Things You'll Need
TIG welding machine
4140 or 4150 type filler material
forge, torch or preheat oven
American Iron and Steel Institute grade S7 tool steel is a high-carbon steel designed to be a shock resistant. It is used in mechanical and industrial processes where repetitive impact can quickly weaken other grades. It is also designed to be air hardened and extremely tough to reduce the possibility of breaking and chipping. However, because of these properties, AISI S7 steel can be difficult to weld if not prepped and executed in an appropriate way.
Place the section of S7 steel in a forge or preheated oven and raise the temperature to between 400 and 600 degrees Fahrenheit. If the piece is too large, heat a smaller piece to the proper temperature. Note the color and use a torch to heat the larger piece to the same color.
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Fill voids, breaks or joints with 4140 or 4150 filler material using the TIG welding machine.
Place the section of steel in a ventilated location and allow it to cool to room temperature.
Grind the weld flat using a disc grinder or sandpaper.
Keep the steel as close to 400 to 600 degrees as possible during the welding process.
Proper safety equipment and procedures must be followed to prevent injury to eyes and skin.