Showing papers on "Microalloyed steel published in 1993"
TL;DR: In this paper, the authors reported fracture toughness results obtained in Ti treated microalloyed forging steels, showing that in coarse microstructures cleavage is nucleated in coarse TiN particles, but that voids originate at the same particles, resulting in ductile rupture.
Abstract: Titanium addition to vanadium microalloyed forging steels is one of the ways proposed to improve fracture toughness Fine TiN particles inhibit austenite grain growth after recrystallization at the high temperatures used to forge these steels TiN particles, however, can be formed in the liquid, and as their sizes exceed one micron, they could act as cleavage nucleation sites, impairing the fracture toughness The present work reports fracture toughness results obtained in Ti treated microalloyed forging steels, showing that in coarse microstructures cleavage is nucleated in coarse TiN particles, but that after refining the microstructure, voids originate at the same particles, resulting in ductile rupture
47 citations
TL;DR: In this article, it was found that both dissolved Nb in austenite and free B are prerequisites for granular bainite formation and there is a critical B content to achieve the complete bainitic transformation strengthening effect.
Abstract: Microalloying with Nb and B leads to a granular bainite microstructure which is composed of a bainitic ferrite matrix and a uniformly distributed martensite/austenite-constituent in the as-rolled condition. Due to this transformation strengthening mechanism, high strength and toughness could be achieved even though the C content was extremely low. It was found that both dissolved Nb in austenite and free B are prerequisites for granular bainite formation. Furthermore, there is a critical B content to achieve the complete bainitic transformation strengthening effect. The critical B content increases with C content. C thus diminishes the effect of B in promoting bainite transformation, due to the formation of boron carbides or the depletion of dissolved Nb in austenite. The effect of Mn, Mo and Ni on the decomposition of austenite is similar. A parameter“Mneq” which relates the effect of these alloying elements on the Bs temperature was derived. It was confirmed that the strength of bainitic steels is inversely proportional to theBs temperature.
43 citations
TL;DR: In this article, it was shown that after hot working and accelerated cooling transforming the austenite mainly in an acicular microstructure, ductile rupture results without any cleavage nucleated in the coarse TiN particles, as occurred when the same material had a coarse ferrite-pearlite micro-structure.
Abstract: Ti addition is becoming common practice in the fabrication of many grades of engineering steels. In general it is used with the aim of refining the microstructure through the inhibiting effect to grain coarsening exerted by small TiN precipitates. Although a number of recommendations are made for obtaining the maximum yield of fine TiN precipitates, nonetheless a certain proportion of the precipitate volume fraction is usually in the form of coarse TiN precipitates. Several authors suggest that such coarse TiN particles are simply ineffective in pinning the grain boundaries without impairing other properties. In a recent paper it was shown that these coarse TiN particles act as cleavage nucleation sites, impairing the fracture toughness of steel with coarse ferrite-pearlite microstructures. The present work reports further fracture toughness results and fracture mechanisms for Ti treated microalloyed forging steels. They show that after hot working and accelerated cooling transforming the austenite mainly in an acicular microstructure, ductile rupture results without any cleavage nucleated in the coarse TiN particles, as occurred when the same material had a coarse ferrite-pearlite microstructure.
34 citations
TL;DR: In this paper, the authors are grateful for the financiai support of DGICYT-Spain (Project PB89-0022) for the development of this project.
Abstract: The authors are grateful for the financiai support of
the DGICYT-Spain(Project PB89-0022).
25 citations
Journal Article•
16 citations
TL;DR: In this paper, a cathodically charged X65 microalloyed pipeline steel containing a weldment was demonstrated to have extensive cracking of the type known as stack cracking, which is due to local concentration of hydrogen gas pressure and a lowering of the cohesive strength of a number of interfaces by hydrogen.
Abstract: Extensive cracking of the type known as stack cracking was demonstrated in a cathodically charged X65 microalloyed pipeline steel containing a weldment. It is shown that the formation and propagation of rolling-plane cracks, which constitute the primary stages of the stack cracking, is due to local concentration of hydrogen gas pressure and a lowering of the cohesive strength of a number of interfaces by hydrogen. The characteristic S-shape of individual cracks which occurred during the linking up of cracks was attributed to stress interactions at crack tips and cleavage cracking normal to the rolling plane. An explanation of hydrogen embrittlement fracture is given in terms of electronic state modifications of the steel, including charge polarization.
12 citations
30 Aug 1993-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a tensile test of notched cylindrical specimens which are obtained by melting and solidification and then tested after rate-controlled cooling with a new specific device available for any standard test machine.
Abstract: Hot steel ductility in continuous casting processes is determined by tensile test of notched cylindrical specimens which are obtained by melting and solidification and then tested after rate-controlled cooling with a new specific device available for any standard test machine. Hot ductility is proposed to be related to ultimate area reduction in the notched zone of the specimens. Experiments in the range of 700–1000°C are achieved on two types of niobium-vanadium microalloyed steels which only differ by their vanadium content. Ultimate area reductions are determinate by using in situ solidified specimens and reheated ones from room temperature, 10 −3 and 0.5 s −1 mean strain rate being considered. The change of ultimate area reductions mainly depends on austenitic grain size, segregation's distribution, dynamic precipitation of niobium-vanadium carbonitrides and so far the recrystallization occurrence of austenite.
9 citations
TL;DR: An effective cyclic plasma nitriding treatment for type 316 stainless steel has been adopted and its advantages are discussed in this paper, where the effects of treatment temperature and ion current on the maximum surface hardnesses obtainable for these steels are examined.
Abstract: Samples of a type 316 stainless steel and a microalloyed steel were plasma nitrided in the temperature range 673–973 K. Detailed analyses of various nitrides in the nitrided zone have been performed using X -ray diffraction and SEM techniques. An effective cyclic plasma nitriding treatment for type 316 stainless steel has been adopted and its advantages are discussed. The effects of treatment temperature and ion current on the maximum surface hardnesses obtainable for these steels are examined. The effect of the chromium concentration in the stainless steel on the constitution of the nitrided zone is highlighted.
9 citations
TL;DR: In this paper, the theoretical equations of Gladman, Kouwenhoven, Licka and Burnett were applied to a connecting rod manufactured with three medium carbon steels in order to calculate the yield strength and the impact transition temperature.
Abstract: Results obtained when increasing quantities of titanium are added to a vanadium microalloyed steel are reported. Starting with the TEM study of the particles and pearlite, the theoretical equations of Gladman, Kouwenhoven, Licka and Burnett were applied to a connecting rod manufactured with three medium carbon steels in order to calculate the yield strength and the impact transition temperature (ITT). Through a comparison of the theoretical and experimental results, it was concluded that Gladman's equation is the best equation for obtaining more realistic results in this kind of microalloyed steel.
6 citations
TL;DR: Torsion tests were conducted to study the static recrystallization of three microalloyed steels manufactured by electroslag remelting (ESR) with different percentages of vanadium, 0.043%, 0.060% and 0.095%, respectively, and approximately equal percentages of the other alloyforming elements as discussed by the authors.
Abstract: Torsion tests were conducted to study the static recrystallization of three microalloyed steels manufactured by electroslag remelting (ESR) with different percentages of vanadium, 0.043%. 0.060% and 0.095%, respectively, and approximately equal percentages of the other alloyforming elements. It was seen that, in contrast to niobium, dissolved vanadium has no influence on the activation energy. The influence only becomes notable when the precipitates start to form and the activation energy increases rapidly, thus inhibiting recrystallization. The critical temperature at which inhibition commences was measured as a function of the vanadium content and the deformation performed, and in all cases it was lower than the dissolution temperature deduced from the solubility products for nitrides, mainly because the testing conditions lacked thermodynamic equilibrium. Finally, a comparison was made of the microstructures obtained in two commercial steels, namely a C-Mn type steel and a vanadium microalloyed steel. Both were subjected to the same cycle of successive deformations, whose temperatures were lower than the critical temperature. After the last deformation, a much harder austenite was obtained in the microalloyed steel than in the C-Mn steel.
5 citations
TL;DR: In this article, it is proposed that Al segregated to the prior austenite grain boundaries during solution treatment, associated with vacancies, and decreased the rate of vacancy migration, thereby retarding the coarsening of cementite.
Abstract: Precipitation in an 0·1C–0·5Si–1·5Mn–0·15Mo–0·5Ni–0·05V–Fe(wt-%) alloy containing from 0·04 to 0·2 wt-%Al was examined in the tempered condition. After hot rolling, the steels were solution treated at 1200°C for 2 h, then quenched in water. Tempering was mainly carried out at 600 or 650°C for 1 h. The precipitates were identified and measured using transmission electron microscopy and energy dispersive X-ray analysis. It was found that coarsening of Fe3C carbides in the prior austenite grain boundaries was associated with low Al content, while the size of Fe3C particles in the lath boundaries was independent of Al content. It is proposed that Al segregated to the prior austenite grain boundaries during solution treatment, associated with vacancies, and decreased the rate of vacancy migration, thereby retarding the coarsening of cementite.MST/1707
01 Mar 1993
TL;DR: In this article, an application of torsion testing and the stress relaxation techniques to measure kinetics of precipitation is described, where the authors use axial compression to reproduce a more realistic hot rolling scenario seems to be very limited as far as austenite conditioning is concerned.
Abstract: Precipitation of Nb(C,N) in austenite of microalloyed steels is a well studied subject. Strain induced precipitates play a critical part in retarding recrystallization of austenite in the finishing passes of hot rolling. Hence, knowledge of how precipitation takes place is of major industrial significance. Measurements of fraction precipitated as a function of time at constant temperature (PTT curves) have been obtained through several experimental methods. One of them uses the principle of stress relaxation in axial compression for measurements of kinetics of TiC precipitation in austenite of Ti microalloyed steels. However, the total true deformation that can be applied in compression is usually limited to about 0.8. On the other hand, deformation of austenite in industrial processes is executed in several passes under continuous cooling before precipitation takes place. Successive cycles of deformation followed by recrystallization leads to substantial grain refinement which in turn may effect the process of precipitation. Therefore, the capability of axial compression to reproduce a more realistic hot rolling scenario seems to be very limited as far as austenite conditioning is concerned. A viable alternative may be torsion testing. Hot torsion can be used, for instance, to apply several passes with strains, strain rates, delay timesmore » and temperatures similar to those found in an industrial process. It would be then desirable to combine the ability of torsion to simulate industrial schedules with the stress relaxation technique to obtain PTT curves. But before building up PTT curves from simulated as hot rolled' austenite, it is necessary to investigate if torsion experiments are able to detect precipitation. This paper describes an application of torsion testing and the stress relaxation techniques to measure kinetics of precipitation.« less
15 Jan 1993-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a method to determine the molar Gibbs energy available for nucleation of complex carbonitrides of NaCl type in austenite and the corresponding most favourable nucleus composition for microalloyed steels containing niobium and vanadium is presented.
Abstract: A method to determine the molar Gibbs energy available for nucleation of complex carbonitrides of NaCl type in austenite and the corresponding most favourable nucleus composition for microalloyed steels containing niobium and vanadium is presented. The method is generalized to include any number of elements in the substitutional lattice of the carbonitride whilst maintaining its relative simplicity.
01 Nov 1993-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the coarsening of NaCl-type (Nb x V 1− x )C carbides in austenite is examined and it is shown that, to reconcile the two equations for carbide growth, namely one for niobium and another for vanadium-controlled growth, the carbide composition must depend on its size.
Abstract: The coarsening of NaCl-type (Nb x V 1− x )C carbides in austenite is examined. It is shown that, to reconcile the two equations for carbide growth, namely one for niobium and another for vanadium-controlled growth, the carbide composition must depend on its size. In principle this would invalidate the classical Lifshitz-Slyozov-Wagner (LSW) approach to coarsening. It is demonstrated, however, that the deviation of the carbide composition from the equilibrium composition may be small, depending on the temperature, alloy content and mean carbide radius. Therefore, it is proposed that, in such cases, the carbides can be regarded to be “quasi-stoichiometric” and it is shown that the LSW method can thus be applied. Although the present work focuses on (NbC) x (VC) 1− x , its results are quite general and, in principle, can be applied to similar systems, namely non-stoichiometric, sparingly soluble compounds of P x Q 1− x , coarsening in a matrix of an element M.
01 Jan 1993
TL;DR: In this article, a model for determining the thermal cycles in pulsed TIG welds in a quenched and tempered microalloyed steel (0.15%C, 1.4%Mn, 0.026%Nb and 0.061%V) was presented.
Abstract: mathematical model is presented for determining the thermal cycles in pulsed TIG welds in a quenched and tempered microalloyed steel (0.15%C, 1.4%Mn, 0.026%Nb, 0.061%V, 0.064%Al, 0.083%Mo, 12 mm th ...
01 Jan 1993
TL;DR: A review of the investigation in the field of microalloyed steel, high strength, weldable reinforcing bars is presented in this article, where the results point toward the modification of the hot rolling facilities, to introduce controlled cooling, to reduce carbon and carbon equivalent for better weldability and to minimize the ammount of micro-alloying elements to reduce cost.
Abstract: A review of the investigation in the field of microalloyed steel, high strength, weldable reinforcing bars is presented. The world market for reinforcing bars is now evolving toward higher strength grades which will eventually substitute the 415 MPa, non-weldable rebars now produced in North America. Since 1991, the Euronorm 18 has established a 500 MPa weldable grade for all the European Community, and there are initiatives to set a 590 MPa weldable grade for the reinforcing bars to be used in the Pacific Rim. Experiences in fabricating 590 MPa weldable grades have been performed in the steel mills of SICARTSA employing niobium and vanadium as microalloying elements of steel. The research to be described has been supported by transmission electron microscopy, microanalysis and mechanical testing. The results point toward the modification of the hot rolling facilities, to introduce controlled cooling, to reduce carbon and carbon equivalent for better weldability and to minimize the ammount of microalloying elements to reduce cost.
TL;DR: In this article, a series of very low carbon, high manganese, microalloyed steels were produced by Bhole and Yu that, after controlled rolling and normalizing, exhibited good strength-toughness properties comparable to the commercially available HSLA steels.
Abstract: As part of an ongoing investigation into alternative compositions to the traditional controlled rolled HSLA or microalloyed steels, a series of very low carbon, high manganese, microalloyed steels were produced by Bhole and Yu that, after controlled rolling and normalizing, exhibited good strength-toughness properties comparable to the commercially available HSLA steels. Manganese is a strong austenite stabilizer and solid solution strengthener in Fe-C alloys and thus is potentially a cost saving substitute for nickel, particularly where high hardenability need not be important such as in the ultra low carbon type steels. In the present work some interesting microstructural observations in relaxed controlled rolled 2.0% Mn - 0.25% Mo - 0.016% C (by weight) steels containing microalloying additions of niobium and vanadium will be reported. The effect of a final roll pass in the intercritical temperature range followed by normalizing on the microstructures will then be explained in terms of the VC and Nb(CN) solubility products.
01 Mar 1993
TL;DR: In this article, the structural characteristics obtained from high-resolution electron microscopy images of precipitates in specimens of B-microalloyed steels were explored and interplanar spacings obtained from HREM images of these precipitates were compared with spacing for some boron compounds reported in the literature.
Abstract: Boron alloying has been recognized as a very attractive method for improving the properties of high strength low alloy (HSLA) steels. Small additions of this element have pronounced effects on the hardenability of the steels. This result has been partially explained as a consequence of the reduction in free energy of austenite grain boundaries due to the segregation of boron atoms. The segregation of this element is thought to occur in certain particular areas of the microstructure such as grain boundaries or precipitates. It has been also pointed out that the alloying elements could give rise to metal borides in steel. Furthermore, experimental evidence shows that boron could be found in certain fcc compounds such as boron carbides and changes in the lattice parameters of vanadium carbides have been also related with the presence of boron in the lattice. The detection of boron in steel is difficult due to the small amounts of boron involved and because it is a light element and therefore difficult to detect by x-ray microanalysis or transmission electron microscopy. The work presented in this investigation explores some of the structural characteristics obtained from high-resolution electron microscopy images of precipitates in specimens of B-microalloyed steels. Threemore » different types of precipitates have been found. Interplanar spacings obtained from HREM images of these precipitates have also been obtained and compared with spacing for some boron compounds reported in the literature.« less