Forge Welding Tricks and Temperatures
Hello Mr. Robertson:
I very much enjoy your website (www.ArtistBlacksmith.com) as I am new to blacksmithing and value the articles as a learning resource.
My two questions deal with technique to follow when hand forge welding:
Q#1) I have used both a gas forge and an oxy/acetylene torch to heat small parts when I need to shape and forge weld tool steels (D2) to mild steels. From my research, I understand that the best forge welding occurs when steel temperatures are both above 2400F and when both surfaces are well cleaned. I have a very difficult time seeing the difference in color between dull yellow/orange, bright yellow and yellow/white to know when the materials are both hot enough to effectively weld. I have tried using "Tempsil crayons" to measure surface temperatures, but these crayons only indicate when surface conditions are above 1850F.
What trick or tool do you use to insure that both steel parts are adequately heated to guarantee a good quality forge weld?
There is a lot going on with a forge weld. You certainly need a high temperature and scrupulously clean all helps. At these temperature it is very hard to see and judge the colors of the steel. I usually tell people to look for a lemon yellow or melted butter color or the same color as the interior of the gas forge running at max. But there are some tricks that can be used.
The first one and will gain you the most success is to use special shade 2 welders glasses. Click Here for selection of Amazon Infra-dura safety glasses. I use either the infra-dura shade 2 or rose dydmium glasses for the forge welding. The infra-dura lens actually filters out more of the harsh light than the dydimium. Both of these lenses allow you to see the surface of the steel at high temperatures. The shade 2 lens is green and you have to get use to the color shift but with a little practice this is not a problem. I would suggest wearing them for all forge work.
When using these glasses I am looking for a surface that has a bright greasy look to it. It should also have a look like it is almost slithering around. This is not liquid but getting close to it. The whole weld area should be the same color with no shadows. If it is an uneven heat turn the bar over in the fire and soak it from all sides. It should be an uniform temperature all the way through.
Another trick to try when starting out is forge a 1/4 inch round bar to a point and bend the point over a 90 degrees. Bring the bar that you want to weld up to temperature with the 1/4 round pointed one beside it. When you think it is right touch the point to the part that you think is at welding temperature in the fore fire. It should stick. If it doesn't stick it is too cold. Soak it longer.
If it sticks ( you should be able to pull it apart) take the weld. Start with simple fold over welds such as handles or even 1/4 by 1 inch flat bars just folded over on itself to learn the temperatures required.
Remember in gas forges this is working right at the top of what they are capable of. A high altitude makes a big difference as well. Above 4000 feet you may need a blower to provide extra air.
Flux is a bit of contentious issue. If using no flux your joints and fire have to be as clean as possible. Flux keeps the scale from forming on the bar. Scale does not weld. Some fluxes contain a ground metalic ingredient that lowers the welding temperature and increases the surface area at the joint. All these are good things when joining mild steel. I have used these compounds and they do work well. Trade names that come to mind are EZ-weld, Cherry heat, Antiborax, There are others. The problem comes when you are welding damascus billets as this metallic grains introduce a new layer into the billet and it can muddy the sharp transition between the layers.
Q#2) I have heard that some blacksmith's prefer flux when forge welding while others strictly refrain from using flux because flux introduces contamination to the weld site. If flux is preferred, what are the best flux formulas for forge welding steels, stainless steels and wrought iron?
20 Mule Team Borax found in the laundry isle has been used for years and works well for all general forge welding. It introduces no metallic contaminate. However there is a downside to using 20 Mule Team Borax. On regular joints it leaves a residue of borax that is very hard to clean off. It can be ground or sand blasted off. The problem with this residue is that it will start to turn white as it is exposed to moisture. So you may have this lovely forge welded piece then it starts to get this frosted appearance at the joints after a couple of years. Not pleasant
Different fluxes for different steels.
I have not forge welded stainless steel, but I understand you require a special flux with a Fluoride component to clean the stainless. Wrought iron should have enough slag in the matrix of the bar that you don't need flux but Borax wouldn't hurt.
I hope this helps