Best Corrosion Protection For Custom Parts

[nullack]

When fitting custom parts to a 4wd whats the best way to protect steel alloys from corrosion? Something that will best endure being scraped on rocks, being caked in mud, having stones thrown at it at highway speeds on dirt roads etcetc

e.g.

Powercoating
Zinc plating
Etch primer and paint
Galvanising

etcetc

Thanks

[Wozza244]

Mate, galvanising will be the most hardy, but ulimately parts like radius arms and shackles will be prone to scrapes and no coating is going to prevent the rock taking it down to bare metal.

Powdercoating would be my next choice.
Some say 2pac is better, six to one half a dozen to the other i reckon.

[Guy]

When fitting custom parts to a 4wd whats the best way to protect steel alloys from corrosion? Something that will best endure being scraped on rocks, being caked in mud, having stones thrown at it at highway speeds on dirt roads etcetc

e.g.

Powercoating
Zinc plating
Etch primer and paint
Galvanising

etcetc

Thanks

Anything that is going to be scraped against rocks is going to end up rusty ... Zinc plating perhaps and then keep a coat of flat black on it, easy to touch up when it does get knocked off.

[droopypete]

A point to remember, if a part is going to be hot dip galvanised and it has any sealed voids, or dead ends where water can sit, they will not accept it. as it may create a massive explosion when it is immersed, the solution is to drill large holes which is probably very undesirable for structural parts.
While Gal is the best option for outright protection from the elements, it doesn't slide across rocks well and when you do scrape the zinc off it is hard to patch.
Peter.

[uninformed]

make them out of stainless steel....

any zinc gal etc is works better when left un covered...ie dont paint over it.

Serg

[nullack]

Thanks folks. Ill prolly go powdercoating.

Stainless steel alloys arent suitable for the tasks I have for a bunch of reasons.

[chimpboy]

Wet paint and thick steel, combined with checking and maintenance imho.

[KiwiBacon]

A point to remember, if a part is going to be hot dip galvanised and it has any sealed voids, or dead ends where water can sit, they will not accept it. as it may create a massive explosion when it is immersed, the solution is to drill large holes which is probably very undesirable for structural parts.
While Gal is the best option for outright protection from the elements, it doesn't slide across rocks well and when you do scrape the zinc off it is hard to patch.
Peter.

For such parts (containing sealed voids), spray galvanising is a great option.
It blows molten zinc spray onto the surface. Not quite as good as hot dip, but suitable for a lot more parts.

If galv gets scratched through, the rest of the zinc prevents the exposed steel from rusting. Provided you haven't painted over the sacrificial zinc of course.

[YN67highlux]

use zinc cote from molytec as your primer b4 powdercoating. Its zinc in a spraypack

[Breaker Brother]

Por15 is the go, if you want abrasion and scratch resistance it's a two pack paint, goes on really easy, and a little bit goes a long way, 1 litre will do a whole chassis.

I can't tell you how good this stuff is, much better than powder coat.
Nothing is going to survive sliding against rocks for to long though, even Gal



http://www.por15.com/

[nullack]

Mate how is por 15 specifically better than powdercoat? Thanks

[error]

Just use some hammertone paint comes in a range of colours, used on industral equipment takes some good hits..

[alien]

you could paint it nicely (2pac or powdercoat) and the areas you know will be scraping you could cable tie on some sheets of 5mm polyurethane so you have a replaceable slippery surface protecting the steel.

[ISUZUROVER]

Mate how is por 15 specifically better than powdercoat? Thanks

Several powdercoaters have told me that 2-pac paint is more durable.

[macca81]

Mate how is por 15 specifically better than powdercoat? Thanks

Several powdercoaters have told me that 2-pac paint is more durable.

have heard the same, from several sources

[chimpboy]

Mate how is por 15 specifically better than powdercoat? Thanks

Several powdercoaters have told me that 2-pac paint is more durable.

have heard the same, from several sources

Me too, and walking around a wrecker reinforces it. Look at an old powdercoated bullbar vs an old painted bullbar.

[uninformed]

have heard same re 2 pac v powdercoating,

and on my rims and tube bar, the powdercoat doesnt bond well to the welds and rust has started to come through pretty quick.....both were sandblasted and primed.

Serg

[nullack]

ok so two pack. Which two pack? por 15??

[uninformed]

Thanks folks. Ill prolly go powdercoating.

Stainless steel alloys arent suitable for the tasks I have for a bunch of reasons.

why not?

there is a guy on pirate that built his whole rig out of S/S....and its hydrostatic drive.....

Serg

[nullack]

Stainless steel do not have the strength (tensile, compression shear) and the toughness of other steel alloys. Yes you can make it out of stainless steel but it wont be an optimal design if the builder wants a tough and strong part. Theres other reasons but for the sake of not writing a book those are the two key ones.

Im looking at using 300M (4340 modified) DOM tubing and heat treating - local aircraft place is overstocked. Its an excellent ultra high strength and toughness steel alloy. This will enable me to use a thinner wall section than say 1026 DOM and still exceed the mechanical capacibilities of 1026. IMHO too many builders ignore the problem of added mass to their vehicles especially in wagons there aint much difference between tare and gross mass when you add up all the stuff they put onto the chassis.

[KiwiBacon]

Stainless steel do not have the strength (tensile, compression shear) and the toughness of other steel alloys. Yes you can make it out of stainless steel but it wont be an optimal design if the builder wants a tough and strong part. Theres other reasons but for the sake of not writing a book those are the two key ones.

Im looking at using 300M (4340 modified) DOM tubing and heat treating - local aircraft place is overstocked. Its an excellent ultra high strength and toughness steel alloy. This will enable me to use a thinner wall section than say 1026 DOM and still exceed the mechanical capacibilities of 1026. IMHO too many builders ignore the problem of added mass to their vehicles especially in wagons there aint much difference between tare and gross mass when you add up all the stuff they put onto the chassis.

I think you're barking up the wrong tree.
Speccing an expensive and extremely intensive material to weld will probably not give you the weight reductions you're expecting to find.

Better design will let you use mild or medium tensile steel for pretty much all of the fabricated parts.
4340 is suitable for gear axles and half-shafts. Not for fabrications.

Remember, to use the 2000 MPa strength of 4340, a part has to flex 10 times further than mild-steel. There aren't many parts where this offers an advantage which makes the extra strength and expense, redundant.

[nullack]

I dont understand the logic of your post mate. It seems contrary to proven designs such as 300M DOM tube landing gear in aircraft, 300M DOM tube engine mounts etcetc. You cant compare the strength and toughness of say rockwell 30 heat treated 300M to say annealled 1020. Besides, the supplier has it cheap.

[ISUZUROVER]

I dont understand the logic of your post mate. It seems contrary to proven designs such as 300M DOM tube landing gear in aircraft, 300M DOM tube engine mounts etcetc. You cant compare the strength and toughness of say rockwell 30 heat treated 300M to say annealled 1020. Besides, the supplier has it cheap.

I think that Dougal's point is that unless you are 100% sure how to get the best out of a material like 4340M/300m, then you may as well use a lower grade material.

Aircraft landing gear designers have teams of people doing FEA optimisation and QC on every individual component...

300M steel is often used in landing gear because of its high strength and high fracture toughness. Conversely, 300M steel is highly susceptible to corrosion fatigue and stress corrosion cracking (SCC), which can lead to catastrophic consequences for aircraft landing gear. Shot peening and plating of the landing gear are used to suppress corrosion fatigue and SCC with limited success. A method that will produce deeper compression in critical regions of landing gear will provide a dramatic improvement in foreign object damage (FOD) tolerance, corrosion fatigue strength and SCC susceptibility. This paper discusses the use of low plasticity burnishing (LPB) to provide a deep layer of residual compression to improve damage tolerance and mitigate SCC of 300M steel.
The fatigue performance of LPB processed 300M steel test samples were compared to those in a shot peened or low-stress-ground (LSG) condition. LPB treatment dramatically improved the high cycle fatigue (HCF) and corrosion fatigue performance with and without a simulated defect. LPB reduced the surface stress well below the SCC threshold for 300M, even under high tensile applied loads, effectively suppressing the SCC failure mechanism. SCC testing of LPB treated landing gear sections at tensile stresses ranging from 1030 to 2270 MPa (150 to 180 ksi) was terminated after 1500 hrs without failure, compared to failure in as little as 13 hours without LPB treatment.

[KiwiBacon]

I dont understand the logic of your post mate. It seems contrary to proven designs such as 300M DOM tube landing gear in aircraft, 300M DOM tube engine mounts etcetc. You cant compare the strength and toughness of say rockwell 30 heat treated 300M to say annealled 1020. Besides, the supplier has it cheap.

Compare the cost of aircraft landing gear to any other fabrication and you'll see exactly what I mean.

4340 has 0.4% carbon, 300m is 0.4-0.46% carbon.
Both of these are basically the upper limit of weldability. The precautions you have to take to prevent hydrogen embrittlement of the welds will make for an extremely slow and expensive welding process with a lot of rework.
Even if the material is free, the end result will be very expensive to guarantee it's crack free.

But my main point is, if you're stressing parts of an offroad vehicle frame to levels where hardened 4340 is needed, then your design needs more work.

[uninformed]

Stainless steel do not have the strength (tensile, compression shear) and the toughness of other steel alloys. Yes you can make it out of stainless steel but it wont be an optimal design if the builder wants a tough and strong part. Theres other reasons but for the sake of not writing a book those are the two key ones.

Im looking at using 300M (4340 modified) DOM tubing and heat treating - local aircraft place is overstocked. Its an excellent ultra high strength and toughness steel alloy. This will enable me to use a thinner wall section than say 1026 DOM and still exceed the mechanical capacibilities of 1026. IMHO too many builders ignore the problem of added mass to their vehicles especially in wagons there aint much difference between tare and gross mass when you add up all the stuff they put onto the chassis.

can you give some examples of what you are making and your designs?

Serg

[nullack]

Its just suspension links and steering links. No section changes, circular. The factory links work for fine dynamic loads in normal situations but they go plastic when shock loaded by being smashed on rocks etcetc. I used to simply sleeve them with 1020 DOM but that wasnt always tough / strong enough. Now Im looking at making whole new links.

Mate I take the point about the pre and post welding procedures of 300M but with my mate whos a professional welder it all costs a few beers and some laughs

[KiwiBacon]

Its just suspension links and steering links. No section changes, circular. The factory links work for fine dynamic loads in normal situations but they go plastic when shock loaded by being smashed on rocks etcetc. I used to simply sleeve them with 1020 DOM but that wasnt always tough / strong enough. Now Im looking at making whole new links.

Mate I take the point about the pre and post welding procedures of 300M but with my mate whos a professional welder it all costs a few beers and some laughs

So buckling under shock loads?
Bigger tubes there will give you far better results than a change in material will.
There is one scenario where higher strength steel will work better. But that's in the rare case when the tube buckles and the load disappears before it's buckled far enough to stay bent.
Is this going to help?

[nullack]

Thats good advice thanks. Yeah I plugged some maths and clearly bigger OD is a good step. Im thinking of going to a 50mm OD but need to see if there is any clearance issues with that size.

[uninformed]

the whole weight argument really goes out the window if your just making some trailing arms and steering links...

if you were building a race buggy or TT i would totally agree and thats why the space frame chassis are made from cromo and links are fabbed from 4340 and heat treated....but they are trying to achive very high strength and light weight....their designs are very important...

for link material a good cost effective choice that is still easlierly weldable is euro-norm from bolher...

Serg

[mhgill]

It dosn't really matter what you coat your arms /sliders in, they will both get scratched and will end up bare metal and rust, besides it's only minor rust, just re paint it or put up with it. Your Not really gonna rust your suspension arms in half in a real hurry.