The additive act in three ways Filler Pozzolanic 1. These fine particles accelerate the rate of hydration and precipitation starts.
They contain one or more alloying elements intentionally added to improve one or more properties. The quantities of material used for inoculation neither change the basic composition of the solidified cast iron nor alter the properties of individual constituents. In gray and ductile cast irons, small amounts of alloying elements such as chromium Crmolybdenum Moor nickel Ni are added primarily to achieve high strength or to ensure the attainment of a specified minimum strength in heavy sections.
Otherwise, alloying elements are used almost exclusively to enhance resistance to abrasive wear or chemical corrosion or to extend service life at elevated temperatures. Classification of alloy cast irons Alloy cast irons can be classified as i white cast irons, ii corrosion resistant cast irons, and iii heat resistant cast irons Fig 1.
Fig 1 Classification of alloy cast irons White cast irons White cast irons are so named because of their characteristically white fracture surfaces. They do not have any graphite in their microstructures. Frequently, complex carbides such as Fe,Cr 3C and Cr,Fe 7C3, or those containing other carbide forming elements, are also present.
White cast irons are usually very hard, which is the single property maximum responsible for their outstanding resistance to abrasive wear.
White cast iron can be produced either throughout the section mainly by adjusting the composition or only partly inward from the surface mainly by casting against a chill. The iron cast with a chill is sometimes called as chilled cast iron to distinguish it from the cast iron which is white throughout.
Chilled cast iron castings are produced by casting the liquid metal against a metal or graphite chill, resulting in a surface virtually free from graphitic carbon.
While producing chilled cast iron, the composition is so selected so that only the surfaces cast against the chill are free from graphitic C.
The more slowly cooled portions of the casting are gray or mottled iron. The depth and hardness of the chilled portion is usually controlled by adjusting the composition of the iron, the extent of inoculation, and the pouring temperature.
White cast iron is a cast iron virtually free from graphitic C because of selected chemical composition. The composition is chosen so that, for the desired section size, graphite does not form as the casting solidifies. The hardness of white cast iron castings is controlled by further adjustment of composition.
The main difference in microstructure between chilled cast iron and white cast iron is that chilled cast iron is fine grained and shows directionality perpendicular to the chilled face, while white cast iron is usually coarse grained, randomly oriented, and white throughout, even in relatively heavy sections.
Fine grain white cast iron is normally produced by casting a white iron composition against a chill. The difference reflects the effect of composition difference between the two types of abrasion resistant cast irons.
Chilled cast iron is directional only since the casting, made of a composition that is ordinarily gray, has been cooled through the eutectic temperature so rapidly at one or more faces that the iron solidified white, growing inward from the chilled face. White cast iron, on the other hand, has a composition so low in carbon equivalent CE or so rich in alloy content that gray cast iron is not produced even at the relatively low rates of cooling that exist in the centre of the heaviest section of the casting.
Corrosion resistant cast irons Corrosion resistant cast irons derive their resistance to chemical attack mainly from their high alloy content.
Depending on which of three alloying elements Si, Cr, and Ni dominates the composition, a corrosion resistant cast iron can be ferritic, pearlitic, martensitic, or austenitic in its microstructure. Depending on composition, cooling rate, and inoculation practice, a corrosion resistant cast iron can be white, gray, or nodular in both form and distribution of carbon.
Heat resistant cast irons Heat resistant cast irons combine resistance to high temperature oxidation and scaling with resistance to softening or microstructural degradation. Resistance to scaling depends primarily on high alloy content, and resistance to softening depends on the initial microstructure along with the stability of the C containing phase.
Heat resistant cast irons are generally ferritic or austenitic as cast. C exists predominantly as graphite, either in flake or nodular form, which subdivides heat resistant cast irons into either gray or ductile cast irons.
There are also ferritic and austenitic white cast iron grades, although they are less frequently used. Effects of alloying elements In majority of the cast irons, it is the interaction among alloying elements including C and Si which has the greatest effect on properties.
This influence is exerted mostly by effects on the amount and shape of graphitic C present in the casting. As an example, in low alloy cast irons, depth of chill or the tendency of the iron to be white as-cast depends greatly on the CE, the Si in the composition, and the state of inoculation.
The addition of other elements can only modify the basic tendency established by the C-Si relationship. On the other hand, abrasion resistant white cast irons are specifically alloyed with Cr to produce fully carbidic cast irons.
One of the benefits of Cr is that it causes carbide, rather than graphite, to be the stable C rich eutectic phase upon solidification.These are more recent and more effective type of water reducing admixtures also known as high range water reducer.
The main benefits of super plasticizers can be summarized as follows. Increased fluidity: Flowing. Self-leveling. Self-compacting concrete. 2 Depending on the origin of the raw materials used and the clinker production conditions, cement contains up to 30 ppm hexavalent chromium (chromate).
Nowadays, hexavalent chromium and its content in Portland cement is very actual and often discussed topic.
The Rosin Rammler Distribution (RRD) is applicable to materials that have been ground by a process that breaks uniform brittle particles in a . Admixtures are those ingredients in concrete other than portland cement, water, and aggre-gates that are added to the mixture immediately before or during mixing (Fig. ). These are more recent and more effective type of water reducing admixtures also known as high range water reducer. The main benefits of super plasticizers can be summarized as follows. Increased fluidity: Flowing. Self-leveling. Self-compacting concrete.
The goal of this study was to observe the influence of different ways of addition of ferrous sulphate heptahydrate on the reduction of hexavalent chromium at the hydration of Portland clinker. The reduction of Cr(VI) to Cr(III) in cement is required in order to limit the chromium(VI) content in the leachate below 2 ppm, according to the EC Directive .
Project Code Research Title; S Integrated Research on the Development of Global Climate Risk Management Strategies S Evaluation of SLCP Environmental Impact and Promotion of Climate Change Countermeasures through Seeking the Optimal Pathway.
2 Depending on the origin of the raw materials used and the clinker production conditions, cement contains up to 30 ppm hexavalent chromium (chromate).