Cast Iron Crack Repair by Lincoln's Cast Iron Expert, Joe Kolasa  

Joe Kolasa

Within the walls of The Lincoln Electric Company are some of the brightest minds in welding, but we wouldn't be The Welding Experts® if it weren't for the expertise of our customers. Learn with us from questions submitted by real customers and answered by the real experts.

Question
In an earlier "Ask the Experts" article, Joe Kolasa recommends stick welding cast iron with either Softweld 55Ni or Ferroweld. That got me thinking about welding 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 the better choice?
• Will either rod 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

Answer
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, let’s start at the beginning. 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 them 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 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; not more than 1200 degrees.
   • Make sure you maintain your temperature 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 every hour until room temperature. Bury in dry sand, wrap in fireproof blanket – anything to slow the cooling rate. Air cooling is too fast!