Otimização do corte de pontas de um aço livre de intersticiais laminado a quente usando tesoura do tipo guilhotina / Optimization the cut edge of a hot rolled interstitial free steel using a guillotine type shearing machine
AUTOR(ES)
Douglas Luciano da Silva Oliveira
FONTE
IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia
DATA DE PUBLICAÇÃO
21/02/2011
RESUMO
The automotive industry\ s demand for high formability steels for use in exposed body panels motivated the development of several interstitial free (IF) steels specifications at Companhia Siderurgica Nacional. The \"IF-Ti\" steel specification belongs to the special deep drawing steels group (CSN EEP-IF), with yield strength <380 MPa, and among all grades of steel processed in the cold rolling lines is the one with the highest amount of deviation by burr marks and other problems related to shearing. The generation of an excessive burr height is related to a poor cut quality. During the cold rolling process the burr can increase in size, break off, mark the work rolls and therefore increase production costs per deviation and early exchange of cylinders. In the pickling lines, the exit shear is the device responsible for separating the coils welded at the beginning of the process and to define the cutting head and tail characteristics, either through guillotine cutting. Aiming to increase quality, productivity, reduce losses during the process and meet the requirements of internal and external customers, it was necessary to develop the guillotine cutting process of the IF steel sheet extremities (head and tail) in the exit shears of Continuous Pickling Lines #3 and #4 at CSN. Through the cutting simulation in the laboratory, using the same forward speed and rake angle adopted in the field equipment, was evaluated the relationship between the adjustment of clearance between blades and the behavior shear force versus displacement. In addition, through the analysis by scanning electron microscopy (SEM) it was possible to observe the effect of several settings on the fracture surface, identifying the different regions cited in the literature and its relation to the microstructural characteristics and to the material properties. It was found that the shear stress during cutting reduced as the gap increased linearly to a range between 6 and 12%t in samples of IF-Ti steel with 1.5 mm thick. In the micrographs taken by SEM, it was observed that the interfaces between burnished and fracture were irregular in all cases, where an intermediate depth, with mixed aspect between the burnished and fracture depths was related to mismatch of crack fronts mainly due to the large fracture angle. Both cut profiles as the fracture surfaces showed that the burnished depth decreased with increasing the gap to some extent, since from the behavior change of shear stress, it started to increase. It was also possible to verify that the fraction of therollover depth increased as larger gaps were tested and the values achieved were much higher than expected for the rollover characteristics of the respective type of cut indicated by the burnished and fracture depths. The best cutting results were obtained for clearance adjustment between 4 and 8%, resulting in burrs below 1.5%t, smaller rollover depth and more regular burnished/fracture interface than in other clearance ranges tested.
ASSUNTO(S)
aços livre de intersticiais corte por cisalhamento guilhotina guillotine interstitial free steels shearing
Documentos Relacionados
- Aperfeiçoamento do corte lateral de aços livres de intersticiais laminados a quente
- Experimental analysis and theoretical predictions of the limit strains of a hot-dip galvanized interstitial-free steel sheet
- Efeitos da adição de monlibdênio e nióbio na microestrutura e propriedades mecânicas de aço 0,5 %C laminado a quente
- INFLUÊNCIA DA MICROESTRUTURA HETEROGÊNEA NAS PROPRIEDADES MECÂNICAS DE UM AÇO C-Mn LAMINADO A QUENTE E UTILIZADO EM AROS DE RODAS AUTOMOTIVAS
- Effect of Rolling Reduction and Temperature on the Oxide Scale of Hot Rolled Mild Steel Strip