The polymorphic metals atomic packing provide the minimum value of the free energy potential in some circumstances and become unstable in others circumstances. In this case at the temperature and pressure change there is a polymorphic transformation. The modifications of polymorphic metal passing one into another with increasing temperature, designated by the α, β, γ and δ letters.
Fig. 1 shows the phase-rule diagrams and changes of the free energy potential of Continue reading →
The outcrop of the crystal screw dislocation, Fig.1.
It creates conditions for the steps formation with the height equal to vector shift dislocation. Especially, they are important for the close-packed faces; in this case, the growth becomes possible even at low degrees of supercooling. The atoms joining to the step leads to spiral growth as each its area has in the initial state a Continue reading →
The requirements to welder qualification test vary for different weld configurations, including the sheet beveling, the sheets preparation to fillet welding, and also the pipe beveling. It is obvious that the qualification test for the sheet beveling allows you only partially to estimate the skills of pipes welding. However, if the welder is attested to the performance of the pipe welding; he is automatically attested to the sheet welding. Also it should be noted that the qualification test on sheet beveling in 3G and 4G positions allows you to attest the welder to all sheets positions. The qualification test for provisions of pipes 6G, 2G or 5G allows Continue reading →
The pore cluster at the root of weld occurs because of the low current, high weld speed and irregular gas feed and lack of welding shielding against intake of moisture.
The pore cluster is a minor defect. The repair is regulated by the regulative documents on welding.
On the picture the pore cluster is visible in the form of the black points located without specified procedure.Continue reading →
At less plastic metals the differences in the characteristics which are obtained in areas of elastic deformation and plastic deformation can be not so noticeable. Therefore, to determine the yield point it is hardly possible to use the «Drop of the Beam» method. The method which is called the «Offset» method gives other opportunities. The dependence curve between tension and deformation is typical for the less plastic metals and is shown in Fig. 1.Continue reading →
