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Off Topic - Steel Hardness

Question asked by Don Cheke on Jul 13, 2018
Latest reply on Jul 13, 2018 by Don Cheke

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Sorry for the off topic query, but I know there are a lot of smart and helpful folks on this forum.

We have a specialized bolt manufactured in China for us. It works along side a door hold-open bracket so both require a Rockwell Hardness C of 45 - 50.

They are producing the bolt with SCM435 steel and I think that is equivalent to AISI SAE 4135H/4137H steel. This seems to have a normal hardness of 15 HRC. Can this steel be treated to reach the desired 45-50 HRC? I am assuming it must, but since I am materials illiterate I was hoping to find some expert input on the topic.

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Sebastyon Champion Jul 13, 2018 12:12 PM
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Yes, you can heat sinc the steel with treated carbon, However this is fairly costly doing it after the initial manufacturing process. I would suggest starting with heat sinc material then molding.
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- Don Cheke @ Sebastyon Champion on Jul 13, 2018 2:49 PM
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  Thanks Sebastyon,
  
  I am not sure what process they are using to manufacture the bolt, but what you state helps me to know that one way or the other the end result can be achieved.
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Frederick Law Jul 13, 2018 12:19 PM
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When you say Rc 45-50, how deep does it need to be? Through?
41xx is able to get through harden.
It should be available as heat treated stress relieve and harden bar stock.
Since its from China, inspect every single piece. Cut a few and make sure inside is Rc 45-50.
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- Don Cheke @ Frederick Law on Jul 13, 2018 2:59 PM
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  Thanks Frederick,
  
  Sadly, I am not knowledgeable enough to know how deep it should go, but part of the problem is that we have been having issues with the bracket part of the hold-open sawing into the bolt. We have been getting the bolts tested and found that there has been whole lots that have come in well under what was spec'd. We are now having the supplier provide data with each delivered lot and we are having numerous samples independently hardness tested by a local US testing lab. I think we have it sorted now for the most part but this whole thing has been quite the learning curve. I will need to review the local test lab results again but I believe they are cutting into them before testing.
  
  On another note, is it safe to assume that if you have two similar metals of the same hardness, that one should not saw into the other (within reason)?
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  - Frederick Law @ Don Cheke on Jul 13, 2018 3:07 PM
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    Don Cheke wrote:
    
    On another note, is it safe to assume that if you have two similar metals of the same hardness, that one should not saw into the other (within reason)?
    
    It depends. Surface contact: if you got a flat bar sliding on the bolt, the bar got more surface to wear then the bolt. The circular surface on the bolt start wear as a point or line contact. It increase with wear. Then there is local work hardening.
    Typically you do not use same material for wear. One will be harder then the other. So you control which one need to be replace.
    
    Send the bolts out to test if its the correct material, not just hardness.
    
    BTW I'm not hating China product, I'm Chinese
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    - Don Cheke @ Frederick Law on Jul 13, 2018 3:26 PM
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      Thanks once again Frederick,
      
      I have used your response (and Sebastyon's) as the basis for some additional questions I am asking our vendor and as some discussion points with our quality engineering team to help with future testing.
      
      Thanks all - for your willingness to help out! I appreciate it so much.
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