What S355JR Round Steel Is
S355JR is a non-alloy structural steel defined in EN 10025-2, and S355JR round steel is the hot-rolled round bar form of this grade, with dimensions typically controlled by EN 10060. The name S355JR tells the story: S for structural steel, 355 for the minimum yield strength of 355 MPa in the base thickness range, and JR for the impact requirement of 27 J at 20 degrees Celsius. It is the default choice across Europe for members and parts that need more strength than S235 or S275 without moving to alloy steel.
Mechanical Properties
The guaranteed properties of S355JR for the common round bar range are:
Yield strength: minimum 355 MPa for thickness up to 16 mm, reducing to 345 MPa for 16 to 40 mm and 335 MPa for 40 to 63 mm.
Tensile strength: 470 to 630 MPa for the thickness range up to about 100 mm.
Elongation: minimum 22 percent in the longitudinal direction for the thinner range.
Impact toughness: minimum 27 J at 20 degrees Celsius.
Modulus of elasticity: about 200 GPa, common to all structural carbon steels.
These values are guaranteed by the heat, verified by testing, and documented on the Mill Test Report to EN 10204.
Chemistry Behind the Properties
S355JR achieves its strength through a balanced carbon-manganese composition with small alloy additions. Carbon is limited to about 0.24 percent maximum depending on thickness, manganese can reach 1.60 percent, and phosphorus and sulfur are held near 0.035 percent to protect weldability and toughness. The steel is fully killed and fine-grained enough for reliable welding and forming, and it is delivered in the as-rolled condition for general use.
Where S355JR Round Steel Is Commonly Used
The combination of strength, weldability and availability makes S355JR round steel a workhorse material:
Shafts, spindles and axles for machines and vehicles, often machined directly from the bar.
Bolts, studs and anchor rods for structural and mechanical connections.
Structural bracing members, tie rods and tension elements in steel frames.
Columns, posts and supports in buildings, platforms and handrail systems.
General fabrication items such as brackets, rollers and conveyor components.
Selection and Verification
When ordering S355JR round steel, specify the diameter, the standard EN 10025-2, the surface condition such as black or peeled, and the delivery length. Require a Mill Test Report showing the heat number, chemistry and mechanical test results, and check that the yield, tensile, elongation and impact values meet the standard for the ordered diameter. For parts that will be hardened or machined to tight tolerances, consider a higher machinability grade or a different specification altogether.
Frequently Asked Questions
Q: What does S355JR stand for?
S means structural steel, 355 is the minimum yield strength in MPa, and JR is the impact requirement of 27 J at 20 degrees Celsius.
Q: What is the tensile strength of S355JR round bar?
The guaranteed tensile range is 470 to 630 MPa for the common thickness range, with a minimum yield of 355 MPa up to 16 mm.
Q: Is S355JR round steel easy to weld?
Yes, the controlled carbon content and fine-grain treatment give good weldability with standard procedures and matching filler metal.
Q: Which standard controls the dimensions of S355JR round bars?
Material is specified to EN 10025-2, and the dimensions and tolerances of hot-rolled round bars are governed by EN 10060.
Q: Can S355JR round bar be used for shafts?
Yes, for lightly to moderately loaded shafts where the as-rolled strength of 355 MPa yield is sufficient, but heavily loaded or hardened shafts need alloy grades.