Hi everyone, ann odd question for you about stainless steel knives

[utepoot]

We recently bought the Thomas Rosenthal Group knives that Tesco are selling (a lot of you may know the ones...via the collectable vouchers). They seem great so far, but my question is this: why is the blade magnetic but the handle is not? I have looked up the properties of stainless steel, and the answers seem to vary as to whether it is magnetic or not...which is all well and good, but how can the same knife completely made out of the same metal be magnetic on one half and not magnetic on the other half? The only thing I can think of is, the handle is hollow...does that somehow affect the magnetic property? I can't find anything online about hollowness affecting anything.

[gen2]

Please clarify the following:
By 'magnetic', do you mean that it can be picked up by a magnet?
OR
do you mean it is magnetised and acts as a magnet to pick up other iron objects?

If the latter, then the act of grinding and working on the blade during manufacture is what has magnetised that part.

[ChuckFickens]

Cold working of stainless steel will make it magnetic and on those knives the handles will have been hot worked whereas the blades would have been cold worked to put an edge on them.

(those knives aren't that good BTW, they don't hold an edge very well at all)

[ChuckFickens]

I should clarify...

When I say "will make it magnetic" I mean a magnet will stick to it.

[Old_Geezer]

Not so good ? Glad I didn't bother with the vouchers then. A cheeky chap behind me asked if he could have mine.

[jake-the-peg]

I think you'll find they're made in two parts from two different grades of steel.

[utepoot]

Hi that hot working and cold working makes sense. Thanks for all your answers. BTW, I didn't expect them to be "high quality" since they were so cheap! We have the sharpener too so keeping them sharp won't be a problem. Someday I plan to get Global knives. Can't afford them just yet though!!

[theprof]

I'm with jake on this one. To my mind, the handle must be made from an Austenitic stainless steel an the blade is probably made from a Martensitic stainless steel.

Austenitic stainless steels are nonmagnetic. Both Martensitic and Ferritic stainless steels types are magnetic but Ferritic types are cheap and not suitable for use as knife steels. Martensitic types are commonly used for tools, machine parts and cutting instruments and I'd take a guess that the blade is made from either Type 414 or Type 420.

There are many specific alloys of both the likely types I've mentioned. There's also the possibility that the blade is made from a Martensitic type and the handle from a Duplex stainless steel. Both of these types have very high weldability and modern technology would allow the join to be virtually invisible.

[utepoot]

Well, either way up they are cheap knives, but we can stick them up on the wall with a magnetic strip, and sharpen them when they go dull. And not worry too much when we need a new set!

[beso]

The knives are probably formed, welded and ground from the stainless steel stock by a machine with minimal human involvement. Materials are relatively cheap The main cost is the original tooling and the marginal cost of each knife made is very low.

The ultimate factor in the cost becomes how many knives the machine can make hence shifting them through Tesco. Double the time and the cost of manufacture appears to almost double. In fact it is far worse.

Machining time also governs how quickly the investment in the machine can be recovered and start turning. The interest cost up before the first knife is made is a substantial part of the total cost of the knife and recovering that is paramount.

Consequently ideal steel for the blade from a physical perspective can be very differnt from that from a financial point of view.

[beso]

... turning a profit.

[skep]

sTANLISS IS NOT MAGNETIC. The term is misunderstood regarding knives and probably many other items.

In a knife the term,,,"stainles" implies the instrument will ot stain as in tool steal ' What it jeans, re knives and other tools is the formula has about 55 nickle and this retards staining but does not override the magnetic attraction of regulat steal.

A knife board, avainable at any quality kitvched store is a good way to store knives making them readiy available.

Anyone familiar with kives wouldn't be caught dead reling on a knife actually made of stainless steal.

Tool steal is the best for kjives but folks don't like the appearance of tool steal after beinh handeled by human hands; thus, the nickle.

Hope this helps.

[skep]

I should have read my writing before posting. Nickle should be 5% not 55%.
I had some typos since I hunt n peck and don;t often check my posts. Sorry.

[gingejbee]

Well it might- were it in English.

[theprof]

Oh dear skep, seems you've been labouring under a misapprehension so let's begin with some facts.

"Stainless Steel" knives of anything other than those you can pick up for a silly amount of money at cheap stores, are indeed made from one of the many types and grades of "Stainless Steel". Now you may be aware of knives that imply that "stainless" means nothing other than metal that refuses to stain, but I was not referring to cheapo stuff in my discussion. Indeed, despite the fact that the knives the OP posted are not expensive, they do meet the criteria of "Stainless Steel" in that they are made of "Stainless Steel", one of a number of recognised alloys.

Stainless Steel does NOT mean it has "about 55% nickel" as you put it. Your phrase "does not override the magnetic attraction of regulat steal" (sic) apart from being bad grammar is incorrect. Bearing in mind that Nickel is magnetic as well as "steel", what are you saying? How could Nickel "overrride" steel? I hope you are not implying that Nickel somehow cancels out the magnetic properties of steel?

"Anyone familiar with kives wouldn't be caught dead reling (sic) on a knife actually made of stainless steal". Think on. Without elaborating too much, if they are good enough for surgeons, they are good enough for kitchen utensils and you.

I would recommend you research your metals a little further before you post again. Pay particular attention to the properties of stainless steels. You may also consider improving your grammar to aid us all in reading your posts.

My wife's dishwasher has a "Stainless Steel" liner and I would be the first to concur that despite being use for 5 years or so, it bears not a single stain. But wait - it also has zero signs of corrosion. Tonight's question skep : On what basis should it be termed "Stainless"? I'll await your reply with anticipation.

[HowardKennitby]

Hi Prof

Long time no hear.

I have neither desire nor intention to defend Skep.

But..
"if they are good enough for surgeons, they are good enough for kitchen utensils and you."
That is a significant and, in my view, a quite erroneous claim.

It is well known everywhere that 'stainless' steel knives are Sugar at obtaining and keeping a sharp edge.

If I was being cut open in a hospital I would be more concerned about the sharpness of the blade than it's ability not to rust in the few minutes it was in contact with my flesh.

[theprof]

Did you admit to a typo and claim knives etc should be 5% Nickel? Sorry, but no. As an example, try looking up the properties of JFE443CT, which contains absolutely zero Nickel. A typical use is indeed, kitchen knives and yes, it is magnetic.

In fact all the 400 series of Stainless Steels contain zero nickel.

[theprof]

You raise a good point HowardKennitby and forgive me for moving into the realms of recent developments in metallurgy in this respect. Yes indeed, there has historically been a problem in maintaining the sharpness of "stainless steels" for use in surgery, but recent developments in alloys have overcome many of the problems.

The problem is that hospitals nowadays continue to rely on disposable "one-time" instruments due to budgetary contraints, problems with sterilisation, tradition and many other issues, but from a metallurgical angle, the stuff is out there to do the job.

MrsProf is a professor of cardiology at a leading uk university and tells me that these new alloys are beginning to be introduced into operating theatres worldwide.