58 research outputs found
THE INFLUENCE OF CHEMICAL COMPOSITION OF HIGH-CHROMIUM CAST IRONS ON THE MACHINABILITY
No full textPurpose. This research is aimed to obtain the regression dependence of the machinability on the chemical composition of pig iron (C, Cr, Mn and Ni) in cast state. Methodology. The method of active experiment planning was used to build a mathematical model. Cast irons of composition 1.09…3.91 % С; 11.43…25.57 % Cr; 0.6…5.4 % Mn; 0.19…3.01 % Ni were studied. Cutting tools with plates 10х10 mm out of ВК8 according to State Standard 19051-80 were used for turning. Cutting modes: cutting depth – 0.8 mm, longitudinal feed – 0.15 mm/rot., spindle’s rotation frequency during turning – 200…360 rot./min. Lubricating and cooling liquids were not applied. Evaluation of iron workability was produced by determining the linear tool flank wear per unit length of the cutting path. Findings. Mathematically probabilistic equation of the regression dependence of the cutting tool’s wear on the C, Cr, Mn and Ni content in the machined cast iron were obtained. It was established that with the increase of Cr content in the cast iron to 14.8 % the cutting tool’s wear decreased as a result of formation of carbide eutectic which destroyed the doped ledeburite continuous frame. Further increase of chromium content promoted appearing of chromic carbides with high microhardness which considerably increased the tool’s wear. The conducted research shown that the minimum cutting tool’s wear 0,18 mkm/m was observed during the machining of cast iron containing: 1.09 % C, 14.8 % Cr, 2.3 % Mn and 1.2 % Ni; and the maximum wear is 48,96 mkm/m – when the content was: 3.91 % C, 11.43 % Cr, 5.4 % Mn and 0.19 % Ni. The tool’s wear reached 47.61 mkm/m during the treatment of cast iron containing 3.91 % C, 25.57 % Cr, 5.4 % Mn and 0.19 % Ni. Originality. Mathematically probabilistic model of the dependence of the cutting tool’s wear on the C, Cr, Mn and Ni content in the machined cast iron has been elaborated by the author. Practical value. The model allows optimizing the compositions of wear-resistant cast irons for castings which require the significant mechanical machining. Cast irons compositions were recommended for different exploitation conditions
PECULIARITIES OF THE WHITE ABRASION-RESISTANT IRONS ALLOYING
No full textRegression dependences of hardness of cast iron of structural components on chemical composition of cast iron in C-Fe-CrMn-Ni system are established by means of method of mathematical planning of experiment
PECULIARITIES OF PROCESSES OF CARBIDE FORMATION AND DISTRIBUTION OF Cr, Mn AND Ni IN WHITE CAST IRONS
No full textDuring crystallization of castings from white cast iron, carbides Me3С, Me7С3, Me23С6 were formed depending on chromium and carbon content. Impeded chromium diffusion caused formation of thermodynamically unstable and non-uniform phases (carbides). During heat treatment process stable equilibrium phases were formed as a result of rearrangement of the carbides’ crystal lattice, replacement of iron, manganese, nickel and silicon atoms by chromium atoms. The allocated atoms concentrated, forming inclusions of austenite inside the carbides. Holding during 9 hours at 720 °С and annealing decreased the non-uniformity of chromium distribution in the metallic base of cast iron containing 11,5 % Cr, and increased it in the cast iron containing 21,5 % Cr. Holding during 4.5 hours at 1050 °С and normalization decreased the non-uniformity of chromium distribution in the metallic base of cast iron containing 21,5 % Cr, and increased it in cast iron containing 11,5 % Cr
Influence of physical and heat processes on the structure and properties of high-chromium cast iron during machining
No full textPurpose. Analysis of changes of high-chromium cast irons' structure and properties under the influence of
physical and heat factors during mechanical machining. Methodology. The methodology of evaluation of the cutting
tool's force and heat influence on the machined material has been developed and applied. Cast specimens underwent
preliminary turning to obtain the diameter of 25 mm. The microsection was made on the end surface of the
specimen with the length of 50 mm. Standard plates with sizes 10×10 mm made of VK8 according to the State
Standard 19051-80 were used in the turning process. Findings. Force influence on the specimens made of highchromium
cast iron caused strain hardening during machining. Temperature influence on the structure and properties
of high-chromium cast iron during machining caused increase of the plasticity characteristics of the metallic
base in the cutting area, fragmentation of the carbide phase and elimination of the strain hardening. During turning
with cutting depth 0.8 mm only force influence of the cutting tool on the specimen took place. Carbide inclusions in
the surface layer didn't undergo sufficient changes; at the same time the metallic base was strain-hardened to 1 100
HV50. As it was drawn away from the turning surface, the microhardness of the metallic base was decreasing and
equaled to 500…520 HV50 at the distance of 1.2 mm from the turning surface. Strain hardening was not observed at the
depth of more than 3mm. Cutting depth increase up to 1.5 mm caused simultaneous influence of force and heat factors.
The temperature influence revealed in increasing of metallic base plasticity in the specimen's surface layers. Strain hardening
of heated surface layers didn't occur. While drawing away from the cutting surface, the influence of the temperature
factor decreased, when the influence of force factor remained the same. Due to the base plasticity decrease the strain hardening
occurred. The metallic base strain was hardened to 490…520 HV50. The overall heating of the specimen caused the
decrease of strain hardening depth to 0.4 mm. Originality. The methodology of change evaluation of high-chromium
cast iron structure and properties under the influence of physical and heat factors during mechanical machining has
been elaborated. Practical value. This methodology allows developing the recommendations for choices of highchromium
cast iron machining modes and conditions
ABOUT THE ISSUE OF CARBIDES FE3C AND FE7C3 FORMATION IN HIGH-CHROMIUM CAST IRONS
No full textPurpose. This article analyzes the formation conditions, transformation and systematization of carbide phases formed in the system Fe – C – Cr.Methodology. Conversion of the elements’ content from mass % into atomic % and vice versa was carried out using standard methods. In order to identify the structural components and etching of carbides the Marble etchant was applied. Cast iron 300Х28Н2 in cast state without heat treatment and after isothermal holding at 1050 °С during 4.5 hours with further normalization was studied. Findings. Isothermal state diagrams of the Fe–C–Cr system don’t take into account the existence of Fe7C3 carbide alloyed with chromium. But there is evidence of the existence of chromic carbides containing 24…37.6 % of chromium, which exceeds its maximum solubility in cementite, but is not enough to form Cr7C3.Analysis of chromium and carbon content in carbide phases which are formed in high-chromium cast irons allowed to substantiate the formation of Fe7С3 carbide, stabilized with chromium. Assessment of the carbide phase by chemical composition in mass percent doesn’t allow determining the main carbide-forming element with sufficient accuracy. It is shown that with the increase of chromium concentration in carbides, mass content of carbon increases. Areas of existence of carbides of different types depending on carbon and chromium content in them were determined. Maximum content of chromium in the carbide (Fe, Cr)7C3 is 44.0 %. Allocation of alloyed cementite occurs on the present carbides Ме7C3 or grain boundaries, and with the increase of cooling rate – in the grain volume. This process is thermodynamically inevitable due to the decrease of carbon solubility in ferrite or austenite at temperatures when chromium diffusion is impeded, and only carbon diffusion is possible. At high chromium concentrations carbide Fe7C3 is formed, which transforms into Cr7C3 carbide as chromium diffusion takes place. Originality. The model of laminated structure of carbides, formed out of the liquid phase in the system Fe–C–Cr was built. The identification of the carbide phase based on the elements’ concentration in atomic percent was suggested. The model of the change of carbon content in carbides of different types depending on chromium concentration was built. Practical value. The suggested system of carbide classification and their structural model allows optimizing the cast irons’ composition and heat treatment modes for different exploitation conditions
INFLUENCE OF ANNEALING ON HARDNESS OF Cr-Mn-Ni CAST IRONS
No full textThe necessary level of material’s hardness is determined by the exploitation conditions and presence of technological operations during manufacturing of articles. Mechanical edge cutting machining of wear resistant materials is impeded because of their high hardness. It is recommended to apply annealing in order to decrease hardness and improve machinability. The purpose of the work consisted in obtaining of regression dependences of cast iron’s macrohardness on its chemical content after annealing at 730 °С. With the use of mathematical experimental design the regression dependences of cast iron’s macrohardness and structural components’ microhardness on С, Cr, Mn, Ni content have been established. The minimal hardness of 27,6 HRC after annealing at 730 °С is obtained in the cast iron containing: 3,9% С; 11,4% Cr; 0,6% Mn; 0,2% Ni. The maximal hardness of 70,4 HRC is obtained when the content is as follows: 1,1% С; 25,6% Cr; 5,4% Mn; 3,0% Ni. Annealing at 730 °С decreases the cast irons’ hardness containing the minimal amount of Cr, Mn and Ni. Annealing at 730 °С is recommended for cast irons alloyed by Mn and Ni for increasing of hardness
Cracks in fiber composites: Determination of the stress intensity factor by the polarization-optical method
No full textFEATURES OF MANGANESE ALLOYING OF WEAR RESISTANT HIGH CHROME CAST IRON
No full textThe influence of alloying by manganese on the structure and hardness of high-chromium wear-resistant cast iron was investigated
FEATURES OF CHROMIUM DOPING OF WEAR-RESISTANT CAST IRON
No full textThe aim of this work analysis of the influence of chromium on the process of carbide formation, changes in chemical composition of the metal substrate in the areas adjacent to the carbides and at the hardness of iron while economy nickel and manganesealloying
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