The Effect of Long-Time Austenization on the Wear Resistance and Thermal Fatigue Properties of a High-Speed Steel Roll
- PDF / 765,345 Bytes
- 7 Pages / 593.972 x 792 pts Page_size
- 94 Downloads / 187 Views
I.
INTRODUCTION
COMPARED with conventional high chromium cast iron rolls, high-speed steel (HSS) rolls show a much higher wear resistance and much better thermal fatigue properties.[1,2] In general, when a large number of hard carbides are formed in a HSS roll, the resistance to wear can be improved, with a corresponding extended life of the roll. However, HSS rolls with a low matrix hardness and a small amount of carbides show better thermal fatigue properties than other HSS rolls.[3] This conflicting phenomenon comes from the fact that HSSs are characterized by a long freezing range and a complex eutectic reaction, which results in segregation of alloying elements and formation of several different types of intercellular carbides during casting and solidification. In particular, centrifugally cast HSS rolls often have a cellular solidification structure, and coarse carbides segregated along cell boundaries may provide an easy crack-propagation path.[4,5] In order to improve the overall mechanical properties, including the thermalfatigue properties, it is desirable to remove or refine the carbides[6] and to induce a more homogeneous carbide distribution.[4–6] It is important therefore to find a way to adjust the shape, volume fraction, and distribution of carbides, and to improve the properties of the matrix by control of the roll casting process and the heat-treatment process in order to improve both the wear resistance and thermal fatigue properties of HSS rolls.
XIAODAN ZHANG, Doctor of Engineering, and WEI LIU and ANDREW GODFREY, Professors, are with the Advanced Materials Laboratory, Department of Materials Science and Engineering, Tsinghua University, 100084, People’s Republic of China. Contact e-mail: [email protected] QING LIU, Professor, is with the Department of Materials Science and Engineering, Chongqing University, Chongqing, 400030, People’s Republic of China. Manuscript submitted June 14, 2008. Article published online July 15, 2009 METALLURGICAL AND MATERIALS TRANSACTIONS A
II.
EXPERIMENTAL PROCEDURE
The HSS material used in this study was taken from a HSS roll manufactured by a centrifugal casting method. The composition is Fe-2.28C-4.66W-4.79Mo6.05V-7.7Cr-0.5Mn-0.8Si-0.6Ni-0.017S-0.026P (wt pct). The composition of the alloy was determined via wet chemical analysis. For this, the alloy was dissolved in aqua regia, and then the solution was tested via a plasma emission spectrometer (IRIS Intrepid II XSP, Thermo Electron, Madison, WI). A horizontal centrifugal caster was used for producing the experimental roll. Molten metal was poured into a mold rotating at a high speed to form the outer shell. Immediately after solidification of the shell, the core, consisting of nodular graphite cast iron, was cast. The final dimensions of the roll were 750 mm in diameter (shell thickness: 60 mm) and 130 mm in length. Specimens were obtained from the outer (shell) part of the roll. The specimens were austenitized at 1000 C for either 2, 4, or 6 hours, in each case followed by oil quenching and a triple-tem
Data Loading...
