of 4 additional elements with which the welding rods must comply: carbon, manganese, silicon, and phosphorus. The standard also provides maximum and minimum allowable concentrations for each of these elements according to the product class and grade (namely, “Low Alloy Steel Welding Rod” class A and class B).
The carbon content defines the wire’s hardness, which is a major factor in its weldability. For Class A Low Alloy Steel Welding Rod products, the allowable range of carbon content is 0.12%-0.18%. For Class B products, the allowable range of carbon content is 0.17%-0.22%. If the carbon content balance is outside of this specific range, the wire may not weld effectively.
Manganese is a unique element present in low alloy steel welding rods. It is used to deoxidize the weld pool and exclude oxygen from the weld zone. The maximum allowable manganese content for Class A Low Alloy Steel Welding Rod products is 0.50%. For Class B products, the maximum is 0.57%.
Silicon is also a major component in the production of low alloy steel welding rods and has several effects on the weld quality. Silicon is used to deoxidize the weld pool and blunt the melting point of the rod, increasing weldability. The maximum allowable silicon content for Class A Low Alloy Steel Welding Rod products is 0.15%. For Class B products, the absolute maximum is 0.20%.
Finally, phosphorus is the last major element included in low alloy steel welding rods. It helps to form a smooth and uniform weld pool, increasing both weldability and weld strength. The maximum phosphorus content for Class A Low Alloy Steel Welding Rod products is 0.035%. For Class B products, this is increased to 0.045%.
In sum, low alloy steel welding rods must meet the chemical composition standards set forth in GB/T 5118-1995 in order to be suitable for welding. These chemical composition standards define the specific concentrations of carbon, manganese, silicon, and phosphorus; welding rod products with excessive or insufficient amounts of these elements can fail to provide the desired weld quality, strength, and heat-resistance. By following the guidelines provided in GB/T 5118-1995, however, the performance of welding rods can be consistently ensured.
