Addition Of Niobium Research Articles

Comparison of the strengthening effects of Nb, V, and Ti on the mechanical properties of 20MnSi low-alloy steel

Abstract Three alloys, containing niobium, vanadium and titanium, respectively, were refined and the strengthening effect attained after adding them individually in a 20MnSi low-alloy rebar steel was investigated. The results show that the strengthening effect attained due to the addition of niobium is the best, whereas that due to the addition of titanium is the poorest. Grain refinement and precipitation strengthening are the main strengthening mechanisms observed in niobium-steel and vanadium-steel, whereas only precipitation strengthening is observed in titanium-steel. Moreover, the average grain size of niobium-steel is the smallest among the four types of steels, while the size of ferrite and pearlite microstructures show almost no obvious change as compared to the base steel in the case of titanium-steel. Furthermore, the volume fractions of ferrite and pearlite in the four tested steels have no noticeable change.

The effect of Al and Nb contents, cooling rate and rolling condition on the microstructure and corrosion behaviour of HSLA steel

The effect of the addition of aluminium and niobium, and processing conditions, including cooling rate and rolling condition, on the corrosion behaviour of HSLA steel in 10 wt% sulfuric acid environment has been investigated. The experimental procedures included electrochemical corrosion techniques using potentiodynamic and electrochemical impedance spectroscopy, as well as weight loss method. The microstructure was examined using optical and scanning electron microscopes in order to investigate the effect of the microstructural features on the corrosion behaviour. Surface films were evaluated by X-ray photoelectron spectroscopy (XPS) to identify the corrosion products formed on the surface. The results showed that increasing the Al content enhanced the corrosion resistance through obstructing pitting attack on the surface by the refinement of grain boundary carbides and the formation of a protective passive layer rich in carbide and oxide compounds. The combination of both Al and Nb promoted the corrosion resistance further, by enriching the passive layer with Nb and higher levels of carbide and oxide compounds, despite the presence of martensite and grain size refinement by niobium carbonitride (NbCN). Increasing the cooling rate reduced the corrosion resistance due to the refinement of grain size, giving a higher density of grain boundaries that act as active sites, besides increasing the level of carbide distribution in the microstructure. Controlled rolling offered higher corrosion resistance than hot rolling, independent of the composition, because of the absence of martensite, the presence of low-angle boundary and the refinement of grain boundary carbides provided by controlled rolling.

Effect of Chemical Composition and Heat Treatments on the Microstructure and Wear Behavior of Manganese Steel

The present paper analyzes the effect of the chemical composition and heat treatments on the microstructure and wear resistance of manganese steels. The studied steels are melted in an electric arc furnace. Alloying elements (Cr + Ni + Nb) are added as ultra-fine powder in a well-heated ladle. Samples are subjected to two heat treatments: one at 1100 °C and the other at 1050 °C, and then quenched in water. Optical microscopy, scanning electron microscopy and X-ray diffraction are used to evaluate the microstructural changes. Hardness and microhardness measurements, mass loss and friction coefficient were also performed to determine the wear behavior of the studied steels. The results indicated that the microstructure of the manganese steel in the as-cast state consists of an austenitic matrix and cementite alloyed with manganese and chromium ((Fe,Mn,Cr)3C). Increasing chromium content increases the size of the alloyed cementite (Fe,Mn,Cr)3C. Addition of niobium leads to the apparition of new secondary carbide (NbC). The heat-treated microstructures consist of martensite, retained austenite and a small quantity of precipitates. Increasing in heat treatment temperature and addition of alloying elements (Cr + Ni + Nb) increase the hardenability of the studied steel and favor the martensitic transformation. As a result, addition of niobium and increasing in chromium and nickel contents improve hardness and wear resistance of the studied manganese steel.

Influence of Niobium Content on the Mechanical Properties and Abrasion Wear Resistance of Heat-Treated High-Chromium Cast Iron

The effect of niobium addition up to 3.4 wt% on the microstructure and mechanical properties of heat-treated high-Cr cast iron containing 13.5 wt% Cr was investigated. Niobium addition caused small hard NbC particles to precipitate within the proeutectic austenite which impede the development of austenite dendrite growth resulting in structure refinement. This austenitic matrix upon heat treatment changed to mainly martensitic one with some retained austenite and reinforced with small amounts of secondary carbides of M7C3 type. It was found that the hardness increased with increasing Nb content due to structure refinement and precipitation of hard NbC particles. These particles caused a depletion of carbon in the austenite matrix and thus most of the austenite was transformed to martensite upon heat treatment. The highest impact value was obtained for the base alloy without Nb addition which could be attributed to the high amount of retained austenite. The high-Cr cast iron alloyed with Nb in the range of 1.55–3.4 wt% showed an increase in hardness without any deterioration in toughness. The wear resistance was significantly enhanced by the presence of hard NbC particles up to 2.52 wt% Nb. Exceeding this optimum amount of addition leads to agglomeration of NbC particles and hence deterioration of the wear resistance through three body abrasion wear mechanism.

Comparison of the strengthening effects of Nb, V, and Ti on the mechanical properties of 20MnSi low-alloy steel

Abstract Three alloys, containing niobium, vanadium and titanium, respectively, were refined and the strengthening effect attained after adding them individually in a 20MnSi low-alloy rebar steel was investigated. The results show that the strengthening effect attained due to the addition of niobium is the best, whereas that due to the addition of titanium is the poorest. Grain refinement and precipitation strengthening are the main strengthening mechanisms observed in niobium-steel and vanadium-steel, whereas only precipitation strengthening is observed in titanium-steel. Moreover, the average grain size of niobium-steel is the smallest among the four types of steels, while the size of ferrite and pearlite microstructures show almost no obvious change as compared to the base steel in the case of titanium-steel. Furthermore, the volume fractions of ferrite and pearlite in the four tested steels have no noticeable change.

The combination of strength and cryogenic impact toughness in low carbon 5Mn–5Ni steel

A low carbon medium manganese steel with additions of nickel and niobium was designed to further enhance cryogenic impact toughness of medium manganese steels and suppress Lüders deformation. It is interestingly found that the steel containing little retained austenite (around 1.5 vol.%) possesses high strength and excellent cryogenic impact toughness after heat treated at 650 °C for 2 h, whereas conventional medium manganese steels containing little or more unstable retained austenite always show poor cryogenic impact toughness after heat treated at a relatively high temperature. The excellent cryogenic impact toughness is mainly attributed to the formation of fine grains and little retained austenite with high mechanical stability. All steels exhibit continuous yielding behavior, and the yielding behavior is independent of heat treatment temperature. Moreover, the Lüders deformation is suppressed by restraining the formation of Cottrell atmosphere through low carbon design, further reduction in free carbon content in matrix via both the partition of carbon from matrix to austenite and the formation of NbC, some mobile dislocations and the formation of α+α′ mixture.

Bending Fatigue in Low-Pressure Carbonitriding of Steel Alloys with Boron and Niobium Additions

In this study, the low-pressure carbonitriding (LPCN) response of four different steel alloys is investigated. The influence of unprotected boron is evaluated by comparing the microstructure and fatigue performance of 20MnCr5 with and without boron additions after LPCN. Similarly, the influence of Nb microalloying is assessed by comparing 8620 steel with and without Nb additions. Low-pressure carbonitriding heat treatments were developed to achieve case depths of 0.65-0.75 mm in each alloy, thus allowing the influence of alloying and microstructure to be explored independent of case depth. The hardness and case microstructure are correlated with bending fatigue response measured with Brugger fatigue specimens, which are designed to simulate the root of a gear tooth. The 20MnCr5 alloys had the highest fatigue strength, and the 8620 alloys had the lowest fatigue strength, despite having the same hardness profile and case depth. Reductions in prior austenite grain size and increased surface hardness appeared to have a positive effect on the endurance limit of the steel alloys. Retained austenite volume fraction on the surface of the steel alloys as well as non-martensitic transformation products subsurface in the case did not have an apparent direct contribution to fatigue performance.

Microstructure and Mechanical Property Improvement of Laser Additive Manufacturing Ti–6Al–4V via the Niobium Addition

Microstructure and Mechanical Property Improvement of Laser Additive Manufacturing Ti–6Al–4V via the Niobium Addition

Thermal conductivity of porous Alumina-20 wt% zirconia ceramic composites

Effect of porosity and temperature on thermal conductivity of the porous Alumina-20 wt% Zirconia (3 mol.% Y2O3) ceramic composites with and without niobia were investigated. The ceramic powders were synthesized by the sol-gel route using alkoxide precursors. The porosity in the composites was maintained in the range of 9.5–65 vol% using starch as a space holder material. After processing, samples were compacted uniaxially and sintered at 1873 K for 3 h. The thermal conductivity of porous ceramic composites with and without niobia dopant was measured at three different temperatures of 300, 473, and 673 K using laser-flash technique. The thermal conductivity of the samples was reduced with increasing temperature and porosity. At temperature of 300 K, the thermal conductivity value of 11 W/m.K was obtained for the undoped sample S0 with 17 vol% residual porosity, dropped to 2 W/mK for the sample S40 containing 65 vol% porosity, and for the same sample it was further reduced to the lowest value of 0.68 W/m.K at 673 K. The measured conductivity values were used to determine the grain boundary thermal resistance value (R) of the samples which exhibited an ascending trend with the porosity. The obtained thermal conductivity for the different porous composites was verified and formulated with the Maxwell-Eucken and Ticha models. The results showed that the experimentally measured conductivity values follow a descending order with the models while at the higher-porosity level (57–65 vol%), it fits well with the Ticha equation with only 9% and 4.6% deviation for undoped and doped samples, respectively. Results also revealed that the addition of niobia significantly reduced thermal conductivity at the lower porosity levels, but at higher porosity level the effect of porosity was more dominant.

Influence of Nb addition on the structure, composition and properties of single-layered ZrN-based coatings obtained by vacuum-arc deposition method

The paper deals with the vacuum-arc deposition of single-layered ZrN-based coatings with and without the addition of niobium in their composition. We generate metal plasma to synthesize (Zr,Nb)N coatings by evaporation of two cathodes (Zr and Nb) by vacuum arc. The niobium concentration in the coating was varied by changing the evaporator arc current with the Nb cathode. The article covers study results of the mechanical and tribological properties of the obtained coatings, their elemental and phase composition, and structural state. The present research illustrates the effect of the niobium concentration on characteristics of the ion-plasma (Zr,Nb)N coatings. It demonstrates that the ZrN-based coatings consist of columns that are divided into the ZrN crystallites with a cubic crystal lattice. Furthermore, it shows that addition of niobium to the composition of ZrN-based coatings results in a significant change in their properties such as refinement of their structural components: the lateral size of the columns ≈ 2 times, the average diameter of crystallites ≈ 1.4 times. The single-layered nanocrystalline (Zr,Nb)N coatings, obtained in optimal conditions, have niobium concentration of 9.8 at.%, high hardness (up to 39.4 GPa), low wear rate (9 · 10−6 mm3 N−1 m−1), relatively low roughness (0.03 μm), and a high degree of elastic recovery (up to 60%).

Effect of Low-Temperature Austempering and Quenching and Partitioning Treatments on Adhesive Wear Resistance of High-Silicon Multiphase Steels

The quest for vehicle safety improvement with weight reduction and consequently lower fuel consumption led the automotive industry to begin research into the third generation of advanced high-strength steels. These steels present complex microstructures, composed of martensite, bainite and stable retained austenite. Two of the main treatments for obtaining these microstructures are the low-temperature austempering and quenching and partitioning (Q&P). The objective of this work is to evaluate the microhardness and adhesive wear performance of C-Si-Mn and C-Si-Mn-Nb steels submitted to the treatments mentioned above. Both austempering and the partitioning steps were conducted at Ms+50 °C. Treatment times were 1 and 3 h for austempering and 10, 30 and 60 min for Q&P. Results show that niobium addition promotes improvement in wear performance despite inferior levels of austenite stabilization and changes in the bainite morphology.

Development of Carbidic Austempered Ductile Iron (CADI)

This study aimed at optimizing impact toughness and high wear resistant carbidic austempered ductile iron (CADI) by controlling the morphology, size and quantity of carbides. The effects of dynamic solidification, niobium addition, combined action of them and heat treatment have been investigated. Investigations were performed by means of the image analyzer, scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS) and X-ray diffraction. Impact toughness, hardness and abrasion wear resistance tests were conducted. Fracture surfaces were studied. Results indicated that microstructural control during solidification is the most valuable tool to attain the optimum combination between impact toughness and wear resistance in CADI. Combined action of Nb addition and dynamic solidification improves impact toughness, hardness and wear resistance even more than the action of each individual factor. In the as-cast condition, impact toughness, hardness and abrasion resistance were improved after dynamic solidification compared to statically solidify one by 31.2%, 18.75% and 87.96% respectively. This enhancement was increased to 36.9%, 25.93% and 128. % by adding 1% Nb. Lower tempering temperature of 275°C exhibit best hardness and abrasion resistance better than higher tempering temperature of 375°C.

Effect of MC carbide formation on weld solidification cracking susceptibility of austenitic stainless steel

The effect of secondary phase formation such as MC carbide during welding on solidification cracking susceptibility of fully austenitic stainless steels with various amounts of alloying elements and carbon was investigated. The solidification cracking susceptibility of Fe-24mass%Cr-26mass%Ni stainless steels with various amounts of niobium, titanium, zirconium, and carbon was evaluated by the Trans-Varestraint test.The addition of alloying elements such as niobium, titanium, and zirconium increased the brittle temperature range (BTR). The BTRs depend on the type and combination of the alloying elements and carbon content. Titanium was the most influential element on the increase in BTR compared to the other elements. The increase in carbon content tended to decrease the BTR, especially for the specimen containing titanium. The alloying elements formed phases such as the film-like MC-type carbide (MC) phase and granular Laves phase in the specimens containing 0.05% C, and a lot of the acicular MC phases in the specimens containing 0.20% C. The start temperature of the secondary phase formation differed depending on the type of the alloying element, and the temperature tended to increase with increasing carbon content. When the additions of niobium and titanium were compared, the amount of titanium segregation during solidification was smaller due to the formation of MC phases. Solidification simulation revealed that a higher amount and faster formation of the MC phase during solidification in 2Ti–20C contributed to reducing the BTR by increasing the carbon content. Thus, it is considered that the weld solidification cracking susceptibility depended on the type and amount of formation morphology, as well as start temperature during solidification corresponding to the composition of alloying elements and carbon.

Effect of Niobium Addition on Microstructure and Mechanical Properties of Fe–7Al–0.35C Low-Density Steel

The present work reports the effect of niobium addition on a Fe–7wt.%Al–0.35wt.%C-based low-density steel. A hot rolling temperature of 1100 °C was selected to carry out rolling in the intercritical (ferrite + austenite) region. The phases formed on adding Nb were predicted by thermodynamic calculations using ThermoCalc. All the alloys exhibited a significant (20% or more) tensile elongation. Niobium addition also resulted in a significant increase in strength and hardness of the hot-rolled steel. About 80% increase in the yield strength is observed as the Nb content increases from 0.2 to 1.0 wt.%. Nb carbides present at rolling temperature resist grain growth and lead to improved mechanical properties. This study demonstrates the advantages of adding Nb to Fe–Al–C-based low-density steels. Earlier attempts to add Nb to low-density steels resulted in very low ductility. This may be related to their susceptibility to hydrogen embrittlement. Melting of high aluminum low-density steels in a controlled atmosphere may lead to a considerable improvement in mechanical properties. Further, it is also important to maintain a high C/Nb ratio to avoid the formation of Laves phases.

Problems of weld overlay of seating surfaces of pipe fitting and solutions

Introduction. A problem of providing the necessary functions of pipe fitting for blockage, control, distribution of the working medium flows under the most adverse operating conditions of oil and gas pipelines associated with abrasive particles, mechanical impurities, hydrogen sulfide, carbon dioxide and organic acids with sulfate-reducing bacteria, is considered.Materials and Methods. High performance properties of seating surfaces of pipe fittings are provided through anticorrosive plating of alloyed and high-alloyed metals based on iron with the addition of chromium, nickel, cobalt and niobium. The basic weld overlay methods are analyzed: metalarc welding, nonconsumable and consumable-electrode weld facing in shielding gases, submerged arc surfacing. Advantages and disadvantages of surfacing methods implemented in recent years are noted: laser, plasma-powder and plasma-arc methods.Research Results. Taking into account the automation capabilities, a high-tech process of robotic anticorrosive surfacing using a consumable electrode with an additional filler metal feed to the front welding puddle for shielding the thermal effect of the arc, is proposed. Industrial application of the proposed technology requires a set of studies related to assessing the effect of technological parameters on the quality of the deposited layers to provide the required operational characteristics of the fitting.Discussion and Conclusion. It is proposed to carry out the above studies using physical and mathematical modeling of the anticorrosive surfacing, which reduces the time and number of experiments. Therefore, the primary task is to develop a mathematical model of the surfacing process with a consumable electrode with an additional filler wire and transverse vibrations of the welding burner. Such a model should virtually reproduce the surfacing process, as well as its thermal cycle followed by calculating the ratio of the structural components of the deposited metal and the substrate metal. The system of equations of the model should be solved by a special computer program. The algorithm presented for solving this class of problems will allow us to make a sound connection of the technological parameters of the surfacing process and the quality parameters of the formation of the deposited layers, to determine the program for their optimization to provide the required operational properties of pipeline fitting.

Effect of niobium addition in grey cast iron: A short review

The effect of alloying element addition in grey cast iron is great interest of materials developers. In the same context, the effect of adding niobium on mechanical properties of grey cast iron is reviewed. Microstructure and hardness test are reviewed to examine the mechanical properties of alloyed grey cast iron. The study indicated that increasing niobium results in increasing hardness due to which wear rate reduces and also reduces the lamellar spacing between the graphite layers. The reduction in lamellar spacing is due to decreases in eutectic temperature with the addition of niobium. Additionally, mechanical properties including hardness and wear resistance were enhanced after adding niobium.

Effects of Heat Input and Niobium Addition on HAZ of Microalloyed Steels for Reinforcing Bars

Abstract: Niobium or vanadium addition provides homogeneous microstructures formation, strengthening and toughness improvement in steels. However, alloying elements increase can negatively affect Pcm (material parameter) value, which can lead to deleterious effects under welding conditions. Thus, welding trials were carried out on a novel microalloyed steel with 0.2%C by autogenous GTAW (Gas-Shielded Tungsten Arc Welding) process. The results indicate that coarse grains region of heat affected zone (CGHAZ) is the most critical area. This was due abnormal grains size (>100µm), achieving more than 4 times the average size of base metal (BM) grains, or the presence of high hardness microstructures. In addition, the results do not indicate softness in any region of HAZ, proving to be an advantage of these materials.

Effect of niobium addition on the properties and microstructure of a high chromium cast iron alloy

High chromium cast iron (HCCI) is usually employed in equipment that experience high abrasive wear and therefore requires high resistance. Niobium could be added to these alloys to improve their resistance to wear. This study consisted in addressing the influence of 0.5% and 1.0% of niobium on the microstructure of a 26% Cr and 2.8% C HCCI alloy. Standard samples – without niobium – and samples with 0.5% and 1.0% Nb were melted, cut and then machined into adequate dimensions for tests. Two groups of samples – with and without heat treatment – were analyzed through X-ray Diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), Vickers and Rockwell-C hardness. Carbides Volume Fraction (CVF) was quantified in the heat-treated samples. The majority of NbC carbides were observed to be thin and presented a hook shaped morphology. In addition, it was noted a precipitation of Nb-rich layers around the M7C3 carbides, which could act as a higher hardness coating. There was significant reduction in carbide volume fraction, from an initial 33.3% to 28.1% for the 0.5 % Nb alloy, and further reduction to 24.9% for the 1.0% Nb alloy, it was also noted an alteration on the quasi-eutectic microstructure to a hypoeutectic microstructure. The NbC carbides prevented hardness reduction as a result of lowering the CVF in heat-treated alloys; however, the alloys without heat treatment experienced reductions in hardness. Keywords: Heat treatment, niobium, high chromium cast iron, microstructure. 1

The Effect of Niobium Addition on the Microstructure and Tensile Properties of Iron-Nickel Base A286 Superalloy

The Effect of Niobium Addition on the Microstructure and Tensile Properties of Iron-Nickel Base A286 Superalloy

The effect of niobium addition on the microstructure and properties of cast iron used in cylinder head

Cylinder head is one of the most important parts of heated components in the engine, while cracking due to low strength and large residual stress at high temperature is the main failure mode of cylinder head. With the growing demand of good performance and high reliability, gray cast iron with trace alloying element and optimized annealing process are probably effective ways in obtaining suitable materials. The effect of niobium addition on the microstructure and properties of cast iron used in cylinder head is studied in this paper. The results show that, the tensile strength, toughness, fatigue properties and thermal fatigue properties of gray cast iron are improved by adding trace niobium elements. The specimen with 0.20% niobium shows better comprehensive mechanical properties than others. The addition of trace niobium elements can not only refine the graphite, eutectic cell, carbide and phosphorus eutectic, but also reduce the pearlite lamellar space, thus strengthening the matrix. The cylinder head is made by cast iron with 0.20% niobium addition, and the annealing process of thermal aging is optimized. The residual stress of cylinder head can be maintained at a low level by adopting annealing process with higher holding temperature, longer holding time, lower cooling rate and lower outlet temperature. The analysis of microstructure, mechanical properties and residual stress for niobium alloyed cast iron is helpful for solving the cracking problem of cylinder head, and providing scientific basis for improving engine reliability.