The following information details and compares several properties of Hard Chrome, also called Chromium, in relation to Hardness, Coefficient of Friction, Coefficient of Linear Thermal Expansion, and Corrosion Resistance. This information will provide a broad, general guide. Prudence suggests that tests be conducted under actual service conditions prior to making design decisions. For assistance or additional information, please contact us.
In the electroplating industry, the two most commonly used measurements of hardness are Vickers (HV) and Rockwell C (HRc). Both these hardness tests measure the indentation hardness of a part or thin section of material.
The Vickers Hardness test is mainly used on applications that have stringent quality requirements. This is because the test is slower, uses less force, and produces a more accurate hardness than the Rockwell test.
The Rockwell test is the more commonly used method of measuring hardness. This is because the test is faster and cheaper to perform, while offering easily readable hardness values without extra equipment. Also, no additional prep or polish is required of the surface material.
Industrial hard chrome can have a broad range of hardness due to the required plating thickness. The average hardness will be in the range of 65-70 HRc or 940-1210 HV. The following table shows comparable materials and surface finishes.
Indentation Hardness (Kg / mm²)
|Aluminum, Type 1100 H18||70 HV|
|Steel, mild cold rolled||150 HV|
|Brass, 70-30 hard||165 HV (5 HRc)|
|Stainless Steel, Type 304||165 HV (5 HRc)|
|Nickel, bright electroplated||300 HV (33 HRc)|
|Stainless Steel, Type 410 hardened||375 HV (39 HRc)|
|Steel, hardened tool steel||450 HV (45 HRc)|
|Chromium electroplated (Hard Chrome)||1210 HV (70 HRc)|
Coefficient of Friction (CoF) is defined as the ratio used to quantify the friction force between two objects in relation to the normal force that is keeping them together. This is relevant for engineers that have multiple parts that come in contact with each other. Hard chrome has a very low coefficient of friction. Applying a surface finish, like hard chrome, would greatly reduce friction, therefore increasing the service life and performance of the parts.
Mathematically, μ = F/N, where F is the frictional force and N is the normal force. The following table shows comparable materials and surface finishes.
|Hard Steel on Hard Steel||0.42||0.03|
|Chromium on Hard Steel||0.15||0.03|
|Mild Steel on Mild Steel||0.57||0.09|
|Nickel on Mild Steel||0.64||0.18|
|Chromium on Mild Steel||0.16||0.05|
|Hard Steel on Babbitt||0.33||0.16|
|Mild Steel on Cast Iron||0.23||0.13|
|Chromium on Cast Iron||0.15||0.03|
|Aluminum on Aluminum||1.4||N/A|
|Mild Steel on Aluminum||0.47||N/A|
Coefficient of Linear Thermal Expansion (CTE) is defined as the fractional increase in length per unit rise in temperature. When subjected to heat, materials will inevitably expand, and over small temperature ranges, the thermal expansion of uniform linear objects is proportional to temperature change. Hard chrome has a lower rate of thermal expansion than many commonly used substrates. If a part will be exposed to high temperatures, hard chrome will protect it and lower the risk of failure. The following table shows comparable materials and surface finishes.
8.1 X 10-6cm/cm/°C
4.5 X 10-6in/in/°F
COMPARISON WITH OTHER MATERIALS
|Material||cm/cm/°C at 20°C||in/in/°F at 68°F|
|Aluminum (99.9+)||22.5 X 10-6||12.5 X 10-6|
|Brass (70Cu-30zn)||19.8 X 10-6||11 X 10-6|
|Cast Iron (Gray)||10.44 X 10-6||5.8 X 10-6|
|Chromium||8.1 X 10-6||4.5 X 10-6|
|Monel (70Ni-30Cu)||14.4 X 10-6||8 X 10-6|
|Steel (1040)||11.34 X 10-6||6.3 X 10-6|
|Steel (18Cr-8Ni Stainless)||9.0 X 10-6||5 X 10-6|
|Titanium (99.0%)||8.55 X 10-6||4.75 X 10-6|
VARIATION WITH TEMPERATURE
|Temperature Range, C||Coefficient of Linear Expansion cm/cm/°C|
|20-400||8.4 X 10-6|
|20-600||9.2 X 10-6|
|20-800||9.8 X 10-6|
|20-1050||11.0 X 10-6|
Electroplated chromium has good resistance to a variety of corrosive environments. It offers protection against chemical sources including Citric Acids, Nitric Acids, Sodium Chloride and Copper Sulphate. The following table shows several corrodents and how resistant chromium is to them.
R – usually completely resistant
SA – some or slight attack, should be tested
NR – not recommended
Unless otherwise noted, inorganic materials were tested in 10% aqueous solutions at 25°C (77°F).
|Acetic Acid, glacial||R|
|Acetic Acid, 50% Aq||R|
|Air, hot oxidizing||R|
|Air, hot reducing||R|
|Aluminum Chloride, 50% Aq||NR|
|Aluminum Sulfate (Alum) 25% Aq||SA|
|Ammonium Chloride, Aq||SA|
|Barium Chloride, Aq||R|
|Biscuit & Bread Dough||R|
|Calcium Chloride, Aq||SA|
|Calcium Hypochlorite, Aq||NR|
|Chlorine, moist gas||NR|
|Chromic Acid, Aq||SA|
|Chromic Chloride, Aq||SA|
|Citirc Acid, Aq||SA|
|Cupric Chloride, Aq||NR|
|Cupric Nitrate, Aq||SA|
|Cupric Sulfate, Aq||R|
|Ferric Chloride, Aq||SA|
|Ferrous Sulfate, Aq||SA|
|Fruit Juices, acid||R|
|Glue, hoof, hot||R|
|Hydrochloric Acid, Aq||NR|
|Hydrofluoric Acid, Aq||NR|
|Iodine, solid & vapor||NR|
|Paper Pulp, sulfite||R|
|Phosphoric Acid, 85%||SA|
|Picric Acid, Aq||R|
|Plastics, melamine or urea formaldehyde||R|
|Plastics, polyethylene or polypropylene||R|
|Potassium Chloride, Aq||R|
|Rubber, mixing or vulcanizing natural||R|
|Sodium Chloride, Aq||R|
|Sodium Carbonate, Aq||R|
|Sodium Hydroxide, Aq||R|
|Sodium Hypochlorite, Aq||NR|
|Sulfer Dioxide, moist||R|
|Sulfuric Acid, 96%||NR|
|Whiskey & Wine||R|
|Zinc Chloride, Aq||NR|
We’re confident US Chrome will be your best option for your chrome plating applications because of our engineering approach, exceptional customer service, and regional locations. Contact us now with your questions or coating challenges.
We’ll help you find the right answer.