Wheelsets & bogies ARCTICLOS ARCTICLOS
Figure 1
yield strength multiplied by fracture toughness. It is clear that on the level of pearlitic steels the metallurgical influence on fracture toughness is minimal. This structure must be maintained for reasons of wear resistance, but it is still possible to improve toughness in parallel with the yield strength. As the new proposed steel grade belongs to the same family, Lucchini RS has worked on a special heat treatment to obtain values of fracture toughness for Arcticlos similar to the requirements for EN ER7 wheels. In fact, values obtained from the production of Arcticlos are in the range of 80-
90MPa√m, compared with the required values that are stated conservatively. Other criteria to compare materials in
terms of RCF and fracture toughness are proposed and applied as an aid in advanced mechanical properties comparison but also as a quality validation. The synthesis of these criteria are
represented by the maps in Figures 1 and 2 correlating a cyclic resistance parameter, the cyclic yield strength
Figure 2
the material ductility Ɛƒ and to the fracture mechanics parameter KQ
C.YS, as fatigue parameter directly to . The
cyclic yield strength C.YS is assumed as a threshold for cyclic plastic strain to occur, while the resistance to cyclic plastic strain accumulation before cracking is correlated by the ductility
parameter Ɛƒ. In both maps, the cyclic yield strength
C.YS is assumed as a threshold for cyclic plastic strain to occur. The resistance to cyclic plastic strain accumulation before cracking is correlated by the ductility
parameter Ɛƒ and by the fracture toughness parameter KQ
. These criteria
are currently in use and can provide a first comparison between different wheel steel grades. We can observe the trend of materials for solid wheels and use these maps as a helpful tool for material design. Figures 1 and 2 show that for the pearlitic steel grades, the parameters
true fracture strain Ɛƒ and fracture toughness KQ
decrease when cyclic
yield strength C.YS increases. Superlos and Arcticlos steel grades guarantee the best combination in ductility, fracture
toughness and cyclic yield strength. Micralos steel grade also has excellent properties but this grade has a bainitic structure. Lucchini RS is trying to improve
wheel life with the Superlos, Arcticlos and Micralos steel grades. Superlos is used today for different applications, while using Arcticlos in low- temperature conditions opens up new opportunities for railways. The technology required for engineering and manufacturing railway solid wheels is very complex and expensive because of the very high investment required for installation and managing dedicated production facilities and laboratories, and monitoring new processes as well as research and development. Integrated manufacturing and testing processes are vital to guarantee the production of materials which achieve increasing levels of performance and safety in service. In any case there is one important
point to mention. Aproper product definition is the first step for successful cooperation between railway and manufacturer. IRJ
WE UNITE THE WORLD!
With innovation, best quality and on continuously welded track.
42
IRJ September 2013
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