What is Ni-Resist cast irons
Ni-Resist cast irons are a family of alloys with sufficient nickel to produce an austenitic structure which has unique and superior properties. The family is divided into two groups.
- Standard or flake graphite alloys and the
- Ductile or spheroidal graphite alloys.
Characteristics of the Ni-Resist Austenitic Cast Iron Alloys
- Corrosion Resistance: The Ni-Resists are specified for handling salt solutions, sea water, mild acids, alkalies and oil field liquids, both sweet and sour. Their corrosion resistance is far superior to that of normal and low alloy cast irons.
- Wear Resistance: They offer excellent wear & galling resistance.
- Erosion Resistance
- Toughness and Low Temperature Stability: Ni-Resist alloys are much superior to gray cast iron, particularly at low temperatures.
- Very good castability & machniability compare to cast iron.
- Heat & oxidation resistance
Material specification for Ni-Resist Cast irons
Below tables shows the ASTM, ISO, DIN & BS Material specification & grades for Ni-resist cast iron grades.
Chemical properties of Ni-Resist Cast Iron
Chemical properties of Ni-Resist cast irons are shown in below table:
Welding of Ni-resist Cast Iron
Welding of Ni Resist 1, 2, 3, 4, 5 & 6 as well as other Ni-resist D series cast Iron shall be made using ENiFe-CI electrode. ENiFe-CI is commonly known as 55% Nickel-iron type welding electrode.
This composition is used for welding ordinary gray cast iron and is suitable for flake graphite Ni-Resist alloys. Most 55% nickel/iron electrodes deposit metal with a tensile strength equal to that of Ni-Resist alloys D-2, D-2B and D-2W. However, they are often lacking in impact toughness. To avoid this problem, the electrode selected to weld spheroidal graphite alloys should be carefully evaluated to provide a deposit with acceptable soundness, toughness and machinability. Ease of operation and freedom from slag inclusions in the weld metal are also important properties.
Preheating for Ni-resist Cast Iron welding
When welding flake graphite Ni-Resist alloys, preheating to 300-350°C (570-660°F) is recommended. The interpass temperature should also be maintained at that level. On completion of welding, care should be taken to allow slow cooling in still air. For complex welds, transfer to a preheated oven or furnace and slow cooling under controlled conditions may be advantageous.
Preheating is normally unnecessary when welding spheroidal graphite alloys. However, in practice, it is sometimes beneficial to use a low preheat to about 100°C (210°F) when welding conditions are not ideal and cold air drafts are present. A low interpass temperature of 150°C(300°F) is essential for the ductile Ni-Resists.
Heat treatment of Ni-resist Cast Iron
Post weld heat treatments are usually not necessary for structure or properties in any Ni-Resist alloy. But stress relief is often required, especially if castings are to be exposed to an environment where stress corrosion cracking is a possibility. The heat treatment procedures for stress relief given previously should be followed.