D2 and water
D2 and water
(OP)
I work in an OSB mill where 44 D2 knifes approx. 1/4" x 4" x 21", treated to 58-60, are used to flake or strand logs. The knives are held in a knife pack that has an outer retaining bar made of mild steel. Occasionally these knife packs load and friction creates heat to I assume, 500 plus degrees F as the edge of the mild steel bars that retain the D2 knifes, turns blue. Then, as part of the process, the cutting ring returns to home where the knife packs are sprayed with water and the cutting process repeats. My question is, what effects if any, does the combination of heating to that temperature and spraying with water have on the knife edges. Occasionally when we change the knife packs the edges are damaged, some appear to be softened and peened over and others seem to be brittle and fractured. Could the heat and water be the culprit.
Thanks-
Thanks-





RE: D2 and water
Have you ever checked hardness on the failed blades?
My hunch is that the blades are getting a lot hotter than 500F.
If they are getting harder (and breaking) then must be reaching 1800F and then being quenched.
If they are soft you can look at a tempering curve to estimate the temp. For example to temper to 45 RC takes about 1100F.
Sound like you need to work on a system to minimize the packing of chips in the knife pack.
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Plymouth Tube
RE: D2 and water
RE: D2 and water
The cooling with water is likely to help the situation, not aggravate it, since the blade would have to get well above the softening temperature for the water cooling to result in cracking. As cracked or nicked knives are scrap, it is beneficial to replace/re-sharpen the blades before they get to this point. And, avoid logs that have imbedded nails, barbed wire, or other metallic “inclusions”.
rp
RE: D2 and water
They could break because of the increased force from being dull, or the dull knives could actually heat enough so that when they are water quenched they become brittle.
Actually changing and resharpening knives more frequently will lead to increased productivity and blades lasting longer.
Can you build spare knife pack and change them quickly? If so then you would be better off stopping before they overheat as much as they do now.
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Plymouth Tube
RE: D2 and water
D2 material is high carbon low alloy steel. High carbon gives high hardness and wear resistance when quenched from austunitie zone. When it get very high amount of stress from cooling & high martensite % then it will tend to break.
soft:
When insufficient amount of cooling done from the austunite zone then huge amount of retained austunie is possible which is soft and will make poor edges.
to fix the problem:
1. control the cooling time, amount and flow
2. time heated to austunite zone.
RE: D2 and water
Maui
www.EngineeringMetallurgy.com