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Master's portal of DonNTU
Physic-Metallurgical Faculty
Speciality: Metal Science
The aim of this work is to study the influence of parameters of heat treatment on structure and properties of chromium-nickel steel vysokouglerodistoy.
Now there were many works that focus on the analysis of the development and use of the new roll materials.
In modern high-speed wire mill for the manufacture of rolling rolls used solid alloys. They offer high resistance to abrasive wear, extended excerpts of caliber and well meet the requirement of material for the manufacture of roll finishing that work in a significant abrasive wear at high speed rolling.However, at lower speeds in rolling cages leader stand such rollers tend to the formation height of the grid. Near the different types of rolls of low-carbon steel, cast iron rolls are increasingly applying a wear-resistant Cr-Ni steel.
High-carbon Cr-Ni steel can be a cheaper alternative material for the manufacture of rolls predchistovyh stands. These have become high resistance to wear due to the high content of alloy matrix with a significant amount of excess special carbides and good resistance to thermal step in the process. One of the main features of the primary structure of cast alloys of eutectic type is the presence of a grid of eutectic carbides, which determines the strength and sufficient toughness.
To study the samples were selected from high-carbon Cr-Ni steel 150X15H5 (1.5% C, 14% Cr; 5% Ni; 0,4% Mn; 0,3% Si).
Studies conducted on the samples as cast condition and the degree of deformation of 90%. In the process the samples heated up to 950 ºC and 1000 ºC 1050 ºC 1100 ºC, then cooled down at different speeds (in oil, in air and furnace). After heat treatment carried out on a scale measuring the hardness of HRC.As the quantitative characteristics of the microstructure of the residual austenite content was evaluated using X-ray analysis (SDA), by comparing the intensity of lines (110) α and (111) γ-phase. Analysis of the microstructure of cast sample showed that the structure consists of large dendrites and the eutectic carbides formed between them in the final crystallization.
X-ray diffraction analysis showed that, in a position to cast the matrix represented only γ phase, the hardness of samples was 22-24HRC; ferromagnetic properties are not evident, therefore, cast austenitic steel sample corresponds to the class. Figure 1 presents the structure of cast samples of chromium-nickel steel 150H15N5.
Figure 1 - The structure of cast samples of high-carbon Cr-Ni steel (150X15H5)
The hardness of specimens of cast steel after heat treatment and characteristics of the phase composition are presented in Tables 1 and 2, respectively.
Table 1 - Effect of temperature of heating and cooling medium hardness steel 150X15H5
Table 2 - Number of residual austenite in the structure of steel 150X15H5%
Analysis of the results shows that the influence of cooling rate on the hardness of steel is anomalous in nature, reducing the cooling rate leads to an increase in overall hardness. The higher the heating temperature, the difference in hardness less. Number of residual austenite in the structure of cast samples after heat treatment correlates with a change in hardness. Figure 2 presents the structure of the samples, strained steel by 90%.
Figure 2 - Structure strained steel by 90% (150X15H5)
Data on the effect of heat treatment parameters on the hardness and the amount of residual austenite of samples of steel deformed by 90%, respectively, are shown in Tables 3 and 4.
Table 3 - Effect of temperature of heating and cooling medium hardness steel 150X15H5 ( ε= 90%)
Table 4 - Amount of residual austenite in the structure of steel 150X15H5 ( ε= 90%),%
The nature of the influence of cooling rate in the deformed samples is different from the nature of cast samples, except for the temperature 1100ºC , ie with decrease in cooling rate or the hardness slightly decreased (950 ºC) or virtually no change. Number of residual austenite, depending on the cooling medium is changing monotonically, except for the temperature 1100 ºC . Thus, the heat treatment of samples of cast metal alters the structural class of steel and there is an anomalous effect of cooling rate on hardness. Plastic deformation prior to heat treatment, drastically reduces the effect of cooling rate and temperature of heating on the hardness of the investigated steel.
