The characteristics of primary carbides in a commercial-sized (one ton) electroslag remelting (ESR) ingot of AISI H13 steel were investigated. The interaction between the primary carbides and ...inclusions was also clarified. The results indicate that there are two types of primary carbides, V-rich and Mo-rich primary carbides, in the H13 ESR ingot. The quantity, the area fraction, and the size of the two primary carbides tend to decrease from the center of the H13 ESR ingot to the outer surface. Additionally, the V-rich primary carbide is obviously larger than the Mo-rich primary carbide. The Al2O3 inclusion can promote the precipitation of the V-rich primary carbide, while the MnS inclusion encourages the precipitation of Mo-rich primary carbide. The CaO∙Al2O3 inclusion cannot act as the nucleation site for the precipitation of the two primary carbides. The solid fraction that the V-rich primary carbide begins to precipitate ranges from 0.965 to 0.983, and that for the Mo-rich primary carbide and the MnS inclusion change from 0.9990 to 0.9998 and from 0.989 to 0.990, respectively.
The aim of this study was to characterize the primary carbides formed in as-cast H13 steel. The composition, morphology, type, and size of primary carbides in as-cast H13 steel were investigated by ...optical microscope (OM), field emission scanning electron microscopy (FE-SEM), electron back-scattered diffraction (EBSD), and X-ray diffraction (XRD) analysis. The number of primary carbides was investigated by ASPEX automated inclusion analysis system. The results indicated that primary carbides in as-cast H13 steel are mainly composed of Cr, Mo, V, and Ti, and there exist four kinds of primary carbides in the interdendritic zones of H13 steel, which are stripy Mo–Cr-rich M
2
C, eutectic Mo–Cr-rich M
2
C, V-rich MC, and V-rich MC with Ti and N. Thermodynamic calculation indicated that M
2
C precipitates in liquid phase at solid fractions larger than 0.99, while MC precipitates in liquid phase at solid fractions larger than 0.96. Statistical results indicated that the number of M
2
C is much greater than the number of other kinds of primary carbides. Most primary carbides are blocky, with lengths of no more than 10 μm and a length/width ratio of no more than 3. The large primary carbides in as-cast H13 steel are mainly M
2
C.
This paper addresses a current debate about the morphology of M
7
C
3
phase in the chrome carbide overlay (CCO) and white iron community. This morphology was investigated using a serial sectioning ...technique in combination with computer post-processing software. A 600×600×300 μm volume of CCO was reconstructed in three dimensions (3D) to determine the difference between blade and rod-like carbide morphologies. The 3D analysis revealed that the two carbides morphologies correspond to the same hexagonal rod-like structures, but are oriented in different directions relative to the sectioning plane.
The Ti element plays a role in pinning grain boundaries but also has a good binding ability to C and N, forming large primary carbides. Therefore, the effect of Ti content on primary carbides’ ...behavior in H13 ingots was comprehensively studied. A non-aqueous electrolysis method was used to determine the three-dimensional (3D) characteristics of primary carbides. We found a great difference between the two-dimensional (2D) and the three-dimensional characteristics of primary carbides. When performing 2D analyses, the density of the primary carbides appeared high, while their size was small. The actual characteristics of primary carbides can be obtained only by 3D observation. The primary carbide showed a typical dendritic structure, whose center consisted of Ti–V-rich carbide wrapped by V-rich carbide. As the Ti content increased, the size of the primary carbide increased from 24.9 μm to 41.3 μm, and the number density increases from 25.6 per/mm2 to 43.9 per/mm2. The Ti4C2S2 phase precipitated first, then changed into Ti–V-rich carbide, and finally further partly transformed into V-rich carbide. The addition of elemental Ti promoted the precipitation and transformation of primary carbides, resulting in an increase of the number density and size.
The hypereutectic HCCI/plain carbon steel bimetal composite hammer which has metallurgical combination layer were prepared by bimetal liquid casting method and the influence of the pouring ...temperatures on the microstructure of the hypereutectic HCCI and the combination layer were studied. The results show that lower pouring temperature was not benefit for refinement of primary carbide and formation of metallurgical combination layer. A bad metallurgical combination layer between two metals which were mixed along the interface exhibited at higher pouring temperature.
Pre-hardened steel of 40HRC is normally used in plastic mold. Because there is no need to adjust dimensional change after heat treatment. However, pre-hardened steel over 50HRC is not common due to ...poor machinability. For improving their machinability, TiAlN or TiN coated cutting tools after cutting several types of 60HRC hardened cold work tool steel were investigated through SEM, EPMA, and TEM. The final aim is to realize pre-hardened steel of 60HRC. The results showed the following : First, flank wear was reduced by decreasing primary carbides of steel. Second, there were plastic deformation areas of TiN coating after cutting all types of steel. Third, the plastic deformation and chipping of cutting tools were prevented by Al based oxide and MnS made from the steel as protective film. Finally, Al based oxide could be used in a wide temperature range. Moreover, MnS inclusion prevented deposition of Fe on the cutting tools during the cutting of steel. These results suggest that it is possible to create 60HRC hardened cold work tool steel of good machinability by decreasing primary carbides of steel and using Al based oxide and MnS made from the steel as protective film.
•Microstructural characterization of a prematurely failed steel chopper blade was done.•Microstructure revealed non-uniform distribution of coarse dendritic irregular shaped primary carbides.•Bands ...of dendritic primary carbides acted as stress raisers.•Cracks initiated under load and propagated through the clustered zone of primary carbides.•Inadequate hot working of as-cast material led to its structural inhomogeneity and ultimate failure.
In the present work, failure investigation of a chopper blade received from an integrated steel plant has been presented. Chopper blades are used in chopping machines for cutting trimmed edges of hot-rolled coils into pieces to convert them into scrap. These blades are manufactured from hot forged or rolled billets or flats of high carbon high chromium cold work tool steel. The investigation consists of visual examination, chemical analysis, microstructural analysis through optical and scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and hardness measurement. The chemical analysis confirmed the steel as equivalent to D2 grade in AISI notation. Carbide volume fraction of the broken blade was in the normal range of 10–15% as commonly observed in D2 tool steel. Microstructural examination under light and scanning electron microscopy showed non-uniform distribution of large eutectic primary carbides of irregular morphology forming strings or bands in tempered martensite matrix preferentially aligned in a specific direction. The uneven carbide arrangement in the matrix made the structure highly anisotropic and susceptible to localized stress concentration. The carbides were identified mainly as M23C6 type. Cracks were observed to initiate at the edges of the blade and propagate to the interior through clustered zones of carbides. SEM study suggests that the crack initiation was associated with decohesion of carbide particles in the cluster which culminated into final fracture by the mechanism of void coalescence and subsequent crack growth.
Four Fe-Cr-C hardfacing alloys with carbon contents of 3˙34-6˙5% were studied. The orientation of primary carbides in the microstructures of hardfacing layers produced by arc surfacing was ...investigated under controlled cooling conditions. Carbon content and cooling conditions were found to play an important role in determining overlayer microstructures. Increasing carbon content or decreasing Cr/C ratio increased the tendency for primary carbides to be oriented perpendicular to the surface of the overlayers, and the carbides in the microstructure became more compact. Under water cooling conditions, the primary carbides were preferentially oriented perpendicular to the surface, which would be expected to improve wear resistance. At lower cooling rates, primary carbides were oriented randomly.
This paper studies the effect of titanium concentration on the morphology of primary M
7C
3 carbides in hypereutectic high chromium white cast iron by means of the optical microscopy (OM), the ...scanning electron microscopy (SEM), the X-ray diffraction (XRD), the energy dispersive X-ray spectrometry (EDS) and Leica image analyzer. Theoretical calculation shows that solute Ti atoms can react with carbon and form TiC particles under certain conditions in the melt of hypereutectic high chromium cast iron. The experimental results show that the morphology of primary M
7C
3 carbides can be improved by adding a suitable amount of Ti. This improvement correlated with the emergence of TiC particles. These particles can act as the substrates for heterogeneous nucleation of primary M
7C
3 carbides, which results in significant refinement of the final grain size.
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