stampable materials to end up with Rc 58-64 after HT

[yshgao]

Hi there,

I have few questions waiting for your help:

1)For a device which works like a gear system, the parts work on very high contact stress, such as 1100 MPa. We probably want to use AISI 1035 or 1040. After heat treatment, such as carburizing or induction hardening, we can get 55-60 HRC. What Uni-directional compressive stress in MPa can this material undergo?

2) A part in this assembly should be cold stamped. Are there any stampable materials that we could heat treat to end up with HRc 58-64 after heat treatment? My selection is 4140. Can this be good for this requirement?

Thanks

 

[TVP]

1. Induction hardening of grades like 1040 or 1045 to 54 HRC minimum will allow a contact stress of ~ 1200 MPa for Grade 1 gears according to ANSI/AGMA 2001-C95 or ~ 1340 MPa for Grade 2. If the hardness range is 50-53 HRC, which is more typical with 1035, then the allowable contact stress is 1170 MPa for Grade 1 and 1310 MPa for Grade 2. Use the following link for some background information:

http://www.geartechnology.com/pa/members/marapr03/section6.pdf

2. 4140 is not the best grade to meet this requirement, since it has so much carbon, which reduces formability. I would suggest something more like 5120, 4118, or 8620, all of which would require case carburizing after forming to achieve a surface hardness of 58-62 HRC. The raw material would require spheroidize annealing in order to be cold formed into the gear shape. When you say cold stamped, do you mean formed out of sheet (stamping, fine blanking) or do you mean formed out of bar/wire (extrusion, forging, etc.)? Either way the materials need annealing before forming, followed by case carburizing.

 

[yshgao]

Thanks, TVP,

In the 2nd question, the part likes a cup, rather than the gear. A small roller contacts it with the contact stress of 1300 MPa. The roller surface will be very hard. Due to its life-time running in the vehicles, I think 4140 or 4340 may have better performance due to their alloy contents for high core strength and impact property. In production, we need to cold stamp this part. Its thickness is 7.0 mm. The raw material is the pre-punched round plate. I need to find a good candidate from 1045, 5120, 8620, 4140 or 4340. Please help.

secondly, if we design the motion device no matter gear to gear, or ball to plate, one part should be harder than another one. Please tell why?