been putting my chef knife in the dishwasher for years... why bad?

[ripe_turnip]

I have a damascus Shun chef knife that I've been putting in the dishwasher for years. Sharp-side up. It doesn't seem to have done anything to it other than erase the writing on the blade.

Occasional spot of surface rust that rubs off with my finger.

I see several things online saying you'll ruin the knife and will go to hell for doing this. These articles don't say "why".

What bad things are happening to my knife in the dishwasher other than sitting in hot water for a while?

 

[SVTFreak]

I’ve read that the heat can mess with the temper. I don’t know how true that is though. I ran my old knives in it, still run the wife’s cheap rado’s. The only detrimental effects I see is the edge gets beat up unless it’s complete alone. And the aluminum handles look like hell.

 

[Danke42]

Dishwasher detergent is very abrasive. Plus the jostling and the banging around. And the heat vs. the handle material.

I bet if you take it out and get it sharpened you'll be surprised.

 

[jc57]

Unless you are looking at the edge with a loupe, you might not notice it, but you can get micro-pitting / edge-wear from those mildly abrasive dishwasher detergents. They are enzyme-based and dissolve food. While the overall effect on the blade itself may be minimal, the edge itself is (or should be) rather thin, and those little spots of surface rust you see on the decorative cladding can cause problems on the exposed cutting core.

Plus it is not really good for the handles, if you care about that.

I mean, every manufacturer (including Shun) says hand-wash only using mild detergents, and FULLY dry the edge before storing. But if you don't want to, and it is not affecting how you use your knife, then go for it.

 

[Bigfattyt]

I’ve read that the heat can mess with the temper. I don’t know how true that is though. I ran my old knives in it, still run the wife’s cheap rado’s. The only detrimental effects I see is the edge gets beat up unless it’s complete alone. And the aluminum handles look like hell.

No....the heat in a dishwasher is no where near hot enough.... tempering temps are 350-450...... even higher for many stainless steels.


Your knife is being abraided every single wash. That is why our etch on the blade is gone.

If you were to sharpen your edge and look at it under magnification, then look again after washing in the dishwasher, you would see the edge was slightly degraded after.

Slow, but steady...

If it does not bother you, don't worry about it.


You will have to sharpen a bit more frequently.

I don't wash my kitchen knives in the dishwasher, even my stainless Cutco... certainly not my carbon steel.

The fact that you are occasionally getting rust in your stainless damascus is another indicator it is doing them no good.


It is so easy and fast to just wash the knives by hand, why machine wash them.

 

[SVTFreak]

No....the heat in a dishwasher is no where near hot enough.... tempering temps are 350-450...... even higher for many stainless steels.

I’ve always found that hard to believe but I am no heat treater or metallurgist. I do believe the part about abrasion. Mine don’t go in. The wife’s do. It’s part of the reason we have our own lol. She rarely cooks though. I enjoy it.

 

[Bigfattyt]

You can look up tempering temperatures for your self.

I know I have....because I have heat treated and tempered my own knives.....

I've also spend time reading heat treat protocols for many steels.



If your dishwasher ever gets hot enough to ruin the temper on your kitchen knives...you have way more problems than the kitchen knives getting a point softer on the HRC scale.

Everything plastic, including some of the internals on your dishwasher will be melted at that point.

Your dishwasher gets to 150-160 F.

1095 with proper heat treat temps and quench speed should test at 66hrc untempered.

300°F will only drop that glass hard 66HRC down to 65HRC.

350°F 63-64 HRC

400°F will get you down to 62-63

450° down to 61-62 HRC.

You will find most production 1095 is run 58-60 HTC, which is in the 500°F range.


440C I've seen recommended temp for tempering at 400°

I've seen Ats-34 recommended at 800-900 temps.

Some steels have a secondary hardening at even higher temps.

 

[Pack Rat]

In 2005 My Mom picked up my Buck 192 Vanguard in S30V with a rubber handle, or what ever the handle is.
She loved it so I gave it to her. Neglected to tell her no dishwasher.
So that knife has been going into the dishwasher ever since with no ill effect other than from normal kitchen use. She would let me know when it got dull.

I frequently stick a Buck 110 in the dishwasher after working up a deer. Again, no ill effect.

 

[Spideyjg]

http://rbnainfo.com/smart-label.php?productLineId=2597

That is one detergent containing 3 different bleaching agents or activators. Lots of makers have a link to smart label lists and several I looked at have beaching stuff which will speed up oxidation.

Not to mention the blade bouncing around hitting and dinging the edge or it ends up in a bad place and someone reaching in gets cut or stabbed. No good reason to put them in a dishwasher.

 

[CAP55]

It takes a couple of minutes to hand wash a knife, why on earth would you want to put it a dishwasher and take any risk of damage to the blade or handle?