Watch the decalescence front. The black line as it cools. the blade is pretty thin so getting it to decalesce recalesce on the short axis of the blade is what I am doing. It takes some time, but I want the center of the thin blade to be a different hardness than both the top and the bottom edges. It stabilizes the blade and pre-stresses it.
The blade pictured is 2.4 mm (.095) at the tip and 3.5mm (.138) at the choil. Reality is the hardening is 1.65 mm (.065) deep on both sides so the blade is basically through hardened. I try to make it into an internal pre-stressed I-beam.
I am purifying the forge by tossing in Live Oak Canyon Oak bark from the downed trees in the stream bed. “Kami Karma”
–G
Meyer Gage
Hardened steel does have the propensity to grow in dimension.
The growth is usually noticed in larger sizes because it is an inch per inch type growth. What happens is when the steel is hardened the molecules are trapped in stasis. Slowly the molecules relax and retained austenite is changed to martensite, as they relax they cause an expansion of the material. The gradual relaxation process takes about a year. The larger the size the more the change is noticed. The tighter the tolerance the more the movement is noticed.
To combat this phenomenon gage makers require that their hardened steel be triple cold stabilized. The process requires the gage to be cycled three times through a freeze/thaw process. This procedure will reduce the probability of gage growth. Note the use of the word ‘reduce’ instead of ‘eliminate’. This a major reason to have gages calibrated on an annual basis even if they have been subjected to little or no use.
The growth is usually noticed in larger sizes because it is an inch per inch type growth. What happens is when the steel is hardened the molecules are trapped in stasis. Slowly the molecules relax and retained austenite is changed to martensite, as they relax they cause an expansion of the material. The gradual relaxation process takes about a year. The larger the size the more the change is noticed. The tighter the tolerance the more the movement is noticed.
To combat this phenomenon gage makers require that their hardened steel be triple cold stabilized. The process requires the gage to be cycled three times through a freeze/thaw process. This procedure will reduce the probability of gage growth. Note the use of the word ‘reduce’ instead of ‘eliminate’. This a major reason to have gages calibrated on an annual basis even if they have been subjected to little or no use.
www.meyergage.com
–G
