Spacing Of Pearlite Research Articles

Influence of Hot Rolling Process on the Microstructure and Mechanical Properties of a Press Hardening Steel

Abstract In this article, microstructure and mechanical properties of a press hardening steel prepared with different rolling parameters are studied, and the effects of the rolling processes are analyzed. The results show that when the finishing rolling temperatures are 870°C and 900°C and the coiling temperature rises from 640°C to 700°C, the strength of the press hardening steel increases and the elongation decreases. The yield strength of the steel prepared with low finishing rolling temperature is high, but the tensile strength has little difference, and the elongation decreases quickly. The microstructures consist of ferrite and pearlite, but as the coiling temperature rises, the amount of the alloy-carbide precipitates in the ferrite, and grain boundary is reduced significantly. The interlamellar spacing of pearlite gradually becomes narrow and the density of dislocation lines in the ferrite increases slightly. The press hardening steel rolled at the finishing temperature of 900°C and coiled at 670°C has excellent balance of mechanical properties. The yield strength, ultimate tensile strength, and elongation are 370 MPa, 598 MPa, and 19 %, respectively.

New mesoscopic constitutive model for deformation of pearlitic steels up to moderate strains

A new constitutive model for deformation of pearlitic steels has been developed that describes the mechanical behaviour and microstructural evolution of lamellar multi-colony pearlite. The model, a two-phase continuum model, considers the plastic anisotropy of ferrite derived from its lamellar structure but ignores any anisotropy associated with cementite and does not consider the crystal structure of either constituent. The resulting plastic constitutive equation takes into account a dependence on both the pearlitic spacing (arising from the confined slip of dislocations in the lamellae) and on strengthening from the evolving intra-lamellar dislocation density. A Kocks-Mecking strain hardening/recovery model is used for the lamellar ferrite, whereas perfect-plastic behaviour is assumed for cementite. The model naturally captures the microstructural evolution and the internal micro-stresses developed due to the different mechanical behaviour of both phases. The model is also able to describe the lamellar evolution (orientation and interlamellar spacing) with good accuracy. The role of plastic anisotropy in the ferritic phase has also been studied, and the results show that anisotropy has an important impact on both microstructural evolution and strengthening of heavily drawn wires.

Modeling of Austenite Decomposition during Continuous Cooling Process in Heat Treatment of Hypoeutectoid Steel with Cellular Automaton Method

The austenite decomposition during continuous cooling process in heat treatment of hypoeutectoid steel is studied with experimental method and numerical simulation. To investigate the phase transformation, quenching experiments are conducted and the microstructure evolution is investigated through metallographic examination. Dilatometric experiments are conducted as well and the experimental results are employed to analyze the phase transformation process during austenite decomposition. Subsequent studies of austenite decomposition in the steel are conducted using a numerical model based on cellular automaton (CA) method. In the simulation, the transformation of austenite into ferrite and pearlite is simulated, and the growth kinetics and average grain size of ferrite as well as the average interlamellar spacing of pearlite were obtained. The simulation results of the effects of cooling rate on the average grain size of ferrite and interlamellar spacing of pearlite agree well with the experimental results. Finally, integrated with a previously developed model for the austenization in heating process of heat treatment, the present model shows a capacity to investigate the effect of the prior austenite grain size on the final microstructure formed at the end of austenite decomposition.

Enhancing Ductility of 1045 Nanoeutectic Steel Prepared by Aluminothermic Reaction through Annealing at 873 K

The 1045 steel with lamellar spacing of pearlite in nanometer was prepared by aluminothermic reaction casting and annealed at 873 K (600°C) with different time. Microstructures of steels were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). Tensile properties of the steels were measured. The results showed that the lamellar spacing of the pearlite increased with the annealing time. It was found that the microstructure of steels consisted of nanocrystalline-ferrite matrix and laminar pearlite phase. The average grain sizes of the ferrite were 26.9, 27.0, 26.1, and 34.9 nm for the cast steel and samples annealed for 2, 4, and 6 h, respectively. As the annealing time increased, the volume fraction of the pearlite almost remained constant, while the laminar spacing of pearlite increased from 146 to 300 nm. The tensile and yield strength varied slightly; the elongation obviously improved. After annealing for 4 h, the elongation increased to be 33%, which was the reported highest value for the steel up to now and about twice of the conventional 1045 steel.

Effects of Chromium, Vanadium and Austenite Deformation on Transformation Behaviors of High-strength Spring Steels

The phase transformation behavior during continuous cooling of high-strength spring steels containing different amounts of Cr was studied. Furthermore, the effects of combining Cr with V as well as austenite deformation on the transformation kinetics were investigated in the method of dilatometry and metallography hardness. The results showed that, with the increase of Cr, the pearlite transformation field was enlarged, the ferrite transformation field was narrowed, and the entire phase field shifted to the right. With the addition of V, the start transformation temperature of undercooling austenite (Ar3) was gradually increased, but the ferrite and pearlite transformation fields were not affected. Besides, the minimum critical cooling rate of martensitic transformation was also reduced. In addition, the dynamic continuous cooling transformation (CCT) curve moves to the top left compared with the static CCT curve. The transformed microstructures showed that the addition of V and the deformation not only refined the overall transformed microstructures but also reduced the lamellar spacing of pearlite. The alloying elements Cr and V promoted the Vickers hardness. However, the effect of Cr on the Vickers hardness of martensite was stronger and the influence of V on that of pearlite was stronger. Moreover, the Vickers hardness affected by the austenite deformation was more complex and strongly depended on the transformed microstructures.

Friction and wear behaviours of surface densified powder metallurgy Fe–2Cu–0.6C material

Surface rolling was employed to fabricate a densified layer on a powder metallurgy (PM) Fe–2Cu–0.6C piece. A densified surface layer with a depth of 335 μm and a surface hardness of 330 HV0.1 was obtained, in which the lamellar spacing of pearlite and grain size of ferrite were refined. Friction and wear behaviours of the surface densified material were studied. Results indicated that friction coefficient of the rolled material decreased as the load increased, which was lower than that of the un-rolled material. Wear volumes were lower than that of the un-rolled material, which increased as the load increased. Wear loss was caused by flake spalling and grooves, and the wear mechanism mainly was abrasive wear. The surface densified layer with higher hardness and lower porosity can hinder the cracks initiation and propagation on the surface and under the surface, which enhance the wear resistance of the PM material.

Microstructure, Precipitation, and Mechanical Properties of V-N-Alloyed Steel After Different Cooling Processes

Three cooling processes (direct air cooling, water cooling to 1023 K and 873 K (750 °C and 600 °C) followed by air cooling) after hot rolling are designed to develop V-N-alloyed 600 MPa grade high-strength steel for architectural construction. Microstructural characteristics, precipitation behavior, and mechanical properties were investigated. Experimental results indicate that all microstructures are composed of polygonal ferrite and pearlite. Compared to the microstructure obtained from traditional direct air cooling, the grain size of ferrite is refined from 6.5 to 4.6 μm and the interlamellar spacing of pearlite decreases from 136 to 45 nm, respectively, by the application of accelerated cooling and lower finish cooling temperature. The number fraction of high misorientation angle boundaries increases from 44 to 51 pct. Moreover, the sheet spacing of interphase precipitates decreases from (23 to 26 nm) to (14 to 17 nm) and the size of V(C,N) particles reduces from (5 to 8 nm) to (2 to 5 nm). Furthermore, the optimal mechanical properties are obtained in the steel water cooled to 873 K (600 °C), of which the yield strength, tensile strength, total elongation, uniform elongation, and impact energy at room temperature are 753 MPa, 922 MPa, 22 pct, 11 pct, and 36 J, respectively. Besides, the high yield strength is primarily attributed to the refined grains and precipitation hardening from interphase and random precipitation of nano-scale V(C,N) particles.

Effect of annealing temperature on the microstructure and tensile properties of a bimodal nano/micro grained 1020 carbon steel prepared by aluminothermic reaction casting

Bulk 1020 carbon steel was prepared by aluminothermic reaction casting. After casting, isothermal aging treatments at different temperatures are performed for different periods up to 8 h. Microstructure characterization was performed using many methods, including optical microscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. It was found that the steel consisted of a nanocrystalline- ferrite matrix and a microcrystalline pearlite phase with a laminar structure. The average grain sizes of the ferrite were 23, 24, 28, and 37 nm for the cast steel and for samples annealed at 600, 800, and 1000 °C, respectively. As the annealing temperature increased, the volume fraction of the pearlite initially increased and then decreased, while the laminar spacing of pearlite increased from 240 to 900 nm. When annealed at 1000 °C, a spherical black micron pearlite particle was formed. The tensile and yield strength dramatically decreased, and the elongation varied slightly with the annealing temperature. A ductile phase was achieved by extending the holding time.

The Interlamellar Spacing of Pearlite

Abstract The interlamellar spacing of pearlite is a very important microstructural parameter for steels containing pearlite, and becomes more important as the pearlite content increases towards a fully pearlitic microstructure. As the amount of pearlite in ferrite-pearlite microstructures increases, so does the strength, but toughness and ductility decrease. For a fully pearlitic steel, as the interlamellar spacing becomes finer, strength, toughness and ductility all increase. Consequently, in structure-property correlations it is important to measure the interlamellar spacing. This paper reviews procedures for performing such measurements. Due to the fineness of the spacing, either SEM images or TEM images of replicas or thin foils can be utilized. The range of spacings in a given specimen will be much narrower if the pearlite in the steel was formed isothermally rather than transformed over a range of temperatures, as in as-rolled or normalized steels.

Effect of tin on microstructure and mechanical properties of compacted graphite iron

This experiment investigated the effect of tin in an amount up to 0·121 wt-% on the microstructure and mechanical properties of compacted graphite iron. Graphite and matrix evolution was emphasised with the help of scanning electron microscopy. The results indicate that Sn in experimental range reduces graphite size. Pearlite quantity would increase with the increasing Sn and reaches over 95% when Sn is >0·057 wt-%. Sn helps to narrow the lamellar spacing of pearlite from sorbitic pearlite (320 nm) to troostitic pearlite (83 nm) when Sn increases from 0·003 to 0·057 wt-%. Appropriate Sn addition promotes the tensile strength and impact toughness, and the samples containing 0·057 wt-%Sn perform the highest values of 410·7 MPa and 9·11 J cm− 2 respectively. Elongation declines with increasing Sn content because of the emergence of more pearlite. Samples containing excessive Sn experience sharp deterioration in mechanical properties due to brittle cementite.

The effect of electropulsing on the interlamellar spacing and mechanical properties of a hot-rolled 0.14% carbon steel

The application of electropulsing treatment to a low carbon ferritic–pearlitic steel is studied. The effect of electric current pulses on the interlamellar spacing of pearlite is investigated. It is found that the interlamellar spacing increases as the number of pulses increases. The mechanism of electropulse-effect was discussed by analysing the change in the free energy and the reduction of electrical resistance due to electropulsing. Mechanical properties are also examined for the samples with and without electropulsing treatment. It is shown that softening occurs during the treatment which is attributed to the formation of precipitation free zone (PFZ), increase in the value of interlamellar spacing and the spheroidization of the lamellar structure.

Experimental research on the effect of induction reheating on the microstructure and mechanical properties of hot-rolled low-alloy steel plate

Electric induction reheating is used to control the temperature of hot-rolled steel products. To investigate the effect of this on microstructure and mechanical properties, hot-rolled low-alloy steel plate was cooled, reheated, and then either quenched or normalized. Analysis of the microstructure and mechanical properties showed that this process had a greater effect on quenched steel plate than on normalized steel plate. Reheating was found to affect the precipitation of alloy carbonitrides, and the recovery and recrystallization of deformed austenite. In the single-phase region, the lower cooling temperature resulted in better mechanical properties. In normalized steel plate, the interlamellar spacing of pearlite (ISP) increased from 118nm to 165nm after induction reheating. In steel plate quenched with a 70oC temperature difference, induction reheating reduced the strength difference from 80MPa to 23MPa. Our results provide useful references for optimizing electric induction and improving the uniformity of the mechanical properties of low-alloy steel.

Test and Research on Controlled Cooling Technology for High Carbon High Silicon Wire Rod of S87B

In this paper, critical temperature of phase transformation and continuous cooling transformation (CCT) curve of S87B were determined by hot uniaxial compression tests. At several of cooling speed, the microstructures were studied. The results indicate that the critical temperature of phase transformation become lower with cooling speed increasing, the min interlamellar spacing of pearlite was 0.125μm when the cooling speed was 4°C/s, the best cooling speed of phase transformation area was during (3-4)°C/s..

A study of manufacturing tubes with nano/ultrafine grain structure by stagger spinning

A new method of manufacturing tubes with nano/ultrafine grain structure by stagger spinning and recrystallization annealing is proposed in this study. Two methods of the stagger spinning process are developed, the corresponding macroforming quality, microstructural evolution and mechanical properties of the spun tubes made of ASTM 1020 steel are analysed. The results reveal that a good surface smoothness and an improved spin-formability of spun parts can be obtained by the process combining of 3-pass spinning followed by a 580°C×0.5h static recrystallization and 2-pass spinning with a 580°C×1h static recrystallization annealing under the severe thinning ratio of wall thickness reduction. The ferritic grains with an average initial size of 50μm are refined to 500nm after stagger spinning under the 87% thinning ratio of wall thickness reduction. The equiaxial ferritic grains with an average size of 600nm are generated through re-nucleation and grain growth by subsequent recrystallization annealing at 580°C for 1h heat preservation. The tensile strength of spun tubes has been founded to be proportional to the reciprocal of layer spacing of pearlite (LSP), and the elongation is inversely proportional to the reciprocal of LSP. This study shows that the developed method of stagger power spinning has the potential to be used to manufacture bulk metal components with nano/ultrafine grain structure.

Effects of high magnetic field on isothermal pearlite transformation and microstructure in a hypereutectoid steel

A high magnetic field was applied during the isothermal pearlite transformation of a hypereutectoid carbon steel at three different temperatures. It was found that the magnetic field applied can increase the transformation rate and the pearlite nodule growth rate, decrease the interlamellar spacing of pearlite and the amount of low angle boundary in ferrite lamella. The magnetic field effects are more obvious at high temperature. The mechanism of field-effect was discussed by analyzing the influences of high magnetic field on the eutectoid temperature, diffusion activation energy in austenite, Gibbs free energy of ferrite and dislocation mobility.

Analysis of Failure in Automobile Spokes Manufactured Using Medium Carbon Steel Wires

Medium carbon steel wires are used to manufacture spokes for motor vehicles, and the integrity of the spokes is very important from the point of view of safety to the driver of the vehicle. In this paper, analysis of failure of one batch of spokes has been presented. The spokes failed during assembling on to the wheels and also during the field trials. In order to understand the root cause of these failures, metallurgical investigation of these spokes was done. It involved fractography, scanning electron microscopy, EDS analysis, optical microscopy, hardness testing, tensile testing, and chemical analysis. Chemical composition and tensile properties of the material were found to be within the values mentioned in the specification. The cause of failure is concluded to be the wrong microstructure that got developed in the material. The microstructure of the material is coarse lamellar pearlite with ferrite decorated along the grain boundary. Ferrite being softer is preferentially getting deformed in comparison with the rest of the microstructure i.e., pearlite. This preferential deformation in the material is leading to initiation of cracks during the manufacturing of spoke. Additionally, due to higher lamellar spacing in pearlite, ductility of the material has also decreased.

Prediction of interlamellar pearlite spacing of tyre bead wires after patenting using electromagnetic techniques

An attempt has been made to correlate interlamellar pearlite spacing with electromagnetic parameters after the patenting stage (??3.1 mm wire) on a tyre bead wire line. Two different techniques were adopted for the above work. One was electromagnetic sorting and the other was measurement of the inductance of a suitable electromagnetic encircling coil at a lower frequency (17.1 Hz). The interlamellar spacing was assessed by the intercept method at a higher magnifcation (??25,000) using a scanning electron microscope. The observed results suggest that the electromagnetic sorting technique was not efficient enough to predict the interlamellar spacing quantitatively, whereas the electromagnetic measurement technique exhibited distinct differences in electromagnetic inductance for samples having different interlamellar spacings. The low-frequency inductance increased with an increase in the interlamellar spacing due to the reduced pinning effect on the magnetic domain wall movement.

MICROSTRUCTURE AND PROPERTIES OF Q235 STEEL TREATED BY NOVEL Q-P-T PROCESS

This paper presents the mechanical properties and welding properties of Q235 steel with minimum yield strength of 235 MPa treated by a novel quenching-partitioning-tempering (Q-P- T) process. The experiments indicate that the strengths of Q-P-T treated Q235 steel (briefly called QPT235 steel) markedly raise compared with Q235 steel, and its yield strength and tensile strength are 435 and 615 MPa, respectively. In addition, the mechanical properties of the welding joint of QPT235 steel are markedly improved compared with Q235 steel when the same welding solder and process are performed for the steel with the two treatments, and the tensile strength and elongation of the former are about 532 MPa and 16.71%, respectively, while those of the latter are about 414 MPa and 12.4%. The microstructural characterization reveals two main factors resulting in the mechanical properties of QPT235 steel superior to those of Q235 steel: the grains of ferrite and interlamellar spacing of pearlite are both refined in the welding heat affected zone (HAZ), and a lot of widmanstatten structures in the welding joint of Q235 steel is avoided for QPT235 steel; there is a mixed microstructure of hard phases of martensite and bainite as well as remained austenite as soft phase in both base metal and HAZ, which replace parts of ferrite and pearlite in Q235 steel.

Effects of Rolling Process on Microstructure and Yield Ratio in a High Strength Building Steel Plate

The microstructures have been investigated in steel plates with different rolling processes to find the reasons of yield ratio overseted standard in few high strength building steel plates produced in Echeng Iron and Steel Corporation. The effects of rolling path, rolling path depress ratio on microstructure and properties. Some reasons of yield ratio overseted standard have been analyzed. The results show that decreasing rolling paths and increasing depress ratio refined grains but unchanged area ratio and interlamellar spacing of pearlite. Yield strength excessively increased but tensile strength unchanged increased yield ratio. So, excellent properties can be obtained by applying the optimization process.

Influence of Co and Al on pearlitic transformation in superbainitic steels

The effect of cobalt and aluminium on the austenite to pearlite transformation in superbainitic steel was investigated. Experimental work showed that the transformation rate of pearlitic and the volume fraction of pearlite both were increased by adding ∼4 wt-%Co and 1·5 wt-%Al to the parent superbainitic steel. The addition of cobalt and aluminium to superbainitic steels desirably accelerated the growth rate of pearlitic microstructure and undesirably reduced the interlamellar spacing of pearlite, resulting in hardness higher than that of the parent steel in the pearlitic condition. Nevertheless, the accelerated pearlitic reaction, as a softening process of superbainitic steels before machining/forming, may make the commercial use of these steels more viable.