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Differences and Applications of Carburizing and Cabonitriding

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Differences and Applications of Carburizing and Cabonitriding DIFFERENCES AND APPLICATIONS OF CARBURIZING AND CABONITRIDING Francisco GUANÍ, Especialidades Térmicas, S.A. de C.V. Fundidores 18 Zona Industrial Xhala Cuautitlán Izcalli, México, C.P. 54714 Carburizing Carburizado También conocido como Endurecimiento de la Capa. Also referred as Case Hardening. Es un tratamiento térmico que produce Is a heat treatment process that una superficie la cual es resistente al produces a surface which is resistant to desgaste, manteniendo la tenacidad y wear, while maintaining toughness and resistencia en el núcleo. strength of the core. Este tratamiento se aplica a partes de This treatment is applied to low carbon acero bajo carbono después de su steel parts after machining, as well as maquinado, también como a aceros de high alloy steel bearings, gears, and rodamiento de alta aleación, engranes y other components. otros componentes. Carburizing increases strength and El carburizado incrementa la tensión y la wear resistance by diffusing carbon resistencia al desgaste, mediante la into the surface of the steel creating a difusión de carbono en la superficie del case while retaining a substantially acero, creando una capa, mientras que el lesser hardness in the core. This núcleo mantiene una menor dureza. Este treatment is applied to low carbon tratamiento se aplica a aceros bajo steels after machining. carbono después de su maquinado. Strong and very hard-surface parts of Partes con superficies duras de formas intricate and complex shapes can be intricadas y complejas se pueden made of relatively lower cost materials obtener a costos relativamente bajos que that are readily machined or formed ya han sido maquinados o formados prior to heat treatment. previo a su tratamiento. Carburizing Carburizado Principle. Principio. At a high temperature, carbon A una alta temperatura, carbón is continuously added on the es añadido continuamente sobre surface of steel component la superficie del acero de una from a solid, liquid or gas fuente sólida, líquida o gaseosa. source. Depending on time, carbon Dependiendo del tiempo, el diffuses into the steel. carbón difunde dentro del acero. Carburizing depth is La profundidad del carburizado controlled by time, %C and es controlada por el tiempo, %C y temperature. la temperatura. Carburizing Carburizado Is a controlled diffusion Es un proceso controlado por process. la difusión. Knowledge of diffusivity of El conocimiento de la difusividad del carbón en el carbon in steel is needed to acero es necesario para control the diffusion depth. controlar la profundidad de difusión. Carburizing Carburizado Effect of Time. Efecto del Tiempo. Carbon penetration below Penetración de carbón por debajo de la superficie a surface at different times. diferentes tiempos. At a given temperature, A una temperatura dada, doble doubling diffusion depth profundidad de penetración requires four time longer requiere cuatro veces más de carburizing time. tiempo de carburizado. Carburizing Carburizado Effect of Temperature. Efecto de la Temperatura. Temperature and time to obtain a case depth of 1 mm Carburizing time as a function Tiempo de carburizado como una of temperature. función de la temperatura. El tiempo requerido para Time required to achieve alcanzar la profundidad deseada desired case depth decreases disminuye con el incremento de with increasing temperature. la temperatura. Carburizing Carburizado Carburizing Temperature. Concentration of carbon after carburizing. Temperatura de carburizado Concentración de carbón después del carburizado. Carburizing CCT Diagram for 20MnCr5 Steel. Martensite formed at the surface. Core contains bainite along with small amount of martensite. Thick parts may contain some ferrite and pearlite along with bainite at the core. Carburizado Diagrama CCT para un acero 20MnCr5. Martensita se forma en la superficie. El núcleo contiene bainita así como pequeñas cantidades de martensita. Partes gruesas pueden contener algo de ferrita, perlita y bainita en el núcleo. Carburizing Carburizado Carburizing methods: Métodos de carburizado: Gas carburizing. Carburizado gaseoso. Vacuum carburizing. Carburizado en vacio. Plasma Carburizing. Carburizado por plasma. Salt bath Carburizing. Carburizado en baño de sales. Pack Carburizing. Carburizado sólido. Carburizing Carburizado Gas carburizing. Carburizado gaseoso. En una mezcla gaseosa, a presión atmosférica o Gas mixture, carried out at atmospheric pressure, a una baja sobrepresión, en equilibrio or at low overpressure, in thermodynamic termodinámico. equilibrium. Se usan atmósferas activas: endoatmósfera, Used active atmosphere: endo-atmosphere or descomposición de metanol. decomposed methanol. 40% nitrógeno, 40% hidrógeno y 20 % CO, el 40% nitrogen, 20% hydrogen and 20% CO, the resto es vapor de agua y CO2. rest is water vapor and CO2. Para un buen carburizado es necesario regular For a good carburizing is necessary to regulate el potencial de carbono de la atmósfera de 0.8 the carbon potential of the atmosphere from 0.8 a 1.0%. to 1%. Carburizing Carburizado Vacuum carburizing. Carburizado en vacio. It is characterized by the absent of oxygen or other oxidant - maintaining the quality oxide- Se caracteriza por la ausencia de oxigeno u otros free surface. oxidantes, manteniendo una superficie libre de oxido. The vacuum carburizing is faster than in the classical gas. Es un proceso mas rápido que el gaseoso. Higher temperature. Temperaturas más altas. Reduction of deformations and internal Reducción de deformaciones y esfuerzos stresses. internas. Low energy consumption and hydrocarbon. Bajo consumo de energía o hidrocarburo. Carburizing Carburizado Liquid carburizing. Carburizado líquido. Steel is placed into a molten salt bath El acero es colocado dentro de un with the purpose that carbon will baño de sal fundido con el propósito de diffuse below its surface. que el carbón difunda dentro de su Diffusion of carbon into the sample is superficie. greater than nitrogen. La difusión de carbón dentro de la Salt bath containing 20% cyanide muestra es mas grande que el operates between 840 – 900 °C and nitrógeno. with 10% cyanide operates between El baño de sales conteniendo 20% 900 - 950°C. cianuro opera entre 840 – 900 °C, con 10% cianuro opera entre 900 - 950°C. Carburizing Carburizado Pack Carburizing. Carburizado sólido. Sample is packed in a steel container La muestra se empaca en un and the sample is completely contenedor de acero y la muestra es surrounded by granules of charcoal completamente rodeada por carbón with sodium and calcium carbonates. en polvo y carbonatos de sodio y calcio. The sample is heated in a furnace for 12 to 72 hours at 900°C. La muestra se calienta en un horno por 12 a 72 horas a 900°C. Due to high temperature, carbon diffuses into the surface of sample. Debido a la alta temperatura, el carbón difunde dentro de la superficie de la muestra. Carburizing Carburizado Hardness Dureza Carburizing Carburizado P Left: Carbon concentration gradient after Izquierda: Gradiente de concentración de carburizing a 8620 steel for 4, 8 and 16 hours carbono después de carburizar un acero 8620 at 927°C. por 4, 8 y 16 horas a 927°C. Right: Different microstructures after Derecha: Diferentes microestructuras después carburizing a 0.15% C steel from 940°C for de carburizar un acero con 0.15% de C a a) 1 hr, b) 2 hrs and c) 4 hrs. 940°C por ) 1 hrs, b) 2 hrs y c ) 4 Hrs. Carbonitriding Carbonitrurado It is an austenitic (above Ac3) case Es un proceso de endurecimiento de hardening process similar to capa austenítica similar al carburizado, carburizing, with the addition of con la adición de nitrógeno (vía gas de nitrogen (via NH3 gas), used to NH3), usado para incrementar la increase wear resistance and surface resistencia al desgaste, dureza hardness through the creation of a superficial, a través de una capa hardened surface layer. superficial endurecida. This process is applied to produce a hard and wear resistant case. Este proceso se aplica para producir una capa dura resistente al desgaste. The diffusion of both carbon and nitrogen increases the hardenability La difusión de C y N, incrementa la of plain carbon and low alloy templabilidad de acero al carbono y steels, and creates a harder aceros de baja aleación, creando una case than carburizing. capa mas dura que el carburizado. Due to the lower temperature required for the carbonitriding, Debido a la baja temperatura compared to carburizing, distortion requerida en comparación con el is reduced. carburizado, la distorsión se reduce. Carbonitriding Carbonitrurado Variant of carburizing where En una variante del carburizado donde nitrogen (up to 0.5%) is diffused nitrógeno ( arriba de 0.5%) se difunde con with carbon. carbono. The process is applicable to most steels. El proceso se aplica a la mayoría de los aceros. Maximum case hardness 800 HV Dureza máxima de 800 HV. Carried out from 775 to 900 °C in gas or salt bath. Llevado a cabo de 775 a 900°C en gas o Slower process due to lower baño de sal. temperature. Proceso mas lento debido a la baja Nitrogen increases hardenability of temperatura. carburized layer El nitrógeno incrementa la templabilidad Ticker cases are possible in steels de la capa. with no alloying elements. Capas mas gruesa son posibles en aceros sin alear. Carbonitriding Carbonitrurado 2 to 12% ammonia is added to the De 2 a 12% de amoniaco se añade a la carburizing atmosphere, which atmósfera carburizante, la cual provee la provides a source of nitrogen. fuente de nitrógeno. Process variables Variables de proceso. ° Temperature: 775 -900°C Temperatura: 775 - 900 C Composición del gas: CO + amoniaco. Gas composition: CO + ammonia. Carbonitriding Carbonitrurado Case composition. Composición de la capa. Composition of a carbonitrided case La composición de la capa dependerá will depend on the type of steel and del tipo de acero y de las variables de on the process variables such as proceso tales como temperatura, temperature, time and atmosphere tiempo y la composición de la composition. atmósfera. The case depth will be lower in La profundidad de la capa será steels containing strong nitride menor en aceros que contengan formers.
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