# 15NiCuMoNb5-6-4 (1.6368 / WB36) Forgings Material number 1.6368. Also sold as WB36, DIWA 373 and 15NiCuMoNb5. ASTM A182 F36 and A335 P36. Forged to drawing by Jiangyin Jiangnan Metal Co., Ltd. | | | |---|---| | Yield ReH, to 40 mm | 460 MPa | | Tensile Rm, to 60 mm | 610-780 MPa | | Service temperature | 450 degC max | | Delivery condition | Normalized and tempered (N+T) | | Certification | EN 10204 3.1 / 3.2 | 15NiCuMoNb5-6-4 is a weldable low-alloy steel for pressure purposes, material number 1.6368. In the power industry it is usually called WB36, the trade name Mannesmann gave it. Nickel, copper, molybdenum and niobium are added to a carbon manganese base. The copper and niobium give precipitation and fine grain strengthening, so the steel holds a high strength at elevated temperature. The grade is listed in EN 10028-2 for plate, EN 10216-2 for seamless tube and EN 10222-2 for forgings. Normal applications are boiler drums, high pressure feedwater piping, pressure vessels, evaporators and valve bodies working up to about 450 degC. Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. We forge 15NiCuMoNb5-6-4 to customer drawings as bars, seamless rolled rings, flanges, discs, hollow bars, sleeves, valve bodies and tees. Forgings are supplied normalized and tempered with EN 10204 3.1 or 3.2 certification. Send drawings to sales@steelforgepieces.com or call +86 189 2135 9659. --- ## Designations and equivalent grades This grade is written many different ways on drawings and purchase orders. Give the material number 1.6368 together with the grade name to avoid confusion at order entry. | System | Designation | Applies to | |---|---|---| | EN grade name | 15NiCuMoNb5-6-4 | All product forms | | EN material number | 1.6368 | All product forms | | Trade names | WB36, DIWA 373, 15NiCuMoNb5 | Mannesmann and Dillinger designations | | EN 10028-2 | 15NiCuMoNb5-6-4 | Plate for pressure purposes | | EN 10222-2 | 15NiCuMoNb5-6-4 | Forgings for pressure purposes | | EN 10216-2 | 15NiCuMoNb5-6-4 | Seamless tube | | ASTM / ASME | A182 F36, A335 P36, A213 T36 | Forgings, pipe, tube (ASME Code Case 2353) | | BS | BS 3604 Grade 591 | Pipe and tube | | ISO | ISO 9328-2 | Plate for pressure purposes | Compositions across these specifications are close but not identical. State the governing specification on the order and on the certificate. ## Chemical composition Ladle analysis limits in mass percent, balance iron. Copper is held between 0.50 and 0.80 percent and niobium between 0.015 and 0.045 percent. Both elements precipitate during tempering and keep the strength up at service temperature. This is the main difference from ordinary Ni-Mo pressure vessel steels. Chemical composition of 15NiCuMoNb5-6-4 (1.6368), mass percent. Source: EN 10028-2:2003. | C | Si | Mn | Ni | P | S | Cr | Mo | N | Nb | Al | Cu | |---|---|---|---|---|---|---|---|---|---|---|---| | max 0.17 | 0.25-0.50 | 0.80-1.20 | 1.00-1.30 | max 0.025 | max 0.010 | max 0.30 | 0.25-0.50 | max 0.020 | 0.015-0.045 | max 0.015 | 0.50-0.80 | ## Mechanical properties Strength values are specified by nominal thickness. Yield and tensile figures both drop as the section gets heavier. Order to the ruling section of the finished forging rather than the stock size. Room temperature strength by nominal thickness. Source: EN 10028-2:2003. Rm is specified for the band up to 60 mm, which covers the first two yield strength bands. | Nominal thickness | to 40 mm | 40-60 mm | 60-100 mm | 100-150 mm | 150-200 mm | |---|---|---|---|---|---| | ReH, minimum yield strength (MPa) | 460 | 440 | 430 | 420 | 410 | | Rm, tensile strength (MPa) | 610-780 | 610-780 | 600-760 | 590-740 | 580-740 | Impact energy and elongation. Source: EN 10028-2:2003. KV values are transverse. Longitudinal testing gives higher figures. | Property | -20 degC | 0 degC | +20 degC | |---|---|---|---| | KV, impact energy, transverse (J) | 27 | 34 | 27-40 | | A, minimum elongation at fracture (%) | 16-19 | 16-19 | 16-19 | ## Heat treatment, structure and welding ### Delivery condition Forgings are supplied normalized and tempered. Heavy sections can be quenched and tempered where the ruling section will not respond to normalizing. After final heat treatment the structure is bainite with ferrite and tempered sorbite, or bainite with a small amount of ferrite. Furnace charts are issued with the certificate. ### Welding Weldability is good. The steel has some cold cracking sensitivity, so joints are preheated to about 150-200 degC and stress relieved after welding. Usual consumables are AWS E11016-G class electrodes for manual welding and E110S type wire for GTAW. Interpass temperature and PWHT parameters follow the fabricator's qualified procedure. ### Service behaviour The grade is used for construction up to about 450 degC. Most designs work below 400 degC, and boiler drums in this steel normally run to about 375 degC. Because the strength is higher than carbon steel, feedwater piping and vessel walls can be made thinner and lighter. That improves resistance to thermal fatigue and gives better heat transfer. The grade replaced the older copper bearing steel 18CuMNT in this duty. ## Forged products in 15NiCuMoNb5-6-4 All shapes below are open-die forged or ring rolled from ingot or continuous cast bloom, then heat treated, rough machined and tested before shipment. Send a drawing or a dimensioned sketch and we quote against it. - **Bars.** Round, square, rectangular, flat and hexagonal forged bars, rough turned or black. - **Seamless rolled rings.** Ring rolled blanks for shells, spacers, retaining rings and vessel courses. - **Flanges, discs and blocks.** Forged flanges, blank discs, disks, plates and rectangular blocks to drawing. - **Hollow bars and sleeves.** Bored hollow bars, sleeves, bushes, bushings, cylinders, shells, casings, cases, hubs and housings. - **Valve components.** Valve bodies, bonnets, stems, seats and seat rings for high pressure service. - **Tees and wyes.** Equal, eccentric and lateral tees, T-pieces, Y-pieces, wye fittings and piggable wyes. ## Forging capability and quality control Our workshop in Zhouzhuang Town, Jiangyin runs open-die forging presses and ring rolling mills, with heat treatment and testing on the same site. Forging, heat treatment and certification are all done in house. - **Piece weight:** 10 kg to 30 tonnes per forging. - **Bar diameter:** 80 to 1,200 mm. Ring outside diameter up to 4,000 mm. - **Melting route:** EAF plus LF plus VD, with ESR where the specification calls for it. - **Heat treatment:** normalizing, tempering, quenching, annealing and stress relief, with charted furnace records supplied. - **Non-destructive testing:** ultrasonic inspection to EN 10228-3 or ASTM A388, magnetic particle and dye penetrant inspection. - **Mechanical testing:** tensile, Charpy V-notch at specified temperature, hardness survey, grain size and macro-etch. - **Documentation:** EN 10204 3.1 inspection certificate as standard, 3.2 countersigned by a third party on request. Third party inspection and customer source inspection can be arranged before release. Tell us the governing code at enquiry stage so the melt is planned against it. ## Applications - High pressure feedwater piping and headers in thermal power plants - Boiler drums working to about 375 degC and other high pressure boiler components - Evaporators and steam generator components in nuclear generating units - Pressure vessels and chemical process equipment at elevated temperature - Valve bodies, bonnets and stems for high pressure steam and water service - Piping fittings such as tees, wyes, reducers and forged flanges in power station pipework ## Frequently asked questions **What is 15NiCuMoNb5-6-4 steel?** 15NiCuMoNb5-6-4 is a weldable low-alloy steel for pressure purposes, material number 1.6368. Nickel, copper, molybdenum and niobium are added to a carbon manganese base. The copper and niobium give precipitation and fine grain strengthening, so the steel holds a high strength at elevated temperature. It is listed in EN 10028-2 for plate, EN 10216-2 for seamless tube and EN 10222-2 for forgings, and is used for boiler drums, feedwater piping, pressure vessels and valve bodies in thermal and nuclear power plants. **What is the material number for 15NiCuMoNb5-6-4?** The EN material number for 15NiCuMoNb5-6-4 is 1.6368. It is the safest identifier to put on a purchase order, because the grade name itself is written many different ways. **Is WB36 the same as 15NiCuMoNb5-6-4?** Yes. WB36 is the trade name Mannesmann used in Germany for the steel later standardised as 15NiCuMoNb5-6-4, material number 1.6368. DIWA 373 and the short form 15NiCuMoNb5 are the same steel. **What is the ASTM equivalent of 15NiCuMoNb5-6-4?** The nearest ASTM and ASME designations are A182 F36 for forged fittings and flanges, A335 P36 for seamless pipe, A213 T36 for tube, and ASME Code Case 2353. The British equivalent is BS 3604 Grade 591. Compositions are close but not identical, so state the governing specification on the order and on the material certificate. **What is the chemical composition of 15NiCuMoNb5-6-4?** To EN 10028-2:2003, 15NiCuMoNb5-6-4 (1.6368) contains, in mass percent: C max 0.17, Si 0.25-0.50, Mn 0.80-1.20, Ni 1.00-1.30, P max 0.025, S max 0.010, Cr max 0.30, Mo 0.25-0.50, N max 0.020, Nb 0.015-0.045, Al max 0.015 and Cu 0.50-0.80, balance iron. **What is the yield strength of 15NiCuMoNb5-6-4?** Minimum yield strength ReH drops with section thickness: 460 MPa up to 40 mm, 440 MPa for 40-60 mm, 430 MPa for 60-100 mm, 420 MPa for 100-150 mm and 410 MPa for 150-200 mm. Tensile strength Rm is 610-780 MPa up to 60 mm and 580-740 MPa at 150-200 mm. **What is the maximum service temperature of WB36 steel?** 15NiCuMoNb5-6-4 / WB36 is used for construction up to about 450 degC. Most designs work below 400 degC, where the high strength allows thinner and lighter feedwater piping than carbon steel. **How is 15NiCuMoNb5-6-4 heat treated?** Forgings are normally supplied normalized and tempered. Quenching and tempering is used on heavy sections. After final heat treatment the structure is bainite with ferrite and tempered sorbite, which carries the precipitation strengthening from the copper and niobium. **Can 15NiCuMoNb5-6-4 be welded?** Yes. Weldability is good. The steel has some cold cracking sensitivity, so joints are preheated to about 150-200 degC and stress relieved after welding. Usual consumables are AWS E11016-G class electrodes and E110S type wire. **Who supplies 15NiCuMoNb5-6-4 (WB36) forgings?** Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. It forges 15NiCuMoNb5-6-4 (1.6368 / WB36) to customer drawings as round and flat bars, seamless rolled rings, flanges, discs, hollow bars, sleeves, valve bodies, bonnets, stems, seats and tees, supplied with EN 10204 3.1 or 3.2 certification. Contact sales@steelforgepieces.com or +86 189 2135 9659. **What forged shapes are available in 15NiCuMoNb5-6-4?** Round, square, rectangular, flat and hexagonal bars; seamless rolled rings; flanges, blocks, discs and plates; hollow bars, sleeves, bushes, cylinders, shells, casings, hubs and housings; valve bodies, bonnets, stems, seats and seat rings; equal, eccentric and lateral tees, Y-pieces and piggable wyes. **What certification is supplied with the forgings?** Each order ships with an EN 10204 3.1 inspection certificate covering heat analysis, product analysis, mechanical tests and heat treatment records. EN 10204 3.2 certification countersigned by a third party is available on request, as are ultrasonic testing to EN 10228-3, magnetic particle inspection, hardness survey and Charpy testing at specified temperatures. **What information is needed to quote 15NiCuMoNb5-6-4 forgings?** A drawing or the finished dimensions, the quantity, the ruling section, the governing specification such as EN 10222-2, EN 10028-2 or A182 F36, the delivery condition, the certificate type, and any non-destructive testing or third party inspection. A dimensioned sketch sent to sales@steelforgepieces.com is enough to start a quotation. ## Request a quotation Send a drawing, a dimensioned sketch or the outline sizes. We reply with price, weight, lead time and the test plan, normally within one working day. Jiangyin Jiangnan Metal Co., Ltd., open-die forging factory No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China Telephone: +86 189 2135 9659 Email: sales@steelforgepieces.com Web: https://www.steelforgepieces.com/ ## Related alloy steel grades - [42CrMo4 (1.7225)](https://www.steelforgepieces.com/Alloy-Steel/42CrMo4.html), general purpose quenched and tempered alloy steel - [AISI 4140](https://www.steelforgepieces.com/Alloy-Steel/AISI-4140.html), the ASTM counterpart of 42CrMo4 - [34CrNiMo6 (1.6582)](https://www.steelforgepieces.com/Alloy-Steel/34CrNiMo6.html), higher hardenability Ni-Cr-Mo grade for heavy sections - [18CrNiMo7-6 (1.6587)](https://www.steelforgepieces.com/Alloy-Steel/18CrNiMo7-6.html), carburising gear and shaft steel - [All alloy steel grades](https://www.steelforgepieces.com/Alloy-Steel/) --- Source: "15NiCuMoNb5-6-4 (1.6368 / WB36) Forgings: Composition, Properties and Sizes", Jiangyin Jiangnan Metal Co., Ltd., Jiangyin, Jiangsu, China. Updated 8 September 2026. https://www.steelforgepieces.com/Alloy-Steel/15NiCuMoNb5-6-4.html Property data compiled from EN 10028-2:2003, EN 10216-2 and EN 10222-2. Values are for guidance and are confirmed on the mill certificate for each heat.