JIS G3106 SM490YB carbon structural steel plate

Product Introduction

01Product Overview

JIS G3106 SM490YB is a rolled steel for welded structures — a 365 MPa-yield, 490–610 MPa-tensile low-alloy, C-Mn high-strength (HSLA) grade that also carries a mandatory Charpy impact of ≥ 27 J at 0 °C (the “B” suffix). The name is a specification, not a marketing line, and every letter matters: S is steel for structure, M is weldable, 490 is the minimum tensile strength in MPa, Y means the yield point is guaranteed at 365 MPa (the plain SM490A/B/C grades guarantee only tensile), and B is the impact class — for SM490YB it means a mandatory 0 °C, ≥ 27 J Charpy V-notch in the base JIS G3106 specification. It is the yield-guaranteed, impact-guaranteed member of the SM490 family, one step beyond SM490YA (same yield, no mandatory impact).

SM490YB is supplied as plate, sheet, section and bar for heavy welded structures that must shrug off low-temperature or dynamic loading — building frames and bridges, ships and marine structures, automobiles and construction vehicles, storage tanks / containers and heavy machinery. Its strength comes from a lean carbon-manganese balance rather than high carbon, so it stays readily weldable with ordinary consumables and is formable in the shop. One wording point worth keeping straight: despite older listings calling it “carbon structural steel” and claiming it “offers low yield and tensile strength”, SM490YB is not plain carbon and is not low strength — 365 MPa guaranteed yield and 490–610 MPa tensile is medium-to-high strength, and the “low” in low-alloy refers to its lean alloy content, not to low strength.

490-610 MPaTensile Strengthmin-max band, not a single value

365 MPa minGuaranteed Yieldthe 'Y' — yields down with thickness

0 °C ≥ 27 JMandatory Impactthe 'B' — required in base spec

JIS G3106Welded structure standard2008 / 2020 / 2024 editions

02Technical Specifications

What this page publishes, and what must be confirmed on the mill certificate when you enquire.

Item	Specification
Executive Standard	JIS G3106 (Japanese Industrial Standard for rolled steels for welded structure). Current edition JIS G3106:2020 (harmonised with the -2008 and -2024 revisions — same SM490YB requirements).
Steel Grade	SM490YB (JIS G3106; S-M-490-Y-B: structure / weldable / 490 MPa min tensile / yield guaranteed / mandatory 0 °C, ≥ 27 J impact)
Steel Category	Low-alloy, C-Mn high-strength (HSLA) welded-structural steel. JIS classifies it under carbon steel, but functionally it is a low-alloy grade — the site category “Carbon and Low-alloy Steel” is kept.
Product Forms Covered	Steel Plate Sheet Section Bar plate and sheet on this page; section and bar by agreement
Thickness Range	6 – 100 mm typical supply (JIS G3106 covers plate up to 200 mm by agreement; the mechanical ladder on this page is shown to 100 mm)
Width Range	1 000 – 4 000 mm
Length Range	4 000 – 12 000 mm
Production Way	As hot rolled (AR), normalized (N) or TMCP — the condition is chosen with the order
Delivery Condition	AR / N / TMCP — see section 07
Impact Requirement	0 °C, ≥ 27 J (V-notch), mandatory in the base JIS G3106 specification (the “B” suffix). This is the defining difference from SM490YA, which has no mandatory impact.
MOQ	1 t mixed sizes negotiable
Lead Time by Quantity	1 – 10 t: 5 days · 10 – 50 t: 10 days · > 50 t: negotiable
Payment Terms	L/C T/T D/P Western Union Paypal Money Gram
Processing Services	Cutting to length and width, profiling, bevelling, bending, drilling, welding, shot blasting and painting
Certification	Mill Test Certificate to EN 10204 3.1, or 3.2 with third-party endorsement; ladle (heat) analysis and mechanical test report

Two wording points worth clearing up. First, SM490YB is a low-alloy, C-Mn high-strength steel for welded structures, not plain carbon — older listings and the site category call it “carbon structural steel”, which is the JIS grouping but understates the grade (its strength comes from the C-Mn balance, not from carbon). Second, the old copy saying it “offers low yield and tensile strength” is misleading: 365 MPa guaranteed yield and a 490–610 MPa tensile band is a medium-to-high strength grade. The “low” refers to its lean alloying (low-alloy), never to low strength. And the key letter here is the “B” — unlike SM490YA, SM490YB carries a mandatory 0 °C, ≥ 27 J Charpy impact in the base specification.

03How to Read the Grade

Every part of SM490YB is a specification, not a marketing name.

Part	Meaning
S	Steel for structure (“Kozô” / structural). It tells you the grade is intended for load-carrying structural use.
M	Weldable (“Yôsetsu” / welded structure). The grade is made to be welded, with tight P/S and a C-Mn balance that keeps it readily weldable.
490	The specified minimum tensile strength in MPa — 490–610 MPa. Note “490” is a tensile number; the yield is set separately by the “Y”.
Y	Yield point guaranteed. SM490YB guarantees a yield point (≥ 365 MPa at ≤ 16 mm). The plain SM490A/B/C grades guarantee only tensile strength, not a specific yield — the “Y” is what makes the yield a guaranteed, certifiable value.
B	The impact class: for SM490YB the “B” means a mandatory Charpy V-notch of 0 °C, ≥ 27 J in the base JIS G3106 specification. (On SM490YA the “A” means no mandatory impact; on SM490A/B/C the letters are the same impact classes without the guaranteed yield.)
JIS G3106	The Japanese standard for rolled steels for welded structure. The edition is -2008 / -2020 / -2024; the SM490YB requirements are consistent across them.

The SM490 family — the “Y” guarantees yield, the letter sets the impact. SM490YB is the impact version of the yield-guaranteed grade.

Grade	Guaranteed yield	Mandatory Charpy impact	Position in the family
SM490A	No (tensile only)	None (A)	Base welded-structural grade, no impact
SM490B	No (tensile only)	0 °C, ≥ 27 J (B)	Adds low-temperature impact
SM490C	No (tensile only)	0 °C, ≥ 47 J (C)	Higher impact energy
SM490YA	Yes ≥ 365 MPa	None mandatory (A)	Yield guaranteed, no impact
SM490YB (this page)	Yes ≥ 365 MPa	0 °C, ≥ 27 J (B) — mandatory	Yield guaranteed + mandatory impact

Pick the grade by what you must certify. If the design needs a guaranteed yield point of 365 MPa, choose SM490YA (no impact) or SM490YB (0 °C, ≥ 27 J) — the non-Y grades (SM490A/B/C) do not guarantee a yield. If the structure also needs a low-temperature impact, choose SM490YB (the “B”); if it needs no impact, SM490YA is the leaner, no-impact twin. The tensile band (490–610 MPa) and the chemistry are the same across the family — only the guaranteed yield and the impact class change.

04Equivalent Grades

SM490YB is the 365 MPa-yield / 490–610 MPa-tensile / 0 °C ≥ 27 J level of the Japanese welded-structural family. The table maps it to its closest international grades — a similar number is not a licence to substitute; check chemistry, toughness and thickness brackets before swapping. Linked grades open their own page.

Standard	Grade	Min. Yield	What to check before substituting
JIS G3106 (this page)	SM490YB	365 MPa	The Japanese grade — yield guaranteed + mandatory 0 °C, ≥ 27 J (the “B”) (this page)
JIS G3106	SM490YA	365 MPa	The exact strength twin of SM490YB with no mandatory impact (the “A”). The direct alternative when the structure needs the guaranteed yield but not the low-temperature impact.
EN 10025-2	S355JR	355 MPa	Closest European grade — about 10 MPa lower yield, +20 °C impact (JR class). The most common substitute; confirm the ∼10 MPa yield gap and the impact class against the design.
EN 10025-2	S355J0	355 MPa	Same 355 MPa yield, 0 °C impact — a lower grade than SM490YB; not stocked on this page, cited for cross-reference.
EN 10025-2	S355J2	355 MPa	Same 355 MPa yield, −20 °C impact — a lower grade; cited for cross-reference.
ASTM A572 / A572M	A572 Grade 50	345 MPa	Closest ASTM grade — about 20 MPa lower yield. Confirm the yield gap; A572 does not mandate impact. Grade 65 (450 MPa) is a closer yield but less frequently stocked.
ASTM A633	A633 Gr A / C / D	345 MPa	Normalized structural steel, ~345 MPa yield — a lower grade; cited for cross-reference.
ASTM A992	A992	345 MPa	Structural-shapes grade (~345 MPa yield), mainly sections, not plate — cited for cross-reference.
GB/T 1591	Q345C / Q355C	345 / 355 MPa	Chinese lower grade, same welded-structural family — about 10–20 MPa below SM490YB; cited for cross-reference.
JIS G3106	SM570	460 MPa	The same JIS family but a higher grade (460 MPa yield) — a step-up, not an equivalent. Relevant when the design genuinely needs more strength.

Strength proximity is not interchangeability. Chemistry limits, toughness classes, thickness brackets and delivery conditions all differ between these standards. The grades that genuinely sit next to SM490YB are SM490YA (365 MPa, no impact, JIS), S355JR (355 MPa, EN) and A572 Grade 50 (345 MPa, ASTM) — each 10–20 MPa below the guaranteed 365 MPa yield, so the swap needs design sign-off. SM570 is higher, not a substitute. SM490YB’s defining feature is the mandatory 0 °C, ≥ 27 J impact — make sure any substitute matches that toughness class.

05Chemical Composition

Ladle (cast) analysis limits in weight percent, per JIS G3106 SM490YB (thickness up to 100 mm). Other alloying elements may be added as agreed. The residual limits the old listing omitted or understated are included here.

Element	Limit (% by mass)
Carbon, C	≤ 0.20
Silicon, Si	≤ 0.55
Manganese, Mn	≤ 1.65 (the current JIS G3106 value; some older listings show 1.60)
Phosphorus, P	≤ 0.035
Sulphur, S	≤ 0.035

Carbon equivalent and weld-crack sensitivity (CEV formula: Ceq = C + Mn/6 + Si/24 + Ni/40 + Cr/5 + Mo/4 + V/14).

Item	≤ 50 mm	> 50 – 100 mm	Note
Carbon equivalent Ceq (as-rolled / normalized, default)	≤ 0.44	≤ 0.47	JIS G3106 main (Table 3) limit
Carbon equivalent Ceq (TMCP condition)	≤ 0.38	≤ 0.40	Tighter limit when TMCP is specified (Table 5)
Weld-crack sensitivity Pcm	≤ 0.24	≤ 0.26	TMCP; as-rolled ≤ 0.28 / ≤ 0.30 by agreement

Read the certificate against this table, not against a one-line data sheet. SM490YB is a lean C-Mn grade — the strength comes from the carbon-manganese balance, not from high carbon, which is why it stays weldable. Two notes: the current JIS G3106 limit is Mn ≤ 1.65 (some older listings show 1.60); and the carbon equivalent has two limits — the default as-rolled/normalized Ceq is ≤ 0.44 / ≤ 0.47, while the TMCP condition tightens it to ≤ 0.38 / ≤ 0.40. The Pcm (weld-crack sensitivity) index, ≤ 0.24 / 0.26 for TMCP, is what shops use to set preheat. JIS classifies SM490YB under carbon steel, but functionally it is a low-alloy grade — keep that in mind when comparing chemistry with plain-carbon grades like SS400.

06Mechanical Properties

Minimum room-temperature values, read against nominal thickness (JIS G3106 Table 7). JIS G3106 covers plate up to 200 mm by agreement; the full published ladder to 100 mm is four brackets. Every figure is a floor the heat is tested against, not a prediction of your certificate.

Thickness (mm)	Yield point R_eH min (MPa)	Tensile R_m (MPa)
≤ 16	365	490 – 610
> 16 – 40	355	490 – 610
> 40 – 75	335	490 – 610
> 75 – 100	325	490 – 610

Elongation & impact — the properties that make SM490YB distinct from its “A” twin.

Property	Requirement
Elongation A (JIS G3106 test pieces)	≥ 19 % (≤ 5 mm, No.5) · ≥ 15 % (> 5–16 mm, No.1A) · ≥ 19 % (> 16–50 mm, No.4) · for plates over 40 mm the requirement rises to ≥ 23 % (No.1A / No.4)
Charpy V-notch impact	Mandatory 0 °C, ≥ 27 J (V-notch, longitudinal) in the base JIS G3106 specification — this is the defining “B” requirement and the key difference from SM490YA (which has no mandatory impact). The test is performed per heat; the acceptance is 27 J average at 0 °C.

The difference from SM490YA, stated plainly. The yield ladder, the tensile band and the chemistry are identical between SM490YB and SM490YA. The only substantive change is the impact: SM490YB carries a mandatory 0 °C, ≥ 27 J Charpy V-notch in the base specification (the “B”), while SM490YA (the “A”) has no mandatory impact — on YA a Charpy is added only by agreement. So if your design calls for guaranteed low-temperature toughness, specify SM490YB; if it needs only the guaranteed yield, SM490YA is the no-impact twin. The yield still steps down with thickness (365 → 325 MPa) and the elongation has sample-thickness brackets as shown above — confirm the exact band for your thickness on the certificate.

07Delivery Condition, Heat Treatment & Additional Requirements

SM490YB can be supplied in several conditions; the order, not the grade, fixes the rest.

Item	Options
Delivery Condition	AR — As hot rolled (usual) N — Normalized TMCP
Additional Conditions	UT Charpy V-notch (0 °C, ≥ 27 J — mandatory) Z15 / Z25 / Z35 Third-party test (SGS) Coated or shot blasted and painting
Surface Treatment	As rolled Shot blasted Primed Painted

What the specification sets, and what has to be added by the order.

Item	Status in JIS G3106	How it is obtained
Delivery condition	AR usual; N or TMCP by agreement	Normalizing or TMCP can be agreed for a tighter, tougher microstructure.
Heat treatment	Not required by the as-rolled grade	Strength comes from the C-Mn balance and controlled rolling; normalizing is an agreed add-on, not a default.
Impact toughness	Mandatory 0 °C, ≥ 27 J (the “B” grade)	Charpy V-notch at 0 °C is tested per heat as part of the base requirement; additional temperatures may be agreed.
Ultrasonic testing	Not specified	JIS G 0901 or an agreed acceptance level, by agreement.
Through-thickness (Z) properties	Not specified	Z15 / Z25 / Z35 by agreement where the joint pulls through the plate thickness.
Third-party inspection	Not specified	SGS, BV, TUV or Intertek at the mill before shipment.
Certificate	MTC per the specification	EN 10204 3.1 as standard, 3.2 with third-party endorsement on request.

Keep the condition in the enquiry. SM490YB is normally delivered hot rolled (or TMCP) and tested per heat; anything beyond that — normalized, UT, Z-direction, third-party inspection — has to be written into the order before rolling, not added afterwards. Unlike SM490YA, the 0 °C, ≥ 27 J Charpy is already mandatory for the “B” grade, so you receive impact-tested plate as standard. For the same grade with no impact requirement, specify SM490YA.

08Typical Applications

Where a yield-guaranteed, impact-tested 365 MPa structural steel carries the load.

Building & Bridge Structures

Building frames, portal frames, bridge girders and support members — primary welded structural members where a guaranteed 365 MPa yield and good weldability matter, with the mandatory impact giving extra margin against brittle fracture.

Ships & Marine / Offshore

Ship hull structures, offshore platform members and marine welded assemblies — a weldable, yield-guaranteed, impact-tested grade widely used in Japanese-spec shipbuilding and marine work.

Automobiles & Construction Vehicles

Chassis, load-bearing frames and structural parts for trucks, trailers, construction and engineering vehicles — strength-to-weight that trims tare weight while staying weldable and impact-tough.

Pressure & Containment Structures

Storage tanks, silos, hoppers and pressure-equipment supports — welded containment where the guaranteed yield and the mandatory impact are both valued.

Heavy Machinery & Equipment

Excavator and loader structures, crane and lifting members, mining and engineering-machine frames — dynamic-load welded structures that benefit from a certified yield point and a guaranteed low-temperature impact.

Why this grade is chosen when the design needs a guaranteed yield AND guaranteed impact: it gives a certifiable 365 MPa yield (the “Y”) and a mandatory 0 °C, ≥ 27 J Charpy (the “B”), welds with ordinary consumables, and sits in a well-known JIS family with a no-impact twin (SM490YA) one step away. What it does not give you is the very-high-strength band of SM570 — that is a different (higher) grade. The lean C-Mn balance keeps it readily weldable despite the mandatory impact.

09Processing, Testing & Supply

From mill plate to a cut, certified, ready-to-fit structural item.

Cutting & Profiling

Plate and sheet cut to length and width, profiled to drawing and bevelled for weld preparation on flame, plasma or laser equipment.

Forming, Bending & Welding

Bending and rolling to radius, cold forming to the radius the thickness allows, plus welded assemblies built under a qualified procedure — preheat is generally not required up to moderate thickness; thick or highly restrained joints call for 50–100 °C with low-hydrogen consumables.

Surface Treatment

Shot blasting to remove mill scale, then shop primer or full paint system, followed by export marking and seaworthy packing.

Inspection & Certified Delivery

Chemical analysis and tensile testing per heat, the mandatory Charpy impact at 0 °C, UT and Z-direction testing when specified, then the MTC carrying the grade, the JIS G3106 edition and any third-party report.

Mill Test Certificate to EN 10204 3.1, or 3.2 with third-party endorsement
MTC stating the grade (SM490YB) and the JIS G3106 edition cited
Heat (ladle) analysis and mechanical test report (yield, tensile, elongation)
Carbon equivalent (Ceq) and, where relevant, Pcm recorded against the condition ordered
Charpy impact report at 0 °C, ≥ 27 J (mandatory for the “B” grade)
Ultrasonic testing report to the agreed acceptance level (JIS G 0901)
Z-direction (through-thickness) test report where Z15/Z25/Z35 is ordered
Third-party inspection by SGS, BV, Intertek or another nominated agency
Export packing, marking and loading supervision

Quote checklist — you get a faster, comparable price if you send: thickness × width × length, quantity, product form (plate, sheet, section or bar), delivery condition (AR / N / TMCP), the mandatory impact requirement (0 °C, ≥ 27 J is standard for “B” — confirm any other temperature), UT acceptance level and any Z-direction requirement, surface treatment, MTC type, destination port and payment terms. MOQ is 1 t.

10Frequently Asked Questions

Q1What does JIS G3106 SM490YB actually mean?

SM490YB is a Japanese rolled steel for welded structures. S = structure, M = weldable, 490 is the minimum tensile strength in MPa (490–610), Y means the yield point is guaranteed at ≥ 365 MPa (the plain SM490A/B/C guarantee only tensile), and B is the impact class meaning a mandatory 0 °C, ≥ 27 J Charpy V-notch in the base JIS G3106 spec. It is a low-alloy, C-Mn high-strength grade; the standard is JIS G3106 (-2008 / -2020 / -2024).

Q2What is the difference between SM490YB and SM490YA?

Both guarantee the same 365 MPa yield (the “Y”). The difference is the impact: SM490YB carries a mandatory 0 °C, ≥ 27 J Charpy (the “B”), while SM490YA has no mandatory impact in the base specification (impact may be added by agreement). The yield ladder, the tensile band (490–610 MPa) and the chemistry are identical — only the guaranteed yield and the impact class change. So pick YB when the design needs guaranteed low-temperature impact, and YA when it needs only the guaranteed yield.

Q3What is SM490YB equivalent to in EN / ASTM / GB?

The closest European grade is EN 10025-2 S355JR (355 MPa, +20 °C impact) — about 10 MPa lower yield. In the US the closest is ASTM A572 Grade 50 (345 MPa). In China the comparable lower grade is GB/T 1591 Q345C / Q355C (345 / 355 MPa). The same-JIS-family SM490YA is the exact strength twin without the mandatory impact. SM570 (460 MPa) is higher, not an equivalent. All are procurement mappings; confirm the actual values against your governing code.

Q4Is SM490YB a carbon steel or a low-alloy steel?

Both descriptions are seen, and both are defensible: JIS groups SM490YB under carbon steel, but functionally it is a low-alloy, C-Mn high-strength (HSLA) grade — its strength comes from the carbon-manganese balance, not from high carbon, which keeps it weldable. It is not plain carbon like SS400, and it is not low strength despite the old “low yield and tensile strength” wording — 365 MPa guaranteed yield and 490–610 MPa tensile is medium-to-high strength. The site category “Carbon and Low-alloy Steel” reflects both.

Q5Can I substitute S355JR, A572 Gr.50, Q345C or SM570 for SM490YB?

Only with the designer’s sign-off against the governing code, and for most the answer is no as a drop-in. S355JR (355 MPa), A572 Gr.50 (345 MPa) and Q345C/Q355C (345/355 MPa) are 10–20 MPa below the guaranteed 365 MPa yield — close, but the yield gap must be accepted or the section resized; their impact classes also differ. SM570 (460 MPa) is too strong and changes the design. The grade that exactly matches the strength is SM490YA (without the mandatory impact). Even those differ in chemistry, impact class and thickness brackets, so the swap still needs design approval.

Q6How thick, how fast, what paperwork, and is the old page’s data right?

From 1 t, with typical lead times of about 5 days for 1–10 t, about 10 days for 10–50 t and negotiable above 50 t. Each heat ships with an EN 10204 3.1 mill test certificate. The figures on this page correct / complete the older listing: SM490YB is a welded-structural low-alloy grade (not plain carbon), the mechanical table shows the full four thickness brackets (365/355/335/325 MPa) instead of two and keeps the 490–610 MPa tensile and the elongation, the chemistry now uses the current Mn ≤ 1.65 and the two Ceq limits (≤0.44/0.47 as-rolled, ≤0.38/0.40 TMCP), and the mandatory 0 °C, ≥ 27 J impact is stated explicitly as the defining “B” feature (the old blank/ambiguous impact line is corrected). The old “SS330 stockist” line and the “620 mm” dimension (a SM570 residue) are fixed. Each change is flagged in a note box above.

More carbon and low-alloy structural grades we supply: JIS G3106 SM490YA welded structural steel plate (yield, no impact) · SM490YB (this page) · EN 10025-2 S355JR carbon structure steel plate · ASTM A572 Grade 50 hot rolled sheet plate · GB/T 1591 Q345C / Q355C low-alloy steel plate · JIS G3106 SM570 carbon structure steel plate · View all carbon and low-alloy steel plate →

Sources and limits: the figures on this page are reference information drawn from JIS G3106 (SM490YB, consistent across the -2008 / -2020 / -2024 editions) and published steel data sheets. SM490YB is a rolled steel for welded structures — a low-alloy, C-Mn high-strength grade with a guaranteed yield point of ≥ 365 MPa (≤ 16 mm), a tensile strength of 490–610 MPa and a mandatory Charpy impact of 0 °C, ≥ 27 J (the “B” suffix); the chemistry limits, the Ceq/Pcm and the tensile / yield / elongation floors are the standard requirements, while actual heat values are recorded on the EN 10204 certificate of the lot supplied. Two points older listings got wrong or incomplete: SM490YB is a low-alloy welded-structural grade (JIS groups it under carbon steel, but it is not plain carbon like SS400) and it is not low strength (365 MPa guaranteed yield, 490–610 MPa tensile is medium-to-high); we have corrected those plus the Mn limit (1.65), the full yield ladder, the Ceq limits and the 620 mm dimension error against the standard, and we publish the key fact that the mandatory 0 °C, ≥ 27 J impact is the defining feature of the “B” grade. BBN supplies, cuts and processes the plate.

Get Your JIS G3106 SM490YB Quotation Now

Send us your standard and edition (JIS G3106-2008 / -2020 / -2024), thickness, width and length, quantity, product form, delivery condition (AR / N / TMCP), the impact requirement (0 °C, ≥ 27 J is standard for the “B” grade — confirm any other temperature) and any UT / Z-direction requirement. We will reply with what the mill can roll and certify at that thickness, plate or cut-length options, mill price and production lead time — and tell you plainly if an impact-tested SM490YB is right, or if a no-impact duty should step down to SM490YA or a higher grade such as SM570.

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