Longer Life Wear Parts - Water Quenched vs Creusabro Steels
Over 2 million tonnes of specialist steels are used globally each year for the production of wear-resistant parts. The most commonly used materials are water quenched steels produced by a wide variety of suppliers with known brand names such as Hardox from SSAB, Dillidur from Dillinger Hütte, Raex from Ruukki, Abrazo from Tata, Xar from Thyssen Krupp, Durostat from Voestalpine and Abro from Abraservice, who are part of the distribution network of Industeel, a wholly-owned subsidiary of ArcelorMittal Group.
In the fight against wear, the hardness of a material is a key factor, so in addition to specialist steels, other potential materials are also available such as white cast iron, chromium carbide overlay, nitriding steel and ceramics, with hardness ranging from 400–600 HB for wear-resistant steels and up to 1,600–2,500 HV for ceramics.
To produce the wear part geometries required, however, the materials need to undergo processing such as flame cutting, welding, rolling, bending, drilling, machining or tapping and for this to be successful materials need to be ductile with a minimum of 10–12% elongation. Ceramics can give excellent wear properties but are brittle and difficult to work with, whilst rubbers offer easy working conditions but poor wear resistance at temperatures <80⁰C. Abraservice say that the optimal combination of high strength with elongation is provided by the Creusabro range, an alternative grade of steel where hardness is intentionally limited at the delivery stage for easy processing but the hardening effect occurs (+70 HB) once the parts are subjected to impact or pressure which causes spontaneous atomic rearrangement of the microstructure, known as the TRIP effect.
In addition, by comparison to water quenched steels which can only work up to 250 degrees C before significant softening occurs, Creusabro grades, due to the significant presence of Cr (chromium) and Mo (molybdenum), can also maintain their wear-resistant mechanical properties up to 450 degrees C, making them suitable for higher temperature applications.
Case Study 1 - Creusabro 8000 vs industry standard water quenched 450 HB steel
At a chromium mine in Eti Krom City, Turkey, a comparative test programme was designed to compare the cost of investment for replacement wear edges with the wear life achieved from the components to prove the cost benefits of specialist steel Creusabro 8000.
Mining excavator buckets were fitted with identical bucket wear edges, 30mm in thickness, produced in the two different steels. They were then tested under very harsh abrasive conditions in a side-by-side comparison programme focussing on areas of impact, dragging and sliding within crushed aggregate in two areas mining for chromite (FeCr2O4) and ferrochrome alloy (FeCr).
The results showed that a 20% investment in higher-cost wear-resistant bucket edges provided an increase in wear life of components of up to a +92%, depending upon the size and density of the aggregate being mined, as well as reducing downtime and significantly increasing periods between maintenance.
Case Study 2 – Creusabro 4800 vs industry standard water quenched 500 HB steel
At a German coal-fired power station wear-resistant Creusabro 4800 has been approved for the manufacture of the injection system and the pipe work that transports coal powder to the power station furnace.
The main square pipe work and the elbows positioned upstream from the burner are manufactured in the same material as the intentionally limited mechanical properties of the Creusabro 4800 allows the processing and shaping of the geometries required as well as providing the necessary temperature resistance required for the application from 300–500 degrees C.
The results show that water quenched materials cannot operate above 250 degrees C, so the wear resistance, ease of processing and working temperature of Creusabro 4800 all meet the application requirements.
As a result of this Creusabro 4800 has been approved and is in use with power suppliers EON (Germany), ENEL (Italy) and EDF (France).
Creusabro is a registered trademark of Industeel ArcelorMittal.
