Elevated temperature sliding wear behaviors of piercing plug tool steels used for production of seamless tube of power plant
Sliding wear behaviors of piercing plug tool steels were investigated at 900 °C against low Cr ferritic steels containing 2 %Cr and 9 %Cr using a pin-on-disc CETR tribometer under condition of applied normal load of 20N in air. Formation of glaze layers consisting of porous Fe-oxides wear debris with rapid growth on worn surface of piercing plug tool and smooth surface of steels containing 2 % Cr resulted in decreased friction coefficient at an initial period followed by exhibited constant value of about 0.3 during the elevated temperature wear tests. It was found on the cross-section underneath the worn surface of the tool steels against the steels containing 2 %Cr that coarse ferrite with equiaxed grains by phase transformation and dynamic recrystallization was formed showing the decrease in hardness. On the other hand, formation of the glaze layers consisting of compact Cr-rich Fe-oxide wear debris on the worn surface of the tool steels at slow rates of materials transfer from the steels containing 9 %Cr resulted in the fluctuated friction coefficient ranging from about 1.0∼1.1 to 0.4 followed by exhibited almost constant value of 0.2∼0.3. It was also found on cross-section underneath worn surface of tool steels against the steels containing 9 %Cr that severely deformed microstructures by cyclic applied loading was formed below compact and continuous oxide layers. The results showed that the elevated temperature sliding wear of the piercing plug tool steels was dominated by oxidation, materials transfer and subsurface degradation such as dynamic recrystallization softening or severe deformation.