Structural steel is used in a variety of sectors such as defence, oil and gas, mining, infrastructureand in the building and construction industries. If welded correctly it is a reliable method of construction, there are many reasons it is so widely used across the entire globe. From large-scale structures like high-rise buildings,bridges and critical mining equipment, structural steel forms the backbone of infrastructure in Australia. Read on for more from Technoweld’s experts.
How do Structural Steels Differs?
Structural steels come in many types in terms of chemistry, manufacturing process and form.
Generally steel used for structural elements are classified into low carbon, carbon manganese, medium carbon, low alloy and quench and tempered steels. In terms of steel classified to Australian Standards they typically have a maximum carbon content of 0.47%. The type of steel, the alloying elements that make up its composition and how it gains its mechanical properties significantly effects their weldability. Often during the design phase the weldability of materials is not a top priority.
So what differentiates structural steel are two key things, strength and toughness from chemistry or strength and toughness from its manufacturing process.
Strength and toughness from chemistry.
Pure iron is very soft and has limited application in engineered structures. To overcome this a number of alloying elements are added to the iron to increase its mechanical properties. Carbon is the most important element added to iron, followed by manganese.
Carbon – Generally increasing the amount of carbon increases strength, toughness and hardenability but it turn it reduces weldability and ductility.
Manganese – Typically is added as it strengthens the steel and further improves toughness but also reduces weldability and increases hardenability.
Reducing weldability means increased controls are required during welding.
Other elements are added for specific purposes like silicon as a deoxidiser, nickel to improve low temperature toughness, phosphorus to increase machinability. Other micro alloys such as chromium, vanadium, copper, aluminium are added to further improve the steel.
How to weld these materials is significantly different than how you approach high strength low alloy, thermo mechanically controlled rolled or quench and tempered materials.
Strength and toughness from manufacturing process.
These materials that fit into the category of high strength low alloy, thermo mechanically controlled rolled or quench and tempered typically have higher strength that allows designers to reduce weight and reduce section size. They get their properties from how they are produced rather than just pure chemical composition.
Generally their weldability is considered to be good to fair but if welding is not controlled properly there is a risk of significantly increasing brittleness or losing strength of the parent material during welding. This risks premature failure of the weldment. Lose of strength and an increase in brittleness is not something that can be detected by non destructive examination and confidence can only come from using a proven welding procedure specification.
Knowing how a steel will react when it is welded based on its chemistry or manufacturing process is a critical part of ensuring the structures performance.
Understanding why a material has been specified is important to ensure the welding consumables are selected to match the intended design.
Contact Technoweld for Material Welding and Joining Consultations
Structural steel is widely used to manufacture many different types of structures, plant and equipment it is a strong, versatile material but only works when welded properly. Technoweld provides guidance and consultancy, inspection services and welding supervision. We can provide welding procedures to ensure builds are compliant and high quality. Contact us today to find out how we can help!