Analysis of the amount of retained austenite in the structure of steel rolls for sheet rolling

The amount of residual austenite in martensitic roll steels is an important technological parameter of heat treatment, which affects the performance properties of the rolls. But determining its amount in roll steels is a complex and not fully solved scientific and technical problem. The aim of the work was to comparatively analyze the amount of residual austenite in the structure of alloy steel rolls by X-ray diffraction, ultrasonic methods and metallography analysis. However, the qualitative difference of microstructures in the content of the light phase - austenite, confirms the results of X-ray diffraction analysis. No correlation was found between the austenite content in the samples and their hardness. It was found that the X-ray method, based on the comparison of the intensities of the α- and γ-phase lines of iron, overestimates the value of the amount of residual austenite in some samples of roll steels. The results of the analysis of residual austenite by ultrasound rate showed better convergence. The amounts of residual austenite, calculated on the sample of stainless steel (100% γ-Fe), had reduced values (2.6-4.5%). The most accurate results on the amount of residual austenite gave the use of the established regression dependence with the selected standard (2.7-7.8%). This dependence is obtained at the speed of sound in austenite ~ 4000 m / s. It is determined that the application of the ultrasonic method allows to determine the content of residual austenite in the samples of roll steels quite quickly and accurately.

Fatigue and Corrosion Fatigue of the Roll Steels with Surface Nanostructure

Fatigue and corrosion fatigue of 50KhN and 60Kh2M roll steels with surface nanocrystalline structure induced by mechanical-pulse treatment were studied. The increment of fatigue and corrosion fatigue of the steels with surface nanocrystalline structure were shown and revealed the factors which causes this increment.

Testing of thermal fatigue resistance of tools and rolls for hot working

In the present contribution two tests for thermal fatigue testing, which have been developed in our group, are presented. First test has provided internal cooling system of sample, while second has external cooling. For both tests heating and cooling of samples are computer guided that enables very reliable results of testing. The first test is more appropriate for testing the base material, i.e. roll cast irons, roll steels, tool steels. The second test is more appropriate for experiments that are aimed for selection of appropriate tool surface treatment, i.e. laser cladding, nitriding, coating, etc., and to compare and to achieve improved resistance against thermal fatigue of produced surface layers.

Effects of Rare Earths on Inclusions Distribution and Modality of 8Cr4MoV Cold Work Roll Cast Steel

A study of rare earth effects on inclusion modality of 8Cr4MoV cold work roll steels was carried out in the laboratory, the steels smelting by a 50kg vacuum induction furnace, atmospheric casting, processing sample after annealing, then inspecting the steels’microstructure, inclusion modality and composition; The results showed that the steels’ microstructure fine, micro-hardness increased with increasing rare earth content, while the average size of inclusions decreased significantly, also the morphology and composition of inclusions significantly changed from the angular black manganese sulfide to the ball white sulfur oxides of rare earth, and thus played roles of deoxidation, desulfurization, purification and deterioration of liquid steel , it will help improving the fatigue performance of the work roll.

Study on Thermal Fatigue Performance of Cold Work Roll Steel

Thermal stability and thermal fatigue performance tests of four kinds of cold work roll steels were done. There are indications that after isothermal 2～6 hours under conditions of 400°C～720°C, the best is 8Cr5SiMoV steel, its thermal stability grows up as isothermal time increase; the second is 8Cr4MoV steel; the worse are 8Cr5MoV steel and 9Cr3MoV steel; and all the thermal stability of four kinds of cold work roll steels are lower than 400°C. Thermal fatigue performance of four kinds of cold work roll steels are basically same as their thermal stability, i.e. the best is 8Cr5SiMoV steel, and the second is 8Cr4MoV steel.