Work Hardening 304 SS above 50 HRC?
Work Hardening 304 SS above 50 HRC?
(OP)
Hi all,
I recently came across a sharp point self tapping fastener that claims to be 304 stainless steel, and can achieve a tip/thread surface hardness between 52-58 HRC solely from cold working. I know it's not uncommon to get core hardness values in the mid 30's to low 40's when wire drawing and thread rolling 304, but I'm having a hard time figuring out how they can get the surface hardness this high just from cold working. Any thoughts as to how this might be possible? The fastener in the picture (link below) likely has a core hardness of 32-50HRC, a surface hardness of 52-58HRC, and a case hardness of 50HRC minimum up to 0.010". Any ideas on how this might be possible?
http://www.sealtite.com/wb-sshss-group.htm
I recently came across a sharp point self tapping fastener that claims to be 304 stainless steel, and can achieve a tip/thread surface hardness between 52-58 HRC solely from cold working. I know it's not uncommon to get core hardness values in the mid 30's to low 40's when wire drawing and thread rolling 304, but I'm having a hard time figuring out how they can get the surface hardness this high just from cold working. Any thoughts as to how this might be possible? The fastener in the picture (link below) likely has a core hardness of 32-50HRC, a surface hardness of 52-58HRC, and a case hardness of 50HRC minimum up to 0.010". Any ideas on how this might be possible?
http://www.sealtite.com/wb-sshss-group.htm





RE: Work Hardening 304 SS above 50 HRC?
RE: Work Hardening 304 SS above 50 HRC?
Also, does all this strain hardening have a drastic decrease in the corrosion resistance of the material?
Thanks,
M
RE: Work Hardening 304 SS above 50 HRC?
I think that what they are advertising is that when they roll out the gimlet point on those parts they are getting a small area at the point that is work hardened up to a pretty high amount, but once you approach the full body diameter it will drop off. Looking at that site, most all those parts are made in China, so I would take the performance claims with a grain of salt.
RE: Work Hardening 304 SS above 50 HRC?
It sort of begs the question of why to use 304 in the first place.
You have formed so much martensite to reach this hardness that you have no toughness left.
It had might as well been an 18% Cr martensitic to start with.
We used to draw fine wire (0.004") and easily reach 240ksi UTS.
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Plymouth Tube
RE: Work Hardening 304 SS above 50 HRC?
In the construction industry there seems to be a hunt for a magic material for fastening wall sheets on metal buildings that has high hardness (Rc 50 or more), extreme corrosion resistance (similar to 302 SS), and low cost (similar to 18-8) and a resistance to SCC. You can get 3 out of 4, but trying to get all of them is pretty difficult.
RE: Work Hardening 304 SS above 50 HRC?
do u form martensite in 304 ss?? i mean if its an austenitic SS then?
so much hardness comes from strain hardening if i am not wrong..
RE: Work Hardening 304 SS above 50 HRC?
For high strength fasteners the trick is to cold draw the rod as high as you can while still being able to form the heads. And then rely on the thread rolling to drive the point hardness higher.
They should try some lean duplex SS grades (2101, 2003, 2201 and so on). They will heave better corrosion resistance than 304 (or any 16-18%Cr grade) and they have some SCC resistance. Not fantastic but at least some.
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Plymouth Tube