Mechanical and microstructural features of plasma cut edges in a 15 mm thick S460M steel plate

In general, the thermal cutting processes of steel plates are considered to have an influence on microstructures and residual stress distribution, which determines the mechanical properties and performance of cut edges. They also affect the quality of the surface cut edges, which further complicates the problem, because in most cases the surface is subjected to the largest stresses. This paper studies the influence of plasma cutting processes on the mechanical behavior of the cut edges of steel and presents the characterization results of straight plasma arc cut edges of steel plate grade S460M, 15 mm thick. The cutting conditions used are the standard ones for industrial plasma cutting. The metallography of CHAZ (Cut Heat Affected Zones) and hardness profiles versus distance from plasma cut edge surface are tested; the mechanical behavior of different CHAZ layers under the cut edge surface were obtained by testing of instrumented mini-tensile 300 µm thick specimens. Also, the residual stress distribution in the CHAZ was measured by X-ray diffraction. The results for the mechanical properties, microstructure, hardness, and residual stresses are finally compared and discussed. This work concludes that the CHAZ resulting from the plasma cutting process is narrow (about 700 µm) and homogeneous in plate thickness

Fatigue Behavior of High Strength Steel S890Q Containing Thermally Cut Straight Edges

This paper evaluates the effect of different thermal cutting methods on the fatigue life of high strength steel S890Q. The investigation covers flame, plasma and laser cutting methodologies, and specimens with rectangular sections and cut straight edges. The experimental program is composed of 30 specimens that were conducted to failure by applying fatigue cycles with a stress ratio (R) of 0.1 in a high frequency testing machine. The resultant best-fit S-N curves have been compared, revealing a better performance for laser cut straight edges. Moreover, the corresponding Eurocode 3 FAT class has been derived for each of the three cutting methods, resulting in FAT160 in all cases. This suggests that the use Eurocode 3 FAT125, which is the fatigue class currently provided for flame cut straight edges, is an overconservative assumption for thermally cut straight edges in steel S890Q, regardless of the thermal cutting technique being used (flame, laser or plasma)

Tensile test models for low-carbon microalloyed steels with high niobium contents

U ovom se istraživanju proučavao utjecaj parametara valjanja (2 redukcijske brzine i 3 brzine hlađenja) i kemijskih elemenata kao što su: C, Mn, Nb, Ti, Mo, Ni, Cr, Cu i B na svojstva čvrstoće niskougljičnih mikrolegiranih čelika s visokim sadržajem niobija (do 0,12 wt. % Nb). U tu je svrhu konstruiran pokusni uređaj zasnovan na inteligentnom dizajnu eksperimenata (DoE), rezultirajući s 26 odljevaka (laboratorijskih odljevaka). Kombinacijom metalografije, Electron Back-Scattered Diffraction (EBSD) i vlačnih ispitivanja proučavalo se kako obradni parametri i kemijski sastav djeluju na čvrstoću. Kada je ispitivanje rezultiralo naprezanjem, rasteznom čvrstoćom, jednoličnom deformacijom ili deformacijom zbog loma, rezultati su statistički analizirani tehnikom višestrukelinearne regresije, koja je dovela do odgovarajućih jednadžbi. Ustanovilo se da se učinak niobija na povećanje čvrstoće smanjuje kako se povećava sadržaj ugljika.In the present investigation, the effect of both: rolling parameters (2 reduction rates and 3 cooling rates) and chemical elements such as: C, Mn, Nb, Ti, Mo, Ni, Cr, Cu and B, has been studied in relation to strength properties in low-carbon microalloyed steels with high niobium contents (up to 0,12 wt. % Nb). For this purpose, an experimental set-up was designed based on an intelligent design of experiments (DoE), resulting in 26 casts (laboratory casts). A combination of metallography, Electron Back-Scattered Diffraction (EBSD) and tensile tests have been performed to study how processing parameters and chemical composition affect the strength. The results, where the proof stress, tensile strength, uniform and fracture elongations are the response variables, have been analysed statistically by means of multiple linear regression technique, leading to response equations. From the results, it was found that the effectiveness of niobium increasing the strength is reduced as carbon content increases

Resilience and ductility of Oxy-fuel HAZ cut

Cutting processes affect the material to a deeper or shallower attached-to-the-cut zone. Its microstructure, its hardness and mechanical properties are changed. Also the cutting process introduces surface roughness and residual stresses. In most cases it is recommended to remove this region by grinding, in order to keep a smoother surface, free from the above mentioned effects. This work presents the characterization results of the Heat Affected Zone (HAZ) of a steel plate of grade S460M, with a thickness of 25 mm, cut by flame oxyfuel gas cutting. The HAZ microstructure is observed (and the depth of the HAZ measured), the hardness profile and the stress vs. strain curves until fracture are measured by testing micro-tensile samples, instrumented with strain gauges. Micro-Tensile specimens are 200 microns in thickness and were obtained from layers of the HAZ at different distances from the oxy-fuel cut. The obtained stress-strain curves are compared with the hardness measurements and the observed metallography

Propuesta de curva S-N de diseño para aceros estructurales con bordes rectos cortados por plasma

Este artículo presenta una propuesta de curva de diseño a fatiga para aceros estructurales con bordes rectos cortados por plasma. El corte por plasma se enmarca, junto al oxicorte y al corte láser, dentro de los métodos de corte térmico. En relación con la vida en fatiga de componentes cortados mediante corte térmico la práctica totalidad de las normas de diseño consideran únicamente el oxicorte, sin que exista respaldo normativo para cortes realizados por plasma o por láser. Por este motivo se presenta en este documento un programa experimental de fatiga (S-N) sobre cuatro aceros (S355M, S460M, S690Q y S890Q) con bordes rectos cortados por plasma. Los resultados obtenidos para cada una de las 40 probetas ensayadas se han usado para determinar la correspondiente clase FAT del Eurocódigo, que ha sido validada finalmente con una amplia revisión de los resultados obtenidos en la literatura especializada.This paper presents a proposal of fatigue design curves for structural steels containing plasma cut straight edges. Plasma cutting is, together with flame cutting and laser cutting, one of the thermal cutting technologies. Concerning the fatigue performance of thermally cut structural components, design standards provide design curves for flame cut straight edges, but both plasma and laser cut straight edges are not covered. For this reason this document presents a fatigue experimental program (S-N) with four steels (S355M, S460M, S690Q y S890Q) presenting plasma cut straight edges. The obtained results in the 40 tested specimens have been used to derive the corresponding Eurocode FAT class, which has been finally validated through its application to a wide number of tests found in the literature.Los autores de este trabajo desean agradecer a la Comisión Europea la financiación del proyecto HIPERCUT: “High Performance Cut Edges in Structural Steel Plates for Demanding Aplications” (RFSR-CT-2012-00027), de cuyos resultados se deriva este artículo

Propiedades mecánicas de las zonas afectadas por un corte láser, corte por plasma y oxicorte de una chapa de acero S460M de 15 mm de espesor

Se presentan los mini ensayos de tracción realizados sobre láminas extraídas en las zonas afectadas por el corte de una chapa de acero S460M de 15 mm de espesor. Los cortes se realizan tanto por láser como por plasma y oxicorte. Se extraen miniprobetas de tracción a diferentes distancias del borde de corte, determinándose cómo varía el límite elástico, la carga de rotura, alargamiento, índice de endurecimiento en función de la profundidad y las diferentes técnicas de corte. Se comparan las profundidades afectadas por el corte y su relación con la microestructura y microdurezas.Mini-tensile tests results are presented. Mini-tensile probes are extracted from Cut Heat-Affected Zones from the cut edge a S460M steel plate with a thickness of 15 mm. Cuts were done by laser beam, plasma arc and oxy-fuel. Minitensile test-piece were extracted at different distances from the cut edge. Yield stress, ultimate tensile strength, elongation, hardening index were obtained vs. distance from cut edge for the different thermal cutting techniques. Comparisons are made of the depth of Cut Heat-Affected Zones and their relation with microstructure and microhardness measurements

Ductilidad y tenacidad de un borde cortado por plasma en una chapa de acero S460M de 15 mm de espesor

Los procesos de corte (y soldadura) son sin duda traumáticos para la microestructura de los materiales, de los que se deriva su comportamiento mecánico. Además esto afecta a la superficie, lo que agrava el problema, pues con frecuencia son las zonas que soportan unos mayores esfuerzos. En este trabajo se propone determinar si un corte por plasma mejora o no su comportamiento mecánico (fundamentalmente de cara a su comportamiento en fatiga bajo cargas alternadas). Se presentan los resultados de la caracterización de un borde cortado por plasma en condiciones industriales. La chapa es de acero S460M de 15 mm de espesor. Se discute la rugosidad superficial introducida en la superficie del borde de corte, la metalografía de la Zona Afectada por el Calor/Corte, el perfil de durezas que se introduce en el material, el comportamiento mecánico del material a diferentes distancias medidas desde la superficie del corte, que se obtiene realizando ensayos de tracción de miniprobetas instrumentadas con bandas. También se presentan las medidas de tensiones residuales, obtenidas mediante difracción de rayos X y se compara el conjunto de resultados.In general, thermal cutting processes of steel plates are considered to have an influence on microstructures and residual stresses distribution, which determines the mechanical properties of cut edges. It also affects the quality of the surface of cut edges, which complicates even more the problem, because in most cases the surface is subjected to the larger stresses. This work deals with the question of whether a plasma arc cutting process has influence on the mechanical behavior of cut edges of steel plate (basically from its future fatigue behavior under alternating loading conditions). The paper presents the characterization results of straight plasma arc cut edges of steel plate grade S460M 15 mm thick, under standard industrial plasma arc cutting conditions. The surface roughness Rz5 of plasma arc cut edges is measured, the metallography of Cut-HAZ (Heat Affected Zone) of cut edges and hardness profiles versus distance from plasma cut edge surface are tested; the mechanical behavior of different CHAZ layers under the cut edge surface, obtained by testing of instrumented (with strain gauges) mini-tensile specimens. Also residual stresses distribution in CHAZ of cut edges is measured by X-ray diffraction and all results are compared

Fatigue performance of thermally cut bolt holes in structural steel S460M

Current fatigue codes only consider the fatigue performance of drilled and punched holes, limiting the use of thermal cutting processes to produce bolt holes. This paper studies the fatigue performance of structural steel S460M plates containing thermally cut bolt holes. The research covers three thermal cutting methods: the traditional one (oxy-fuel cutting) and two more modern processes (plasma and laser cutting). Specimen geometry is defined by a rectangular cross section with a cut hole in the middle. All the specimens were conducted to failure by applying fatigue cycles, the stress ratio (R) being 0.1. The corresponding S-N curve and fatigue limit were obtained for each cutting method. Fatigue results have been compared with previous researches on fatigue performance of drilled and punched holes, and with the predictions provided by current fatigue standards, analyzing the possibility to extrapolate their S-N curves, focused on drilled and punched holes, to thermally cut holes

Efecto del método de corte sobre el comportamiento a fatiga de un acero estructural de alta resistencia S690Q

Este artículo estudia el efecto de los diferentes métodos de corte térmico en la vida a fatiga de un acero estructural de alta resistencia S690Q. Se han seleccionado tres sistemas de corte térmico mecanizado ampliamente utilizados en la industria (oxicorte, corte por plasma y corte por láser) y dos detalles estructurales: bordes rectos cortados térmicamente y orificios obtenidos mediante corte térmico para su posterior empleo en uniones atornilladas. El programa experimental está constituido por 60 probetas, las cuales se han llevado a rotura por fatiga en una máquina de resonancia. El valor de la relación de tensiones (R) seleccionado es igual a 0.1. Por cada combinación de método de corte y detalle estructural se ha obtenido su correspondiente curva S-N y límite de fatiga. Se ha llevado a cabo un análisis de la rugosidad superficial y dureza de la Zona Afectada Térmicamente con objeto de determinar la influencia de los métodos de corte térmico en la vida en fatiga. Los resultados obtenidos se comparan con los valores de diseño propuestos por las normativas de diseño en fatiga, evaluando la posibilidad de extrapolar sus curvas S-N tanto a bordes rectos como agujeros cortados mediante cualquiera de los tres sistemas de corte térmico.This paper analyses the effect of different cutting methods on the fatigue life of high strength steel S690Q. The research covers three cutting methods (oxy-fuel, plasma and laser) and two specimen geometries: plain specimens with rectangular sections and cut edges, and specimens with machined edges and a cut hole in the middle section. All the specimens were conducted to failure by applying fatigue cycles, the stress ratio (R) being 0.1, and the corresponding SN curves were obtained for each combination of cutting method and specimen geometry. Measurements of roughness and hardness have been performed in order to explain the influence of the cutting method on the fatigue life of this particular steel. Fatigue results have been compared with the predictions provided by current fatigue standards, analysing the possibility of extrapolating their S-N curves, focused on oxy-fuel cuts, to plasma and laser cuts.HIPERCUT: High Performance Cut Edges in Structural Steel Plates for Demanding Aplication

Evaluación de las propiedades de tracción mediante ensayos Small Punch en la zona afectada por los cortes térmicos

Los sistemas de corte térmico provocan una alteración de la zona de material anexa a los bordes de corte, pudiendo así afectar a su comportamiento en servicio. Este artículo pretende aplicar la técnica Small Punch para comparar las propiedades a tracción en el material base y en la Zona Afectada Térmicamente (ZAT) generada por los distintos procesos de corte. El material seleccionado es un acero estructural S460M y se consideran tres métodos de corte térmico con gran trascendencia en ingeniería (oxicorte, corte por plasma y corte por láser). En los bordes de corte resultantes tras cada uno de estos tres procedimientos se ha obtenido la microestructura, se han realizado perfiles de dureza y se han determinado las propiedades de tracción mediante probetas Small Punch. Se ha observado una modificación significativa de las propiedades en la ZAT respecto de las obtenidas en el material base y una variación de las mismas en función de la técnica de corte seleccionada.Thermal cutting processes cause variations in the material next to cutting edges, which may affect its subsequent inservice behaviour. The aim of this paper is to apply the Small Punch technique in order to compare the tensile properties of the base material and the Heat Affected Zone (HAZ) generated by different cutting processes. S460M structural steel has been chosen for this purpose, analysing three different thermal cutting methods of great influence in engineering (oxy-fuel, plasma and laser cutting). Microstructure, hardness profiles and tensile properties by means of Small Punch specimens have been obtained at the resulting cutting edges after the employment of each of these three processes. As a result, a significant deviation of the HAZ properties from the ones obtained for the base material has been observed, as well as an influence of the applied cutting method on the alteration of these properties