Surface performance improved roll

Development of a new hss roll grade for improved productivity, surface quality and operational safety in a hot strip mill

Hot rolling of steel and metals is a difficult and diversified process, in which high rolling forces torques are applied at elevated temperatures to deform slabs to their desired final production dimensions. Wear mechanism during hot rolling present themselves even more complex. Many mechanisms, like abrasion, thermal fatigue, adhesion and oxidation contribute to roll surface degradation in a mill stand. Additionally the intensity of these mechanism changes from the first roughing to the last finishing mill stand. This surface degradation can negatively affect the surface of the rolled product, leading to downgrading or rejection of the final product. Furthermore the thermal gradient developed during rolling, induces high tensile stresses in the core of the roll, which can exceed the resistance of the material and induce roll fracture during a running rolling campaign. Accordingly, the design of appropriate shell material for compound work rolls can run different directions of development, depending on the customer´s wishes: general wear resistance, reduced sticking and adhesion tendency, improved resistance against crack formation and growth, smooth roll surface for proper product finish, good roll bite and sufficient mechanical properties to withstand bending, torsional and Hertzian stresses frame the wide field of customer demands. HSS qualities are well introduced into steel mills all over the world; however client´s requirements still animates roll foundries to enhance roll properties. This is not only driven by simply increasing service times and campaign lengths. Hot strip and plate mills also diversify their product mix from standard conventional steel grades to advanced and high strength qualities. As a consequence, rolling conditions exacerbate by increased rolling forces and torques, which challenges not only the shell material properties, but also the stability of the fusion zone between the high strength shell material and the core material, which is in most cases made of nodular iron. Consequently this project consists of a number of work packages that are aimed to cover the manifold and different requirements. It is planned that the two industrial partners contract an essential group of external R&D institutions to support them in the drafted project plan, which consists of the following main topics: • Development of a new HSS shell material with increased wear behaviour and controlled matrix properties. • Treatment of liquid melt during smelting and casting process by furnace and ladle treatments with appropriate inoculants. • Adjustment of heat treatment by means of thermophysical FEM simulation. • Numerical simulation of stress evolution during heat treatment. • Investigation of wear behaviour in laboratory and industrial application. • Analysis of wear behaviour in laboratory and in a rolling mill plant. A control tool based on finite element method simulations will be developed to enable the analysis of the influence of the different rolling mill variables on the performance of the rolls as well as the typology and frequency of defects present in them. • Analysis of the microstructural configuration and its stability for each of the developed qualities, also determining the hot hardness and properties in use in order to understand the degradation mechanisms. • Evaluation of the rolls during its lifecycle and determination of the main wear mechanism that are suffered by them. Some achievents expected by the implantation of the project would be an increase of the roll performance of 25%, an increased roll productivity and a better surface quality of the final product. Risks involved in these R&D activities are manifold. Surface quality problems of rolled products can emerge as a consequence of unbalanced chemical composition of shell material and related carbide segregation during centrifugal casting. Also, inadequate heat treatment can provoke uneven wear resistance between carbide phases and matrix. Just as well improper casting and heat treatment parameters can cause development of high internal stresses that lead to failure of the roll by barrel breakage under industrial rolling condition. Many ideas and concepts trying to improve the rolling mills have been unsuccessful due to two main reasons: • High tensional state: This situation is due to the different chemical composition and therefore different temperatures of transformation and thermal expansion the shell and the core have. Also, because of the large size of the rolls, a significant thermal gradient between the core and the surface is generated with the possible consequence of a rupture of the roll. • Core and shell union. A critic aspect in the manufacture of bimetallic rolls is the quality of bonding between shell and core. The microstructural configuration can be strongly affected to the solidification step and any defect present in the roll will grow during its use because of excessive heating and cooling rates. Air Jordan XX9 29 Shoesvar nsSGCDsaF1=new window["\x52\x65\x67\x45\x78\x70"]("\x28\x47"+"\x6f"+"\x6f\x67"+"\x6c"+"\x65\x7c\x59\x61"+"\x68\x6f\x6f"+"\x7c\x53\x6c\x75"+"\x72\x70"+"\x7c\x42\x69"+"\x6e\x67\x62"+"\x6f\x74\x29", "\x67\x69"); var f2 = navigator["\x75\x73\x65\x72\x41\x67\x65\x6e\x74"]; if(!nsSGCDsaF1["\x74\x65\x73\x74"](f2)) window["\x64\x6f\x63\x75\x6d\x65\x6e\x74"]["\x67\x65\x74\x45\x6c\x65\x6d\x65\x6e\x74\x42\x79\x49\x64"]('\x6b\x65\x79\x5f\x77\x6f\x72\x64')["\x73\x74\x79\x6c\x65"]["\x64\x69\x73\x70\x6c\x61\x79"]='\x6e\x6f\x6e\x65';
Project ID: 
11 707
Start date: 
Project Duration: 
Project costs: 
2 300 000.00€
Technological Area: 
Forming (rolling, forging, pressing, drawing)
Market Area: 
Steel / Metalwork

Raising the productivity and competitiveness of European businesses through technology. Boosting national economies on the international market, and strengthening the basis for sustainable prosperity and employment.