Heat bending or not a 316 SS rod?

Discussion in 'Metal Boat Building' started by raf pali, Dec 30, 2015.

  1. raf pali
    Joined: Mar 2012
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    raf pali Junior Member

    Bending a 316 stainless steel rod 10mm-3/8 DIA to a tight radius to make a U bolt that fits inside a 50mm – 2” DIA pipe. The U bolt is to be 300mm – 1' long.
    My question: can this kind of bending be done cold without cracking? Or, would that be preferable to heat bending? And, would heat bending weaken the SS tensile properties?
    Thanks in advance.
    Cheers.
     
  2. Barry
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    Barry Senior Member

  3. raf pali
    Joined: Mar 2012
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    raf pali Junior Member

    Thank you Barry From the SS data I got confused here- Annealing: Heat to 1020 oC - 1100 oC, hold until temperature is uniform throughout the section. *Soak as required. Quench in water to obtain optimum corrosion resistance.*Actual soaking time should be long enough to ensure that the part is heated thoroughly throughout its section to the required temperature, 30 minutes per 25 mm of section may be used as a guide.

    From dictionary - Annealing Definition: heat (metal or glass) and allow it to cool slowly, in order to remove internal stresses.

    And: ..."Actual soaking time should be long enough to ensure that the part is heated thoroughly"...(?)

    From dictionary - Soaking Definition: make or allow (something) to become thoroughly wet by immersing it in liquid.

    Could please anyone shed some light here?
    Thank you so much
     

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  4. baeckmo
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    baeckmo Hydrodynamics

    Don't worry about heat treatment, just bend it cold. The resulting cold working is not severe enough to require annealing.
     

  5. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Just bend it cold as Baeckmo has suggested.

    We do not know your application from the limited information provided in the original post. Tensile strength can improve with cold working within certain limits. 316 ( and most other stainless used for fasteners and components commonly used) are non- magnetic in their supplied state but can become slightly magnetic with cold working. This should not be a problem with a common u-bolt in normal operating conditions. Note if this u-bolt is going to be cycled hundreds of thousands of time close to the yield stress in an extremely corrosive environment, then it could become a problem.
    Annealing would get the stainless back to its original state but as stated above probably not required.

    It would be difficult to compress even the most basic theory of metal crystal structure into a paragraph or two but here is an acutely short attempt

    Most stainless steels are magnetic but 316 is not in its annealed state.
    It starts out annealed in a crystal structure ( austenitic) which gives it its specific properties, strength, ductility, corrosion resistance, etc. If you cold work it, bend it, the altered structure/grain configuration can change the metals properties ( martensitic) . IF your u-bolt is required to have the original annealed specific properties, you would have to anneal it to get it back to specs.
     
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