Inconel 625 N06625 2.4856 Nickel–Chromium-Iron Alloy Pipe & Tube

Introduce

Inconel 625 has excellent strength at temperatures up to 816℃. At higher temperatures, its strength is generally lower than that of other solid solution strengthened alloys. Inconel 625 has good oxidation resistance at temperatures up to 980℃ and shows good resistance to aqueous corrosion, but is relatively moderate compared to other more capable corrosion resistant alloys.

Application

Chemical process industry and sea water application. Inconel 625 is used in short term applications at temperatures up to 816℃. For long term service, it is best restricted to a maximum of 593℃, because long term exposure above 593℃ will result in significant embrittlement.

Standard

alloy 625 is designated as UNS N06625, Werkstoff Number 2.4856 and ISO NW6625 and is listed in NACE MR-01- 75.

Rod, Bar, Wire and Forging Stock:  ASTM B 446; ASME SB 446 (Rod & Bar), ASTM B 564; ASME SB 564 (Forgings);  AMS 5666 (Bar, Forgings, & Rings); AMS 5837 (Wire), ISO 9723 (Rod & Bar), ISO 9724 (Wire), ISO 9725 (Forgings), VdTÜV 499 (Rod & Bar), BS 3076NA21 (Rod & Bar), EN 10095 (Rod, Bar, & Sections), DIN 17752 (Rod & Bar), ASME Code Case 1935 (Rod, Bar, & Forgings), DIN 17754 (forgings), DIN 17753 (Wire).

Plate, Sheet and Strip: – ASTM B 443; ASTM SB 443 (Plate, Sheet & Strip), AMS 5599; 5869; MAM 5599 (Plate, Sheet & Strip), ISO 6208 (Plate, Sheet & Strip), VdTÜV 499 (Plate, Sheet & Strip), BS 3072NA21 (Plate & Sheet), EN 10095 (Plate, Sheet & Strip), DIN 17750 (Plate, Sheet & Strip), ASME Code Case 1935.

Pipe & Tube: ASTM B 444; ASTM B 829; ASME SB444; ASME SB 829 (Seamless Pipe & Tube), ASTM B704; ASTM B 751; ASME SB 704; ASME SB 751 (Welded Tube), ASTM B705; ASTM B 775; ASME SB 705; ASME SB 775 (Welded Pipe), ISO 6207 (Tube), AMS 5581 (Seamless & Welded Tube), VdTÜV 499 (Tube), BS 3074NA21 (Seamless Pipe & Tube), DIN 17751 (Tube), ASME Code Case 1935.

Other Product Forms: ASTM B 366; ASME SB 366 (Fittings), ISO 4955A (Heat Resisting Steels & Alloys), DIN 17744

Grade Comparison

AMS: 5599, 5666, MS: 5837, ASME: SB 443 Gr 1, SB 446 Gr 1, ASTM: B 443 Gr 1, B 446 Gr 1, EN: 2.4856, ISO: 15156-3, NACE: MR0175-3, UNS: N06625, Werkstoff: 2.4856

Chemical composition

Average Hardness and Tensile Data, Room Temperature

Heat Treatment

Alloy 625 has three basic heat treatments:

(1)High Solution Anneal – 2000/2200°F (1093/1204°C), air quench or faster.

(2)Low Solution Anneal – 1700/1900°F (927/1038°C), air quench or faster.

(3)Stress Relieve – 1650°F (899°C), air quench.

The time at the above temperatures depends on volume and section thickness. Strip, for example, would require shorter times than large sections. Temperatures for treatments No. 1 and 2 are generally held for 1/2 to 1 hour, 1 to 4 hours for treatment No. 3.

Treatment No. 1 is not commonly used for applications below 1500°F (816°C). It is generally used above 1500°F and where resistance to creep is important. The high solution anneal is also used to develop the maximum softness for mild processing operations such as cold rolling or drawing.

Treatment No. 2 is the used treatment and develops an optimum combination of tensile and rupture properties from ambient temperatures to 1900°F (1038°C). Ductility and toughness at cryogenic temperatures are also very good.

Treatment No. 3 is recommended for application below 1200°F (649°C) when maximum fatigue, hardness, tensile and yield strength properties are desired. Ductility and toughness at cryogenic temperatures are excellent. When a fine grain size is desired for fatigue, tensile and yield strengths up to 1500°F (816°C), treatment No. 3 is sometimes used.

Hot Working

Hot working may done at 2100°F (1149°C) maximum furnace temperature. Care should be exercised to avoid frictional heat build-up which can result in overheating, exceeding 2100°F (1149°C). Alloy 625 becomes very stiff at temperatures below 1850°F (1010°C). Work pieces that fall below this temperature should be reheated. Uniform reductions are recommended to avoid the formation of a duplex grain structure. Approximately 15/20% reduction is recommended for finishing.

Cold Forming

Alloy 625 can be cold formed by standards methods. When the material becomes too stiff from cold working, ductility can be restored by process anneal.

Machineability

Low cutting speeds, rigid tools and work piece, heavy equipment, ample coolant and positive feeds are general recommendations.

Corrosion Resistance

Alloy 625 has withstood many corrosive environments. In alkaline, salt water, fresh water, neutral salts, and in the air, almost no attack occurs. The nickel and chromium provide resistance to oxidizing environments. Nickel and molybdenum provide for resistance to nonoxidizing atmospheres. Pitting and crevice corrosion are prevented by molybdenum. Niobium stabilizes the alloy against sensitization during welding. Chloride stress-corrosion cracking resistance is excellent. The alloy resists scaling and oxidation at high temperatures.

Pickling

Sodium hydride baths are necessary to descale this alloy. After the sodium hydride treatment, the material should be immersed in a sulfuric acid bath 165°F (74°C) for approximately 3 minutes. A 25-minute immersion in a nitric-hydrofluoric bath 145°F (63°C) is then necessary. Rinse. Sulfuric solution: 16% by weight, H2SO4. Nitric solution: 8% HNO3 by weight and 3% HF by weight. Acid etching for macro-inspection-expose material electrolytically to a 3-to-1 HCl to HNO3 solution, saturated with CuCl2 at a current density of 0.645 amp/in² (25.4 A/m)