Volume Fraction Of Primary Carbides Research Articles

Определение объемной доли первичных карбидов в микроструктуре композиционных покрытий с применением семантической сегментации

In the process of formation of composite coatings, partial dissolution of hardening particles (most often carbides) in the matrix is possible; therefore, in some cases, the material creation mode is chosen taking into account the volume fraction of primary carbides not dissolved during coating deposition. The methods currently widely used for calculating the volume fraction of carbides in the structure of composite coatings (manual point method and programs implementing classical computer vision methods) have limitations in terms of the possibility of automation. It is expected that performing semantic segmentation using convolutional neural networks will improve both the performance of the process and the accuracy of carbide detection. In the work, multiclass semantic segmentation was carried out including the classification on the image of pores and areas that are not a microstructure. The authors used two neural networks based on DeepLab-v3 trained with different loss functions (IoU Loss and Dice Loss). The initial data were images of various sizes from electron and optical microscopes, with spherical and angular carbides darker and lighter than the matrix, in some cases with pores and areas not related to the microstructure. The paper presents mask images consisting of four classes, created manually and by two trained neural networks. The study shows that the networks recognize pores, areas not related to the microstructure, and perfectly segment spherical carbides in images, regardless of their color relative to the matrix and the presence of pores in the structure. The authors compared the proportion of carbides in the microstructure of coatings determined by two neural networks and a manual point method.

Evaluation of layer adhered on PCBN tools during turning of AISI D2 steel

Polycrystalline cubic boron nitride (PCBN) tools have high abrasion resistance and are thus suitable for application in the machining of steels with a high volume fraction of primary carbides in their microstructure. These tools are usually applied in the machining of steels with hardness above 45–50 HRC and in the case of application to steels with hardness below 45 HRC, the formation of an adhered layer on the rake face of the tools often occurs. This paper reports a study on the impact of the layer adhered on PCBN tools during the turning of AISI D2 steel, with 35 and 50 HRC. The microhardness and microstructure of the adhered material were determined, as well as the tool wear based on volumetric wear parameters. The layer adhered on the PCBN tool rake face has the same chemical elements as the machined steel alloy. Its microstructure is oriented in the direction of the chip flow and the primary carbides were fragmented. For the sample with 35 HRC the amount of material adhered (WAM) on the rake face of the PCBN tool was approximately 360% higher than the steel with 50 HRC. The material layer adhered on the PCBN tool rake surface in the case of the 35 HRC steel acts as an edge (assuming the cutting function), while for the 50 HRC steel, the adhered layer intensifies the adhesion wear mechanism through spalling on the tool rake face. The results obtained provide important information for the selection of materials and grades for the development of new cutting tools.

Precipitation Mechanism and Reduction of Amount of Primary Carbides During Electroslag Remelting of 8Cr13MoV Stainless Steel

The precipitation and growth of primary carbides in 8Cr13MoV steel during electroslag remelting (ESR) were studied. The effects of melting rate and fill ratio of ESR on the reduction of primary carbides were clarified. Primary carbides M7C3 precipitated from liquid steel at the final stage of solidification, which is attributed to an enrichment of carbon and chromium in liquid steel. The carbon content in the residual liquid steel was the determining factor for the formation of primary carbides. The growth of primary carbides was affected mainly by the chromium-concentration and temperature-field gradients. An appropriate melting rate facilitated the nucleation and growth of dendrites, which caused dendrite closure and prevented the further enrichment of carbon atoms. Primary carbides were refined and their amount was reduced when using a lower ESR melting rate. The fill ratio can affect the uniformity of the temperature field in the liquid metal pool and heat transfer from the slag pool to the liquid metal pool, and an optimal fill ratio resulted in a minimum mushy zone and less primary carbides. The volume fraction of primary carbides was reduced by 23 pct when the melting rate decreased from 150 to 133 kg/h and the fill ratio increased from 0.23 to 0.33.

Martensitic Transformation of a High-speed Tool Steel During Continuous Heat Treatment

This study focuses on the evolution of the amount of martensite, retained austenite and the volume fraction of primary carbides during the austenitisation process. The high-speed tool steel HS 6-5-2 is investigated. The continuous heat treatment is simulated in a quenching dilatometer with heating rates of 500K/s and varying holding times. For each holding time, the martensite start temperature is identified, which gives some indication of the carbon content in solution. The volume fraction of retained austenite is analyzed by applying X-ray diffraction measurements and using Rietveld analyses. Atom probe tomography is used to characterize the matrix and the amount of primary carbides is investigated by scanning electron microscopy. The results are discussed in comparison to a conventionally heat treated material.

Primary and secondary carbides in high-speed steels after conventional heat treatment and laser modification

Complex structure examinations were performed on high-speed steels of different grades obtained using conventional metallurgy and produced by application of powder metallurgy. Hot hardness measurements were focused on the secondary carbide precipitation. Transmission electron microscopy and X-ray diffraction studies established the type of primary carbides and the amount of retained austenite. Scanning electron microscopy examinations were used to calculate the volume fraction of primary carbides. The contribution of the applied heat treatment and laser modification by diode laser remelting to the residual stress state was studied. Energy filtering was used to study the secondary carbides of nanometer size.

Influence of microstructure and chromium content on oxidation behaviour of spin cast high speed steels

The influence of the chromium content and of the volume fraction of primary carbides on the thermal oxidation behaviour of spin cast high speed steels and semi-high speed steels used for the production of hot mill rolls was studied at 700°C. Oxidation nucleates at the carbide–matrix interface and carbides have a higher oxidation resistance than the matrix. Moreover carbides dissolve a higher amount of chromium than the matrix. As a consequence of these effects, the oxidation rate of these steels decreases by increasing the chromium content of the matrix and by decreasing the carbide volume fraction.

The role of primary carbides in the wear of high speed steels

A study of the wear behaviour and microstructure of three high speed steels of the molybdenum type, M1, M15 and M42, has been made in the region of the secondary hardening peak arising during tempering. The maximum wear resistance was found to be associated with the peak hardness. The wear resistance of samples which had been overtempered at tempera- tures beyond the peak hardness was found to be lower than that of samples tempered at temperatures below the peak hardness for samples having the same hardness. In the secondary hardening region in high speed steels many microstructural changes take place since new phases precipitate. These phases are different in size, morphology, composition and crystal structure compared with the previous precipitates. These changes in microstructure cause a deviation from the linear relationship between wear resistance and hardness. In over-tempered high speed steels primary carbides have been shown to act as abrasives which contribute to the drastic fall in wear resistance when steels are tempered beyond peak hardness. Quantitative studies of the type, volume fraction, size and size distribution of primary carbides and measurements of wear resistance have shown that primary carbides have no role in enhancing the wear resistance of high speed steels. Further, the wear resistance of high speed steels is independent of the volume fraction of primary carbides.

A New Procedure for Determining Volume Fraction of Primary Carbides in High-Speed and Related Tool Steels

A new analytical procedure was developed for estimating volume fractions of primary carbides in tool steels. The method utilizes electrolytic extraction of carbides, EDX analysis, and X-ray powder diffraction. Chemical compositions of individual carbide species are compared with the bulk carbide composition to find weight fractions of each species, and the volume fractions are calculated using the computed theoretical densities of the carbide species. Chemical composition and density of the matrix are also obtained as by-products of the procedure. The new procedure was successfully applied to AISI M2 high-speed steel and corresponding matrix tool steel in as-annealed and as-hardened conditions. It was shown that the etching process used in conventional metallography can cause overestimates of carbide volume fraction by 20 pct or more.

Controlling residual stresses in 52100 bearing steel by heat treatment

Compressive residual stresses can be induced in the surface of quenched and tempered 52100 steel (1 pct carbon, 1.5 pct chromium) by austenitizing in a carburizing atmosphere, even though the austenitizing temperature is well below that needed to dissolve all pri-mary carbides. The carburized surface layer contains a larger volume fraction of pri-mary carbides, more retained austenite and is slightly harder than the interior. Rolling contact fatigue tests show that carburizing can produce a 50 pct improvement in the fa-tigue life of 52100 steel.