José Federico Chávez Alcalá

The aging process affects the mechanical properties of steel used in oil and gas pipelines worldwide, causing them to decline the more they are used. The mechanical properties of pipelines that have been in service for more than 20 years are particularly affected. This paper presents a comparison of the mechanical properties of tensile strength, Charpy (CVN) values, hardness, and microstructure under isothermal heat treatment at 500 °C for API 5L grade B and X52 low-carbon steels at different times—0 h, 500 h, 1000 h, and 1500 h—simulating the natural aging process. It is important to note that the literature reviewed indicates that the corrosion rate of API 5L steels can be influenced by the aging condition of the material. The microstructure of the steels was observed using scanning electron microscopy (SEM). The mechanical properties of yield stress (σ_Y), ultimate tensile stress (σ_UTS), Charpy energy, and hardness decrease as the aging time increases. Charpy specimens show a decrease in toughness because low-carbon steels become embrittled as the aging time increases. The microstructure of Gr B steel remained constant across all times, at approximately 75% ferrite and 25% pearlite, whereas X52 steel was 77% ferrite and 23% pearlite. Finally, the literature data further indicate that aging can influence the corrosion behavior of API 5L steels.

The new requirements for materials with improved properties and resistance to hazardous aggressive environments is very important in industrial incinerators and stoves. Thus, the present manuscript is dedicated to the study of the chemical interaction between Fe-Cr alloys at high temperatures (500–600 °C). Four alloys with different Al, Si, and Mo chemical composition were tested to determine their resistance to active laboratory conditions. The conditions were established based in those inside waste disposal incinerators. Laboratory equipment was set up to reproduce an enclosed aggressive but controlled atmosphere. Cylinders filled with N₂ and O₂ generated an 8% vol, and other containers produced a 220 vppm of HCl, 360 Vppm of H₂O, and 200 vppm of SO₂. The exposition was not continuous because the goal was to analyze the material response along different exposition times. The corrosion products that resulted after chemical etching were characterized using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and taking an average of various thermo-gravimetric measurements. The main products were Cr₂O₃, Fe₂O₃, Fe_0.6Cr_0.4, and Fe and Cr. The alloy with the best performance was found and theoretical principles of corrosion were analyzed to understand the corrosion mechanisms, which were driven by the formation of non-protective oxides.

Understanding the corrosion mechanism inside waste incinerators is very important in order to prevent possible damage due to high operational temperatures in chemical reactions for burning raw hazardous materials. Moreover, it is critical to understand the corrosion mechanisms to identify whether the oxides formed are protective or not, enabling us to prevent mass change on the steel walls of heat exchangers in waste incinerators. Thus, the present work comprises a high-temperature corrosion study on four Ferritic alloys with different contents of Al, Si, and Mo which are capable of replacing expensive materials such as stainless steel. The corrosion behavior was evaluated in atmospheres with H₂O_(g), HCl_(g), and an additional mixture of both atmospheres at 500 and 600 °C over 300 h. A thicker but porous heterogeneous oxide scale was formed in the HCl atmosphere, mainly composed of Fe₂O₃ and Cr₂O₃. Under the water vapor atmosphere, the presence of (Fe0.6Cr0.4)₂O₃ was observed. Meanwhile, in the mixed atmosphere, the presence of FeCr₂O₄, Cr₂SiO₄, and (CrFe)₂O₃ was observed. The biggest mass loss was measured inside the water vapor atmosphere. In comparison, inside the mixed atmosphere, the oxide scale was thinner. Finally, it was concluded that the alloy with the best corrosion resistance in HCl and H₂O atmospheres was Fe9Cr1.5AlSi3Mo steel.

Nowadays it is common to see the production of complex and critical automotive and aeronautical components reduced in weight for energy efficiency using light alloys with improved microstructural and mechanical properties. The casting processes involved in this trend are strong; in this study, an optimized design of a vertical serpentine channel and a novel design of a horizontal serpentine channel to produce semi-solid slurry (S2S) with thixotropic behavior by self-stirring for rheocasting of A380 and A356 alloys are tested. Simultaneously, chilling during solidification, flow development, and shearing on the alloys to improve the performance of solid fractions and self-stirring at high shear rate are applied. The effects of these conditions on the modification of the morphology transition of the α(Al) phase from dendrite to equiaxed grain are discussed. The results suggest the ability of the mentioned processes to promote the morphological transition of the primary solid due to the produced equiaxed grains of α(Al) phase having sizes between 25–50 µm from A380 alloy processed by vertical self-stirring. On the other hand, the treatment of the A356 alloy using the new horizontal serpentine channel produces equiaxed grains with an average size of 39 µm. Unexpected Si crystals, trapped in the α(Al) phase using both methods with both alloys, are detected. The applied operation parameters were aided by gravity-pouring close to the liquidus temperature, and the obtained microstructural results show the ability for S2S to form alongside thixotropic behavior and non-dendritic solidification by mean of self-stirring in the serpentine channels, suggesting the potential for further experiments under die-casting conditions.

Different processing routes have been developed to increase the strength and hardness of camshafts for automotive applications. In this work, two carbidic austempered ductile irons (CADIs), alloyed with 0.2 and 0.4 wt% Cr, were evaluated to determine their suitability in the camshaft production by microscopy techniques and mechanical tests. The CADIs were produced at austempering temperatures of 265 and 305 °C, during 30, 60, 90, and 120 min. The microstructural characterization was carried out by optical microscopy, while Rockwell C Hardness, tensile, Charpy impact, and block-on-ring wear loss tests were evaluated for mechanical characterization from the camshaft and standard keel block. The volume fraction of high-carbon austenite was determined for the heat treatment conditions by X-ray diffraction measurements. The process window was found in the range from 60 to 120 min, for both austempering temperatures, while the highest amount of ausferrite was obtained at 90 min. The formation of carbides was increased as the chromium content was increased. The highest hardness (49 HRC) and wear resistance (0.252 mm³) were obtained for the lower austempering temperature (265 °C, 90 min) and higher chromium content (0.4%). The highest austempering temperature (305 °C, 90 min) and lowest chromium content (0.2%) allow for obtaining the highest toughness (22.91 J) and elongation (4.2%), while the highest tensile strength (1027 MPa) was obtained for the CADI containing 0.2% Cr heat-treated to 265 °C.

Ductile iron camshafts low alloyed with 0.2 and 0.3 wt % vanadium were produced by one of the largest manufacturers of the ductile iron camshafts in México “ARBOMEX S.A de C.V” by a phenolic urethane no-bake sand mold casting method. During functioning, camshafts are subject to bending and torsional stresses, and the lobe surfaces are highly loaded. Thus, high toughness and wear resistance are essential for this component. In this work, two austempering ductile iron heat treatments were evaluated to increase the mechanical properties of tensile strength, hardness, and toughness of the ductile iron camshaft low alloyed with vanadium. The austempering process was held at 265 and 305 °C and austempering times of 30, 60, 90, and 120 min. The volume fraction of high-carbon austenite was determined for the heat treatment conditions by XRD measurements. The ausferritic matrix was determined in 90 min for both austempering temperatures, having a good agreement with the microstructural and hardness evolution as the austempering time increased. The mechanical properties of tensile strength, hardness, and toughness were evaluated from samples obtained from the camshaft and the standard Keel block. The highest mechanical properties were obtained for the austempering heat treatment of 265 °C for 90 min for the ADI containing 0.3 wt % V. The tensile and yield strength were 1200 and 1051 MPa, respectively, while the hardness and the energy impact values were of 47 HRC and 26 J; these values are in the range expected for an ADI grade 3.

Resumen: Los procesos de soldadura por fricción son utilizados en áreas diversas tales como el sector naval, automotriz y aeroespacial. Estos procesos ofrecen una gran flexibilidad y eficiencia energética en la generación de uniones. La soldadura de fricción por aglomeración es un proceso de unión en estado sólido, en el que una herramienta giratoria opera a lo largo de una línea de unión entre dos piezas generando calor por fricción y agitación mecánica para formar la unión de soldadura. En este trabajo, se presenta el diseño y construcción de una máquina de soldadura de fricción por aglomeración, considerando las etapas: a) diseño de disco de soldadura, b) cálculo en la preparación de láminas, c) selección del motor - tornillo de avance y d) cálculo de la estructura de soporte. En la evaluación del equipo se desarrollaron uniones de soldadura en aleaciones ligeras de Zn-22% Al-2% Cu (zinalco) y Al A380 generando cordones de soldadura con un flujo continuo de material.

This research work reports the effect of boron micro-additions (180 and 470 ppm) on the solidification structure, magnetic properties and hot ductility behavior of an advanced low-carbon highly alloyed twinning-induced plasticity (TWIP) steel. For this purpose, three experimental TWIP steels were fabricated by melting commercial raw materials and casting into metallic molds. Solidification structure was characterized by means of optical and scanning electron microscopy techniques, and a statistical study was carried out to measure dendrite features. A vibrating sample magnetometer was used, at room temperature, to determine magnetic properties, and a X-ray diffraction analysis was performed in order to identify the related phases during magnetic measurements. Finally, the hot ductility in the as-cast condition was evaluated at 700, 900 and 1100 °C, under a constant strain rate of 0.001 s⁻¹. The results indicate that boron micro-additions cause an overall refining solidification structure and austenitic grain size. However, as the boron content increases, segregation of this element promotes formation of ferrite and ε-martensite, leading to ferromagnetic behavior. Nonetheless, with subsequent hot- and cold-rolling, the single austenitic phase is achieved, and this behavior is eliminated. Hot tensile tests revealed that boron micro-addition is beneficial to the hot ductility behavior. The greatest influence was observed for the higher concentration of boron (470 ppm). In comparison with the steel without boron content, the reduction of area (RA) is more than the triple of the hot workability during straining at 900 °C. Thus, present results demonstrate that boron micro-addition has an excellent potential for refining dendritic microstructure and improving the hot-deformation behavior of present low-carbon highly alloyed TWIP steel.

The actual trend in order to supply lightweight critical components to automotive and aeronautical industries is the enhancement of mechanical properties of Al-Si alloys by modifying chemical composition, heat treatments and novel forming processes. Nowadays the top in manufacturing is the development of components reduced in weight replacing in many cases of typical heavy steel and cast iron applications. This work describes the rheological treatment in a binary alloy with 8.79%w of Si and A380 commercial alloy performed by mechanical stirring at low cooling rate, with addition of 100 ppm of Sr, 0.33 of solid fraction, 28.33 s⁻¹ of shear rate and atmospheric pouring in a ductile iron mold. It is reported the accomplishment of control of solid fraction during solidification, aided by a thermodynamic model for calculation of real percent of primary α-Al solid phase during freezing as a function of temperature. The microstructural characterization in both alloys shows a globular α(Al) phase surrounded by fine Si eutectic structure. High Resolution SEM-EDS micrographs and mapping shows the Si distribution in the binary alloy with the most content of the eutectic structure and less in the primary solid. In commercial alloy, Cu and Fe forming coarse precipitates are located outside from α(Al) and eutectic structure, it is reported the chemical microanalysis in this region of the commercial alloy.