17-4 cr es 1

[djoser]

Hi,

We've been asked to produce a gear blank in this materiel (17-4 CR ES) I understand it's american 416 range but can find no documentation on it. Is this material available and machinable ?

thanks for any info

 

[TVP]

The designation is meant to be 17-4 CRES where CRES means Corrosion REsistant Steel. 17-4 is a common designation for a precipitation hardening stainless steel with the UNS designation S17400, also called Type 630. Standards for bars & wire include SAE AMS5643 and ASTM A 564. Forgings are covered by ASTM A 705. Suppliers of bars and wire in the US include Allvac and Carpenter. You can obtain more information by using the following links:

http://www.alleghenytechnologies.com/allvac/pages/Steel/UNSS17400.htm

http://www.cartech.com

click on Technical Information then Alloy Category then Stainless Steel then Precipitation Hardenable Stainless Steels then Carpenter Stainless Custom 630 or Project 70+® Custom 630 Stainless (better machining version)

 

[djoser]

thanks for your rapid response, I now have to find out if the material could be gear cut as the hardnes appears to be 68 Rockwell C. Any ideas ?

 

[TVP]

I am not sure where you got 68 HRC, but that is not correct. 17-4 is a precipitation hardenable stainless steel, meaning that the material is first solution annealed, and subsequently artificially aged to increase the strength/hardness. In the annealed condition, the hardness will be ~ 36 HRC. In the peak aged conditio (H900) the hardness will be ~ 44 HRC.

A typical fabrication route would be to obtain bar/wire in the solution annealed condition. Forming or machining would take place, and then the precipitation hardening treatment. This allows for easy forming and machining, and since the aging treatment takes place at a relatively low temperature, this is little distortion. Since you are making a gear, you will likely perform a final grinding operation after aging, but the hardness will be much lower than a hardenend or carburized alloy steel gear would be. If the gear is to be completely machined, then I highly recommend you investigate the Project 70+® Custom 630 Stainless with Carpenter, as this will be a big improvement in machinability.

 

[jagad5]

17-4PH can also be nitrided to harden the surface. We have done that in the past to make some rack and pinion style gears. However, the nitride can have a detrimental effect on the fatigue strength of the material (and it can also have a positive effect on the fatigue strength.)

Doug

 

[djoser]

sorry 68 was a mistype... d'oh!

Thanks for the info, really helpfull.


Kind regards

 

[Carburize]

Slight thread drift - but can anybody enlighten me on the type of service conditions that would make 17-4 PH an attractive gear material over more conventional gear alloys?

 

[TVP]

Possibilities:

Subzero temps - better fracture toughness than alloy steels.

Elevated temps - above usual tempering temperature for alloy steels? 900 F aging temp is about 480 C, so maybe for temperatures in the range of 300-450 C?

Corrosion - environments that might contaminate oil and initiate corrosion in alloy steels might be ok for PH stainless.

 

[Carburize]

Disagree on the toughness issue -tests I have performed show that 9310 is as good as 17-4PH

Temperature possibly but there are carburizing grade materials such as CBS50N from Timken that have much better performance at elevated temperatures.

If the oil gets contaminated then it won't work very well as a lubricant for any material.

Not meaning to sound chicken***t - I am really interested in the decision process that arrived at this alloy for this application.

 

[mcguire]

No one would use 17-4 over alloy steel for any other reason than corrosion resistance in my experience. It costs too much to be correctly chosen for any other reason, unless you need a non-magnetic gear.

 

[unclesyd]

17/4 is usually chosen for it's ease of heat treatment to achieve good physical properties. If you are going to Nitride this material,I would recommend a Kolene type liquid nitrding process to eliminate any possibility of a brittle case. There best is QPQ which is done after heat treating. Liquided Nitrided 17/4 is one of the best wear and galling resistant materials known. The use of 17/4 for gears is dependent on the class of the gear your making. Size change can be significant for gears. Most machinist prefer to machine it in the heat treated state, which will eliminate this problem.
There are some very good booklets on 17/4 that were published by ARMCO Steel. If you could find one of these it could be a great help.

 

[TVP]

Carburize,

I was thinking more along the lines of 4118, 8620, 8822H, etc. I agree with you that 9310 should have equivalent fracture toughness down to ~ 120 K (- 150 C).

What do you think about a relatively light load application at very low temperature where conventional "oils" are no longer suitable. MoS[sub]2[/sub] may be the lubricant, and carburized 9310 doesn't have sufficient corrosion resistance. That's about the best that I can come up with.

 

[Metalguy]

Mcguire,

17-4 PH non-magnetic? Probably just a broken keyboard. <g>

 

[gstark]

Also be aware that 17-4PH shrinks during heat treat operations. Values range from 0.0004 to 0.001 in/in for the H900 and H1150 conditions. Refer to Mil-HDBK-5 or Aerospace Structural Metals Handbook for further info.

 

[mcguire]

Metalguy
Red face here. 17-4, not 17-7.

 

[RPstress]

Nitriding may reduce corrosion resistance. We had some malcomized 15-5 bushes which started to rust in (probably moist) air.