Revistas
Autores:
Martins, C. A. (Autor de correspondencia); de Faria, G. L.; Mayo Ijurra, Unai; et al.
Revista:
METALS
ISSN:
2075-4701
Año:
2023
Vol.:
13
N°:
2
Págs.:
405
Obtaining high levels of mechanical properties in steels is directly linked to the use of special mechanical forming processes and the addition of alloying elements during their manufacture. This work presents a study of a hot-rolled steel strip produced to achieve a yield strength above 600 MPa, using a niobium microalloyed HSLA steel with non-stoichiometric titanium (titanium/nitrogen ratio above 3.42), and rolled on a Steckel mill. A major challenge imposed by rolling on a Steckel mill is that the process is reversible, resulting in long interpass times, which facilitates recrystallization and grain growth kinetics. Rolling parameters whose aim was to obtain the maximum degree of microstructural refinement were determined by considering microstructural evolution simulations performed in MicroSim-SM (R) software and studying the alloy through physical simulations to obtain critical temperatures and determine the CCT diagram. Four ranges of coiling temperatures (525-550 degrees C/550-600 degrees C/600-650 degrees C/650-700 degrees C) were applied to evaluate their impact on microstructure, precipitation hardening, and mechanical properties, with the results showing a very refined microstructure, with the highest yield strength observed at coiling temperatures of 600-650 degrees C. This scenario is explained by the maximum precipitation of titanium carbide observed at this temperature, leading to a greater contribution of precipitation hardening provided by the presence of a large volume of small-sized precipitates. This paper shows that the combination of optimized industrial parameters based on metallurgical mechanisms and advanced modeling techniques opens up new possibilities for a robust production of high-strength steels using a Steckel mill. The microstructural base for a stable production of high-strength hot-rolled products relies on a consistent grain size refinement provided mainly by the effect of Nb together with appropriate rolling parameters, and the fine precipitation of TiC during cooling provides the additional increase to reach the requested yield strength values.
Revista:
METALS
ISSN:
2075-4701
Año:
2021
Vol.:
11
N°:
1
Págs.:
112
Intercritically deformed steels present combinations of different types of ferrite, such as deformed ferrite (DF) and non-deformed ferrite (NDF) grains, which are transformed during the final deformation passes and final cooling step. Recently, a grain identification and correlation technique based on EBSD has been employed together with a discretization methodology, enabling a distinction to be drawn between different ferrite populations (NDF and DF grains). This paper presents a combination of interrupted tensile tests with crystallographic characterization performed by means of Electron Backscatter Diffraction (EBSD), by analyzing the evolution of an intercritically deformed micro-alloyed steel. In addition to this, and using the nanoindentation technique, both ferrite families were characterized micromechanically and the nanohardness was quantified for each population. NDF grains are softer than DF ones, which is related to the presence of a lower fraction of low-angle grain boundaries. The interrupted tensile tests show the different behavior of low- and high-angle grain boundary evolution as well as the strain partitioning in each ferrite family. NDF population accommodates most of the deformation at initial strain intervals, since strain reaches 10%. For higher strains, NDF and DF grains behave similarly to the strain applied.
Revista:
METALS
ISSN:
2075-4701
Año:
2021
Vol.:
11
N°:
2
Págs.:
219
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 (lambda: 0.27 mu m), 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 (lambda: 0.10 mu m) and upper bainite microstructures are more prone to spheroidization, and the minimum G2/L2 IFI rating is achieved under subcritical annealing at 720 degrees 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 degrees C. Annealing treatments conducted at 660 degrees C and 600 degrees 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.
Revista:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
ISSN:
0921-5093
The mechanical properties of intercritically rolled microstructures have been scarcely reported in literature. Although the strengthening effect of intercritical rolling is generally recognized, there is no a clear opinion on its effect on toughness. Therefore, a greater knowledge of how different process parameters affect the mechanical properties during intercritical deformation is required. With the aim of evaluating the relationship between microstructure and mechanical properties on intercritically deformed low carbon steels, plane strain compression tests were carried out. Plane strain compression tests allow for both the characterization of the microstructural features and the evaluation of mechanical properties, via tensile and Charpy tests. Firstly, the intercritically deformed microstructures were characterized using the EBSD technique, and then a discretization methodology was used to distinguish both intercritically deformed and non-deformed ferrite populations. Next, strength and toughness properties were measured by means of tensile and Charpy tests. The results indicate that the reduction of the deformation temperature leads to an increment of yield strength for both steels, but at the same time toughness properties worsen. Deformed ferrite fractions higher than 25% result in a very pronounced loss of ductility. The yield strength was predicted by estimating the contribution of different strengthening mechanisms (solid solution, grain size refinement, dislocation density) corresponding to each ferrite population by considering a nonlinear law of mixtures. Similarly, the impact of different microstructural parameters (solid solution, grain size, microstructural heterogeneity, contribution of dislocation density and secondary phases) on toughness was evaluated and a new equation able to predict ductile to brittle transition temperature for intercritically deformed microstructures was developed.
Revista:
METALS
ISSN:
2075-4701
Revista:
MATERIALS CHARACTERIZATION
ISSN:
1044-5803
Año:
2019
Vol.:
147
Págs.:
31 - 42
Heavy gauge structural plates has been widely rolled in the austenite/ferrite two phase region, in order to meet the demanding market requirements regarding tensile properties. Even though strength levels can be increased by intercritical rolling, toughness properties may be impaired. Therefore, a greater knowledge of how different austenite-ferrite balances affect the microstructural evolution during intercritical deformation is required. With the aim of gaining a deep comprehension of the evolution of the microstructure during intercritical deformation, dilatometry tests were performed simulating intercritical rolling conditions. Different ferrite populations are identified in the resulting microstructures, composed of intercritically deformed ferrite and non-deformed ferrite transformed during final air cooling. In the deformed ferrite grains well defined substructure is clearly noticed, whereas the non-deformed grains formed during air cooling step do not show any evidence of substructure. In the current work, EBSD advanced characterization technique was used to develop a methodology that is able to differentiate the intercritically deformed ferrite from non-deformed ferrite for low carbon steels. Based on the Grain Orientation Spread (GOS) parameter, a threshold value of 2 degrees was defined to distinguish deformed and non deformed ferrite grains. The proposed procedure allows distinguishing both ferrite populations and quantifying microstructural parameters of each family. The effect of the addition of C and austenite-ferrite balance on the microstructural evolution of each ferrite type was analyzed.
Revista:
METALS
ISSN:
2075-4701
Año:
2019
Vol.:
9
N°:
10
Págs.:
1049
Heavy gauge line pipe and structural steel plate materials are often rolled in the two-phase region for strength reasons. However, strength and toughness show opposite trends, and the exact effect of each rolling process parameter remains unclear. Even though intercritical rolling has been widely studied, the specific mechanisms that act when different microalloying elements are added remain unclear. To investigate this further, laboratory thermomechanical simulations reproducing intercritical rolling conditions were performed in plain low carbon and NbV-microalloyed steels. Based on a previously developed procedure using electron backscattered diffraction (EBSD), the discretization between intercritically deformed ferrite and new ferrite grains formed after deformation was extended to microalloyed steels. The austenite conditioning before intercritical deformation in the Nb-bearing steel affects the balance of final precipitates by modifying the size distributions and origin of the Nb (C, N). This fact could modify the substructure in the intercritically deformed grains. A simple transformation model is proposed to predict average grain sizes under intercritical deformation conditions.
Revista:
TRATER PRESS
ISSN:
1888-4423
Año:
2018
Vol.:
65
Págs.:
18 - 26
Revista:
METALS
ISSN:
2075-4701
Cost-effective advanced design concepts are becoming more common in the production of thick plates in order to meet demanding market requirements. Accordingly, precipitation strengthening mechanisms are extensively employed in thin strip products, because they enhance the final properties by using a coiling optimization strategy. Nevertheless, and specifically for thick plate production, the formation of effective precipitation during continuous cooling after hot rolling is more challenging. With the aim of gaining further knowledge about this strengthening mechanism, plate hot rolling conditions were reproduced in low carbon Ti-Mo microalloyed steel through laboratory simulation tests to generate different hot-rolled microstructures. Subsequently, a rapid heating process was applied in order to simulate induction heat treatment conditions. The results indicated that the nature of the matrix microstructure (i.e., ferrite, bainite) affects the achieved precipitation hardening, while the balance between strength and toughness depends on the hot-rolled microstructure.
Revista:
MATERIALS SCIENCE FORUM
ISSN:
0255-5476
Año:
2018
Vol.:
941
Págs.:
71 - 76
Niobium in steels can be used as substitutional solid solute or as precipitates. In solution, Nb exerts a solute drag effect delaying but usually not interrupting static recrystallization during hot rolling and increasing hardenability during post rolling cooling. Fine precipitates generated during rolling/cooling can interrupt recrystallization in finishing and precipitate in the ferrite matrix increasing strength. As a relatively fine precipitate Nb can also inhibit austenite grain growth during reheating.This paper highlights the idea that micro-additions of Nb, up to 0.02%, to ordinary commodity C-Mn structural steels can improve their strength. Industry trial results are presented giving evidence that mechanical properties can be improved, and a leaner/optimized chemistry may be used by adding these micro-quantities of Nb to otherwise ordinary commodity C-Mn steels.Microstructural analysis of a C-Mn vs. a leaner/optimized C-Mn-micro Nb steel along with austenite evolution modeling using MicroSim-PM© helped identifying which type of metallurgical mechanisms are in-play resulting in higher strengths. This alternative composition has led to lower costs, lower CE, improved microstructure and a more stable process.
Revista:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
ISSN:
1073-5623
Año:
2018
Vol.:
49
N°:
3
Págs.:
946 - 961
The use of microalloyed steels in the production of thick plates is expanding due to the possibility of achieving attractive combinations of strength and toughness. As market requirements for high strength plates are increasing and new applications require reduced weight and innovative designs, novel approaches to attaining cost-effective grades are being developed. The mechanism of precipitation strengthening has been widely used in thin strip products, since the optimization of the coiling strategy offers interesting combinations in terms of final properties and microalloying additions. Precipitation strengthening in thick plates, however, is less widespread due to the limitation of interphase precipitation during continuous cooling after hot rolling. With the main objective of exploring the limits of this strengthening mechanism, laboratory thermomechanical simulations that reproduced plate hot rolling mill conditions were performed using low carbon steels microalloyed with Nb, NbMo, and TiMo additions. After continuous cooling to room temperature, a set of heat treatments using fast heating rates were applied simulating the conditions of induction heat treatments. An important increase of both yield and tensile strengths was measured after induction treatment without any important impairment in toughness properties. A significant precipitation hardening is observed in Mo-containing grades under specific heat treatment parameters.
Revista:
TRATER PRESS
ISSN:
1888-4423
Año:
2018
Vol.:
Nov.
N°:
67
Págs.:
19 - 25
Revista:
METALS
ISSN:
2075-4701
Low carbon microalloyed steels show interesting commercial possibilities by combining different ¿micro¿-alloying elements when high strength and low temperature toughness properties are required. Depending on the elements chosen for the chemistry design, the mechanisms controlling the strengths and toughness may differ. In this paper, a detailed characterization of the microstructural features of three different microalloyed steels, Nb, Nb-Mo and Ti-Mo, is described using mainly the electron backscattered diffraction technique (EBSD) as well as transmission electron microscopy (TEM). The contribution of different strengthening mechanisms to yield strength and impact toughness is evaluated, and its relative weight is computed for different coiling temperatures. Grain refinement is shown to be the most effective mechanism for controlling both mechanical properties. As yield strength increases, the relative contribution of precipitation strengthening increases, and this factor is especially important in the Ti-Mo microalloyed steel where different combinations of interphase and random precipitation are detected depending on the coiling temperature. In addition to average grain size values, microstructural heterogeneity is considered in order to propose a new equation for predicting ductile¿brittle transition temperature (DBTT). This equation considers the wide range of microstructures analyzed as well as the increase in the transition temperature related to precipitation strengthening.
Revista:
MATERIALS SCIENCE FORUM
ISSN:
0255-5476
Año:
2017
Vol.:
879
Págs.:
84 - 89
Revista:
MATERIALS SCIENCE FORUM
ISSN:
0255-5476
Año:
2017
Vol.:
879
Págs.:
1465 - 1470
Revista:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
ISSN:
1073-5623
Año:
2017
Vol.:
48
N°:
6
Págs.:
2801 - 2811
As thin slab direct rolling technologies are moving to the production of higher quality steel grades, chemical compositions based on Nb-Ti and Nb-Mo become a good option. However, with the use of multiple microalloying additions, the as-cast austenite conditioning becomes more complex. This paper analyzes some of the microstructural features that should be taken into account during the as-cast austenite conditioning in Nb-Ti and Nb-Mo microalloyed steel grades. In the case of Nb-Ti grades, it has been observed that the process parameters during solidification and post-solidification steps affect the austenite evolution during hot rolling. This is due to the differences in the size and volume fraction of TiN particles that can be formed. Fine TiN precipitates have been shown to be able to delay recrystallization kinetics. Moreover, the solute drag effect of Ti cannot be ignored in the case of hyperstoichiometric Ti/N ratios. It is observed that Nb-Ti grades tend to have lower non-recrystallization temperatures compared to Nb grades, which means that pancaking of the austenite is more difficult for these steels. The opposite is observed for the Nb-Mo grades, although in both cases the behavior is affected by the nominal content of Nb. (C) The Minerals, Metals & Materials Society and ASM International 2016
Revista:
KEY ENGINEERING MATERIALS
ISSN:
1013-9826
Año:
2016
Vol.:
716
Págs.:
281 - 290
Revista:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
ISSN:
0921-5093
Año:
2016
Vol.:
651
Págs.:
358 - 369
The hot deformation and static softening behavior of various high Mn (20-30 wt%) austenitic steels microalloyed with different V (0.1, 0.2 wt%), C (0.2, 0.6, 1 wt%) and N (0.005-0.025 wt%) contents were investigated. Double-hit torsion tests at temperatures in the range 700-1100 degrees C were carried out and specimens quenched at selected conditions were examined using advanced microscopy techniques (EBSD-TEM) to characterize the recrystallization and strain-induced precipitation behavior. The results show that precipitation of vanadium at the hot working temperature range is sluggish. It mainly occurs for the combinations of 20%Mn-0.6%C-0.2%V and 30%Mn-1%C-0.1%V. When the carbon content is reduced to 0.2%C, strain-induced precipitation is suppressed at typical hot working temperatures, independently of the N level. The flow stress behavior was affected by the amount of C and by modifying the base composition from 30%Mn to 20%Mn-1.5%Al. However, the effect is complex and depends on deformation conditions. In the absence of strain-induced precipitation, the static softening kinetics was accelerated by increasing C content. However, no effect of Mn or V in solid solution was observed. In those cases where strain-induced precipitation took place, static recrystallization was severely delayed, leading to a major contribution of recovery to softening kinetics.
Revista:
TRATER PRESS
ISSN:
1888-4423
Año:
2016
Vol.:
52
Págs.:
29 - 36
Revista:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
ISSN:
1073-5623
Año:
2016
Vol.:
47
N°:
1
Págs.:
412 - 423
The influence of strain, strain rate, and temperature on deformation-induced transformation (DIT) in a low-alloy medium carbon steel is studied. The strain promotes the nucleation of ferrite (deformation-induced ferrite) and also pearlite (deformation-induced pearlite), this last being characterized by a fine interlamellar spacing and morphological instability. At strains epsilon > 0.5, intragranular nucleation activates and further ferrite nucleation over the newly created alpha/gamma interface takes place, which gives rise to the precipitation of cementite (deformation-induced cementite) at the ferrite boundaries. Soft annealing treatments have been performed on the microstructures obtained by DIT, and the degree of spheroidization has been quantified by image analysis techniques. In comparison to non-deformed conditions, the application of DIT results in a higher degree of spheroidization after soft annealing. Moreover, the EBSD analysis denotes that ferrite grain size refinement is achieved with respect to non-deformed conditions. The degree of spheroidization is highly influenced by the applied strain level and subsequent holding temperature.
Revista:
ISIJ INTERNATIONAL
ISSN:
0915-1559
Año:
2016
Vol.:
56
N°:
6
Págs.:
1038 - 1047
During hot rolling, austenite recrystallization determines the grain size evolution and the extent of strain accumulation, and therefore, it can be used to control the microstructure and improve the mechanical properties of the final product. However, at the moment, experimental data and models describing the recrystallization kinetics of high-Mn steels are scarce, and they do not take into account the effect of the different C and Mn alloying contents usually present in these steels. The aim of this work is to provide a quantitative model for the determination of the static recrystallization kinetics and recrystallized grain size that is valid for a wide range of high-Mn steel compositions. In order to do this, softening data determined in previous works for steels with different Mn (20 to 30%), Al (0 to 1.5%) and C (0.2 to 1%) levels were considered. In addition, new tests were carried out to determine the effect of deformation conditions on the static softening kinetics and the recrystallized grain size. The static recrystallization kinetics of the high-Mn steels follows Avrami's law, with n Avrami exponents which are temperature dependent and lower than those determined for low C steels. A dependence of the 2'0.5 (time for 50% fractional softening) on the carbon content has been observed and it was incorporated into an equation for the calculation of this parameter. An expression that is valid for predicting the recrystallized grain size as a function of deformation conditions is also proposed.
Revista:
TRATER PRESS
ISSN:
1888-4423
Año:
2015
Vol.:
47
Págs.:
32 - 42
Revista:
MATERIALS & DESIGN
ISSN:
0264-1275
Año:
2014
Vol.:
62
Págs.:
296 - 304
The application of high heating rates in tempering treatments can provide a valuable tool for refining carbide sizes, mainly those located at high angle grain boundaries. This work analyses the influence of heating rates ranging from 1 to 300 degrees C/s during the tempering treatment of a 0.42%C low alloy steel. The results indicate that when high heating rates are combined with short holding times, predicting hardness will require the inclusion of the heating up and cooling down cycles in addition to the holding time and temperature used in the definition of the conventional Hollomon-Jaffe tempering parameter (TP). The effect of heating rate on carbide size distribution has been quantified, distinguishing between particles located at high (HAB) and low (LAB) misorientation angle boundaries. The former correspond to those carbides nucleated at prior gamma grain, martensite block or packet boundaries whereas the latter refer to those nucleated within martensite laths and at lath boundaries. The refinement obtained has been evaluated from the point of view of hardness behaviour. (C) 2014 Elsevier Ltd. All rights reserved.
Revista:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
ISSN:
1073-5623
Año:
2014
Vol.:
45
N°:
3
Págs.:
1470 - 1484
Warm deformations have been applied to a low-alloy medium carbon steel (AISI 5140) to promote faster spheroidization during soft annealing treatments. The application of warm deformation leads to the fragmentation of cementite lamellae and the formation of defects on both cementite and the matrix. This induces faster lamellae break-up according to a boundary splitting mechanism, which is responsible for the improved spheroidization after annealing. The substructure developed in the matrix enhances pipe diffusion through the sub-boundaries, which helps the lamellae terminations to coarsen and causes lamellae fast splitting and finally yields a coarse cementite particle distribution. When deforming up to epsilon = 0.3, almost fully spheroidized microstructures are obtained after annealing at 993 K (720 A degrees C), independently of the initial pearlite features. By means of the EBSD technique, it has been observed that the applied warm deformation, in addition to enhancing the degree of spheroidization, allows a much finer microstructure to be formed after annealing. Grain refinement takes place as a consequence of a continuous recrystallization process, which is directly related to cementite spheroidization in the long term. (C) The Minerals, Metals & Materials Society and ASM International 2013
Revista:
MATERIALS SCIENCE FORUM
ISSN:
0255-5476
Año:
2014
Vol.:
783-786
Págs.:
777 - 782
Revista:
MATERIALS SCIENCE FORUM
ISSN:
0255-5476
Año:
2013
Vol.:
753
Págs.:
453 - 458
Revista:
MATERIALS SCIENCE FORUM
ISSN:
0255-5476
Año:
2013
Vol.:
753
Págs.:
443 - 448
Revista:
MATERIALS SCIENCE FORUM
ISSN:
0255-5476
Año:
2012
Vol.:
715-716
Págs.:
711 - 718
Revista:
IRON & STEEL TECHNOLOGY
ISSN:
1547-0423
Año:
2012
Vol.:
9
N°:
10
Págs.:
122 - 128
A spheroidization kinetic study has been carried out in a low alloy medium carbon steel by means of image analysis techniques. Two different initial pearlite microstructures, coarse and fine pearlite, have been generated at two different transformation temperatures of 700 and 630ºC. The effect of a deformation application once the steel is completely transformed has been analyzed and compared with that observed in non deformed samples. The deformation accelerates spheroidization kinetics and leads to a higher spheroidization degree. Several phenomena that take place during the spheroidization treatment contribute to the matrix softening.
Artículo premiado con el 2012 Gilbert R. Speich Award (AIST). PR-264-049 - 2011
Revista:
MATERIALS SCIENCE FORUM
ISSN:
0255-5476
Año:
2012
Vol.:
706-709
Págs.:
2752 - 2757
Revista:
MATERIALS SCIENCE FORUM
ISSN:
0255-5476
Año:
2012
Vol.:
706-709
Págs.:
157 - 164
Revista:
JOURNAL OF IRON AND STEEL RESEARCH INTERNATIONAL
ISSN:
1006-706X
Año:
2011
Vol.:
18
N°:
Sup.1
Págs.:
459 - 465
HSLA steels constitute one of the main types of steels produced technologies (TSDR). Among microalloying elements, the most widely used different roles during the austenite evolution in TSDR. Regarding austenite worldwide by Thin Slab Direct Rolling are V, Nb and Ti. These elements play conditioning before transformation, the limitations in the total reduction that can be applied in TSDR technologies need to be considered when composition/process parameters are selected. In this context, whereas an important number of studies have been focused on Nb microalloyed grades, a less systematic analysis has been performed concerning the role of vanadium on austenite conditioning. This paper analyzes these singularities taking into account different process parameter conditions, such as total reduction and initial rolling temperature.
Revista:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
ISSN:
0921-5093
Año:
2011
Vol.:
528
N°:
6
Págs.:
2559 - 2569
Top25 Hottest articles en Materials Science and Engineering A durante el período enero-marzo 2011
Deformation dilatometry has been used to simulate controlled hot rolling followed by cooling of a Nb-V low carbon steel, looking for conditions corresponding to wide austenite grain size distributions prior to transformation. Recrystallization and non-recrystallization deformation schedules were applied, followed by controlled cooling at rates from 0.1 degrees C/s to about 200 degrees C/s, and the corresponding continuous cooling transformation (CCT) diagrams were constructed. The resultant microstructures ranged from polygonal ferrite (PF) and pearlite (P) at slow cooling rates to bainitic ferrite (BF) accompanied by martensite (M) for fast cooling rates. Plastic deformation of the parent austenite accelerated both ferrite and bainite transformations, displacing the CCT curve to higher temperatures and shorter times. However, it was found that the accelerating effect of strain on bainite transformation weakened as the cooling rate diminished and the polygonal ferrite formation was enhanced. Moreover, it was found that plastic deformation had different effects on the refinement of the microstructure, depending on the cooling rate. An analysis of the microstructural heterogeneities that can impair toughness behavior has been done.
Revista:
JOURNAL OF MATERIALS SCIENCE
ISSN:
0022-2461
Año:
2011
Vol.:
46
N°:
11
Págs.:
3725 - 3737
Plane strain compression tests of two V microalloyed steels and one plain C-Mn steel have been done to analyse the influence of the deformation temperature, in the warm working range, on the final microstructure and subsequent mechanical behaviour. In the case of V microalloyed steels, the reheating temperature has an effect on the amount of vanadium in solution prior to deformation. This factor influences the austenite evolution during warm deformation and the transformation during cooling. As a consequence, in the microalloyed steels complex multiphase microstructures are obtained that lead to a wide range of strength-toughness combinations. In contrast, in the case of the plain C-Mn steel minor effects are observed in the deformation range from 800 to 870 A degrees C.
Revista:
JOURNAL OF IRON AND STEEL RESEARCH INTERNATIONAL
ISSN:
1006-706X
Año:
2011
Vol.:
18
N°:
Sup.1
Págs.:
822 - 826
Nowadays there is a continuous demand, particularly from the automotive industry, for cheaper, lighter and more reliable components. It is not surprising then that steel research has been focused during the last decades in new qualities and processes. This paper is dealing with the use of vanadium microalloyed steels on one of those new processes, warm forging. For its low precipitation temperature and its recognised ability to strengthen steel microstructures via austenite grain growth control, precipitation hardening and interference of the static recrystallization process, vanadium in microalloyed steels seem to be an appropriate candidate for warm forging.
Revista:
MATERIALS SCIENCE FORUM
ISSN:
0255-5476
Año:
2010
Vol.:
638-342
Págs.:
3350 - 3355
Revista:
ISIJ INTERNATIONAL
ISSN:
0915-1559
Año:
2010
Vol.:
50
N°:
4
Págs.:
546 - 555
Este artículo quedó finalista en el Vanadium Award 2010
Multipass torsion tests were carried on with several V-microalloyed high carbon steels, using different deformation sequences in order to modify the austenite state prior to transformation. Both recrystallized and deformed austenite microstructures were studied. After deformation, different cooling rates were applied. The results show that accumulating strain in the austenite before transformation seems to slightly increase the interlamellar spacing for a given cooling rate, this increase being related to the pearlite transformation taking place at higher temperatures because of the increase in the austenite grain boundary area per unit volume (S(v)). On the other hand, the retained strain significantly contributes to a refinement of the "ferrite units' effect being more significant as vanadium and nitrogen contents rise. A relationship between the mean "ferrite unit" size with S(v) and cooling rate was determined. Similarly, empirical expressions to predict strength as a function of vanadium microalloying addition, S(v) and cooling rate were derived.
Revista:
MATERIALS SCIENCE FORUM
ISSN:
0255-5476
Año:
2010
Vol.:
638-642
Págs.:
687 - 692