Pulse magnetic method [1] of testing mechanical properties is developed in the Institute of Applied Physics of Belarus Academy of Sciences including the strength of low carbon and low-alloyed sheet steels and pipes after hardening, tempering or annealing of products without manufacturing the special pieces using the devices of type IMA and IMPOK, which are widely used in industry. Pulse magnetization of products with superimposed solenoid without core and local measurement of the residual magnetization field is thus executed. However the availability of complex structural transition zones near the seam of welded joint requires at the magnetic testing of mechanical properties significant localization of the residual magnetization field as the parameter of testing.

Research of distribution of residual magnetization field at the magnetization of a product by a superimposed solenoid without core has shown the impossibility of improvement of space localization at the expense of reduction of the sizes of solenoid and amplitude of magnetizing pulses in the place of arrangement of a measuring element. It is established that the magnetization of object by a sequence of pulses with decreasing amplitude generated by two in opposite connected rectangular superimposed solenoids permits to reduce the size of magnetized section for some times in comparison with use of usual pulse mode of magnetization by cylindrical solenoid. Thus the localization has dominant orientation that is important at availability in the object under test of narrow bands of a metal distinguishing a structure, as, for example in the welded joint.

The new device, developed on such basis, executes the magnetization of a section of a product by a sequence of pulses with specially chosen amplitude and form, then with the help of ferroprobe a signal from the magnetized section of a product serving as the parameter of testing is measured. Tests of a device have shown that in mass of main metal a band of the same metal in width of 0, 5 mm having other heat treatment can be found out. As far as between the indications of a device and the temperature of hardening of low-carbon and low-alloyed steels influencing their mechanical properties there is unambiguous correlation, the device can be used for determination the strength of welded joints these steels after their checking on absence of the defects of continuity. So on the welded pipes from low-carbon steel good conformity of the device indications and the distribution of hardness on whole zone of thermal influence and main metal of object is received. Stable correlation between the device indications and the strength is received also at static tension.

Thus the described method of localization of residual magnetization field permits to receive the information on mechanical properties of object from narrow extended zones parallel to the seam of welded joint in the zone of thermal influence of welding and to compare it to the information from a main metal. For establishment of a particular kind of correlation and choice of reject thresholds before the industrial use of the method and the device, parallel measurements on particular objects (type of products, quality of steel, thickness) by direct method on pieces and by magnetic method on a product with the subsequent processing of measuring results is necessary.

REFERENCE

1. M. A. Melgui, V. B. Kratirov, V. F. Matyuk, V. D. Piunov, S. G. Sandomirskii and E. A. Shidlovskaya, New Methods and Means for Magnetic Pulse Testing of Mechanical Properties of Steels, Proc. 12th World Conf. on NDT, Amsterdam, pp. 299-304, 1989