Effect of Precipitation on Cryogenic Toughness of N-Containing Austenitic Stainless Steels After Aging

This chapter shows the effect of intergranular precipitation on the cryogenic toughness of N-containing austenitic stainless steels in comparison to that for 316-type austenitic stainless steels. First part of the chapter deals with the thermodynamic stability and growth kinetics of the precipitated phases in the austenite matrix based on Thermo-Calc software. To continue, the experimental evolution of precipitation for N-containing steels is compared to that of 316-type steel and the difference between them are explained based on the Thermo-Calc PRISMA-calculated results. Finally, the effect of intergranular precipitation on the cryogenic fracture toughness is also analyzed using Charpy V‐Notch impact test results. The fracture mode is also related to the precipitation characteristics

Application of Phase-Field Method to the Analysis of Phase Decomposition of Alloys

This chapter is focused on the application of the phase-field method to the analysis of phase decomposition during the isothermal aging of alloys. The phase-field method is based on a numerical solution of either the nonlinear Cahn-Hilliard equation or the Cahn-Allen equation. These partial differential equations can be solved using the finite difference method among other numerical methods. The phase-field method has been applied to analyze different types of phase transformations in alloys, such as phase decomposition, precipitation, recrystallization, grain growth, solidification of pure metals and alloys, martensitic transformation, ordering reactions, and so on. One of the main advantages of phase-field method is that this method permits to follow the microstructure evolution in two or three dimensions as the time of phase transformations progresses. Thus, the morphology, size, and size distribution could be determined to follow their corresponding growth kinetics. Additionally, the evolution of chemical composition can also be followed during the phase transformations. Furthermore, both Allen-Cahn and Cahn-Hilliard equations can be solved simultaneously to analyze the presence of ordered phases or magnetic domains in alloys

Precipitation Process in Fe-Ni-Al-based Alloys

This chapter covers first the precipitation and coarsening processes in Fe-Ni-Al alloys aged artificially at high temperatures, as well as their effect on the mechanical properties. These results show the precipitation evolution, morphology of precipitates, coarsening kinetics and mechanical properties such as hardness. Additionally, the effect of alloying elements such as copper and chromium is also studied on the precipitation and coarsening processes. The main results of this section are concerning on the coarsening kinetics and its effect on hardness. Besides, the diffusion couple method is employed to study the precipitation and coarsening process in different Fe-Ni-Al alloy compositions, as well as its effect on the hardness. All the above aspects of precipitation and coarsening are also supported with Thermo-Calc calculations

Assessment of Hardness Based on Phase Diagrams

This chapter summarizes the methodology and development of a general equation, in order to obtain a series of equations to assess the hardness of different Al-Cu-Zn alloys, based on their chemical composition. This methodology produces an assessment of hardness with a maximal deviation of 5%, in as-cast, homogenized and quenching alloys, for both alloys created in laboratories like commercials. This method entails the generation of linear equations by a linear regression method, obtained from a zone of the phase diagram, when the composition is changed from linear to planar form. Therefore, if the chemical composition of samples varies, the percentage of each phase will also vary, causing a change in mechanical properties in a linear manner. If the heat treatments are the same for all samples, then the changes in mechanical properties are proportional for each of them, maintaining the linear relationship in mechanical properties in accordance with chemical composition. This methodology is applicable for any ternary alloy along with its equilibrium diagram

Endurecimiento por precipitación en aleaciones al-4%cu-0.5%mg modificadas con ag

El estudio del endurecimiento por precipitación en la aleación Al-4%Cu- 0.5%Mg con adiciones de 0.5-4%Ag se realizó mediante microscopía electrónica de transmisión (MET) y microdureza Vickers. Las aleaciones fueron homogeneizadas a 525°C durante 7 días y templadas. Los tratamientos de precipitación se realizaron a 150, 200 y 250°C por diferentes tiempos. La adición de hasta 3%Ag promueve un aumento en dureza para todos los tratamientos de envejecido. Adicionalmente, los resultados muestran que la coexistencia de las fases θ’ y Ω son las responsables de promover el aumento en dureza. Por otra parte, los análisis de MET confirman que la fase Ω tiene una estructura fcc, es coherente con la matriz, y su morfología es hexagonal con intercaras alineadas en las direcciones [311]α, [022]α y [111]α. Finalmente, la disminución en la dureza de las aleaciones se atribuye a la desaparición de la fase θ’ y al engrosamiento de la fase Ω

Efecto de la precipitación en la tenacidad criogénica en aceros inoxidables con nitrógeno

Los aceros inoxidables austeníticos JK2, JJ1 y JN1 se envejecieron isotérmicamente a temperaturas de 600 a 900 ºC por distintos tiempos, para estudiar la evolución microestructural y su efecto en la tenacidad a la fractura a temperaturas criogénicas. La energía de fractura Charpy muesca-V a 77 K muestra una significante disminución con el tiempo de envejecido en los aceros JJ1 y JN1 debido a sus altos contenidos de C y N. Las fractografias de MEB de las muestras ensayadas por CMV muestran fractura frágil cuya fracción aumenta con el tiempo y temperatura de envejecido