Hardening SS 304 sheet
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    Default Hardening SS 304 sheet

    We want to improve stiffness of our clip. It is to be manufactured by pressing 0.2 mm thick annealed AISI SS-304 grade sheet. But the clip is found to be too weak for our purpose. We want it more stiff (spring back to hold a component). (dwg attached)

    Is it possible to make SS 304 stiffer by semi-hardening or tempering? After hardening, is it convenient to press-work after it is 3/4 or semi hardened? Please give your valuable insight.
    Attached Thumbnails Attached Thumbnails battery-clip-dwg.jpg  

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    Stiffness of a part is a function of Young's Modulus (look it up) and the geometry of the part. Hardness has no effect upon Young's Modulus for a given material, so you need to change geometry or pick a different material.

    Hardness does affect strength, but that is completely different from stiffness. The way to harden 304 is to roll it thinner; there is no heat treatment available.

    This is something learned in first year mechanical engineering classes, so find an engineer to help you out. You may be confusing stiffness with strength.

    Larry

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    Is age hardening SS-304 annealed sheet possible?

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    afaik, 304 is hardened only by mechanical means- hammering , rolling , punching... etc.
    a way to really get it nice and hard is to gall it with a dull cutter turning way too fast . ever seen some fool
    try to drill stainless on a pos drill press @ 1500rpm with a marginally sharp 1/2 HSS twist drill- the tool is smoked,
    and the hole is hard as quartz....never to be drilled again....

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    0.2 mm? If you double your material thickness to 0.4 mm you will triple it's stiffness, and not really have to modify your die.

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    Spring temper is a cold working achievement. It may take a lot of overbend to form the part. I'd imagine that you'd have to actually coin the part (many tons of pressure required) at the moment it is formed to make it both formable and springy when released from the die.

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    You must buy 304 that has been cold rolled to a higher strength.
    Don't buy annealed sheet, buy 1/2 hard or full hard sheet.

    The stuff you all ready have on hand cannot be made to work for this job.

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    Not applicable to this situation, but 304 can be nitride hardened, which is a type of case hardening. Very shallow (generally less than .010), but quite hard.

    These people sell 301 stainless for spring applications.
    31 Stainless Steel Full Hard Temper - Sheet & Coil AMS 5519 | Precision Steel Warehouse

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    L Vanice nailed it.

    Pretty much all steels have similar Young's modulus, and work-hardening, or hardening by heat treat cannot significantly increase the Young's modulus.

    Strength and hardness do not equal stiffness.

    Age-hardening can be obtained using special alloys, but 304 isn't one of those alloys. 300 series (austenitic) stainless steels cannot be hardened by heat treatment. They can be hardened by cold-working. But, as L Vanice pointed out, hardening doesn't change the Young's modulus. There is no way to make your 304 part stiffer using any treatment or process. You MUST use either a thicker 304 (I think Red James' suggestion is a good one), or use your current 304 sheet, but double it up to give you twice the thickness of metal*, or a different steel. Alternately, you might put ridges in the part to act as gussets. Or you could make the part wider.

    Cro-Moly steels are a bit stiffer than chromium-based steels, but only by about 10%, and they don't have 304's chemical/corrosion resistance.

    In sum, you cannot process this problem away using current design. You must change the material thickness, or change the design (thicker sheet, or doubling up the current sheet, or make the part wider, or add ridges/gussets to the part, etc).

    *Note that Red James' suggestion, to use thicker sheet, is a better and stiffer solution to doubling up the 304.

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    Quote Originally Posted by Red James View Post
    0.2 mm? If you double your material thickness to 0.4 mm you will triple it's stiffness, and not really have to modify your die.
    Doesn't the stiffness go up on thickness^3 so double thickness is 8 times stiffer.

    Maximum deflection before yield limit on the other hand goes down when you increase thickness so those locking "latches" that are bent at 162 degrees can handle even less bending (more force, less deflection before they yield and loose the set angle)

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    Quote Originally Posted by MrWhoopee View Post
    Not applicable to this situation, but 304 can be nitride hardened, which is a type of case hardening. Very shallow (generally less than .010), but quite hard.

    These people sell 301 stainless for spring applications.
    31 Stainless Steel Full Hard Temper - Sheet & Coil AMS 5519 | Precision Steel Warehouse
    MrWhoopee has it, if you haven't purchased material work hardened to your needs the only "non buildup (i.e. chrome plating) method I'm aware of is a specialized nitriding:

    UltraGlow(R) Ion Nitriding Stainless Steel Parts

    I suspect (but don't have numbers) that the additional nitrogen atom case does increase the modulus a little bit, but not significantly.

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    If you can add some ribs to the part, that would help quite a bit

    Tom


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