Brazing tungsten carbides with a large surface area to unalloyed steels

[ArkadiuszP]

Here is nothing particularly difficult about brazing small parts to steel. However, when the tungsten carbide is, say, 300 [mm] long and its width exceeds 10 [mm], a problem arises. The first problem is how to remove the old carbide from the element in one piece? (I know you need to heat, but how?).
The most important problem is how to solder such a large carbide so that it does not break? It's not about the materials because that's clear. What and how to heat?

Regards and thank you for your help.

 

[EdStainless]

People typically induction heat the steel. This gives you very precise control over the heating.
You also have to decide if the large pieces are really worth it.
The carbide is so stiff that it easily cracks if there is any flexure.

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P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

For a large piece I would assume they are furnace brazed.

Removal is simple. Suspend the assembly so that one of the components can drop off once it is heated sufficiently.

 

[arunmrao]

ArkadiuszP,

I use a tungsten carbide insert of a similar dimensions as described by you.These are fixed on inlet and exit ports of a horizontal shaft impactor machine for crushing quartz .

I mill a slot and applying a quick fix glue tap the carbide insert into the slot. No brazing is done and they last long.

 

[3DDave]

The glue makes the most sense. Looking at the differential CTE between carbide and steel it seems unlikely that anything but a thick layer of interposing weak material can successfully bridge it.

 

[EdStainless]

With a socket glue works, there are epoxies made for this application. Contact your supplier.

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P.E. Metallurgy, consulting work welcomed

 

[ArkadiuszP]

Thank you all for trying to help.

Replying to posts:
The glue does not work, the carbide falls off
Weglik does not go into the slot but is soldered flat. The working surface is the largest plane that is worn away.

In my opinion, you should:
- for steel, give flux and solder
- give a copper sheet with a thickness of 0.4 [mm] for this
- for this flux and solder
- finally carbide

The problem is in what order is it all heated?
Should I start with the bottom, i.e. with steel?
Should I start from the top, i.e. with carbide?
Do you heat everything at one time?

 

[TugboatEng]

Everything should be done at one time, you don't want to be remelting brazed joints. There are brazing alloy strips/tapes that will facilitate the this.

 

[ArkadiuszP]

I have no choice but the tungsten carbide has to be in one piece.

 

[EdStainless]

I have never seen carbide soldered (low temp), it is always brazed (higher temp, usually with some Ag).
You can get a brase paste or strip that will let you clean the steel, apply the braze, place the carbide, and then heat.
You need some kind of fixture to hold the carbide aligned if there is no pocket machined for it and you need some slight down force to assure that is lays flat. Not too much though because you don't want the braze joint too thin.
Why do you want to use a Cu sheet in between?
If you do feel that for some reason you need the Cu then you have to decide, to either use the same braze for both joints and braze it all at once or to use two different braze alloys and do the higher temp one first and the lower temp one second.

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P.E. Metallurgy, consulting work welcomed

 

[nosivadbor]

ArkadiuszP , not sure if you have completed the job, but there are many variables that come into play when brazing carbide parts of this size. You will need to heat up the entire assembly essentially at the same time but depending on the size of the steel component you re brazing onto, you may want to preheat the carbide.

Another point is absolutely try to use a trimet braze strip with ~ 50%Ag to help with different CTE of Steel vs carbide. I would need to see the overall design to give further advice.

Regards,
Rob

 

[ArkadiuszP]

Thanks again to everyone for your help.
As of today, the case looks like this:
- I have the correct solder paste.
- I bought a triple solder-buffer-solder tape
- heating will be by means of resistance heaters controlled by thermocouples.
- the whole thing will be fixed in a special device so that nothing moves.
The carbide weighs 130g, so the pressure will be significant. however, there will still be an austenitic steel element on it, slowly giving off heat to press down and slow down the cooling of the carbide.

 

[EdStainless]

So this is a solder and not a braze?
It will be interesting to see if it is strong enough.
It sounds like you have a good plan.
Let us know how it turns out.

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P.E. Metallurgy, consulting work welcomed

 

[ArkadiuszP]

Mistake on my part. We talk about brazing all the time.