High-carbon Cast Research Articles

Cause of bending fracture in high-strength fasteners and heredity of surface recarburization in high carbon steel

In this work, the cause of bending fracture in high-strength fasteners after electroplating was investigated and the heredity of surface recarburization from continuously cast high carbon steel blooms to the final fastener products was explored. The fracture surface of the fasteners displayed intergranular cracking and numerous intergranular facets accompanied by ductile tearing. Hydrogen-induced stepwise cracks were identified near fracture zones, indicative of hydrogen embrittlement. The surface decarburized layer on the fasteners featured a significant number of fine partial decarburization grains and a high carbon content, resulting in low electrical conductivity. The observed dense coating, possibly induced by the poor conductivity of the decarburized layer, could elevate the hydrogen content in the substrate, ultimately resulting in hydrogen embrittlement. Additionally, the surface carbon pick-up at the corners of the blooms could be inherited by the rolled billet. The extensive deformation experienced during the hot rolling process resulted in the uniform distribution of recarburization on the surface of both the wire rod and spheroidized wire rod. Consequently, this recarburization contributed to a low degree of decarburization on the surface of the fasteners. Simulation results obtained through DICTRA also indicated that the recarburization on the surfaces of various samples could not be eliminated during the heat treatment process.

On the Macrosegregation of Continuous Casting of High Carbon Steel Billet with Strand Reduction Process

A mathematical model of the macrosegregation of continuous cast high carbon steel billet was developed based upon a representative volume element, considering the flow of enriched liquid, solidification rate, and solidification shrinkage as well. It was found that a lower casting velocity, higher cooling intensity, and shorter solidification interval positively contributed to the inhibition of macrosegregation in a continuously cast billet when a mechanical reduction process was not applied. A numerical expression for the relative flow velocity of liquid was further proposed incorporating such aspects as casting velocity, densities of different phases, and the variation of cross section areas as well. The analysis based on this numerical expression indicated that the overall effect of the reduction process on the macrosegregation of billets depended not only on the reduction zone but also on the reduction amount and its distribution for the active reduction rolls. The test results of further practical plant trials demonstrated a reasonable agreement with the predictions obtained from the proposed numerical model, indicating the reliability of this analysis model to be employed for the continuous casting of high carbon steel billet with strand reduction process.

Estimation of the segregation in a high carbon cast steel by thermoelectric power means

This research study proposes the hot-cold tip thermoelectric power (TEP) method to estimate alloying elements segregation and the microstructure variation of high carbon steel cast in a mold. Optical Emission Spectrometry (OES) showed a higher concentration of carbon, nickel, chromium and aluminum at the ingot center. That elemental saturation produced an increase in perlite content as well as hardness. The non-destructive technique of thermoelectric power was applied varying the hot tip temperature (40 oC, 50 oC, 60 oC, 70 oC), where higher temperature values showed to be more sensitive to segregation and microstructural changes. The statistical analysis showed that the thermoelectric power technique is more sensitive to detect the nickel and chromium concentration changes.

Estimation of the Segregation in a High Carbon Cast Steel by Thermoelectric Power Means

Estimation of the Segregation in a High Carbon Cast Steel by Thermoelectric Power Means

Laser repairing nodular cast iron with improved interface and performance using Fe-14Ni-19Cr austenitic powder

The generation of defects, such as large-sized brittle phases and cracks, remains challenging due to the high carbon diffusion during repairing cast iron. To resolve this problem, a new austenitic Fe-14Ni-19Cr material was designed to repair QT500-7 by laser cladding under N 2 protective atmosphere. The results show that the defect formation was effectively suppressed, and a low-content carbon (∼0.18 %) was diffused from QT500-7 substrate into the laser-repaired layer. The microhardness increased steadily from the substrate of ∼200 HV 0.2 to the laser-repaired layer of ∼257 HV 0.2 . The laser-repaired specimen exhibits mechanical properties with ultimate tensile strength of 490 MPa, yield strength of 401 MPa and elongation of 7.7 %, which is equivalent to the QT500-7 substrate. This study will be potential in repairing high-carbon cast iron offering high performance at low cost.

ショットライニングとレーザ照射によるアルミニウム合金の表面改質

The surface modification of aluminum alloy by shot lining and laser irradiation was investigated to form a hard Fe-Al intermetallic compound having excellent corrosion resistance. A centrifugal-type peening machine with an electrical heater was employed. The shot medium was high-carbon cast steel. The substrate was a commercial aluminum alloy. The sheet was commercially available pure aluminum, and the powder was an electrolytic iron. The shot lining process was carried out at 573 K in air using a peening machine. The top surface of the lined workpiece was melted by laser beam irradiation. The intermetallic Fe-Al layer was formed on the irradiated surface. The lined substrates exhibited a harder layer of aluminum-rich intermetallic in the irradiated part. The present method could be used for the formation of functional films on aluminum alloy.

Effect of Microshot Peening on Fatigue Strength of Austenite Stainless Steel

The effects of the peening conditions on the surface characteristics and fatigue strength of stainless steel were investigated by microshot peening (MSP). In recent years, MSP technology has attracted attention. The use of MSP technology with minute media has become more widespread in consideration of the reduction of the notch effect in the material surface. However, the effect of MSP technology on stainless steel has not been much studied. In the present study, an air-type machine was used. The media used was high-carbon cast steel (490 HV) and Fe-Cr-B alloy (1130 HV), with an average diameter of 0.1 mm. The peening time was in the range of 0 - 100 s. Four types of stainless steels, SUS304, SUS304L, SUS316, and SUS316L, were tested. The workpieces were annealed at 1100 K for 1.2 ks in air. In the measurement of fatigue strength, the workpieces were machined in hour-glass shape. As the results, surface roughness of the workpieces treated by MSP was small. Work hardening was evident to the depth of approximately 0.2 mm from the surface. This depth was about twice the diameter of shot media. However, the effect of the peening time on the hardness distribution was not large. The compressive residual stress was added in the surface vicinity. It is assumed that the fatigue limit had increased because the work hardened layer was formed near the workpiece surface.

Role of metal oxidation at high temperature

ABSTRACT Different cast steels (low-, medium- and high-carbon cast steel) converted into the wrought form by hot rolling and forging processes, the temperature of hot rolling and forging processes are kept 1000°C and then these cast and wrought steel samples prepared and subjected to high temperature oxidation in air under cyclic heating condition for 50 cycles, every cycle consisting of 1-h heating and 20-min cooling. Oxidation kinetics was established by thermo-gravimetric methods by measuring the weight changes at the end of each cycle. The oxidised samples with oxide-scaled surface were investigated for X-ray analysis, scanning electron microscopy (SEM) and Energy Dispersive X-Ray Analysis (EDAX) . All the steel samples suffered oxidation attack in the air which resulted in intense spalling of the oxide scale. It is also observed that the high temperature oxidation rate is maximum for casted samples and is minimum for the rolled samples and for forged samples it lies between cast and rolled steel.

On the material characteristics of a high carbon cast austenitic stainless steel after solution annealing followed by quenching in a CNT nanofluid

AbstractSolution annealing followed by quenching in carbon nanotubes (QCNT) nanofluid treatment was applied to generate very high interstitial carbon content,≈0.30 wt.%, in an austenitic stainless steel (ASS). The high interstitial carbon content leads to remarkable improvement in mechanical properties with essentially no loss of ductility, with no chromium carbides and/or martensite formation. To evaluate the localized corrosion tendency and passivity behavior, 3.5 wt.% NaCl and borate buffer solutions were used, respectively. Based on the electrochemical corrosion results, both high carbon and low carbon (0.030 wt.%) QCNT-treated ASS alloys show comparable passivity and localized corrosion performance. In addition, Mott–Schottky plots revealed that the anodic films on QCNT-treated samples exhibit similar semiconducting characters.

Effect of Different Shot Peening Treatments on Fatigue Life in Ti Alloy

The effects of peening conditions on the surface characteristics and fatigue life of titanium alloy was investigated using microshot peening, ultrasonic shot peening, and multiple shot peening. The use of microshot peening technology with minute media has become more widespread in consideration of the reduction of the notch effect in the material surface. The ultrasonic shot peening that uses media of several millimeters in size with ultrasonic vibration has attracted attention as a means to reduce the surface roughness. In the present study, an air-type and an ultrasonic type machine were used. In the microshot peening process, the media used was high-carbon cast steel and the hard powder, with an average diameter of 0.1 mm. The workpiece was commercial titanium alloy Ti-6Al-4V. In the microshot peening (MSP), work hardening was evident to the depth of approximately 0.3 mm from the surface. This depth was approximately three times the diameter of the media. However, the influence of the peening time on the hardness distribution was not great. In the ultrasonic shot peening (USP), work hardening was deeper in the material. This is because the diameter of the media used for ultrasonic machining was large. On the other hand, in the combined shot peening (CSP), a degree of hardness was higher at the top surface. However, the hardness patterns and values were pretty much identical to ultrasonic shot peening. The fatigue limit was thought to be greater in the microshot peening experiment because the work-hardened layer was formed near the workpiece surface.

Kinetic Description of (Cr, Fe)<sub>7</sub>C<sub>3</sub> Carbide Precipitation from Austenite in High-Carbon Fe-Cr-C Ternary Alloys

The paper develops a model of precipitation of secondary (Cr, Fe)7C3 carbides from austenite in high-carbon chromium white cast irons of the ternary system Fe–Cr–C. Description of isothermal kinetics is based on traditional approaches to diffusionally controlled growth of particles, and approximation of the shape of isothermal TTT curve by a parabola permitted to apply the Scheil–Steinberg integral for transition to continuous cooling conditions. Model parameters were determined from literature experimental data on the change of Ms temperature after continuous cooling with different rates. Dependences of these parameters on alloy composition were then also defined. Results of the work, combined with the previously proposed model of carbide dissolution in the gamma phase during austenitization, permit to calculate isothermal (TTT) and continuous cooling (CCT) precipitation curves for an arbitrary ternary Fe–Cr–C alloy after given austenitization mode.

Nitrogen as an alloying element improving material properties of the high carbon cast steel for ball mill liner plates

This paper presents an experimental analysis, which was carried out to evaluate the addition of nitrogen as an element complementing a chemical composition used for such cast parts. It has been demonstrated that nitrogen is very advantageous in the process of austenitizing and quenching, improving the stability and homogeneity of the alloy structure. Plates used as a lining of rotary mills operating in cement plants are castings, which acquire their properties mainly through proper heat treatment. Together with an appropriate microstructure and chemical composition, correct heat treatment allow to improve the wear resistance and significantly reduce the abrasive corrosion. Extensive investigations enabled establishing an optimum nitrogen content in the chemical composition of thick-walled castings used in cement industry. Results of experiments, managed for the steel of ledeburate type containing 0.8–1.2% of carbon, have found that the optimal level of nitrogen is in the amount of 0.07–0.10%. The proposed modification helped to reduce the amount of an expensive chromium, increase the hardness of the material (by about 2 HRC to 4 HRC), and to achieve the uniform microstructure and hardness, which noticeably improved the lifetime of the rotary mills plates.

Development of a new composite material for bits of supporting and centering devices

Research has been conducted on the development of a new composite material for bits of well-supporting and -centering devices. The highly durable composite makes it possible to reduce frictional energy losses on straightline wellbore sections while ensuring a highly destructive effect at wellbore sections that are being explored. High-carbon high-alloy cast irons reinforced with titanium carbide have been proposed as the composite matrix. It has been shown that the hardness of the new material is comparable to that of hard alloys, while the minimum power losses for sliding friction under abrasion are lower than for hard alloys and diamond-bearing materials.

Effect of Dendritic Morphology and Central Segregation of Billet Castings on the Microstructure and Mechanical Property of Hot-Rolled Wire Rods

Microscopic dendritic morphology and central macrosegregation in continuously cast high carbon steel billets with a cross section 150 × 150 mm2 are investigated to elucidate their effect on the microstructure and mechanical property of the following hot-rolled wire rods, whose diameters are 10 and 6.5 mm, respectively. Experimental observations and numerical simulations for the steel billets under different casting conditions are carried out. It is found that the secondary dendrite arm spacing (SDAS) in the billets increases with the increase of superheat temperature, while decreases with the increasing specific water flow. Smaller SDAS in the billet center leads to lower segregation index of carbon (rC) and manganese (rMn) due to the low permeability in the final solidification stage. The measured rMn and rC in billets are in an approximately linear relationship. In addition, for the same rolling and cooling process, the severer carbon segregation in the center of the billets is, the lower the sorbite rate of the rods and the worse stability in the mechanical property of the rods. The tensile strength of wire rods can be improved by adjusting the casting parameters to decrease the SDAS and reduce the central carbon segregation of the billets.

Effect of microshot peened treatment on the fatigue behavior of laser-melted W6Mo5Cr4V2 steel gear

In this paper, W6Mo5Cr4V2 steel gear tooth flank was firstly melted by laser irradiation, and then treated by microshot peening (MSP) with shot particles of different materials and peening time. The materials of shot particles were high-carbon cast steels and ceramics. The peening time was from 20s to 100s. The fatigue behavior of gear was tested using Forschungsstelle für Zahnräder und Getriebebau (FZG) back-to-back spur gear test machine. The experimental results have showed that the microhardness of gears increased, and the surface roughness of gears decreased after microshot peening treatment. In addition, the residual stress state in the near-surface layer of microshot peened gears was changed from tensile stress to compressive stress. The microshot peening treatment has improved the fatigue strength of gears in comparison with gears undergoing the laser surface melted (LSM). The material of microshot particle influenced the fatigue behavior of gears going through laser surface melting and microshot peening (LSMMSP). The fatigue properties of LSMMSP gears did not enhance with an increase in shot peening time. The effects of the relaxation mechanism of the compressive residual stress on the fatigue performance of LSMMSP gears have also been discussed. Retained austenite has played a positive role in improving the fatigue limit of LSMMSP gears.

マイクロショットと超音波の複合ピーニングによるチタン合金の疲労改善

The fatigue improvement of titanium alloy by microshot peening and ultrasonic peening was investigated. In the peening process, the equipment were used an air-type machine and ultrasonic peening machine. The microshot used were high-carbon cast steel with an average diameter of 0.1mm. The surface hardness data showed that, in the case of microshot peening, work hardening extended deeper than the mean diameter of the media. In addition, in the case of ultrasonic peening, the surface hardness increased slowly with the projection time. The rotary bending fatigue tests were carried at a frequency of 3150 cycles/min. Improvement of the fatigue strength was observed by both treatments.

超音波ショットピーニングとマイクロショットピーニングによるステンレス鋼の疲労特性

The effects of projection conditions on the surface hardness and fatigue strength of stainless steel was investigated. In the peening process, the equipment were used an air-type machine and ultrasonic peening machine. The microshot media used were high-carbon cast with an average diameter of 0.1mm. The surface hardness data showed that, in the case of microshot peening, work hardening extended deeper than the mean diameter of the media. In addition, in the case of ultrasonic peening, the surface hardness increased slowly with the projection time. The rotary bending fatigue tests were carried at a frequency of 3150 cycles/min. Improvement of the fatigue strength was observed by both treatments. The higher effect was found in the ultrasonic peening treatment, because a work-hardened layer was formed deeper in the material.

マイクロショットピーニングを施したチタン合金の疲労特性

The effect of microshot peening on the surface hardness and fatigue strength of titanium alloy was investigated. Shot peening is a widely used surface treatment method for improving fatigue life. This process imparts compressive residual stresses on the surface, thus improving the fatigue life of the machine parts. In the peening process, the equipment were used an air-type machine and ultrasonic peening machine. The microshot used were high-carbon cast steel with an average diameter of 0.1mm. The surface hardness data showed that, in the case of microshot peening, work hardening extended deeper than the mean diameter of the media. In addition, in the case of ultrasonic peening, the surface hardness increased slowly with the projection time. The rotary bending fatigue tests were carried at a frequency of 3150 cycles/min. Improvement of the fatigue strength was observed by both treatments. The higher effect was found in the ultrasonic peening treatment, because a work-hardened layer was formed deeper in the material.

Development and Application of Final Permanent Magnet Stirring during Continuous Casting of High Carbon Rectangular Billet

Production of continuously cast high carbon steel that very low center macrosegregation is an important object in meeting high quality requirements. Apart from the widely known methods of reducing macrosegregation during continuous casting, final permanent magnet stirring (FPMS) provides an alternative for producing steel with low macrosegregation. The permanent magnet stirring featuring with low power dissipation and high intensity of magnetic field, which is suitable for final stirring conditions. In the present research, a three-dimensional unsteady coupled mathematical model based on the electromagnetic field analysis software Opera-3D and the flow field software Fluent has been developed to analysis the magnetic flux density, the electromagnetic force and the molten steel flow under different stirring frequencies of FPMS. The calculated results in the residual liquid pool show that the center magnetic flux density is nearly invariable equals to 1335 Gs, the maximum electromagnetic force increases from 12 kN/m3 to 59 kN/m3 and the maximum tangential velocity in the width direction various form 0.09 m/s to 0.45 m/s as the stirring frequency increases from 1 Hz to 5 Hz. The industrial trials reveal that the FPMS with a stirring frequency of 5 Hz can effectively decrease the centre carbon segregation and improve the final product quality of high carbon steel.

G0400401 ばね鋼の疲労強度に及ぼす硬質マイクロショットピーニングの影響

In shot peening, the surface of the material receives a so-called peening effect where strong local deformation forms a work-hardened layer or causes compressive residual stress. More recently, a new type of microshot has been developed to enhance the peening effect. In the present study, the effect of microshot peening on the surface characteristics and fatigue strength of spring steel was investigated. The workpiece was commercial spring steel SUP9. In the microshot peening process, the equipment was used an air-type machine. The microshots used were high-carbon cast steel and cemented carbide with an average diameter of 0.1mm. Air pressure was 0.6 MPa and peening time was in the range of 10-100s. Surface roughness and Vickers hardness for the peened workpiece were measured. The out-of-plane bending fatigue tests were also carried at a frequency of 200 rpm. As the peening time increased, surface roughness for the peened workpiece decreased. The use of microshot was the very effective means of reducing surface defect. The microshot peening process was very efficient in improving the fatigue life of spring steel, especially at a high number of cycles. It was found that the use of the hard microshot was found to cause a significantly enhanced peening effect for spring steel.