Mechanical Properties Of Hot Rolled Steel Research Articles

Influencia de la ubicación y orientación de muestras en las propiedades mecánica del acero estructural laminado en caliente: Reporte experimental

Para un modelado adecuado del comportamiento de las estructuras, es esencial una determinación precisa de las propiedades mecánicas del acero estructural. La caracterización mecánica debe satisfacer las prescripciones de las normas; en consecuencia, las muestras deben ser tomadas de una posición y orientación especifica; y las propiedades obtenidas de estos especímenes son usadas para caracterizar, de manera única, el acero. El proceso de laminado en caliente usado en la manufactura de perfiles de acero estructural, que implica la aparición de tensiones residuales, puede afectar a la homogeneidad e isotropía del producto final; por ello, la uniformidad de las propiedades mecánicas a lo largo de la sección no está garantizada. La variación de estas propiedades depende de la orientación y la locación y es estudiada en este artículo. Un programa de ensayos a tracción ha sido llevado a cabo, donde las curvas esfuerzo – deformación son registradas y usadas para obtener las propiedades mecánicas en condiciones elásticas y plásticas desde diferentes posiciones y orientaciones. No se encontraron trabajos experimentales similares en la literatura, excepto en el caso de acero conformado por doblado en frío. Los resultados no muestran diferencias significativas en la mayoría de casos; no obstante, las propiedades relacionadas con la estricción y falla muestran una clara dependencia con la ubicación. Las diferencias más importantes se hallaron en las muestras localizadas en el centro del ala; además, la investigación realizada denota que la orientación no influye en la variación de las propiedades mecánicas del acero laminado en caliente.

Effect of the Chemical Composition on the Structural State and Mechanical Properties of Complex Microalloyed Steels of the Ferritic Class

The most promising direction for obtaining a unique combination of difficult-to-combine properties of low-carbon steels is the formation of a dispersed ferrite microstructure and a volumetric system of nanoscale phase precipitates. This study was aimed at establishing the special features of the composition influence on the characteristics of the microstructure, phase precipitates, and mechanical properties of hot-rolled steels of the ferritic class. It was carried out by transmission electron microscopy and testing the mechanical properties of metal using 8 laboratory melts of low-carbon steels microalloyed by V, Nb, Ti, and Mo in various combinations. It was found that block ferrite prevails in the structure of steel cooled after hot rolling at a rate of 10–15 °C/s. Lowering of the microalloying components content leads to a decrease in the block ferrite fraction to 20–35% and the dominance of polygonal ferrite. The presence of nanoscale carbide (carbonitride) precipitates of austenitic and interphase/mixed types was detected in the rolled steels. It was established that the tendencies of changes in the characteristics of the structural state and present phase precipitates correlate well with obtained values of strength properties. The advantages of titanium-based microalloying systems in comparison with vanadium-based are shown.

Изучение микроструктуры и механических свойств низкоуглеродистой стали, микролегированной бором

The paper presents the results of the study of non-metallic inclusions, the structure and mechanical properties of low carbon steel, microalloying by boron. The study of the amount and composition of nonmetallic inclusions showed that with the introduction of boron the volume fraction of oxide and oxysulfide inclusions increases and the volume fraction of sulfide inclusions significantly decreases. At the same time, the alloying of steel with boron increases to 99.7% the proportion of inclusions with a size of no more than 5 microns against 80.6% in the metal without boron. In the metal with boron, nonmetallic inclusions larger than 10 μm are absent, while in the metal without boron their share is 13.6%. Studies have shown that in a metal containing 0.011% boron, independent boron-containing inclusions were not detected. Boron was not detected in the composition of the studied nonmetallic inclusions. In all samples, steel nonmetallic inclusions are represented mainly by oxide, oxysulfide and sulfide inclusions. In the boron-free steel, a small amount of perlite is present along with the ferritic phase. Steel microalloying by boron is accompanied by the formation of a dispersed ferrite-bainite structure, which consists of fine-grained ferrite with bainite sites with a tendency to form bainite strips along the rolling direction. The microhardness of ferrite and perlite in steel without boron does not exceed an average of 180 and 214 HV10, respectively. It is noted that the presence of boron in steel in an amount of 0.011% increases the microhardness of ferrite to 260 HV10 and bainite to 335 HV10. The mechanical properties of hot-rolled steel with a thickness of 10 mm from boron-containing low-alloyed steel, due to the predominant formation of small rounded inclusions with a size of no more than 5 microns and the formation of a fine ferrite-bainite structure, are characterized by enhanced strength properties with preservation of plastic characteristics. The absolute values of the yield strength and temporary resistance of steel with boron reach 575 and 650 MPa, respectively. With such strength properties of metal, high plastic characteristics are preserved. Rolled steel without boron is characterized by reduced to 540 and 610 MPa tensile strength and temporary resistance, respectively.

Experimental investigation into the post-fire mechanical properties of hot-rolled and cold-formed steels

Hot-rolled Q235, Q345, and Q420 steel members and cold-formed Q235 hollow sections are widely used in building structures. During fire hazards, steel structures are inevitably exposed to elevated temperatures; provided that structural collapse does not occur after fire events, the residual performance of such structures must be estimated accurately to determine whether they should be dismantled, repaired, or directly reused. Therefore, an experimental investigation was conducted to reveal the post-fire mechanical properties of hot-rolled Q235, Q345, and Q420 steels as well as of cold-formed Q235 steels that underwent different levels of cold working. Specimens were heated to various preselected temperatures up to 1000 °C and subsequently cooled down to ambient temperature via two different methods, namely, air and water cooling. Tensile coupon tests were performed to obtain the post-fire stress–strain curves, elastic moduli, yield strengths, ultimate strengths, and ductility. Additional tests were also conducted to investigate the effects of cyclic heating–cooling. The post-fire mechanical properties of hot-rolled steels changed significantly after exposure to temperatures exceeding approximately 700 °C; the corresponding temperature for cold-formed steels was 300 °C. The influences of different cooling methods were notable, whereas the effects of cyclic heating–cooling were insignificant. Thus, new predictive equations that incorporated the influences of various cooling methods were developed to evaluate the post-fire mechanical properties of both hot-rolled and cold-formed steels studied.

Feasibility of using neural networks for real-time prediction of the mechanical properties of finished rolled products

This article examines the feasibility of predicting the mechanical properties of hot-rolled steel in flat-rolled-products shop No. 10 with the use of artificial neural networks. The mechanical properties are determined by means of a mathematical model constructed on the basis of data on the chemical composition of heats with allowance for the nominal thickness of the finished product, finishing temperature, and coiling temperature. Implementation of the findings is making it possible to reduce labor costs incurred in sample preparation, reduce metal waste, determine the soundness of batches while strip is being coiled, and eliminate the problems of the statistics-based nondestructive testing method currently in use.

Influencing the formation of the steel structure by suitable temperature control in the run-out sections of hot-strip mills

Increased demands on the mechanical properties of hot-rolled steel require a fixed adjustment of the steel structure. A procudure wil be introduced, which influences discrete on/off cooling position elements in the run-out section of a hot-strip mill. The procedure can also be used for continuous water-quantity readjustment. The procedure is divided into two parts: predetermination of the spraying pattern and predetermination of the control decision tables and, secondly, coiler-temperature regulation based on the decision tables