ASTM A588 Grade K Steel Plate | A588 Gr.K Weathering Steel supplier

ASTM A588 Grade K, also searched as A588 Gr.K, A588GRK, A588-K, A588 Gr K, ASTM A588 Gr.K and A588 Grade K 50ksi, is the niobium grade in ASTM A588/A588M. That book covers high-strength low-alloy structural steel plates, shapes and bars with atmospheric corrosion resistance for welded, riveted or bolted construction. The main use is welded bridges and buildings where weight saving or unpainted durability matters.

The current book lists three grades: A, B and K. This page is Grade K. Grade A and Grade B use vanadium. Grade K drops the vanadium minimum and adds niobium (columbium) 0.005–0.05%. Copper is higher than Grade B: 0.30–0.50%. Molybdenum is allowed to 0.10% max. Mechanical properties follow the same thickness table. Do not treat A588 as ASTM A572 Grade 50 unless the file does not need weathering. Do not treat A588 as ASTM A36. A36 has no 50 ksi yield and no Cu-Cr patina system. Do not treat A588 as a pressure-vessel plate. That work sits on ASTM A516 or pressure vessel steel plates.

Buyers also type Corten A, Corten B and A242. Corten A and Corten B are trademark names. ASTM A242 is a different weathering book. Dual mark only when both chemistries and both mechanical tables are met. European comparisons are EN 10025-5 S355J2W and EN 10025-5 S355K2W.

A588 Grade K develops a stable oxide film in wet-dry outdoor air. Niobium refines grain and helps thick plate stay uniform. The book asks for an atmospheric corrosion-resistance index of 6.0 or higher by ASTM G101 on heat analysis. Indoor wet service, standing water and marine splash still need coating review. Weathering steel is not stainless steel.

General requirements follow A6/A6M. Steel is produced to fine-grain practice. Thickness in the book goes to 8 in / 200 mm. To 100 mm the minimum yield is 50 ksi / 345 MPa and the minimum tensile is 70 ksi / 485 MPa. Over 100 mm the yield name drops. Density is 7.85 g/cm³.

SHH STEEL is a global steel mill sourcing partner and steel manufacturer & exporter (mill-direct, China origin). We source A588 Gr.K from first-line Chinese mills, print heat and product analysis when ordered, record the G101 index when requested, and ship plate to fabricators in the United States, Europe, the Middle East, Southeast Asia, Africa and South America.

Related category pages: weathering steel plates, structural steel plates, EN 10025-5 and high strength low alloy plates.

Sister grades in the same book are Grade A and Grade B. Nearby pages that buyers compare, but must not swap blindly, include Corten A, Corten B, EN 10025-5 S355J2W and A572 Gr.50.

Grade K is the niobium-bearing Cu-Cr grade. Heat analysis is the mill table. Product analysis, when ordered, follows A6 product tolerances on that heat.

Heat Analysis and Product Analysis — ASTM A588 Grade K

The 0.005% Nb minimum is waived on plate under ½ in / 13 mm. For each 0.01% carbon below the 0.17% max, manganese may rise 0.06%, up to 1.50% Mn on heat analysis. Grade A and Grade B use vanadium and do not require niobium. Grade K copper starts at 0.30%, higher than Grade B. If the purchase order writes product analysis, SHH STEEL prints both columns.

Do not treat this chemistry as A572 Gr.50. A572-50 has no mandatory Cu-Cr-Nb weathering window. Do not treat it as S355JR. S355JR is ordinary structural steel.

Buyers search A588 Gr.K mechanical properties, A588GRK yield, A588 Grade K 50ksi and A588-K tensile.

Tensile Properties — ASTM A588 plates and bars

Structural shapes keep 50 ksi yield and 70 ksi tensile at all listed thicknesses. Grade A, Grade B and Grade K share this table. The grade letter does not change the yield name.

Impact is not automatic. Bridge work that needs Charpy values must write temperature, joules and orientation. A709 Grade 50W is the bridge-book twin when the file is an AASHTO bridge, not a building frame. Grade K is often picked on thicker plate because Nb keeps grain fine.

Density is 7.85 g/cm³. Typical hardness after rolling sits around 130–180 HBW. Hardness is not a Table 2 limit.

There is no official one-to-one worldwide twin for A588 Gr.K. What buyers compare is a 345 MPa weathering plate with Cu-Cr-Nb.

In the United States the sister grades are A588 Grade A and Grade B. Bridge files often rewrite weathering chemistry as A709 Grade 50W. Corten A and Corten B are trademark names. ASTM A242 is a thinner-product weathering book, not a free substitute.

In Europe compare S355J2W, S355K2W and S355J0W. Phosphorus weathering grades S355J0WP and S355J2WP are a different chemistry family. See EN 10025-5 and weathering steel plates.

In China compare GB/T 4171 Q355GNH, Q355NH or Q415NH. Dual mark only when both books are fully met.

Buyers pick A588 Gr.K when a bridge, tower, hopper, facade or unpainted frame wants 50 ksi yield, a patina, and Nb grain control on thicker plate. Search phrases such as A588GRK, A588 Grade K, A588-K and A588 Gr K 50ksi all point here.

It is the wrong plate for a pressure vessel. That work is A516 Grade 70 or the ASME SA662 family. It is the wrong plate for a painted 50 ksi building that does not need copper and chromium. That work is A572 Gr.50. It is the wrong plate for a 70 ksi HPS bridge girder. That work is A709 HPS 70W. It is the wrong plate for stainless cladding. That work sits on stainless steel sheets and plates.

Unpainted A588 needs wet-dry cycles. Standing water, buried faces and constant spray do not form a stable film. SHH STEEL will say that on the quotation when the drawing shows a tank floor or a splash zone.

ASTM A588 Grade K is weldable HSLA plate. Treat welding as structural production welding, not as ordinary A36 shop practice.

Typical consumables are matching weathering wires or E8018-C3 / E80C-G type electrodes qualified on a 50 ksi weathering family. If the fillet will be painted and the file allows it, some shops use E7018 and accept a color mismatch at the toe. A procedure written for Grade A or Grade B is usually acceptable on Grade K after the WPS heat range is checked. A procedure written for A572 Gr.50 may miss the copper and chromium effect on the HAZ color. A procedure written for S355JR is not a weathering procedure.

Preheat follows thickness and hydrogen control. After heavy cold forming, a stress relief may be required. The fabricator owns the WPS. SHH STEEL can share mill heat data, product analysis, CEV and the G101 index for that review.

Usual delivery from SHH STEEL for A588 Gr.K is as-rolled or normalized when the mill route or the purchase order asks for it.

A588 is not a QT vessel book. Do not order it as SA517 or A514. Normalizing, when used, is typically 880–920 °C, soaked through, then air cooled. Fine-grain practice plus Nb is part of manufacture.

If the fabricator hot-forms outside the mill window, a new normalize or a controlled cool may be required. Simulated PWHT is uncommon on weathering bridges and only applies when the order writes it.

The certificate lists ASTM A588 Grade K; heat number; heat analysis and product analysis when ordered; tensile by thickness band; fine-grain practice; G101 index when ordered. Certificates may be EN 10204 3.1 or EN 10204 3.2.

Usual supply range from SHH STEEL for A588 Gr.K weathering steel plate:

• Thickness: commonly 6 mm – 100 mm, heavier plate to 200 mm by enquiry
• Width: 1500 mm – 4000 mm
• Length: 3000 mm – 12000 mm

Cut-to-size girders, flanges and facade panels are available. Browse more sizes on weathering steel plates, structural steel plates and the products index.

Dimensional limits for ASTM A588 Grade K follow A6 / A6M unless the purchase order names another table.

Typical A6 thickness tolerance idea for A588 Gr.K

Width on 1500–4000 mm plate is commonly held to about ±20–25 mm unless a tighter extra is named. Length on 3000–12000 mm plate is commonly held to about +50 / 0 mm or ±25 mm by mill practice. Flatness follows A6 unless a tighter class is written. SHH STEEL will not assume a zero-minus extra on A588GRK unless the order says so.

Grade K already defines chemistry and the 50 ksi table to 100 mm. Extra items still have to be written on the purchase order.

Book name. Write ASTM A588 Grade K. Write A709 Grade 50W if the file is a bridge to AASHTO.

Impact details. Write temperature, joules, location and orientation.

Product analysis. Write it if the file needs the second chemistry column.

G101 index. Write it if the owner wants the corrosion index on the certificate.

Through-thickness / Z-test. When needed on thick flanges.

NDE. UT to the named class.

Shot blast and primer. Only when the plate will not stay bare. Bare weathering plate is usually shipped with mill scale or a light blast, not a full paint system.

Identification and stamping. Heat number, A588 Grade K, thickness and mill logo.

Third-party witness. EN 10204 3.2 with SGS, TÜV, BV, ABS or the inspector named.

A588 Grade K is the plate for a file that wants 50 ksi yield, a patina and Nb grain control. It is the wrong plate for a painted warehouse that can use A36 or S355JR. It is the wrong plate for a QT 100 ksi member. That work sits on A514 Grade Q or A709 HPS 100W.

SHH STEEL sources ASTM A588 Grade K from first-line Chinese mills and ships it on worldwide terms. Partner mills include Wuyang (Wugang), Angang, Shougang, Hanye, Anyang Iron & Steel, Baosteel, Xinyu, Xingcheng, TISCO (Taiyuan), Jiuquan (JISCO) and other qualified mills when the size requires it.

Mill test certificates are issued to EN 10204 3.1 as standard. EN 10204 3.2 is arranged when the order names a third-party hold point. Dual marking to A709 Grade 50W or GB/T 4171 Q355GNH is available only when both books are met.

Usual stock and rolling thickness: 8 mm, 10 mm, 12 mm, 16 mm, 20 mm, 25 mm, 30 mm, 32 mm, 40 mm, 50 mm, 60 mm, 80 mm, 100 mm.

Processing: CNC or flame cutting, bevel, flattening, shot blast, UT to the named class.

Trade terms: FOB Shanghai main, CIF destination available. Payment: TT, LC, or TT + LC.

Ocean time from Shanghai: US West 14–18 days; US Gulf 28–35 days; Rotterdam / Antwerp 28–35 days; Jebel Ali 18–25 days; Singapore 7–12 days; other ports quoted.

Third-party: SGS, TÜV, BV, ABS, CCS, GL, VL, DNV, RINA, NK, KR, or the inspector named.

SHH STEEL is a global steel mill sourcing partner with mill partnerships in China. We supply ASTM, ASME, EN, DIN, JIS and GB steel to buyers in the United States, Europe, the Middle East, Southeast Asia, Africa and South America. Origin is mill-direct, China origin.

SHH STEEL has supplied steel plates to the USA, Mexico, Argentina, Peru, El Salvador, Spain, Netherlands, Germany, UAE, Saudi Arabia, South Africa, India, Thailand, Singapore, Vietnam, the Philippines, Japan and Korea.

Typical lead time: ex-stock 5–7 days; standard rolling about 30–45 days; normalized or 3.2 inspection about 45–60 days.

Experience on this grade is simple: print A588 Grade K, keep Cu 0.30–0.50% and Nb 0.005–0.05% on heat analysis, and do not ship Grade A or A572-50 as Grade K. SHH STEEL as a global steel mill sourcing partner and steel manufacturer & exporter (mill-direct, China origin) will not drop niobium to save alloy, will not mark Grade B chemistry as Grade K, and will not treat A588 as A36.

We keep the book on the order. A588GRK is not A572 Gr.50. A588 Grade K is not Corten A unless the trademark chemistry is also met. A588 Grade K is not S355J2W unless both books are on the certificate. If the drawing is a bridge to AASHTO, we will ask whether the stamp should read A709 Grade 50W.

ASTM A588 Grade K Steel Plate is 50 ksi weathering structural plate for bridges, towers and unpainted frames, with 345 MPa yield to 100 mm and Cu-Cr-Nb chemistry. Whether the inquiry says ASTM A588 Grade K, A588 Gr.K, A588GRK, A588-K, A588 Gr K or A588 Grade K 50ksi, SHH STEEL as a global steel mill sourcing partner and steel manufacturer & exporter (mill-direct, China origin) supplies plate with Grade K chemistry, heat and product analysis as ordered, A6 tolerances and EN 10204 3.1 or 3.2 certification.

SHH STEEL supplies ASTM A588 Grade K / A588 Gr.K Weathering Steel to the United States, Europe, the Middle East, Africa, Asia and the Americas for work that actually names this grade.

Contact SHH STEEL for mill rolling, dual A709 50W marking, cutting, blast, 3.2 inspection or a worldwide quotation.

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