Defects and Properties of Cast Metals: Cast Iron & Steel
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Solidification Committee
Program Organizers: Mark Jolly, Cranfield University; Charles Monroe, University of Alabama; Brian Thomas, Colorado School of Mines; Peter Lee, University of Manchester
Wednesday 8:30 AM
March 1, 2017
Location: San Diego Convention Ctr
Session Chair: Lifeng Zhang, University of Science and Technology Beijing; Peter D. Lee, The University of Manchester
8:30 AM Introductory Comments
8:35 AM Invited
In-situ Observation of Spheroidal Graphite Formation and Measurement of Apparent Volume Expansion in Ductile Cast Iron: Hideyuki Yasuda1; Akira Sugiyama2; Kohei Morishita1; Tomoya Nagira3; Masato Yoshiya3; Kentaro Uesugi4; Akihisa Takeuch4; 1Kyoto University; 2Osaka Sangyo University; 3Osaka University; 4JASRI / Spring-8
In-situ and time-resolved observation of ductile cast iron solidification with 3.6-3.7mass%C and 0.002-0.04mass%Mg) was performed using synchrotron radiation X-ray. Addition of Mg reduced the temperature range that graphite particles grew as a primary phase and promoted spheroidal graphite formation. However, some of the graphite particles tended to deviate from spheroidal shape and the coupled eutectic of austenite and graphite occurred in Al2O3 crucible. On the other hand, the spheroidal shape remained until the end of solidification and the coupled eutectic did not occur in MgO crucible. SEM observation showed that the crucibles modified types of inclusions in the melt. The types significantly influenced nucleation and growth of graphite. The result provides new insights for controlling microstructure of ductile cast iron. In this presentation, we would present in-situ measurement of stress induced during solidification due to the spheroidal graphite growth and discuss shrinkage defects in the cast iron.
X-ray Synchrotron Tomographic Investigation of Graphite Evolution in Near Eutectic Cast Irons: Mohammed Azeem1; Mathias Bjerre2; Niels Tiedje2; Robert Atwood3; Peter Lee1; 1Manchester University; 2Technical University of Denmark; 3Diamond Light Source
Cast irons are a special class of industrial metallic materials with a wide variety of applications ranging from high pressure internal combustion engines through to energy sector where their damping characteristics are used in various housings. This unique blend of properties is closely associated with the morphology and distribution of graphite phase that has been established empirically and through mathematical modeling over past several decades. Here we present a first 4D (3D + temperature) in situ synchrotron X-ray tomographic investigation of various graphite morphologies during conventional solidification in a near eutectic cast iron alloy. The number density and distribution of regular and degenerated graphite nodules will be discussed and correlated with the austenite shell size. The compact graphite was observed to grow from the sample periphery in a complex branching morphology. Some of these branches were observed to nucleate on surface inclusions.
Microstructural Characterization of Graphite Nodules in Fatigue-tested Ductile Cast Iron: Søren Fæster1; Yubin Zhang1; Niels Hansen1; Dorte Juul Jensen1; 1Technical University of Denmark
Thick-walled ductile iron casts have been studied by applying (i) cooling rate calculations by FEM, (ii) microstructural characterization by 2D SEM and 3D X-ray tomography techniques and (iii) fatigue testing of samples drawn from components cast in sand molds and metal molds. An analysis has shown correlations between cooling rate, structure and fatigue strengths demonstrating the benefit of 3D structural characterization to identify possible causes of premature fatigue failure of ductile cast iron. These results are presented and discussed. Also the first results of synchrotron X-ray residual stress measurements at local sites in the matrix near graphite nodules are presented.
Effect of Molybdenum Content, Pouring Temperature and Cooling Rate on the Casting Defects of High Chromium White Cast Iron: Izudin Dugic1; 1Linnaeus University
High chromium white cast are commonly used in application requiring excellent abrasion resistance, as central parts for pumps. The specifications and requirements applied for the white cast iron components are among the most stringent used within the iron foundry branch. One of the biggest problems for the production of these components is hot tearing. Irrespective of the name, this phenomenon represents the formation of an irreversible failure (crack) in the still semisolid casting. This paper aims to investigate the effect of molybdenum content, pouring temperature and cooling rate on the casting defect hot tearing. The procedure to achieve this was to study one casting component, impeller, in a production scale. The experiments showed that molybdenum content and pouring temperature had an important influence on casting defects. It was also observed that the solidification rate has a strong effect on the hot cracking.
Numerical Predictions of Local Residual Stresses around Individual Graphite Nodules in Ductile Iron and Experimental Validation: Tito Andriollo1; Niels Tiedje1; Jesper Thorborg2; Jesper Hattel1; 1Technical University of Denmark; 2Magma GmbH
Residual stresses in ferritic ductile iron castings have been studied for decades. However, very little attention has traditionally been given to the local residual stresses which may arise in the microstructure as a result of the thermal expansion mismatch between the matrix and the graphite nodules during solid-state cooling. Recently the authors proposed a new model for calculating local residual stresses in ductile cast irons, and showed that they may be 100-150 MPa, hence of the same order of magnitude as the material macroscopic yield stress. These preliminary analyses neglected the influence of important factors such as time-dependent inelastic deformation in the ferrite. In this work, more accurate numerical estimates are proposed on the basis of a detailed experimental characterization of the thermo-mechanical behavior of the matrix at different temperatures. The results are then compared with residual stress measurements from differential aperture synchrotron X-ray microscopy.
10:15 AM Break
10:35 AM Invited
Nucleation and Growth of Graphite in Ductile Cast Iron - Coupling between Experiments and Modelling: Niels Tiedje1; Mathias Bjerre1; Mohammed Azeem2; Jesper Hattel1; Peter Lee2; 1Technical University of Denmark; 2The University of Manchester
Nucleation and growth of graphite in ductile cast iron has been a topic for investigation for several decades. Particularly the degeneration of graphite to forms such as chunky and exploded forms has been discussed in the literature. Models have been developed that are able to describe nucleation and growth of nodules with some precision. For degenerate types of graphite some models have been suggested, but they have not yet been widely used. This presentation shows relations between experimental data and numerical models for solidification of ductile cast iron. Differences between experimental results and models will be shown and discussed. Focus will be on traditional 2D metallographic characterisation of nodules but also 3D tomography data for nodules and degenerate forms of will be presented. Models describing growth of degenerate graphite will be outlined and discussed in relation to new models for growth of degenerate graphite forms.
Effect of Various Aluminum Content on the Formation of Inclusion: Yan Luo1; Lifeng Zhang1; Yang Wen1; Ping Shen1; 1University of Science and Technology Beijing
The effect of various aluminum content on the formation of inclusions in a nitrogen-rich atmosphere was investigated using vacuum induction furnace and high temperature contact angle device. The growth and evolution of the precipitation in a subsurface oxygen-depleted region were evaluated by means of optical microscope, scanning electron microscope and non-aqueous solution electrolysis. The depth of the internal oxide and nitride zones were different in the samples containing various aluminum content. Increasing aluminum content to a given value has an influence on modifying the surface oxide scale composition and increasing its continuity, which gradually decreased the internal precipitation zones with increasing aluminum content. For the sample with higher aluminum content a thick continuous oxide layer formed and completely prevented nitrogen penetration into the bulk of the samples.
Effect of Segregated Alloying Elements on the High Strength Steel Properties: Application to the Large Size Ingot Casting Simulation: Chunping Zhang1; Davood Shahriari1; Abdelhalim Loucif1; Mohammad Jahazi1; Louis-Philippe Lapierre-Boire2; Rami Tremblay2; 1L`École de Technologie Supérieure de Montréal; 2Finkl Steel - Sorel
Macrosegregation is one of the most significant defects which exert a determining effect on the properties of heavy ingots. The objective of this work is to study the influence of segregated solute elements on the physical and mechanical properties of a medium carbon high strength steel during large ingot casting process. The solidification process of a 20 Metric Tons (MT) ingot is simulated using Thercast® FEM code. Different segregation levels of solute elements are picked up from a longitudinal section in the top of the ingot. Input steel data, including physical and mechanical properties, are determined by means of Thermo-Calc®, JMatPro and a material database. Casting parameters are selected according to actual industrial operational conditions used for casting of large size ingots. Thermic and thermomechanic simulations are employed for calculating the solidification time. Results are analyzed in the framework of diffusion controlled solidification theory and the influence of alloying elements.
11:35 AM Keynote
Non-metallic Inclusions and Precipitates in High Quality Steels: Lifeng Zhang1; Seetharaman Sridhar2; 1University of Science and Technology Beijing; 2University of Warwick
Non-metallic inclusions and precipitates in spring steels and oriented silicon steels were extracted via variuous methods. The thermodynamics and kinetics for the generation and growth of these particles were discussed. The quantitative effect of oxide inclusions on the properties of spring steel and AlN and MnS precipitates on the oriented silicon steel were investigated.