Hard Chrome

What is Hard Chrome?

Hard Chrome is a surface coating of metallic chrome settled in a galvanic way to provide special properties to the parts.

Electrolytic Chrome Plating is divided into two main processes:

- HARD CHROME is the process accomplished by CROMOFIX, which aims to provide surface hardness, thus wearing out resistance. That quality is reached with layers thicker than 10 microns, applied directly on the metal base. The aspect of hard chrome coating is bright or opaque, depending on which finishing has been applied before the treatment, since hard chrome plating follows the previous roughness of the part.

Example of chromed parts: extrusion moulds (packaging industry) and thermo injection, thermoplastic and elastomers; stamping and wire drawing tools/dies and hydraulic cylinders.

Decorative chrome (WE DO NOT MAKE THIS SERVICE) is composed of a very thin layer around 0.1 microns of chrome, usually applied on a bright nickel layer aiming to improve the visual decorative aspect and corrosion resistance. For example: wire baskets, bumpers and car wheels.

Hard Chrome and Corrosion Resistance

CROMOFIX works with equipment and process that are able to provide micro cracked hard chrome coating, besides the traditional macro cracked hard chrome. Cracks comes from internal stresses that are responsible for the hardness of the chrome layer.

Micro cracked hard chrome improves the corrosion resistance compared to traditional macro cracked hard chrome, due to changes of surface corrosion potential, it can reach more than 100h of salt spray test without red corrosion, according to Standard ASTM B117.

Chrome in a texturized surface
Chrome part

Advantages of Hard Chrome

Chrome application is done to obtain the following characteristics:

  • Wear resistance : it is the most attractive advantage of hard chrome properties. Tests have shown that a piece covered with hard chrome endures from 5 up to 8 times more than a regular piece of steel.
  • Corrosion resistance : chrome is resistant to corrosion, protecting the steel part efficiently, which achieves an electro chemical potential of noble metals. A rectified piece receives a 0.03- mm-chrome film on it to its protection.
  • Scratch resistance : this property is connected to the chrome hardness. At MOHS scale, with 10 degrees only, which is from talc up to diamond, chrome is located at 8.9. Scratch resistance also depends on the steel part hardness which chrome will be applied to.
  • High surface hardening without generating stresses in the part : hardness in one of the most important characteristics of chrome, due to the existence of hardness that it is resistant to wearing out and scratching. Hard chrome usually presents an average hardness of 70 HRC, equivalent to 750 Brinell and 1000 Vickers, approximately. Chrome layer hardness starts to diminish from 350°C. Layer thickness does not matter on how hard it is.
  • Low Coefficient of static friction : meanwhile between two steel parts have 0.30 of static friction, on the other hand, between a steel and chrome part is 0.17.

Material to be chromed:

  • Carbon steel
  • Nickel steel
  • Chrome nickel steel
  • Stainless steel
  • Cast steel
  • Cutting tool steel

Chromed with special procedures

  • Steel treated thermically
  • Ductile cast iron
  • Alloy, brass and copper parts

Not possible to provide hard chrome surface treatment onto:

  • Gray cast iron, due to its high porosity and flake graphite .
  • Metals with surface problems (inclusions, precipitations and porosity)
  • Nitrided (salt baths, gas and plasma), black oxidized and Parkerized (phosphatized) steel.

Thickness of Hard Chrome coats or layers:

It can vary between 0.003 up to 0.3 mm, depending on its application. In special cases, we can apply thicker coats, but economy and technical matters must be discussed beforehand.

Coats over 0.6mm are not recommendable.

Definition of Hard Chrome coat

Atmospheric, mechanical, chemical and heat aspects must be analyzed, checking out what are the original steel, hardness and surface finishing (roughness).

Layer Thickness usually applied:

Hydraulic rods 0,025 up to 0,050mm
Plates or sheets 0,025 up to 0,050mm
Dies and moulds 0,010 up to 0,030mm
Cylinders 0,025 up to 0,400mm
Protection coats to corrosion 0,020 up to 0,050mm
Layer for post grinding 0,050 up to 0,070mm
Recovered parts 0,100 up to 0,300mm
Special coats 0,002 up to 0,500mm

See Properties Table

See Corrosion Resistance Table

See Application Table

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Cromofix Cromo Duro Ltda.
Plant 1: Rua Evaristo de Antoni, 1458 - Caxias do Sul - RS | Plant 2: Rua Evaristo de Antoni, 1053 - Caxias do Sul - RS - Brazil - Phone: +55 54 2101.9898 Fax: 55 54 2101.9898