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EQUIPMENT wears when two components or particles slide, roll, scratch or hammer on each other. Even tiny grains of sand can destroy a heavy component made of steel plate when they scratch repeatedly over the surface: an abrasive paper can even remove steel.
Examples for applications with increased wear are linings in chutes for crushers, pipes for dredging, rolling of wheels over rail tracks, shovels which break into stony ground or facings in cement mills.
Early replacement of parts involves enormous costs. Even worse is when a production facility comes to a standstill because of unforeseen failure of a wear part.
The solution is to use wear-resistant steel.
Dillinger Hutte offers heavy plates, which come with a thickness ranging between 6 mm and 400 mm (approximately 200 mm for wear-resistant steel grades).
Modern steel plates get wear resistant through controlled quenching, a process of rapidly cooling steel through the temperature range critical for hardening. Figure 1 illustrates the cooling from austenising temperature – a temperature above 900 deg C depending on the steel grade – to ambient temperature. The quenching process results in a fine grain martensitic microstructure. Today, modern roller quenching lines can ensure very accurate quenching parameters, resulting in homogenous steel properties, excellent flatness, smooth surface and relatively homogenous internal stresses.
Quenching increases the hardness of steel with a relatively low content of carbon and alloying elements up to 500 Brinell or even higher. The advantage of quenched steel compared with normalised steel is its good workability despite the high hardness.
A hardness of 500 Brinell means that a ball made of extremely hard metal is pressed with a force of 30 kN (weight of two cars) into the plate surface. The resulting mark on the surface has a diameter of only 3 mm. This mark would be much larger in conventional steel.
The higher hardness of the plate the more is its resistance to wear. Depending on the wear system, its lifespan can be increased significantly compared with conventional structural steel. For example, Figure 2 shows results of a test in a so-called ‘wear pot’. Abrasion of 400 Brinell steel is approximately one-fourth of a conventional structural steel with a yield strength of 355 MPa (S 355 J2+N is similar to grade 50). Thus, a 400 Brinell grade, like Dillidur 400 V, steel lasts four times longer than conventional structural steel.
But just being hard is not enough. A shovel made of hard steel plate, which breaks easily under rough conditions is not a benefit for the user. Today with the know-how of an experienced heavy plate producer, it is possible to produce a hard wear plate with sufficient toughness and good ductility. Furthermore, a sophisticated metallurgical balance must allow for economical fabrication in the customer’s workshop: the plate should be oxy-cut, bend, drilled, machined and welded in an economical way. Customer-orientated producers give recommendations for processing to their customers.
Dillinger Hutte has been offering the wear-resistant Dillidur brand for almost 50 years. Today, controlled-quenched Dillidur 400 V, 450 V and 500 V are available in a wide range of dimensions even with extreme thicknesses of up to 180 mm. The ‘400’ stands for the nominal surface hardness measured in Brinell. Dillinger Hutte gives a warranty on the surface hardness in a tight range between 370 Brinell and 430 Brinell, for example, for Dillidur 400 V.
However, for economical serial production as in the production site of big OEMs (original equipment manufacturers), plates with exactly the same properties are desired. The controlled parameters in production of Dillidur plates result in a very tight scatter band of the properties. For example, 95 per cent of all Dillidur 400 V plates with thickness up to 50 mm have hardness between 400 and 430 Brinell. Thus, the fabrication conditions as regards the springback when cold forming (bending) are almost identical.
For special applications, Dillinger Hutte can offer specific solutions. For instance, Dillidur 325 L is offered for elevated temperatures in fabrication (hot forming) or in service, while Dillidur Impact offers extra crack resistance. This is essential for thick-wall welded components as in mining shovels or recycling equipment, where a conventional 400 Brinell grade would be too sensitive to cracking in workshop or service. The choice of the right wear-resistant grade is made depending on the application and the fabrication and service conditions. Table 1 shows different Dillidur grades and gives criteria for the right choice.
