Problem Overview

The non-uniform shrinkage during continuous casting of steel slabs leads to the formation of longitudinal and transverse corner cracks in the slabs.  These defects need to be removed before these slabs go for the further processing in the downstream units.

Casting speed and grade of steel are the main factors, which increase the probability of these defects during continuous casting. Hence, the scarfing process is deployed to remove the defects, and it is deployed selectively based on the criteria of casting speed and grade. But it is still inadequate to prevent these defects going to further processing stages, which causes huge internal rejection of the material processed. So, it is essential to have a system for online inspection of the slabs for the longitudinal cracks, and transverse corner cracks.

Challenges during inspection of slab:

• The slab needs to be inspected for the following defects:
  • Longitudinal Cracks
  • Transverse Corner Cracks
• The inspection needs to be done while slab moves at a speed of 6 m/min.
• Surface temperature of the slab is above 600 °C.
• The surface cracks are masked by scale and oscillation marks. Especially the transverse cracks are masked by the mold oscillation marks, because they tend to form near the mold oscillation marks.
• Size of the Cracks: Length of 20- 30 mm, and depth of 3 mm. Hence a solution with higher sensitivity to detection of cracks will be preferred.

Desired Solutions

An NDT (non-destructive testing) System for online inspection of slabs for surface defects at hot condition in slab caster.

Benefit of having such solution:

• Online slab inspection will help in selectively scarfing, which will increase productivity.
• Condition based scarfing will improve the current practices to eliminate the current internal rejection.