Abstract
The object of research is the structural lamellar graphite cast iron, where the carbon equivalent (C eq ) is in the range of (4,214-4,372) % and the carbon content (C) is in the range of (3,425-3,563) %. The aim of research is to describe the distribution of values of tensile strength of cast iron series in the factor space C–C eq at a fixed level of Cr-Ni-Cu-Ti alloyed complex in narrow ranges. To achieve this aim, there are the next objectives. 1. Build a workable analytical description of the impact of the selected input variables on the tensile strength of cast iron. 2. Study the response surface and identify the most informative point of the factor space for further detailed investigation of the microstructure in these points. It is shown that polynomial regression equation provides forecast accuracy, exceeding the accuracy using a linear regression equation in 1,23 times. An existence of a saddle point is revealed on the basis of the canonical transformation of response surface. It is an informative indicator, which suggests that the respective values of the input variables C = 3,492 %, C eq = 4,28 % when the content of alloying elements , form a microstructure that guarantees the value of cast iron tensile strength TS = 203 MPa. In view of the resulting confidence interval, this value with a probability of 95 % is in the range of TS = (193-213) MPa. Metallographic microstructure description in the saddle point is important and can be obtained by the development of modeling results. It is noted that there is a fundamental opportunity to improve accuracy and obtaining more precise description of the response surface – due to numerical building of D-optimal plan or artificial orthogonalization of full factorial experiment , inside the considered in this work
Highlights
Structural cast irons are unique ferrous alloys
In accordance with the technological regulations of the enterprise, samples were selected for chemical analysis, and samples were filled to determine the tensile strength of cast iron in accordance with GOST 27208-87
In accordance with this aim of research, the possibilities are opened for predicting the limit on the tensile strength of cast iron for the described area C–carbon equivalent (Ceq), the calculation of the optimal burden composition and to identify the mechanisms of formation of properties for the described chemical composition range
Summary
Structural cast irons are unique ferrous alloys. Range of their application covers most sectors of the economy thanks to a good combination of performance and processing properties. Cast iron processability allows to control the properties through the effective regulation of the processes of structure formation in the smelting step and the subsequent temperature-time processing This provides the possibility of increasing the mechanical properties or imparting special properties for specific operating conditions: wear resistance, heat resistance, corrosion resistance, specific magnetic characteristics. Despite the above advantages, it is well known the real problems associated with control of properties They are related to multifactor impact on the structure formation processes, as well as to the uncertainty at the stage of establishing of quality dependencies in the chain «chemical composition – structure – properties». At the same time the process of obtaining the results can be implemented only in specific production conditions It is particular noted the relevance of research of che mical composition effect on the mechanical properties of cast iron from the following considerations. A necessity to solve the problem of alloy composition synthesis problem, which provides acceptable strength characteristics, is defining but the priority in its manufacture is to reduce the costs of the smelting process
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