For measuring Brinell hardness test is usually used a steel ball 10 mm in diameter and a load 3000kgf. However, since the test conditions such as the hardness and thickness of the sample can vary, may require different type and diameter of the ball, and the value of the applied load. Among other types of balls which can be used it is possible to call a 5-mm ball from the tempered steel and a 10-mm ball from tungsten carbide. For soft metals it is possible to use loadings no more than 500 kgf. The equivalent results can be received with loads from 500 to 3000 kgf. When testing Brinell in the field to create a fingerprint is often used hammer Continue reading →
The crystals growth (Part 4).
The heat released during solidification is removed and the liquid crystal phase, and at a high rate of heat dissipation is high rate of crystal growth. In all cases, the melt from the crystallization front is maintained in a supercooled state, and this supercooling ΔТ determines the rate of crystal growth.
Let’s say that the side grows at the s area of the normal in the direction x with Up speed. During dt the side will promote in the direction of liquid on distance
Welder Qualification Test (Part 5).
After performance of the control welded seam, the designation is applied on it and the name of the welder, position at test is entered, and also sample top tags in case of the pipe welding in provisions 5G and 6G. Further, it is specified in the norms and rules collection whether carrying out nondestructive tests, and also type and quantity of the required control samples is necessary. In general, the welder qualification test requires smaller quantity of samples, than for technology certification. At the welder qualification test some norms and rules collections allow carrying out only nondestructive tests like radiography instead of the usual Continue reading →
The polymorphic transformations in metals (Part 3).
The required for homogeneous nucleation energy fluctuation is so great that it is in solid metals are not usually found. Before overcooling (or overheating) reaches the value at which it is possible to homogeneous nucleation, the germs has originated in the defective areas: on the surface of the crystals, in clusters of dislocations or vacancies on the inclusions of impurities, defects in the packaging. If defects in the polymorphic metal aren’t enough or they have insufficient excess energy, the initial modification strongly overcooled. Especially strongly faultless threadlike crystals overcool.
The lack of root penetration.
The lack of root penetration arises because of small current and high welding speed.
The lack of root penetration is admissible defect. Repair of the lack of root penetration is regulated by regulating documents on welding.