Process Metallurgy & Product Applications
In Al-killed steels, the ability to remove sulfur is frequently studied. It has been determined that the presence of silicon affects the sulfur equilibrium. This aids in the ability for the slag to capture sulfur more effectively. A comparison of equations for sulfide capacities in slags was evaluated. The ability to predict final sulfur in an addition to sulfur equilibrium was also investigated. A new equation was suggested to calculate the sulfur equilibrium to be able to predict final sulfur more accurately for the current data set. Also, the accepted conditions for desulfurization were explored. The data set showed good agreement with the accepted conditions needed for desulfurization.
Grain refinement of the as-cast structure of Cr-Ni stainless steel alloys solidified with primary face-centered cubic (FCC), body-centered cubic (BCC) and mixed FCC/BCC phases was experimentally studied using a melt treatment that promotes the formation of heterogeneous nuclei. This melt treatment was designed using solidification simulations with FactSage 7.1 thermodynamic software. Refinement of the primary solid phases was achieved in both cast ferritic and austenitic grades. However, imposing a mixed solidification sequence of FCC and BCC phases resulted in a macrostructure without a recognizable columnar-to-equiaxed transition zone (CET). Non-metallic inclusions in the casting were analyzed using automated scanning electron microscopy/energy-dispersive x-ray spectroscopy (SEM/EDS) method, and compared with the thermodynamic simulations. A computational fluid dynamics (CFD) analysis was employed using ANSYS 18.1 Fluent software to simulate the thermal gradient (G) and isotherm velocity (V) in the casting, and their values were plotted on a Hunt’s criteria map and compared qualitatively to experimental CET position for the different steels.
This study examines plate with a nominal chemistry of 30% Mn, 9% Al and 0.9% C that is precipitation-hardenable and exhibits a range of microstructures and properties strongly dependent on the thermal history. Experimental and modeling techniques have been integrated to accelerate the processing technology of this alloy with the goal of enhanced industrial-scale utilization.
Optimization of laminar cooling practice is essential for achieving the desired microstructure, mechanical properties and weldability of hot-rolled steel products. This paper presents the development of a mathematical model incorporating both heat transfer and phase transformation for the laminar cooling at the SSAB Iowa mill. The model was validated by comparing the predicted finish cooling temperatures and microstructures with the temperatures measured by the in-line pyrometers and the microstructures from metallography performed on final products. The model can also be used as an off-line tool to perform troubleshooting and to optimize the cooling strategy for existing and new products.
In equipment manufacturing, there are occasions that the base metal needs to be hot- or cold-worked prior to welding. After welding, the components have to be submitted to a normalizing or stress-relieving heat treatment. In this work, different low-alloy steel weld metals were obtained by adding different alloying elements such as Ni, Zr, Ti-B and Cr-Mo. The effect of normalizing and stress-relieving heat treatments were investigated by means of microstructural analysis and mechanical properties. It was pointed out the care and potential advantages coming from the careful selection of welding consumable and post-heat treatment of the welding joint.
Dillinger has put a fully vertical caster into operation. The thickness varies from 300 to 600 mm. Each strand consists of nine segments, allowing the ideal strand geometry to be aligned at any position during the casting process. Soft reduction adjustment of these segments guarantees the lowest levels of segregation and microporosity. The new caster offers the advantages of a record-setting maximum slab thickness of 600 mm and solidification solely in vertical orientation. By cutting the slabs with horizontal torch cutters, bending and unbending of the strand is no longer required, and therefore metallurgical benefits for highest quality demands are achieved. This article provides an overview of the design and the functionality of CC6 and gives a first impression of the challenge of casting a slab with a thickness of 600 mm.