Papers by Keyword: Cementite

Abstract: This work is devoted to research of the structural-phase condition and changes in the mechano-tribological properties of 0.3C-1Cr-1Mn-1Si-Fe structural steel after plasma electrolytic cementation. Using metallographic and X-ray analysis, mechano-tribological tests, it was found that 0.3C-1Cr-1Mn-1Si-Fe steel in the initial state belongs to the ferritic-pearlitic class, which contains ~ 65% of pearlite grain and 35% of ferrite grain. When samples of 30HGSA steel are saturated with carbon, a modified surface layer with a thickness of 25μm is formed on the surface of the studied samples, including α-Fe ferrite, cementite Fe₃C, iron Fe₃C₂ carbide and an alloying element. It was established that the intensity of wear of the samples after modifying decreased by 2 times, and the surface microhardness after cementation increased 3 times, depending on the original sample.

Abstract: With the help of the Thermo-Calc software package, arrays of calculated data were created for carbon concentrations in ferrite and austenite, corresponding to the para-equilibrium of these phases and their para-equilibrium with cementite, as well as for the corresponding temperatures A₁ and A₃. Marked arrays were obtained in wide temperature ranges for ranges of carbon concentrations and the most important substitution alloying elements (Mn; Si; Cr; Ni; Mo), covering the respective ranges for medium carbon and moderately alloyed steels. Analytical formulas were developed on the basis of the reference data arrays for calculating para-equilibrium concentrations of carbon in ferrite and austenite (depending on temperature and chemical composition), as well as temperatures A₁ and A₃ (depending on chemical composition), which allow to reproduce with high accuracy the results obtained using Thermo-Calc.

Abstract: The spheroidization mechanism from different initial microstructures during spheroidizing heat treatment was studied in Fe-0.68C-2.33Mn alloy. Two types of initial microstructures, i.e. pearlite and martensite, were obtained by varying the cooling rate. The microstructure and property evolution during spheroidizing annealing was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The DICTRA software, assuming local equilibrium conditions, was used to simulate the carburizing process of different initial microstructures through different cooling rate. The results indicate that the spheroidization mechanism of cementite was related to the initial microstructures and the smaller lamellar spacing of pearlite inhibited the coarsening of cementite, resulting in the size of cementite smaller than that of martensite as the initial structure.

Abstract: The paper analyzes the regularities of structure formation in low-alloyed carbon steels. During the investigation of ferritic-pearlitic steel samples it has been found that the structure formation in pearlite essentially lags behind structural changes in ferrite grains, and this delay is observed at all stages of deformation. An important feature of structure formation in pearlite is crack nucleation in cementite, accompanied by dislocation pile-up in the ferrite interlayers of pearlite. Using the method of dislocation dynamics, the relationship between structural transformations and the parameters of strain hardening is analyzed. It is demonstrated that the proposed method of computer analysis reflects well the processes taking place in a material during plastic deformation. The character of the theoretical curve of strain hardening is determined by the dislocation structure that forms in a material at various stages of deformation.

Abstract: Elasto-plastic tensile deformations in multi-colony structures are studied by finite element analyses to investigate how the deformation in multi-colony structures influence the strain concentration around colony boundary. The results obtained from plastic strain distributions show that plastic strain concentrates around colony boundary when there is a large difference of deformation between adjacent colonies and around the point where boundaries of differently aligned colonies meet.

Abstract: The influence of chromium cast iron Cr8 treatment by Fe-45Si-6Mg-0,5REM modifier on the structure, phase transformation and heat resistance was studied experimentally.It is demonstrated that during modifying of chromium cast iron Cr8 the alloying effect takes place. The initial cast iron structure which consists of alloyed ferrite, carbide (Cr,Fe)₇C₃ and cementite (Fe,Cr)₃C is transformed as in the process of chromium alloying according to modifier consumption increase. At the modifier consumption of 0,15 % the mass quota of cementite (Fe,Cr)₃C decreases from 3,2 % to zero, and the mass quota of carbide (Cr,Fe)₇C₃ increases from 20 % up to 30 %.

Abstract: The cementite precipitation behavior in the martensite and banite of the H21 tool steel under high temperature axisymmetric compression test and double temper was investigated. The main purpose on this work is to develop a better understanding regarding the transformation mechanism of bainite and martensite in a H21 tool steel. The selected deformation temperatures were 1100 ^oC and 1000 ^oC and the double temper process was carried out at 650 ^oC for 1 hour respectively. The results showed that the cementite was sensitive to the stress. The applied stress has affected the Fe₃C precipitation behaviour by decreasing the number of variants carbides in tempered martensite and decreasing the number of a single variant carbides in tempered lower bainite. The results were in agreement with a displacive mechanism of martensite and bainite transformation. It was also found that hot deformation temperatures selected in this work have the same contribution in decreasing number of variant carbides in tempered martensite and decreasing number of single variant carbides occurred in tempered lower bainite.

Abstract: The effect of different cutting (mechanical heat treatment) on the structural-phase condition and the internal stress field in the surface layers of the product is considered in the article. The regularities of acoustic characteristics depending on the parameters of the structure and stress for the development of nondestructive method for assessing the quality of the surface layer are identified

Abstract: Elasto-plastic tensile deformations in pearlite lamellar and two-colony structures are studied by finite element analyses to investigate the effects of lamellar thickness ratio and difference of lamellae orientation of two colonies in pearlite microstructure. The results obtained from plastic strain distributions in lamellar and colony structures show that plastic deformation in cementite lamellar stabilized when ferrite lamellar is thicker than cementite lamellar thickness and plastic strain concentrates when the difference between cementite lamellar orientation in two colonies are larger than 45°.

Abstract: Effect of Mn, Si and Cr on spheroidization of cementite in Fe-1mass%C steel has been investigated over a range of austenitizing temperatures. In Fe-1C steel, a fully spheroidized structure is obtained but some large cementite particles are formed. The addition of 1.5 mass% Si or Cr accelerates spheroidization of cementite. An addition of Cr remarkably refine the cementite particle size, but the influence of Si addition on the cementite particle size is not remarkable. A fully spheroidized structure fails to develop in steel with the addition of 1.5% Mn under the condition used in present study. Some lamellar cementite still exist in the 1.5Mn steel. The pearlite-promoting effect of Mn is possibly attributed to the inhomogeneous distribution of cementite particles during the intercritical austenitization.