Ricardo Artur Sanguinetti Ferreira

Study of phase transformations In API 5L X80 Steel in order to increase its fracture toughness

Phase transformations in API 5L X80 steel were studied in different thermomechanical sequences with a view to increasing the fracture toughness of this steel. Dilatometry tests performed on the quenched steel detected a phase transformation occurred, during heating, in the temperature range 593-618 K. This phase transformation was identified as the dissolution of M-A islands. Based on preliminary dilatometric tests, ten thermal and thermomechanical treatments were performed on X80 steel samples. Initially, the material was hot rolled and quenched and only quenched. On the material without deformation, aging was also performed at temperatures of 603, 673, 723, 773, 823 and 873 K. These treatments resulted in the formation of the acicular ferrite constituent, among others. Tensile tests showed that the aging treatments produced reductions in yield strength and increases in the elongation and toughness of X80 steel. All the treatments resulted in an increase in the tensile strength of steel.

Development of methodology for measurements of residual stresses in welded joint based on displacement of points in a coordinated table

Residual stresses in a welded joint of ASTM A131 grade AH32 steel was measured either by the X-ray diffraction or by displacements of referenced points measured on a coordinate measuring machine before and after heat treatment. For all tests, the welding was performed with Shielded Metal Arc Welding, vertical-up position, by a certified welder. After welding, some specimens were subjected to marking, made through small holes evenly spaced and mapped on a coordinate measuring machine. After labeling, the samples were subjected to heat treatment at temperatures nearby recrystallization. After heat treatment, the samples were subjected to new measurements by coordinate measuring machine to evaluate the displacements of the points produced by the recrystallization. In parallel, residual stress measurements were made by XRD for validation of this new methodology. The results obtained either by X-ray or by coordinate measuring machine showed a good correlation between the two measurement methodologies employed.

Matrix consolidation mechanism in 1D-Ti/SiC/C composites produced by continuous binder-powder coating

In this workmatrix consolidation mechanism has been investigated in 1D-Ti/SiC/C composites produced by Continuous Binder-Powder Coating - CBPC. Titanium metal matrix composites reinforced with continuous SiC/C filaments were analysed in different densification conditions. The results show that during processing, densification occurs by several mechanisms including a complex elasto-viscoplastic flow and diffusion bonding. The matrix consolidation depends on many processing conditions such as pressure and temperature, mainly. Using correct conditions of pressure and temperature, the titanium matrix composites produced by this process present a good matrix consolidation without porosity and a weak interaction between matrix and fiber. These good agreements between matrix consolidation and weak chemical interaction between matrix and fibre are obtained when pressures up to 150 MPa and temperatures below β-transus are applied. In these conditions, supplementary heat treatments can be performed either in alpha or beta domains.

Evenmatched FCAW process in API 5L X80 steel welded joint

The evenmatched welding conditions in FCAW-G process were used in API 5L X80 steel. In this study, two joint geometries (bevel 25° and 35°) with different process parameters were used. Each type of joint was welded with one type of consumable: AWS E81T1-Ni1C (evenmatched), with variation of heat input. During welding the voltage and current varied in a range, in order to preserve the transfer mode by short circuit. For each welded joint, it was studied the influence of these welding parameters in the weld metals quality and, the influence of the bevel angle in the extent of heat affected zones and their correlated mechanical properties. The microstructures were characterized by optical and scanning microscopy, in which the qualitative analyses of microconstituents were performed in transverse sections of weld bead. The mechanical properties for each condition were obtained by uniaxial tensile, hardness, impact and bending tests, allowing the comparison between the different parameters. The tensile test results obtained with a smaller bezel angle had mechanical resistance slightly higher than those of bigger angle joint. Consumables with the same mechanical strength of the base metal (evenmatched) presented performances consistent with their levels of resistance and proved to be viable, depending on the application.

Study of Sintering Behavior of Ceramic Composite Al2O3-TiO2 Rare Reinforcing with La2O3 Possible Application as Ceramic Cutting Tools

In this work, composite ceramic was produced to base Al2O3 reinforced with 35% weight TiO2 and variation 0-2% La2O3, were evaluated properties to study their microstructural characteristic and mechanical properties as applicable cutting tools. The ceramic composites were produced by thermo-mechanical process. It was observed from the results of XRD after sintering no new phase is formed, besides the characteristics of the precursor oxides. According to the result of particle size analysis before and 24 hours after milling, there was a reduction of the average diameter of agglomerate 95.25% which is suitable to assist sintering of the composite, because this reduction increases the reaction rate the raw material during firing. At microdurezavickers test it was observed that the sample with 1.5% La2O3 showed better hardness results.

Obtaining an Acicular Microstructure by Thermomechanical Sequences in X-80 Steel

Microstructural modification is one of the routes to increase strength and toughness in high-strength low-alloy (HSLA) steels. Considering the good mechanical properties of acicular ferrite, thermomechanical sequences, with continuous cooling or isothermal treatment, were applied in an X-80xa0HSLA steel to obtain dominant acicular microstructure. Electron microscopy and electron back-scattered diffraction (EBDS) analyses were performed to identify and quantify microstructural changes. It was possible to correlate the misorientation boundaries profile with the occurrence of acicular microstructure, which was characterized by a high quantity of substructured and deformed units. Thermomechanical sequences with continuous cooling were more effective for obtaining acicular microstructure than sequences of isothermal treatments.

Effects of Thermomechanical Treatment on the Occurrence of Coincident Site Lattice Boundaries in High Strength Low Alloy Steel

Many studies propose thermomechanical routes to improve HSLA (high strength low alloy) steels by microstructural modification but ignore the study of occurrence of CSL boundaries. The occurrence of these special boundaries is influenced by thermomechanical treatment in which the modification of misorientation profile is related with the increase of Σ3 and Σ11 boundaries and inhibition of Σ5 Σ7 and Σ9 ones. The formation of Σ3 boundaries, beneficial to improve strength, is highly stimulated by this treatment in which deformation plays an important role in the development of CSL boundaries.