Misconception: More the Hardness, More is the wear resistance

In Maintenance and repair welding, there is increasing demand regarding the life of the component. It is misinterpreted in the industry that more hardness of the weld built up will give more life. Yes, theoretically it is true partially. But what actually the thing which enhances the life of component is in the microstructure of the weld.

Carbide formation in the weld built up metal is responsible for giving good life. These carbides are having excellent wear resistant property. For different applications different carbide forming elements are alloyed which forms stable carbide by combining with carbon. Refractory elements like W,Mo,Nb. etc. are alloyed for high temperature wear applications.

So, if i have two weld built up having same hardness but with different microstructure than wear resistant of the weld having more carbides will be good compared to other. Below shown is the microstructure of Martensite phase and Chrome-carbide phase. Martensite will have less wear resistant property than chore-carbide phase(Hexagonal white portion is chrome carbide)

Chrome carbide phase with Fe matrix.

Chrome carbide phase with Fe matrix.

martensite phase

martensite phase

Wear Factor:

  • It is the measurement of the wear rate of the metal/alloy. Wear factor depends on the Microstructure– % volume fraction on carbides, Size of Metal carbides, Mean free path between carbides & Hardness of Matrix.
  • Wear testing is practiced according to ASTM G-65. It gives mass loss of the metal. Rubber wheel is rotated at fixed rpm for particular no. of revolutions and in between rubber wheel and metal sand is feed continuously at fixed sand flow rate. This will generate abrasion in the metal thus causing mass loss.
  • Wear testing equipment

    Wear testing equipment

    Calculating wear factor:

  • Volume loss(gm) = weight loss/density
  • Wear factor = 1/ volume loss
  • More the wear factor, more wear resistant and longer service life.

So, check for microstructure if you really want to enhance the component life.

Keep Reading, Happy welding

Thank you,

KP Bhatt

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3 thoughts on “Misconception: More the Hardness, More is the wear resistance

  1. Very good info. Like can you comment anything on hardness and density. What is d relationship between hardness and density?

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    1. Thank you.
      As such there is no direct linear relation between hardness and density. It is generally said that as density increases, that means less pores, overall mechanical property increases. So, some how we can relate it to hardness also, hardness increases. But carbon-diamond has density 3.51 gm/cc and well known steels have 7.87 gm/cc and we know which one is harder. So, I can conclude that their no direct relationship and if it is there then it will be very complex to understand.

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  2. Density is a volume property and Hardness is a surface property.Density takes the complete mass of the substance into consideration whereas hardness is only related to the case and the subsurface might not be the same as the surface..So, their should be no direct relationship between Density and Hardness.

    Liked by 2 people

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