Building frames are ordered in whichever structural steel grade the local code recognises, which is why SS400, SS490, A36, S235JR, S355JR and the older ST37 designation all appear on the same procurement list. Five of the six are current standards in Japan, the United States and Europe; ST37 was withdrawn when EN 10025 replaced the older German national standards. Comparing them on minimum yield strength, impact testing and chemistry shows where they can be used interchangeably and where a design check is required.
The Six Grades at a Glance
Minimum yield values apply to material up to 16 mm thick, the reference thickness common to the relevant standards.
| Grade | Standard | Min. yield | Tensile strength | Status |
|---|---|---|---|---|
| SS400 | JIS G3101 | 245 MPa | 400-510 MPa | Current |
| SS490 | JIS G3101 | 285 MPa | 490-610 MPa | Current |
| ASTM A36 | ASTM A36/A36M | 250 MPa | 400-550 MPa | Current |
| S235JR | EN 10025-2 | 235 MPa | 360-510 MPa | Current |
| S355JR | EN 10025-2 | 355 MPa | 470-630 MPa | Current |
| ST37 | DIN 17100 | 235 MPa | 360-510 MPa | Withdrawn, superseded by S235JR |
Two corrections to common assumptions are worth noting. SS490 does not have a minimum yield strength of 490 MPa; the number refers to the tensile strength class, and the minimum yield strength is 285 MPa. Carbon content for SS400 and SS490 is not specified by JIS G3101, which defines these grades by mechanical properties alone; composition limits that appear in mill certificates are mill practice rather than a standard requirement.
Similarities and Differences Between the Mild Steel Grades
SS400, A36, S235JR and ST37 form a family of low carbon structural steels with comparable yield strengths within about 15 MPa of one another. All four weld with conventional low hydrogen consumables and need no preheat at ordinary thicknesses, all have good ductility, and all are produced in large volumes, which keeps them widely available and competitively priced. The differences that matter in practice are the standard to which they are certified, the thickness ranges over which the guaranteed yield strength applies, and whether any impact toughness is required.
ASTM A36 applies to plates, shapes and bars and carries no mandatory impact test.
JIS G3101 SS400 and SS490 are specified by tensile and yield properties, with SS490 offering about 16 percent more minimum yield than SS400.
EN 10025-2 S235JR and S355JR include room temperature impact testing as part of the designation.
ST37 should no longer be ordered for new work; S235JR is its recognised replacement, and certificates should be issued against EN 10025-2.
S355JR and SS490 in Heavier Construction
S355JR offers a minimum yield strength of 355 MPa, about 42 percent above A36 and S235JR, and SS490 offers 285 MPa with a higher tensile band. For the same section, the higher strength grades carry more moment and more axial load, so columns and long span beams can often be reduced in size, which lowers steel tonnage, welding volume and transport cost. The trade-off is a slightly higher unit price and, for thick sections or cold conditions, marginally more care in welding. Where a project demands documented low temperature toughness, the impact tested variants such as S355J2 at minus 20 degrees C are the appropriate choice; SS490 has no direct European or United States equivalent, so its design values must be used as published in JIS G3101 rather than read across from another grade.
Weldability and Fabrication Notes
All six grades are weldable structural steels. The lower strength grades in the family require no preheat at typical fabrication thicknesses and accept manual metal arc, gas shielded and flux cored processes without difficulty. Higher strength grades such as S355JR and SS490 contain small additions of manganese and other elements that raise hardenability, so for thick webs and flanges, or at low ambient temperature, a modest preheat in the region of 100 degrees C is a prudent precaution against hydrogen assisted cracking. Consumable strength should match the parent grade: an electrode rated for 490 MPa tensile is suitable for A36 and SS400, while a higher strength consumable should be used for S355JR and SS490 to avoid an under-matched joint.
Inspection and Verification on Delivery
Documentation: check the mill test certificate against the ordered grade, and confirm that heat analysis and tensile results fall inside the standard limits.
Surface condition: light mill scale is normal, while flaking rust, deep pits, cracks or transverse scratches indicate handling or storage problems that warrant rejection.
Dimensions: measure depth, flange width, web and flange thickness and length, and compare the results with the tolerances of the applicable standard such as ASTM A6, EN 10034 or JIS G3192.
Markings: the grade, heat number, size and mill identification on the flange should agree with the certificate and the packing list.
Independent testing: for critical or high value orders, a sample can be sent to a laboratory for tensile or chemical analysis to confirm the grade independently.
Packaging, Delivery and Storage
Beams are supplied in strapped bundles of matched size and grade, with corner protectors to prevent strap damage and, for international shipments, waterproof wrapping to keep out sea moisture. Small and medium bundles are handled by crane or forklift directly; larger consignments may be placed on timber pallets that are compliant with ISPM 15 for international movement. Every bundle is labelled with grade, size, heat number and length so that material can be released to the correct drawing without unpacking the whole consignment.
On site, beams should be stored clear of the ground on timber bearers with drainage, because standing water on the bottom flange is the most common cause of early corrosion. Indoor or dry conditions call for little more than a primer coat, while outdoor, coastal or humid environments normally require hot-dip galvanising to ISO 1461 with a minimum local coating of 70 micrometres on steel thicker than 6 mm, or a protective coating system applied after fabrication.
Delivery planning depends on whether the section is a stock item or a mill rolling programme item. Stock sizes ship in days, while non-standard sections are produced in the next available rolling campaign, so the section list should be frozen early in the procurement programme. International orders add sea freight time on top of production time, and it is normal to agree a phased delivery schedule for large projects so that erection can start before the final batch arrives.
Frequently Asked Questions
Q: What do SS400, A36 and S235JR have in common?
All three are low carbon structural steels with minimum yield strengths between 235 MPa and 250 MPa, so they behave similarly in lightly and moderately loaded frames. They weld easily without preheat, are ductile enough to redistribute stress, and are produced in large volumes worldwide. They differ in the standard they are certified to and in whether impact testing is mandatory.
Q: Why choose S355JR or SS490 instead of A36?
Because their higher minimum yield strength allows a smaller or lighter section to carry the same load, which reduces steel tonnage, fabrication effort and transport cost. S355JR is about 42 percent stronger than A36 in minimum yield, and SS490 about 14 percent stronger. The higher grades also provide more reliable properties where documented toughness is needed.
Q: Is SS490 actually a 490 MPa yield steel?
No. The designation refers to the tensile strength class. JIS G3101 sets the minimum yield strength of SS490 at 285 MPa for thickness up to 16 mm, with a tensile range of 490 MPa to 610 MPa. Design checks must use the yield value from the standard, not the number in the grade name.
Q: Can ST37 still be supplied?
ST37 belongs to the withdrawn DIN 17100 series and has been replaced by the EN 10025-2 grades. Material supplied today for a new project should normally be certified as S235JR, which occupies the same strength position. Where an existing structure specifies ST37, the equivalent grade should be confirmed before any replacement member is fabricated.
Q: Are these grades compatible with different national building codes?
Each grade is written into the standards of its own region, and most codes allow an equivalent grade when the design values are verified. A36 is widely accepted in North America, SS400 and SS490 in Japan and other parts of East Asia, and S235JR and S355JR under EN 10025-2 in Europe and in many other markets. The purchase order should name the code, the grade and the certificate type required.
Q: How should H beams be stored after delivery?
Stack them clear of the ground on timber bearers that allow air movement, keep them away from standing water and wet concrete, and separate grades and heat numbers so that traceability is preserved. For long term outdoor storage, apply a primer or specify galvanising, and lift bundles with slings rather than dragging them across one another to avoid surface damage.