Inconel 690 Alloy Steel Bar

 

INCONEL alloy 690 is a high-chromium nickel alloy having excellent resistance to many corrosive aqueous media and high-temperature atmospheres. The alloy’s high chromium content gives it excellent resistance to aqueous corrosion by oxidizing acids (especially nitric acid) and salts, and to sulfidation at high-temperatures. In addition to its corrosion resistance, alloy 690 has high strength, good metallurgical stability, and favorable fabrication characteristics.

 

The substantial chromium content gives the alloy outstanding resistance to oxidizing chemicals and to high-temperature oxidizing gases. The high level of nickel imparts resistance to stress- corrosion cracking in chloride-containing environments as well as to sodium hydroxide solutions.

 

The properties of INCONEL® alloy 690 are useful for various applications involving nitric or nitric/hydrofluoric acid solutions. Examples are tail-gas reheaters used in nitric acid production and heating coils and tanks for nitric/hydrofluoric solutions used in pickling of stainless steels and reprocessing of nuclear fuels.

 

The alloy’s resistance to sulfur-containing gases makes it an attractive material for such applications as coal-gasification units, burners and ducts for processing sulfuric acid, furnaces for petrochemical processing, recuperators, incinerators, and glass vitrification equipment for radioactive waste disposal.

 

In various types of high-temperature water, alloy 690 displays low corrosion rates and excellent resistance to stress-corrosion cracking. Thus, alloy 690 is widely used for steam generator tubes, baffles, tubesheets, and hardware in nuclear power generation.

 

INCONEL® alloy 690 (UNS N06690/W. Nr. 2.4642) is a high-chromium nickel alloy having excellent resistance to many corrosive aqueous media and high- temperature atmospheres. In addition to its corrosion resistance, alloy 690 has high strength, good metallurgical stability, and favorable fabrication characteristics.

 

The substantial chromium content gives the alloy outstanding resistance to oxidizing chemicals and to high-temperature oxidizing gases. The high level of nickel imparts resistance to stress- corrosion cracking in chloride-containing environments as well as to sodium hydroxide solutions.

 

The properties of INCONEL® alloy 690 are useful for various applications involving nitric or nitric/hydrofluoric acid solutions. Examples are tail-gas reheaters used in nitric acid production and heating coils and tanks for nitric/hydrofluoric solutions used in pickling of stainless steels and reprocessing of nuclear fuels.

 

The alloy’s resistance to sulfur-containing gases makes it an attractive material for such applications as coal-gasification units, burners and ducts for processing sulfuric acid, furnaces for petrochemical processing, recuperators, incinerators, and glass vitrification equipment for radioactive waste disposal.

 

In various types of high-temperature water, alloy 690 displays low corrosion rates and excellent resistance to stress-corrosion cracking. Thus, alloy 690 is widely used for steam generator tubes, baffles, tubesheets, and hardware in nuclear power generation.

 

VDM® Alloy 690 is resistant to a wide range of corrosive media and atmospheres. The high chromium content makes  the material particularly suitable for strongly oxidising conditions. The high chromium content also confers resistance to high-temperature corrosion in gases having an oxidising and sulphidising effect. Due to its high nickel content, VDM® Alloy 690 is exceptionally resistant to stress corrosion cracking which can occur in the primary water loops of nuclear power stations. The material also shows good resistance in mixtures of nitric and hydrofluoric acid. It demonstrates remarkable behaviour in concentrated (98.5 %) sulphuric acid at temperatures of up to 150 °C (300 °F).

 

Applications:

 

Thanks to its excellent resistance to wet and high-temperature corrosion, and its good mechanical properties, VDM® Alloy 690 is suitable for a wide range of applications.

 

Typical applications include:

  • treatment of radioactive waste,
  • components in boilers and steam generators in pressurised water reactors,
  • production of alkali metal sulphates using Mannheim furnaces,
  • fittings in combustion units for crude oil (oil ash corrosion) and
  • glass and silicate production.

 

 

Fabrication and heat treatment:

 

VDM® Alloy 690 can be processed using standard industrial production techniques.

 

Heating:

 

Workpieces must be clean and free of any contaminants before and during heat treatment. Sulphur, phosphor, lead and other low-melting-point metals can lead to damage when heat treating VDM® Alloy 690. This type of contamination is also contained in marking and temperature display paints or crayons, and also in lubricating grease, oils, fuels and simi- lar materials.

 

Fuels should contain as little sulphur as possible. Natural gas should contain less than 0.1 % by weight of sulphur. Hea- ting oil with a sulphur content of maximum 0.5 % by weight is also suitable.

 

Electric furnaces are to be preferred due to precise temperature control and freedom from contamination due to fuel. The furnace atmosphere should be set between neutral and slightly oxidising, and should not change between oxidising and reducing. Direct flame impingement needs to be avoided.

 

Hot working:

 

VDM® Alloy 690 can be hot worked at a temperature range of between 1,230 and 900 °C (2,250 and 1,650 °F) with subsequent rapid cooling down in water or by using air nozzles. The workpieces should be placed in the furnace heated to hot working temperature in order to heat up. Once the temperature has equalised, a retention time of 60 minutes for each 100 mm of workpiece thickness is recommended. After this, the workpieces should be removed immediately and formed during the stated temperature window. If the material temperature falls below the minimum hot working tempera- ture, the workpiece must be reheated. Heat treatment after hot working is recommended in order to achieve optimum properties and corrosion resistance.

 

Cold working:

 

Cold working should be carried out on annealed material. VDM® Alloy 690 has a higher work hardening rate than auste- nitic stainless steels. This must be taken into account during design and selection of forming tools and equipment and during the planning of forming processes. Intermediate annealing may be necessary for high degrees of cold working deformation. Before use, heat treatment is required after cold working with more than 10 % deformation.

 

Heat treatment:

 

Solution annealing should be carried out at temperatures between 1,020 and 1,070 °C (1,870 to 1,960 °F). If use in a high-temperature range with increased creep resistance is intended, the solution annealing temperature should be rai- sed to between 1,080 and 1,150 °C (1,980 to 2,100 °F).

 

Water quenching should be carried out on workpiece thicknesses over 1.5 mm so that the optimum corrosion resistance of the material can be reached. Workpieces of less than 1.5 mm thickness can be cooled using air nozzles.

 

If use in pressurised water reactors is intended, a subsequent heat treatment of around 10 hours at between 700 and 740 °C is necessary in order to ensure that carbides are segregated specifically at grain boundaries.

The cleanliness requirements must be followed for any form of heat treatment.

 

Descaling and pickling:

 

Oxides of VDM® Alloy 690 and discolorations in the area around welding seams are more adherent than on stainless steels. Grinding using extremely fine abrasive belts or grinding discs is recommended. It is imperative that grinding burn is avoided. Before pickling – which may be performed in a hydrofluoric acid mixture – the surface oxide layer must be broken up by abrasive blasting, by carefully performed grinding or by pre-treatment in a fused salt bath. The pickling baths used should be carefully monitored with regard to concentration and temperature, since pickling for too long can damage the material surface due to intercrystalline corrosion.

 

Machining:

 

VDM® Alloy 690 should preferably be machined in the annealed condition. Since the material exhibits a considerable work hardening rate, low cutting speeds should be used and the tool should remain continuously in contact. An adequa- te cutting depth is important in order to cut below the previously formed work-hardened zone.

 

Optimum heat dissipation through the use of large quantities of suitable, preferably aqueous, lubricants has considerab- le influence on a stable machining process.

 
 

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