Thread: Galvanising radius arms etc ?

Murray,
Hope your not after a short answer on this one.

Glen

Originally Posted by Dorian

Murray,
Hope your not after a short answer on this one.

Glen

A long one will do, if someone can explain.

Maybe someone can give a medium length answer

Cheers, Murray

Hi Murray,
So I'm not a metallurgist, but have needed to know enough of this stuff to get me into trouble.
But if there is a Metallurgist around please feel free to correct me.
Ignoring forging and drawing for the moment, when you are looking to get particular properties of of a steel, you will need to heat treat it in some way.
This usually involves heating it up white hot and quenching it in water (hardening), then heating it up to a "cherry red" for a while and quenching it in oil (tempering).

When you heat it up white hot and quench it quickly, you end up with a hard brittle steel. There are at least three types of crystals (often a few more) that will form in most steels, these have great names and the text books talk in terms of crystal structure and carbon / iron composition but for me they are the hard one, the soft one (imparts toughness) and then the rest. I am pretty sure (memory not that great) the hard ones form first and then as the steel cools the softer crystals form, once these have used up the carbon from the cooling steel, the "rest" form. Understand this is a pretty quick explanation of the subject, also the "rest" is very important especially in exotic steels like chrome moly, vanadium and machining steels.

So at this point the steel has larger hard crystals because they have formed reasonably well at the high temperature, but the soft (tough) and the "rest" crystals have been forced into the remaining spaces because of the speed of the cooling. It's hard because of the larger hard crystals but it's brittle because it has lots of small tough crystals forced into the bits in between the hard crystals. Because the tough crystals aren't joined together the steel breaks along the edges of the hard crystals.

When you do the second process you heat up the steel enough to allow the soft (toughness) crystals and the "rest" to join and grow into larger crystals (usually not big just larger), some of the hard crystals also give up their edges to be made into soft crystals. So the steel becomes tough (or soft) but will lose hardness. This process is time as well as temperature dependent. So depending upon the steel, the tempering range can be between 200 and 600 degrees Celsius. From memory there are only a few steels that will treat as low as 200 but depending upon what you want, tempering the same steel at 600 for 60 seconds or 300 for 2 hours will change the properties of the steel, though differently. The dipping in oil is to give a constant rate of cooling that's slow enough to let the crystals sort themselves out, but quick enough to stop crystal growth.

When you forge steel you are doing a similar thing but in reverse, You temper the steel for a long time, allowing the crystals to become large and then when you strike the steel in the forge the crystals are smeared,so there is no clear line of fracture along the crystal edges, only certain steels forge well as the crystal structure has to be specific. Drawing is a similar process.

So in the Gal dip, the steel is usually left in for a few minutes (this is often pretty random based on the operator and the largest piece of steel on the rack, at 600 degrees this will allow a fair bit of crystal change in the steel, given you don't really know the specific chemistry of the steel or the dipping time and temperature you are probably going to lose tensile strength but how much and is this a good loss or too much will be a lot random.



Hope this is a "medium" answer.

Cheers Glen

From playing with Landy radius arms/ steering rods/ panhards/ upper and lower links my impression is they are made of nothing special - low carbon steel (forged or machined)
I could be wrong but I'm guessing they will be pretty impervious to heating and quenching
Ie unable to harden or temper no matter what you do

I would have zero qualms about Hot dipping them and I fact will be doing exactly that for a boat Trailer Build I have nearly finished running radius arms and a panhard rod

Once done and a shaken down I'll dissemble the axle, links and panhard - press the bushes out and get them all dipped - the only issue I foresee is tidying up bushing sleeves following dipping

Steve

That's enough of a warning for you Murray. I haven't seen or heard of it being done either. If I were you I'd hold off and seek the advice of an Engineer or Metallurgist.

It is not my area of expertise, but there are thousands of galvanised components used in steel structures without a problem, but the process may depend on the type of "steel".

What about powder coating? It may be a better option.

Galvanizing Process | American Galvanizers Association

I'd expect the radius arm steel is fairly plain low carbon steel also.

I'm not going to get into the metallurgy side of things... much..... but all steels can be heat treated, but for low carbon steel unless the gal dipping heats the steel to red (it doesnt) and then it is quenched (it isn't) you wont harden the radius arm as the metal structure wont transform into or remain in the martensite structure which produces the hard and brittle property.

Originally Posted by Dorian

Hi Murray,

Hope this is a "medium" answer.

Cheers Glen

Thanks Glen,
And thanks for all the other responses.
I guess we haven't got a definitive answer, but we're a lot more enlightened.
You were correct Glen, there is no short answer.
This provides a bit more info, but I think they're referring more to structural building steel rather than automotive components The galvanizing process has no effect on the mechanical properties of the structural steels commonly galvanized

Cheers, Murray