The forming behaviour at high temperature of a modified 9%Cr-1 %Mo (P91) ferritic steel containing Band Ti for elevated temperature service was investigated. The microstructure of the as-received material is mainly martensite at room temperature, but special etching revealed prior austenite grains of about 25 urn in size. Torsion tests were conducted at temperatures in the range 850 to 1250°C to simulate the hot rolling process under comparable conditions of temperature, strain rate and strain. The deformation data obtained from these tests were correlated with the Garofalo equation with a stress exponent of 4.6 and an activation energy of 315 kJ/mol. This equation was used to predict the formability behaviour for the rolling process and also to determine the maximum forming efficiency and stability of the steel. A temperature of 1200°C is recommended to conduct the forming process.Keywords: 9% Cr steel, P91 steel, creep resistant steel, torsion testing, forming behaviour, efficiency and stability maps. 26 steel research int. 75 (2004) NO.1

The effect of the application of forced convection during the continuous solidification of Al-Si alloys has been presented in this work. The investigation has been made on the hypothesis that as an alloy solidifies under the action of a rotating magnetic field, a nondendritic casting structure would be obtained. The Al-Si alloy has been studied in its three different states (original, modified, and modified with a grain refiner), using a magnetic stirring equipment with permanent magnets, a device that has allowed the study of the effect of the rotational speed (degree of stirring) on the micro-and macro-solidification structure, as well as on the material's mechanical properties. With the purpose of validating the hypothesis, different analyses and tests have been carried out, such as thermal analysis of the solidification process, micro-and macrostructural analysis, and hardness measurements for the different process conditions studied. The results have shown that magnetic stirring affects the cooling curves, expanding the solidification range. A microstructural evolution of the alloys has also been observed, from a 100% dendritic structure to a mature rosette type structure, in addition to a notable decreasing of grain size, which results in the improvement of the material's mechanical behavior.

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This paper presents the characterization of a secondary cone crusher concave liner made of Hadfield steel used in Chilean mining after crushing copper minerals during all service life. During use, a cone crusher concave liner suffers indentation (cold working) and abrasion; this combination provides the concave with a layer that constantly renews itself, maintaining a surface highly resistant to abrasive wear. The results presented here were obtained using optical microscopy, microhardness test, measuring abrasion using the dry sand/rubber wheel apparatus, and x-ray diffraction peaks analysis through the classic Williamson–Hall method. After analysis of results, two hardened surfaces have been found—one a product of heat treatment and the other due to deformation during use. This work proposes ways to explain them; the first one uses a thermodynamic model to calculate stacking fault energy, and the second compares the liner with cold-rolled samples.

The deformation behavior at high temperature of a Type 800 Incoloy alloy reinforced by TiC particles was investigated by tensile and torsion tests at temperatures ranging from 800 to 1 200°C. The as-received material exhibited a microstructure of coarse equiaxic grains with subgrains decorated by small TiC particles. The material showed an activation energy for plastic flow of 400 kJ/mol similar to the activation energy for lattice diffusion in austenitic stainless steels. The stress exponents varied strongly with testing conditions. After testing at temperatures up to 1 000°C, the initial austenitic grains were elongated in the tensile direction, but the subgrain structure did not change with stress. In contrast, a microstructural refinement was observed after tensile testing at 1 100°C, which was associated with a process of dynamic recrystallization that occurs during deformation. At this temperature the deformation behavior of the material can be described by a slip creep mechanism. At the rest of the test temperatures the controlling mechanism is that of constant-structure slip creep.KEY WORDS: iron-base superalloy; microstructure; high temperature mechanical behaviour; constant structure creep.cidate the controlling deformation mechanism, the investigation was completed with a detailed microstructural analysis of the as received and deformed materials. Experimental ProcedureThe as-received material was supplied as a bar of 400 mm, which was prepared by hot rolling a bar of 600 mm in diameter heated to 1 200°C for 45 min and then air cooled. The chemical composition of the alloy used in the present study was determined by Inductively Coupled Plasma, except for nitrogen and carbon that were determined by infrared absorption after combustion in an induction furnace. The composition was the following (wt%): 30Ni-19Cr-0.8Mn-0.5Al-0.5Ti-0.45Si-0.12C-0.01N, balance Fe.The microstructures of the as-received material and after deformation were studied by optical microscopy, and scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) microanalysis. Metallographic preparation included mounting the samples in baquelite and polishing by the conventional method. The microstructure was revealed by etching at room temperature with a solution of 45 mL of HCl, 15 mL of HNO 3 and 20 mL of distilled water.Elevated temperature mechanical properties were characterized by tensile and torsion tests. The tensile tests were performed at strain rates ranging from 3ϫ10 Ϫ6 to 2ϫ 10 Ϫ3 s Ϫ1 in the temperature range 800 to 1 100°C. Tensile samples with a rectangular cross section of 3ϫ5 mm and a gage length of 20 mm were machined in the direction parallel to the bar axis. In order to minimize the effect of oxidation, tensile tests were performed under a protective argon atmosphere. True tensile strains, stresses and strain rates were calculated from the load-deformation curves with the assumption of uniform deformation and conservation of volume.Hot torsion tests were performed at equivalent strain rates ranging f...

Durante la realización de este trabajo se aunaron las fuerzas de dos empresas, una siderúrgica proveedora del alambrón y una fábrica de electrodos de soldadura AWS 70S-6. Éstos se fabrican a partir de rollos continuos en básicamente dos etapas de trefilación: en seco, que consta de 9 hileras aplicando reducciones desde los 6,00 mm hasta los 2,21 mm, y en húmedo (10 hileras) desde los 2,21 mm hasta 0,90 mm, sin tratamiento térmico intermedio. La motivación fue poder utilizar la capacidad instalada de la planta de 1000 ton/mes. Previo a este trabajo, la productividad era cercana a 800 ton/mes. Esta baja productividad se atribuyó principalmente a los cortes no deseados que ocurren durante el proceso de trefilado en húmedo que entorpecen la continuidad de la operación. Este trabajo tuvo como objetivo disminuir la cantidad de cortes en la etapa de trefilación en húmedo, mediante la modificación de la distribución de las tasas de reducción de trefilado, implementando un tren de trefilación dinámico, que consideró las distintas tasas de desgaste de las hileras que se hacen mayores conforme disminuye la sección transversal del alambre. Tras la modificación en la distribución de hileras, se observó una disminución en los cortes por trefilación en húmedo, lo que se tradujo en un aumento de la productividad de la planta y en una disminución del consumo de hileras. Palabras Clave: Trefilación húmeda de aceros; aumento de productividad.

The possibilities to improve the properties of steels for tubes exposed at high temperatures are explored. The mechanical properties and forming behavior of an experimental casting of type 9Cr-ferritic steels, P92, containing 2%W, are studied. The hardenability was determined by means of continuous cooling diagrams associated with hardness measurements and microstructure observations. Tensile tests from room temperature to 650°C were carried out to determine the variation of the strength and ductility in this temperature range. In addition, Charpy impact tests were conducted to characterize the toughness of the steel and the ductile-brittle transition temperature. Finally, hot torsion tests at various temperatures and strain rates were carried out and the generalized stresses and strains to rupture for each test are determined. With these data forming stability maps were generated to characterize the best forming conditions.

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