APPLICATION OF EXPERIMENTAL PLANNING METHODS IN EVALUATION OF СТ3ГПС STEEL QUALITY ASSESSMENT

Abstract

Introduction. Low-carbon low-alloy steels are widely used in construction. Therefore, despite the existence of a significant number of methods and ways to assess their quality criteria, the task of operational forecasting of these criteria is urgent. Difficulties in predicting the quality criteria of metal products from steels lie in the complexity of the technology of their production. If the parameters of the technology deviate from the normative documents, the properties of the material can differ significantly. In this regard, it is proposed to apply the method of experimental planning to estimate the tensile strength of low-carbon steel. Materials and methods. Samples of steel of ordinary quality Ст3Гпс made of a circle with a diameter of 24 mm were studied. The chemical composition of steel and its strength indicators varied within the normative documents in accordance with ГОСТ 380 and ДСТУ 2651. In the state of factory supply, the steel structure was ferritic-pearlitic. The content of the pearlite component, depending on the amount of carbon in the steel ranged from 11,2 to 17,6 %, the remaining fraction fell to ferrite. The results of the experiment. At the first stage of research the analysis of influence of each chemical element of steel on limit of its durability was carried out. To this end, with the help of the program "Expert", implemented on a computer, obtained one-factor models of strength forecast. In the second stage of research, the number of rows was reduced from 32 to 16 by implementing the matrix of experimental planning using the technique of small replicas. This approach significantly reduces the cost of experiments. The obtained multifactor (X1…X5) model for predicting the strength limit of steel St3Gps is adequate according to Fisher's and Cochren's criteria. According to Fisher's criterion, the coefficient of convergence of the results was 1,029 with a critical value of 2,400. The model is also adequate according to the Cochren test of 0,335 with a critical value of 0,547. At the third stage of research, based on the results of the analysis of the coefficients of the multiparameter model, histograms of complex assessment of the influence of chemical composition elements on the strength of steel are constructed. Conclusions. An adequate model for predicting its strength and histograms of the effect of its chemical composition on Ст3Гпс Steel was obtained. It makes sense to use the obtained results for the operational forecast of the strength of low-carbon steels in the state of factory delivery.