I am working with load cells made from S7 Tool Steel (T41907) that have already been machined and are heat treated in the following manner: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 checked (59-61) 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 Qu1nn