Continuous Cooling Transformation of Under-Cooled Austenite of SXQ500/550DZ35 Hydropower Steel

The expansion curves of the continuous cooling transformation of undercooled austenite of SXQ500/550DZ35 hydropower steel at different heating temperatures and cooling rates were measured by use of a DIL805A dilatometer. Combined with metallography and Vickers hardness measurement, the continuous cooling transformation diagrams (CCT) of the studied steel under two different states were determined. The results show that in the first group of tests, after the hot-rolled specimens were austenitized at 920 °C, when the cooling rate was below 1 °C·s−1, the microstructure was composed of ferrite (F), pearlite (P) and bainite (B). With the cooling rates between 1 °C·s−1 and 5 °C·s−1, the microstructure was mainly bainite, and martensite (M) formed as the cooling rate reached 5 °C·s−1. When the cooling rate was up to 10 °C·s−1, the microstructure was completely martensite and the hardness value increased significantly. In the second group of tests, after the hot-rolled specimens were quenched at 920 °C and then heated at an intercritical temperature of 830 °C, in comparison with the first group of tests, and except for additional undissolved ferrites in each cooling rate range, the other microstructure types were basically the same. Due to the existence of undissolved ferrite, the microstructures of the specimens heated at intercritical temperatures were much finer, and the toughness values at low temperatures were better.

Uncertainty of measurement -Important parameter for product conformity assessment

The measurements are widely used to ensure the quality of products. It is known that the measurement process is influenced by many factors which lead to measurement errors. The uncertainty of measurement is an essential parameter because the expression of the results accompanied by uncertainty offers more confidence in the results. The research presented in this article focuses on methods forcalculating uncertainty and explaining the rules for making decisions when we use uncertainty. Two case studies are presented, one for dimensional measurements and the other for the estimation of the uncertainty of Vickers hardness measurement for one material, steel OLC15, in order to establish the relevance of the results and quality assessment. The results obtained on several measurements and the uncertainties of measurement associated are presented in the article and a discussion of the results is undertaken.

Effect of Natural and Artificial Aging on the Mechanical Properties of Two Al-Mg-Si Alloys

AlMgSi alloys (6XXX series) provide a good strength due to the precipitation of β” and β (Mg2Si) phases. They have also very good formability which is required for different forming process after appropriate heat treatments.This work was carried out to investigate the effect of the addition of copper and the excess of Si on the response of natural and artificial aging of two Al-Mg-Si alloys. The aging parameters on precipitation sequence of two Al-Mg-Si alloys with and without excess Si were studied by DSC, MET and Vickers hardness measurement. The combined effect of Cu, Fe and excess of Si was found to accelerate the precipitation of the hardening phases. The additions of copper to the AlMgSi refine the average of the grain size and have a greater hardening effect compared to the excess silicon addition.