TPT March 2014

Technology News

Steel castings for tube mill rolls with fatigue resistance

The low-carbide microstructure of the GP4M material is also of benefit during the manufacture of rollers. This means that thermal internal stresses between case and core occur in heat treatment during heating up and cooling down, since the core lags in terms of temperature depending on the wall thickness. During hardening the thermal internal stresses are overlaid by additional transformation internal stresses, so that in the case of standard material GX155CrVMo12-1 the crack risk is extremely high, because it is not good at accepting tensile internal stresses due to its carbide network. The trans- formation behaviour of GP4M cast steel material is even slightly more beneficial than in the case of standard material GX155CrVMo12-1. This means that quenching can take place more gently during heat treatment without the material having a reduced hardness level. With the use of the GP4M material, the realisation of more complex roller geometries is easier than with previously available standard materials. With a settable working hardness of up to 60 HRC and a tougher microstructure, the GP4M material also shows itself to have a high resistance against surface fatigue during operational deployment.

with chromium, molybdenum and vanadium, has a pronounced secondary hardness maximum. Setting of a tough martensitic microstructure matrix with a hardness of 58-60 HRC can also be achieved in this case through the use of high tempering temperatures. Unlike the case of the carbide-rich standard material GX155CrVMo12-1, the microstructure of the GP4M special material stands out due to the lack of the brittle carbide network. The toughnessandductility is therefore increased in comparison with standard material. This can be noticed especially during operational deployment, where there is a surface fatigue hazard due to continuous over-rolling of the tool. The increased toughness can prevent overload fracture during impact loading, and can also prevent existing surface cracks extending. Shaping roller made of GP4M hardened to 58-60 HRC

ROLLERS and rolling dies are subject to cyclical pressure loads. In addition to sufficiently high hardness and a good resistance to wear, the tool materials used must provide a sufficiently high fatigue resistance against over-rolling, according to Dörrenberg Edelstahl GmbH. In many cases, steel castings made of carbide-rich cold worked steel GX155CrVMo12-1 (M. no.1.2382) are used. This material’s hardness tempering behaviour is characterised by a secondary hardness maximum due to its alloy composition. The setting of a working hardness of 58- 60 HRC can, therefore, take place at tempering temperatures above 500°C, with which the martensitic matrix of its microstructure can decompress considerably and increase in toughness. In addition to this, 1.2382 steel castings contain a carbide volume of around 12 per cent, which has a positive effect on the wear resistance. However, the carbide is formed as a brittle network, which means that cracks form along the carbide network in the case of mechanical overloading or fatigue, and this can result in early failure due to spalling (pitting) or fracture. In this case, the special steel casting material GP4M ® represents a further technical development. Its alloy composition has been optimised so that it shows a comparable hardness tempering behaviour to standard material 1.2382. GP4M, which is alloyed

Dörrenberg Edelstahl GmbH – Germany Fax: +49 2263 79 412 Email: info@doerrenberg.de Website: www.doerrenberg.de

Cutting heavy ID scarf GEBRÜDER Lennartz manufactures and supplies carbide-tipped circular saw blades for the ferrous and non- ferrous industry. service life of the blades was poor and the cost per cut high.

machine manufacturers, have shown the ECOmax Scarf blades achieve up to 7m² of material removal on welded tubes with wall thickness up to 14mm. Further wear life tests and enhancements are planned to improve the blades’ performance.

Because of its special tooth form and cutting geometry, and in combina- tion with a new proprietary coating, the ECOmax Scarf saw blade is suitable for this application. The new design works on single head machines as well as on twin saws with the simultaneous opera- tion of two saw blades. Successful trials and on-going production usage, together with target customers and

The company’s new ECOmax Scarf circular saw blade is customised for cutting tubes and profiles with heavy ID scarf on flying cut-off units. Previously, conventional blades could be heavily damaged after only a few cuts because they cut the high strength weld bead inside the bottom of the tube. The

Gebr Lennartz GmbH & Co KG – Germany

Fax: +49 2191 99 6060 Email: info@lennartz.de Website: www.lennartz.de

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M arch 2014