Heat Treat for 4140 to Increase Wear Resistance?

[farmer2]

4140 as cast pin in sliding contact with 8620 flat surface experiencing considerable wear when flat surface is a little rough (150-250 microinch). Light load on pin, moly grease used between the two surfaces. Wear considerably less when 8620 is 60-100 microinch, but difficult to consistently machine to this finish.

4140 is Rb 85-100, as cast, 8620 is heat treated to Rc 30-35.

If 4140 is heat treated, how hard can it be to increase wear resistance and not cause galling or wear of 8620 surface? What should detailed heat treatment be?

Thanks,

 

[arunmrao]

You can flame or induction harden the 4140 casting. Else you may hard face the alloy suitably.

Perhaps a change to 4340 will result to better response to heat treatment and also improve hardenability.

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[farmer2]

arunmrao, thanks for your reply.

Can either flame or induction hardening be done on a batch of small parts? Is there a procedure and hardeness target?

How about a through hardening heat treat process or would this likely result in warpage?

 

[Robertmet]

For your question we need more info on size, shape etc.You could expect HRc 40 with excellent toughness.Galling shouldn't be a problem at that hardness.

 

[farmer2]

Part is a U-shaped yoke with a cross-section of .25 inch x .62 inch and 2.0 x 3.5 inches overall.

Which process would give Rc 40 and should the pins be harder than the mating surface which is Rc 30-35?

 

[Robertmet]

Is it the pin that you're more concerned about wear or the 8620.Are you getting wear or just polishing [smoothing of the surface] ? 8620 is a carburizing grade ,would you want that harder ? What kind of application ?

 

[farmer2]

Pin wear is the concern. Wouldn't want the 8620 harder.

Since pin as cast is varying between Rb85 and Rb100, it seems it should be harder. What process would get it to Rc30-35? Is galling a problem if the two are near the same hardness or does this apply only to softer materials?

 

[redpicker]

4140 is generally considered an oil quenching grade. Austenitization should be done in a controlled atmosphere to prevent decarburization and scaling. If through hardened, a tempering temperature of around 1100 F should be give you around 35 HRC. I would not want to use 4140 casting much over 35 HRC as I would be afraid it would be too brittle.

Galling betweent two steel parts will if there is metal to metal contact under high enough load. The lower the hardness of either component will increase galling tendency. Good lubrication will reduce galling. Once both surfaces are work hardened, galling will not be much of an issue.

rp

 

[Robertmet]

Galling [cold welding] is worsened by low hardness ,similar hardness of the two metals ,lubrication. Getting the 4140 to HRc 35 [even though the same as the 8620] would help a lot.Give it a try.