Combined Addition Of Nb Research Articles

Analysis of the Generation State of Fine Precipitates in Steel

Fine precipitates in steel have various effects on the properties of steel products. Therefore, it is important to investigate the state of existence of precipitates in steel in order to consider their effect on the material. In this study, the size and shape of Nb and V precipitates were observed by electron microscopy and the amount of precipitates was evaluated by electrolytic extraction analysis in martensitic stainless steels which has excellent heat resistance. For steels with a certain chemical composition, stable chromium nitride (Cr2N) formation was observed when only Nb was added, whereas combined addition of Nb and V suppressed the formation of Cr2N and produced extremely fine precipitates in the steel (in lath martensite). The fine precipitates could be observed in thin film samples by using a high-resolution transmission electron microscope (TEM). In order to evaluate the state of formation of the fine precipitates in the steel quantitatively, the difference in the precipitation behaviors between the two materials was investigated by the size-classified quantitative analysis method. This method is considered to be a useful analytical technique in the development and design of high performance steels using fine nitrides and carbides with sizes of the several nm order.

Analysis of the Generation State of Fine Precipitates in Steel

Fine precipitates in steel have various effects on the properties of steel products. Therefore, it is important to investigate the state of existence of precipitates in steel in order to consider their effect on the material. In this study, the size and shape of Nb and V precipitates were observed by electron microscopy and the amount of precipitation was evaluated by electrolytic extraction analysis in austenitic stainless steels which has excellent heat resistance. For steels with a certain chemical composition, stable nitride (Cr2N) formation was observed when only Nb was added, whereas combined addition of Nb and V suppressed the formation of Cr2N and produced extremely fine precipitates in the steel (in lath martensite). The fine precipitates could be observed in thin film samples by using a high-resolution transmission electron microscope (TEM). In order to evaluate the state of formation of the fine precipitates in the steel quantitatively, the difference in the precipitation behaviors of the two materials was investigated by the size-classified quantitative analysis method. This method is considered to be a useful analytical technique in the development and design of high performance steels using fine nitrides and carbides with sizes of the several nm level.

Compositional Optimization of High-Performance Ferritic (HiperFer) Steels—Effect of Niobium and Tungsten Content

The combined addition of Nb and W provides increased solid solution and precipitation strengthening by (Fe,Cr,Si)2(Nb,W)-Laves phase particles of ferritic, 17 wt.% Cr stainless high-performance ferritic (HiperFer) steel. Based on alloy modifications and the obtained hardness, tensile, and creep testing results; a new high alloying variant is proposed as a candidate steel for future structural application up to approximately 680 °C in power engineering and the process industry.

Corrosion and SCC initiation behavior of low-alloy high-strength steels microalloyed with Nb and Sb in a simulated polluted marine atmosphere

Corrosion and stress corrosion cracking (SCC) behavior of some low-alloy high-strength steels microalloyed with Nb and Sb were in detail studied in a simulated polluted marine atmosphere. The results indicated that the high-strength steel without Nb and Sb was badly damaged by corrosion and very susceptive to SCC in a SO2-containing marine atmosphere, which was characterized by high corrosion rate and a large number of potential initiation sites for SCC cracks. By contrast, Nb addition affected little on atmospheric corrosion rate, but weakened the role of hydrogen at the boundaries of prior austenite grain and lath bainite. Sb addition significantly reduced the corrosion rate by optimizing the properties of rust layer through its synergy with Cu, and inhibited the localized anodic dissolution and acidification effect underneath. Thus, the combined addition of Nb and Sb increased the resistance to atmospheric corrosion and substantially inhibited SCC initiation.

Microstructural changes and mechanical behaviour of a near lamellar γ-TiAl alloy during long-term exposure at 700 °C

Ti-44Al-5Nb-1W-1B with a near lamellar microstructure was exposed at 700 °C for up to 10000 h in air. The changes in microstructure were investigated using scanning and transmission electron microscopy. It has been found that the combined addition of Nb and W can restrict parallel decomposition of α2 lamellae into ultrafine γ lamellae, but causes prevalent precipitation of fine β(B2+ω) particles from α2 lamellae and precipitation/growth of ω particles from β(B2) grains. However, although 3/4 of α2 lamellae dissolved and majority of them transformed to β(B2+ω), tensile ductility is reduced only by 30% while the strengths remain essentially unchanged for the thermally exposed alloy. This is attributed to the widespread distribution of β(B2+ω) particles. On the other hand, fatigue limit was found to decrease during the first 5000-h exposure but finally increased by 11% after 10000-h exposure. The reasons for the decrease and increase of fatigue strength at different exposure stages are discussed by considering two contradictory effects on the exposed alloy: 1) exposure-induced embrittlement due to microstructural changes (harmful); 2) annealing of fatigue samples in a warm air environment for prolonged time (beneficial).

Hot stamped parts with desirable properties in medium Mn TRIP steels

Abstract With the increasing requirements of the automotive industry for reduced weight and safety improvement, high strength steel hot stamping parts have been increasingly applied in the automotive industry. But the process is along with higher equipment requirements and tool wear because of the high temperature.In this study, warm tensile deformation behavior of 6Mn, 6MnNb and 6MnNbMo steels was investigated, in conjunction with warm stamping to understand the role of Mn and Mo and evaluate the mechanical properties of Ushaped parts.The results show that the hotstamped6MnNbMo Ushaped parts at both 700 ° C and 760 ° C exhibited the desirable mechanical properties, e.g. the SDB (Strength Ductility Balance) values reached 23.6-36.8 GPa·%, which were more than double or triple times higher than those of hotstamped boron steels. The work hardening rate increased with addition of Nb and Mo, while it decreased with flow stress.As the stamping temperature decreased from 760 to 700 ° C, the fractions of soft phase ferrite and retained austenite increased, resulting in the enhanced elongation with reducing tensile strength from 1600-1814 MPa to 1361-1467 MPa.The combined addition of Nb and Mo raised UTS with a slight decrease in El, and improved the distribution uniformity of mechanical properties, which is of great importance when applying medium Mn steels to the automotive structural components for ensuring safety of passengers.

Grain refining potency of Nb–B inoculation on Al–12Si–0.6Fe–0.5Mn alloy

In a recent work we reported that the combined addition of Nb and B has higher grain refinement effectiveness than the addition of these individual chemical elements. In this work a commercial Al–12Si–0.6Fe–0.5Mn alloy is employed to fully characterise the refining potency of Nb–B inoculation. It is found that the addition of Nb powder and KBF4 flux to Al–Si melt introduces potent nuclei with low lattice mismatch with the primary α-Al dendrites (i.e. low undercooling) and, thus, promote noteworthy grain refinement through heterogeneous nucleation. Nb–B inoculation induces a significant increment of the volumetric number of grains, decreases the undercooling needed for solidification and makes the grain size of the Nb–B inoculated material less sensitive to the cooling rate employed to solidify the material.

Texture formation of hot-deformed nanocomposite Nd2Fe14B/α-Fe magnets by Nb and Zn additions

The effect of Zn addition on the magnetic properties and microstructure of bulk hot-deformed (NdDy)11.5Fe82.5−xNbxB6 (x = 0–2) alloys has been investigated. The remanence (Br) and coercivity (Hci) can be enhanced substantially by the addition of Nb and can be further improved by the combined addition of Nb and Zn. The addition of Nb increases the volume fraction of intergranular phase and promotes more Zn to diffuse into the grain boundary. This grain boundary with changed properties may benefit the c-axis texture formation during hot-deformation. Additionally, the coercivity of alloys with both Nb and Zn increased up to 22% with increasing deformation ratio, which may be due to the further diffusion of Zn into the grain boundary and the enhancement of magnetic decoupling effect between Nd2Fe14B grains.

Thermal stability of Ti–44Al–4Nb–4Zr–0.2Si–1B alloy

A near lamellar γ−TiAl alloy Ti–44Al–4Nb–4Zr–0.2Si–1B was ingot cast and exposed at 700 °C for up to 10,000 h. The combined addition of Nb and Zr rather than Nb alone has a positive effect on stabilization of α2 lamellae. Compared to alloy Ti–44Al–8Nb–1B, less amount of α2 dissolved and less amount of β (B2 + ω) formed in the alloy after the same exposure scheme. However, the exposure-induced embrittlement is still severe in this alloy. The ductility after 10,000-h exposure is only 1/4 of the original value. The exposure-induced embrittlement is attributed to the profound changes in prior β regions: the precipitation of fine D88-ω particles in the B82-ω matrix; the prevalent formation of γ grains inside the prior β regions; and the widespread precipitation of silicide particles at cell interfaces and β grain boundaries. The tensile strengths remain essentially unchanged while fatigue limit increased significantly. The mechanism behind the microstructural changes and mechanical properties is discussed in detail.

Austenite Grain Ultrarefinement and the Formation of Nanocrystallized Structure through Transformation of Low Carbon Steels

The effects of chemical composition, original microstructure, and heating rate on austenite grain refinement were investigated, and the results indicated that ultrafine austenite with grain size 1 µm can be obtained from the original microstructure of ferrite/pearlite after being warm rolled and cold deformed, and the ultrafine austenite could also be obtained through combined addition of Nb–V–Ti and by properly increasing heating rate. The transformation of the ultrafine austenite was also investigated, and the results indicated that when the heavy deformation was applied below Ar3 during cooling, the uniform and equiaxed ferrites with grain size of 0.1 ∼ 0.3 µm, close to nanosize, can be obtained. The main mechanism of deformation-induced transformation of ultrafine austenite to ferrite is that the nucleation of ferrite along austenite boundary is enhanced by the boundary slipping of austenite grains.

Role of Combined Addition of Niobium and Boron and of Molybdenum and Boron on Hardnenability in Low Carbon Steels

Effects of the combined addition of niobium (Nb) and boron (B) and of molybdenum (Mo) and B on hardenability were investigated using low carbon steels. Strength synergically increases due to the combined addition of Nb and B and that of Mo and B. It is thought that strength increases due to these combined additions because austenite (y) to ferrite (a) transformation is retarded and bainite transformation is promoted due to the increase in the segregated B along the y grain boundary before y to a transformation. The mechanism for the increase in the segregated boron along the y grain boundary by these combined additions is considered below. Fe 23 (C, B) 6 precipitates formed along the y grain boundary are suppressed by these combined additions because of the suppression of C diffusion towards the y grain boundary due to the precipitation of the fine dispersive niobium-titanium carbonnitride (Nb, Ti)(C, N) or titanium-molybdenum carbonnitride (Ti, Mo)(C, N) and the formation of C clusters of Nb and Mo during rolling or during cooling after rolling. Therefore, the segregated B along the y grain boundary increases and y to α transformation is retarded. The combined addition of Nb and B or that of Mo and B in low C bainitic steel is effective for increasing strength without deteriorating low temperature toughness. It is clarified that the increments of hardenability by the combined addition of Nb and B is different from that of Mo and B due to the difference of the amount of carbide precipitates.