Microstructure of Surface Layer Formed at Low Temperature and High Carbon Concentration Carburizing with Rare Earth Element

A suitable carburized microstructure with fine granular dispersed carbides in hypereutectoid zone,ultra fine martensite in matrix and recrystallized austenite to be refined to the grain size of 12～14 has been obtained by a new process,which is a high carbon concentration carburizing with rare earth element at low temperature(860～880℃)in a discontinuous gas carburization furnace.There was not much difference for the microstructure in eutectic zone between this and conventional process.Forming mechanism of granular carbides has been also studied in this paper.

Effect of electromagnetic stirring in mold on the macroscopic quality of high carbon steel billet

An industrial plant trial for optimizing the process parameters in a round billet continuous casting mold with electromagnetic stirring （M-EMS） was performed, in which the influences of stirring parameters with M-EMS on the solidification macrostructure of high carbon steel were investigated. The results show that the billet quality is not well controlled under the condition of working current and frequency with EMS, in which the subsurface crack of grade 1.0-2.0 ups to 38.09%, the central pipe of grade 1.0-1.5 reaches to 14.28%, and the central porosity of grade 1.5 is 14.29%. The parameters of current 260 A and frequency 8 Hz as the final optimum scheme has a remarkable effect for improving the macroscopic quality of billet, in which the subsurface crack, central pipe and skin blowhole are all disappeared, and the central porosity and carbon segregation are also well improved.

Effect of Cr/Mn segregation on pearlite–martensite banded structure of high carbon bearing steel

The effect of Cr/Mn segregation on the abnormal banded structure of high carbon bearing steel was studied by reheating and hot rolling.With the use of an optical microscope, scanning electron microscope, transmission electron microscope, and electron probe microanalyzer, the segregation characteristics of alloying elements in cast billet and their relationship with hot-rolled plate banded structure were revealed.The formation causes of an abnormal banded structure and the elimination methods were analyzed.Results indicate the serious positive segregation of C, Cr, and Mn alloy elements in the billet.Even distribution of Cr/Mn elements could not be achieved after 10 h of heat preservation at 1200℃, and the spacing of the element aggregation area increased, but the segregation index of alloy elements decreased.Obvious alloying element segregation characteristics are present in the banded structure of the hot-rolled plate.This distinct white band is composed of martensitic phases.The formation of this abnormal pearlite–martensite banded structure is due to the interaction between the undercooled austenite transformation behavior of hot-rolled metal and the segregation of its alloying elements.Under the air cooling after rolling, controlling the segregation index of alloy elements can reduce or eliminate the abnormal banded structure.

Apparent Morphologies and Nature of Packet Martensite in High Carbon Steels

The apparent morphologies of packet martensite in eight high carbon steels were researched by using optical microscope, scanning electron microscope, and transmission electron microscope. It was found that the apparent morphologies, substructures, and habit plane of packet martensite in high carbon steels are entirely different from that in low carbon steels; the substructures of packet martensite in high carbon steels possess fully twinned structure, while the substructures of individual coarse martensite plates in these steels bear both fully and partially twinned structures. The formation reason for apparent morphologies, substructures and two habit planes （i. e, { 111 }, and { 225}r） of high carbon martensite were discussed in detail.

WELDING BETWEEN HIGH MANGANESE STEEL AND HIGH CARBON STEEL

Manuscript received 30 July 1999 Abstract The shielded metal arc welding (SMAW) of a manganese steel part as a crossing of railway track to a carbon steel part as the rails of the railroad is the welding of dissimilar steel. It are was known that it is not possible to the the rail of railroad directly to the cross- ing of railway track made from a steel containing about 14% of manganese (wt. ) because of so many differences between the two kinds of steels such as composition, microstructure,mechanical properties and weldability.A method was used to solve the problem by presetting an intermediate layer on each side of the joint and other special procedures were used.The result of test indicated that a good weld joint was obtained.

Study on the Interaction between Rare Earth and Carbon in High Carbon Steel

A certain quantity of RE is dissolved in high-carbon steel. The dissolved RE not only segregates on grain boundary, but also exists in grains. It exists in cementite much more than in ferrite. RE makes the carbides spheroidal and fine, and the carbides distribute uniformly. RE also changes the morphology of pearlite. By means of the analysis of Auger energy spectrum, we find that RE, which is dissolved in cementite, changes the composition and structure of cementite. In the case of higher content of RE and carbon, RE carbide can be formed.

Effect of quenching-partitioning treatment on the microstructure, mechanical and abrasive properties of high carbon steel

The present work employed the X-ray diffraction, scanning electron microscopy, electron backscattered diffraction, and electron probe microanalysis techniques to identify the microstructural evolution and mechanical and abrasive behavior of high carbon steel during quenching-partitioning treatment with an aim to enhance the toughness and wear resistance of high carbon steel.Results showed that, with the increase in partitioning temperature from 250 to 400℃, the amount of retained austenite(RA) decreased resulting from the carbide precipitation effect after longer partitioning times.Moreover, the stability of RA generally increased because of the enhanced degree of carbon enrichment in RA.Given the factors affecting the toughness of high carbon steel, the stability of RA associated with size, carbon content, and morphology plays a significant role in determining the toughness of high carbon steel.The analysis of the wear resistance of samples with different mechanical properties shows that hardness is the primary factor affecting the wear resistance of high carbon steel, and the toughness is the secondary one.

New Spheroidizing Technique of Ultra-High Carbon Steel With Aluminum Addition

A new spheroidizing process of ultra-high carbon steel （UHCS） containing C 1.55%, Cr 1.45%, and Al 1.5% in mass percent has been proposed. The effect of processing parameters on the microstructure was analyzed. The UHCS produced by this new process has a microstructure with recrystallized ferrite matrix and fine and uniform carbide particles. After this spheroidizing, the UHCS exhibits good mechanical properties at ambient temperature, for example σb= 1 100 MPa, σs =915 MPa, δ=8% and high ratio of σs/σb.

Effect of Rare Earth Alloy Modification on High Carbon Equivalent Gray Cast Iron of Automotive Brake Drum

Effect of rare earth alloy modification on properties and microstructure of high carbon equivalent gray cast iron was investigated.The experimental results show that in the way of mechanical property,when the addition of rare earth alloy is 0.2% and 0.3%,the tensile strength of cast iron increases.In the way of microstructure,the addition of rare earth alloy increases the number of primary austenite dendrites,reduces secondary dendritic arm spacing,and changes the eutectic size and quantity.When rare earth alloy is added into gray cast iron,the morphology and quantity of graphite play a major role on the improvement of tensile strength.

Evolution of carbides and carbon content in matrix of an ultra-high carbon sintered steel during heat treatment process

DTA, thermal expansion, XRD, and SEM were used to evaluate the effect of quenching temperature on the mechanical properties and microstructure of a novel sintered steel Fe-6Co-1Ni-5Cr-5Mo-1C. Lattice parameters and the mass fraction of carbon dissolved in the matrix of the steel quenched were investigated. It is discovered that the hardness of the steel increases with quenching temperature in the range of 840-900℃ and remains constant in the range of 900 to 1100℃. It decreases rapidly when the temperature is higher than 1100℃. The mass fraction of carbon dissolved in the matrix of the steel quenched at 840℃ is 0.38, but when the quenching temperature is increased to 1150℃, it increases to 0.98. The carbides formed during sintering are still present at grain boundaries and in the matrix of the steel quenched at low quenching temperatures, such as 840℃. When the quenching temperature is increased to 1150℃, most of the carbides at grain boundaries are dissolved with just a small amount of spherical M23C6 existing in the matrix of the quenched steel.

Microstructural morphology of the semi-solid high carbon steel T12 before and after rheo-rolling

The semi-solid high carbon steel T12 was rolled in a closed box groove under a certain condition by the rheo-rolling equipment, and the microstructural morphology of the semi-solid T12 before and after deformation was investigated by optical mi- croscope to analyze and summarize the microstructure evolution law of T12 deformed in semi-solid state. The experiment results show that the grain shape before deformation of the semi-solid T12 steel displays globule or ellipse by the electromagnetic stirring, the distribution of solid and liquid phases is homogeneous. But the microstructure of semi-solid product after rheo-rolling exhibits macrosegregation that the distribution of liquid and solid phases changes, the liquid phases divorce from the solid phases. In the transverse section, most of the solid phases get together in the center of the specimen, the liquid phases flow to the surface or the edge of the specimen, and the grains occur plastic deformation while reduction increased. In longitudinal section, the middle micro- structure of the specimen is more homogeneous than that at the head or tail, the head microstructure is similar to the tail and the size of the grains is not homogeneous.

Microstructure and Property of High Carbonic-Chromium Cast Steel with Different Hot Deformation Ratio

The microstructure and properties of high carbonic-chromium cast steel subjected to different hot deformation ratios were studied.The experimental results show that the microstructure and properties of high carbonic-chromium cast steel are obviously improved after hot deformation,and the best mechanical properties of the cast steel can be obtained under hot deformation ratio of 40 %-50 %,which leads to the morphology change of eutectic carbide and the precipitation of granular carbides.

RE-Carbide in High Carbon Steel

In order to determine the morphology of RE in high carbon steel, it was studied by means of electrolytic extraction and X-ray diffraction analysis. Meanwhile, as a new experimental technique, the gas chromatography analysis ha;i been used to investigate the necessary condition for the formation of RE-carbide and its chemical property. The results show that the RE-carbide could be formed with which the mischmetal content was about 0. 036 wt% in heavy rail steel, and the ternary compound Fe2Ce2C3 was also identified in which the cerium content exceeded 0.25 wt%. The RE-carbide and Fe2Ce2C3 were both moisture-sensitive.

Enrichment characteristic of carbon atoms in solid-liquid zone of high carbon steel under different directional solidification rates

To reveal the formation mechanism and main influencing factors of C-segregation in high carbon steel under different solidification rates(40,80,160,200 and 320μm·s^(-1)),the enrichment characteristics of carbon atoms in the solid-liquid zone of Fe-0.61%C steel were studied using a zone melting liquid metal cooling apparatus and electron probe microanalysis.The relationships among micro-segregation of carbon atoms,solid-liquid interface morphology and solidification rate were fully discussed.The results show that large dendrite spacing and a slow-moving dendritic interface create less resistance and more time for the migration of interdendritic carbon atoms to liquid zone.This results in the continuous enrichment of carbon atoms in liquid zone,further expands the solid-liquid temperature range,prolongs the solidification time of molten steel,and causes the formation of carbon micro-segregation at the solidification end as the solidification rate is 40μm·s^(-1).Conversely,abundant and elongated secondary dendrite arms with small spacing seriously impede the diffusion of interdendritic carbon-rich molten steel to liquid zone.As a result,there is only obvious dendrite segregation,but little difference in the carbon content along the solidification direction as solidification rate exceeds 200μm·s^(-1).

Effect of Rolling Process on Microstructure and Wear Properties of High Carbon Equivalent Gray Cast Iron

Rolling process based on the plastic deformation as a surface strengthening treatment was employed,aiming to improve the wear resistance ability and functional performance of the high carbon equivalent gray cast iron(HCEGCI).The microstructures and tribological performance of the untreated and rolled samples were characterized.In addition,the wear mechanism of HCEGCI samples was also studied via pin-on-disc tests.The experimental results show that the as-rolled samples possess the structure-refined layer of 15μm and work-hardened layer of 0.13 mm.In comparison with the surface hardness of untreated samples,the surface hardness of as-rolled samples increases by 84.6%(from 240HV0.1 to 443HV0.1)and the residual compressive stresses existed within the range of 0.2 mm.The wear rates of as-rolled samples were decreased by 38.4%,37.5%,and 44.4%under different loads of 5 N,10 N,and 15 N,respectively.The wear characteristics of the untreated samples mainly exhibit the peeling wear coupled with partial adhesive and abrasive wear.However,as for the as-rolled samples,the adhesive wear was limited by the structure-refined layer and the micro-crack propagation was controlled by the work-hardened layer.Therefore,the wear resistance of as-rolled samples can be improved significantly due to the low wearing degree of the friction contact zone.

The micro structure of high carbon low alloy steel for easy drawing

For better processing performance of high carbon low alloy steel wire rod,an investigation about the influence of cementite lamellar spacing on wire 'easy drawing' performance is completed.It is pointed out that too thin cementite lamellar spacing(<80 um) reduces the strain hardening level of wire drawing, and reduce the torsion performance of drawn wire at same time.For the wire or wire rod from industrial production,compared with the micro-structure with troostite,the micro-structure with sorbite or sorbite mixed with pearlite is more suitable to the drawing process with high reduction ratio.

Effect of Continuous Cooling Conditions on Microstructure and Mechanical Properties of High Carbon Steel Rod

The effect of cooling rate and austenitizing condition on the mechanical properties of high carbon steel (SWRH82B) has beeninvestigated. Specimens were made of high carbon steel rod and heat-treated by Gleeble-2000 to produce a wide variation in prior austenite size. Different cooling rates were carried out, and then pearlite interlaminar spacing and mechanical properties were measured andtested respectively. According to the results, it could be found that under the continuous cooling with the increase of cooling rate, tensilestrength greatly increases and reduction in area exhibits a slightly increase for an equivalent value of prior austenite grain size. Whenprior austenite size increases, reduction in area decreases, and tensile strength increases slightly for an equivalent value of pearlite interlaminar spacing. It is concluded that prior austenite size primarily controls ductility and pearlite interlaminar spacing controls tensilestrength. Mathematical formulae are given for these relations.

Niobium alloying effect in high carbon equivalent grey cast iron

The effect of niobium on the formation of NbC phase and solidification structure in high carbon equivalent grey cast iron was investigated.The experimental results indicated that an increase in the niobium content is favorable to refining the graphite and eutectic cell;and the pearlite lamellar spacing is reduced.Based on the thermodynamic calculation the formation of NbC is prior to the eutectic reaction.The reduction in the pearlite lamellar spacing is mainly attributed to the decrease of eutectic temperature with the addition of niobium.Additionally,properties including hardness and wear resistance were improved after the addition of niobium.

High Carbon Alloy Steels with Multiple Types of Ultra-fine Carbides and Their Characteristics

Under normal forging and annealing conditions, there are different ultra fine carbides (M3C, M23C6, M7Cj, M6C and MC) in high carbon alloy steels when alloy composition design is carried out properly. On the basis of carbides transformation orderliness, the alloy composition design of the high carbon alloy steels is conducted by phase-equilibrium thermodynamic calculation for Fe-Cr-W-Mo-V-C system. The nucleation and growth of new carbides, dissolution of previous partial carbides in these steels during annealing process, all these lead to ultra-fine distribution of carbides. Due to different crystal structures of carbides and different thermodynamics as well dynamics parameters of the carbides dissolution and precipitation, the range of quenching temperature of these steels is widened, and the good temper-resistance is obtained. The characteristics of heat treatment process and microstructure variance, and the carbides transformation for different temperature are explained by the phase-equilibrium component satisfactorily. Their bend and yield strength, flexibility and toughness all are advanced markedly comparing with that of kindred steels. Results of the applications have proved that the microstructure of ultra-fine carbides in these steels played importance roles in the enhancement of edginess and fatigue crack resistance of the die and knives.

Spheroidization and Ostwald Growth of Carbide in Isothermal Process of Hot-Deformed High Carbon Chromium Cast Steel

In isothermal spheroidizing process,the spheroidization and growth of the carbide formed in hot-deformed high-carbon chromium cast steel at high temperature were investigated.The results showed that the spheroidizing growth of carbide proceeds in such a way that the bigger carbide particles swallow the smaller ones,and the short rhabdoid carbides dissolve and are spheroidized by itself.When the samples were held at 720℃ for more than 3 h,the spheroidization is not obvious.The feature of the process is the size increment and the amount decrement of carbide particles.The empirical equation for growth rate of carbides was obtained.The volume fraction of carbides keeps constant.The growth process agrees well with Ostwald Ripening Law.