I am working with load cells made from S7 Tool Steel (T41907) that
have already been machined and are heat treated in the following
1) individual 1"x1"x3" are placed in a steel foil bag, and evacuated.
2) the pieces are placed in an oven that has been sitting at
1200-1300F and soaked for 1/2 hr
3) the pieces are transferred to a 1750F oven and held at 1hr.
4) the pieces are removed from the oven and are allowed to sit in an
ambient air (typically opened garage door) for 2-3min and then cooled
by forced air via fans to about 100F and the rockwell hardness is
5) the parts are then placed into an oven that is at 1060F and held
there for 2 hrs. Again the pieces are cooled as in step 4.
6) the parts are again subjected to step #5 - 2 more times (except at
1000F) for a final desired rockwell hardness of 50-51.
I am under the impression that ramp rates (hot to cold, cold to hot)
if done at a controlled rate will help to eliminate stresses. Seeing
that these parts are being used in a wheatstone bridge application I
would believe that you would want to keep any residual stresses to a
minimum. Could creep at full scale range / non linearity /
non-repeatability be attributed to internal stresses caused by
inconsistencies in heat-treat?
Thanks for your time
- posted 18 years ago