UNS N07080 Exhaust Valve Alloys For High Power Internal Combustion Engine Exhaust Valve

Alloy 80A (UNS N07080) for high power internal combustion engine exhaust valve

PRODUCT

High temperature Alloy 80A (UNS N07080) for high power internal combustion engine (diesel engine and gasoline engine) exhaust valves for automobile, locomotive, tractor, ship, tank, oil rig, construction machinery and mobile power station, etc.

EQUIVALENT DESIGNATION

GH4080A, NIMONIC® alloy 80A, VDM® alloy 80A (Nicrofer 7520 Ti), W.N.2.4952, 2.4631, NiCr20TiAl, ATGS3, NC20TA, 2HR1, 2HR201, 2HR401, 3HR601, DTD736B

OVERVIEW

UNS N07080 is a wrought, age-hardenable nickel-chromium alloy, strengthened by additions of titanium, aluminum and carbon, developed for service at temperatures up to 815°C (1500°F). It is produced by high-frequency melting and casting in air for forms to be extruded. Electroslag refined material is used for forms to be forged. Vacuum refined versions are also available.

SKETCH OF EXHAUST VALVE

PRODUCTION PROCEDURE OF EXHAUST VALVE

Blanking → Electric heating upsetting forging of head blank → Heat treatment of head blank and rod → Friction welding → Rough turning or grinding → Finish turning → Cut fixed length → Semi-fine grinding the stem → The valve stem chrome plating → Fine grinding the stem → NDT of the finished valve → Delivery

SURFACE CONDITION OF EXHAUST VALVE

PRODUCTION SITE OF EXHAUST VALVE

ALL PRODUCT FORM OF UNS N07080

UNS N07080 is available in forms of bar and rod, wire, strip, sheet, forging, circular blank, ring, extruded section, pipe and tube etc.

Rod and bar delivery condition: forged, rolled, drawn, heat treated, oxidized, descaled or pickled, twisted, peeled, ground or polished

Strip delivery condition: cold rolled, heat treated, pickled or bright annealed

Forged bar: 600mm diameter max.

Hot rolled bar: 120mm diameter max.

Cold drawn bar and rod: dia.4.0mm - 25.0mm

Bright bar and rod: dia.4.0mm - 25.0mm

Cold drawn wire: dia.0.10-10mm

Other shapes and dimensions, such as circular blanks, rings, forgings, extruded section, pipe and tube can be requested.

APPLICATION

UNS N07080 is currently used for gas turbine components (blades, rings, washers and discs), bolts, nuclear boiler tube supports, die casting inserts and cores, and for automobile exhaust valves.

Additional applications are connecting elements, exhaust valves in combustion engines and other highly stressed components which are used in the aforementioned temperature range.

CHEMICAL COMPOSITION (wt%):

PHYSICAL PROPERTY

Density:ρ=8.19 g/cm³

Melting range:1320-1365℃

(Other detail physical properties available from our brochure)

MECHANICAL PROPERTIES

The following mechanical properties of UNS N07080 apply to the described conditions and specifications in the specified semi-finished forms and dimensions (cf. Availability). The properties for larger dimensions must be agreed separately.

Mechanical short-term properties of solution-annealed UNS N07080 at room temperature and elevated temperatures as table below

(1) values according to DIN10302

(2) according to ASTM B637

Creep limit and creep strength according to DIN EN 10302 as table below

The creep resistance of the material may be influenced by cold deformation after the heat treatment.

(Other detail mechanical properties available from our brochure)

CORROSION RESISTANCE

UNS N07080 has a high resistance to oxidation under cyclic temperature changes. The alloy forms a firmly adhering oxide layer (Cr₂O₃), which protects against progressive corrosion and oxidation attacks. The alloy is resistant to scaling up to 1000°C (1832°F). The material has proven its resistance to vanadium pentoxide, sodium and sulphur compounds for exhaust valves in engines operated with heavy oil.

MICROSTRUCTURE

UNS N07080 is an age-hardenable, austenitic nickel-chromium alloy with admixtures of titanium and aluminum, which retains its strength through the γ'-precipitations (Ni3(Al,Ti)).

FABRICATING

UNS N07080 can be easily formed both hot and cold and can also be machined. However, machines that take ac-count of the mechanical properties are necessary for any processing work.

Heating

It is important that the workpieces are clean and free of any contaminants before and during heat treatment. Sulphur, phosphorus, lead and other low-melting-point metals can result in damage during the heat treatment. This type of contamination is also contained in marking and temperature display paints or pens, and also in lubricat-ing grease, oils, fuels and similar materials. Fuels must have as low a sulphur content as possible. Natural gas should contain less than 0.1% by weight of sulphur. Heating oil with a maximum sulphur content of 0.5% by weight is also suit-able. Electric furnaces are to be preferred due to precise temperature control and lack of contaminants due to fuel. The furnace temperature should be set between neutral and slightly oxidizing and should not change between oxidizing and reducing. The workpieces must not come in direct contact with flames.

Hot working

UNS N07080 should be hot worked in the range 1050-1200°C (1920-2190°F) with subsequent rapid cooling down. For special applications where the endurance strength is more in focus than the creep resistance (e.g. valves), this temperature window should be expanded downwards in order to achieve a fine-grained microstructure. 980°C (1796°F) should not be fallen below. The workpieces are placed in the furnace heated up to hot-forming temperature in order to heat up. Once the temperature has equalized, a retention time of at least 60 minutes for each 100 mm of workpiece thickness should be observed. After this, the workpieces are removed immediately and formed during the stated temperature window. If a temperature of 980°C (1800°F) is fallen below, the workpiece should be heated up as described above, as otherwise it would be too firm for further hot forming. Heat treatment after hot forming is recommended for the optimization of mechanical properties and corrosion resistance.

Cold working

UNS N07080 is ideally cold-formed in the solution-annealed state. The material has a significantly higher work hardening rate than austenitic stainless steels. This must be taken into account during the design and selection of forming tools and equipment and during the planning of forming processes. Intermediate annealing at 1040°C (1904°F) followed by a quick cooling down may be necessary at high cold-forming temperatures in order to restore further formability.

Descaling and pickling

High temperature materials develop a protective oxide layer in service. The necessity for descaling should therefore be checked on ordering. Oxides of UNS N07080 and discolorations in the area around welds adhere more strongly than in stainless steels. Grinding using extremely fine abrasive belts or grinding discs is recommended. Discolorations caused by grinding (grinding burn) are to be avoided. If pickling is to be carried out, the pickling times (as for all high - temperature materials) should be kept short, because they can otherwise be subject to inter-crystalline corrosion attack. Furthermore, the temperature of the pickling line must be checked. Before pickling in nitric-hydrofluoric acid mixtures, dense oxide layers should be destroyed by blasting or grinding, or pre-treated in salt baths.

Machining

While UNS N07080 in the solution-annealed condition is easier to process and the strain on tools is less, better surface quality is achieved in the age-hardened condition. The best results in terms of the surface quality and dimensional accuracy of the finished product are achieved by pre-treatment before hardening and by finishing in the age-hardened condition. For reasons of the increased tendency to work hardening in comparison with low-alloy austenitic stainless steels, a lower cutting speed should be selected and the cutting tool should stay engaged at all times. An adequate chip depth is important in order to cut below a previously formed work-hardened zone.

Nimonic 80A should be in the fully heat treated condition for all machining operations. The high material hardness in this condition (250-350 HV) requires the use of stringent machining techniques.

Welding

UNS N07080 sheet is readily joined by any of the resistance welding processes. Fusion welding by conventional processes such as T.I.G. or M.I.G. (dip or pulsed transfer) is satisfactory for section thicknesses up to about 5 mm (0.2 inch). Above this thickness micro-fissuring may occur in the weld and the heat affected zone.

Electron beam, friction, inertia and flash-butt welding have all been successfully used for thickness greater than 5 (0.2 inch).

The normal precautions for welding nickel alloys should be observed and welding should be carried out on solution treated material. Post-weld heat treatment is necessary to achieve optimum properties.

HEAT TREATMENT

In general, the heat treatment of UNS N07080 includes three stages:

(1) Solution annealing at 1050-1080°C (1922 – 1976°F) for 8 hours followed by air cooling.

(2) Stabilizing annealing at 840-860°C (1544 – 1580°F) for 24 hours followed by air cooling.

(3) Age hardening annealing at 690-710°C (1274 – 1310°F) for 16 hours followed by air cooling.

The stabilizing annealing is used to specifically eliminate carbides at the grain boundaries. The particularly high-strength increasing γ‘-precipitates are generated during subsequent age hardening. For applications where the endurance strength is in focus instead of the creep resistance (e.g. valves), the solution annealing should occur in the temperature range from 1010-1050°C (1850–1922°F) in order to counteract any coarse grain formation that would be detrimental to this application. The mechanical properties can be specifically adjusted in a wide range through variations in the forming and heat treatment parameters. For every heat treatment, the material should be inserted into the furnace already heated up to the annealing temperature and the information mentioned in the chapter “Heating” should be observed.

STANDARD SPECIFICATION

Rod, bar, wire and forging

BS 3076

BS HR 1

BS HR 601

ASTM B637 / ASME SB637

AECMA PrEn 2188 / 2189 / 2190 / 2396 / 2397

AIR 9165-37

DIN 17240

DIN EN 10090

Plate, sheet and strip

BS HR 201

AECMA PrEn 2191

DIN 17742

DIN EN 10302

ISO 6208

Pipe and Tube

BS HR 401

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) Average grain size 9 or finer.

BUSINESS TERM