Fine Pearlite Research Articles

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.

Analysis of the influence of groove welds of oxy-acetylene welding joints on tensile strength and microstructure on steel ST 37

In this study, the authors conducted a study on the analysis of the effect of oxy-acetylene welding joints on tensile strength and microstructure in the HAZ and weld metal areas on st 37 steel plates. The results of this study indicate that the average value of the highest tensile strength value is at V groove weld with the average strength of the welded joint is 4.796 kgf/mm2. While the lowest tensile stress is on the I groove weld of 4.674 kgf/mm2. Meanwhile, from the microstructure test, it can be seen that in the HAZ area each groove. Microstructure in the HAZ area shows that the double V groove weld types are fine ferrite, coarse pearlite and martensite. In type V groove weld the structures formed are ferrite, coarse pearlite and martensite. In type I groove weld the structures formed are ferrite, grain boundary ferrite and fine pearlite. Whereas in the weld metal area, and the results of the microstructure test of the weld area on the V seam, it shows a dense microstructure arrangement, the arrangement is identical to pearlite (dark color) so that the specimen is harder.

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.

Hardening of bucket teeth made from creusabro 8000 steel by using the induction hardening method

Excavators are often used in mining projects such as for penetrating, excavating, dredging, gouging, and crushing mineral rocks. Bucket teeth are an excavator component that is often being replaced due to failure. The most common failure mode that occurred in bucket teeth was wear on the tip or front section of it. To reduce the wear of the bucket teeth material then its hardness should be increased. As the hardness value increases, the resistance to wear increases. The bucket teeth were made of Creusabro 8000 steel and a hardening process was then carried out on the front section of the bucket teeth components by using an induction furnace. The power used in the induction furnace varies from 28, 35, 42 and 49 kW (kilowatts) and the holding time varies between 3 and 5 minutes. The heat treatment process used oil as a cooling medium. The analysis was carried out to determine the area that experienced an increase in hardness and its occurred microstructure. Microstructure examination was carried out with an optical microscope, and hardness test by using a Vickers microscopy. It can be concluded from the result of the analysis that the large area experienced an hardness increase is directly proportional to the electric current magnitude and holding time. The microstructure has changed from fine pearlite to martensite thus hardness of Bucket Teeth can be increased up to 100% of the initial hardness.

PROPERTIES OF HIGH-CHROMIUM CAST IRON/LOW-CARBON STEEL BIMETAL FABRICATED BY HOT-ROLLING

A bimetal composite plate including a high-chromium cast iron (HCCI) and low-carbon steel (LCS) cladding was fabricated with hot-rolling bonding in the form of a sandwich structure. In this work, the microstructure and mechanical properties of the bimetal composite were analyzed. Experimental results showed that the brittle HCCI layer achieved good thermoplastic deformation under the action of carbon-steel cladding. After hot rolling, the two metals were well bonded due to mechanical and metallurgical bonding, showing an excellent joint. C atoms diffused uphill the interface. A decarburization area was formed near the LCS side and a fine pearlite diffusion band with a thickness of about 2–3 µm was formed on the bonding interface. The tensile strength of the bimetal composite was 249.5 MPa, and a cleavage fracture appeared on the HCCI side. Interfacial delamination cracks and tunnel cracks of the HCCI were observed in the bimetal composite during a bending test.

Failure mechanism in the pearlite structure with lamellar graphite due to temperature

Critical operating temperature can be determined for the machine components that form the key functional part of the device. This article describes a change of the failure mechanism in the material of an engine, where the material structure consists of fine pearlite layers with lamellar graphite equivalent to grey cast iron. The mechanical properties of this material influence not only the layers formed by the perlite, but also the lamellar graphite acting as a stress concentrator. To assess the failure mechanism in the material, a fractographic analysis of the fracture areas was performed after the impact test. The range of test temperatures at which the impact test was performed on the test specimens with notch ranged from -80°C to +180°C. The occurrence of brittle fracture was detected at the low temperatures by cleavage along and over the planar layers of the lamellar graphite. The brittle fracture initiation at the higher temperatures was observed by cleavage in the basic layer of the perlite. Depending on the failure mechanism of the test specimens fracture area, critical temperatures were determined, in which the measured value of the notch toughness decreased. Regression of temperature dependence of notch toughness allows very precise quantification of this decrease.

Effect of Microstructure on the Corrosion Fatigue Crack Growth of Low and Medium Steels

This article studies the effect of microstructure on the corrosion fatigue crack growth behavior of low and medium carbon steels. 45 steel and 15CrMo were selected and five typical microstructures were obtained by different heat treatment processes. The microstructures of 45 steel and 15CrMo after annealing and normalizing are both ferrite and pearlite, but the proportions of ferrite and pearlite in the four microstructures are different. The quenching and tempering microstructure of 45 steel is tempered fine pearlite. Corrosion fatigue tests were conducted on specimens with different microstructures of the two materials. Expressions of corrosion fatigue crack growth rate and da/dN∼ΔK fitting curves of different microstructures were obtained. Comparison of da/dN∼ΔK curves of 45 steel shows that tempered fine pearlite has the best resistance to corrosion fatigue crack growth, and the content of pearlite has a great impact on the corrosion fatigue crack growth behavior for specimens with the microstructure of ferrite and pearlite. In the low ΔK region, the corrosion factor plays a dominant role in fatigue crack growth, and the corrosion resistance of pearlite is weak, which leads to a higher da/dN in the normalized state. In the high ΔK region, fatigue factor dominants, since the fatigue resistance of pearlite is strong, da/dN of the annealed state is higher. The experimental results of 15CrMo showed the same crack growth rate change regulation as that of 45 steel, which further proves the effect of pearlite on the corrosion fatigue crack propagation behavior.

Effect of heat treatment process on precipitation of V microalloyed steel

ABSTRACT Controlled rolling and controlled cooling processes achieve high-strength alloys due to their combined effects on the grain refinement, dispersion, and phase transformations. This paper studies the dissolution of V in austenite by normalizing treatments. The samples were then annealed to form uniform, fine, and dispersed V-based precipitates which in turn facilitated subsequent phase transitions in the steel. The results showed that V fully dissolved into austenite when the steel was treated. Besides, when the steel was annealed, V precipitated in the form of V(C, N), and the V(C, N) precipitates promoted the formation of ferrite. At the same time, fine pearlite phases also formed, and the V(C, N) precipitates were distributed among the pearlite lamellae. The uniformly dispersed V(C, N) precipitates further regulated the microphase organization, refined the grains, and acted as the microalloying element, making the steel more uniform, and improving the mechanical properties of the steel.

Improvement of Mechanical Properties of 20CrMnTi Steel through Microstructure Modification

Microstructure modification is an effective approach to improve the mechanical properties of materials. In the present study, expanded graphite (EG) was added in a 20CrMnTi matrix to form pearlite microstructure and proeutectoid cementite after sintering. Mechanical alloying was used to obtain a fine milled mixture with a ball/powder weight ratio of 20:1. After mechanical alloying for 10 h, the milled mixtures with different EG contents were pressurelessly sintered at 1250 °C for 10 min and then hot-pressed at 1150 °C under 30 MPa for 30 min in Ar to obtain dense and modified 20CrMnTi materials. The content of EG has a profound influence on the microstructure and mechanical properties of 20CrMnTi. A high tensile strength of 1088 MPa and a high Vickers hardness of 4.7 GPa were achieved in the 1% EG-modified 20CrMnTi, which were increased by 105% and 28%, respectively, compared with the pure dense 20CrMnTi. The formed fine pearlite and small proeutectoid cementite in the modified microstructure contributed to the improved mechanical properties of 20CrMnTi.

Evaluation of optimum condition to improve the microstructure in hot-rolled medium carbon steel by elimination of coarse pearlite patches

The present study is aimed to eliminate the undesirable microstructure in the real working condition of the steel unit. In this work, the microstructure of hot-rolled medium carbon steel (grade 45C8) is studied for application in the automotive industry. The effect of the temperature and rolling rate on the microstructure has been thoroughly investigated by analyzing the microstructure containing ferrite and pearlite phases after each trial run of hot-rolled steel. The desired microstructure of fine ferrite and pearlite is very much essential in hot-rolled medium carbon steel for better strength and uniform properties of the material. The formation of coarse pearlite is undesirable, which may lead to breakage during drawing and hardness variation in the hot-rolled steel. Therefore, this study is focused to find the optimum condition for achieving the microstructure containing uniform distribution of fine pearlite and ferrite without the presence of blocky pearlite patches.

Machine Learning‐Guided Design of Pearlitic Steel with Promising Mechanical and Tribological Properties

Herein, attempts have been made to design and develop pearlitic steels for application in heavy‐haul rails. The hardness plays a vital role in studying the mechanical and tribological properties, which is theoretically related to the alloying composition of steel. With aid of machine learning (ML) method, the particle swarm optimization (PSO) improved generalized regression neural network (GRNN) is utilized to model the relationship between composition and hardness of pearlitic steel. The results show that the designed steel exhibits superior hardness and mechanical properties with fine pearlite lamellar microstructure. In addition, the wear behavior of the steel and its wear mechanism are systematically studied by tribological testing and electron probe microanalysis (EPMA) observations of worn surface and wear particles. With composition optimization, the wear resistance has further improved as evidenced by the lower friction coefficient and reduction of wear volume. The pearlitic steels exhibit a combined wear mechanism including adhesive wear, abrasion, delamination, and plastic deformation. As a result, the designed steels offer high hardness with very good mechanical and tribological properties which are far superior to previously reported pearlitic steels. This work may assist in developing the appropriate composition to create the desired hardness, mechanical, and tribological properties.

Effect of induction post-heating temperature on the morphology, microstructure and mechanical performance of the heat affected zone in laser-induction hybrid cladding of full-scale rail

Abstract In the present work, the laser-induction hybrid cladding technology with induction post-heating (post-LIHC) was utilized to deposit coatings on the full-scale rail surface, and the effects of different induction post-heating temperature on the morphology, microstructure and mechanical performance of the heat affected zone (HAZ) were first in-depth analyzed. Results indicate that with the increase of the average induction post-heating temperature (Ta) in post-LIHC, the microstructure of the HAZ first transforms from the fine acicular martensite structure to the composite structure of martensite and pearlite, then changes to the pure pearlite structure, and finally retransforms to the coarse martensite structure. Especially, the morphology of the “Martensite Zone” (MZ) in HAZ undergoes three remarkable change with Ta increasing: “flat-U-shaped” → “flat-W-shaped” → “vanished” → “flat-V-shaped”. Under the induction post-heating window of Ta = 508 °C ~ 565 °C, not only the MZ in HAZ can be inhibited absolutely, but also fine pearlite with much lower interlamellar spacing, smaller grain size and higher grain misorientation forms instead, making the strength and toughness are both enhanced significantly than the other three type HAZs and the rail substrate. In addition, increasing the induction post-heating temperature within the window of Ta = 508 °C ~ 565 °C can increase the interlamellar spacing and reduce the ferrite grain misorientation of the pearlite structure in HAZ, but has no obvious effect on the grain size therein.

Effect of austenitizing temperatures on the microstructure and mechanical properties of AISI 9254 steel

Abstract In this study, the effect of austenitizing temperatures and low-temperature isothermal heat treatment (below martensite start temperature) on the microstructure and mechanical properties of AISI 9254 high silicon spring steel has been investigated. Experimental studies show that ultra-fine carbide-free bainite, tempered martensite and carbon enriched retained austenite could be observed in isothermally heat-treated samples where the as-received sample consisted of fine pearlite. A high tensile strength of ~2060 MPa, a total elongation of ~8 %, and absorbed energy of 105 J were achieved in a commercial high-Si steel by austempering below the Ms temperature. A good combination of strength and ductility has been obtained in prolonged austempering below the martensite start temperature (225 °C) from an austenitizing temperature of 870 °C.

Effect of quenching media on microstructural evolution, mechanical and wear properties of AISI4135 steel

The aim of this work is to study the effect of various quenching media on the microstructural evolution and properties enhancement of AISI 4135 alloy steel. The formation of dual microstructures and their effect on mechanical and wear properties are investigated in this work. An attempt is made to correlate the microstructure-properties relation based on the quenching method used. Steel is heated above the austenitic temperatures (A3) and subsequently cooled down through various quenching media to obtain the variations in microstructures and related properties. The heat treated samples were investigated for microstructural evolution through optical microscopy and scanning electron microscope; mechanical characterization through microhardness study, tensile testing and impact testing; and wear characterization through pin on disc tribometer. It was observed that increased cooling rates increased the volume fraction of martensitic structures whereas oil quenching enhanced fine pearlite and bainite formation. The air cooling led to the formation of fine pearlite along with ferrite structures. Strength, hardness and wear resistance is favored with martensite formation but toughness decreases.

Enhancement of the AISI 5140 Cold Heading Wire Steel Spheroidization by Adequate Control of the Initial As-Rolled Microstructure

The effect of the initial microstructure and soft annealing temperature on cementite spheroidization and microstructure softening is studied on an AISI 5140 hot-rolled wire. In coarse pearlite microstructure (λ: 0.27 μm), the cementite spheroidization progresses slowly under subcritical treatment, and the microstructure does not achieve the minimum G2/L2 IFI rating defined in the ASTM F2282 to be used in cold forming operations under any of the annealing treatment studies. Fine pearlite (λ: 0.10 μm) and upper bainite microstructures are more prone to spheroidization, and the minimum G2/L2 IFI rating is achieved under subcritical annealing at 720 °C for 6 h. Independent of the initial microstructure, even in the case of martensite, low hardness values within 165–195 HV are attained after imposing a 10 h long treatment at 720 °C. Annealing treatments conducted at 660 °C and 600 °C on pearlitic microstructures give rise to very poor softening. The G2/L2 rating is not achieved in any of the treatments applied at these two temperatures in this study. In pearlitic microstructures, the spheroidization progresses according to a fault migration mechanism, enhanced by the presence of defects such as lamella terminations, holes, and kinks. In the upper bainite, the row-like disposition of the cementite along the ferrite lath interface provides necks where dissolution and consequent lamellae break-up take place quickly under annealing.

Influence of normalizing post carburizing treatment on microstructure, mechanical properties and fracture behavior of low alloy gear steels

<abstract> <p>Steel is a versatile metal, got a wide range of applications in all the fields of engineering and technology. Generally, low carbon steels are tough and high alloy carbon steels are hard in nature. Certain applications demand both properties in the same steel. Carburization is one such technique that develops hard and wear resistant surfaces with a soft core. The objective of this work is to study the influence of post carburizing treatment (normalizing) on three grades of steels (EN 3, 20MnCr5, and EN 353). Post carburizing treatments are necessary to overcome the adverse effects of carburization alone. Here carburization was carried out in the propane atmosphere by heating the gas carburizing furnace to 930 ℃ for more than a day. Normalizing was carried out at 870 ℃ for 1 h and cooled in air. Tensile, hardness, Charpy impact tests along with SEM (scanning electron microscopy) and EDAX (energy dispersive X-ray analysis) were conducted to analyze the phase transformation, failure mode analysis in all the samples. Carburized steels displayed the formation of ferrite, pearlite, and sometimes bainite phases in the core and complete coarse pearlite in the case regions, whereas in the post carburized steels, increased amount of ferrite, fine pearlite, and bainite in the core and fine pearlite with traces of bainite in the case region was observed. Normalizing also refines the grain with increased UTS (ultimate tensile strength), hardness, and impact resistance. EN 353 showed higher UTS among the steels with 898 MPa after carburization and 1370 MPa after normalizing treatment. Maximum hardness of 48 HRC was observed in 20MnCr5 and toughness was superior in EN 3 with energy absorbed during test i.e., 8 and 12 J before and after normalizing treatment. Based on the fracture surface analysis, in EN 353 steel, a finer array of dimples with voids and elongated bigger clustered dimples containing ultrafine dimples array are observed in the core and case respectively during carburizing whereas, more density of river pattern and cleavage failure (brittle) are observed in the core and case respectively after post carburizing (normalizing) treatment. There is a reduction in the ductility of the steels after post carburizing treatment. It was observed that normalizing treatment produces superior mechanical properties in the carburized steels by grain refinement and strong microstructures like bainite. Normalizing as post carburizing treatment can be recommended for engineering applications where ductile core and hard surface are of great importance.</p> </abstract>

Mechanical properties and microstructural characteristics of rotating arc-gas metal arc welded carbon steel joints

Abstract The main problem associated with high thickness carbon steel plate's narrow range or “V” groove welding in conventional welding processes is the sagging of the molten pool due to gravity, which in turn leads to defects formation and deteriorates mechanical properties. This problem could be overcome by the rotating arc gas metal arc welding (RA-GMAW) technique. This investigation aims to evaluate mechanical properties and metallurgical characteristics of high thickness IS2062 Gr-B carbon steel joints welded by RA-GMAW technique. The experimental results show that RA-GMAW joint exhibited higher (598 MPa) tensile strength, higher hardness (220 HV) at weld metal region, and lower impact toughness (137 J) than the unwelded base metal. This is due to the presence of fine acicular ferrite and widmanstatten ferrite matrix mixed with fine lamellar pearlite microstructure in the weld metal region.

The effect of low tempering, medium tempering, and high tempering heating temperature variations in the type of medium carbon steel ST 60 on microstructure, hardness, and toughness

To determine the changes in the microstructure, impact strength, and hardness of the carbon steel medium type ST 60 with variations in temperature: quenching, tempering 200°C, tempering 400°C and tempering 600°C, then a heat treatment was given at 850°C for 30 minutes then quenched with brine solution with a salt content of 10% and continued with tempering for 30 minutes with variations in tempering temperature: 200°C, 400°C and 600°C. The chemical composition of the ST 60 steel specimen obtained that the main constituent elements are iron (Fe) = 98.1%, manganese (Mn) = 0.572%, silisium (Si) = 0.246%, and carbon (C) = 0.362%. Meanwhile, the hardness, impact, and microstructure test results show that the quenching specimen has the hardest and softest material properties. This is indicated by the highest hardness value of 772.67 VHN and the smallest impact value of 1.24 J / mm2. The martensite phase structure formed causes the material properties to be the hardest. In the 200°C tempering specimen the hardness began to decrease and the ductility increased as indicated by the hardness value of 625 VHN and the impact value of 2.02 J / mm2. In this specimen, a tempered martensite phase was formed, which is softer than martensite. In the 400°C tempering specimen, the hardness value was getting smaller, but the ductility increased as indicated by the hardness value of 448.67 VHN and the impact value of 2.56 J / mm2. The bainite phase structure with ductile / malleable properties was formed in this specimen. In the 600°C tempering specimen the properties of the resulting material were the most ductile and softest indicated by the lowest hardness value of 295 VHN and the highest impact value of 3.11 J / mm2. The structure of the ferrite and fine pearlite phases with very soft properties was formed in this specimen.

Effect of Alloying Composition on Microstructure and Mechanical Properties of Ultranarrow Gap Welded Joints of U71Mn Rail Steel

A new welding method, ultranarrow gap welding with constrained arc by flux band, is proposed to compensate for the low quality of rail thermite welded joints. This article presents the results of research on the microstructure and mechanical properties of ultranarrow gap welded joints of U71Mn rail steel made using three types of alloying composition content flux bands. Results indicated that the base metal metallographic microstructure consisted mainly of pearlitic, the HAZ was mainly composed of fine pearlite, and the microstructure of the welded bead was composed of acicular ferrite, while the weld grain size decreased as the alloy composition increased. The average hardness noticeably changed in weld metal as the alloy composition increased, and when the alloy composition reached 19%, the hardness was equivalent to the base material. The average hardness value of the HAZ (35.8 HRC) was higher than that of the base metal (24.8 HRC). The tensile strength increased, and the percentage elongation after fracture decreased with increasing alloying composition from 9% to 19%. The impact absorbing energies were decreased as the alloying composition increased. Consequently, all the mechanical properties of rail ultranarrow gap welding were higher than those of the standard requirements of the rail flash welding. And the optimal alloying composition of flux band was 19%.

Optimizing the Shape of Welded Constructions Made through the Technique “Temper Bead Welding”

Welded constructions are subject to high stresses during operation. One solution for improving the behavior in exploitation of welded constructions in various cases is to use the welding technique “temper bead welding” (TBW). In the paper, the optimization of the geometry of the welded joints by the TBW technique was performed. Thus, corner welded joints made of S355 steel were analyzed. To make the welded joints, three layers of welding seams were deposited, and the intermediate layers were processed through cutting with various radii. To analyze the influence of the size of these rays on the behavior of welded constructions, a research program based on factorial experiences was designed. The samples were tested in terms of fatigue behavior by applying loads between ±8 kN and ±12 kN. The research also focused on determining the hardness of the materials in the joints welded and on determining the microstructure of the materials in the heat affected zone (HAZ). Research has shown that it is possible to improve the characteristics of joints made by the TBW technique in the sense that it can be achieved an improvement in fatigue stress, a decrease in the hardness of the HAZ material and an improvement in the metallographic structure of the HAZ material, meaning that it has a structure made of ferrite and fine pearlite.