Effect of torch process on the steels used for bucket, shovel handle, and other high-tonne mining equipment

The gouging torch process using air carbon arc cutting (CAC) device is a standard maintenance procedure carrying out in high-tonne equipment used in the minery industry. The application of this process could locally affect the mechanical properties and the microstructure in the thermally affect zone (HAZ). The changes involve variation in the local carbon concentration and a tempering effect. In commonly used steels in the manufacture of buckets (SAE 5130) and shovel handles (ASTM 514 grade S), the processes influence negatively the work lifetime and the future maintenance works on the device.

Hardness, metallographic analysis trhough optical (OM) and scanning electron microscopy (SEM) were used to evaluate the affected zone.

An increasing carbon content up to 2 wt% C was observed in the affected area of the sample, on the slag adhered to it. Presumably, the rest of carbon is lost by evaporation during the process.

The hardness measured on the surface of the cut zone shows an increased value for ASTM A 514 grade S, which does not present a notable change for SAE 5130. However, both steels showed a tempering effect. Micro-cracks of 20 to 40 μm appear, and in a few opportunities, a larger crack was found, reaching a total length of 1480 μm.