Extra Low Carbon Steel Research Articles

New Etching Technique to Reveal the Austenite Grains in Low and Ultra Low Carbon Steels Using a Dilatometer / Eine neue Ätztechnik zur Darstellung der Austenitkörner in kohlenstoffarmen und sehr kohlenstoffarmen Stählen

From literature we know that the prior austenite grains in low carbon (LC), extra low carbon (ELC) and ultra low carbon (ULC) steels can be revealed by thermal etching [1]. The austenite grain size influences the mechanical properties of steels through the phase transformations of austenite to ferrite. The conventional chemical etching techniques require a certain hardenability of the austenite and hence can only be applied to steels with relatively high carbon contents. The chemical etching technique is not suitable for revealing the prior austenite grain size in ELC- or ULC-steels. By using a dilatometer in combination with mechanical and chemical polishing, the γ-grains in LC, ELC and ULC steels can be revealed. Using this method it is also possible to measure the grain size applying quantitative image analysis to obtain quantitative results.

Precipitation and Recrystallization Behavior in Extra Low Carbon Steels.

Effects of precipitation on the recrystallization behavior of two Ti-added extra low carbon sheet steels were compared. The recrystallization temperature of the higher Ti-containing steel is higher than that of the lower Ti-containing steel. Small Angle Neutron Scattering (SANS) technique revealed no additional carbonitrides precipitation during the recrystallization annealing procedure in the low Ti-containing steel. However, in higher Ti-containing steel, new TiC precipitates, with a size range of several nm to several tens of nms, form during the recrystallization annealing process. This dynamic interaction of the precipitation of fine TiC particles with the recovery of dislocations seems the primary source of the retardation of the recrystallization in the higher Ti-containing extra low carbon steel.

The Deformation Microstructure and Recrystallization Behavior of Warm Rolled Steels.

The deformation microstructure of various warm (ferritic) rolled steels was characterized and its influence upon the subsequent annealing behavior determined. The materials investigated included three interstitialfree (IF) steels (stabilized with either titanium or niobium), an extra low carbon (ELC) steel, and four experimental low carbon chromium steels with varying levels of boron, nitrogen and phosphorus. Single pass rolling experiments were conducted in a pilot mill at temperatures between 440 and 850°C and the asrolled microstructures were examined using optical microscopy. Particular attention was paid to the nature and intensity of the in-grain shear bands produced. Partial annealing was conducted to examine the nucleation of recrystallization in the deformed microstructure. Shear bands of moderate intensity were usually formed in the IF steels, which tended to be insensitive to rolling temperature. For the ELC steel, intense shear bands were formed at low rolling temperatures, but at higher temperatures this intensity was found to be drastically reduced. The development of shear bands at the higher rolling temperatures was significantly enhanced by alloying with chromium. The differences in shear band frequency and intensity are explained in terms of the dynamic strain aging behaviors of the various materials. Recrystallized grains were found to nucleate preferentially on the shear bands during annealing, regardless of their morphology or intensity.

Study of ageing in strained ultra and extra low carbon steels by thermoelectric power measurement

Similarly to aluminium alloys, interrupted ageing in steels may increase hardness by 10%. By adding an intermediate stage between quenching and tempering, where quenched martensite is left to age at room temperature, carbon forms finer precipitate microstructures, which become more stable at room temperature. Using thermoelectric power to model carbon segregation to dislocations, it appears that room temperature ageing increases the number of effective nucleation sites for the subsequent tempering stage, as reflected in the microstructure and hardness.

1%Mn-0.034%Ti添加極低炭素鋼板の変態集合組織に及ぼす微量炭素添加量の影響

1%Mn-0.034%Ti添加極低炭素鋼板の変態集合組織に及ぼす微量炭素添加量の影響

High temperature oxidation studies of yttrium implanted pure iron and various steels

Yttrium implanted and unimplanted pure iron, extra low carbon steel, low manganese steel, and low manganese–carbon steel were analysed at 700°C and under an oxygen partial pressure PO2 of 0·04 Pa for 24 h to show the effect of yttrium implantation on high temperature oxidation resistance. Specimen oxidation weight gains were studied by thermogravimetry, and structural analyses were carried out by in situ high temperature X-ray diffraction (XRD) with the same experimental conditions. The aim of this paper is to show that the initial nucleation stage of the main compounds induced by oxidation at high temperature depends on the initial specimen composition and the surface treatment (yttrium implantation). The results obtained by in situ high temperature XRD will be compared with those from thermogravimetry for a better understanding of the weight gain curves observed during oxidation tests. This study is a fundamental approach which demonstrates the improved corrosion resistance of yttrium implanted specimens at high temperature.

In-situ high temperature X-ray diffraction characterization of yttrium implanted extra low carbon steel and pure iron

Yttrium implanted and unimplanted extra low carbon steel and pure electrolytic iron samples were investigated at high temperature ( T=700°C) under oxygen partial pressure P O 2 =0.04 Pa to observe their oxidation resistances under these experimental conditions. High temperature oxidation tests were carried out by thermogravimetry and by in-situ high temperature X-ray diffraction. The aim of this paper is to show the initial nucleation stage of the main compounds induced by oxidation at high temperature according to the initial sample treatment (yttrium implanted or unimplanted). The results obtained by in-situ high temperature X-ray diffraction will be compared to those by thermogravimetry to show the existing correlation between weight gain curves and structural studies. Our results allow to understand the improved corrosion resistances of yttrium implanted extra low carbon steel and pure iron at high temperature.

High temperature behaviour of yttrium implanted pure iron and extra low carbon steel

High temperature behaviour of yttrium implanted pure iron and extra low carbon steel were analyzed at T = 700°C and under oxygen partial pressure PO2 = 0.04 Pa for 24 h to show the benefit of yttrium incorporation to the improvement of the implanted sample corrosion resistance at high temperature. Compositions and structures of yttrium implanted and unimplanted samples were investigated prior to high temperature oxidation studies by several analytical and structural techniques (RBS, RHEED and XRD) to observe the initial yttrium implantation depth profiles in the specimens. High temperature oxidation tests performed by thermogravimetry and by in-situ high temperature X-ray diffraction were carried out with the same experimental conditions on yttrium implanted and unimplanted samples to have reference analyses. The aim of this paper is to show the initial nucleation stage of the main compounds induced by oxidation at high temperature according to the initial sample treatment. The results obtained by in-situ high temperature X-ray diffraction will be compared to those by thermogravimetry to show the existing correlation between weight gain curves and structural studies. Our results allow to understand the improved corrosion resistance of yttrium implanted pure iron and extra low carbon steel at high temperature.

In Situ High-Temperature X-Ray Diffraction Characterization of Yttrium-Implanted Extra Low-Carbon Steel

Yttrium-implanted and unimplanted extra low-carbon steel samples were analyzed at T = 700°C and under an oxygen partial pressure P O2 = 0.04Pa for 24 h to show the yttrium implantation effect on extra low-carbon steel high-temperature corrosion resistance. Sample oxidation weight gains were studied by thermogravimetry, and structural analyses were performed using in situ high-temperature X-ray diffraction with the same experimental conditions. The aim of this paper is to show the initial nucleation stage of the main compounds induced by oxidation at high temperatures according to the initial sample treatment (yttrium-implanted or unimplanted). The results obtained by in situ high-temperature X-ray diffraction will be compared to those by thermogravimetry to show the existing correlation between weight gain curves and structural studies. Our results allow one to understand the improved corrosion resistance of yttrium-implanted extra low-carbon steel at high temperatures.

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.

Yttrium implantation effects on extra low carbon steel and pure iron

Extra low carbon steel and pure electrolytic iron samples were yttrium implanted using ion implantation technique. Compositions and structures of pure iron and steel samples were investigated before and after yttrium implantation by several analytical and structural techniques (RBS, SIMS, RHEED and XRD) to observe the yttrium implantation depth profiles in the samples. This paper shows the different effects of yttrium implantations (compositions and structures) according to the implanted sample nature.

On critical polyhedrons for B.C.C. and H.C.P. materials

Abstract The present paper deals with a new method to calculate the vertices of a critical polyhedron taking into account glide and twinning. This method has been validated in the case of an extra low carbon steel and compared to that of Orlans-Joliet et al. (Orlans-Joliet, B., Bacroix, B., Monthiellet, F., Driver, J.H., Jonas, J.J., 1988. Yield surface of B.B.C. crystals for slip on the {110}〈111〉 and {112}〈111〉 systems. Acta Met., 36, 1365.). It has been applied to α titanium to simulate rolling textures as well as the anisotropic Lankford coefficient R ( α ). Deformation texture calculations have been performed for the triclinic symmetry of the sample. In the case of B.C.C. metals the simulated rolling texture is similar to that obtained by the Orlans-Joliet et al. (1988) method and in good agreement with the experimental ones. Let us remark that the simulated textures have been calculated in the homogeneous deformation assumption so as in the inhomogeneous deformation frame. The inhomogeneous model is an Arminjon type model (Ceccaldi, D., Yala, F., Baudin, T., Penelle, R., Royer, F., Arminjon, M., 1994. Deformation textures and plastic anisotropy of steels using the Taylor and nonhomogeneous models. Int. J. of Plasticity, 10 (6), 643.).

RBS and GAXRD Contributions to Yttrium Implanted Extra Low Carbon Steel Characterization

Extra low carbon steel samples were yttrium implanted using an ion implantation method. Composition and structural studies were carried out before and after yttrium implantations by several analytical and structural techniques (Rutherford backscattering spectrometry, reflection high energy electron diffraction, scanning electron microscopy, X-ray diffraction, and glancing angle X-ray diffraction) to characterize the yttrium implantation effect on extra low carbon steel. The aim of this article is to show the contributions of Rutherford backscattering spectrometry (RBS) and glancing angle X-ray diffraction (GAXRD) to the determination of yttrium depth profiles in the samples. The results obtained by these techniques are compared to those of the other analyses performed in this work to show the existing correlation between composition and structural studies. Our results allow a better understanding of the effect of yttrium implantation in extra low carbon steel before studying their corrosion resistance at high temperature.

連続焼鈍過程における極低炭素鋼板の脱炭挙動の速度論的解析

連続焼鈍過程における極低炭素鋼板の脱炭挙動の速度論的解析

Factors of Non-propagation of Fatigue Crack in a Low-carbon Steel. Effect of Oxide Induced Crack Closure.

Rotating bending fatigue tests were carried out in air and in pure argon to clarify the effect of the oxide-induced crack closure on the crack non-propagation. The used material were Ti added extra low carbon steel with no strain ageing, 0.02%C steel with single ferrite phase and annealed 0.2%C steel. The result obtained are as follows. (1) Threshold stress for fatigue crack growth was smaller for Ti added extra low carbon steel in the argon than in the air, though the fatigue crack has the tendency which propagates slowly in the argon than in the air. The above result shows that the oxide-induced crack closure plays role in crack non propagation. (2) It seems that the influence of oxide-induced crack closure on crack non-propagation is smaller compared with influences strain ageing and micro structures. (3) Non-propagating crack was observed in material with single ferrite phase even when strain ageing and oxide induced crack closure did not occur.

Effects of centerline macrosegregation on necking of P-added extra low carbon steel sheet

Effects of centerline macrosegregation on necking was examined by the stretching experiment for cold rolled P-added extra low carbon steel sheets. The centerline macrosegregated zone containing high concentration of Mn and P was elongated in the rolling process. The elongated macrosegregated zone induced instability in the strain state when the sheet was stretched, thus resulted in the waved sheet surface. The formability of cold rolled steel sheet was deteriorated due to the wave formed by the macrosegregation. The waved surface was thought to be caused by the higher hardness in the macrosegregated zone compared to the segregation free zone. The experiments on the stretching of sheet including macrosegregation showed that the macrosegregation was the important source of instability in that of the cold rolled steel sheets. A 3D FEM analysis was carried out for the quantitative evaluation of waved surface. It was confirmed that the main source of the waved surface was the macrosegregation. Stretching in the transverse direction under the plane strain condition made the cold rolled steel sheet more inhomogeneous than stretching in any other strain condition. The thickness difference in the stretched sheet was linearly increased when the ratio of hardness in the macrosegregated zone to that of the segregation free zone was increased. The macrosegregation formed in the internal crack close to the surface was more harmful to the formability in the cold rolled steel sheet than the centerline macrosegregation.

Recrystallization and Related Phenomena. Influence of Hot Rolling and Cooling Conditions on the Grain Refinement of Hot Rolled Extralow-carbon Steel Bands.

In this paper, the effect of various operational parameters in a hot strip rolling process on the grain refinement of hot rolled plain extralow-carbon steel bands has been investigated. The finishing temperature and the onset time of cooling after hot rolling influence the grain refinement significantly. The finishing temperature just above Ar3 is optimum for the grain refinement. The reducing of the onset time of cooling not only refines the grain size, but also decreases the finishing temperature-dependence of grain size. The increase in the reduction of the final hot rolling refines the grain size as well. The cooling rate does not affect the grain size of hot bands in the range between 40 and 120°C/sec significantly. The mechanism of the grain refinement has been discussed with a relation of recrystallization and transformation behavior of austenite and it is concluded that in the case of extralow-carbon steel without Ti and Nb addition, the grain refinement of hot bands is strongly influenced by not only the recrystallization but also grain growth behavior of austenite.

Influence of Grain Refinement of Hot Band and Cold Rolling Reduction on the Formation of Textures and R-Value of Cold Rolled Plain Extralow-Carbon Steel Sheets

A textural analysis was carried out to explain the cause of the planar anisotropy of r-value of cold rolled plain extralow-carbon steel sheets. For a detailed analysis, a model for calculating r-values from ODF-data of texture was applied and the influence of each or a group of crystal orientations of the recrystallization texture on the planar anisotropy of r-values was studied. The following results were obtained:A development of {111}〈110〉−{443}〈110〉−{332}〈110〉−{221}〈110〉 enhanced the V-type planar anisotropy of r-values. A decrease in the intensity of these orientations by increasing the cold rolling reduction or the refinement of the hot band microstructure reduced the r-values in L and C directions and hardly affected the r-value in D direction, and as a result, the V-type planar anisotropy of r-values was improved. On the other hand, an increase in the intensity of {111}, {334} orientation by increasing the cold rolling reduction or the refinement of the hot band microstructure raised r-values in sequence of L < D < C directions and contributed to the reduction of V-type planar anisotropy of r-values as a whole.

The Prediction of the Flow Stress of an Extra-Low Carbon Steel in the Two-Phase Region Using Continuous Cooling Curves

Continuous cooling curves of an extra-low carbon steel under three cooling rates are measured. The flow stress of the steel is established in compression tests during which the temperature is continuously decreasing. The phase transformation temperatures are determined from the cooling rate curve. The latent heat during phase transformation is calculated. A new variable, related to the volume fraction of transformation, is defined. Experimental results show that the relationship between the softening ratio of the flow stress due to phase transformation and this new variable may be described by a quadratic relationship. Based on this relationship and the continuous cooling curves, the flow stresses in the two-phase region are successfully predicted.

Effect on Strain Ageing on the Non-propagation of Fatigue Crack of Low-Carbon Steel.

Rotating bending fatigue tests of Ti added extra low carbon steel with no strain ageing were carried out. The results obtained are as follows; 1) At the stress of the fatigue limit, fatigue cracks did not propagate when N (number of repetitions) reaches 107. This was confirmed to the extent of N=8×107 in this experiment. That the strain ageing plays an important role in fatigue is well-known, but the above result shows that it is not always necessary for the non-propagation of fatigue cracks. 2) Apparent coaxing effect could not be observed in this experiment. Thus it is clear that strain ageing is an inevitable factor in the coaxing effect. Although propagation of crack tips become slightly harder during fatigue stressing, other regions are not reinforced to the crack initiation by strain ageing. Therefore new fatigue cracks initiate and propagate, resulting in failure, when the stress amplitude is increased.