Effect of carbide heterogeneity on surface defects in high-speed steel slotting mills

Conclusions

• 1. The reason for the formation of both types of surface defects on slotting mills made of R18 steel is the carbide heterogeneity.

• 2. There is no connection between the formation of defects of either type and the cold working of the mills or the presence of nonmetallic inclusions.

• 3. Defects of the first type result from etching out of segregation bands on the surface during chemical cleaning of the mills after quenching and tempering. These defects occur a) when the etching temperature exceeds 70\dgC, b) when the etching time exceeds 20 min, c) when the hydrochloric acid concentration exceeds 7% at high temperature (70\dgC or higher).

  The optimum etching conditions are: a) etching bath temperature of 30–50°C; b) etching time 15–20 min; c) hydrochloric acid concentration up to 15%.

• 4. The probability of defects of the second type increases with the quenching temperature and the degree of carbide heterogeneity.

• 5. Shallow defects of both types can be removed by polishing. Deeper defects of the second type cannot be removed.

  The quality of the slotting mills, particularly the larger sizes, can be improved by reducing the carbide heterogeneity of the original rolled steel.