Brazing Filler Material for 4140 HT 3

[csquaredng]

Hi all,

I am designing a hot tap pilot drill insert holder (1/2" diameter) that is to be brazed onto a sleeve 1" long. Both the holder and the collar are to be made of 4140 25-32 HRC. Can anyone share their insight on which filler material should I use for this application? Also, first time designing this tool holder, so I'm definitely interested to see any of your input on the holder material, as well.

Thanks!

Csq

 

[TugboatEng]

Is cadmium ok or no? Alloys with cadmium have a lower melting point. I prefer this when torch brazing stainless steel as I am less likely to get oxides that will prevent the filler from wetting the surface.

This sounds like a slip fit. If the clearance is tight, 50N (BAg-24) has strong capillary action. If there are gaps or fillets, 56 (BAg-7) is superior.

If cost is an issue considering a coppper-zinc alloy.

My experience is only torch brazing.

https://princeizant.com/silver-brazing-filler-metals

 

[EdStainless]

4140, I presume that it is Q&T?
If so, then your brazing temp has to be below the tempering temp.
Fortunately, this sounds like at least a 1200F temper so you should have options.
Perhaps start looking at BAg-7 and BAg-36.

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P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

I got a laugh while looking up the AWS classifications.

https://weldingwarehouseinc.com/products/aws-a5-8-filler-metals-for-brazing-braze-welding/

You should definitely not overlook BAg-24 because it's "good for stuff too".

 

[gtaw]

Thanks for sharing that tidbit.

Braze filler metal is unlikely to be as "strong" as the metals being joined. Lap joints overcome the problem by increasing the surface area to produce a joint "as strong" as the base metals being joined.

Brazing and soldering both depend on capillary action to distribute the filler metal throughout the joint. A small clearance is required to provide the capillary action needed, i.e., you don't want a tight joint without clearance, nor do you want a loose fit that provides too much clearance. The filler metal selected should be appropriate for the base metals being joined and the clearance provided. Filler metals with a narrow liquidus-solidus temperature range require less clearance, whereas filler metals with a wide liquidus-solidus temperature range can "fill" a joint with more clearance.

In your case either a BCuP-X or a BCuZn will probably work.

Best regards - Al

 

[csquaredng]

The clearance is between 2-8 thou (an article from a steel company noted 2-3 thou is optimum) and the 4140 will be tempered at 1100F max to get the 25-32 HRC. Thank you all for the input. This gives me a starting point to discuss with the machinist. Greatly appreciated!

 

Lap joints overcome the problem by increasing the surface area to produce a joint "as strong" as the base metals being joined.

True, but a narrow gap also gives effective strength to a joint because of triaxial constraint from the stronger base metals. But it's a tradeoff because of the risk of incomplete filling of narrower joints, say less than 0.003".

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[EdStainless]

Your hardness range and temper temp don't go together., unless the alloy is actually 4130.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed