Is 17-4 PH, aged at H900 Suitable for a Wrench like Tool? Or is H1025 Better Suited 2

[PressEquip]

Hello,

I've been asked to help design a wrench like tool that will be used at ambient temperatures and exposed to grease, fastener lubricant, rain/snow and a petro-chemical plant environment.

A material that came up was 17-4, precipitation hardened to H900. The condition H900 has high strength and high hardness as shown in the typical data below.

Typical Mechanical Properties
Condition: H900, UTS=200 ksi, YS= 185 ksi, Elong%= 9, Hardness=45 HRC
Condition: H1025, UTS=170 ksi, YS= 165 ksi, Elong%= 10, Hardness=38 HRC

Should I be concern about using H900 due to potential brittleness of the material? Low impact resistance? The workings may be using it at temperature 0F on rare occasions but the tool is used for precise torquing so it shouldn't be smashed around like a mechanics wrench. I was considering that the condition H1025 may be a better choice since because of improved impact resistance but the hardness really drops and the wrench needs high bearing strength where it engages the fastener.

Is there a better suited commonly available (1" thick plate or flat bar), high strength and mildly corrosion resistant material that I should consider?

Thank you for taking the time to read this and many thanks to those who respond.

A Fan of EngTips, share the knowledge

 

[EdStainless]

I would go to the 1025/1050 condition just for toughness.
If the tolerances are not real tight you should be able to finish machine and then age harden.
It will shrink by 0.0008"/inch when you age it.
This would be easier to make than in an alloy that requires quench and temper (and then finishing hard).


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P.E. Metallurgy, Plymouth Tube

 

[metengr]

I would use a tool steel (oil hardening) versus 17-4PH. With tool steel you have strength and toughness following proper heat treatment.

 

[PressEquip]

Thank you for the responses!

"I would use a tool steel (oil hardening) versus 17-4PH. With tool steel you have strength and toughness following proper heat treatment."

I'm looking into the availability of 1" thick flat bar in O1 tool steel, it is looking hopeful a supplier in North America will have it.

To obtain ~60-62 HRC, Hardened at 1,475F, oil quenched and then Tempered at 375F

I found some data regarding hardness and compressive strength

Hardened to 60 HRC, Compressive Yield Strength = 312,000 psi

I found one reference(G.L. Huyett Handbook) to yield strength of 50-99 ksi but that may be in the soft annealed condition. I couldn't find any information I have confidence in regarding tensile yield strength of hardened O1.

If the part was made out of O1 it could be zinc/magnesium phosphate coated to improve the corrosion resistance.

Any further thoughts

? Is 60 HRC too hard/brittle for O1? What might be the tensile yield strength of the O1 in the hardened condition?

Thanks


A Fan of EngTips, share the knowledge

 

[metengr]

PressEquip;
I don;t want to misguide or provide a recommendation because I am not a tool expert. You need to determine two requirements - minimum yield strength needed and resistance to impact (notch toughness) loads based on severe service conditions. Once you have these two parameters selected, you can determine the heat treatment schedule for 01 tool steel.

 

[EdStainless]

Real hand tools (like a SnapOn wrench) are ductile enough that you can actually twist them or bend them without fracture.
Breaking is the last failure mode that you want.
When I have tested hand wrenches I have always found hardness that is roughly equivalent to 100-125ksi UTS.
Hand tools are not crazy strong, the strength is in the design and size.

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P.E. Metallurgy, Plymouth Tube

 

[PressEquip]

Thank you for the insightful replies!

A Fan of EngTips, share the knowledge

 

[ornerynorsk]

Wow this must be some kind of wrench. 200-300 ksi ??? 4140 has been my go-to for almost any kind of a special tool. If you need localized hardness to prevent wear/fretting, it can be further flame or induction hardened. It's "mildly" corrosion resistant, depending on what your notion of corrosion resistance is. It's cheap, available everywhere, all the heat treaters know how to work with it, easy to machine.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[Tmoose]

I apologize if the OP has done all their homework in regards to elastic deformation, but without drawings and pictures it is hard for me to have any opinion, other than to be wary because design, especially geometry, trumps material properties in MANY cases.

So I offer a most emphatic X 2 to EdStainless' "........ the strength is in the design and size."

 

[WKTaylor]

The obvious factors about tool design relate to attaining the proper proportions for the 'work' at hand.

Shallow/thin wall for a high torque application is a bad idea... wear/deformation are issues; whereas overly hard tools can be brittle and prone to fracture.

Also, 'Quality of fit for the expected' nut or bolt head [hex, 2x-hex, spline, etc] is vital for wear resistance of the tool and the Nut/Bolt-Heads. A poor quality match [misss-match] can completely bugger-up nuts/bolt-heads drives.

Also, in the petrochemical plant, is there any 'need' for the tool to be 'non-sparking'... especially if intended to be 'struck'?

You might be specifications useful (among many-others)...

ASME B107.100 FLAT WRENCHES

ASME B107.110 SOCKET WRENCHES, HANDLES AND ATTACHMENTS

ASME B107.300 TORQUE INSTRUMENTS

GGG-W-636 [CX] WRENCHES (BOX, OPEN END, AND COMBINATION)

GGG-W-641 [CX] WRENCH, SOCKET; (AND SOCKETS, HANDLES, AND ATTACHMENTS FOR SOCKET WRENCHES; HAND)


Regards, Wil Taylor

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