COF - Case Hardened Steel to Case Hardened Steel
COF - Case Hardened Steel to Case Hardened Steel
(OP)
I have a small mechanism to design with the sharp edge of one part rubbing on the flat surface of another. I am assuming a small break on the edge of the first part and this edge will rest on the second part over about 1/8' to 5/32". The distance the first part will rub over the second part is about .125" until it falls off edge of the second part (kind of a pawl-like mechanism).
Materials are identical case hardened steel, 8620 or 1018 or similar steel hardened to .010" deep at 60 Rc (~90 R15-N). Finish on the second part is about a 32 ground finish.
I am trying to minimize the effort to operate the mechanism and have the parts return to rest under a light spring pressure (~12 lb normal through the edge of the first part).
Coatings or surface treatments are out of the question, different materials (brass, bronze) are not an option and operational conditions preclude the assumption of consistent good lubrication (a moly grease).
How can I modify or change the composition of the base steel to get a smooth, low COF rubbing action? I notice that different steel parts in this application have very different friction properties in relation to their composition.
Some steels exhibit a stick-slip action, others are glassy smooth and others just seem to drag and scrape their way across each other. Can alloy content affect this behavior? From my limited work I am finding that the 1018 steel will have a lower COF than the steels with low amounts of nickle and chromium.
Any assistance is most welcome
Bill
Materials are identical case hardened steel, 8620 or 1018 or similar steel hardened to .010" deep at 60 Rc (~90 R15-N). Finish on the second part is about a 32 ground finish.
I am trying to minimize the effort to operate the mechanism and have the parts return to rest under a light spring pressure (~12 lb normal through the edge of the first part).
Coatings or surface treatments are out of the question, different materials (brass, bronze) are not an option and operational conditions preclude the assumption of consistent good lubrication (a moly grease).
How can I modify or change the composition of the base steel to get a smooth, low COF rubbing action? I notice that different steel parts in this application have very different friction properties in relation to their composition.
Some steels exhibit a stick-slip action, others are glassy smooth and others just seem to drag and scrape their way across each other. Can alloy content affect this behavior? From my limited work I am finding that the 1018 steel will have a lower COF than the steels with low amounts of nickle and chromium.
Any assistance is most welcome
Bill





RE: COF - Case Hardened Steel to Case Hardened Steel
RE: COF - Case Hardened Steel to Case Hardened Steel
Jim Treglio
Molecular Metallurgy, Inc.
RE: COF - Case Hardened Steel to Case Hardened Steel
Plaiting one part with electroless NiP would also help. the NiP plating will age harden and it is very smooth and slick.
= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm
RE: COF - Case Hardened Steel to Case Hardened Steel
I would be comfortable trying a coating if it could be applied over the case hardened skin, would not flake and would keep the sharp edge.
thanks
Bill
RE: COF - Case Hardened Steel to Case Hardened Steel
There are several others that will not hurt the edge.
Any coating that is used by the razor blade people would be a candidate, even the old Pt coating.
RE: COF - Case Hardened Steel to Case Hardened Steel
What is the old Pt coating??????
RE: COF - Case Hardened Steel to Case Hardened Steel
I don’t know if I still have any information but will look around.
I think the TiN with all it’s variations is probably the way to go.
RE: COF - Case Hardened Steel to Case Hardened Steel
One thing to be careful of is that TiN is not TiN is not TiN. By that I mean TiN is the composition of the coating, but the composition is just one factor, and a minor one at that, in determining the suitability of the coating. Other factors include adhesion to the substrate -- the coating isn't worth much if it doesn't stick to the part -- stress in the coating, coating structure, et al. The amazing thing is that engineers familiar with all of the variations of chrome plating -- and all of the things that can go wrong -- assume that all TiN coatings are the same. It just ain't so.
Jim Treglio
Molecular Metallurgy, Inc.
RE: COF - Case Hardened Steel to Case Hardened Steel
I think heating the parts to 450 for another hour would lower the hardness of the case to a point below 90 R15N. I might be able to get away with that temp for 15 min or so...... How long is the heating time for CrN and could you suggest a supplier?
many thanks
Bill
RE: COF - Case Hardened Steel to Case Hardened Steel
RE: COF - Case Hardened Steel to Case Hardened Steel
Is the NiHard you are referring to a cast alloy (from what I gather on an Internet search)? If so I don't think it would be a substitute for the low alloy steel I am using.