Ni Hard Castings

The high-alloy white irons are primarily used for abrasion-resistant applications and are readily cast into the parts needed in machinery for crushing, grinding, and handling of abrasive materials. The chromium content of high-alloy white irons also enhances their corrosion-resistant properties.

The high-alloy white cast irons fall into two major groups:

Nickel-chromium white irons, which are low-chromium alloys containing 3 to 5% Ni and 1 to 4% Cr, with one alloy modification that contains 7 to 11% Cr,
Chromium-molybdenum irons containing 11 to 23% Cr, up to 3% Mo and often additionally alloyed with nickel or copper.

The nickel-chromium irons are also commonly identified as Ni-Hard types 1 to 4.

Ni-Hard Casting or Nickel-Chromium White Irons

The oldest group of high-alloy irons of industrial importance, the nickel-chromium white irons, or Ni-Hard irons, has been produced for more than 50 years and is very cost-effective materials for crushing and grinding.

Ni-Hard is a metal with chrome content of 1.4% to 28%. It is an abrasive iron for low and high stress abrasion in Mining, Milling, and Earth Handling uses.

It is also used extensively in the Power Plant Industry, Brick Plant Industry, Asphalt Industry, Cement Industry, and Rock Crushing Industry.

The optimum composition of a nickel-chromium white iron alloy depends on the properties required for the service conditions and the dimensions and weight of the casting. Abrasion resistance is generally functioning of the bulk hardness and the volume of carbide in the microstructure.

Ni - Hard is an extremely wear resistant material and in cast form is ideal for use with abrasive products, giving a much more extended life when compared with cast iron or mild steel when incorporated in pneumatic conveying systems.

Nickel content increases with section size or cooling time of the casting to inhibit pearlitic transformation. For castings of 38 to 50 mm thick, 3.4 to 4.2% Ni is sufficient to suppress pearlite formation upon mold cooling. Heavier sections may require nickel levels up to 5.5% to avoid the formation of pearlite. It is important to limit nickel content to the level needed for control of pearlite; excess nickel increases the amount of retained austenite and lowers hardness.