To restrain the formation of primary carbides in M35 high speed steel, the present work investigated the effect of cerium on the microstructure, primary carbides and inclusions in electroslag ...remelted M35 high speed steel based on experimental characterizations and thermodynamic calculations. The primary carbides in M35 high speed steel are M2C-type carbides with orthorhombic crystal structure and MC-type carbides with FCC crystal structure. M2C-type carbides are the dominant carbides, whose precipitation is prior to the MC-type carbides. With adding cerium content to 0.0230wt%, the evolutionary process of inclusions is: MgO∙Al2O3→Ce2O3, CeAlO3 and Ce2O2S→Ce2O3, Ce2O2S and Ce2O3 core surrounded by Ce–As–P layer. Adding cerium content from 0 to 0.0230wt% causes the secondary dendrite arm spacing to decrease from 36.8 μm to 29.4 μm, as the heterogeneous nucleation of Ce2O3, Ce2O2S and CeAlO3 inclusions, as well as the effect of dissolved cerium including the increase in the constitutional undercooling and the drag on the migration of liquid–solid interface. Ce2O3, Ce2O2S and CeAlO3 are the less effective heterogeneous nucleation cores for M2C-type and MC-type primary carbides precipitation than MgO∙Al2O3 inclusions, which is conducive to the decrease in the area fraction of primary carbides with adding 0.0067wt% cerium. Further increasing cerium content to 0.0230wt%, the formation of Ce–As–P inclusions surrounding Ce2O3 promotes the precipitation of M2C-type primary carbides, causing the increase in the area fraction of primary carbides.
The microstructure of as-cast ingot and three-dimensional microstructure of carbides were analyzed by optical microscope and scanning electron microscope. The types of carbides were identified by ...X-ray diffraction. Directional solidification of electroslag remelting effectively reduced the segregation of alloying elements in as-cast ingot. The growing direction of dendrites in as-cast ingot refined by directional solidification of electroslag remelting was paralleled to crystallographic orientation. The solidification microstructure of austenitic hot-work die steel was composed of austenite and primary carbides (V8C7-type and Mo2C-type) which distributed along grain boundaries. Compared with conventional electroslag remelting, the directional solidification of electroslag remelting process reduced the size of primary carbides and improved dispersed distribution of carbides, but not changed the types and compositions of carbides. The direction of driving force for carbides growth was irregular in conventional electroslag remelting, while that was nearly parallel to crystal in directional solidification of electroslag remelting.
The microstructure of liquid phase sintered M3:2 high speed steel and the effect of adding carbon and silicon on the microstructure was characterized by scanning electron microscopy, dispersive ...spectrometry, and X-ray diffraction. Various types of carbides were formed depending on the added carbon and/or silicon, the sintering atmosphere and the cooling rate. The microstructure of sintered M3:2 high speed steel samples in vacuum conditions without the addition of Si and graphite is composed mainly of MC and M6C carbides inside cells and primarily at cell boundaries. The M2C eutectic carbides in these samples were formed at cell boundaries and their amounts and morphology depends on the cooling rate. Sintered samples in N2 atmosphere with added carbon and silicon, M6C eutectic and M7C3 eutectic carbides were dominantly formed while carbonitrides were formed in smaller amounts.
•The microstructure of liquid phase sintered M3:2 high speed steel has various types of carbides were formed depending on the added carbon and/or silicon, sintering atmosphere and the cooling rate.•The M2C eutectic carbides in these samples were formed at cell boundaries and their amounts and morphology depends on the cooling rate.•Sintered samples in N2 atmosphere with added carbon and silicon, M6C eutectic and M7C3 eutectic carbides were dominantly formed while carbonitrides were formed in smaller amounts.
With the high temperature confocal laser scanning microscope applied, the effect of cooling rate, temperature interval, and cooling mechanism on the solidification microstructure and primary carbide ...participation in GCr15 steel are investigated. The solute distribution in interdendritic segregation and participation carbide are analyzed by electron probe microanalysis. The results show that solute concentrate is low in the dendrite zone but it increases clearly in the segregation zone. The carbon concentration in the precipitation can reach 6.49%, which means the primary carbide is M3C. In the heating process, the segregation zone and carbide participation melt first before it reaches the solidus temperature. During the solidification stage, the microstructure is refined and the size of primary carbide is reduced with a higher cooling rate, but the number density of primary carbide is increased. Moreover, it is found that the microstructure is formed in the earlier solidification, before the temperature declines to 1673 K. While the primary carbide participates in the later cooling stage and the transition temperature for the primary carbide is 1503 K. In addition, the primary carbide size can be reduced with the cooling rate larger than 300 K min−1 in the subsequent cooling stage.
The solidification behavior of GCr15 steel with different cooling mechanisms is investigated by the high‐temperature confocal laser scanning microscope (HT‐CLSM). The solidification microstructure forms in the earlier solidification process, while the primary carbide participates in the later cooling stage. The primary carbide size can still be reduced with a higher cooling rate in the subsequent cooling stage.
In situ experimental investigations of partial melt phenomenon in as-cast H13 steel at elevated temperatures between 1150°C and 1300°C was carried out using a confocal laser scanning microscope ...(CLSM) observation. Stripy primary carbides composed of Cr, Mo, V and Ti were observed in the interdendritic zone of as-cast H13 steel. In the interdendritic zone there existed obvious Cr and Mo segregation and slightly C and V segregation. At temperatures above 1150°C, the liquid phase was observed at the primary carbides-matrix boundary, even though this temperature is much lower than the solidus temperature of H13 steel. A higher heat temperature and longer holding time result in the generation of an increased amount of liquid phase. The maximum fraction of the liquid phase in the present investigation was 6%. Two effects are responsible for the premature appearance of the liquid phase, namely the alloying elements segregation in the interdendritic zone and the decomposition of primary carbides. The presence of the liquid phase accelerates alloying elements diffusion in the interdendritic zone, and cavities will be generated because of the shrinkage of the liquid phase during rapid cooling.
To realize an industrial production of a cerium‐treated electroslag remelted H13 steel, electroslag remelting (ESR) of H13 steel using a CaF2–CeO2–CaO–Al2O3 system slag combined with a Si–Ca ...reductant addition is studied. The influence of the Al2O3 content in the slag on the cerium treatment effect of cerium‐oxide‐containing slag is investigated to determine the appropriate slag. A 52.2 wt% CaF2–26.7 wt% CeO2–17.8 wt% CaO–3.3 wt% Al2O3 slag (RE‐Slag) is employed for the industrial ESR production of H13 steel. An H13 steel remelted by a 70 wt% CaF2–30 wt% Al2O3 slag (CA‐Slag) is used for comparison. Al2O3 can suppress the reduction of cerium oxide by changing the activities of slag components. ESR with RE‐Slag achieves a cerium treatment of H13 steel. However, an uneven distribution of Ce is obtained due to the limitation of the reductant addition method. The H13 steel remelted with RE‐Slag (RE‐Slag‐H13) has higher cleanliness, finer dendritic structures, and finer primary carbides than those of the steel remelted with CA‐Slag (CA‐Slag‐H13). Compared to the forged CA‐Slag‐H13 steel, the banded segregation of the RE‐Slag‐H13 steel is suppressed, and the impact toughness is increased by 30%.
The cerium treatment of industrial electroslag remelted H13 steel is achieved using 52.2 wt% CaF2–26.7 wt% CeO2–17.8 wt% CaO–3.3 wt% Al2O3 slag combined with Si–Ca alloy addition. The cerium‐treated H13 steel has finer microstructures, finer primary carbides, and higher toughness than that processed by electroslag remelting using the traditional 70 wt% CaF2–30 wt% Al2O3 slag.
The present work deals with the effect of B, V, Ti on the microstructural evolution and mechanical behavior of high chromium white cast iron. The comparison is also made with Ni-hard iron in as-cast ...condition. The destabilization treatment provided after casting resulted in decomposition of austenite into martensite and secondary carbides and further tempering treatment resulted in decomposition of martensite into ferrite and secondary carbide phases. Phase analysis by x-ray diffraction revealed two main phases, i.e., a BCC-Fe matrix and a primary carbide phase. In addition to this, high chromium white cast iron and Ni-hard alloys contain austenitic phase (FCC-Fe) (Fig. 2(a)). The primary carbides are M7C3 for V additions whereas for all other cases, they are M3C2. Ti and B additions led to the formation of secondary carbides of M7C3 and M23C6, respectively. Effect of alloying elements on phases formed and further modification of the microstructure are discussed in detail. The hardness of unalloyed high chromium white cast iron is highest amongst all the alloys tested, however, Ti and V additions to it retained this hardness to almost the same extent. V addition to the alloy showed not only highest tensile strength but also longer elongation to fracture, thereby, resulting as toughest alloy in the lot. On the other hand, Ni-Hard iron showed the least tensile strength and elongation before fracture. This study, thereby concludes that high chromium white cast iron with V additions is suitable for manufacture of coal pulveriser grinding media owing to its higher hardness and toughness.
A finer microstructure generally helps to increase the wear resistance of materials. It was reported that Ti could act as an inoculant to generate fine microstructure for white cast iron, one of ...widely used in industrial materials. To confirm this, we investigated influences of Ti addition (up to 6
wt.%) on microstructure of a hypereutectic high chromium cast iron (Fe–25wt.%Cr–4wt.%C). Ingot samples were prepared using an arc furnace by melting pieces of the cast iron with titanium powder. Microstructures of the samples were examined by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray diffraction. It was demonstrated that the added titanium did not act as an inoculant to reduce the size of coarse primary carbides. Instead, as the titanium amount was increased, the cast iron changed from a hypereutectic microstructure to a hypoeutectic one due to the depletion of carbon that was consumed by Ti to form titanium carbides. When 2
wt.% Ti was added, the finest microstructure was achieved, which corresponded to the eutectic structure with mixed chromium carbides and titanium carbides. The eutectic structure exhibited the highest wear resistance and hardness due to the refined microstructure as well as the fact that an amount of chromium carbides were replaced by Ti carbides, which are harder than the former.
Cast austenitic chromium-nickel steel is commonly used for the manufacture of machine parts and components, which are exposed to the attack of corrosive media and abrasive wear during operation. The ...most commonly used grades include GX2CrNi18-9 and X10CrNi18-8 as well as GX2CrNiMo17-12-2 and X6CrNiMoNb17-12-2. To improve the abrasion resistance of cast chromium-nickel steel, primary niobium carbides were produced in the metallurgical process by increasing the carbon content and adding Fe-Nb. The microstructure of the obtained test castings consisted of an austenitic matrix and primary niobium carbides evenly distributed in this matrix. The measured hardness of the samples after heat treatment ranged from 215 to 240 HV and was higher by about 60 units than the hardness of the reference cast GX10CrNi18-9 steel, which had a hardness of about 180 HV. Compared to the reference cast steel, the abrasive wear resistance of the tested cast chromium-nickel steel (measured in Miller test) with contents of 4.4 and 5.4 wt% Nb increased only slightly, i.e., by 5% for the lower niobium content and 11% for the higher niobium content. Compared to ordinary cast GX10CrNi18-9 steel, the addition of 9.2 wt% Nb reduced the abrasive wear by almost 2.5 times.
Although there are many primary carbides in the cutting edge of knives made of high-carbon martensitic steel, the effect of primary carbides on the sharpness of knives has not been clarified. In this ...paper, the evolution of primary carbides during the production process of 8Cr13MoV steel was presented. The effect of size and amount of primary carbides on the sharpness of knives was studied via employing rolling forging and diffusion annealing process, respectively. Results indicated that primary carbides easily fell off from cutting edge during cutting process, which would decrease the wear resistance of knives. The refinement of primary carbides could not only improve the wear resistance of cutting edge, but also weaken the fluctuation of sharpness during the service process of knives. By decreasing the amount of primary carbides, the wear resistance of knives would increase effectively, which improved the cutting performance effectively. Reducing the amount of primary carbides and refining the primary carbides in cutting edge were both effective ways to improve the sharpness of knives.
