Abstract
The paper presents the results of the research aimed at possibilities of renovation of functional surfaces of back-up rolls that are part of the hot strip rolling mill operating line using new types of additive materials. Experimentally, four melts of alloyed steel were produced in laboratory conditions from which four types of filler materials in the form of wires were made. They were made by pulling through dies to a diameter of 2.4 mm. The renovation of functional surfaces was performed on the batch of rolls with the outer diameter of 1000 mm and length 3000 mm. Cladding technology submerged arc welding (SAW) was applied for cladding of four spirals with 40 mm oscillation onto the base material of the 31CrMoV9 (EN 10085) sub-roll. The base flux marked WLDC 17-AWS A5.17-89 EM13K with basicity index 3 was used for cladding. The four-layer weld deposition was made to eliminate the effect of mixing the surfacing layers with the base material. The refurbished rolls were annealed after welding. Surface quality was assessed by visual inspection (VT) according to EN ISO 17637. The presence of internal errors was determined by ultrasound control (UT) in accordance with EN ISO 11666 and EN ISO 17640. The quality of the clad layers was analysed on metallographic sections using light microscopy. The microhardness of the individual clad layers was evaluated according to Vickers according to EN ISO 9015-2. Based on realized experiments it can be stated that the selected cladding parameter was suitable, and the overlay layers showed no surface or internal defects. Mechanical and tribological tests were carried out, but they showed significant influence of chemical composition of additive materials on mechanical properties, or wear resistance of the layers.
Highlights
Steel making is a technologically demanding and complex process during which a significant wear occurs on the metallurgical primary operations technology and equipment
No surface defects were found on the evaluated surfaces
The quality of the overlay was confirmed capillary test according to EN ISO 23277
Summary
Steel making is a technologically demanding and complex process during which a significant wear occurs on the metallurgical primary operations technology and equipment. There are many factors influencing functional parts of this equipment. Direct external factors such as abrasive wear, adhesive wear, erosive wear, thermal fatigue, corrosion at high temperatures in combination with negative effect of fluxes and mould powders, as well as secondary indirect factors that originated during fabrication of the part, or during its previous renovation [1,2,3,4]. Diverse fabrication and inner defects are included, as well as residual stress. In order to provide for a continuous and trouble-free operation of the manufacturing process it is necessary to regularly inspect and maintain the parts and if needed replace them with new ones. Rolls play an essential role in the steel making processes with respect to steel-making on continuous strip rolling mills, processing of slabs on the hot strip rolling
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