Product Scope
Angle iron, also called angle steel or angle bar, is a hot rolled L shaped section with two legs at 90 degrees. It is one of the most widely traded structural profiles because it can be bolted, welded or riveted in almost any orientation, and because the two legs give stiffness in two directions from a single inexpensive piece. Standard product is delivered in the as rolled condition, in random or fixed lengths, with mill edge and a mill test certificate.
Classification of Angle Steel
| Classification | Description | Typical use |
|---|---|---|
| Equal angle | Both legs have the same width | Frames, bracing, towers, transmission poles |
| Unequal angle | Legs have different widths | Purlin connections, brackets, built up beams |
| Single angle | One section used alone as a member | Lattice diagonals, small supports |
| Double angle | Two angles back to back or toe to toe | Heavily loaded struts, crane jibs |
Hot rolled angle is produced from a square billet passed through a series of grooved rolls, so the leg surfaces carry a slight draft and the inner corner has a fillet radius. Cold formed angle is made by bending strip and is available in thinner gauges with sharper corners; the two products are not interchangeable where the design assumes a hot rolled section.
How Angle Sizes Are Written
Metric practice expresses an angle as leg width times leg thickness. An equal angle with 30 mm legs and 3 mm thickness is written as 30x30x3, or in the older symbol form as an angle sign followed by 30x3. Under EN 10056-1 an equal angle is written with a single width, for example L 50x50x5, while an unequal angle lists both legs, for example L 75x50x8. Under JIS G3192 the leg widths and thicknesses are tabulated in millimetres, and the theoretical mass per metre is taken directly from that table rather than recalculated. The 2 to 7 mm thickness steps that exist within one leg width are an important purchasing point, because the same nominal 50 mm angle is stocked in several thicknesses at quite different weights per metre.
Common Models and Size Ranges
| Equal angle designation | Leg width, mm | Thickness range normally available, mm |
|---|---|---|
| L 20x20 | 20 | 3 |
| L 25x25 | 25 | 3 - 4 |
| L 30x30 | 30 | 3 - 4 |
| L 40x40 | 40 | 4 - 5 |
| L 50x50 | 50 | 4 - 6 |
| L 63x63 | 63 | 5 - 8 |
| L 75x75 | 75 | 6 - 10 |
| L 90x90 | 90 | 6 - 10 |
| L 100x100 | 100 | 8 - 12 |
| L 125x125 | 125 | 10 - 12 |
| L 150x150 | 150 | 10 - 15 |
| L 200x200 | 200 | 14 - 20 |
The thickness sets offered for each leg width are fixed by the dimensional standard of the producing country, so the ranges above indicate normal mill availability rather than a free choice of thickness. Unequal angles are usually stocked in combinations such as 75x50, 100x75, 125x75 and 150x90 with the thickness selected to suit the application.
Grades and Matching Standards
| Grade | Standard | Minimum yield strength | Tensile strength |
|---|---|---|---|
| Q235B | GB/T 700 | 235 MPa up to 16 mm | 370 - 500 MPa |
| Q355B | GB/T 1591 | 355 MPa up to 16 mm | 470 - 630 MPa |
| SS400 | JIS G3101 | 245 MPa up to 16 mm | 400 - 510 MPa |
| S235JR | EN 10025-2 | 235 MPa up to 16 mm | 360 - 510 MPa |
| A36 | ASTM A36/A36M | 250 MPa | 400 - 550 MPa |
Q235B is the default general purpose grade for domestic and export work, and its B suffix indicates a room temperature impact test. Q355B is chosen when the section works harder or when a lower mass is required for the same load. SS400 differs from the Q series in an important way: the number 400 refers to minimum tensile strength rather than yield strength, which is why its minimum yield value of 245 MPa looks lower than the grade number suggests.
Dimensional Standards, Lengths and Certification
Dimensions and mass per metre of hot rolled angle are controlled by GB/T 706 for the Chinese system, EN 10056-1 for dimensions and EN 10056-2 for tolerances in the European system, JIS G3192 for the Japanese system, and ASTM A6/A6M for general requirements on structural shapes in the American system. Delivery length is usually 4 to 12 m, with 3 to 9 m also common for lighter sizes; fixed length, multiple length and random length ordering are all normal, and cut to length service is available. Straightness, leg squareness and allowable edge burr should be agreed at the enquiry stage. Material is normally certified to EN 10204 3.1 with heat number traceability, and third party inspection or independent chemical and mechanical testing can be added when a project specification requires it.
Frequently Asked Questions
Q: How is the size of an angle iron written?
A: As leg width by leg thickness. An equal angle with 30 mm legs and 3 mm thickness is written 30x30x3, or L 30x30x3 in European notation.
Q: What is the difference between equal and unequal angle?
A: Equal angle has two legs of the same width and is the standard structural product; unequal angle has two different leg widths and is used where the connection geometry requires it.
Q: Which grade is the usual default?
A: Q235B to GB/T 700 is the most common general purpose grade, with SS400 to JIS G3101 and S235JR to EN 10025-2 used for the same duty in other markets.
Q: What does the 400 in SS400 mean?
A: It refers to a minimum tensile strength of 400 N/mm2, not yield strength. The specified minimum yield strength for thickness up to 16 mm is 245 MPa.
Q: What delivery lengths can be ordered?
A: Fixed length or multiple length in ranges such as 3 to 9 m and 4 to 12 m are standard, and cut to length service is available for specific fabrication requirements.
Q: Can several thicknesses be supplied in one leg width?
A: Yes. A single leg width is normally produced in several thickness steps, so the thickness must be stated in the order because the mass per metre changes accordingly.