Two Grades at the Same Strength Level
S355JR is defined in EN 10025-2 as a non-alloy structural steel, and Q355B is defined in GB/T 1591 as a low-alloy high-strength structural steel. Both are named for their guaranteed minimum yield strength of 355 MPa in the base thickness range up to 16 mm. For channel sections produced to EN 10279 and GB/T 706 respectively, they are treated as equivalent in many international projects, but the two standards differ in chemistry, testing and marking.
Comparing Tensile Strength Requirements
The tensile strength requirements of the two grades are effectively the same:
S355JR: minimum yield 355 MPa for thickness up to 16 mm, tensile strength 470 to 630 MPa.
Q355B: minimum yield 355 MPa for thickness up to 16 mm, tensile strength 470 to 630 MPa.
Both also require elongation of about 22 percent minimum in the longitudinal direction for the thinner thickness range. In practice, a S355JR channel and a Q355B channel of the same size behave almost identically under static loading, and either can be substituted for the other when the project specification permits cross-standard substitution.
Differences in Chemistry
Although the strength levels match, the chemistry limits differ between the two standards. S355JR allows carbon up to about 0.24 percent in the thicker range, while Q355B controls carbon by thickness and generally aims lower, around 0.20 percent maximum with additional limits on niobium, vanadium and titanium microalloys. The phosphorus and sulfur limits are similar in both standards, around 0.035 percent for phosphorus and 0.035 percent for sulfur for the B quality level, but the way the two standards treat grain-refining elements and residual elements is not identical.
Differences in Impact Testing
The quality designations reflect different impact testing conventions. The JR in S355JR requires a minimum Charpy V-notch impact energy of 27 J at 20 degrees Celsius. The B in Q355B requires a minimum of 34 J at 20 degrees Celsius. The test temperature is the same, but the energy level is higher for Q355B, so a Q355B channel is expected to show slightly better toughness at room temperature. Neither grade is intended for severe low-temperature service; for that, S355J2 or Q355D with lower test temperatures are used.
Practical Selection Guidance
For a channel order, specify the standard and grade that the project code recognizes. If the design follows Eurocode 3, use S355JR to EN 10025-2 with dimensions to EN 10279. If the design follows Chinese codes, use Q355B to GB/T 1591 with dimensions to GB/T 706. When a buyer needs to substitute one for the other, compare the Mill Test Reports to confirm yield, tensile, elongation and impact values, and check the section dimensions and tolerances of the two standards for the same nominal size.
Frequently Asked Questions
Q: Are S355JR and Q355B the same steel?
They are close equivalents with the same 355 MPa yield and the same 470 to 630 MPa tensile range, but they follow different standards with different chemistry limits and testing rules.
Q: Which grade has a higher tensile strength?
Neither; both guarantee a tensile range of 470 to 630 MPa for the base thickness range, so the nominal tensile strength is identical.
Q: Is Q355B tougher than S355JR?
At 20 degrees Celsius, Q355B requires a higher minimum impact energy of 34 J versus 27 J for S355JR, so it is specified as slightly tougher at room temperature.
Q: Can a channel ordered as S355JR be delivered as Q355B?
Substitution is possible only with the buyer approval and only when the dimensions, tolerances, mechanical values and documentation meet the project requirements.
Q: Which standard governs channel dimensions for these grades?
S355JR channels use EN 10279 for dimensions and tolerances, while Q355B channels use GB/T 706 in the Chinese system.