A review of the development and application of microalloyed medium carbon steels

Microalloyed medium-carbon steels with ferrite-pearlite microstructure were developed in the FRG in early 1972, with the primary aim of saving the cost of heat treatment. A steel with roughly 0.47% C, 0.75% Mn, 0.060% S and 0.1 % V was first used for crankshafts in cars manufactured by one of the largest European automobile companies. The effect of microalloying elements such as vanadium and niobium (niobium instead of columbium is used in this paper) in these steels and their dependence on the cooling rate from drop-forging temperatures is reviewed. Although niobium is more effective than vanadium, it leads to problems while manufacturing these steels with ~0.47% C, due to the high solution temperature of the niobium precipitates, so that preference has been given to vanadium. Further development work carried out to improve the ductility of these steels is reported. Steel compositions, which could make these steels applicable for various automobile and other engineering components, are presented.     

VN12合金在钒氮微合金化钢中的应用研究

通过在２０ＭｎＳｉＶ、１６ＭｎＶ钢中,加入钒铁合金ＶＦｅ（５１．６％Ｖ）及美国钒公司提供的专利产品富氮钒合金ＶＮ１２（８０％Ｖ,１２％Ｎ）的对比试验,研究了钒、氮复合微合金化对钢的力学性能的影响。与使用ＦｅＶ（５１．６％Ｖ）相比,采用富氮钒合金化时,因钒用量的减少使得其技术经济性更加显著。     

Precipitation and fine structure in medium-carbon vanadium and vanadium/niobium microalloyed steels

Hot-rolled and continuously cooled, medium-carbon microalloyed steels containing 0.2 or 0.4 pct C with vanadium (0.15 pct) or vanadium (0.15 pct) plus niobium (0.04 pct) additions were investigated with light and transmission electron microscopy. Energy dispersive spectroscopy in a scanning transmission electron microscope was conducted on precipitates of the 0.4 pct C steel with vanadium and niobium additions. The vanadium steels contained fine interphase precipitates within ferrite, pearlite nodules devoid of interphase precipitates, and fine ferritic transformation twins. The vanadium plus niobium steels contained large Nb-rich precipitates, precipitates which formed in cellular arrays on deformed austenite substructure and contained about equal amounts of niobium and vanadium, and V-rich interphase precipitates. Transformation twins in the ferrite and interphase precipitates in the pearlitic ferrite were not observed in either of the steels containing both microalloying elements. Consistent with the effect of higher C concentrations on driving the microalloying precipitation reactions, substructure precipitation was much more frequently observed in the 0.4C-V-Nb steel than in the 0.2C-V-Nb steel, both in the ferritic and pearlitic regions of the microstructure. Also, superposition of interphase and substructure precipitation was more frequently observed in the high-C-V-Nb steel than in the similar low-C steel.     

鞍钢钒、钛、铌微合金钢的应用与开发

对钒、钛、铌在钢中的微合金化作用作了全面阐述,并介绍了鞍钢在开发钒、钛、铌微合金钢方面所进行的工作及前景。     

Titanium microalloyed steels

Compared with niobium and vanadium, titanium has been regarded as a relative minor element in microalloyed (MA) steels. More recently, titanium compounds in MA steels have been recognised as having a wider role than just involved in austenite grain refinement. A brief history is followed by considering the physical state of titanium and its compounds characterized in MA steels. Their solubility in iron and the morphology of the precipitates they form, lead to their functions in controlling mechanical and toughness properties of MA steels often involving the multiple alloying with niobium, vanadium, carbon and nitrogen. Titanium has become an important element in the development of linepipe steels, which can develop bainite/acicular ferrite (AF) microstructures. The influence of Ti on nucleation of AF is an active research area, particularly in welding of MA steels. Finally, the influence of titanium on hot ductility, continuous casting and thin slab direct-charging processes is discussed.     

Effect of Microalloying Additions on the Microstructure and Mechanical Properties of Low Carbon Steel

Low carbon steels are characterized by good weldability,formability and fracture toughness properties.However,the low strength levels of these steel grades limit their wide applications.On the other hand,increasing the strength by increasing the carbon content and alloying elements deteriorates the other properties.In this study,the microalloying technique was used to examine the possibility of attaining low carbon steels with good combination of strength,ductility and impact properties.A low carbon steel microalloyed with single addition of vanadium and another one microalloyed with combined addition of vanadium and titanium were used in this investigation and their properties were compared with non-microalloyed low carbon steel having the same base composition.Furthermore,other two nonmicroalloyed and V-microalloyed steels with higher carbon,silicon and manganese contents were also investigated to reveal the effect of base composition.Tensile,hardness,room and zero temperature Charpy V-notch impact tests were conducted to evaluate the variations in the mechanical properties of low carbon hot forged steel containing vanadium and combinations of vanadium and titanium.In addition,the microstructures of the different investigated steels were observed using both optical microscope and scanning electron microscope.Furthermore,the hardness of the ferrite phase was also determined using micro-hardness technique.The results showed improvement of the mechanical properties of the investigated steels by both single V-and combined V + Ti-microadditions.Tensile,hardness and impact tests results indicated that good combinations of strength,ductility and impact properties can be achieved by V-microalloying addition.Steel with combination of V and Ti microaddition has much higher hardness,yield strength,ultimate tensile strength and impact energy at both room and zero temperatures compared with non-microalloyed and single Vmicroalloyed steels.Higher C,Si and Mn contents result in increasing the strength accompanied with decrea     

Application of thermodynamic computations to the solution behaviour of niobium and vanadium carbonitrides

On the basis of well-known thermodynamic equations, a model is proposed which allows the computation of both the solution behaviour and the composition of the carbonitride precipitates of the microalloying elements in steel. Apart from the concentration of the microalloying elements and the carbon and nitrogen content, the following aspects were taken into account: the non-stoichiometric composition of carbonitrides, a regular solution behaviour of the mixture of carbide with nitride, the effect of third elements on the activity of carbon and nitrogen, the possible primary binding of nitrogen by aluminium. The calculation is based on the knowledge of the solubility products of pure carbides and nitrides. Comparison with experimental results of carbonitride precipitates in microalloyed niobium and vanadium steels support the model-based predictions concerning the temperature-dependent composition and solubility of carbonitrides under equilibrium conditions.     

Effects of vanadium and nitrogen on recovery and recrystallization during and after hot-working some HSLA steels

The effects of vanadium/nitrogen additions on dynamic and static recovery and recrystallization have been studied in a set of aluminum-killed HSLA steels containing 0.1 pct carbon, 0.01 to 0.02 pct nitrogen, and either vanadium (0.1 or 0.2 pct), niobium (Cb) (0.03 pct), or vanadium and niobium together. Most, but not all, of the tests were carried out at 1173 K (900°C), a temperature at which precipitation of VN might be expected under some conditions. The net effect of dynamic recovery, recrystallization, and precipitation was monitored by measuring the change in compressive flow stress with strain at a constant temperature. Static changes were followed by measuring the change in compressive flow stress on isothermally holding unloaded specimens after a hot precompression. These kinetic data were supplemented by metallographic and electron-microscopic examinations of quenched specimens and of carbon extraction replicas taken from them. Evidence is presented which indicates that, at a holding temperature of 1173 K (900°C), static recrystallization occurs in vanadium steels containing 0.1 pct vanadium before any precipitation is detected. The progress of this recrystallization is arrested by the precipitation of vanadium nitride. At a higher vanadium concentration, 0.2 pct, recrystallization does not start. The effects of V/N ratio, austenitizing temperature (between 1373 K (1100°C) and 1523 K (1250°C), and isothermal holding temperature (between 1173 K (900°C) and 1273 K (1000°C)) on the kinetics of static softening and hardening are compared in some vanadium steels and plain-carbon and niobium steels of similar base-composition.     

Tribological property of in situ directly nitrided and sintered Al/AlN composite

Abstract

An in situ directly nitrided and sintered Al/AlN composite was developed using a chemical reaction between aluminium and nitrogen gas at temperatures below 823 K. It is clear from SEM and TEM observation that the composite has good bonding of the in situ formed AlN to the aluminium matrix. The composite shows an unusually low friction coefficient (0·004–0·008) under oil lubrication, and also has excellent wear resistance and antiseizure properties when compared with hard anodised aluminium alloys. AlN particles protruding from the matrix create oil microgrooves and which work as oil pits to enhance the formability of oil films. Therefore, it is easy to form hydrodynamic lubrication with continuous oil films on a sliding surface.     

Low carbon manganese steels microalloyed with vanadium and nitrogen

With the objective of studying the effect of vanadium and nitrogen microalloying on microstructure and strength of low carbon steels with different manganese contents, three series of low carbon steels (0.1% C) with manganese content (between 0.8 and 3.5%), vanadium content (up to 0.17%) and nitrogen content (up to 0.025%) have been designed and investigated in the hot forging condition using a preheating and finish forging temperatures of 1200 and 950°C, respectively. Steels with a manganese content up to 2.3% revealed ferrite-pearlite structures, whereas higher manganese contents from 2.7 to 3.5% resulted in the formation of bainitic structures. A pronounced effect of manganese on the mechanical properties of steels was detected at lower manganese contents < 1.5%, due to solid solution and grain refining effects, and higher manganese contents > 2.3, due to bainite formation. Manganese content in the range of 1.5-2.3% had less pronounced effect due to solely solid solution hardening. Vanadium microalloying effectively increased the strength of steels through solely precipitation strengthening or both precipitation strengthening and grain refining effect. The effectiveness of vanadium was greatly enhanced by increasing the nitrogen content. The grain refinement of vanadium-nitrogen microalloying seems to be due to inhibition of austenite grain growth as a result of precipitation of vanadium nitride in austenite during forging. Precipitation strengthening of these steels is achieved by precipitation of vanadium carbide and nitride in ferrite or bainite. Nitrogen enhanced the precipitation strengthening of vanadium microalloyed steels which could be attributed to the finer vanadium nitride dispersion precipitates compared with vanadium carbide. Up to 70% of the total nitrogen content of steel precipitates as vanadium nitride which could be achieved with V/N ratio of about 6-7. Microalloying of low carbon-manganese steels (0.1% C and 1.8% Mn) with 0.15% vanadium and 0.025% nitrogen was found to be effective in attaining high levels of yield and ultimate tensile strengths of 835 and 940 N/mm², respectively in the forging condition.     

Dynamic precipitation and solute hardening in a titanium microalloyed steel containing three levels of manganese

The effect of increasing the manganese concentration on the dynamic precipitation kinetics of TiC was investigated in three microalloyed steels containing 0.1 wt% Ti and 0.5, 1.1 and 1.6% Mn. The lowest manganese level was associated with a carbon concentration of 0.06%, while the remaining two steels contained 0.1% C. Compression tests were carried out in the strain rate range from 10⁻⁴ to 10⁻¹ s⁻¹ at testing temperatures of 925, 975 and 1025°C. The dependence of the peak strain on strain rate and composition was established at each of the three temperatures and the dynamic precipitation kinetics (PIT curves) of TiC were determined in this way. The nose of the PTT curve for the dynamic precipitation of TiC in austenite containing 0.1% Ti, 0.5% Mn and 0.06% C is located at about 4s and 1000°C, and is estimated to advance to approximately l s when the carbon concentration is increased to the standard level of 0.1%. By contrast, the nose position for steels of equivalent titanium and carbon concentration (i.e. 0.1% for both elements) shifts to the vicinity of 6 and 7s respectively when the manganese concentration is increased to 1.1 and 1.6%. This phenomenon is discussed in terms of the influence of manganese on the activity coefficient of carbon and on the diffusivity of titanium. The increase in the yield strength and the solute retardation of dynamic recrystallization resulting from the addition of 0.1% Ti are also considered. These effects are compared to the influence of other microalloying additions, such as molybdenum, niobium and vanadium.     

Development of forging quality high strength low alloy steels

Abstract

The effect of alloy composition and heat treatment on the structure and properties of a set of high strength low alloy (HSLA) steels has been investigated. By addition of a relatively high dose of niobium (0·17–0·23%)along with nickel (0·2%), chromium (0·4–0·6%), and manganese (1·5–1·8%) to 0·2%steels, it is possible to develop high strength forging grade steels having baintic or autotempered martensitic matrixes. The microstructure and mechanical properties of these steels are sensitive to cooling rate and heat treatment.     

Delta ferritic heat-resistant chromium-molybdenum steels with improved rupture strength

Nine experimental delta-ferritic steels have been examined as potential low expansion heat-resistant steels for use in fossil fuel power generation, nuclear power generation, nuclear process heat plants and coal gasification plants. The steels contain 10 to 14 pct Cr and 2 to 6 pct Mo, with additions of columbium, titanium, vanadium, aluminum and boron. Room-temperature tensile properties and oxidation resistance of all steels were determined. Selected steels were aged for 1000 h at 760 °C (1400 °F) and subjected to elevated temperature tensile tests at the aging temperature. Creep-rupture properties of selected steels were determined at 760 and 815 °C (1400 and 1500 °F). Extensive metallographic and phase identification studies were conducted. Of the two steels tested for creep-rupture strength, the 10Cr-6Mo-0.5Cb steel, with good room-temperature ductility, has rupture strength exceeding that of martensitic 12Cr-1Mo-V steel. The 14Cr-3Mo-0.5Cb-lTi-2Al steel exhibits an even higher rupture strength, but has only marginal ductility at room temperature.     

Microstructure and Precipitation Behavior in HAZ of V and Ti Microalloyed Steel

Three steels containing 0. 05%C-0. 1%V-0. 01%N (steel V-LN), 0. 05%C-0. 1%V-0. 02%N (steel V-HN), and 0. 05%C-0. 1%V-0. 02%N-0. 01%Ti (steel V-HN-Ti), which were all essentially vanadium microalloyed steels, were subjected to simulating the microstructure of a coarse grained heat affected zone (CGHAZ). The process involved reheating to 1 350 °C, rapid cooling to room temperature, and varying the welding heat input from 15 kj/cm to 54 kj/cm, including four cooling rates of t_8/5 equal to 7. 5 s, 20 s, 40 s, 100 s, and the relationship of heat input to tg/_s was calculated by Quiksim software. The microstructure and precipitation of vanadium and titanium carbon nitrides are studied. The results indicate that the microstructure consists of granular bainite and some side plate ferrite in the grain boundary when the steels are produced with the highest heat input. As the heat input decreased, numerous polygonal ferrites and grain boundary ferrites appeared, and the size apparently increased. When the steel contained high nitrogen, it was considerably easier to form martensite-austenite island, which was even worse for the toughness and other properties of the steel. For the limitation of cooling time, vanadium carbon nitrides could not precipitate sufficiently, but as titanium was added, the unmelted or precipitated TiN on cooling absorbed some fraction of nitrogen in the matrix and made more precipitate positions for the round V(C, N), and thus several useful round particles could be seen in titanium-contained steel, and most of them were around TiN. By this experiment, we can conclude that with the help of titanium, nitrogen-enhanced steel had a better prior austenite grain size, was considerably easier to precipitate, reduced free nitrogen in the matrix effectively, and provided a very effective mechanism for restriction grain growth in the HAZ.     

Contributors

Abstract

The chemistry of a high performance cast superalloy, ZhS6–K (Ni–10Cr–5Co–5W–5Al–3·5Mo–3Ti–0·2C–0·02B), was modified by slight reductions in carbon, titanium, and aluminium content and minor additions of niobium and hafnium. Two variants of the modified alloy chemistry with different boron contents (0·02 and 0·08 wt–%) were prepared by vacuum induction melting, argon atomization, and consolidation by hot isostatic pressing at three temperatures. It was observed that, unlike carbon, an increase in boron content did not promote the formation of continuous precipitates at the prior powder particle boundaries. Increased boron content narrowed down the consolidation temperature range and changed the morphology of γ′ particles from cuboidal to dendritic. Precipitation of an eutectic γ + γ′ structure and formation of continuous boride films at the grain boundaries severely degraded the mechanical properties of the high boron PM superalloy that was consolidated at a temperature marginally above the γ′ solvus. An optimum consolidation schedule was determined for the high boron alloy, which after a suitable heat treatment produced significant property improvement in stress rupture and tensile properties. PM/0416     

Effect of molybdenum,niobium, and vanadium on static recovery and recrystallization and on solute strengthening in microalloyed steels

The effect of molybdenum, niobium, and vanadium on the occurrence of static recovery and recrystallization after high temperature deformation was investigated in a series of microalloyed steels. The steels had a base composition of 0.05 pct C and 1.40 pct Mn. To this, single additions of 0.30 pct Mo, 0.035 pct Nb, and 0.115 pct V were made. Interrupted hot compression tests were performed at 900 and 1000 °C, and at a constant true strain rate of 2 s^-1. The load-free time was decreased from 5000 s to 50 ms, and the degree of static softening during this period was determined. Both graphite and glass were used as lubricants. Percent softeningvs delay time curves are presented and the retarding effect of molybdenum, niobium, and vanadium addition on the rate of static recovery and recrystallization is discussed. The greatest solute retardation of static recovery and recrystallization is produced by niobium addition, followed by that of molybdenum, vanadium leading to the smallest delay. Although the rank order of this effect is the same as found under dynamic softening conditions, the relative contribution of niobium is more profound for the static condition. The solute strengthening attributable to each element was also assessed, and found to follow the same order as for the recovery and recrystallization results. At 900 °C, the onset of the static precipitation of Nb (CN) was detected at approximately 10 seconds, somewhat earlier than previously reported. Formerly Graduate Student at McGill University, Montreal, Quebec.     

Review of effect of oxygen on room temperature ductility of titanium and titanium alloys

Abstract

Room temperature tensile ductility is an important property of titanium (Ti) and titanium alloys for structural applications. This article reviews the dependency of tensile ductility on oxygen for α-Ti, (α+β)-Ti and β-Ti alloys fabricated via traditional ingot metallurgy (IM), powder metallurgy (PM) and additive manufacturing (AM) or three-dimensional printing methods and recent advances in understanding the effect of oxygen on ductility. Seven mechanisms have been discussed based on case studies of individual titanium materials reported in literature. The dependency of ductility on oxygen is determined by both the composition and microstructure of the titanium alloy. For Ti–6Al–4V (wt-%), as sintered Ti–6Al–4V shows a critical oxygen level of about 0·33 wt-% while additively manufactured Ti–6Al–4V exhibits different critical levels ranging from about 0·22% to well above 0·4% depending on microstructure. Rare earth (RE) elements are effective scavengers of oxygen in titanium materials even just with a small addition (e.g. 0·1 wt-%), irrespective of the manufacturing method (IM, PM and AM). High cycle fatigue experiments revealed no initiation of fatigue cracks from the resulting RE oxide particles over the size range from submicrometres to a few micrometres. A small addition of RE elements offers a practical and affordable approach to mitigating the detrimental effect of oxygen on ductility.     

Microalloying effects in hot-Rolled low-Carbon steels finished at high temperatures

As part of a program to improve the toughness of steels for structural shapes and thick plates, the effects of columbium (niobium) (0 to 0.24 pct) or vanadium (0 to 0.23 pct) in conjunction with aluminum (0 to 0.06 pct) on the properties of hot-rolled 0.1 pct carbon steels were determined. Experiments were conducted on a laboratory mill to obtain 25 mm (1 in.) plate. Although the primary interest was to improve toughness in materials finished above 980 °C (1800 °F), finishing temperatures in the range 845 to 1150 °C (1550 to 2100 °F) were investigated. Impact properties of columbium steels finished above 980 °C (1800 °F) were very poor. This effect was attributed to the presence of acicular Widmanstatten structures and relatively coarse grain-boundary precipitates. Toughness improved dramatically at finish-rolling temperatures of 955 °C (1750 °F) and below as a result of the combined effects of grain refinement and reduced precipitation hardening. For the vanadium steels, variations in finish rolling temperature did not have such a marked effect on properties. Aluminum additions considerably lowered the impact transition temperature of the vanadium steels. Although aluminum also improved the impact properties of the columbium steels, the effect was not sufficient to produce good toughness in steels finish-rolled above 980 °C (1800 °F). Thus, although superior properties may be obtained in the columbium steels finished below 925 °C (1700 °F), vanadium steels generally had better impact properties at higher finishing temperatures.     

Development of Steel Microalloying System for Cold-Resistant Coiled Product Designated for Pipes Under CRC Conditions

Metallurgist - are provided for a study of the effect of microalloying steel with niobium, titanium,, and vanadium on the level of mechanical properties and cold resistance of coiled rolled product...     

Annealing Response of Cold-Rolled Vanadium Microalloyed Sheet Steels

Vanadium microalloying is widely employed in hot-rolled HSLA products;because of its relatively high solubility in austenite,vanadium plays a special role in thin-slab cast hot-rolled products where reheating is limited prior to direct-rolling.In cold-rolled and annealed sheet steels,vanadium technology has been employed in bake-hardenable drawing-quality steels,and in HSLA products.Recent studies have investigated the continuous and batch annealing response of vanadium-containing cold-rolled HSLA steels,with an emphasis on aluminum and nitrogen variations (because of the special importance of nitrogen in vanadium microallyed steels,and interesting interactions between vanadium,aluminum and nitrogen).The present contribution reviews some key aspects of vanadium-microalloyed coldrolled sheet steels,and highlights the results of selected studies showing the influence of steel composition and processing.