Stainless alternatives to 42CrMo4

[ErikDi]

Hi all,

A certain part is currently made from 42CrMo4 low-alloy steel. It performs well in terms of mechanical strength, wear, impact resistance etc. However, I've been asked to find a stainless alternative to 42CrMo4.
What would be a good alternative?

17-4PH with a H1050 HT, or 420 or 431 stainless steels are options I found so far. Are there any major differences between 42CrMo4 and any of these steels that might cause the part to fail? For example resistance to fatigue?

Cost of the material or machinability are of secondary importance as the part is only made in low quantities.

Thanks,

EDi

 

[MJCronin]

You have to decide what property of the material is most important to you, based on the ultimate usage of your part.

42CRMo4 was developed for parts such as axles, crankshafts, gears, and induction hardened pins. To me, there is no good stainless substitute.

Why must you have a stainless steel substitute ?.. Is this for appearance purposes ?

https://www.hillfoot.com/download/f...h Hardening Steel - Hillfoot Multi Metals.pdf

MJCronin
Sr. Process Engineer

 

[ErikDi]

Hi MJCronin,

Thanks for your quick reply.
The part concerned can be described best as a sort of latch. Part of the latch is operated by hand and the contact surface develops some superficial rust. Also, the part is rather exposed in the application and we want to be able to extend its use to outdoor applications. This is why a stainless alternative is prefered.

The main required properties are tensile strength and toughness, as the latch is loaded with impact once it engages, and statically after engagement. These values match between 42CrMo4 and the proposed stainless steels. Also based on calculations, the tensile strengt of all proposed stainless steels is more than sufficient. Similar to 42CrMo4, 431 reportedly is often used for axles and valves, so I figured this to be a good replacement.

My main concern is that there is some other difference between 42CrMo4 and any of these stainless steels that I'm not aware of.

You write that to you there is no proper stainless replacement for 42CrMo4. Could you please explain this in some more detail? Is there a specific property that 42CrMo4 has that stainless steels don't have?

Thanks again,

EDi

 

[shu60]

EDi,
What size is the part? What is mating alloy? Any lube or surface coatings? How fabricated: casting, machined part? What YS needed? Is it for load carrying ability or wear resistance. 300 series Stainless can be "soft" but have better wear properties/life. Just substituting a similar SS with heat treat capabilities may not be the best option. 420 is barely a stainless and will probably show rusting in a relatively short time. 431 is better but still not as good as 17-4 PH. The tempered heat treatments of 420 and 431 will not yield maximum corrosion protection.
Shu60

shu60

 

[ErikDi]

Hi shu60,

Part size is around 50mm. It sits in a larger stainless steel 304 part, but has to engage with a non-stainless steel counterpart. Hardness of this counter part is around 30HRC. Some limited sliding between these parts can occur. No surface coatings, and practically no lubrication. Required yield strength is at max 700MPa.
Of all alternatives, you'd say 17-4 would be best? Any idea on the wear resistance?

Best regards,

EDi

 

[Martinos]

I recmmend you to focus to martensitic stainless steels group as X46Cr13, X30Cr13 or X17CrNi16-2.

 

[mcguire]

There is a wealth of candidates, 431 and 17-4Ph will certainly work. Cold drawn 304 0r 301 will do wonderfully if the shape permits.

Michael McGuire

 

[EdStainless]

50mm long or diameter?
There are other PH grades, 13-8 being one of my favorites, tougher and more corrosion resistant.
The idea of using cold worked 3xx is also a very good one. You can get cold rolled sheet and cold finished wire at various strengths.
Check out A666 and A313

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[shu60]

At the hardness level for a 700 MPa YS carbon steel, the metal-to-metal wear resistance (unlubed) is not good based on my tests on 4130 (not 4140). At this hardness level, carbon is not so important, so 4130 is an appropriate reference alloy. Direct comparison with 17-4PH in all heat treat conditions shows that 4130 has far inferior wear resistance even up to HRC 40 hardness levels.

I fully agree with Michael McGuire re 301 and 304 which my testing shows are even better than the PH alloys due to their high straining capacity. Cold worked strength levels are only necessary if the load-carrying ability is required. Cold working these austenitic alloys will NOT improve their wear life. Wear data supporting these comments may be found in the Product Data Bulletin for UNS 21800 (NITRONIC 60) which is even better than 301 and 304.

Shu60

shu60

 

[WKTaylor]

CAUTION: similar CRES-on-CRES... or any similar [high-nickel-alloy]-on-[high-nickel-alloy]... rubbing contact... is a possible galling problem.

Regards, Wil Taylor

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