Austenitic grain size evolution and continuous cooling transformation diagrams in vanadium and titanium microalloyed steels

The evolution of the austenitic grain size in medium carbon steels microalloyed with vanadium and titanium was studied as a function of reheating temperature, heating rate, and titanium content. High resolution dilatometric techniques were used to determine the continuous cooling transformation (CCT) diagrams for two different austenitization temperatures. The microstructure and hardness were determined for different cooling rates. The results revealed a significant effect of titanium concentration on the austenitic grain growth control. The smallest grain size was found in the steel with a Ti concentration = 0.019 wt%. Low heating rates produced smaller grain sizes than high heating rates although an abnormal grain growth took place. In these steels, at temperatures above 1050 °C the influence of the reheating temperature on their hardness for cooling rates around 2 °C · s^–1 was negligible. The higher reheating temperatures caused a slight increase in their hardenability. Finally, it was found that the greater the titanium content, the greater the hardness of these steels, but only when the titanium percentages were higher than 0.020 wt%.     

Effects of vanadium on magnetic properties of semi-processed non-oriented electrical steel sheets

The effects of vanadium inclusions on the magnetic properties of non-oriented electrical steel sheets were investigated. The magnetic induction and core loss of test specimens deteriorated at a vanadium content of 0.016 wt%. Electron microscope study revealed that the deterioration was caused by the pinning effects of vanadium carbonitrides on the recrystallization of cold-rolled sheets.     

Effect of copper additions in directly quenched titanium–boron steels

The present study concerns the effect of copper additions on the microstructural evolution and mechanical properties of directly quenched Ti–B steels. Ti and B are added as microalloying elements with an aim of achieving adequate austenite hardenability and Cu is added to retard the austenite (γ) → ferrite (α) transformation. Therefore, the microalloying and Cu additions together allow the transformation of austenite to occur at a lower temperature, resulting in a finer microstructure containing martensitic constituents. The direct-quenching route is adopted with an aim of facilitating the nucleation of the constituent phases from the deformed austenite. In order to circumvent the hot-shortness due to the Cu addition, 0.79 wt% Ni has been added to one of the 1.5 wt% Cu microalloyed steels. The present study has demonstrated that the Ni-containing 1.5Cu–Ti–B steel is capable of providing an attractive combination of strength and ductility comparable to the high strength varieties of HSLA steels in directly quenched condition.     

The influence of copper addition on microstructure and mechanical properties of thermomechanically processed microalloyed steels

The present study concerns the influence of Cu addition on the microstructural evolution and mechanical properties of directly air-cooled microalloyed thin-gauge steel. For this purpose, 1.5 wt% Cu was added to a Ti–B microalloyed steel. It is known that Ni addition to Cu-containing steel is beneficial to eliminate hot shortness caused by Cu. Therefore, the effect of Ni addition (half that of Cu in wt%) on the microstructure formation and mechanical properties has also been studied. Microstructures and mechanical properties of the directly air-cooled steels have demonstrated that addition of 1.5 wt% Cu along with 0.8 wt% Ni in Ti–B microalloyed steel results in a dual phase-like microstructure, which yielded attractive tensile strength (746 MPa) and ductility (31%). However, Cu addition deteriorated the impact toughness of the directly air-cooled Ti–B microalloyed steels.     

Observed behavior of various oxide inclusions in front of a solidifying low-carbon steel shell

The engulfment and pushing (extrusion) of inclusions during solidification play an important role in the formation of a steel structure and, as a result, for the mechanical properties of the final steel product. The aim of this study is to gain knowledge about the behavior of non-metallic inclusions at the interface between a growing solid front and a liquid phase. The focus is on the effect of the titanium and titanium oxide content on the inclusions and the different phenomena, which occurs at the solid/liquid interface. This was studied in samples of low-carbon steels de-oxidized by different combinations of Al, Ca, and Ti. For this purpose, each metal sample of 0.19 g was melted at a temperature close to 1550 °C in an argon atmosphere and solidified under different solidification rates. A direct observation of inclusion behavior during solidification was made using a confocal scanning laser microscope equipped with an infrared gold image furnace. The alloying elements in the sample varied between: C 0.002–0.044; Si 0.02–1.33; Mn 0.12–1.33; P 0.003–0.016; S 0.003–0.01; Al 0.002–0,033; Ni 0–0.28; Cr 0–0.25; Ti 0.008–0.065; Ca 0.0007–0.002; O 0.002–0.0114 and N 0.0028–0.0056 (mass%). Several types of inclusions with different morphologies were found within the sample. The morphology of the observed inclusions on the molten steel surface varied from round alumina and calcium-oxide-rich inclusion to needle-shaped titanium oxide-rich inclusions. The observed motions of the inclusions at the vicinity of the front of the solidifying steels were classified. At a low solidifying velocity and a small inclusion size, inclusions flowed away from the solidifying front. Furthermore, they also or got pushed a distance and thereafter flowed away from the interface. At a medium velocity and a slightly bigger size, inclusions tend to get pushed in front of the solidifying front. Another observation was that at a high velocity and a large particle size, inclusions tend to get engulfed or pushed and then engulfed by the progressing front. The relationship among the morphology, chemical composition of inclusions and the solidifying velocity is discussed in this article.     

Effect of structure on properties of vinyl ester resins

The paper describes the synthesis of vinyl ester resins based on diglycidyl ether of bisphenol-A (epoxy equivalent = 450–465 g/eq) (VR resin) and tetrabromobisphenol-A (epoxy equivalent = 380–420 g/eq) (VR-1 resin). The viscosity of styrenated VR resin was higher than VR-1 resin. The effect of styrene andα-methyl styrene on curing of VR resins was studied. An increase in styrene from 30 to 50 wt% resulted in an increase in gel time and a decrease in exothermic peak. Addition ofα-methyl styrene delayed and depressed the exotherm. The mechanical properties of VR resin sheets and glass fabric reinforced laminates were better than VR-1 resins; whereas LOI of VR-1 was higher. A resin formulation containing 20–30 wt% of VR: VR-1 showed optimum mechanical properties and LOI.     

Effect of titanium on the structure and mechanical properties of Cu-Al-Ti alloys

The structure and mechanical properties of Cu10 wt% Al base alloys with 0–2.5 wt% Ti additions were investigated using transmission electron microscopy, optical microscopy and tensile tests. Addition of titanium has a decreasing effect on the grain size after quenching fromα + β region and causes significant strengthening of alloys. Alloy containing 1 wt%Ti quenched from 900° C shows mixture ofα, retainedβ (DO₃), disorderedβ′ (3R) and orderedβ′ ₁ (18R) martensites. Alloy with 2.5 wt% Ti addition after quenching containsα, retainedβ (DO₃), ordered T₁ phase of L2₁ superlattice and orderedβ′ ₁ martensite with either R18 or L1₀ structure indicating different stacking of ordered planes as the effect of titanium addition.     

Influence of titanium and nitrogen on hot ductility of C–Mn–Nb–Al steels

Abstract

The influence of small additions of titanium on the hot ductility of C–Mn–Nb–Al steels has been examined. Titanium and nitrogen levels varied in the ranges 0·014–0·045 and 0·004–0·011 wt-%, respectively, so that a wide range of Ti/N ratios could be studied. The tensile specimens were cast and cooled at average cooling rates of 25, 100, and 200 K min^-1 to test temperatures in the range 1100–800°C and strained to failure at a strain rate of 2 × 10^-3 s^-1. It was found that ductility in the titanium containing niobium steels improved with a decrease in the cooling rate, an increase in the size of the titanium containing precipitates, and a decrease in the volume fraction of precipitates. Coarser particles could be obtained by increasing the Ti/N ratio above the stoichiometric ratio for TiN and by testing at higher temperatures. However, ductility was generally poor for these titanium containing steels and it was equally poor when niobium was either present or absent. For steels with ～0·005 wt-%N ductility was very poor at the stoichiometric Ti/N ratio of 3·4 : 1. Ductility was better at the higher Ti/N ratios but only two of the titanium containing niobium steels gave better ductility than the titanium free niobium containing steels and then only at temperatures below about 950–900°C. One of these steels had the lowest titanium addition (0·014 wt-%), thus limiting the volume fraction of fine Ti containing particles and the other had the highest Ti/N ratio of 8 : 1. However, even for these two steels ductility was worse than for the titanium free steels in the higher temperature range. The commercial implications of these results are discussed.     

One role of titanium compound particles in aluminium nitride sintered body

Microstructure of titanium compound particle in polycrystalline aluminium nitride (AlN) has been investigated using micro-auger electron spectroscopy (μ-AES). AlN-0.5 wt% TiO2-1.5 wt% Y2O3-0.4 wt% CaO system was sintered at 1850°C in nitrogen atmosphere using a graphite furnace. The AES studies show that the composition of the titanium compound particle is titanium, aluminium, carbon, oxygen, nitrogen and calcium. On the other hand, no calcium is observed by AES in the AlN grains and grain boundary. It is found that one role of the titanium compound particle is to trap calcium included in polycrystalline AlN. This revised version was published online in November 2006 with corrections to the Cover Date.     

Fe-Zn phase formation in interstitial-free steels hot-dip galvanized at 450°C: Part I 0.00 wt% Al-Zn baths

Interstitial-free alloy steels containing various combinations of solute additions of titanium, titanium + niobium and phosphorus, were hot-dipped in a pure zinc (0.00 wt% Al) at 450°C in order to study the morphology and kinetics of Fe-Zn phase formation. Uniform attack of the substrate occurred on all of the steels leading to the formation of a three-phase alloy layer morphology containing gamma, delta and zeta Fe-Zn phases. Titanium and titanium + niobium solute additions had no effect on the growth kinetics of any of the Fe-Zn phases. Phosphorus additions were found to retard only the kinetics of gamma-phase growth, without influencing the growth kinetics of the other Fe-Zn phases. In fact, the gamma-phase layer in the phosphorus-containing substrates was no longer discernable in light optical microscopy after 120 s immersion. The growth kinetics of the total Fe-Zn alloy layer (gamma + delta + zeta) was dominated by the growth of the zeta-phase layer which was in contact with liquid zinc during immersion in the zinc bath. The zeta-phase layer followed a two-stage growth process governed by t1/3 kinetics. The delta-phase layer also exhibited two-stage growth with parabolic t1/2 kinetics. The gamma phase followed t1/4 growth kinetics, indicative of grain-boundary diffusion-controlled growth. This revised version was published online in November 2006 with corrections to the Cover Date.     

Synthesized silicon-substituted hydroxyapatite coating on titanium substrate by electrochemical deposition

Silicon-substituted hydroxyapaptite (Si-HA) coatings were prepared on titanium substrates by electrolytic deposition technique in electrolytes containing Ca²⁺, PO₄ ³⁻ and SiO₃ ²⁻ ions with various SiO₃ ²⁻/(PO₄ ³⁻ + SiO₃ ²⁻) molar ratios(η_si). The deposition was all conducted at a constant voltage of 3.0 V, with titanium substrate as cathode and platinum as anode, for 1 h at 85°C. The coatings thus prepared were characterized with inductively coupled plasma (ICP), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), field-emission-type scanning electron microscope (FSEM). The results show that the silicon amount in the coatings increases linearly to about 0.48 wt% at first with increasing η_si between 0 and 0.03, then increases slowly to about 0.55 wt% between 0.03 and 0.10 and finally maintains almost at a level around 0.55 wt% between 0.10 and 0.30. The tree-like Si-HA crystals are observed in the coatings prepared in the electrolyte of η_si = 0.20. And the presence of silicon in electrolytes decreases the thickness of the coatings, with effect being more significant as η_si increased. Additionally, the substitution of Si causes some OH⁻ loss and changes the lattice parameters of hydroxyapatite (HA).     

Effect of ageing on the mechanical properties of directly quenched copper bearing microalloyed steels

The present work aims to study the ageing behaviour of directly quenched Cu-added microalloyed steels. Temperatures related to precipitation of Cu and recovery of dislocations retained in the microstructure after quenching of the steels from finish rolling temperature are determined by differential scanning calorimetric method. Ageing of the directly quenched steels has resulted in the reduction in hardness and strength with concomitant improvement of ductility. 1.5 wt% Cu-added Ti–B microalloyed steel has yielded the most attractive combination of strength and ductility. Presence of Ni in the 1.5 wt% Cu-added Ti–B microalloyed steel indicates sluggish kinetics of Cu precipitation. Ageing has generally deteriorated the impact toughness except for Ni containing Cu-added microalloyed steel above −25 °C temperature. Formation of recovered dislocation cells and fine ?-Cu precipitates during ageing have contributed to the microstructural softening and hardening, respectively.     

Mechanical properties and fracture behavior of high-strength steels

Typical thicknesses of high-strength steels (HSS) sheets used in the car industry are inapplicable for standardized testing procedures. The aim of this study is to propose an appropriate methodology for testing and comparing of thin HSS sheets. Microstructures were observed by means of light and scanning electron microscopy. The modified Charpy impact tests and fracture toughness tests were used in order to compare the fracture properties of three different HSS sheets (Docol 1200 M, Multiphase 1200 and BTR 165). Ductile-to-brittle transition curves and tearing resistance (J − Δa) curves were measured. From the fracture toughness linked to the specimen thicknesses the value of fracture toughness K_Ic was estimated. Fractographic analysis of broken specimens has revealed that due to the fine microstructure of mixed ferrite-martensite fracture mechanism remains ductile even at low temperatures (down to −100°C). __________ Translated from Problemy Prochnosti, No. 1, pp. 155–158, January–February, 2008.     

Development Of New Low-Alloy Steels For Rock Roller Drill Bits

We consider the influence of complex microalloying on the mechanical properties, wear resistance, and contact fatigue of steels used for rock roller drill bits. We established that the complex microalloying of new steels with niobium, titanium, and rare-earth metals increased the mechanical characteristics and abrasive wear resistance by 20% and the contact fatigue by 75%. The optimum ratio of carbide-stabilizing elements, namely, niobium and titanium, in the steel, which is additionally microalloyed with rare-earth metals, is determined. As an alternative to high-nickel steels, we developed new low-alloyed 20KhGN2MBTA and 20KhGNBTChA steels. Translated from Fizyko-Khimichna Mekhanika Materialiv. Vol. 36. No. 3, pp. 102–107. May-June. 2000.     

Dissolution amounts of nickel, chromium and iron from SUS 304, 316 and 444 stainless steels in sodium chloride solutions

The release of nickel and chromium from stainless steels by sweat, is often responsible for allergic contact dermatitis. The amounts of metal released from stainless steels were in trace amounts, because corrosion resistance was excellent. However, measurement of dissolution amounts is difficult, and if these amounts are not known, the improvement and development of stainless steels with excellent resistance to NaCl solution is difficult. In this work, trace dissolution amounts from the main components of stainless steels which can cause an allergy were investigated. SUS 304, 316 and 444 stainless steels were used in this test. The test solutions used were 0.9 (isotonic sodium chloride solution), 1, 3, 5 and 10 wt% NaCl solutions. Nickel,chromium and iron ions in the test solutions were rapidly determined by stripping voltammetry. The detection limits of Ni(II), Cr(VI) and Fe(III) ions in 1 wt% NaCl solution were 1.0, 0.1 and 0.5 ng cm^-3, respectively, with standard deviations of five tests at 5 ng cm^-3 Ni(II), Cr(VI) and Fe(III) ions, of 6.4%, 1.8% and 2.2%, respectively. Generally, the amounts of the metals dissolved increased in direct proportion to the immersion, in the range 30–60 days for nickel, 30–90 days for chromium and 30–120 days for iron. The dissolution amounts of nickel from SUS 304 and 316 stainless steels increased rapidly over 60 days, while that of chromium increased rapidly over 90 days, in isotonic sodium chloride solution. The ratio of the three dissolved metal ions was not consistent with the composition of the specimens. The ratio of dissolved nickel in SUS 304 and 316 stainless steels was larger than that in the specimen, and dissolved preferentially. The dissolution ratio of chromium and iron in SUS 444 stainless steel approximately agreed with the composition of the specimen. This revised version was published online in November 2006 with corrections to the Cover Date.     

Thermal and electrical conductivity of Al(OH)<Subscript>3</Subscript> covered graphene oxide nanosheet/epoxy composites

Al(OH)₃ functionalized graphene composites (Al–GO) were prepared using a simple sol–gel method. In this protocol, graphene oxide (GO) was prepared according to the Hummers method and functionalized to enhance its reactivity with aluminum isopropoxide by a LiAlH₄ treatment. The functionalized graphene sheets were characterized by X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. These analyses confirmed that GO had been fabricated and the Al(OH)₃ layer could have a homogeneous distribution with large and dense coverage onto GO sheets. In addition, the thermal and electrical conductivity of the epoxy composites with GO and Al–GO fillers were measured. The thermal conductivities of the composites with graphene-based fillers were enhanced by the addition of fillers. In particular, the thermal conductivity of GO/epoxy composite containing 3 wt% was approximately two times higher than that of pure epoxy resin. In addition, the electrical conductivity of Al–GO embedded composites degenerated compared to GO composites.     

Effect of pre-deformation on the precipitation process and magnetic properties of Fe–Cu model alloys

The effect of pre-deformation on the precipitation process and magnetic properties of Fe–Cu model alloys was investigated. These specimens simulate irradiation embrittlement of nuclear reactor pressure vessel (RPV) steels. Fe–1 wt%Cu alloys with and without pre-deformation in solid-state solution were thermally aged at 773 K for various times and the evolution of hardness, conductivity, and microstructure were investigated. Pre-deformation enhanced Cu precipitation and caused precipitation at dislocations. The coercive force tended to decrease for the pre-deformed specimen and the underlying mechanism is discussed. The results obtained are related to the magnetic characteristics of irradiated RPV steels.     

Phase selection in supercooled Cu–Nb alloys

Electromagnetic levitation was used to determine Cu–Nb phase diagram and to study supercooling effects on solidification characteristics of the alloys containing 5–70 wt% Nb. The Cu–Nb stable phase diagram was found to exhibit near-flat liquidus with a peritectic reaction at 1093 °C. Melt separation was found only for specimens containing approximately 20 wt% Nb. The results indicate that melt separation in the alloy requires supercooling exceeding 230 K combined with high cooling rates during solidification. Some specimens quenched from the solid + liquid zone on a copper chill also show evidence of melt separation which is attributed to minor oxygen impurities. Nb-rich liquid which nucleates below the T ₀ curve solidifies as a metastable Nb-bcc lattice containing only 67 wt% Nb as compared to 96 wt% of the regular Nb dendrites.     

Fe-Zn phase formation in interstitial-free steels hot-dip galvanized at 450°C: Part II 0.20 wt% Al-Zn baths

The effect of solute additions of titanium, titanium and niobium and phosphorus on interstitial-free steels on Fe-Zn phase formation after immersion in a 0.20 wt% Al-Zn bath was studied to determine the morphology and kinetics of the individual Fe-Zn phases formed. These results were contrasted to the previous study using a pure zinc (0.00 wt% Al) bath in Part I. It was found that in the 0.20 wt% Al-Zn bath, an iron-aluminide inhibition layer prevented uniform attack of the steel substrate. Instead, localized Fe-Zn phase growth occurred, termed outbursts, containing a two-phase layer morphology. Delta-phase formed first, followed by gamma-phase. Zeta-phase did not form in the 0.20 wt% Al-Zn bath, in contrast with zeta-phase formation in the pure zinc bath. As in the pure zinc bath, the growth kinetics of the total layer was controlled by the Fe-Zn phase in contact with the liquid zinc during galvanizing. For the 0.20 wt% Al-Zn bath, the Fe-Zn phase in contrast with the liquid zinc was the delta-phase, whereas the zeta-phase was in contact with liquid zinc in the pure zinc bath. The delta-phase followed t1/2 parabolic growth, while the gamma-phase showed essentially no growth after its initial formation. Titanium and titanium + niobium solute additions, which enhance grain-boundary reactivity, resulted in more rapid growth kinetics of the gamma- and delta-phases. Phosphorus additions, which decrease grain-boundary reactivity, generally increased the incubation time and retarded the growth rate of the gamma-phase. These results further confirm the concept that solute grain-boundary reactivity is primarily responsible for Fe-Zn phase growth during galvanizing in a liquid Zn-Al bath in which an iron aluminide inhibition layer forms prior to Fe-Zn phase formation. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effects of Sr-modification,iron-based intermetallics and aging treatment on the impact toughness of 356 Al–Si–Mg alloy

Impact toughness as a property has been acquiring increased importance in recent years, since data regarding this property can provide a means for assessing alloy ductility under high rates of deformation. The main objective of this study is to investigate the effects of Sr-modification, Fe-based intermetallic phases and aging conditions on the impact toughness of widely used 356 alloys. The total absorbed energy was measured using a computer-aided instrumented Instron Charpy impact testing machine. Increasing the level of iron additions decreases the impact energy values of 356 alloys to a noticeable degree (~35–57%). The addition of 0.1 wt% Mn to non-modified 356 alloys seems to have no observable effect on the impact energy, while increasing the Mn addition to 0.4 wt% produces a slight improvement in the impact energy values for non-modified and Sr-modified 356 alloys compared to that of those containing only iron under the same conditions. The application of solution heat treatment in combination with Sr-modification was found to significantly improve the impact energy of as-cast 356 alloys, particularly at low iron additions. Artificial aging of non-modified and Sr-modified 356 alloys at 180 °C diminishes the impact energy values with an increase in the aging time up to 8 h compared to those obtained under the solution heat-treated conditions. On the other hand, aging at 220 °C for 12 h increases the impact energy values of Sr-modified 356 alloy containing 0.12 wt% Fe and combined 0.2 wt% Fe–0.1 wt% Mn to about 20 and 18 J, respectively. The fracture behavior of non-modified 356 alloys containing 0.12 wt% Fe is mainly controlled by the acicular eutectic Si particles whereas β-iron platelets act as crack initiation sites and provide further path for final crack propagation in non-modified 356 alloys containing 0.9 wt% Fe. The β-iron platelets and π-iron phase particles contribute largely to crack initiation and propagation in the Sr-modified 356 alloys containing 0.9 wt% Fe.