Estudo do critério de Niyama na formação de porosidade em fundidos de aço com distintos intervalos de solidificação

Abstract

This study concerns the analysis of the application of the Niyama Criteria as a tool to predict porosity formation on steel castings made from steel with different solidification gaps. Therefore, test coupons were project in order to allow porosity formation. The test coupons were simulated on the Magma Soft- Ware. The behaviour of temperature gradient, cooling rate, feeding and Niyama were analysed in the software as a function of the three plate thickness. The materials used in the simulation and foundry of the test plates were the carbon steel WCC class, the martensitic stainless steel CA6NM class and the corrosion resistant steel CA15 class. After the test coupons been casted, they were classified according to their material and cut in halves thru their middle. The faces along the test coupon length were milled in order to get accuracy on the analysis phase. The surfaces were inspected with dye penetrate test in order t determine the pore distribution along the profile. The pore location, size and incidence were that after compared to the simulation results. The analysis showed low pore incidence on the thinner test coupons. It also showed that the CA15 steel, which has the largest solidification interval presented fine, pores spread on an extensive area, more than expected from the Niyama criteria for lower values than 1. The steel with smaller solidification gaps showed pores with a larger dimension and more concentration. It was also evidenced the existence of analogy of porosity location and dispersion among the plate size of one material, nevertheless the size of the pore indication increases with the increases of the plate thickness.