Outstanding UNS N06625 Special Alloys For Aerospace And Defense Excellent Weldability

Outstanding Alloy 625, UNS N06625 for aircraft engine exhaust, thrust chamber tubing for rocket, etc.

PRODUCT

High tensile, creep, and rupture strength; out-standing fatigue and thermal-fatigue strength; oxidation resistance; and excellent weldability and brazeability are the properties of alloy 625 that make it interesting to the aerospace field. It is being used in such applications as aircraft ducting systems, engine exhaust systems, thrustreverser systems, resistance-welded honeycomb structures for housing engine controls, fuel and hydraulic line tubing, spray bars, bellows, turbine shroud rings, and heat exchanger tubing in environmental control systems. It is also suitable for combustion system transition liners, turbine seals, compressor vanes, and thrust-chamber tubing for rocket.

EQUIVALENT DESIGNATION

NS336, GH3625, UNS N06625, W.Nr.2.4856(EN), NiCr22Mo9Nb(EN), INCONEL® 625, Haynes® 625, VDM^® Alloy 625(Nicrofer 6020 hMo), NC22DNb(ISO), NW6625(ISO), NC22DNb(AFNOR), ASME Code Case 1935

PRODUCT FORMS

Alloy 625 is furnished in a wide range of standard mill forms including pipe, tube, sheet, strip, plate, round bar, flat bar, forging stock, hexagon, shaped section and wire.

CHEMICAL COMPOSITION

Table 1 (wt%)

OVERVIEW

Alloy 625 is a nickel-chromium-molybdenum-niobium alloy with excellent strength up to 1500°F (816°C) and excellent resistance to a variety of corrosive media. In the soft annealed condition (grade 1; annealed at 950 to 1,050°C (1,742 to 1,922°F)), the alloy is used for wet corrosion applications and is approved by TÜV for pressure vessels in a temperature range from -196 to 450 °C (-320 to 842 °F). For high temperature applications above 600 °C (1,112 °F), the solution annealed variant (grade 2; annealed at 1,080 to 1,160 °C (1,976 to 2,120 °F)) is generally used. The strength of Alloy 625 can be enhanced by heat treatment.

OTHER APPLICATION (except for aerospace)

Alloy 925 is used in various applications requiring a combination of high strength and corrosion resistance. Because of the alloy’s resistance to sulfide stress cracking and stress corrosion cracking in “sour” (H₂S containing) crude oil and natural gas, it is used for down-hole and surface gas-well components including tubular products, valves, hangers, landing nipples, tool joints and packers. The alloy is also useful for fasteners, marine and pump shafting and high-strength piping systems.

PHYSICAL PROPERTIES

Density: 8.44gram/cm³

Melting range: 1290-1350°C

MECHANICAL PROPERTIES

Minimum short-time mechanical properties at room temperature and at elevated temperatures for Alloy 625 according to VdTÜV data sheet 499 (above 500 °C typical values) shown in table 2.

Minimum mechanical properties at room temperature according to VdTÜV data sheet 499 shown in table 3.

Table 2

Table 3

MICROSTRUCTURE

Alloy 625 is a solid solution matrix stiffened face centered cubic lattice alloy. The alloy may contain carbides, which are inherent in this type of alloy. Carbides that can be found are MC and M6C (rich in nickel, niobium, molybdenum, and carbon). In addition M23C6, a chromium-rich carbide, appears in solution treated material exposed at lower temperatures.

The hardening effect that takes place in the material on exposure in the range centered around 1200°F is due to sluggish precipitation of a nickel niobium rich phase, gamma prime. This phase gradually transforms to orthorhombic Ni3Nb when the alloy is heated for long times in the intermediate temperature range.

Extensive investigation of the stability of alloy 625 following exposure for extended periods in the 1000 to 1800°F temperature range has shown complete absence of embrittling intermetallic phases such as sigma.

CORROSION RESISTANCE

Optimum corrosion resistance can only be obtained if the material is in the correct metallurgical condition and possesses a clean structure.

Under these circumstances In the soft annealed condition Alloy 625 (grade 1) has excellent corrosion resistance to a variety of corrosive media:

Excellent resistance to pitting and crevice corrosion in chloride-containing media

Virtual immunity to chloride-induced stress corrosion cracking

High resistance to corrosion attack by mineral acids such as nitric, phosphoric, sulfuric, and hydrochloric acid; as well as by concentrated alkalis and organic acids, both under oxidizing as reducing conditions

Very good resistance in seawater and brackish water, even at elevated temperatures

High resistance to intergranular corrosion after welding and heat treatment

High resistance to erosion corrosion

In the solution annealed variant Alloy 625 (grade 2) is highly resistant to many corrosive gas atmospheres:

Good resistance to carburizing and scaling under static and cyclic conditions

Resistance to nitriding

Good resistance to gases containing halogens, and hydrogen chloride

HOT FORMING

Alloy 625 may be hot worked in the temperature range 1176 to 900°C (2150 to 1650°F) with subsequent rapid cooling down in water or by using air. The workpieces should be placed in the furnace heated to hot working temperature in order to heat up.

COLD FORMING

Cold working should be carried out on annealed material. Alloy 625 has a higher work hardening rate than austenitic stainless steels. This must be taken into account during design and selection of forming tools and equipment and during the planning of the forming processes. Intermediate annealing may be necessary at high degrees of cold working deformation. After cold working with more than 15 % of deformation the material should be soft annealed (grade 1) or solution annealed (grade 2).

HEAT TREATMENT

Alloy 625 is used in applications where the operating temperatures are below 600°C (1112°F) in the soft annealed condition (grade 1). The soft annealing is carried out at temperatures of 950 to 1050°C (1742 to 1922°F); a temperature of 980°C (1796°F) is preferred.

For applications above 600°C (1112°F), the solution annealed variant of Alloy 625 (grade 2), which provides optimized creep strength, is used. The solution heat treatment should be carried out in the temperature range between 1080°C and 1160° C (1976 and 2120°F), preferably at 1120°C (2048°F).

STANDARD SPECIFICATION AND CODE

Alloy 625 is an approved material of construction under the Boiler and Pressure Vessel Code of the American Society of Mechanical Engineers (ASME). Allowable design stresses for Grade 1 material for Section VIII, Division 1 construction up to 1200°F, for Section III, Class 2 and 3 construction up to 800°F, and for Grade 2 material for Section VIII, Division 1 construction up to 1600°F are reported in Table 1B of ASME Section II, Part D. Design stress intensity values for Section III, Class 1 construction for Grade 1 material are found in Table 2B of ASME Section II, Part D. Allowable stresses and rules for Section 1 construction with Grade 1 material up to 1100°F are found in ASME Code Case 1935.

Alloy 625 is listed in NACE MR-01-75.

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ASTM B446 / ASME SB446 Rod & Bar

ASTM B564 / ASME SB564 Forgings

ASTM B704 / ASME SB704 Welded Tube

ASTM B705 / ASME SB705 Welded Pipe

ASTM B751 / ASME SB751 Welded Tube

ASTM B775 / ASME SB775 Welded Pipe

ASTM B829 / ASME SB829 Seamless Pipe & Tube

SAE AMS 5599 Plate, Sheet & Strip

SAE AMS 5666 Bar, Forgings, & Rings

SAE AMS 5837 Bare welding rods & wire

SAE AMS 5869 Plate, Sheet & Strip

ASME Code Case 1935 Rod, Bar, & Forgings

ISO 6207 Tube

SAE AMS 5581 Seamless & Welded Tube

COMPETITIVE ADVANTAGE:

(1) More than 50 years experience of research and develop in high temperature alloy, corrosion resistance alloy, precision alloy, refractory alloy, rare metal and precious metal material and products.
(2) 6 state key laboratories and calibration center.
(3) Hundreds of patent technologies.
(4) Ultra-purity smelting process VIM + IG-ESR + VAR.

(5) High performance material.

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