less magnetic after hardening???

J

jlmetcalf

Joined
Jul 5, 2005
Messages
75
For you metalurgy types....

I've noticed that the magnetic chuck on my surface grinder does not hold pieces as securely after they have been hardened. It seems that this is more pronounced in stainless than carbon steel. It also seems that the pieces are the least magnetic in the as-quenched condition and gain a little magnetism back after tempering.

What's going here? Are all thermal hardening steels so effected?

Thanks,

Jim
 
Ferrite and martensite are magnetic , austenite is not .If you had significant retained austenite you would notice the blade was less magnetic . I don't know of any difference between ferrite and martensite as far as martensite being less magnetic.
 
I believe that grain size has some effect on magnetic response. I have noticed that after doing some thermal cycles that the magnetic response improves and in some cases dramatically. My experience is with normalized and not hardened steels. I can demonstrate this effect...Take Care...Ed
 
Mete,

I guess it could be RA but I see it with 416 and with D2 that I've drawn back for springs. I draw the D2 springs and rockers twice at 1175F. I would not think that they would have much RA after the high temp temper.

I did find this when I google'd "magnetic martensite ferrite":

"The 300 series of stainless steels is austenitic (non-magnetic) while the duplex stainless steels are mixed austenite and ferrite. In the field, the amount of ferrite is measured through its magnetic response. The portable meter is calibrated for % ferrite and it is called the "ferrite number". Martensite gives a magnetic response, but not as strongly as ferrite, so when it is present it contributes to the "ferrite number"."

I've also noticed that the hardened pieces are magnetized when they come off the chuck and the annealed pieces are not.

This might be one of those "who cares" issues but I was curious and thought I would throw it out.

Thanks:)
 
Except the ferrite in things like 416 is DELTA ferrite which forms at 2600 F in carbon steels .I don't know if delta ferrite has the same magnetic strength as alpha ferrite ..Confused are you ???
 
Except the ferrite in things like 416 is DELTA ferrite which forms at 2600 F in carbon steels .I don't know if delta ferrite has the same magnetic strength as alpha ferrite ..Confused are you ???

Yes, somewhat confused. I guess when you learn from trial and error you end up knowing a good bit; you just don't understand everything you "know"
:)

Jim
 
I've noticed this at times, as well...but nothing extreme....i try not to touch any post-ht knives with magnets because i can't stand the tiny metal hunks that stick to the blade afterwards and make final finishing tougher by sticking to the blade....maybe i should use cheaper magnets that can't magnetize a blade.
 
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