Structural steel types
Description and features
Structural steels are usually employed in the building sector, although they are often used in mechanics. In the sector of long (they can be hot rolled or cold rolled) rolled products, these steels are regulated by the UNI EN standard 10025-2.
All the steels present in this standard are unalloyed steels, i.e. carbon-only steels, with the possible addition of manganese as an alloying element, with maximum values of between 1.40- 1.70, depending on the steel. These steels are denominated by the letter S (for structural applications) or by the letter E (for mechanical applications) followed by three digits indicating the minimum yield strength to be guaranteed at room temperature for thicknesses below or equal to 16 mm (the minimum yield strength decreases for greater thicknesses),
and an alphanumeric code which gives indications regarding the resilience test(JR, J0, J2, K2).
The denomination can be completed with the addition of the letter C, which stands for a particular application (e.g. suitability for cold rolled) and letters +N, +AR, +M which represent the delivery condition.
EN 10025-2 is a harmonized standard and it is therefore possible to issue products with the CE mark.
The reference standard for cold finished steels is EN 10277. The steels present in this standard have a chemical composition which is very similar to their counterparts in the laminate standard but they do not have to guarantee any resilience value regarding their mechanical characteristics.
Structural and construction steels are used to produce parts for the building sector such as anchor bolts, tie rods, masonry sleeve anchors, reinforcing elements for damaged structures. In the field of mechanics they are instead used to produce shafts which are subject to little stress, parts intended to be welded, forged fittings, profiles for locks, ferrules, flanges.
Classification based on chemical composition
The presence of carbon in steel modifies some important physical-mechanical parameters. Specifically, the lower the carbon rate, the lower the mechanical strength, while the ductility and weldability of the iron increases. Based on the amount of carbon they contain, steels are divided into:
Low-carbon steel, or extra-mild steel: 0.05% to 0.25% carbon content.
Mild: carbon content between 0.25% and 0.40%;
Medium: carbon content 0.40% – 0.60%;
Hard: carbon content 0.60% – 0.70%;
Very hard: carbon content 0.70% – 0.80%;
Extra hard: carbon content 0.80% – 0.85%.
Steels used un metalwork are divided into: unalloyed steels: these are are steels in which the contents of the alloying elements fall within the limits indicated in Table 1I of UNI EN 10020: carbon steel, black steel; alloyed steels: steels in which at least one of the limits in the above-mentioned Table 1 is exceeded.