Possible consequences caused by reducing the number of samples during acceptance tests of a unit of metal products to assess its quality

For 13G1S-U sheet steel and large forgings made of improved 38KhN3MFA-Sh steel, produced by existing technologies, the possible con­sequences for quality assessment of metal products were analyzed related to changes in the number of samples used in testing a single product unit (batch, forging). Based on the calculation of skewness and kurtosis coefficients, the authors estimated the change of distribution type of impact strength values accompanying the change in the number of samples. The sampling of impact strength range values ​​obtained from testing two samples (three possible paired combinations) per unit of products were compared using the Student’s and Smirnov’s criteria, both among themselves and with the original sampling (three samples for evaluating one batch of sheet). The obtained results also showed that in conditions when the statistical nature of values distributions of the metal products quality parameters differs from the normal distribution type, it is necessary to use the criteria of nonparametric statistics. The risks of possible loss of information on the metal products’ quality when reducing the number of samples tested within a single batch were assessed. In order to obtain adequate results of statistical analysis, it is necessary to identify and eliminate possible side effects that distort results of analysis: trends, seasonal fluctuations, and data recording errors. For metal products characteri­zed by the developed heterogeneity of structures, obtaining objective information on the toughness reserve of steels can be obtained on the basis of micromechanical tests of samples whose dimensions are comparable to the scale of structural heterogeneity. The obtained results can be useful in the statistical analysis of production process and product control databases in metallurgy to obtain reasonable technological recommendations (within the framework of operation of the end-to-end quality management system) aimed at improving the uniformity of metal product.