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.

Analysis of Surface Roughness and Wear Mechanism when Cutting Hardened Steel Rolls

In modern steel industry, hardened steel rolls are very important tools. The increase of the automobile and the mould keeps the amount of rolls increases fairly quickly. In cutting process, hardened rolls are very difficult to turn or mill, there for, almost all hardened rolls are cut only by grinding, which causes low efficiency, besides in grinding process and a lot of cutting fluid are used. In this paper, surface roughness of workpiece was analyzed of the ceramic tools in different cutting conditions. Wear machanism of crack and abrasive of cutting tools were also analyzed. The experimental and theoretical analysis confirmed that when the ceramic tools cutting cold rolls, the generation and expansion of the cracks the most important role that affect tool life and workpiece surface roughness.

Wear Mechanisms of Ceramic Cutting Tool when Cutting Hardened Steel Rolls

Rolls are important tools in the steel industry. With the increase of the automobile and the mould, rolls are increasing rapidly. Hard rolls are very difficult to cut, almost all hard rolls are cut by only by grinding, and the grinding efficiency is relatively low, and it consumes a lot of cutting fluid. In this paper, the life and tool wear of ceramic tools in different cutting conditions were analyzed. Crack, chipping of cutting tools were analyzed. The experimental and theoretical analysis confirmed that the generation and expansion of the crack are the main wear mechanism of the tool failure, when the ceramic tools cutting cold rolls.

Microstructure and Tribological Properties of a Material with Cementite Eutectic Applied for Metallurgical Rolls

Three prototype metallurgical rolls were produced on the basis of G200CrNiMo4-3-3 material. The method applied for the microstructure forming was different for each roll: the roll marked WOT – as cast state (without a modification and heat treatment); the metallurgical roll marked WMT – during its casting the FeCaSi deoxidizing was applied and then modification by a complex inoculant and argoning; the metallurgical roll marked WNT – subjected to a heat treatment (incomplete normalizing).The mentioned above differences in the technology of making rolls caused changes in their microstructure.The cementite eutectic and pearlitic matrix occurred in each roll. The main differences in the microstructure of cast steel rolls concerned a morphology of precipitates of hypereutectoid cementite. In the WOT roll cementite was mainly in the Widmannstӓtten system. Precipitates of hypereutectoid cementite in the WMT roll occurred along grain boundaries of primary austenite. A large fraction of spheroidal hypereutectoid cementite, precipitated in the whole volume of the primary austenite grain, appeared in the WNT roll. The microstructure influenced the rolls hardness and was equal 260 ÷ 350 HBW.Tribological investigations indicated decreasing the abrasive wear resistance with increasing the hypereutectoid cementite fraction within the primary austenite grains.