Repairing Cracks in Cast Iron


Q: I want to weld my cast iron dutch oven that has a crack in it. Before I start, I have several questions:

Since the oven is 1/4" thick, is Ferroweld™ stick electrode the better choice?

Will Ferroweld™ work with AC current?
I have a 25-year-old AC-225 "buzz-box"

What about weld prep / preheat?
I’m concerned about the thermal cycling that the oven will undergo during use, so I suspect that a complete penetration weld is called for. Obviously the braze material will have to be ground off, but what else is necessary?

Should the welds be short sections to control heat input?
How about one-inch long sections - even through I know more starts and stops equals more opportunity for weld defects!

Would you recommend drilling a small < 1/8" hole at the tip of the crack?
I want to try to keep it from running as the iron heats up

A: I would choose 1/8" Softweld® 55Ni. This rod can be used on AC Polarity but DC+ is preferred.

As far as the rest of your questions, follow these steps to repair the crack:

1. Locate the cracked area using a commercial dye penetrant or rub with kerosene and then chalk over the crack. The kerosene will absorb through the chalk to
    show how long the crack really is. Sometimes it’s difficult to see the crack with the naked eye.

2. Once the crack is located, drill a 1/8” hole at the end of the crack.

3. Clean and grind the area 2 inches at each end of the crack to prevent it from continuing further. If you’re using a grinder, heat the bevel with an oxidizing
    flame to burn off carbon before welding.

4. Grind, chip, machine or saw the crack to create a bevel. Gas cutting or arc gouging can be used on a casting that is preheated for welding. Be sure to get the
    bottom of the crack. On sections more than 3/16” thick, bevel the edges so the root of the joint is 1/8” to 3/16” wide. If the crack extends through the section, 
    leave about 1/8” gap and 1/16” land.

5. Preheat entire casting slowly and evenly to remove surface oils and dirt:

    At least 500 degrees F; not more than 1200 degrees F  
    Make sure you maintain the temperature of the casting from start to finish
    Preheat the entire casting, not just the area to be welded

6. Weld the cast iron using low currents for minimum penetration
    Make 1-inch to 3-inch welds to limit heat input. Immediately strike (or peen) the face of each weld with a small ball-peen hammer to relieve stresses in the 
    weld. Skip weld – move around the cracked area – do not keep heating the same area. Run your beads in the same direction.

7. Cool very slowly - oven or furnace cooling is preferred. Drop 50 degrees F every hour until room temperature. Bury the casting in dry sand, wrap in
    fireproof blanket – anything to slow the cooling rate. Air cooling is too fast!

Note: For machineable welds, use Softweld® 99Ni or Softweld® 55Ni. Ferroweld™ deposits are not machineable.