Pearlite Phase Research Articles

Enhancing strength and toughness in a pearlitic rail steel via multi-alloying and accelerated cooling

The demand for higher speeds and heavier loads has emphasized the necessity to tackle the inherent trade-off between strength and toughness in pearlitic rail steels. Herein, the co-additions of Cr, Ni and Cu and accelerated cooling rate on the microstructure and mechanical properties of a medium carbon pearlitic steel were systematically investigated. In comparison with base alloy, the new steel exhibits smaller prior austenite grain size (PAGS) due to the drag effect of Cu and Ni solutes. The finer PAGS and lower C content increased the volume fraction of proeutectoid ferrite. The finer pearlitic nodule size (PNS) and pearlitic colony size (PCS) were attributed to the small PAGS and greater extent of undercooling due to the combined effect of multi-alloying and accelerated cooling. Additionally, the synergistic effects of multi-alloying and accelerated cooling rate decrease the pearlitic phase transformation temperature, accountable for the finer interlamellar spacing (IS). Compared with the base steel, the yield strength and ultimate tensile strength of the new steel increased from 587 MPa to 1069 MPa to 740 MPa and 1178 MPa, respectively, with a simultaneous increase of ductility from 12.4 % to 14.7 %. The strength increments are mainly attributed to the finer IS in the new steel. Meanwhile, the new steel possesses a higher impact toughness compared to the base steel due to the increased volume fraction of proeutectoid ferrite, and finer PNS and IS.

Hardness and Microstructure Characterization of Hardfacing Alloys Deposited by The Shielded Metal Arc Welding (SMAW) on AISI 1045 Medium Carbon Steel

A ring frame is a machine used for yarn production in the textile industry. Continuous use of the machine results in wear on the shaft timing pulley on the ring frame machine. To improve this condition, repairs are needed, one of which uses the hardfacing method. This study aims to determine the effect of hardfacing on the microstructure and hardness of the shaft timing pulley made from AISI 1045. The hardfacing process used the shielded metal arc welding (SMAW) method with welding current variations of 115 A, 125 A, 135 A, 145 A, and 155 A. In this study, the electrode used was AWS A5.1 E7018 with a diameter of 3.2 mm. The hardfacing product obtained was then finished with a lathe to produce a shaft with a final diameter of 30 mm. In this study, microstructure and hardness tests were carried out on specimens before and after finishing. The results of this study showed that an increase in current caused an increase in the number of pearlite phases in the weld metal and HAZ (heat-affected zone) areas. While in the base metal, the increase in current increased the number of ferrite phases. The highest hardness value was found in specimens that were hardfaced with a current of 145 A. However, the hardness of the hardfacing layer will decrease with the use of currents greater than 145 A. The hardness of the specimens with hardfacing treatment at a current of 145 A resulted in hardness in the weld metal, HAZ, and base metal of 225 HV, 209 HV, and 203 HV, respectively. After the finishing process, the weld metal, HAZ, and base metal in this specimen produced a hardness of 225 HV, 217 HV, and 208 HV, respectively.

Study on Characterization of Phase Transition in Continuous Cooling of Carbon Steel Using In Situ Thermovoltage Measurement

In this paper, a self-designed and enhanced thermovoltage measuring device was built to capture thermovoltage curves of 45 steel during continuous cooling. The phase zones of the thermovoltage curve were interpreted based on the Engel–Brewer electron theory and Fe-Fe3C phase diagram. The results show that the curve was stratified into three homogeneous phase zones and two-phase transition zones as follows: Zone Ι: single-phase austenite (A) zone; Zone III: austenite and ferrite (A+F) homogeneous phase zone; Zone V: ferrite and pearlite (P+F) homogeneous phase zone; Zone II: austenite to ferrite (A-F) phase transition zone; and Zone IV: austenite to pearlite (A-P) phase transition zone. Notably, the deflection point marked the transition temperature, which indicates that the thermovoltage curve can quantitatively characterize phase formation and transformation, as well as the phase transformation process. Furthermore, the sample was quenched at the measured ferrite phase transition temperature. Microstructure observations, electron probe microanalyzer (EPMA) and microhardness measurements corroborated our findings. Specifically, our experiments reveal ferrite precipitation first from the cold end at the phase transition temperature, leading to increased carbon content in adjacent austenite. The results of this study achieved the in situ characterization of bulk transformations during the materials heat treatment process, which expands the author’s research work conducted previously.

Investigating the effects of partitioning temperature fluctuations on the mechanical properties of ASTM A36 carbon steel using Q-P-T heat treatment: an experimental study

In the continuum of time and technological advancement, the use of metals, specifically carbon steel, has significantly increased as primary materials in various operational and industrial domains, including tool fabrication and automotive components. To meet the evolving demands of industries, precise heat treatment processes have been developed to enhance the metallic properties. This study specifically focused on the application of the Quenching-Partitioning-Tempering (Q-P-T) method to ASTM A36 steel. The study investigated different partitioning temperatures, namely 300℃, 350℃, and 400℃, with 15-minute intervals. A comprehensive set of mechanical tests, including hardness, tensile, and microstructural analyses, were conducted to assess the response of the material to the treatment. The results reveal significant findings: a partitioning temperature of 300℃ yields the highest hardness value of 164 Vickers Hardness Number (VHN). Furthermore, the tensile tests demonstrate that a partitioning temperature of 300℃ is optimal, achieving a maximum stress value of 515.73 MPa. Conversely, a partitioning temperature of 400℃ exhibits the highest strain value at 21.08% and the highest elastic modulus value at 11.47 GPa. Microstructural evaluations highlighted the presence of pearlite and ferrite phases, with the partitioning temperature of 300°C displaying the highest proportion of pearlite phase at 38.5%. This meticulous investigation expands our understanding of metallurgy and underscores the intricate relationship between partitioning temperatures and the mechanical properties of ASTM A36 steel. It provides valuable insights for material design and application methodologies and facilitates advancements in industrial practices

Characterizing pearlite transformation in an API X60 pipeline steel through phase-field modeling and experimental validation

This study explores the microstructural characterization of pearlite phase transformation in high-strength low-alloy API X60 steel, which is used in pipelines. Understanding the formation, phase percentages, and morphology of the pearlitic phase is crucial since it affects the mechanical properties of the considered steel. In this research, a phase-field model, particularly the Cahn–Hilliard approach, was used in order to simulate the formation and morphology of the pearlite phase in response to different heat treatments. Both double- and triple-well potentials were considered for comprehensively studying pearlite’s morphology in the simulations. The simulation results were then compared with experimental outcomes obtained by metallography and field-emission scanning electron microscopy analyses. Considering the double-well potential can help simulate only two phases, ferrite and cementite, which is less compatible with the experiment results than the triple-well potential, which gives the possibility of simulating a three-phase microstructure, ferrite, cementite, and austenite, and a better match with experimental data. The study revealed that as the cooling rate increases, the interlamellar spacing and layer thickness decrease. Additionally, the difference between experimental and simulation results using triple-well potential was approximately ∼10%. Therefore, triple-well potential formulation predictions have better agreements with experimental results for the development circumstance of pearlitic structures.

RESEARCH ON THE RELATIONSHIP BETWEEN THE THICKNESS AND THE STRUCTURAL CONDITION OF ROLLED METAL FROM LOW-CARBON LOW-ALLOY STEEL 10G2FB

When choosing steels for the design of high-rise and long-span buildings with increased load-bearing capacity, it is advisable to give preference to thick rolled steel from low-carbon, low-alloy steels, since it, with the same level of strength as construction steels, has a higher level of plasticity. At the same time, the problem of using thick rolled steel from low-carbon, low-alloy steels in the construction industry are the anisotropy of the rolled metal properties, which can increase with an increase in the thickness of the rolled metal. Currently, in Ukraine, controlled rolling is one of the most promising technologies of high-temperature thermomechanical processing for the production of thick rolled metal from low-carbon, low-alloy steels. At the same time, with an increase in the thickness of the rolled metal, which is produced with this technological scheme, the effect of the regulated formation of the structural state decreases due to the influence on the temperature of the surface layers of the rolled metal, the thermodynamic state of the inner layers and the inability of the rolling equipment available at domestic enterprises to deform the metal over the entire cross-sectional area. Therefore, the task of obtaining such a structural state in the thick sheet metal roll, which will ensure the reduction of the anisotropy of the properties, which will allow the use of such rolled metal in the construction industry, is urgent. Purpose of the article is to study of the structural state of low-carbon low-alloy steel 10G2FB, which was produced using the technology of controlled rolling, depending on the thickness of the rolled metal. Conclusion. The relationship between the structural state and the thickness of rolled metal from low-carbon low-alloy steel 10G2FB, which was produced by controlled rolling technology, was studied. It was established that with the increase in thickness, the percentage content of the ferrite component increases with a simultaneous decrease in the percentage content of the pearlite phase. It is shown that changes in the formation languages of structural components begin with an increase in the thickness of the rolled metal over 30 mm, which is explained by the influence of the temperature of the inner layers on the processes of forming the structural state, namely, with an increase in the thickness of the rolled metal, the thermodynamic rate of phase transformations in the middle layers of the rolled metal samples decreases. This conclusion is confirmed by two factors: firstly, an increase in the size of pearlite colonies, and secondly, a change in the morphology of the cementite framework of pearlite colonies from zigzag (thickness 16...30 mm) to ribbon (thickness 40...100 mm).

Effect of Austempering Holding Time Variations of 30, 60, and 90 Minutes at 300 °C on The Microstructure and Toughness of Nodular Cast Iron

The phases of the nodular cast iron matrix are similar to those of steel. Therefore, heat treatment of steel can be applied to nodular cast iron. A potential heat treatment for nodular cast iron is austempering. This study aimed to determine the effect of austempering holding time at 300 °C on the microstructure and toughness of nodular cast iron. The austempering process begins with austenitizing at a temperature of 850 °C for 60 minutes, then the quenching process is carried out in a salt bath until a temperature of 300 °C is held with variations of 30, 60, and 90 minutes, then cooled to room temperature. Metallographic testing was conducted to determine the phase change before and after the austempering process using a Scanning Electron Microscope (SEM). Meanwhile, impact testing was carried out to determine changes in toughness before and after the austempering process. At a holding time of 30 minutes, metallographic testing on the raw material produced a gray coarse pearlite phase, black nodular graphite surrounded by white ferrite. After the austempering process, gray fine pearlite and black nodular graphite appeared. At the holding time of 60 and 90 minutes, the graphite sizes were bigger. Austempering withholding times of 30, 60, and 90 minutes resulted in impact energy of 4.2, 10, and 11 Joule. From the results of the study, it was concluded that an increase in holding time would increase the size of the graphite and the toughness of nodular cast iron.

Evolution of mechanical properties of ferrite and pearlite phases during spheroidization process and their relationship to the overall properties of low alloy steel

Mechanical properties of ferrite-pearlite low alloy steel are strictly determined by the properties of ferrite and pearlite phases. In this present paper, the evolution of mechanical properties of ferrite and pearlite phases during spheroidization process is investigated by using nanoindentation tests. Meanwhile, the overall mechanical properties of the material were measured using uniaxial tensile tests. Test results indicate that with the intensification of spheroidization of layered cementite in pearlite, the hardness and yield strength of pearlite phase decrease from 2.72 GPa to 1.73 GPa and 411.5 GPa–256.1 GPa, respectively. However, the mechanical properties of ferrite phase exhibit an opposite trend, with hardness and yield strength increasing from 1.6 GPa to 1.67 GPa and 188.1 GPa–208.4 GPa, respectively. Uniaxial tensile tests results indicate that overall yield strength of steel decreases significantly as the degree of spheroidization increases, from the original 276 MPa–229 MPa. Although the strength of pearlite decreased by 38%, the overall strength of alloy steel decreased by only 15% due to an 11% increase in ferrite strength. During spheroidization process, the relationship between pearlite hardness, yield strength, and interlayer spacing of cementite in pearlite can be expressed in Hall-Petch type relationships as: H=0.482×S−12+1.34 and σy=91.44×S−12+149; and the relationship between the strengths of ferrite-pearlite aggregate and ferrite and pearlite phases is σy=Vf1.95σf+(1−Vf1.95)σp.

Underwater Friction Welding of Low Carbon Steel

In this study, an attempt was made to obtain a welded joint from the underwater friction welding (UFW) process. The workpiece material used in this experiment was AISI 1018 low carbon steel. The experiment was carried out on a friction welding machine which was designed and manufactured for this purpose. The UFW process was carried out by varying the spindle rotation used to rotate one of the workpieces. The friction force was kept constant. The quality of the welded joints resulting from UFW was determined by measuring the misalignment that occurs in the weld joint, the macro and micro structures formed, as well as the mechanical properties of the welded joint. For comparison, friction welding in air (FW) was also carried out. The results obtained indicate that low spindle rotation results in high misalignment of the welded joint between the two workpieces. During the UFW process, rapid cooling occurs so that the microstructure of the weld metal, TMAZ and HAZ is dominated by a fine pearlite phase so that the hardness and strength of the weld joint are higher than those produced by FW process in air.

Graphite Cast Iron GGG40 for Disposal Containers: The Corrosion Mechanism in Opalinus Clay Water

The overpack of the Pollux® 10 container, taken as a reference for the storage of fuel elements in different types of host rocks, is manufactured from spheroidal graphite carbon steel (GGG 40 / 0.7040) [1]. The near field environment after emplacement is constituted by bentonite, which turns moisty, warm, and anaerobic after some decades because of the decay of the heat generation and the consumption of oxygen by reaction with the container wall, microbes, and minerals [2]. Thus, the corrosion mechanism of metal containers in these conditions is an essential issue for the design of repository concepts of radioactive waste.For a better understanding of the corrosion processes taking place at the interface of steel and saturated bentonite, electrochemical and surface chemical analysis, including SEM-EDX and local XPS were performed on steel in Opalinus Clay water under different temperatures, pH´s and pressures. Electrochemical measurements were carried out in a dedicated reactor cell for working at high temperature and high pressures (up to 150 bars). A Solartron electrochemical interface 1287 connected to a frequency analyzer 1260 was used.Polarization curves performed in deaerated solutions are characterized by a low cathodic constant current separating the onset of water reduction and the active dissolution. The presence of oxygen increases the current of the cathodic plateau shifting the corrosion potential towards more positive values. The metallographic structure of the steel give rise to local predominantly anodic and cathodic elements, i.e., ferritic, and pearlitic phases, on the one side and cementite and graphite on the other side, respectively.The dissolution of the active phases is controlled by the formation of an oxide film mainly constituted by magnetite and silicates containing Fe, Al, Mg and Cr formed by oxidation of the silicon contained in the alloy. SEM pictures obtained after 48 h of corrosion under anaerobic conditions and 5 bar of pressure show the deposition of silicates with different morphologies: as clusters of spheres and as hexagonal platellets (see fig.1). Under 100 bar of pressure, however, an rather etched aspect can be observed, revealing clearly the different metallographic phases.The impedance diagrams obtained at the corrosion potential shows an inductive loop at low frequency. Based on the shape of potentiostatic anodic current transients, the inductive loops can be ascribed to the dynamic of formation-dissolution of the interfacial oxide-silicate film. The effect of hydrostatic pressure is particularly interesting. The shiny optical aspect of the surface after corrosion under pressure can a priori be explained by the reducing atmosphere created by water reduction under these conditions.The significance of the formation of silicates is evident in the surface analysis of samples after long-term experiments in contact with Wyoming bentonite saturated with pore Opalinus Clay water. TEM pictures of a cross sectional lamella including part of graphite sphere shows the formation of a silicate film covering the corroding surface with an irregular adherence. The accumulation of silicates at the surface creates an additional barrier for the metal dissolution, which reduces the corrosion rate by a factor of thousand.

Pengaruh Variasi Gerakan Elektroda Pada Pengelasan Smaw Terhadap Uji Kekuatan Bending Baja ST 42

This study aims to determine the effect of straight groove, zigzag groove, and U pattern groove movement on the hardness and mechanical properties of the material in ST42 steel welding. The welding method used is shielded metal arc welding (SMAW) with a current strength of 100 Amperes. The test results show that the movement of the straight groove electrode gives the highest stress value in the bending test with an average of 1,168 MPa. The zig-zag groove electrode movement gave an average stress value of 1.127 Mpa, while the U pattern groove electrode movement gave an average stress value of 1.905 MPa. Microstructural testing showed that all electrode movements produced pearlite and ferrite phases, but straight groove electrode movements had more pearlite phases than the other movements. In addition, the zig-zag groove electrode flow and U pattern. This study provides a better understanding of the effect of electrode movement on the quality of welded joints, as well as providing important information in the development of industrial welding techniques.

Lap Joint on St.37 Steel Plate with Friction Welding Clamping Method

Friction stir (FW) welding is a relatively fresh method that was created and has been continually refined and adapted to industrial applications due to its benefits. This approach for solid-state joining entails connecting the components at a temperature below their melting point and then heating them up. Clamp joint applications are widely used using external heating and hitting with high strength, but the clamped joints with the FW method are rarely done. The research studied the characteristic of clamped joints at various plate thicknesses using the FW method. In this study, 30 specimens were used in the form of a St.37 low carbon steel plate with a size of 50 mm x 100 mm and a thickness of 3 mm, 5 mm, and 9 mm, and several holes were made with a diameter of 5 mm. The plate was connected by 2 clamps, and 4 clamps then the FW method was conducted in a milling machine. The results indicate that the plates were connected well. The highest hardness value was 256.4 VHN on the FW of 9 mm plate. The microstructure is dominated by ferrite and a little pearlite phase. The largest shear force is 66.54 kN obtained at 4 clamps with a plate thickness of 9 mm, and the lowest is 13.46 kN, obtained at 2 clamps with a plate thickness of 3 mm.

Evolution of near homogenous mechanical and microstructural properties in wire-arc based directed energy deposition of low carbon steel following trochoidal trajectory toolpath

In the present work, the application of wire-arc-based directed energy deposition (DED) for the building up of three-dimensional structures of low-carbon steel (ER70S6) is proposed. The classical trochoidal-trajectory-based toolpath is employed to rapidly build up the structures with near homogeneous mechanical properties of the built. A robust as well as simple methodology has been developed, which is capable of building up thick walls of height 5 − 6 mm and width ∼ 20 − 22 mm in a single pass. During the deposition process, a uniform and fine distribution of grains with degenerate pearlite phases revealed, which is not usual in the layer-by-layer deposition of low-carbon steel. The trochoidal trajectory of the toolpath leads to the reheating of the deposition layer at 900 K and results in the formation of degenerate pearlite. The Electron Back Scatter Diffraction (EBSD) analysis confirms the formation of homogeneous and equiaxed grains of size 8μm throughout the built part. The mechanical properties of the built-up part improved with a uniform hardness of ∼174 HV and tensile strength of ∼ 494 MPa. Even, 40% elongation and 48.7% better wear resistance with respect to the base material are achieved for the deposited wall in different directions. This work presents a novel methodology to achieve near isotropic propery of arc-based DED process.

SSAW 용접기법이 강재의 용접부 미세조직에 미치는 영향

This study investigated the effects of self-shielded arc welding on the microstructures of welded parts in laminar-cooled-thermo-mechanical-controlled-process (LC-TMCP), titanium nitride (TiN), and B grade steels. The microstructure of the fusion zone was the same in all three samples, consisting of ferrite (grain boundary ferrite (GBF)+acicular ferrite+ferrite side plate) and pearlite phases, and the LC-TMCP and TiN steels had a higher volume fraction of ferrite and smaller grain sizes than those of the B grade steel. In all three samples, the microstructure near the fusion line consisted of ferrite and pearlite phases with a small amount of bainite, and the grain sizes of the LC-TMCP and TiN steels were smaller than those of the B grade steel. In addition, the TiN steel was smaller than the TMCP steel, and the volume fraction of ferrite (GBF, etc.) was the highest in the B grade steel and lowest in the TiN steel. The microstructure of the heat-affected zone included a phase in which a small amount of bainite was present in the ferrite and pearlite phases near the fusion line (1 mm) in all three samples. However, the shape was different from that of the base material, and the grain size was the largest in the B grade steel and smallest in the TiN steel. The volume fraction of ferrite (GBF, etc.) was the highest in the B grade steel and lowest in the TiN steel. All three samples had the same shape as the base metal phase at 5 mm from the fusion line. However, grain was growth.

Influence of the Cooling Rate on Mechanical and Corrosion Properties of Ferritic Si–Mo Ductile Cast Iron

In this study, the effect of the cooling rate controlled by different castings thickness ranging from 3 to 25 mm on the mechanical and corrosion behavior of Si–Mo ductile iron (DI) castings was investigated. SEM-EBSD investigations demonstrated that the nodule counts, nodularity, and ferrite phase increased while the ferritic grain size decreased with decreasing in the casting wall thickness; this in turn led to improvements in the tensile properties of the DI. The corrosion behavior of Si–Mo DI castings was investigated after different immersion times in a 3.5 wt pct NaCl solution via electrochemical experiments. The electrochemical results showed that the corrosion resistance of Si–Mo DI decreased in the following order: 3 > 5 > 13 > 25 mm. The results indicated that all of the tested DI samples exhibited galvanic corrosion between the nobler carbide and ferritic matrix phases. SEM analysis showed that the dissolution of the ferrite phase with the pearlite phase exposed and accumulated on the DI’s surface, which led to intense corrosion acceleration. The higher corrosion rates that were observed for those samples with higher casting wall thicknesses could be associated with the higher contents of pearlite/carbide.

In situ observation of pearlite phase transition in high-carbon steel under different holding temperatures and cooling rates using confocal laser scanning microscope

The pearlite phase transition behavior of the high-carbon steel (0.82% C) under different holding temperatures (1050 °C and 1450 °C) and cooling rates (60, 300 and 600 °C/min）were investigated using a confocal laser scanning microscope (CLSM). The phase diagram of the researched steel in an equilibrium state was calculated by JMatPro software, and the identifications of the pearlite lamellar spacing and dislocation density were conducted by SEM and TEM analysis, respectively. The in situ observation showed that the pearlite formed at the grain boundary and grew into austenite grains. As the cooling rate increased, the beginning and finishing temperature of pearlite transition moved in a lower direction as a whole. Compared with the normal heat treatment of 1050 °C, the pearlite formation temperature increased by 30 °C with a holding temperature of 1450 °C at the same cooling rate of 60 °C/min, which was contributed to the enhancement of dislocation density along the grain boundary. In addition, the liner relationship between average phase transition temperature and reciprocal of pearlite lamellar spacing was obtained.

Phase Transformation Behaviors of Medium Carbon Steels Produced by Twin Roll Casting and Compact Strip Production Processes

Medium carbon steels have been widely used in the fields of tool and die manufacturing due to their outstanding hardness and wear resistance. In this study, microstructures of 50# steel strips fabricated by twin roll casting (TRC) and compact strip production (CSP) processes were analyzed to investigate the influences of solidification cooling rate, rolling reduction, and coiling temperature on composition segregation, decarburization, and pearlitic phase transformation. The results show that a partial decarburization layer with a thickness of 13.3 μm and banded C-Mn segregation were observed in the 50# steel produced by CSP, leading to the banded distributions of ferrite and pearlite in the C-Mn poor regions and C-Mn rich regions, respectively. For the steel fabricated by TRC, owing to the sub-rapid solidification cooling rate and short processing time at high temperatures, neither apparent C-Mn segregation nor decarburization was observed. In addition, the steel strip fabricated by TRC has higher pearlite volume fractions, larger pearlite nodule sizes, smaller pearlite colony sizes and interlamellar spacings due to the co-influence of larger prior austenite grain size and lower coiling temperatures. The alleviated segregation, eliminated decarburization and large volume fraction of pearlite render TRC a promising process for medium carbon steel production.

Metallurgical analysis of ASME SA213 T12 boiler vertical water-wall tubes failure

Low carbon steel (SA213-T12) tubes were used as vertical water-walls of a boiler in a power plant of an electrical power generation, several tubes failed after serving for only 13,140 h. The failed tubes were located near the heat source (burner) at the entrance of the hot water before it was converted into steam. A failure analysis of the broken tubes was carried out to reveal the reasons behind their premature damage. The fractured surfaces of the failed tubes were examined by non-destructive testing. The metallurgical investigation of the failed tubes was carried out via optical and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and X-ray diffraction. The metallurgical characterization revealed that the structure of the sound part of the tubes consisted of proeutectoid ferrite and pearlite phases. However, the microstructure of the bulging area exhibited a complete decomposition of the pearlite, as well as formations of voids and cementite at the grain boundaries of the ferrite. It was concluded that the failure of the pipes happened due to creep damage associated with a localized overheating in the failed regions having outer and inner scales. Certain recommendations were also presented to prevent the repetition of this type of failure mechanism.

Effect of Complex Strengthening on the Continuous Cooling Transformation Behavior of High-Strength Rebar.

The effects of niobium and composite strengthening on the phase transformation characteristics and precipitation behavior of continuous cooling transformation of high-strength rebar during thermal deformation and subsequent cooling were investigated. The results show that when the cooling rate was within 0.3-5 °C/s, ferrite transformation and pearlite transformation occurred in the experimental steels. The Nb content increased to 0.062 wt.%, and the starting temperature of the ferrite transformation decreased. Meanwhile, the ferrite phase transformation zone gradually expanded, and the pearlite phase transformation zone gradually narrowed with the increase in the cooling rate. When the cooling rate was 1 °C/s, bainite transformation began to occur, and the amount of transformation increased with the increase in the cooling rate. It was found that the main precipitates in the experimental steels were (Nb, Ti, V)C, with an average particle size of about 10-50 nm. When the Nb content was increased to 0.062 wt.% and the cooling rate was increased to 5 °C/s, the ferrite grain size was reduced from 19.5 to 7.5 μm, and the particle size of the precipitate (Nb, Ti, V)C could be effectively reduced. The strength of the steel was significantly improved, but the elongation of the steel was reduced. However, the comprehensive mechanical properties of 0.062 wt.% Nb experimental steel was significantly improved at a cooling rate of 5 °C/s.

Failure Analysis on Tube Arm Cylinder Hydraulic Excavator

The Failure on tube rod arm cylinder hydraulic excavator caused to lose production and processing time on mining site. Investigation included visual inspection, chemical analysis, metallography analyze, and microhardness test. Tube material used high silicon material type while the standard used ST52 carbon steel type. The tube was broken and crack to several pieces. The chemical composition of the tube has different in sulfur and silicon content. From hardness test with micro hardness method, sample tube broken has lower hardness compared to standard hardness. Metallography analysis obtained the phase of tube has same phase with standard which is ferrite and pearlite phase but has different grain size. Based on this study, it can be resumed failure on tube is because impurities and different specification on raw material.