Brazing Tool Steel

[Clockwork]

I'd like to braze the flange to the v-block which appears to be made
from hardened tool steel. Can I do this with brass?

http://www.flickr.com/photos/28879558@N04/8456264393/in/photostream

Thanks, Joel

[Ethan Labowitz]

Only one way to find out...try it.

Seriously, one of the benefits of brazing over welding is that a braze is generally less prone to cracking than a weld. Weld cracking would be something to be concerned about if you tried to weld that joint.

ESAB publishes (and distributes free of charge) an O-A Handbook that covers brazing, as well O/A welding of most metals: http://www.esabna.com/EUWeb/oxy_handbook/589oxy2_1.htm

The section therein on welding high-carbon steels has this to say:

High Carbon Steels

Almost every item made from high-carbon steel must be heat-treated after forming or fabrication to achieve the right combination of hardness and toughness required in service. Welding high-carbon steel by the oxy-acetylene process, even when filler metal of high carbon is employed, will always result in substantial modification of those properties in the base metal. Therefore, high-carbon steel items can seldom be repaired by welding unless facilities for correct heat-treating after welding are available. If, in an emergency, you ever feel the need to weld something which is probably made of high-carbon steel (such as a knife blade or spring) use the best steel filler metal you have, use an excess-acetylene flame (to cause carbon pickup by the molten metal), and try to work as fast as you can, melting no more of the base metal than is absolutely necessary to insure complete fusion.

The caution concerning modification of the heat-treatment would apply to brazing as well as welding--indeed, it would apply anytime a heat-treated steel object is heated over, say, 400 F, or, worse yet, over its critical temperature.

You could always restore hardness post-brazing by heating above the critical temp, quenching, and tempering, though you would likely see some amount of heat distortion in the process. Another option would be to case-harden, which is actually probably what I would do. There's this stuff called Cherry Red that works pretty well. 

Ethan Labowitz

snowed in, in Somerville, MA

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[Brian Smith]

Joel,

Assuming you have enough fuel and tip orifice size, I can see no problem with this task.  I've done similar things many times without issue.

-Brian

On Fri, Feb 8, 2013 at 6:32 PM, Clockwork <jo...@clockworkbikes.com> wrote:

[jon norstog]

Joel,

Sounds like a job for Welco 17 and a great big torch.

jn


"Thursday"

[Clockwork]

Thanks for the responses.

It brazed just fine and it's fine if the steel normalized since I'm
just using them the hold seatstays in a mitering fixture.

http://www.flickr.com/photos/28879558@N04/8456832689/in/photostream

http://www.flickr.com/photos/28879558@N04/8456831921/in/photostream/

I'll post more pics of the fixture when I'm done.

-Joel

[M-gineering]

I think you'll be much happier with two decent bolts, and perhaps two
dowelpins if you decide to get fancy

--
Marten Gerritsen
Kiel Windeweer
Netherlands

[Paul Anthony Judd]

Brazing has it's own inherent problems as well besides heat affecting the base steel. Zinc from the brass will dissolve into steel to make brittle inter-metallics, effectively small ceramic particles that will act as stress concentrators and crack initiators. Hence I will only silver solder high quality tubing, in fact Reynolds will absolve it self of any guarantee if 571  is anything but silver soldered.
Having said that I have done an emergency repair and a friends clutch arm (high carbon steel) using high quality hard copper coated filler using excess acetylene and it never need repairing or replacing even after he gave the car to his sister many years later.
Speed (time at temperature) is the essence of high carbon steel welding/brazing/silver soldering to minimize the heat affected zone.

-- Paul Judd B.App.Sc. Secondary Metallurgy, Dip Electrotechnology Renewable Energy,  Dip Sustainability Trainer and Sustainability Advisor     PAJeco    Sustainable Education     Sustainability: Learning to live today but leaving enough to live tomorrow     http://www.pajeco.com.au     paul....@pajeco.com.au     +61415518134

[Tony Pereira]

Paul,

If these "facts" are true it's hard to imagine how the millions of
bronze brazed bicycles made over the past 150 years haven't exploded.
Your assertions would be more believable if #1 you qualified how you
know this and #2 you hadn't referred to a Reynolds tube designation that
doesn't exist (571).

In case you are referring to 531, I'd be pretty surprised if Reynolds
does not stand behind any joining method besides silver "solder" when it
has been bronze brazed for over 100 years in aircraft, motorcycles,
autos and bicycles. This page might clear things up:
http://reynoldstechnology.biz/faqs/welding_joining/1

I'm not saying you are entirely wrong, just that you didn't back up your
claims and that "brittle inter-metallics" might not matter with regard
to making bicycles. Maybe it's because we use bronze filler, not brass?

-Tony

Pereira Cycles
Portland, Oregon, USA
www.pereiracycles.com
503.333.5043
twitter: @pereiracycles

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[Alistair Spence]

On Sun, Feb 10, 2013 at 2:01 PM, Paul Anthony Judd <sukii...@gmail.com> wrote:

Brazing has it's own inherent problems as well besides heat affecting the base steel. Zinc from the brass will dissolve into steel to make brittle inter-metallics, effectively small ceramic particles that will act as stress concentrators and crack initiators. Hence I will only silver solder high quality tubing, in fact Reynolds will absolve it self of any guarantee if 571  is anything but silver soldered.
Having said that I have done an emergency repair and a friends clutch arm (high carbon steel) using high quality hard copper coated filler using excess acetylene and it never need repairing or replacing even after he gave the car to his sister many years later.
Speed (time at temperature) is the essence of high carbon steel welding/brazing/silver soldering to minimize the heat affected zone.

I think you're referring to Reynolds 753 (?), which is heat treated 531. Reynolds did say it was only to be silver brazed, and even made builders pass a certification test, but I've seen Ernest Csuka quoted as saying that they bronze brazed 753 at Alex Singer Cycles without issue. I imagine there were/are others, and I've read quotes from other builders saying that the whole 753 certification process was a bit of a dog and pony show anyway.

As for brass or zinc inclusions in steel as a result of brass/bronze brazing, you're right, it can happen, but you have to really overheat the joint. With decent heat control it's not an issue at all. Witness the millions of bronze brazed bikes that have been in service around the world for decades.

Never heard of Reynolds 571.

Agree with your last point regarding "time at temp" of the brazed joint being important, and not just for high carbon steels. Low alloy steels used in bike frames benefit from minimal heat input too, assuming it's enough to properly flow the joint.

Alistair.