How hot to ruin a HT?

When it comes to kitchen knives in full metal, it's OK if you run the machine at low temps, but the detergent will mildly dull the edge and you'll get spots on the blade.

Listen, there are dishwashers which have specific trays for cutlery and eating utensils, so they won't bang against each other,
so that part isn't always an issue. You can always secure the knife so that it won't bang around.
I've got a bunch of Global knives which are full metal with a nice blade steel.
I've put them in the dishwasher a lot of times just because I was lazy after a dinner and a bit too drunk to start doing dishes.
I've since taken them to scary sharp several times and they seem to keep the edge quite well, despite having been put in the machine.
However, they have a LOT of ugly pitting and oxidations due the detergent used in the dishwasher, so I don't recommend it.

I only recommend putting knives in a dishwasher if:

*they are securely placed, so they do not bounce around and get dull and they are NOT placed so that you can cut yourself when grabbing stuff out of the dishwasher.
*the knives you put in there are users and you don't give a damn about the finish, because you'll get spots on them.
*they don't have wooden handles or glued on handle slabs, as these will dry out and crack, swell, the glue will dissolve and the handle will just become deformed and look plain ugly.
*the knives aren't expensive. Expensive knives deserve educated use and handling, so as to maintain their value. It's also about respect for your invested money and the maker's efforts (particularly customs).

Basically, molecular changes will probably occur in the steel due to washing knives in the dishwasher (heat treat), but the changes are so minute that if you've only done it a few times you'll probably not even notice them.
If you wash them habitually in the dishwasher though, that edge may start to perform differently after a year or two (just guessing).

Best bet is to just not do it in the first place and wash them by hand. After all, it's a very simple thing to do and you'll have more room in the dishwasher for other stuff.
 
Just thought I'd add this, if you are grinding an already heat treated blade (finishing, sharpening, anything) and you get it hot enough to leave a blue looking oxide layer, then you've effectively ruined the temper - at least in that spot.

This is a good point- while there isn't much risk of damaging the heat treat by cutting hot meat, you CAN damage the heat treat sharpening on a grinder or belt sander.

The heat treat issue does depend on the steel. For most of my life I had heard about "high speed" steel and I understood that it was a good tool steel for drill bits and such but I never knew why it was called "high speed". More recently I learned that it could be used to make tooling that operated at high speed so that the heat generated by high speed would not affect the heat treat of the steel. IOW this particular steel is heat treated at higher temps than other steels.
 
Just a comment on high speed steel. It's awesome for knives, if you can grind it or heat treat it. I haven't used anything I like better for my own knives. That is all.
 
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