Heat Treated Stainless 2

[Tuptus]

Hi.
Does anyone know what grade of martensitic stainless steel is most commonly used to tooling exposed to water. We are considering 17-4 PH(630) or 440C.
Does anybody have expierence with that - we are looking for grade with high corrosion resistance at room temperature for clean water and good magnetic properties (for easy of machining after heat treating - grinding on magnetic chuck)
Thanks
Tuptus

 

[Metalguy]

For starters, what hardness/strength do you think you'll need? 17-4PH will give you Rc44-5 max., while 440C will go up to Rc57 or so-a huge difference. Neither will corrode in clean water at reasonable temps., but hydrogen cracking could be a concern, depending on stresses, etc.

 

[Tuptus]

The higher the better, but what I was afraid of is that 440C will not be not magnetic enough to hold firmly to magnetic chuck during grinding - is it correct?
Thanks
Tuptus

 

[lgearhart]

We use a lot of both 17-4 and 440C in our valves and acutators. 440C is easily held on a magnetic chuck. Yet I feel it's corrosion resistance is minimal for a stainless steel, and would only recommend it's use in a water environment if flash rusting is not a concern of yours.

Lee

 

[Tuptus]

Well, we are going to use it as a tooling material for our submerged wire edm, so one of the major concerns is rust ressistance - it will see probably 6-8 hrs water exposure at a time and we can not use any rust inhibitor or protection. And becouse cost of tool making will be significant and it will have o maintain its accuracy rusting could be very expensive.
Tuptus

 

[HardMetal]

How about bubbling nitrogen gas through the water. This would remove oxygen and prevent corrosion.

Paul

 

[Metalguy]

Guess you can't EDM under oil as it's usually done, right?

440C may get flash rust, but that isn't going to affect it's dimensions, unless you're measuring at the micron level.

 

[Tuptus]

No we can't do any nitrogen bubling - we would heve basically rebuilt whole machine.
My concern about flush rusting is that it would become problem after sevetral months of tooling use and tooling will loose its accuracy - we have to maintain it in .0001" range.
Regards
Tuptus

 

[HardMetal]

What are your strength / hardness requirements for the tooling? That would be helpful before deciding what material to use.

Paul

 

[Tuptus]

The higher the better. It does not have to be to realy strong - it is a part of mounting-clamping system

 

[HardMetal]

Consider PH13-8Mo (

http://www.alleghenytechnologies.com/allvac/pages/Steel/UNSS13800.htm).

It can be heat treated to tensile strengths above 200 ksi. It has excellent corrosion resistance.

Also, AerMet-for-Tooling Alloy by Carpenter (

http://www.cartech.com/products/index.html).

Paul