How to Weld Cast Iron Effectively; Steps Involve
As there is a general knowledge that cast iron welding is difficult, welding cast iron effectively is often asked by people who want to overcome the difficulties they encounter.
Before getting into the how-to's, we would answer commonly asked questions about cast iron and its welding.
This is to enable you to learn about cast iron and the reason for specific procedures in this article.
Frequently Asked Questions about Cast Iron Welding:
Is it possible to weld cast iron?
Yes, it is doable to weld cast iron. However, it isn't easy because it is made up of different materials (usually iron, carbon, and steel) at different proportions.
This makes it hard to identify how strong the metal you're working with is and how much heat it can withstand before cracking.
# What welding technique is the best to use? Every welding technique has its pros and cons. Therefore, the best welding technique to use in welding cast iron would be dependent on their suitability to the cast iron alloy being welded.
# What are the best rods to use for welding? 99% Nickel rods. This rod produces highly machinable welds that work best on casting with low or medium phosphorus contents. They are, however, expensive to purchase.
Pre-Steps to Cast Iron Welding:
Before getting right into the welding process, there are steps to ensure that the iron welded does not suffer a crack and choose the right welding process to use. These steps include:
Identifying the Alloy:
This is the first pre-step to be taken. Not correctly placing the alloy you are about to weld can cause a crack during the welding process. The different alloys of cast iron are:
Grey Cast Iron:
This shows grey and a fracture point due to the graphite in its microstructure.
White Cast Iron:
This is whiter along a fracture due to its cementite.
Ductile, nodular, or malleable iron:
This alloy is also entirely white along the fracture. However, it is much more weldable than White Cast Iron.
Selecting a preheat temperature:
As cast iron is prone to cracking under stress, a proper heat control mechanism should be set in place to avoid breaking. The process of ensuring this includes Preheating — Low heat input — Post-heating Cooling.
Preheating and Post-heating cooling are performed because cast iron undergoes thermal expansion due to its temperamental nature. When warmed, it expands. Besides, a too-quick change from room temperature to welding temperature builds stress on the metal, causing it to crack. In like manner, if the cast iron cools too fast after welding, contraction occurs, this creates brittle and easily fractured welds.
Preheating is done between the temperature of 260- 650 degrees Celsius. Once the welding temperature goes above 780 degrees Celsius, overheating occurs. It is performed by using a blowtorch to heat the material.
When proper heating is not obtainable, one should minimize heat input — select a low-temperature welding process and low melting point welding rods or wires.
Post-heating Cooling is obtained by using a Charcoal BBQ to sit the piece of iron in a bucket of sand or by placing the chip on top of a wood fire oven, allowing it to cool down as the fire dies. This eliminates fast calm, thereby reducing hardening and contraction stress.