Help please, I am looking for a Stainless to replace EN32b

[martone380]

Hi,

Firstly appologies if this is in the wrong area.... :-(

Ok now my questions, I have been making steel suspension parts for racing for some years, however I have just been asked to make a set out of stainless steel for a road car ? I have always "shied" away from STST because of stress, fracture, fatigue etc.... are there improved STST that can be used ? The part is under compressive, tensile and bending stresses, it sits under a car so water, salt etc get to give it a good going over. One end is threaded and the threaded section has been known to fail (not on any of mine I hasten to add) I use a 7/16unJf thread form and bead blast then ZINC PASSIVATE. Ok so the STST won't be bead blast or should it ??? IWe can't afford to lose business, however better that than lives... Many thanks for any advice. Martin

 

[EdStainless]

What strength level do you need? That will be a place to start. I presume that this part is machined from bar or plate, right?

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Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[martone380]

Hi,
Thanks for the reply, it is machined from 5/8"bar, with a 1/2" dia stepdown, then stepping down to 7/16unJf using EN32B (approx 460N/mm^2) steel I calculate that the core is 0.3762" 9.556mm

:- CSA = (pi*D^2)/4 = 71.71mm^2 :- culminating in about 3360Kg Of tensile load... I understand that there is STST's with high tensile properties, however I am more worried about the fracture, fatigue issues that I have heard about STST, i.e. origination from high localised areas of Chromium etc...

 

[EdStainless]

is that about 66ksi? Ultimate tensile strength? If so you might want to look at duplex stainless grades.

= = = = = = = = = = = = = = = = = = = =
Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[martone380]

What's KSI ? I am unfamilier with this term.

Also I have looked at Duplex and super duplex, they appear to have excellent qualities, however, what are the fracture and fatigue qualities, I couldn't find any results for the duplex range of STST's.....

 

[kenvlach]

ksi = old-fashioned American units, sometimes called kips (by structural engineers)

1 ksi = 1000 pounds_f/inch² = 6.89475 MPa

Zinc passsivated SS? Zinc is undesirable on SS; it de-passivates a normally passive SS surface. Zinc can also embrittle SS at high temperatures. The typical nitric acid passivations for SS remove zinc contamination along with free iron.

 

[martone380]

No I wouldn't be Zinc Passivating the STST, I currently use EN32B which we do Zinc Pass in Gold........ But it's interesting to hear about the nitric acid passivations etc.. Always willing to learn more.

 

[EdStainless]

Sorry, I should have spelled it out.
I would stay away from the super duplex because of limited availability.
You do roll the threads right? Trust me, you will want to.
Look into 2205. I am sure that there is fatigue data available. It is a very common grade.

= = = = = = = = = = = = = = = = = = = =
Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[martone380]

I am not currently rolling the threads, why would I need to roll the threads when using STST, is this normally the case ??

However I do bead blast to help with fatigue etc... I have seen similar products to mine that are not bead blast and the threads have been undercut normal UNF form

I use a capstan for manufacturing these could I use a thread rolling machine on this machine... haven't rollers got to worked at a higher speed... than normal thread cutting ?

 

[EdStainless]

Thread rolling isn't at very high speeds, I have seen it done on lathes. The rolled threads will be stronger and smoother. Most stainless grades do not machine cleanly, they tend to tear and smear. The rolling will save you tooling headaches also.
Where are you located? I know someone here that would be willing to look at it for you.

= = = = = = = = = = = = = = = = = = = =
Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[martone380]

East Midlands area...... Kettering.

 

[unclesyd]

Might be a little expensive but is a very good material. I have never used S53 but have used another alloy from Questek. This material has a low temperature heat treatment. It was good enough to have Carpenter pick up on it.

http://www.questek.com/PDF/ferriums53.pdf

http://ir.cartech.com/phoenix.zhtml?c=64522&p=irol-newsArticle_print&ID=960171&highlight=