PLASMA STRENGTHENING OF THE SURFACE OF THE ROLLS OF SECTION MILLS

摘要

Improving the durability of rolling-mill rolls is one of the most important ways of lowering the cost of the finished product. The surfaces of parts are strengthened by technologies based on the use of concentrated energy sources - electron-beam and laser treatments [1,2] that expose small areas of the surface to powerful high-density energy flows. The experience of the Krivorozhstal' plant has shown the promise of strengthening the passes of light-section mills by micro-plasma treatment - their durability is increased 40-60 percent [3,4]. The treatment was administered at KrivorozhstaF by an OB-2322 direct-action plasmotron with a 4-mm-diam. nozzle and an intake power of 16 kVA. To roll beams Nos. 12-16 in accordance with GOST 26020-83 in the universal stands of the finishing train of its 450 mill, the West Siberian Metallurgical Combine employs horizontal 900-mm-diam. rolls of cast iron SShKhNF with a maximum hardness of 54 HS. The microstracture of the working layer of the rolls consists of pearlite, cementite, and spheroidal graphite. To improve the service properties of the rolls, the combine resorted to plasma quenching of the lateral surfaces of the roll body. During the rolling of beams, those are the surfaces that are subjected to both mechanical and thermal loads and are thus liable to undergo the greatest amount of wear. The plasma strengthening operation involves high-temperature heating of a section of the surface (the anode spot) by a plasma flow and the section's subsequent intensive cooling at rates high enough to ensure the formation of the austenite-martensite structures normally formed during quenching [2, 5].