Low Carbon Ferritic Steel Research Articles

Monte Carlo Modeling of Low Carbon Steel Recrystallization: Role of Thermo-Mechanical Treatment and Chemical Composition

The recrystallization process of two low-carbon ferritic steels with low fraction of alloying elements are modelled. The difference in chemical composition and initial thermomechanical treatment between these two steels can be the cause of the difference in the stored energy distribution after 40% deformation by cold rolling or plane compression simulated by Finite Element Modelling (FEM). In both cases the deformation texture is characterized by the presence of a g- fibre with a reinforcement for the {111}<112> component. The microstructure simulated by FEM is used as initial structure for Monte-Carlo simulations of recrystallization. In these simulations, the variation in chemical composition and initial thermo-mechanical treatment is introduced by the difference in stored energy distribution while recovery, nucleation and grain growth are simulated assuming that grain boundary properties mainly depend on misorientation. Modelling results are in agreement with experimental observations: that is the presence of a g- recrystallization fibre which corresponds to the initial deformed state and the development of {111}<110> component which is not sharp in the deformation microstructure.

Production of Bulk Metallic Nano- and Submicrocrystalline Materials by the Method of Severe Plastic Deformation

It is shown that nano- (Dg < 100 nm) and submicrocrystalline (100 nm < Dg < 1 µm) structures can be obtained in low-carbon and corrosion-resistant austenitic and ferritic steels and aluminum and magnesium alloys by severe plastic torsional deformation under hydrostatic pressure and by equal channel angular pressing.

Formation of ultrafine grained ferrite in low carbon steel by heavy deformation in ferrite or dual phase region

The microstructural refinement supplies an alternative approach to improve the strength of low carbon steel without loss of room temperature ductility. This paper reports the methods to obtain the ultrafine grained ferritic microstructure by the heavy deformation of low carbon steel in ferrite or dual phase region. Various initial microstructures before deformation were selected. The deformation microstructure was analyzed by optical microscopy and electron back-scattered diffraction (EBSD) technique. It has been demonstrated that the equiaxed ferritic microstructure with a grain size of around 3 μm was obtained. The coarse pre-eutectoid ferrite dynamically recrystallized to form the ultrafine grained ferrite and the undercooled austenite was transformed to the ultrafine ferrite by the strain-induced austenite to ferrite transformation.

The production of ultrafine ferrite in low-carbon steel by strain-induced transformation

An investigation into the production of ultrafine (1 µm) equiaxed ferrite (UFF) grains in low-carbon steel was made using laboratory rolling, compression dilatometry, and hot torsion techniques. It was found that the hot rolling of thin strip, with a combination of high shear strain and high undercooling, provided the conditions most suitable for the formation of this type of microstructure. Although high strains could be applied in compression and torsion experiments, large volume fractions of UFF were not observed in those samples, possibly due to the lower level of undercooling achieved. It is thought that ferrite refinement was due to a strain-induced transformation process, and that ferrite grains nucleated on parallel and linear deformation bands that traversed austenite grains. These bands formed during the deformation process, and the undercooling provided by the contact between the strip and the work rolls was sufficient to drive the transformation to homogeneous UFF grains.

Determining phase volume fraction in steels by electron backscattered diffraction

The relative sharpness of electron backscattered diffraction (EBSD) patterns is used to quantify the volume fraction of ferrite in low-carbon steels. EBSD pattern quality (PQ) maps are shown to improve imaging of martensite and ferrite over optical and secondary electron imaging. Ferrite volume fraction in isothermally reacted Fe–0.12C–3.28Ni are quantified using PQ maps by manual point counting and image thresholding.

Strain aging behavior of austenitic stainless steels containing strain induced martensite

Transformation of austenite to martensite during deformation is widely used to strengthen metastable austenitic stainless steel grades. It has been reported that aging of cold worked material can result in further strength increases through the formation of additional martensite. Alternate interpretations of the effects of aging on the strength of stainless steels containing strain induced martensite may also be hypothesized. It is well known that plastically deformed ferritic steels can be strengthened by the diffusion of interstitial solute atoms (carbon and nitrogen) during aging at low temperatures. It is anticipated that plastically deformed metastable austenitic steels containing the body-centered martensite phase may also be strengthened in a similar manner. This assumption appears reasonable as martensitic steels, with low carbon content similar to the austenitic steels of interest, have been shown to exhibit aging effects similar to those observed in low carbon ferritic steels. Thus the purpose of the present study was to evaluate the effects of time and temperature on the stress-strain behavior and strength of cold worked metastable 300 series stainless steels to determine the degree to which observed strength increases might be attributed to strain aging.

Non-Metallic Inclusions and Acicular Ferrite in Low Carbon Steel

The formation of non-metallic inclusions with variations in various oxygen, nitrogen and titanium contents in low carbon steels has been studied. The relationship between the nature of non-metallic inclusions and the formation of acicular ferrite has been also investigated. It is found that the non-metallic inclusions observed in this study are mainly consist of Ti 2 O 3 and TiN together with a small amount of other complex oxides containing Mn and Si. It has been confirmed that Ti 2 O 3 and TiN play an important role in formation of acicular ferrite as a nucleation site and an austenite grain refiner, respectively. But it is not clear yet whether TiN acts as a nucleation site or not. It is also found that the volume fraction of inclusions is more effective than the type or size distribution of the non-metallic inclusions on the formation of acicular ferrite.

Annealing Textures for Drawability: Influence of the Degree of Cold Rolling Reduction for Low-Carbon and Extra Low-Carbon Ferritic Steels

This work considers the optimization of deep drawing properties by studying the influence of hot rolling conditions, cold reduction rate, and final annealing on the evolution of steel sheet textures. Two steels have been selected: a low-C steel used for enameling applications, and an extra-low-C steel of the interstitial-free type. Results show that the intensity of {111} component—and, consequently, drawability—is considerably higher in the textures of cold-rolled and annealed sheets than in hot-rolled sheets. It is suggested that drawability of sheets annealed after cold rolling improves if greater than conventional reduction rates are used during rolling. Finally, it is shown that, contrary to what has sometimes been claimed, improvements of the “ r” coefficient are not accompanied by a “pancake” morphology of the ferrite grains.

On the effects of predeformation on work hardening of ultra-low-carbon sheet steel

Predeformation affects the work-hardening behavior of sheet metals in sequential forming operations by producing various strain histories in different parts of the sheet. Several investigators have reported the effects of two-stage deformation on the behavior of sheet metals, particularly justification has been presented on face-centered cubic (fcc) alloys. However, the works on low-carbon ferritic steels are not conclusive. This article reports some new findings of the effects of two modes of predeformation on the subsequent stress-strain relationship in ultra-low-carbon sheet steels. The details of a laboratory test system are presented along with methods used to reduce the data. The effect of the stability ratio, a measure of the degree to which the interstitial atoms are free, on the hardening rate at second-stage of deformation was studied. For stabilized sheet steels, it was found that changes in strain path from equibiaxial stretching to uniaxial tension cause an increase in the flow stress relative to the flow stress at similar effective strain in continued monotonic. For unstabilized sheet steels, a significant increase in the flow stress was not observed with either equibiaxial prestraining or cold rolling and equibiaxial stretching.

Effects of changes in strain path on work hardening in cubic metals

Effects of abrupt changes in strain path on work hardening in stretching 1200 aluminum, OFHC copper, 70-30 brass, a low-carbon ferritic steel, and 310 and 304 austenitic steels have been investigated. Tests were made with first-stage extension in uniaxial and equibiaxial tension. Second-stage stretching was in uniaxial tension. It is shown that all of the above materials have some susceptibility to transient reductions in work-hardening rate,dσ/de, after changes in strain path. Some of the material and process variables which can influence the form and magnitude of the transients are identified. Within the group of materials tested, stacking fault energy (SFE) appears to be the most generally influential material variable. The magnitudes of prestrain required to give significant reductions indσ/de·1/σ after strain path changes are higher in the low SFE alloys. Changes in strain path are accompanied by a reduction in the effective extension at the first onset of strain localization, when the reduction indσ/de is sufficient to causedσ/de·1/σ to fall below unity. Within the ranges of prestrain explored, the maximum reductions indσ/de·1/σ were in the range of 0.5 to 1.0. Thus, none of the changes in strain path investigated caused a reduction in the limit of effective uniform elongation, until the prestrain was sufficient to reducedσ/de·1/σ in monotonic deformation to less than a value in the range of 1.5 to 2.0. For these reasons, the possible reductions in effective uniform elongation were much more severe in the high SFE materials than those in the low SFE alloys.

Possible areas of use of low-carbon high-chromium ferritic steels in certain basic chemical production facilities

Possible areas of use of low-carbon high-chromium ferritic steels in certain basic chemical production facilities

Cleavage fracture of low carbon ferritic steels with fine grain size

AbstractMicromechanisms of transgranular cleavage fracture in ferritic steels have been investigated, particular attention being paid to the dependence of cleavage fracture stress σf on grain size over the range from 3·5 to 34·3 μm. It is found that σf increases less than linearly with d−1/2, where d is the grain diameter, whereas the Hall–Petch relation holds for the yield stress. Based on the experimental results, where σf was measured in the steels and their grain size and carbide size were changed independently, it is suggested that in the grain size range cited, the predominant mechanism was the propagation of a microcrack, which formed in the discrete carbide, into contiguous ferrite grains. The measured values of σf were discussed in a quantitative manner based on a model into which an equilibrium distribution of dislocations produced by the double pile-up mechanism was incorporated.

Effects of the Intercritical Rolling on Structure and Properties of Low Carbon Steel

Recovery and recrystallization behavior of ferrite in low carbon steel during and after intercritical rolling have been investigated using a laboratory mill. The results obtained are as follows:(1) Dynamic recrystallization of ferrite occurs in the intercritical rolling at a high reduction of about 80%.(2) Dynamically recovered ferrite structure formed during intercritical rolling is very stable compared with that formed in the rolling below Ar1.(3) Fine ferrite-pearlite structure is obtained from austenite worked in the intercritical range.Making use of these beneficial effects of intercritical rolling, stronger and tougher steels can be produced by reheating steels at lower temperatures, followed by rolling both in the low temperature range of austenite and intercritical range where the fraction of transformed ferrite is less than that of non-transformed austenite. It is also necessary, for this purpose, that the rolled products be air-cooled or heat treated at a temperature below Ar1. If the total rolling reduction is the same, the properties of the steel obtained by intercritical multipass rolling are nearly equal to those obtained by single pass rolling.

Micromechanisms of fatigue crack growth at low stress intensities

Abstract Results from investigations of the fatigue crack growth behaviour and ∆K threshold levels in α-titanium, α-brass, and low-carbon ferritic steels are presented. The observations show that microstructure has a substantial influence on the mechanisms and modes of fatigue crack growth. The role played by transgranular and intergranular modes of failure in the intermediate and low ∆K regions are considered. The development of irregular fracture faces due to out-of-plane crack trajectories with the associated ‘non-closure‘ of the fatigue cracks is suggested as a substantial contributor to the factors determining ∆K threshold levels.

低炭素鋼におけるγ→α変態域圧延効果の基礎的研究

Recovery and recrystallization behavior of ferrite in low carbon steel during and after intercritical rolling have been investigated using a laboratory mill. The results obtained are as follows:(1) Dynamic recrystallization of ferrite occurs in the intercritical rolling at a high reduction of about 80%.(2) Dynamically recovered ferrite structure formed during intercritical rolling is very stable compared with that formed in the rolling below Ar1.(3) Fine ferrite-pearlite structure is obtained from austenite worked in the intercritical range.Making use of these beneficial effects of intercritical rolling, stronger and tougher steels can be produced by reheating steels at lower temperatures, followed by rolling both in the low temperature range of austenite and intercritical range where the fraction of transformed ferrite is less than that of non-transformed austenite. It is also necessary, for this purpose, that the rolled products be air-cooled or heat treated at a temperature below Ar1. If the total rolling reduction is the same, the properties of the steel obtained by intercritical multipass rolling are nearly equal to those obtained by single pass rolling.

Heat treatment of steel of the 01Kh28 type

1. It is established that it is possible to obtain consistent high values of the fracture toughness of low-carbon ferritic steel 01Kh28 after quenching from 850–950° in water. Heating in this temperature range leads to primary recrystallization and intensive refining of the structure. 2. The most favorable structure of steel 01Kh28 (with fine grains and boundaries free of precipitates) is obtained after quenching from 850–900°, when the rate of grain boundary migration is higher than the diffusion rate of carbon.

Changes in static yield properties of a ferritic steel during fatigue cycling

AbstractChanges in the macro-yield strength of a low-carbon ferritic steel induced by cyclic loading have been investigated. For zero-to-peak axial loading (R = 0) tests there is a progressive increase and for completely reversed axial loading (R = −1) a progressive decrease in the yield strength as compared with the static tensile value. The yield strength finally attained for both loadings was equal to the cyclic stress applied, which was significantly below the static yield strength in the R = −1 tests. For both loadings the change in the yield strength with cycling was preceded by a stage involving the gradual elimination of the yield drop and Luders strain. An attempt to explain the elimination of discontinuous yielding in terms of the Johnston-Gilman theory is made by considering the premature yielding of the surface layers of the steel in the microstrain region.

Further observations on the plastic deformation of a normalized low carbon steel

The plastic deformation of a commercial grade low carbon steel has been investigated using microhardness and grain strain measurement techniques. Two distinct modes of deformation during plastic flow in low carbon ferritic steel have been identified. The initial stage involves the propagation of the Luder's band along the gauge length of the sample by slip strain in the surface and near surface grains only, the strain accommodation in the interior of the material being attained by a predominantly grain translation mode. The second stage involves the propagation of a strain hardening front through the cross-section of the material as the macro-strain is increased through the flow stress region.

Effect of nitrogen on the properties of low-carbon ferritic steel with 25% Cr

To improve the working capacity of steels of the 000Kh25 type the nitrogen content must be limited to 0.01%.

Casting magnesium-lithium alloys: V P Latenko et al, Space Investigations in Ukraine, Coll, No 1, Nauk Dumka Kiev 1973, 22–28 ( in Russian)

Electricity in many countries such as the US and China is produced by burning fossil fuels in steam-turbine-driven power plants. The efficiency of these power plants can be improved by increasing the operating temperature of the steam generator. In this work, we adopted a combined surface science and computational thermodynamics approach to the design of high-temperature, corrosion-resistant steels for this application. The result is a low-carbon ferritic steel with nanosized transition metal monocarbide precipitates that are thermally stable, as verified by atom probe tomography. High-temperature Vickers hardness measurements demonstrated that these steels maintain their strength for extended periods at 700 °C. We hypothesize that the improved strength of these steels is derived from the semi-coherent interfaces of these thermally stable, nanosized precipitates exerting drag forces on impinging dislocations, thus maintaining strength at elevated temperatures.