SST hardness 1

[morkman]

Good afternoon everyone. I am having trouble with a 303 sst machined component where the hardness of a material is called out on the print as ASTM-A582 condition A. Unfortunately there is only a maximum hardness 282 Brinell scale specified. Does this mean that the supplier can produce any hardness of material as long as they are under the 282 Brinell scale?

I performed a micro hardness test on some components and found that batch A consistently produced around 60 RA and batch B produced in the low 50's RA. One of the components from batch B produced harnesses of 57 RA and 51 RA when tested at different surfaces. Is this normal to see that great of a variation from the same piece of metal.

Also is 55 RA compared to 60 RA a significant decrease in hardness or something that I should be concerned about?

Any insight would be appreciated.

 

[dgallup]

If there is only a max value in the spec then anything below that is permissible. Of course there will be some intrinsic lower limit due to the nature of the material. You are not going to get stainless steel as soft as butter no matter what you do to it.

Depending on what operations are done to a piece of austenitic SS there can be a wide range in hardness throughout the part. Cold work will substantially increase the hardness.

We know nothing about the function of your part, no idea if you should be concerned about 5 hardness points.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[EdStainless]

Normally we work in RB for annealed SS.
Most alloys have a 90 max, and we sometimes see values as low as 65.
Yes this is a big difference.
If it matters to the application then you need to find a way to control it.
The problem is that the min hardness on annealed SS is set by the min mechanical properties in the spec.
Let's hope that those properties were used in you design.
You cannot have an annealed SS part with higher properties without introducing a lot of other problems.

If you need more strength move to a lean duplex alloy (2101, 2202) they have higher min strengths (and therefore higher min hardness) and they machine very well for SS even though they are not free machining.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[TVP]

morkman,

You need to use either Brinell hardness (HB) or Rockwell B (HRB). Rockwell A (HRA) is not good for testing annealed SS. It is a compressed scale, meaning that small changes in HRA are indicative of large changes in absolute hardness. HRA is best used for testing hardened steels with shallow case depths or through hardened parts that have thin sections.