High hardness result after heat treat SS465, H950

[BiPolarMoment]

Hi guys,

I'm not in the business of metallurgy so I wanted to get some info about something that has come up.

A vendor (manufacturer) of ours has made some parts for us out of Carpenter SS465 and after heat treat (H950) it's coming out at 52 Rockwell. From what I've found on the internet it looks like ~50 Rockwell is about the max unless it's cold worked or thin sections (our part is neither--about 0.5" round). The question is should we expect a compromise on material properties from this result (assuming material cert and heat treat cert are in order)?

Last option is that 52 is within the normal response for H950, but I can't find anything to assure me of that.

Any suggestions?

Thanks

 

[BiPolarMoment]

I'm going to reply to my own message. I found ASTM A564 and it specifies 47 HRC as a minimum for S46500, H900. In my case it's not the hardness I'm concerned with so I'm guess I don't have a problem.

 

[israelkk]

Don't be surprise even if the hardness will be even higher. for all PH stainless steel the hardness can vary a lot for the same tensile strength. For example: for PH 15-5 it can vary up to 10RC for the same heat treatment. This is why you will never find in MIL-HDGK-5 a requirement for hardness. but, only for tensile strength. We had cases where for Custom 455 H950 we receives over 55RC and for other batches it was less than 50RC.

 

[DABwilldo]

Couple thoughts,

I agree with israelkk in that the hardness for these precipitation hardened stainless steels can vary widely. Having worked with 17-4PH in the past, my experience has been that the final properties can vary greatly, depending on the processing methods.

For example, if you're heat treating in a large batch, with the material stacked together in the furnace, the parts at the center of the mass will have different properties than those at the surface. The quench rate for the parts in the center is effectively slower than those at the surface. It takes careful planning of how the furnace is loaded to minimize these differences. A lot depends on the experience of the heat treatment shop.

You're dealing with 0.5" dia round stock. This is pretty small diameter, and you could be seeing some measurement error with the hardness tester as well. Unless the operators have good procedures, appropriate correction tables, and consistent measuring technique, you'll see several points of scatter in the hardness measurements.

 

[EdStainless]

If you are concerned then measure the tensile properties. If you can't, well then it must not matter to you.

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

 

[israelkk]

EdStainless

This may matter if you use the part for metal to metal pneumatic or hydraulic seal. You want one part to be less hard than the other, therefore, if for example, a 440C 58RC precision hard ball in a check valve is pressing against the 465 with cylindrical orifice having 55 RC hardness instead of the desired 45 RC then the seal will not hold for long because, the too hard 465 will injure the 440 ball.

What I wanted to emphasis is that PH stainless steels can not be trusted for exact hardness values.

 

[EdStainless]

Let me word it this way. I don't believe a Rockwell hardness on a PH stainless. Knoop or DPH maybe.
If you are worried about your check valve mismatch then you should measure the compressive yield since that is really the failure mechanism.

I know hardness is fast and easy, and it is a near proxy for many other characteristics. But it isn't a measure of any of them. I have never seen an application where Rockwell hardness was the critical property.

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