The Use of Thermal Analysis to Study the Structure and Properties of Roll Steels

Abstract

The possibility of the application of thermal analysis to the selection of a method for heat-treating roll steels is examined. The temperatures that should be used for the solution annealing and quenching of steel 60Kh2SMF produced by electroslag remelting are determined.Given the stiff competition in the current market for rolled products, attention is being focused on the products' quality and the cost-effectiveness of the production process. To a large extent, these two factors depend on the condition of the work rolls of cold-rolling mills. Improving the properties of these rolls is a prerequisite to improving the quality of rolled products, increasing rolling speeds, and increasing the productivity of rolling mills.Tool steels and high-speed steels have been widely used to make rolling-mill rolls. The work rolls of cold-rolling mills are made of high-carbon steels alloyed with chromium, vanadium, tungsten and other elements. The carbon content of the steels is usually within the range 0.6 -0.9%. The grades of the steels are regulated by the standard GOST 3541-79.During service, the rolls are subjected to frequent changes in temperature (the temperature of the roll surface can reach 300°C at the outlet of the deformation zone and be 90 -110°C at the inlet of that zone). The rolls of cold-rolling mills are also subjected to very high contact pressures. As a rule, these pressures are several times greater than the yield strength of the metal at room temperature. Thus, the rolls need to have the appropriate strength and hardness. The hardness of the body of the work rolls is usually within the range 90 -102 HSD (Shore hardness). High hardness is obtained in the steels by quenching them to martensite and subjecting them to low-temperature tempering. The composition and heat-treatment regimes for the steel should optimize the structure of the homogeneous martensite, which contains highly dispersed carbides.In light of the foregoing, the heat treatment which is administered is one of the most important operations in the production of rolls for cold-rolling. To improve that treatment as much as possible, it is necessary to make a detailed study of the different aspects of the phase transformations which take place in alloys during heating and cooling. Other methods besides optical and electron microscopy are now available to perform such studies. Important data on the kinetics of the phase transformations can often be obtained more simply and more quickly by an indirect method -by measuring a given physical characteristic. There is a wide range of physical methods of analysis (dilatometry, differential thermal analysis (DTA), differential scanning calorimetry (DSC), etc.) that make it possible to determine the temperature intervals in which phase transformations take place and obtain information on the critical temperatures for different metals and alloys.In our opinion, DTA and DSC are the most promising of the methods based on thermal analysis. These methods can be used to observe and study structural and phase tr...

Diagnostics and Forecasting of Defects in Rotation Details

“…Analysis of acoustic methods showed that the most satisfactory method to assess the quality of a roll and to control the presence of defects (for example, cracks) in the surface layer of work rolls for cold-rolling mills is the echo method in jet variant. This method is a relatively simple way to detect defects of a mill roll [7][8][9][10].…”