Triple normalisation

[HJA]

Recently came across this interesting channel that just uploaded a video about normalisation of steel. The TL;DW is that carbon steel triple normalisation is a waste of time because if each cycle resets the grain size, only the final normalisation will matter. Perhaps if the previous normalisations were too hasty there could be irregular grain sizes left subsequent cycles would fix. But I thought it was an interesting topic and if the reality matches the theory, maybe Kailash can simplify their process by switching to one normalisation cycle only — but I suppose this also requires accurate temperature measurements. Maybe a magnetism check is enough.

Anyway, thought it was interesting and I'd post here to see what the more knowledgeable people here think about it.

 

[Kailash Blades]

Recently came across this interesting channel that just uploaded a video about normalisation of steel. The TL;DW is that carbon steel triple normalisation is a waste of time because if each cycle resets the grain size, only the final normalisation will matter. Perhaps if the previous normalisations were too hasty there could be irregular grain sizes left subsequent cycles would fix. But I thought it was an interesting topic and if the reality matches the theory, maybe Kailash can simplify their process by switching to one normalisation cycle only — but I suppose this also requires accurate temperature measurements. Maybe a magnetism check is enough.

Anyway, thought it was interesting and I'd post here to see what the more knowledgeable people here think about it.

Interesting! It does seem that doing multiples of these processes does cause a lot of debate. For triple quenching my understanding is that it can often allow those with forges with imperfect heat control to avoid a high temperature soak. With an accurate kiln you can evenly hold a blade at a certain heat to allow all of the carbon to go into solution and be converted into martensite from a single quench. If you're in a situation where your blade might be heated unevenly or may accidentally get overheated leading to grain growth, higher stress etc then triple quenching can allow a lower uneven temperature to safely render all carbon into martensite over multiple events.

Regarding triple normalisation, we do it for a few reasons. The first is stress relief- our blade steel is highly stressed and exhibits cold work hardening from their previous life underneath a truck. Secondly it's quite heavily forged, potentially with less than ideal heat control, which can lead to very large grain size and again new stresses inside the blade that need relieving. As a result of this, two of our normalisation cycles are performed after forging. The final cycle is performed after grinding, to help normalise any inconsistencies that have arrived through the harsh initial grinding process, like parts that have been heat affected and become soft or parts that are thin in section and became heated and then air hardened.

Finally For us, a blade that is finer grained, with higher strength and toughness is a fair tradeoff for lower hardness on a large chopping blade. Triple normalisation is something that's used pretty widely in the knifemaking world for this reason, with some lowering the temperatures each time and others repeating at the same temp. This guy is a metallurgist so I'm not remotely in a league to butt heads, but here's an often referenced thread showing grain refinement being achieved through repeated normalisation cycles.

PaleoPlanet-Normalization/Grain Size Control Experiment (or why you should normalize)

Eric has been wanting to post a thread, with photos, about the importance of proper HT, especially normalization. I agreed to help with the photos,

www.tapatalk.com

I'd love for what Graham is saying to be true and for us to be able to streamline our heat treat, but I also don't really see how that information can be compatible with the seemingly solid experimentation in the thread I linked, as well testing by other knifemakers. It seems like his views are mostly centered around normalisation in regards to hardening response and as a prep for repeatable quench. It might be that our situation is outside the scope of what he considers a usual knifemaking scenario? Would love to see some further discussion on the topic from those more knowledgeable than me (a lot of people).

Take care,
Andrew and the team at Kailash