Nitrogen Content In Steel Research Articles

Effect of nitrogen content on the precipitation and growth behavior of eutectic carbides M7C3 in electroslag remelted 7Cr13 steel

The effect of nitrogen content on the type, distribution, morphology, precipitation, composition, growth and aggregation behavior of eutectic carbides in 7Cr13 steel ingots were studied. The results show that the eutectic carbide type (all M7C3) and composition do not change when the nitrogen content in the 7Cr13 steel varies from 0.043% to 0.164%. The increase of N content in the steel refines the eutectic carbides, but the heterogeneous nucleation effect of (Ti,V)N particles increases the number density of eutectic carbides precipitated. As the N content increases, the eutectic carbide area fraction at the edge of the ingot gradually increased. However, the area fraction of carbides first decreases and then increases at other locations in the ingot. Eutectic carbides in steel consist of aggregates of carbide particles of different morphologies and orientations. The higher supersaturation of Cr atoms at the beginning of carbide precipitation in high-N steels will favor the formation of brain-like carbides. The morphology of the eutectic carbide changes from blocky-fibrous (closely linked to the blocky carbide) - spherical to brain-like as the N content increases from 0.043% to 0.164%. The refinement of secondary dendrites and the inhibition of eutectic carbides precipitation by nitrogen make the space for eutectic carbide growth smaller with increasing nitrogen content in the steel, which reduces the precipitation of fibrous carbides (independent existence) that serve as a bridge between different carbides in low-nitrogen steels. This allows the network carbide structure to gradually disappear and promotes the uniform distribution of carbides.

Effect of Nitrogen Content on the High Cycle Fatigue Properties of Titanium Microalloyed Steel

The high cycle fatigue properties of three industrial 0.12% Ti microalloyed steels with different nitrogen contents (56, 40, and 30 ppm in molten steel of tundish) are investigated. The results show that <20% of the fatigue crack initiation sites are oxide inclusions of size in 16.8 μm ≈ 55.9 μm, while the rest 80% are surface defects. No TiN inclusions cause fatigue failure and the fatigue limit strength slightly decreases with increasing N contents as the yield strength decreases with a coarser ferrite grain. Inclusions characterization in the section near the fracture shows that the average sizes of TiN inclusions in H56, M40, and L30 steels are 3.50, 3.22, and 2.89 μm, and the maximum sizes are 6.92, 6.67, and 6.23 μm, respectively. Calculating for a cooling rate of 0.2 K s−1 using ChemAppPy precipitation model, the size of TiN inclusions will increase from 6.1 to 7.1 μm, when increasing N content from 30 to 60 ppm. The relationships between nitrogen content, TiN inclusions, and fatigue failure quantified by experimental test and modeling show that the nitrogen content in steel can be relaxed up to 60 ppm when considering economical denitrogenization and fatigue safety.

High-throughput nitride and interstitial nitrogen analysis in ferritic/martensitic steels via time-of-flight secondary ion mass spectrometry

The following work focuses on characterizing nitrogen in several modified alloys of the precipitation strengthened ferritic/martensitic steel HT9 (12Cr-1MoWV (wt%)). Alloy HT9 is a candidate material for fuel rod cladding and ductwork in the core of the Versatile Test Reactor and other next-generation nuclear fast reactors. Nitrogen content has been shown to have a significant effect on irradiated properties in alloy HT9. To explore that theory, a more comprehensive assessment of the location of nitrogen must be performed; however, locating nano-precipitates, such as nitrides and light interstitial elements like nitrogen in steel, has proven difficult. To begin answering questions surrounding the location of nitrogen, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) was employed as a primary analysis technique, together with extensive transmission electron microscopy, internal friction testing, and thermodynamic simulations, providing verification and context to trends found in the ToF-SIMS data. For the first time, ToF-SIMS was demonstrated to reliably measure relative differences in the vanadium carbonitride precipitate volume fraction across several chemistries and heat treatments of ferritic/martensitic steels. Additionally, associating matrix elements (iron and chromium) to nitrogen-containing ion clusters significantly reduced the ‘matrix effect that biases nitrogen detection towards nitride precipitates, providing a potential, high-throughput method for the measurement of relative interstitial nitrogen content in steels with ToF-SIMS. • ToF-SIMS provided a new high-throughput analysis method for microalloy precipitate and microstructure design. • ToF-SIMS was employed for semi-quantitative, bulk detection and measurement of nitrides and interstitial nitrogen in steel. • S/TEM provided a quantitative comparison of nitride content, while internal friction testing provided a semi-quantitative comparison of interstitial N.

SHS Introduction of Nitrogen in the Composition of Alloy Steel under Gas Pressure

The possibility of producing cast alloyed nitrided steel (up to 1.3 wt % N) by SHS metallurgy is shown. The initial mixture for making alloy cast steel includes iron, chromium, manganese, nickel, molybdenum, vanadium, silicon, and aluminum oxides. Chromium nitride is used as the main nitrogen source. Initial mixtures are shown to be capable of burning over a wide range of reagent ratios, and the combustion temperature exceeds the melting temperature of the condensed combustion products (steel, reducing-metal oxide), which makes it possible to perform their gravitational separation and to make steel in an as-cast form. Experimental studies are carried out in a reactor under nitrogen pressure and in a centrifugal installation under the combined action of overload and pressure to exclude the spread of a mixture during combustion. When the pressure in the reactor is increased from 0.1 to 5.5 MPa, the nitrogen content in steel alloyed with chromium, manganese, nickel, molybdenum, vanadium and silicon is found to increase from 0.4 to 1.3 wt %. Under overload (150g) and an increase in the pressure from 0.1 to 1 MPa, the nitrogen content increases from 0.4 to 0.55 wt %. According to X-ray diffraction and electron-probe microanalysis data, the base of the steel has the γ-Fe lattice and is a solution of alloying elements in iron. The shift of the diffraction peaks and their broadening indicate the dissolution of alloying elements in iron. α-Fe precipitates and point inclusions of vanadium, chromium, and impurity-aluminum nitrides are also detected.

Objective Laws of Nitrogen Removal in the Vacuum Tank Degasser

This article discusses the problems of efficient removal of nitrogen in the vacuum tank degasser operating at the electric arc furnace shop of Uralskaya Stal (Ural Steel) OJSC in the course of manufacturing of high-quality low carbon steel grades by means of steel grades «2» and «T». In order to determine the reasonable and balanced treatment parameters that ensure the required level of nitrogen content in the above steel grades, an analysis of production data for the period of November-December 2016 has been carried out. This analysis is the basis for identifying the vacuum degassing parameters in compliance with the technological capabilities and well-balanced levels, which allow predicting the level of nitrogen content in steel. To assess the cumulative quantitative effect of the main parameters of vacuum degassing on nitrogen removal, there has been performed a regression analysis. As a result, there have been obtained multiple regression equations describing a rational combination of steel treatment parameters for achieving the required nitrogen removal level.

High nitrogen steels

The article provides a brief overview of the properties and production technology of high-nitrogen steels (HNS), which have several advantages over traditional ones. The main advantages are: up to four times higher yield strength with unique preservation of the remaining characteristics; reduction in consumption or a 100 % elimination of the use of some expensive alloying elements, such as Ni, Mo, Co, W, and others; effective alloying with unconventional elements (Ca, Zn, Pb, etc.). The basics of HNS technology, dependence of the properties on nitrogen content in steels, producing technologies for ferritic-pearlitic, martensitic and austenitic steel, their properties and applicability are discussed. Alloying with nitrogen for ferritic-pearlitic steel requires more precise adherence to the chemical composition in order to prevent the formation of insoluble nitrides during heat treatment (due to its greater solubility compared to carbon). Features of martensitic steels are associated with the possibility of formation of nitrides and carbonitrides during tempering. The possible effect of nitrogen in these steels may be as a decrease in the size of nitride particles as compared with carbide ones. Increased stability temperature of nitrides and carbonitrides provides increased mechanical and physical properties. In austenitic steels, nitrogen, due to the strong γ-forming equivalence to nickel, replaces it in a ratio of 1 kg of nitrogen ≈ 6 – 39 kg Ni. In austenitic-martensitic steels, the main role is played by thermal martensite. Stable austenite is obtained in the process of its aging at operating temperatures. Examples of effective use of HNS in important details are described.

Determination of Nitrogen Content in the Slags of CaO — Al2O3 System by Kjeldahl Method

Due to the expansion of the nomenclature of steel grades in the industry and the development of new special alloys with increased strength and corrosion-resistant properties, both in the metallurgical industry and in welding, researchers are very interested in the dissolution of nitrogen in metals and slag. Gas permeability of slag is one of the reasons for the appearance of gases in both the base metal and the weld metal. It is determined by two properties: solubility and mass transfer of gases in slag. In addition, in real conditions, the process of dissolving gases in slag is influenced by the transmission of gases by convection and the initial content of gases in the slag. The transfer of gases to the metal through slag is observed mainly in electroslag processes and welding under flux when there is no direct contact of molten metal with a gas phase. To evaluate the nitrogen permeability of the slag and the mechanism of nitrogen solubility in the high alloys it is necessary to have a reliable, highly sensitive and economical method of gas analysis of nitrogen in metals and slags.
 A review of nitrogen determination methods in steels is presented. The method of analysis of nitrogen in slags of the CaO — АL2O3 system by the Kjeldahl method was tested. The results of the analysis of slag compositions of the CaO — АL2O3 system allowed us to conclude that it is possible to use the Kjeldahl method (determination of nitrogen content in steels) for the determination of nitrogen content in slags. This technique and installation can be recommended for use by metallurgists and welders as a reliable, simple and inexpensive method for nitrogen content analysis in metals and slags.

Influence of Nitrogen and Nitride-Forming Elements on Properties of Boron-Treated Steel

Microalloying has received increased attention in recent years. The aims of the study were to identify and to examine the influence of nitrogen concentration in steel and small additions of nitride-forming elements on the hardenability of a boron-treated manganese-vanadium steel 40GF-VI. The study has shown that the increase in nitrogen concentration from 0.004% to 0.015% increases the hardenability of steel. It was found that a small amount of titanium (about 0.02%) in steel with low concentration of nitrogen (0.004%) is sufficient to bind it to nitrides, which makes it possible to save the most of boron in an active state (in a solid solution). A residual amount of titanium and aluminum in the range of 0.015-0.020% of each in steel with nitrogen concentration in the range of 0.010-0.015%, which is typical of an electric arc melting steel, is insufficient to bind all nitrogen. As a result, a part of nitrogen is spent on the formation of boron nitrides, which reduces the effect of boron on the hardenability of manganese-vanadium steel microalloyed with boron. Some methods of protecting boron in steel are briefly described. The study has established that grain refinement is observed with increasing nitrogen content in steel. Introduction of boron, in absence of titanium, does not change the size of the austenite grain in the entire range of the investigated temperatures. The optimum combination of strength, plastic and ductility characteristics in steel microalloyed with boron and additives of aluminum and titanium was obtained.

Strain-Induced Precipitation Kinetics of Vanadium Carbonitride Precipitates with the Cubic Structure in High-Strength Weathering Steels

The strain-induced precipitation kinetic model of vanadium carbonitride [V(C, N)] precipitates with the cubic structure in vanadium-nitrogen (V–N) microalloyed high-strength weathering steels was constructed and validated. The V(C, N) precipitates possess an fcc structure with the lattice sites and octahedral interstitial sites (O-sites) being occupied with V atoms, and C and N atoms, respectively. The model is based on the cubic structure for V(C, N) precipitates instead of the spherical one, since recent experimental results clearly demonstrate that the strain-induced precipitation of V(C, N) in austenite is of the cubic structure. The nitrogen content effect on precipitation–temperature–time (PTT) curve pattwerns was also studied. With the nitrogen content, the PTT curve nose temperature increased, and the curves shifted left. When the nitrogen content in steels was dropped, PTT curves of V(C, N) precipitates in austenite acquired an S-shape, since free energy conversion is nonlinear. Additionally, thermodynamic software was employed to calculate the phase equilibrium of V(C, N) precipitates in the new high-strength weathering steels. The N site fraction of N during the V(C, N) precipitation was much larger for steels with high N contents, compared to those with low ones.

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

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 for pipe purposes produced under conditions of the OMK-Stal casting and rolling complex (CRC). It is shown that with a standard nitrogen content in steel (less than 0.008%) under CRC conditions introduction into pipe steel of microadditions of vanadium does not provide strengthening for coiled rolled product by a precipitation hardening mechanism. Precipitation of vanadium carbide phase is difficult as a result accelerated strip cooling on the run-out table before winding strip on a coil and use of relatively low coiling temperatures under CRC conditions. Separation of VC particles after tempering at 650°C confirms retention of vanadium in solid solution. The presence of fine VN particles in steel with an increased nitrogen content may be explained by the fact the vanadium nitride phase may precipitate at higher temperatures compared with carbide. Research work has made it possible to assimilate production of cold-resistant coiled rolled product more than 10 mm thick of strength class up to K60 under CRC conditions without microalloying steel with vanadium.

Effect of Bottom Blowing Time and Bottom Blowing Rate on the Nitrogen Content of High Nitrogen Steel

The Cr18 - Mn18 steel was prepared by the high temperature and high pressure reaction kettle. With bottom blowing time and bottom blowing flow as object to do single factor experiment, the relationship between the nitrogen content in steel smelting process and the bottom blowing time, the bottom blowing flow were studied.The research results show that when the other conditions must be, the nitrogen content in steel increases with the bottom blowing time increasing gradually, when the bottom blowing time reach more than 35 min, the variation of nitrogen content in steel decreases. With the increase of bottom blowing flow rate, the nitrogen content in steel increases gradually, when the bottom blowing flow rate reaches more than 0.24 m3/h, the nitrogen content in steel close to the maximum value and does not change with bottom blowing flow rate.

Effect of Temperature and Pressure on the Nitrogen Content of High Nitrogen Steel

In this study, nitrogen content greater than 0.9% of 18Cr18MnN austenitic stainless steel were prepared by high pressure reaction kettle. The relationships between nitrogen content and temperature, pressure were studied. The results show the nitrogen content in steel increases with increasing melting pressure, at air pressure 1.0MPa<P<1.4MPa, the increase of nitrogen content in steel is evident particularly. In the 1813k<T<1913k temperature range, the nitrogen content in steel decreases with the increasing temperature, there are differences in variation in the temperature range. When temperature is up to 1813K, nitrogen content can be as high as 1.075%. The best thermodynamic condition of melting a nitrogen content of 0.9% 18Mn18Cr austenitic stainless steel is: pressure and temperature are 1.32MPa, 1873k, respectively.

Production of steel with limited nitrogen content

The nitrogen content of pipe steel is tracked during smelting and ladle treatment. The electro-smelting of steel with limited nitrogen content (no more than 0.008%) in the Zheleznyi Ozon 32 system (introduced in 2011 at OAO Pervoural’skii Novotrubnyi Zavod) is considered. Data for the production of continuous-cast billet from pipe steel containing up to 0.012% are considered; the final mean nitrogen content in steel is 0.0078% with vacuum treatment and 0.0084% without vacuum treatment. The results show that increasing the oxygen consumption in the arc furnace may increase the steel’s nitrogen content, rather than reducing it. The optimal treatment time of the steel in the ladle-furnace unit is of great importance in the production of steel with limited nitrogen content. Brief treatment in the ladle-furnace unit is likely to result in steel with high nitrogen content. Prolonged and very prolonged treatment also increases the nitrogen content.

Research on Effect of Temperature on Nitrogen Solubility in Steel

The experiments of high nitrogen steels refining have been researched with high pressure and bottom-blown nitrogen in laboratory. We can gain high nitrogen nickel-free stainless steels that its content is more than 0.9%. The research indicates that the temperature influences nitrogen content greatly in the processes of smelting and concreting. The results are shown that saturated nitrogen content in steel increased slightly. When the temperature is as high as 1913K, the nitrogen content can reach 1.191%.

Effect of the charge composition on the nitrogen content in a metal during steelmaking in an ASF using a solid charge

The behavior of nitrogen is studied during steelmaking in a 120-t arc furnace using a solid metal charge. The nitrogen content in steel is shown to be decreased when the fraction of a light metal scrap in a charge increases and the fraction of a heavy metal scrap decreases.

The Study of Nitrogen Absorption with Slagging in High Nitrogen Steels Smelted by High Pressure and Bottom-Blowing Nitrogen

The experiment studied the influence of slag system on nitrogen content in high nitrogen steels which refined by the method of high-pressure and bottom-blowing nitrogen under the conditions of 1.0Mpa. The results shows that nitrogen content are up to 1.0% without the over of slag, and after adding slag, nitrogen content are up to 1.39%; Alkalinity of protecting slag has little effect on the nitrogen content, however, there are very effective to increase nitrogen after using CaF2 instead of SiO2 ,and its nitrogen content are as high as 1.48%; the effect of increasing nitrogen are clear by adding no more than 0.5% pure aluminum, but when aluminum content are more than 0.5%, the nitrogen content in steel are not change significantly, meanwhile, if adding CaF2 slag system, it will be more effective increase nitrogen than only adding pure aluminum.

Comprehensive Analysis of High Nitrogen Steel Refining Factors with High-Pressure and Bottom-Blowing Nitrogen

The experimental results on high nitrogen steels refining with high-pressure and bottom-blowing nitrogen were analyzed by the theories of thermodynamics and kinetics in high nitrogen steels smelting. It was shown that nitrogen content in steel increases with the increase of the following factors, that is, pressure, alloying elements (Cr and Mn), bottom-blowing time and bottom-blowing flow. While the nitrogen content in steel decreases with the temperature increase, but it is not obvious. The nitrogen content in steel can also increase with the surface active elements (O and S) decreasing.

Effect of the purity of oxygen used for blowing on the nitrogen content of steel made in high-power arc steelmaking furnaces at ural steel

Given the high rate of injection of steel with oxygen in modern high-power arc steelmaking furnaces (close to the rate attained in basic oxygen furnaces), the purity of the oxygen becomes the deciding factor in determining the nitrogen content of the steel. An analysis is made of the factors that affect nitrogen content in the production of steel in modern electric-arc furnaces at Ural Steel. In particular, a determination is made of the extent to which the purity of the oxygen that is used affects the steel’s nitrogen content. The injection of steel with oxygen in modern high-power arc steelmaking furnaces ‐ which is done to speed up melting of the scrap and oxidation of the impurities in the charge ‐ is carried out at very high rates. For example, the highest injection rate on arc furnaces Nos. 1 and 2 in the electric steelmaking shop at Ural Steel is 12000 m 3 /h. At rates this high (close to the rates used in basic oxygen furnaces), the purity of the oxygen is of critical importance because its injection can change the nitrogen content of the steel. Thus, basic oxygen furnaces and all large modern arc steelmaking furnaces (ASFs) are operated with the use of commercially pure oxygen (O 2 content no lower than 99.5%). The literature data [1‐10] and experience with the operation of basic oxygen furnaces show that even a slight decrease in the purity of the oxygen (at high rates of injection) has a marked effect on the nickel content of the steel. As regards the effect of the parameters of the injection of steel with oxygen (oxygen consumption, oxygen purity) on furnace performance, the technical literature offers complete information only for converters and less productive arc steelmaking furnaces used earlier. No such investigations have yet been conducted for modern ASFs. Thus, Ural Steel performed an analysis of different heats in order to refine information on the factors that affect nickel content when steel is made in modern electric-arc furnaces. Also, since many metallurgical plants cannot use commercially pure oxygen when making steel in arc furnaces (due to the lack of a modern oxygen plant or a deterioration in the condition of the existing plant), they employ industrial-grade oxygen (with an O 2 content below 95.0%). There may be a significant difference in the nickel contents of steel made using oxygen of commercial and industrial purity. Use of the latter makes it more difficult to produce grades of steel used in critical applications, such as tube steels. The nickel content of such steels cannot be any greater than 0.008%. To determine the extent to which the purity of the oxygen used in the steelmaking operation affects the steel‘s nickel content, we analyzed heats made with the use of oxygen of different degrees of purity. Method of investigation. The trial heats were made in 120-ton arc steelmaking furnaces Nos. 1 and 2 at Ural Steel with the use of up to 45% liquid pig iron in the metallic part of the charge. This part of the charge was introduced into the

Principle and Practice of High Nitrogen Steel Melting by Blowing Ammonia Gas

During the high nitrogen steel (HNS) melting process, the absorption reaction of nitrogen in the liquid steel by blowing NH 3 and N 2 was investigated respectively. In order to obtain higher content of nitrogen in steel, the liquid steel should be deoxidized and desulfurized because the oxygen and sulfur as surface activity element are not favorable to the absorption of nitrogen in melting process. Based on the metallurgical thermodynamics, the coupling reaction of NH 3 with oxygen can improve the generation of activity nitrogen atom in liquid steel. Nitrogen atom is easier to be absorbed than nitrogen molecule. At the same time, blowing ammonia gas can remove the oxygen from liquid steel and decrease the inclusion in the steel. Experiments of HNS melting were carried out in a 10 kg induction furnace, and the results indicated that for liquid steel containing the same content of alloys and blowing the same mole of nitrogen, the absorption effect of nitrogen by blowing NH 3 is obviously higher than that of blowing N 2. The technical process of melting HNS by blowing NH 3 under normal pressure is feasible in industrial production.

Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels

Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels (HNSS) were investigated by electrochemical and immersion testing methods in chloride solution, respectively. The chemical constitution and composition in the depth of passive films formed on HNSS were analyzed by X-ray photoelectron spectrum (XPS). HNSS has excellent pitting and crevice corrosion resistance compared to 316L stainless steel. With increasing the nitrogen content in steels, pitting potentials and critical pitting temperature (CPT) increase, and the maximum, average pit depths and average weight loss decrease. The CPT of HNSS is correlated with the alloying element content through the measure of alloying for resistance to corrosion (MARC). The MARC can be expressed as an equation of CPT=2.55MARC–29. XPS results show that HNSS exhibiting excellent corrosion resistance is attributed to the enrichment of nitrogen on the surface of passive films, which forms ammonium ions increasing the local pH value and facilitating repassivation, and the synergistic effects of molybdenum and nitrogen.