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Steel Quality S550MC

  • 1.  Steel Quality S550MC

    Posted 07-28-2021 05:44
    Dear all,
    We buy S550MC material to our cold stamping process, to obtain steel flat sheets with min Rm required of 25KN. Normally we buy material with 600 Rm min and it is enough to obtain our parts with the mechanical properties required. Nevertherless, we now have problems with a new supplier and we do not see where is the problem. I attach the chemical composition for your analysis. Is the different Si content detrimental? It is under the quality limit but higher than the material we normally use. Wich could be  the Si role here?
    Thanks a lot for your time.


    Cert Re Rm A% C Mn P S Si Al Ni Nb V Cr Cu N Ti Pb Mo Sn B Ceq CET CEV
    46260 556 627 25 0,061 0,790 0,007 0,003 0,010 0,040 0,040 0,048 0,010 0,020 0,020 0,005 0,060       0,000 0,2 0,143 0,203
    26776 622 662 10,2 0,063 1,230 0,017 0,001 0,024 0,035 0,000 0,052 0,002 0,000 0,000 0,000 0,001 0,000 0,000   0,000   0,186 0,268
    46916 610 663 21,4 0,043 1,607 0,010 0,003 0,317 0,030 0,067 0,043 0,003 0,060 0,132 0,005 0,058   0,012 0,010 0,000   0,216 0,339

    Gemma Bertran Vidal
    Consultora Industrial
    Mb. (+34) 646190321


  • 2.  RE: Steel Quality S550MC

    Dayton Chapter Admin
    Posted 07-29-2021 12:37
    Greetings!

    What exactly IS the problem?






  • 3.  RE: Steel Quality S550MC

    Posted 07-30-2021 02:24
    The problem is that when we test the finished part it does not arrive to 25KN. We tested the raw material and the result confirmed the one certified by the supplier but when we stamp the part and we test the part we do not arrive to 21KN, with normal values of elongation. I wonder which more there is that affects our process from the raw material point of view. If there were inclusions problems I guess that other mechanical properties would also be affected.

    Thanks!

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    Gemma Bertran
    Doctor in Chemistry and Materials Science
    Igualada
    +34 646 19 03 21
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  • 4.  RE: Steel Quality S550MC

    Posted 07-31-2021 20:23
    I am not an expert in this area but it could be either an effect of prior history and/or chemistry
    Maybe the original material was cold rolled to get 600MPa but the new material gains strength from additional Mn+Cu+Si to balance the lower Carbon. The lower C of the new material would reduce strain hardening, improving formability but reducing the strength of the final product.
    These are the immediate thoughts of an old metallurgist so I hope they help
    cheers

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    Rod Mackay Sim
    Paddington Nsw
    61411158443
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  • 5.  RE: Steel Quality S550MC

    Posted 08-02-2021 10:20
    Gemma,

    A few questions about the process overall:

    • Do you perform any heat treatment on this material after stamping?
    • Does the new supplier use a different melting/conversion practice than the previous suppliers did?
    • Is the new supplier reputable (and/or located in a reputable country) such that you are confident that whatever capability testing they may have reported on the MTR is accurate?
    • Has your stamping process (or any other relevant internal processes, such as test specimen location) changed at all?

    My first inclination is to conclude that the higher levels of Si and Cu shouldn't hurt your strength; they are elevated but not terribly high and I agree with your assessment that if they were to do anything, it'd be to hurt ductility which you state has not occurred. The only strengthening element you're really lower in here is carbon (which is also going to be the most impactful one); the others like Nb/Cr/Ni/Mn are present in greater quantities than the historical heats although their impact on strength will depend on your heat treat condition. 

    Conclusion: provided that the only relevant variable to have changed is chemistry, I would conclude that the lower carbon content is responsible and I'd suggest that you specify a minimum of 0.06% for future heats (or whatever other number would be supported by other historical data you might have).

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    Sean Piper
    Product / Process Metallurgist
    Ellwood Texas Forge Houston
    Houston TX
    (713) 434-5138
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