ArcelorMittal is proposing a full range of High Strength Steels with enhanced weldability performances.
- Among its offer, sheets and heavy plates, in addition to Histar® long products, show very good welding capabilities, especially concerning:
- Thermomechanical rolled steels from S355M/ML to S460M/ML
- Normalised or Normalised rolled steel from S355N/NL to S460N/NL
The above mentioned are in accordance with EN 10025 standard for structural steels.
- ArcelorMittal's weathering steel range, called Indaten® range, has excellent weldability with all the usual welding processes due to its low carbon content and fine-grained structure.
- Ultra-high strength steels, called Amstrong®, are also offering good weldability performances with yield strength up to 960 MPa, and are suitable for mechanical engineering manufacturing.
- Welding Heavy Sections, such as JUMBO profiles, requires specific attention. For that reason, ArcelorMittal beam finishing centre C3P offers a complete range of fabrication and finishing operations to improve the technical capabilities of our partners, steel fabricators and general contractors: cold sawing, drilling, cambering, bending, oxyacetylene cutting, flame cutting, robotic plasma cutting. In addition, we provide value added service such as weld preparation of JUMBO profiles, with exceptional cutting tolerances and quality workmanship.
Welding of metal parts is a joining process designed to ensure metallic continuity across the joint. This continuity is obtained by heating, to produce local melting (in fusion welding) or diffusion. In most processes the heat is applied directly, e.g. by using an electric arc, flame or laser beam, or it is the result of, for instance, friction or electrical resistance (Joule heating).
In addition to heat, the joining process can include the incorporation of a filler metal, the application of pressure and/or protection from atmospheric gas contamination. The quality of the weld is related to the skill with which the weld was made, and thus refers to the severity and quantity of imperfections such as pores, undercut and cracks found in the weld. The quality is ascertained by means of appropriate test techniques, which can be destructive (e.g. bend testing or cross-sectioning) or non-destructive (e.g. ultrasonic testing or radiography). The properties, on the other hand, refer to the mechanical performance and physical properties of the weld, examples of which are tensile strength, ductility and impact toughness.
Weldability, or the ability of steel to be welded to another material by the application of heat, is a very relative concept. Operational weldability, on the other hand, considers the suitability of a material to be joined using a specific welding process and is thus somewhat more dependent on technological advances in these processes and equipment. What might be termed regulatory weldability, involves criteria stipulated in specifications, standards and general codes of practice and, as such, combines the two. These different weldability factors all have an essential impact on the economics of welding.
One property that is often used as an indication of weldability is the hardenability of the steel. It links the chemical composition and cooling rate during welding to the microstructure, and consequently welds properties.
Successive improvements in steel welding techniques enable good-quality joints to be obtained with high productivity. Significantly further progress has been achieved by the use of highly localised energy sources, such as laser, laser-MAG hybrid welding or cold metal transfer (CMT) arc welding, with considerably narrower heat-affected zones (HAZ). This is particularly important for maintaining the properties of sophisticated modern steel products.
Specific attention is drawn to the Heat Affected Zone (HAZ), due to the presence of different transformation products of varying hardness and brittleness. In the case of the HAZ, this is evaluated by means of the carbon equivalent value (Ceq), which aims to allow the hardening effect of different alloying elements to be combined in a single value, thus making it possible to compare different steels.
The use of a metallic and/or organic coating must be considered when evaluating weldability. Generally speaking, welding parameters must be adapted when switching from an uncoated sheet to a coated product, to maintain operational and/or metallurgical weldability.
For construction products and solutions manufacturing, the most common welding processes are:
- Resistance spot welding, to be used with metallic coated steels, e.g. small welded tubes.
- Arc welding process methods (plasma, TIG, MAG), but MAG is recommended when possible because it is the most productive. Arc welding process is typically used for steel structure fabrication.