CCS AH420 Shipbuilding Steel Plate

Technical Reviewer: Jack | SHH STEEL Material Solutions Department · Updated: 2026-10-27

China Classification Society titles extra-high-strength plate at 0 °C as CCS AH420 (CCS AH420) — W16 form with H (AH420, not A420). IACS Unified Requirement W16 covers this strength band (yield 420 N/mm²); CCS implements corresponding requirements in CCS Rules for Materials. Minimum yield is 420 N/mm², tensile 530–680 N/mm², elongation 18 % min., with Charpy at 0 °C. It sits above the A/AH–F/FH 40 higher-strength family (max yield 390 N/mm² under UR W11). GB 712 lists Grade AH420 in the same EHS band as a Chinese product standard; CCS class work still needs the CCS AH420 stamp. Commercial enquiries use CCS AH420 or CCS AH420 shipbuilding steel plate.

Equivalent grades: CCS AH420 ≈ ASTM A131 (no direct grade at this strength) ≈ ABS AH42 / AQ43 ≈ DNV NV A420 ≈ LR AH42 ≈ BV A420 ≈ NK KA420 ≈ KR RA43 ≈ RINA A420 ≈ GB 712 Grade AH420 (all class-approved, stamped by the issuing society).

Naming note: China Classification Society titles this strength band as AH420 / CCS AH420 (with H — write AH420, not A420 or AH42). Bureau Veritas titles the same yield as A420 (no H). DNV often titles AH420 / DNV NV A420. LR titles AH42. ABS often titles AH42 (official ABS AQ43). ASTM A131 has no grade at this strength. Write CCS AH420 on the CCS purchase order.

CCS AH420 is almost always produced TM or QT by a CCS-approved mill to order rather than taken from open stock. SHH STEEL sources extra-high-strength plate from mills with China Classification Society approval for the grade, under Surveyor attendance, with optional multi-class (ABS/DNV/LR/BV) and EN 10204 3.2.

Maximum plate thickness depends on delivery condition and the mill’s CCS approval sheet — typically TM up to about 100–150 mm and QT higher, but treat the approval limit as governing (UNCERTAIN without local CCS Materials PDF). Primary commercial scope we quote is within ~100 mm unless the mill approval and CCS survey confirm otherwise.

Product (check) analysis column: CCS Rules for Materials and Welding specify heat (ladle) limits; no numeric product-analysis tolerance is tabulated in the rule text reviewed, so product (check) limits are agreed on the order or taken from the approved mill specification and certificate.

Source: IACS UR W16 chemistry envelope (ABS 2-1-8 Table 4A aligned) as implemented by China Classification Society for CCS AH420 via CCS Rules for Materials — exact ladle limits depend on delivery condition (TM vs QT) and toughness letter. GB 712 Grade AH420 lists a related product-standard chemistry band; class work follows the CCS / UR W16 envelope on the mill approval. Values above are the rule envelope with every alloy / microalloy row listed; the purchase order and mill approval sheet govern. Product analysis: as per standard and mill certificate. All intentionally added elements and Ceq (or CET/Pcm) are to be reported. Flagged UNCERTAIN where a local CCS Materials PDF was not available to quote paragraph numbers.

Final acceptance values are as per standard and mill certificate under CCS survey. For thick plate, additional mid-thickness tensile/impact positions may apply — confirm at enquiry. Test frequency is typically each heat-treatment batch of same cast/condition/thickness.

Charpy temperature is fixed by the grade letter: AH → 0 °C. Indicative average energy 42 / 28 J (L/T) from IACS UR W16 aligned tables — confirm exact figures on the CCS-endorsed certificate. Unlike UR W11 higher-strength tables, EHS energies are usually stated as a single pair rather than rising through many thickness bands; thick-plate mid-thickness rules may still apply.

Allowed delivery conditions are primarily TM and QT within the mill’s approved thickness. Vacuum degassing is commonly required for higher categories and for thicker plate — follow the mill approval. State TM or QT on the PO; do not leave delivery condition blank for AH420.

China Classification Society applies IACS UR W13 unless the PO states otherwise (confirm minus class on PO; see UNCERTAIN). Surface repair limits follow the applicable CCS / UR rules; state primer/surface class on receipt if needed. For QT plate, avoid notching cut edges; follow mill cutting recommendations.

Extra-high grades such as CCS AH420 are rarely held as open stock; the table shows the size bands we quote against scheduled mill rolls. Quantities are indicative. All plates sold as CCS class carry CCS AH420 marking and a China Classification Society–endorsed mill certificate. Typical mill lead time including CCS survey is about 6–10 weeks (commercial estimate — confirm per quote). Send your size list and we will reply with the next available rolling slot.

Packing. Plates are bundled by size with steel strapping, marked with heat number, grade and CCS stamp, and shipped in containers (up to about 11.8 m) or break bulk for longer plates.

These are comparisons, not substitutions. Always write the CCS stamp CCS AH420 on the PO, plus any additional society stamps you need. Other CCS EHS siblings are linked via CCS until each product page is live.

Use AH420 when scantlings need yield 420 N/mm². Do not substitute AH40/EH40 (390 N/mm² max under UR W11) without redesign. Within the 420 band, letter choice is toughness: AH 0 °C → DH −20 °C → EH −40 °C → FH −60 °C. Neighbouring strengths are A/AH–F/FH 40 / 460 — swapping strength needs class approval of the drawing change.

When CCS CCS AH420 is the right choice: typical uses are extra-high-strength hull girder plating and primary members on CCS-classed ships and offshore units where 0 °C toughness and yield above 390 N/mm² are specified at extra-high yield — weight-critical hull girder strakes, polar and ice-class primary structure, and offshore units where 420 N/mm² is specified. See offshore platform steel plates for related offshore grades.

Typical uses: extra-high-strength hull girder plating and primary members on CCS-classed ships and offshore units where 0 °C toughness and yield above 390 N/mm² are specified at ReH 420 N/mm²; strength deck and shell of large container ships and gas carriers where EHS is specified; ice-belt and polar primary structure; selected offshore members. See offshore platform steel plates.

Welding: CCS AH420 is an extra-high-strength steel supplied TM or QT. Welding must follow a procedure qualified for this grade and approved by CCS. Ceq/CET/Pcm from the ladle analysis govern hydrogen control, preheat, interpass and heat-input windows. Too much heat input can lower HAZ strength and toughness in QT plate. We send the certificate values before shipment so your welding engineer can confirm the procedure fits. We do not give generic preheat temperatures.

Processing notes: CCS AH420 owes its strength to TM or QT processing. Hot forming or stress relieving above the tempering temperature can lower the properties, so any heat treatment after delivery must be agreed with the mill and CCS. Cold forming and bending radii should follow the mill’s data sheet. Thermal cutting parameters follow mill recommendations so the cut edge is not damaged.

CCS survey at the mill; certificate includes ladle chemistry (full alloy set + Ceq/CET/Pcm as applicable), tensile (ReH ≥ 420, Rm 530–680, A ≥ 18 %), Charpy at 0 °C, delivery condition, UT if ordered, and plate identity. Optional EN 10204 3.2 and multi-class with ABS/DNV/LR/BV.

On receipt: verify CCS AH420 stamp, 0 °C impact data, energies ≥ ordered/certified minima, thickness within tolerance, Surveyor endorsement (not GB 712 alone), UT report if required.

Charpy acceptance for CCS AH420 (IACS UR W16 aligned; actual results as per standard and mill certificate):

For thickness above ~100 mm, additional mid-thickness rules may apply — confirm at enquiry. If the PO asked for 3.2, the inspector’s report must name the witnessed tests and plate numbers.

• Ordering “CCS 420” without the letter (AH) — toughness missing
• Writing A420 / BV A420 style (no H) on a CCS PO — CCS official W16 form is AH420 (with H)
• Writing ABS AH42 or DNV AH420 or LR AH42 or BV A420 on a CCS-class PO without arranging that society’s survey (wrong stamp)
• Leaving delivery condition blank (TM vs QT changes price, mill and properties)
• Expecting ASTM A131 dual-cert at this strength (A131 has no EHS grade)
• Skipping UT on thick EHS plate when the yard specification requires it
• Missing CCS endorsement / assuming GB 712 Grade AH420 alone is class approval
• Omitting alloy / microalloy rows (Al, Nb, V, Ti, Cu, Cr, Ni, Mo, B, N) from the certificate check

Write grade (AH420, with H), TM/QT, impact temperature, UT level and certificate type into the PO.

Specify CCS AH420 (CCS AH420), delivery condition TM or QT, thickness × width × length × qty, Z/U/UT level, multi-class, certificate type, port. Send to SHH STEEL.

Sample PO line: “Steel plate to China Classification Society Rules for Materials, Grade AH420 (CCS AH420), delivery condition [TM/QT], 30 × 2500 × 12000 mm, 10 pcs, marked CCS AH420 / CCS AH420, certificate endorsed by CCS Surveyor, EN 10204 3.2 [if required], UT [EN 10160 / ASTM A578 level], CIF [port].”

CCS AH420 / CCS AH420 is extra-high-strength hull steel (IACS UR W16 band; CCS W16 naming with H): yield 420 N/mm², tensile 530–680 N/mm², Charpy at 0 °C, marking CCS AH420. GB 712 Grade AH420 lists the same EHS band as a product standard — CCS Surveyor endorsement is still required. Lock on the order: TM or QT, UT level, Ceq/CET/Pcm reporting, multi-class and 3.2.

SHH STEEL supplies CCS AH420 plate rolled by Chinese mills that hold China Classification Society works approval for the grade, so every plate carries the CCS AH420 stamp and a Surveyor-endorsed certificate traceable to its heat. Sizes are scheduled into the mill rolling cycle with CCS survey arranged at the mill. On request we add EN 10204 3.2 certificates with third-party witness (TÜV, SGS, LR or another agency) and joint certification with ABS, DNV, LR, BV, NK, KR or RINA.

We accept T/T or L/C payment, with inspection before the balance is paid. Small quantities in several sizes, or CCS AH420 with neighbouring EHS sizes or higher-strength A/AH–F/FH 40 where the drawing allows, can be combined in one container. A dedicated coordinator sends production and shipping updates with photos, and our own workshop cuts to size, bevels, drills and machines plates before shipment so they arrive ready for fabrication.

Request a quotation: send SHH STEEL the grade (CCS AH420 / CCS AH420), thickness, width, length, quantity per size and destination port, plus any multi-class, Z/U or 3.2 certificate requirement. We reply with price, available stock and lead time.