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Brazing steel

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David Canham27/04/2019 21:29:55
50 forum posts
15 photos

Hi Guys,

My issue is that i need to braze two steel items together. One of the pieces is en3b but the other is definitely free machining, i checked it by trying to run an arc weld on it and it bubbled up nicely.

I have just re read the book by Keith Hale on brazing but cannot find anything definitive apart from a sentence that says it is inadvisable to use a silver based brazing rod due to the lead in the free machining steel.

I do however possess some Sifbronze No 1 rods and sifbronze flux powder. Would this be suitable and what sort of joint gap are we looking at.

The en3b is a 6mm thick plate with a hole in to take a 9mm Dia rod shouldered out to 12.7.

Cheers, David.

vintage engineer27/04/2019 21:33:59
232 forum posts
1 photos

We used to braze hydraulic fittings using ready fluxed brazing rods. Hydraulic fittings are made from leaded mild steel.

David Canham27/04/2019 22:10:13
50 forum posts
15 photos

Hi Mr Vintage,

Sounds like Sifbronze is ok to use then.


John Reese27/04/2019 22:28:35
824 forum posts

Not all free machining steels are leaded. Sulfur and phosphorus are common additives to improve machinability.

Thor28/04/2019 05:51:03
1174 forum posts
33 photos

Hi David,

I have silver soldered (brazed) mild steel to leaded free-cutting steel without any problems when fabricating a small cylinder for a steam/compressed air engine.


David Canham28/04/2019 08:52:36
50 forum posts
15 photos

Hi John,

very true but it was the way the material reacted when i did a trial MMA weld and it was very porous that makes me think there could be lead in it.

Thanks Thor,

From what i have heard from you guys it should be fine. Time to give it a go i think.

Thank you people.


mechman4828/04/2019 12:27:30
2586 forum posts
392 photos

Have used Sifbronze rods on a small job for my daughters school, worked nicely, & solid. Always used Sifbronze rods & Flux powder when I was training apprentices back in the day, we always used oxy / acetylene torch to heat up test pieces, quickly got up to nice cherry red, warm up & dip the rod into powder coat the test pieces then apply rod, bob's your granny... thinking… just remember to heat the thicker material first & allow the heat to transfer into the thinner piece,have some rods ( bought off eBay last year ) tucked away in cabinet along with flux powder ( at least 30 year old, from my teaching days, & still useable ).


Brian Wood28/04/2019 12:46:08
2072 forum posts
37 photos

Hello David,

I have used Sifbronze to make joints and repairs to all manner of steel parts, it really isn't fussy in that respect. You might also like to know it works well on cast iron.

For that case do go to the trouble of careful slow cooling to help any locked in stress to dissipate and use a big propane flame to heat up the parts you want to join before going in with oxy-acetylene for the brazing itself.

In some cases of castings, I use the propane torch to slow down the cooling

So, have a go.


duncan webster28/04/2019 14:22:36
2424 forum posts
39 photos

Leaded EN1 has only about 0.4% lead content, SAE660 bronze is 7%. Manufacturers data sheet says SAE660 is OK for brazing **LINK**

even LB4 which is 9% bronze is quoted as good for brazing **LINK**

If something with 9% lead is OK it doesn't feel right that 0.4% will be a problem, or is brazing so different from silver soldering? It would be good if someone who knows what he is talking about (not me obviously, probably a metallurgist) could comment. Come on CuP alloys man.

David Canham28/04/2019 16:46:49
50 forum posts
15 photos

Fantastic stuff guys.

So Sifbronze is a pretty versatile rod, i am glad i got hold of some from a previous employment.

Brian, the job i am going to use it on is the drop arm mod from your book so it is quite appropriate to have you involved.

Thank you all so much.


Brian Wood28/04/2019 18:52:13
2072 forum posts
37 photos

Hello David,

Brazing will be perfectly OK on that component, it is likely to need more post joint cleaning to remove the scale. Try painting the other surfaces with Tippex before heating to reduce the scaling

Silver solder would be kinder in that respect,



CuP Alloys 130/04/2019 07:58:15
226 forum posts

Hi all.

Back onto more familiar ground from that of the Mercedes Benz chocolate fireguard!

Using a silver solder to braze steel presents no problem. The common difficulty is not realising that steel needs more heat to reach brazing temperature. A little patience or a bigger burner and a longer life flux eg HT5 normally overcomes.

The difficulty with leaded steel is that the lead is not alloyed but is present as little globules of free lead. It sits there on the surfaces of the joint. As the joint is heated, the lead melts. When the silver solder melts later, the two mix.

Lead in silver solder makes it less fluid or free flowing. It can affect the penetration of the alloy into the joint and hence the joint strength.

Reduce the effect of the lead. Dilute the lead content in the filler metal by having a larger joint gap say 0.2mm.

Thereafter carry on as normal. The same principles for successful brazing apply. It's still all about capillary flow.


David Canham01/05/2019 18:02:27
50 forum posts
15 photos

Hi Keith,

You have just given me the last piece in the jigsaw, open up the joint gap a bit to allow for flow due to the lead.

Many thanks to you all.


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