Soft arcing - ESR ingot defects

Soft arcing - ESR ingot defects

Figure 1: Comparison of ingot appearance with the generation of soft arcing.

Defect name: No data.
Record No.: 3349
Type of defect (Internal/Surface): Internal, surface
Defect classification: ESR ingot defects
Steel name: 9CrMoCoB steel
Steel composition in weight %: No data.
Note: For the USC(Ultra Super Critical) HIP(High and Intermediate Pressure) rotor, the high cleanliness and homogeneous ingots without interior defects such as Non-metallic inclusion, porosity and segregation are required. For these demands, most turbine manufacturers have developed and applied an ESR (Electro Slag Re-melting) process to produce 9~12% Cr heat resistance steels. Among ESR conditions, slag composition and melt rate are the important factors because slag composition gives the remarkable influence on the content of major elements and cleanliness and melt rate also has a great effect on segregation. Therefore it needs to decide carefully slag compositions and melt rate.
For the 9CrMoCoB steel(COST FB2) used up to as 630 C class USC power plant materials, it is very important to control the solute element such as Si, Nb and B in homogeneous and optimum range because the exchange reaction of the solutes between slag and molten metal occurs due to their thermodynamic equilibrium during ESR process.

In sequence, the effect of soft arcing on interior/exterior quality of the ingot was also investigated. In the case of surface quality of the ingot as shown in figure 1, it can be seen that slag skin becomes thicker and deep ripple is formed on the ingot surface when soft arcing is occurred. Cleanliness in middle part of the ingot height was compared according to generation of soft arcing. It can be seen that cleanliness in the ingot without soft arcing is better than that in the ingot with soft arcing.
Reference: Not shown in this demonstration version.