Room Temp and Subzero Charpy Values 1

[Burrito5000]

Hello all, this is my first post in these forums. I'm a product engineering manager at an oil & gas manufacturing plant. We make some parts using 17-4 H1150D and have an internal spec that gets its values from ASTM A 564. Lately our incoming material certs have had charpy tests which were taken at all sorts of sub zero temperatures instead of room temperature. Because of this, I'm trying to make a chart or graph that shows the correlation between charpy at various temperatures. This is intended to make it easier on our clerks who review the incoming material certs. There seems to be limited data available for 17-4 conditions in sub zero temps, but I have found a few references. One of which is an 'American Society for Metals' book (1982) we have here in the office. Some others were found on the web including a place called 'Web Interlloy'. These both seem to have the same data. I'm a bit confused with the data I have uncovered. In the ASM book there is a chart entitled 'Typical Mechanical Properties in the Longitudinal Direction' which shows charpy of most of the various 17-4 conditions. I assume this chart is at room temperature but I can't find anything that confirms this. The chart has H1150 typical charpy of 50 ft-lbs. Then directly below this chart is one entitled 'Impact Strength at Subzero Temperatures' showing charpy at 75, 10, -40, -110, and -320F. It states that the charpy at 75F (room temp) is 95 ft-lbs. So this is my question, why is there seemingly conflicting data on the room temp charpy? One chart says typical value is 50 the other says 95.
I can't use the data in my charpy vs temp chart if there are two very different starting points at 75 F.

Any ideas, or possible sources of 17-4 subzero charpy data?

Here is a picture of the page from the ASM book:

Thanks.

 

[EdStainless]

There is no correlation.
If your spec is 90ft-lb at RT (or whatever) then if someone chooses to test colder that is fine, but they still must meet your 90ft-lb.
Do not try to build a correlation, differences in chemistry and heat treat can change this dramatically.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[TVP]

I agree with Ed. Impact tests, whether using Charpy or a different type of test/specimen, are extremely dependent upon the microstructure and nominal mechanical properties, and therefore the test data will have considerable scatter based on chemical composition, segregation, amount of hot working, amount of cold deformation (if any), heat treating times and temperatures, etc.