TPT July 2010

Thermo-mechanically rolled seamless pipes THE tendency towards lightweight construction in the automotive industry and structural steel works is increasing. In addition the applied load for construction parts is rapidly growing. Therefore the demand for seamless steel pipes with optimised mechanical properties combining high strength with improved toughness continues to rise. Until now the only process for reaching high strength in steel pipe production has been heat treatment. The thermo-mechanical treatment has been used as a successful tool to produce speciality steel products with optimal mechanical properties, but up to now it has not been available for seamless pipes. The objective of a joint R&D project between voestalpine Tubulars and the chair of metal forming at the University of Leoben was the application of thermo-mechanical treatment in the seamless pipe rolling process. Based on a comprehensive analysis of this process the main parameters to reach a fine grained microstructure and optimised mechanical properties were identified. The work was continued by parameter studies through the DoE (Design of Experiments) method and process modelling of the pipe rolling mill. The rapid cooling after the final deformation step at the stretch reducing mill produces the biggest effect in strengthening the material. For this purpose the rapid pipe cooling system was developed and finally installed in the production line in the fiscal year 2007/2008 supplemented by the installation of other necessary equipment. The implemented process technology is the basis for further material and product development for seamless pipes. In addition to the classical approach to increase the mechanical properties through the carbon equivalent by adding more alloying elements the thermo-mechanical treatment provides the tool to influence the mechanical properties through the process parameters in a wide range. The properties can be adjusted in a tight range and fine tuned to customers’ requirements. To implement the innovative project results to the production of seamless pipe the thermo-mechanical treatment was applied to two different products for the utility vehicle industry. The conventional heat treatment was substituted for one product and for the second product the steel chemistry was modified by reducing the volume of expensive alloying elements. Thermo-mechanically rolled seamless steel pipes from voestalpine Tubulars are sold under the brand name ToughTubes. This new product fulfils the following requirements on high strength seamless steel pipes: high hardness, tensile and yield strength combined with exceptional toughness, extremely fine-grained microstructure, improved weldability through the low carbon equivalent, excellent cold formability and improved surface quality. These characteristics make ToughTubes suited for: high- strength line pipe, mechanical tubes, pipe for crane construction and for the automotive industry. voestalpine Tubulars GmbH & Co KG – Austria Fax: +43 50304 63 531 Email: alexandra.zelisko@vatubulars.com Website: www.vatubulars.com

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