endstream endobj 94 0 obj <> endobj 95 0 obj <>/Font<>/ProcSet[/PDF/Text]>>/Rotate 0/Type/Page>> endobj 96 0 obj <>stream Composition and Cooling Rate of Cast Irons 3. In this article we will discuss about:- 1. Carbon, in cast iron, may be in the combined form as cementite, or in the free form as graphite, or both. Thus, white cast iron is hard and brittle and has a white crystalline fracture because it is essentially free of graphite. 2) You may not distribute or commercially exploit the content, especially on another website. Silicon mainly controls the form of carbon present in the cast iron. Content Filtration 6. White cast iron is of hypoeutectic composition and shows austenite dendrites that have transformed to pearlite during cooling with interdentritic ledeburite eutectic. However, rapid cooling can be used to solidify a shell of white cast iron, after which the remainder cools more slowly to form a core of gray cast iron. Silicon accelerates various reactions taking place during heat- treatment; it decreases solubility of carbon in austenite, increases the diffusion rate of carbon in austenite; raises the austenitising temperature significantly as given in equation 15.2; reduces the volume of cementite in pearlite, i.e., carbon content of pearlite is less than 0.77%, and can be 0.50% with 2.5% silicon. For example, at temperature T (≈ 900°C), austenite has a carbon content of around 1.1% in it. The lower critical temperature of cast iron is calculated as: Lower Critical temperature, °C = 730 + 28 (% Si) – 25 (% Mn) …(15.2). (2004). This material may also be called Ni-Hard 1. January 1993. 15.1 (a) shows that greatest structural strengths is obtained when carbon is about 2.75% and silicon about 1.5%, i.e., when the matrix is completely pearlitic. A subscale of iron silicate forms, which can only be removed by molten salt electrolysis (Kolene process). With a lower silicon content (containing less than 1.0 wt% Si - graphitizing agent) and faster cooling rate, the carbon in white cast iron precipitates out of the melt as the metastable phase cementite, Fe3C, rather than graphite. 15.2 illustrates the effect of section size, (i.e., the rate of cooling) and the carbon equivalent value on the type of structure, and thus, the type of cast iron obtained. González-Viñas, W. & Mancini, H.L. %%EOF DOE Fundamentals Handbook, Volume 1 and 2. Composition of White Cast Iron. Heating the graphitic iron can modify its matrix. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1. Princeton University Press. With the same steel-matrix, the ductility (as given by % elongation) of cast irons changes with different shapes of graphite as given  i.e., ductility appears to be more dependent on shape and size of graphite than on metallic matrix in graphitic irons. For example, Ni-Cr-HC martensitic white cast iron (Nickel-Chrome-High Carbon Alloy), ASTM A532 Class 1 Type A, is martensitic white cast iron, in which nickel is the primary alloying element because, at levels of 3 to 5%, it is effective in suppressing the transformation of the austenite matrix to pearlite, thus ensuring that a hard, martensitic structure will develop upon cooling inthe mold. Depending primarily on composition, cooling rate, and melt treatment, the carbon-rich phase can solidify with formation of either a stable (austenite-graphite) or a metastable (austenite-Fe3C) eutectic. h�b```�P!aAd`B�����L'��x;կK���p�q� W0�wS&Ϲs Malleable irons are difficult to cast (as white iron), and there is restriction about the section-size than S.G. iron. More direct effects of manganese include strong cementite-stabilising effect on eutectoid-graphitisation (around 1% Mn may be added to get pearlitic matrix in graphitic cast irons), hardening of iron, refinement in grains and an increase in strength. B���� " J���-@Lc�Q��A-����'������p 10H�E�.ak�\��p�q s�1�5��\ޖ�O�R6�p0�~�l�cCu��!�h(�1pw*iF �b[�ܭ`>�20|i�] �;2pϬ���` �6�� ISBN 978-0-7506-8391-3. Cast irons are iron-carbon (and silicon) alloys having carbon or carbon equivalent value, more than 2% (actually it is 2.1 1%), i.e., more than the maximum solid solubility of carbon in austenite such that the eutectic reaction occurs during solidification. Fig. Silicon also lowers eutectoid carbon content. Privacy Policy 9. 15.2 shows that pearlitic grey iron of CEV = 4.2, should be of size between 15 mm to 4.5 mm thick plate, or 30 mm to 8.5 mm dia. endstream endobj startxref As was written, cast irons are one of the most complex alloys used in industry. Depending on its content (and the rate of cooling), silicon not only helps to precipitate graphite during solidification, but may also graphitise the secondary as well as eutectoid cementite. A fracture surface of this alloy has a white appearance, and thus it is termed white cast iron. Fig. Gaskell, David R. (1995). The heat-treatment of grey iron can result in other structures of matrix such as tempered martensite, which normally possesses higher strength properties, but the important properties like tensile strength, toughness, and ductility do not change much, because the flakes cause brittle fracture. endstream endobj 98 0 obj <>stream Ni-Hard 1 is an abrasion resistant material used in applications where impact is also a concern as the wear mechanism. William D. Callister, David G. Rethwisch. Before uploading and sharing your knowledge on this site, please read the following pages: 1. As nodule form of graphite in S.G. iron (as well as in malleable iron) is not a sharp stress-raiser, and does not act like a crack, a change in microstructure of the matrix by suitable heat-treatment results in appreciable increase in strength properties of S.G. iron (also of malleable iron), and are thus given different heat treatments. 8���ʓ ��J��P�߄���|]n� d�W����Ś�U����޼�W�������\n�s�>:�-kE��Oa.��2�����II{n���B���dž�2J3hd�[f�m��>6���A,����Ѓ�,lj�Y�2��DRd�m�e�ì��9�xςՌVq������3�ӰKg��_z4��i؈}J2蝈�R�`J�7ͻKy#]ۃ.u�T*@�ͷ��7���-�(����~t�Ng>��=�T��������[2�}�Xۜ,=��o�#ݦmiƿ���f}�^`�o�/�?3������z_�?bZ[���I���,4K D �ג�ń&� Its fracture surface is white, therefore known … It explains how we use cookies (and other locally stored data technologies), how third-party cookies are used on our Website, and how you can manage your cookie options. As the higher carbon contents make them more brittle, industrial cast irons have carbon normally in the range of 2.11 to 4% and silicon 0.5 to 3% (along-with … h�T��N� �����&^.��T�jl��´�X Sz���Y�3��烟���x���Q0-&蝷�S�� �qpd֙�Uk4���3�.S±�}��f�=�S�v�����y�u�{q��,��캻��3w�9�o�'�X�?��x�#����n��Z��I�8Em��j!�V9I)���uV�R��|ibW�B� �I�+��m��R�{1gf��{]�j�r/{�!���a? ISBN 978-1-56032-992-3. Comparison of Properties 4. But, more the graphite formed, lower are the mechanical properties. h޼WmO�8�+��j��ۑVH������LJ�5�m�$H˿�g��4��ޝ"׉=���y�B1΄�Lt���2�znj��=���S�bBB��H��w4"�T"R1i9�h���Ôr�}��ͮ�d&�|*�S��������L�m�0����m6�^N�H�{����?�L. h�bbd```b``�"����d=�`3��% �e��̾&���`qWY�"�4�$c�[�.ش ����� h��P� Cementite is hard and brittle and dominates the microstructure of white cast iron.


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