Blacksmithing Forge Weld Temperature Calculator

Borax (anhydrous or 20 Mule Team) is the most common and affordable flux for forge welding. It melts at around 1400°F and dissolves iron oxide scale effectively. For higher-carbon steels or difficult welds, commercial fluxes like EZ-Weld or Iron Mountain contain added iron filings that help clean the surface more aggressively. Borax works well for most mild and medium-carbon steel combinations, while commercial fluxes are preferred for Damascus billets with high-carbon steels.

Most carbon steels need to reach 2100°F to 2400°F for a successful forge weld, depending on the alloy. Low-carbon steels like 1018 and A36 weld at the higher end of this range (2300-2400°F), while high-carbon steels like 1095 and W1 weld at the lower end (2050-2250°F). The steel should appear bright yellow to white hot. Going too far above the welding range risks burning the steel, which permanently destroys its grain structure and cannot be repaired.

Yes, forge welding dissimilar steels is the entire basis of Damascus steel making. The key requirement is that both steels must have overlapping welding temperature ranges. Common pairings like 1084 and 15N20, or 1075 and 15N20, work well because their welding ranges overlap significantly. You must weld at the lower temperature of the two steels to avoid burning the more heat-sensitive alloy. Pairing steels with very different carbon contents requires more care with flux application and heat management.

The most common causes of failed forge welds are insufficient heat, dirty surfaces, too little flux, and poor hammer technique. The steel must be at full welding temperature throughout its thickness, not just on the surface. All mill scale and rust must be removed before stacking. Flux should be applied early (at cherry red) and reapplied if the steel is held at heat for more than a few seconds. Your first hammer blow should be firm and centered, pushing outward from the middle to expel flux and trapped gas.

Each forge weld cycle typically results in 2-3% material loss from oxidation and scale formation. This loss occurs because the steel surface oxidizes at welding temperatures, and the flux dissolves and carries away this oxide layer. Over multiple welds, the loss compounds. For example, a Damascus billet welded 6 times may lose 12-18% of its original mass. Experienced smiths minimize loss by working quickly at welding heat and maintaining a reducing atmosphere in the forge.

Plain borax (sodium tetraborate) melts at about 1400°F and dissolves iron oxide effectively, making it suitable for most forge welding. Commercial fluxes like EZ-Weld and Iron Mountain add iron filings, fluoride compounds, or other active ingredients that more aggressively dissolve scale and lower the melting point. Commercial fluxes are easier to use for beginners and better for high-carbon steels, but they cost significantly more than bulk borax and can produce more toxic fumes.

The general rule is approximately 1 minute of soak time per quarter inch of billet thickness at welding temperature. A 1-inch-thick billet needs about 4 minutes of soak time to reach uniform temperature throughout. Insufficient soak time means the interior of the billet is cooler than the surface, which leads to incomplete welds in the center. Over-soaking wastes fuel and increases scale formation. Watch for the steel to reach an even, consistent color across its entire surface before pulling it from the forge.