Instruments for Magnetic Phase Analysis of Articles Made of Austenitic Corrosion-Resistant Steels

Abstract

A brief review in the field of investigation of properties of austenitic alloys is presented. New instruments developed for nondestructive testing of the phase composition and magnetic properties of austenitic corrosion-resistant steels at the Institute of Metal Physics, Ural Division, Russian Academy of Sciences, are described. The first section of the paper is devoted to such directions as "ferritometry." Instruments intended for the testing of magnetic characteristics of slightly magnetic steels, such as the magnetic permeability and susceptibility, are described in the second section of the paper. I. DETERMINATION OF A FERROMAGNETIC PHASE IN AUSTENITICAND AUSTENITIC-FERRITIC STEELS It is known that service properties of articles made of austenitic and austenitic-ferritic steels not only are determined by alloying but also depend substantially on their structure and phase composition, namely, on the presence (or the absence) of a certain ferrite content [1]. The content of ferrite in many of chromiumnickel steels must vary within exactly defined ranges. For example, the ferrite contents in welding wires of grades ë‚ -08 ï 16 ç 8 å 2 and ë‚ -0 ï 18 ç 8 É 2 Å (in accordance with GOST 2246) are 2-6 and 3-8%, respectively. In the absence of or at a low content of the ferrite phase in the wires, welds are found to exhibit a tendency toward the formation of "hot" cracks; at a higher content of the ferrite phase, the tendency toward a decrease in the plasticity and impact strength after high-temperature holdings (600-800 ° C) and a decrease in the corrosion resistance in corrosive media is observed [2][3][4][5]. From this point of view, requirements for the ferrite phase content (FPC) are more stringent than those for the chemical composition of steel. Therefore, strict requirements are imposed on testing methods since a small inaccuracy in measurements of FPC can cause an erroneous conclusion when estimating the quality of materials. The fulfillment of a given FPC can provide the required level of manufacturing and service properties of steels.The maintenance and testing of the FPC in chromium-nickel steels of austenitic and austenitic-ferritic classes are constituents of measures undertaken to provide good-quality articles in many branches of Russian and foreign industries. These problems are being solved by magnetic ferritometry [6][7][8][9][10].In Russia, the magnetic ferritometry arose and developed virtually independently of foreign ferritometry as one of the trends of magnetic phase analysis in the science of metal physics. Magnetic ferritometry is based on the consideration of the ferrite phase in austenitic and austenitic-ferritic steels as a finely dispersed complexly alloyed ferromagnet whose content and distribution in the paramagnetic matrix are studied by appropriate techniques and equipment [8,[11][12][13][14][15]. Abroad, the testing of the FPC arose as an engineering problem and developed on the basis of the techniques and instruments intended for magnetic measurements of thickness [16][17]. Russian ...