Pearlitic Cementite Research Articles

Contribution of EBSD for the Microstructural Study of Archaeological Iron Alloy Artefacts from the Archaeological Site of Loiola (Biscay, Northern Spain)

Iron palaeometallurgy was carried out on three artefacts, classified as nails and excavated from the archaeological site of Loiola (La Arboleda, Biscay, northern Spain), to investigate Roman manufacturing techniques. Energy Dispersive Spectroscopy (EDS) coupled with Environmental Scanning Electron Microscopy (ESEM) and micro-Raman spectroscopy were used to obtain elemental composition and structural characterization of mineral phases. Metallurgical properties and crystallographic texture were studied by combining microscopic methods such as optical microscopy (OM), Electron Backscatter Diffraction realized in environmental mode (EBSD) and measurements of local Vickers microhardness. The three artefacts had different microstructures, distinguished by a large gradient of carbon content, although important segregations (inclusions) were observed in all of them. Two pearlite-rich artefacts showed a high density of structural defects (geometrically necessary dislocations and large crystallographic orientation gradients in pearlitic ferrite, curved pearlitic cementite) resulting from a high level of plastic deformation that occurred during the manufacturing process. The third artefact consisted of pure ferrite without structural defects. This one was clearly manufactured differently from the two others, so it probably had another functionality.

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.

Stabilizing austenite in flash-annealed lean steel via laminate chemical heterogeneity

Retained austenite (RA) is especially valued in advanced high strength steels for its transformation-induced plasticity (TRIP) effect during deformation. However, the stabilization of RA in lean steels (C < 0.2, Mn < 2 wt%) is challenging due to the lack of austenite stabilization elements. In this study, a flash austenitization heat treatment approach was used to shorten the low-carbon TRIP steel processing time. This achieved a dual-phase microstructure composed of mass retained austenite and fine-grained ferrite in place of traditional bainite. Blocky, lamellar, and granular RAs were observed in the microstructure. Mn heterogeneity in the initial pearlitic cementite and ferrite was found to prevail in the retained austenite. Following the designed annealing route, phase-field simulations revealed that the ferrite transition kinetics accelerated in the Mn-depleted region which induced efficient carbon enrichment in austenite. The pronounced chemical heterogeneity of C and Mn co-resulted in the nonuniformity of the phase transition driving force from austenite to bainite and martensite, thus aiding the stabilization of austenite.

Simulation and Experimental Study on Rolling Friction and Wear of Heavy Haul Wheel Tread

Rolling friction and wear testing of heavy haul wheel tread was performed. The results show that a new and dominant vibration was generated owing to the surface wear, resulting in the polygonalization wear of the wheel specimen. The slip between wheel and rail specimens accelerated the formation of polygonalization wear. The pearlite and proeutectoid ferrite in the outermost layer were completely fragmented to form a fine grain layer. There was an extreme state for the deformation of the microstructure in the outermost layer, and there was a corresponding extreme value for the hardness. The slip accelerated the surface microstructure to reach the plastic hardening limit, but it had little effect on the extreme value of hardness. The stress distribution of the wheel specimen surface was simulated. The results show that there were alternating principal tensile and compressive stresses at the contact surface of the wheel specimen and shear stresses with alternating directions in the subsurface of the contact patch. The depth of the maximum shear stress from the surface was mainly related to the normal load, while the slip has no significant effect on it. A coupling modeling method of finite-element method (FEM) and smoothed particle hydrodynamics (SPH) was used to simulate the microstructure evolution of CL70 wheel steel. The simulation results show that there was mutual mechanical interaction between ferrite and cementite in pearlite. Their deformation was inconsistent owing to their different mechanical properties, resulting in large tensile stress at the boundary between them, even in the compressive stress area below the contact patch.

Formation mechanism for the white etching microstructure in the subsurface of the failure pearlite wheel steel

The subsurface white etching microstructure (WEM) was an important reason to cause the rolling contact fatigue (RCF) failure of wheel materials. The WEM formation mechanism in the subsurface layers of failed pearlite steel wheel was analyzed by using a scanning electron microscope, transmission electron microscope, and nanoindenter. The results showed that RCF cracks were mostly at the interface between the WEM and pearlite matrix. A large amount of the WEM was found in areas with no RCF cracks. This indicates that the WEM was formed prior to the RCF cracks. The WEM was comprised of nanostructured ferrite grains and residual cementite particles, and its hardness (approximately 920 HV) was about 3 times as high as that of the pearlite matrix. A soft area model for WEM formation is proposed based on the microstructural characteristics of two types of ferrite grains and the dissolution of cementite in pearlite resulting from continuous plastic deformation. During the wheel–rail contact, continuous plastic deformation in the subsurface under high contact stress conditions causes the successive refinement of the proeutectoid ferrite (PF) with low strength and ferrite grains in pearlite, the dissolution of cementite, and the improvement in the corrosion resistance, which cause the WEM to look white under an optical microscope. The WEM formation processes induced by alternating fatigue load were similar to that of surface nanocrystallization through surface mechanical attrition treatment. The great difference between the WEM and the pearlite matrix in the strength results in the crack propagating along their interface, therefore the nonuniform distribution of the WEM along both edges of RCF cracks was found commonly.

Effect of Post-Weld Heat Treatment Temperature on the Mechanical Properties and Microstructure of Carbon Steel Base Metal

The effect of post-weld heat treatment (PWHT) on the mechanical properties and microstructure of carbon steel base metal was investigated. MDF A 105, 106-B, 216-WCB, 516-415, and 516-485 carbon steels were employed, and the steels were each subjected to heat treatment with holding temperatures of 610, 650, 690, and 730 ℃ for 8 hours for the simulation of PWHT. The tensile strength and impact toughness of the steels showed a tendency to decrease with increasing holding temperature; this behavior was mainly attributed to the spheroidization of cementite in pearlite and the precipitation of cementite at grain boundaries.

3D Growth of Intragranular Pearlite in an Aged 100Mn13 Steel

The morphology and microstructure of intragranular pearlite in 100Mn13 high‐carbon, high‐manganese steel aged at 600 °C are observed by a scanning electron microscope (SEM) and transmission electron microscope (TEM) and analyzed, and growth models describing the morphology and growth process in 3D space are proposed. The results show that pearlite could nucleate directly in the austenite grain and present a 3D morphology after deep etching, and ferrite and cementite in pearlite keep the orientation relationship (OR) with austenite, , , , and . Also, the overall continuous ledges at the lamellar ferrite surface and end surround the whole ferrite lamellae, corresponding to a fringe structure and a curved frontier interface in 2D space, which shows a terraced morphology in 3D space. The different structures of the α/γ interface in 3D directions result in different growth rates of ferrite lamellae, that is, edgewise grows fastest along the direction of due to the incoherent interface composed of with a 28% mismatch, and sidewise grows slowest along the direction of due to the coherent interface composed of with a 1.9% mismatch.

Corrosion Resistance of Finer/Coarser Pearlitic Structures of Carbon Steel

Corrosion performance on pearlite structures of carbon steels has been researched using scanning Kevin probe force microscopy and energy-dispersive X-ray spectroscopy. The corrosion test was conducted by immersing in borate buffer solution containing NaCl. In the coarser pearlite structure, we detected an increase in the Volta potential at pearlitic cementite–ferrite boundaries after corrosion, in accordance with the following: increasing C concentration, and decreasing Mn concentration. We detected little change in the Volta potential and inorganic element concentrations in the finer pearlite structures. Crack-like trenches, with a depth less than several nanometers, formed along the boundaries where the Volta potential increased in the coarser pearlite structures. We demonstrated the importance of the concentration of inorganic elements (such as Mn and C) in promoting the initiation of corrosion, and higher corrosion susceptibility for the coarser pearlite structures.

Investigation of strengthening mechanism in Ni–38Cr-3.8Al alloy with fine lamellar structure by in situ neutron diffraction analysis

The strengthening mechanism of Ni–38Cr-3.8Al (mass%) alloy with fine lamellar structure composed of the γ/γ' and α-Cr layers, which is formed by discontinuous precipitation, was examined by in situ neutron diffraction analysis. The contribution of each constituent phase on the deformation behavior could be separated by the in situ analysis. The plastic deformation occurred preferentially in the γ and γ' phases, while the α-Cr phase deformed more elastically even beyond the yield point of the γ and γ' phases, which is similar to the cementite in pearlite of a steel. Fine nano-lamellar structure formed by the discontinuous precipitation is found to be mainly responsible for high strength of the alloys, while the influence of the γ' precipitates on strength is likely to be small. Furthermore, the strengths of the α-Cr and γ phases in the lamellar structure increased linearly with increasing inverse square root of the width of the α-Cr and the γ phases, and therefore, the strengthening mechanism of this alloy is consistent with the Hall-Petch relationship of fine lamellar structure.

Study of partition to non-partition transition of austenite growth along pearlite lamellae in near-eutectoid Fe-C-Mn alloy

The austenite formation from lamellar pearlite was studied in a near-eutectoid Fe-0.6mass%C-2mass%Mn alloy with focus on the transition between partitioned and non-partitioned growth of austenite. The austenite was nucleated at pearlite colony boundaries and grew along the lamellae of pearlite. The isothermal austenite transformation curves revealed that the transition from slow to fast growth of austenite occurred over a narrow temperature range (720–725 °C). The ghost pearlite which had formed above the transition temperature transformed to a very fine mixture of martensite (previously pearlitic ferrite) and austenite (pearlitic cementite) upon cooling to room temperature. According to thermodynamic analysis which takes into account carbon transport from θ/α and θ/γ interfaces toward γ/α interfaces the transition temperature appears to be closer to experiment and significantly (ca. 20 °C) lower than that previously proposed assuming that the austenite was nucleated at the θ/α interface. Phase field simulation of the carbon and Mn distributions around the tip of a cementite lamella also seems to indicate the change of diffusivity which plays a leading role in the growth of austenite.

Low‐temperature annealing and graphitizing of white‐solidified low‐alloy cast irons

AbstractHypoeutectic iron‐carbon and iron‐carbon‐silicon model alloys as well as conventional cast irons GJL‐250mod and EN‐GJS‐600‐3 have been produced and processed by different solidification techniques, i. e. mold casting, electron beam surface remelting and melt spinning. The white‐solidified alloys exhibit different degrees of microstructural refinement indicated by a secondary dendrite arm spacing of 0.3 μm–12 μm. The effects of microstructural refinement and silicon content on the hardness as well as on coarsening of cementite and graphitizing at temperatures of 540 °C to 670 °C have been investigated. The hardness of the as‐solidified alloys increases with decreasing secondary dendrite arm spacing and increasing silicon content. High silicon content effectively retards coarsening of pearlitic cementite, and thus is beneficial to retain the hardness at small thermal load. On the downside, high degree of microstructural refinement and high silicon content promote and accelerate graphitizing at temperatures &gt; 600 °C. The results are discussed in terms of the applicability of a recently developed two‐step surface treatment for cast irons, i. e. electron beam remelting followed by nitriding.

Effect of Sliding Wear on Surface Microstructure and Wear Property of D2 Wheel Steel

In this paper, the surface microstructure and wear property of D2 wheel steel under sliding wear condition were studied by MRH-30 sliding wear tester. After testing, a transmission electron microscope (TEM), scanning electron microscope (SEM) with electron backscatter diffraction (EBSD), and micro-hardness testers were used to characterize the surface microstructure of samples with different cycles. The results show that the wear losss samples are increased as the increase of cycles, and the wear loss of wheel samples is higher than that of rail samples. The surface hardness and thickness of deformation layer of wheel samples are increased as the cycles increase. After sliding wear, the samples surfaces form the white etching layer with the thickness of several microns. Through the analysis of surface microstructure of sample with 12,000 cycles, the lamellar cementite in pearlite is fragment into cementite particles with the decrease of depth from surface, and the cementite is dissolved at surface to lead to the form of white etching layer. The ferrite grains are refined gradually and the fraction of high angle grain boundary is increased with the decrease of depth from surface. The nanosgrains layer of ferrite grains with 5 μm thickness is formed. According to the result of finite element simulation of contact surface temperature, the formation of surface nanograins and the dissolution of cementite are caused by the severe plastic deformation. The fiber structure of samples is formed after sliding wear, with direction of .

Metastable bcc-Cu precipitation behavior and its effect on microstructure and strengthening of as-cast Fe–B alloy containing 3 wt% copper content

The metastable bcc-Cu precipitation behavior, with particular focus on effect of metastable bcc-Cu on microstructural evolution and strengthening is investigated by experiment and calculation simulation in an as-cast Fe–B alloy containing 3 wt% Cu content. The results show that the metastable bcc-Cu precipitates with the size of 3 to 5 nm can precipitate from the α-Fe (pearlite). During the precipitation process, the metastable bcc-Cu can act as the highly effective heterogeneous nuclei of pearlitic ferrite, which results in the formation of abnormal pearlite. Additionally, the existence of bcc-Cu will lead to the refinement of abnormal pearlitie, the dissolution of abnormal pearlitic cementite, and the strengthening of pearlite. The microstructural evolution process can be essentially described as: L (liquid phase) → γ (austenite), L → γ + M2B(boride), γ → P(normal pearlite), γ → P + bcc-Cu1 (the first precipitates), γ → P + P*(abnormal pearlite) + bcc-Cu2 (the second precipitates) + bcc-Cu1, and γ → M (martensite). Moreover, the calculation simulation analyses are in good agreement with the experimental results.

Microstructure and properties of low carbon steel after surface alloying induced by high current pulsed electron beam

Abstract To improve the surface properties of low carbon steels, Cr alloying layer was introduced on the steel substrate irradiated by high current pulsed electron beam (HCPEB) alloying treatment. The microstructures of the Cr alloying layer were studied by means of XRD, OM, SEM and TEM. The properties of microhardness and corrosion resistance were also tested. Microstructure observations revealed that after HCPEB alloying, the surface was remelted and the thickness of the remelted layer was about 4–6 μm. The content of Cr in the remelted layer was higher than that of the matrix. TEM results revealed that the cementite in pearlite was dissolved, and a high density of dislocations and tiny reinforcing phases were formed in the alloying layer. Both of the microhardness and corrosion resistance of the irradiated samples were significantly improved after HCPEB alloying treatment.

Influence of on-line tempering parameters on microstructure of medium-carbon steel

A new process involving ultra-fast cooling (UFC) and on-line tempering (OLT) was proposed to displace austempering process, which usually implements in a salt/lead bath and brings out serious pollution in the industrial application. The optimization of the new process, involving the evolution of the microstructure of medium-carbon steel during various cooling paths, was studied. The results show that the cooling path affected the final microstructure in terms of the fraction of pearlite, grain size and distribution of cementite in pearlite. Increasing the cooling rate or decreasing the OLT temperature contributes to restraining the transformation from austenite to ferrite, and simultaneously retains more austenite for the transformation of pearlite. It is also noted that bainite was observed in the microstructure at the cooling rate of 45 °C/s and the OLT temperature of 500 °C. Through either increasing the cooling rate or decreasing the OLT temperature, the distribution of cementite in pearlite is more dispersed and grain is refined. Taking the possibility of industrial applications into account, the optimal process of cooling at 45 °C/s followed by OLT at 600 °C after hot rolling was determined, which achieves a microstructure containing nearly full pearlite with an average grain size of approximately 7 μm and a homogeneously dispersed distribution of cementite in pearlite.

Effect of Cr on Lamellar Spacing and High-Temperature Stability in Eutectoid Steels

In order to clarify the refinement behavior of the lamellar spacing and high temperature stability of the lamellae in pearlite by the addition of Cr, the effects of supercooling, the diffusion coefficients of C and Cr and spheroidizing of cementite were investigating using Fe-0.8%C binary and Fe-0.8%C-Cr ternary steels.The equilibrium transformation temperature of pearlite was increased by the addition of Cr. In comparison with the Fe-0.8%C steel, at a fixed pearlite transformation temperature, the pearlite lamellar spacing of the Cr-added steel was refined by increasing supercooling, and at the same supercooling, the lamellar spacing was refined by increasing the Cr content. This is caused by a decrease of the diffusion coefficient of C in the austenite by addition of Cr.Spheroidizing of cementite in pearlite at high temperature was inhibited by increasing the Cr content. The spheroidizing rate was reduced by the addition of Cr. Spheroidizing of cementite in pearlite by increasing the Cr content was inhibited due to the increased contribution of Cr diffusion for the coarsening reaction of cementite.

Quantitative Analysis of Cementite Spheroidization in Pearlite by Small-Angle Neutron Scattering

Small-angle neutron scattering (SANS) was used to investigate the spheroidization of cementite in pearlite upon annealing. Globally averaged information on the shape and size of cementite particles was collected by using the SANS profile analysis of 0.8 mass pct C pearlitic steel (0.8C) samples annealed at 973 K (700 °C) for 3.6 to 86.4 ks. The change in the total area of the ferrite–cementite interface or aspect ratio determined by ex situ SANS exhibits excellent correspondence with scanning electron microscopy observations. Then, in situ SANS data were collected during isothermal annealing of the 0.8C steel and the commercially available 0.45C carbon steel (JIS-S45C). The shape change of the cementite plate was monitored, and the spheroidization rate of the 0.8C steel was found to be faster than that of the 0.45C steel.

탄소강의 초석페라이트와 시멘타이트 구상화가 미끄럼마멸 거동에 미치는 영향 분석

The current study elucidates the effects of cementite spheroidization and pro-eutectoid ferrite on the sliding wear resistance in medium carbon (0.45wt%C) and high carbon (1wt%C) steels. Both steels were initially heat treated to obtain a fully pearlite or ferrite + pearlite microstructure. Spheroidizing heat treatments were performed on both steels to spheroidize the pearlitic cementite. Sliding wear tests were conducted using a pin-on-disk wear tester with the steel specimens as the disk and an alumina (Al2O3) ball as the pin. The sliding wear tests were carried out at room temperature in air with humidity of 40±2 %. Adapted sliding distance and applied load was 300m and 100N, respectively. Sliding speed was 0.1m/s and the wear-track radius was 9 mm. Worn surfaces and cross-sections of the wear track were examined using an SEM. Micro Vickers hardness of the wear-track subsurface was measured as a function of depth from the worn surface. Hardness and sliding-wear resistance of both steel decreased with increased spheroidization of the cementite. The decrease was more significant in the fully pearlitic steel (1wt%C steel). The steel with the pro-eutectoid ferrite showed relatively higher wear resistance compared to the spheroidized pearlitic steel.

Brittle-to-ductile transitions and its relation to the deformability of cementite in fully pearlitic steels

Temperature dependence of the absorbed impact energy in fully pearlitic steels was investigated. Two-step brittle-to-ductile transitions were observed. The value of the activation energy associated with the first transition is comparable to that of low carbon ferritic steels, indicating that the first transition is the brittle-to-ductile transition of ferrite phase in pearlitic steels. It suggests that the first transition is controlled by the dislocation glide in ferrite. The value of the activation energy associated with the second transition is higher than that of the first transition. Micrographs of fracture surfaces and side surfaces after fracture tests suggest that the activation energy associated with the second transition should relate to the deformability of cementite in pearlite, that is, the second transition is controlled by the dislocation activity in cementite of pearlite.

Effects of Coarsening of Cementite in Pearlite before Austenitization on Formation of BWING and Mechanical Property in a Steel

Effect of pre-treatment before austenitization on mechanical property in a steel has been investigated. Pre-treatment was done at 500°C for 600, 1200 and 1800s before austenitization at 1440°C for 120s. This pre-treatment was performed in order to introduce dislocation network into austenite, which acts as nucleation site for “bainite laths within austenite grain (BWING)”. BWING was formed with isothermal holding at 500°C for 10s after austenitization. Micro-Vickers hardness is measured in a steel with and without pre-treatment. The steel with appropriate pre-treatment exhibits high hardness, because large amounts of BWINGs are formed. In the case of cementites in pearlite being coarsened and the distance between cementites becoming large, dislocation network is apt to be introduced into γ. The dislocation network acts as nucleation site for BWING, resulting in the suppression of formation of intergranular bainite. BWINGs strengthen the steel.