Papers by Keyword: Carbon Equivalent

Abstract: Studying how shrinkage porosity changes size when varying the composition of ductile irons is still of interest for manufacturing sound cast parts and defining optimised processing conditions. Usual changes in carbon and silicon contents strongly affect shrinkage, so that a detailed analysis of the effect of alloy composition and of inoculation level on porosity was carried out in the present study. Two test castings have been used to evaluate the extent of porosity formed using different compositions and inoculation levels. It has been observed that increasing carbon content from hypoeutectic to near-eutectic compositions reduces the amount of defects while a further increase of shrinkage porosity is detected for hypereutectic compositions. Thus, a minimum in shrinkage tendency exists for slightly hypereutectic compositions. Although inoculation decreases shrinkage, the relevance of this parameter varies as a function of carbon equivalent.

Abstract: This study examined the effect of fluid convection on microstructures of directionally solidified high-chromium white cast iron (ASTM A532-87 Class III) with carbon equivalents of 4.5. The iron was first melted in a high-frequency induction furnace, and then poured into a sandwiched cylindrical Furan resin sand mold. The middle part is a chilled copper mold kept cold by circulating water, enabling simultaneous directional solidification in the upper and lower zones. The microstructure thus solidified is affected by directionally chilled between these parts. Distribution of temperature in the mold during cast solidification was measured by K-type thermocouples. The measured results show that the lower zone has stronger thermal convection and faster cooling rate than the upper zone. The lower zone has smaller liquidus and solidus gradients than the upper zone.

Abstract: The content of magnesium in various parts of a nodular iron casting is measured by using spectrum analyzer. The results show that the skin of castings has an enrichment of magnesium, and the inner has a gradient distribution of magnesium, not an average distribution. Discussions on the results indicate that bubbles in the liquid metal would not move upward under the action of buoyancy, but migrate toward all directions and the bubble stranded below the surface of the liquid metal form blowholes, because these bubbles can not migrate with the obstruction of oxide films and dendrites. The results of production practices show that increasing carbon equivalent in the liquid metal is helpful to avoid blowhole defects.

Abstract: Establish the uniform regression relation expression for these three parameters including composition of over ten kinds of common steels, composition tempering temperature and hardness (HRC) of steel, which can accurately calculate the relative values of these three parameters of over ten kinds of common steels within the discussed scope. Binary regression analysis can be expanded to any Tempering temperature and each kind of steel grade, and the work can be fulfilled with computer. Furthermore express other thermal treatment process parameters and its corresponding mechanical property of each kind of steel with the uniform mathematic relation, so that related uniform regression relation expression can be used into the actual production process, and this is what the author will complete further.

Abstract: The influence of post-inoculation and of cerium and antimony additions on the solidification process and on the formation of chunky graphite in ductile iron heavy-section parts have been studied previously in the case of near-eutectic alloys. It appeared of interest to complement these works by analysing the effect of carbon equivalent on graphite degeneracy. In the present work, hypo-, hyper- and near-eutectic melts have been cast in large blocks and standard cups. Analysis of the corresponding cooling curves recorded during solidification as well as microstructure observations on these casts have been carried out. A clear effect of carbon equivalent as promoter of chunky graphite formation is observed. The results have been added to the set of data already available and various correlations are discussed.

Abstract: The mechanical properties of temper-grade steels can be modified in a wide range by heat treatment. The principle of heat treatment lies in the good hardenability, so when such steels are welded it is very likely that the heat affected zone is hardened. Considering the fact that in the case of design simplifications it may be needed to weld temper-grade steels, as well therefore it is of crucial importance to eliminate cold cracking. There are many methods available to determine preheat temperature. The applicability of methods for determination of preheat temperature was checked by experimental welding for both two and three dimensional heat conduction. According to our experience the different methods cannot be applied in general namely they are valid only under certain conditions.

Abstract: With the regard to the development of modern car bodies the focus lies on low production costs, environmental sustainability and high security standards. In order to meet these requirements the weight of modern car bodies has to be reduced consistently. Amongst other things, this becomes possible by the use of new high and ultra high strength steels. These materials are characterised by their high strength, good ductility and a high absorption capacity. In addition they have a lower density in comparison to other steels. TRIP and TWIP steel belong to these high and ultra high strength steels as well as iron-manganese steel. The development of new materials also puts new demands on the joining technologies used for producing semi finished products and parts of car bodies. Due to its high flexibility, its good automation and the minor influence on the work piece, laser beam welding is an established procedure in the automotive series production. The high cooling rates in combination with a carbon equivalent of the new materials which is usually higher then 0.4% lead to a martensitic solidification of the weld seam. Martensite is characterized by its low ductility and thus affects the forming capability as well as the absorption capacity of the welded parts. In order to avoid this effect a new process has been developed within the scope of the collaborative research program 362 (SFB 362, 1993-2005) at the Laser Zentrum Hannover. Using that process the weld seam structure is inductively annealed directly after the welding process. Experiments with high strength steel like TRIP700 and H320LA have shown that the tempering leads to an increase of ductility. The process is suitable for butt joints and overlap joints and is to be transferred into industrial usage within the scope of the project “Laser Beam Welding of Car Body Parts Made of High and Ultra High Strength Steel”. Based on the results obtained in the SFB 362 continuous investigations will be made in order to qualify the process for boron alloyed steel and iron-manganese steel.