A666- Hardness Question

[jdesouza]

My company has a product which uses thin (0.003") 316 st/st disks and we form them with a die. A recent shipment came in and the hardness of the steel was higher than previously and cannot be formed without major re-tooling. The hardness was Rc32 (according to the cert)

The vendor claims that they did not violate ASTM A666 1/4 hard specs because tensile and yield values are minimums only. However, this is a hardness issue and I don't see hardness called out for anything on this standard except for the annealed state. What should this hardness be? Perhaps we are using the wrong standard to call out this material? Any help would be appreciated!



~Jeff~

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[israelkk]

The hardness can be anything if the standard doesn't have a requirement for it. I doubt that you will find any standard with hardness requirement for 316 sheet or strip of that thickness.

This is exactly what happens when designers don't bother (or do not have/given the time) to read the standard and assume that all batches of materials will be the same as the first one they found.

 

[unclesyd]

I don't have the ASTM spec but all my literature calls for 1/4 Hard SS strip to be in range of 25/30 Rc with a tensile of 125,000 min. This hardness range is common to several sources. Just looking at your information combined with the material and thickness of the strip your numbers are not out of line.

The alternative is to order the strip as "Soft". this should give you a hardness of around 85 Rb and the metal should be workable.

If you have a quantity of the 1/4 hard material that is unworkable as is here is one thing you might try.
Try different lubricants during the forming process.

If you can stand a little color (oxide) you can soften the disks by holding at 1550° F for a couple of minutes and air cooling. You will get 98% of the ductility of a full anneal.

 

[EdStainless]

The limit on the upper strength in A666 is the elongation requirement. Does this material still make 10% elong?

If you need the strength and this is an issue for you then you need to specify a range of properties. Maybe 125-149ksi UTS would do the trick?

On the hardness question, what was actually measured? You should not be using Rockwell, not even superficial for material this thin.

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