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Nitrocarburizing of Plain carbon steel

  • 1.  Nitrocarburizing of Plain carbon steel

    Posted 03-05-2021 14:46
    Hi ASM team,

    We are planning to perform liquid ferritic nitrocarburizing on AISI1010 steel. I would like to know what would be the minimum and maximum compound layer hardness that can be achieved for this steel. I appreciate it if you share with me any similar experiences. 

    Thanks,

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    Neda Mandkarian
    Metallurgist
    McLAren Engineering
    Livonia MI
    (248) 752-2355
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  • 2.  RE: Nitrocarburizing of Plain carbon steel

    Posted 03-06-2021 08:09
    Edited by Donato FIRRAO 03-06-2021 08:14
      |   view attached
    Dear Ms. Neda,
    your apparently simple question calls for a rather complex reply.
    First of all, AISI 1010 steel (equivalent to the European C10) is liquid nitrocarburized only to reduce the friction coefficient in low contact pressure applications. Thus, you do not want to control hardness of treated parts, but the constitution of the top carbonitrides layer, which has to be formed mainly by the epsilon solid solution of the Fe-C-N phase diagram, since such a phase has a HCP crystal structure, which is similar to that of graphite and has the same lubricant features.Too a high load will have the tip of the indenter tobreak through the layer; conversely, too a low load will test only the immediate surface layer microhardness. In fact, microhardness through a 10 micrometers (microns) layer varies across the depth (distance from the surface) in a 1010 treated steel, starting at 600 HV ca., descending to less than 500 HV at mid thickness and then going back to 600 HV at the layer/matrix interface, where C content is the highest due to carbon counterdiffusion. Carbon is the only element that controls epsilon phase hardness and toughness. Nitrogen does not play any role. Constitution assessment calls for XRD analysis, which is not usually done in industrial laboratories.
    My expert advice is that there is no mean to control the liquid nitrocarburizing process by means of hardness tests. The only way to put some type of pressure on your heat treater is to check top layer depth upon sectioning a treated piece. Depth has to be at a 10 microns value +/- 1 for a 2 h treatment, which is  the optimum duration to avoid spalling.

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    Donato FIRRAO FASM
    Professor
    Politecnico di Torino
    Torino
    +393351494032
    Italy
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