Brazing 4130N steel fittings

[mike newall]

Here is my 2p worth.

My mate races Formula 2 sidecars and their frames are all 4130 and brazed.

I've just got this from him and tend to agree.

Brazing creates a diverging temperature gradient through the heat affected zone so stopping embrittlement but you risk distortion.

I believe it is also better for larger areas of contact - i.e. washers.

While TIG is great, it requires a lot more skill and if you are welding a washer on would input a lot of localized heat into the area.

When used properly and with a suitable filler rod, a tig weld is virtually impossible to detect on the NDT slices of test coupons, but when you weld thick to thin, you have to be exceedingly careful.

[Bill McCarthy]

In my submarine days I was heavily involved from the quality control side of things in the detection and making good hundreds of socket brazes in system pipeware. Our boat was the same design as USS Thresher which went in the Atlantic down due to a failure of the same system - a pinhole leak at a braze in ours set us off in a very lengthy and costly investigation and repair. In hundreds of sockets there was not a single one with full joint fill, the worst, just 5% - a small fillet round the edge of the socket. It was modern ultrasonic detection methods which were not available at build which revealed the horror story and we were perhaps one deep dive from disaster. I would not contemplate brazed joints in any way for high integrity duty. If I could not weld, then I would rather have a thicker plate milled down to leave the support profile. As an aside, are the build plans of an age that required brazing rather than more up to date assembly ?

[Ian Law]

Thanks Mike and Bill,

As you guessed, Bill, the plans were drawn up in the early 80s, I think. I have assumed that this could well be the reason for indicating brazing for some operations. All references are to gas welding, of course. I assume safe TIG welding was not readily available to amateurs at that time.

The designer of the Boredom Fighter, Don Wolf, was the training Director for Grumman, in New York in his later years. I suspect that had he not died some years ago, he would have been happy to consider more modern methods and techniques, where appropriate.

Interesting that you suggest milling the part as the ideal; this crossed my mind but though very attractive is, of course, pure fantasy considering my budget! I'm awaiting a call from my Inspector about this and other matters, but in the meanwhile I'm hoping I don't have to re-make these parts; that would be a major set-back to my project in time and cost & I certainly don't have the time to waste.

Many thanks again for all your suggestions.

Ian