Formation behaviours of blowhole and chill layer by GTAW in cast iron

ABSTRACT

Cast irons have some excellent characteristics in wear resistance, vibrational damping etc., and are widely used in many industrial machinery applications. But, the weldability has been much inferior originated from its high-carbon content. Several researches have reported that some of the important factors affecting the weldability were formation of blowhole and chill layer during fusion welding and subsequent rapid cooling.

In this study, the formation behaviours of those were investigated in both flake and nodular graphite cast irons. Tungsten inert gas arc welding was performed using several kinds of filler metal varied nickel and chromium content.

The study was made by paying attention to carbon behaviour and influence of nickel and chromium in filler metal on it.

Experimental results obtained were as follows.

1. The amount of blowhole increased with nickel content and decreased with chromium content.

2. On the other hand, the amount of chill layer increased with chromium content and decreased with nickel content.

3. It was estimated that both blowhole and chill layer formation were related to activity and diffusivity changes of carbon affected by nickel and chromium content. Then consequently they have a correlation relationship each other.

KEYWORDS:

• Cast iron
• flake/nodular graphite
• GTAW
• filler metal
• blowhole
• chill layer
• chemical potential
• activity
• diffusion
• constitutional supercooling