Hot water dulls my knife??

I

ichor

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Aug 27, 2002
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Years ago my father-in-law claimed that really hot tap water or a dishwasher (heaven forbid) would dull the edge of a sharp knife. I always thought it was hokum.......old wives tale. However, this guy was for quite a few years, after he retired, one of about five people in the country who would be sent to various parts of the world to act as a consultant on certain aspects of maintaining/building nuclear submarines, so he was obviously no dummy.

Now, years later, I still wonder, so thought I would put the question to the forum. Comments?
 
Very hot water could take the temper out of the very edge, causing the metal to go soft, and making the knife dull very quickly under use.
 
Hot water may accelerate rust/corrosion, of course. Putting a knife in a dishwasher introduces other conditions as well that can be damaging to a fine edge.

Though if you have *really* hard water ... :eek:
 
sounds like a farse to me....but what do I know?

:p
 
Steven Roos said:
Very hot water could take the temper out of the very edge, causing the metal to go soft, and making the knife dull very quickly under use.
Click to expand...

Water doesn't get that hot under normal circumstances (that includes dishwashers).
 
It's half truth.
Heat makes metal expand so when you heat up a blade either with dry heat or wet heat, your keen edge gets thicker and thus becomes temporarily duller. The edge returns to its original thickness when the blade cools down.

Most blades are tempered at over 500 degrees so boiling water at just over 200 degrees isn't going to do anything to the temper so don't worry.

Alternatively, you think sharpening a hot blade will make for a keener edge when it cools down?
 
I have noticed that some of my knives are duller after having washed them in hot water. However i don't think that water temp has anything to do with it. I DO think that rattling around in a stainless steel or porcalin(sp?) sink with other dishes, and being scrubbed with abrasive dish cleaning pads DOES have something to do with the knife being duller.
 
I never noticed any dulling from hot water per se if you're hand washing in a pan. The dishwasher will definitely dull a good edge though. As was mentioned by Colorado Dave, it's a different environment. I wouldn't be surprised if you get both chemical (solvents) and mechanical (small particle abrasion) attack on a blade in a dishwasher.
 
Takes more physics than I got, but recalling your father in law's work, even "small" reactors in submarines may cook up a super heated water environment that might (at least temporarily) affect the structure of metal (turbine blades?) and in the long term, after repeated exposure to a super heated environment, perhaps more so. Some great junk science, A?
 
UnknownVT said:
Can a knife blade be de-tempered by 100degC (212degF)?
Click to expand...

No, under normal circumstances water cannot get hot enough to de-temper steel (that's what I wanted to say).
 
More myths!! Hot water will not dull the knife unless you put it into the superheated steam ( ~1000 F) .You have to be very dull if you put a fine knife into a washing machine .A knife such as a fine chefs knife should be washed by hand ,without abrasives,immediately after use,dried and put away.
 
The heat of a dishwasher is not going to detemper most blade steel. To affect the temper, you have to heat the blade above the final heat treatment temperature. Even the lowest final temperature commonly used today is about 350F. Boiling water is nominally 212F. So, you've got about 150F margin there.

To superheat water, to get it above boiling temperature (nominally 212F) and yet remain liquid, requires rather careful conditions. It's not going to happen inside your dishwasher. It can happen, though, in a common household microwave oven when water is heated in a glass cup. Superheated water is explosive, so you need to be very careful about that.

The problem with knives in dishwashers is not the temperature nor the water. It's the detergent. Dishwasher detergents are very harsh and corrosive. Most contain a lot of chlorine.

You should not, for example, put china with gold or silver or platinum patterns on it (this is very often on the rim of the plates and cups on some china patterns), or glasses with gold plated rims or decorations in the dishwasher because the detergent will wash the metal off (often doing noticable damage in just one wash). The detergent is actually dissolving the metal and washing it off!

Don't wash leaded crystal in a dishwasher either. The detergent washes the lead out of the surface of the glass making it look cloudy and dull.

The very edge of a knife is very thin. Just as that harsh detergent can wash the lead out of glass and wash a thin layer of gold or silver off of a china plate or cup, it can actually wash away the very edge of a knife. It can actually dissolve the steel and wash it right down the drain. And it is washing away that very edge of the steel that dulls the knife.
 
The heat of a dishwasher is not going to detemper most blade steel. To affect the temper, you have to heat the blade above the final heat treatment temperature. Even the lowest final temperature commonly used today is about 350F. Boiling water is nominally 212F. So, you've got about 150F margin there.
Click to expand...

You might say, "Well that's the water, but what about the heated drying cycle?"

When a household dishwasher doesn't lock closed during operation (I've never seen one that does), UL limits the internal temperature to something like (and I'm recalling this off the top of my head) 250F. The limit is way below 350F, I'm sure. Manufacturers are going to stay way below the limit too so that they've got margin. I ran my dishwasher some time ago with a thermalcouple inside and it barely got to 200F peak.
 
If you had a pyramid on the sink, wouldn't that counterract the dulling from the water?















:p
 
mete said:
More myths!! Hot water will not dull the knife unless you put it into the superheated steam ( ~1000 F) .You have to be very dull if you put a fine knife into a washing machine .A knife such as a fine chefs knife should be washed by hand ,without abrasives,immediately after use,dried and put away.
Click to expand...

Whoa.....guys, guys, guys. I daresay that there are very few on this list that don't know how to treat a fine chef's knife. I guess I should have expressed myself more clearly. I have never put a quality knife in the dishwasher (don't even have a dishwasher now and didn't use it most of the time when I did. I mean, what's it take to wash a glass, a plate, a knife and fork...and maybe a pan?)I shouldn't have mentioned dishwasher at all). .

I don't use weird chemicals or abrasive cleansers or any of the vast array of things that have been mentioned. I never even considered the fact that this low temperature could affect the temper of the blade as it is clearly, and obviously, not hot enough.

I just thought that with all the sharpening talk and references to minuscule "aligning" of the edge, yada yada yada, that really hot tap water (mine will burn your hand in an instant), might, conceivably, have some effect on a very sharp knife edge. I have learned much about the characteristics of steel, on this forum, that I didn't know before. If the answer to my question was yes, it would not be as strange as some of the info/facts about steel that are supported here. Thanks tho', for all the info about "superheated" water, small nuclear reactors and such. :D
 
Just plunking a blade into boiling water won't hurt it. I've boiled folders before, especially after cooking with them. It never hurts.
 
Hey Guys..

I sharpen my knife under hot water..
No stones nothing fancy.. I just run the hot water, and rub the blade with my fingers until its sharp.

I had the blade on my LCC replaced with a candy cane,,sometimes I spin it in my mouth to get the tip really pointy....

ttyle

Eric....
 
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