Nitrogen Content In Steel Research Articles

Regulating the nitrogen content in steel and alloys

The behavior of nitrogen in the decarburization of iron and alloy melts is analyzed. In laboratory conditions, nitriding from the gas phase is studied, as well as the removal of nitrogen from alloy (Cr-Ni and Cr-Mn) melts. Parameters are established for the regulation of the nitrogen content in steel in gas-oxygen refining and ladle treatment. The results permit the development of guidelines for the alloying of steel with nitrogen and for regulation of the nitrogen content by means of the gas phase (N2, Ar) in smelting and ladle treatment.

Influences of Aging Precipitation on Corrosion Resistance of 18Cr-18Mn-2Mo-0.77N HNS

Influences of aging precipitation of Cr2N and Chi (χ) phases on the resistance to pitting corrosion and intergranular corrosion of 18Cr-18Mn-2Mo-0.77N high nitrogen steel (HNS) as a type of fundamental and structural materials were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) pattern and electrochemical methods. Intergranular, cellular Cr2N and χ phases precipitate gradually along grain boundaries and inward grains. The volume fraction of precipitation presents a C-curve with a nose temperature of 850°C during 2h aging treatment. The solution-treated (ST) HNS exhibits the highest pitting corrosion potential because of high nitrogen content in steel, and especially no precipitation. The pitting corrosion resistance of aged HNS decreases because of the formation of aging precipitation which results in the depletion of Cr and Mo in the matrix. The pitting corrosion potentials firstly decrease then increase as the same tendency as the amount of precipitation expect 850°C and 900°C. Double loop electrochemical potentiokinetic reaction (DL-EPR) results show that the change tendency of IGC susceptibility is well consistent with the amount of precipitation of aged HNS for 2h at various temperatures. With prolonging the aging time at 850°C, aged HNS presents more obviously intergranular sensitization due to the formation of aging precipitation which results in the depletion of Cr and Mo.

Control of titanium nitride in bearing steel

The formation thermodynamics of the existed TiN inclusion and the control theory of titanium and nitrogen in bearing steel were studied. Then based on the theoretic calculation results, the industrial trials of GCr15 bearing steel were carried out in a steel plant. The results showed that the higher the titanium or nitrogen content in steel is, the higher the precipitation temperature of TiN, and the bigger the size of precipitates;the use of low-Ti alloy materials can effectively reduce the Ti content;using low-Ti molten iron and reducing the TiO2 content to less than 1.0% in furnace slag can control the Ti content effectively. The use of low-titanium synthetic slag can make Ti content of the steel drop from the original 37×10-6 to 30×10-6. Optimized and improved refining processes protective casting process can reduce the N content of 33×10-6. With the degree of solidification segregation decreases, the precipitation of TiN inclusion is reduced.

Low-nitrogen coal as a carburizer in the production of special steels

Residual elements in the batch have a considerable influence of the quality of converter steel. Of these, nitrogen is the most difficult to regulate in smelting and represents one of the main obstacles to the production of high-quality steel—in particular, steel for wire rod, springs, and cord [1–3]. High nitrogen content in steel produces strain aging and is associated with lower plasticity of cold-rolled and tempered low-carbon steel sheet. Carbon-bearing materials—carburizers—are used for ladle treatment of such special steels. Such materials must have a low content of nitrogen and sulfur (≤ 0.5%). In addition, their moisture content and yield of volatiles must be as low as possible. They are confined to size class 6-1 mm.

Investigation into secondary phases in steels microalloyed with vanadium and nitrogen

In the present work two nitrogen and vanadium microalloyed steels were compared in terms of the nitride or carbonitride phases present. The thermal evolved gas analysis clearly showed that one of the steels contains a higher volume fraction of nitrogen bound as vanadium carbonitride than the other steel in a natural relation to the total nitrogen content in steels. For the promotion of this statement, the content of free nitrogen with the use of the hot hydrogen extraction method was analysed and the thermodynamic prediction of the equilibrium composition of precipitating phases in microalloyed steels by the CALPHAD method with the use of the Thermo-Calc software was carried out.

Investigação do efeito do teor de intersticiais sobre o grau de sensitização em aços inoxidáveis ferríticos a 600ºC

O objetivo do presente trabalho foi investigar o efeito do teor de carbono e nitrogênio em aços inoxidáveis ferríticos com 17%Cr (16%Cr-0,04%C-0,032%N; 17,2%Cr-0,02%C-0,0062%N; 18,5%Cr-0,008%C-0,0213%N) sobre o grau de sensitização (GS). Os aços foram solubilizados a 1200°C e resfriados em água. Tratamentos isotérmicos foram realizados a 600°C entre 5 minutos e 16 horas. Foi realizado o ensaio de reativação eletroquímica potenciodinâmica de ciclo duplo (DL-EPR) em solução 0,5M H2SO4 a (25 ± 2)°C. O GS foi medido através da relação entre as densidades de correntes anódicas máximas nas etapas de reversão, i r, e ativação, i a. O exame microestrutural dos corpos-de-prova foi realizado nos microscópios óptico e eletrônico de varredura após ataque metalográfico com reagente Vilella. Os resultados mostram variação do GS com o tempo. Um máximo de GS foi obtido para cada aço e, posteriormente, foi observada diminuição do GS. A intensidade do GS e o tempo de ocorrência variaram em função dos teores de carbono e nitrogênio nos aços.

Effect of the Converter Steelmaking Technology on the Nitrogen Content of Steel

Effect of the Converter Steelmaking Technology on the Nitrogen Content of Steel

Recent advances in the fundamentals of the kinetics of steelmaking reactions

G.R. Belton was the leader in developing our understanding of the kinetics of metallurgical reactions. Selected recent kinetic studies, based on this understanding and the application of the results to actual processes, are presented in this article. In particular, the rates of reaction of carbon and carbon in iron with CO2 and H2O gases and FeO in slag are reviewed and applied to the iron smelting process. In addition, our basic understanding of the kinetics of the nitrogen reaction with iron is reviewed, and the results are used in comprehensive models, which can predict the nitrogen content in steel as a function of operating variables in the basic oxygen furnace, electric arc furnace (EAF), and vacuum degassing.

Mathematical model for nitrogen control in oxygen steelmaking

A mathematical model was developed to quantify the effects of different operational parameters on the nitrogen content of steel produced during oxygen steelmaking. The model predicts nitrogen removal by the CO produced during decarburization and how the final nitrogen content is affected by different process variables. These variables include the type of coolants used (scrap, direct reduced iron (DRI), etc.), the sulfur content of the metal, combined gas blowing practices, and the nitrogen content in the hot metal, scrap and oxygen blown. The model is a mixed control model that incorporates mass transfer and chemical kinetics. It requires a single parameter that reflects the surface area and mass-transfer coefficient that is determined from the rate of decarburization. The model also computes the rate of decarburization and the change in surface active elements, such as sulfur and oxygen, that affect the rate of the nitrogen reaction. Nitrogenization of steel in the converter is also predicted with the model. The computed results are in good agreement with plant data and observations.

Strengthening Mechanisms in Vanadium Microalloyed Steels Intended for Long Products.

The present work has concentrated on the roles of vanadium, nitrogen and carbon in controlling the microstructures and strength of steels designed for hot rolled long products. Effects of cooling rate and additional microalloying with titanium have also been included. The degree of precipitation strengthening of ferrite at a given vanadium content depends on the available quantities of carbon and nitrogen. The nitrogen content of the ferrite is approximately the same as that of the austenite from which it forms, i.e. the total nitrogen content in steel. It was confirmed that nitrogen is a very reliable alloying element, increasing the yield strength of V-microalloyed steels by some 5 MPa for every 0.001% N, essentially independent of processing conditions. Carbon content, on the other hand, has usually been considered not relevant to precipitation strengthening when the precipitation occurs in ferrite because of the very small carbon content in solution in ferrite at equilibrium. We demonstrate that the effective carbon for precipitation in ferrite may be much greater than this during the period of phase transformation, which in turn has a great effect on precipitation strengthening. Such behaviour is explained on the basis that the activity of carbon in ferrite is abnormally high in the presence of under-cooled austenite and before cementite nucleation so that profuse nucleation of vanadium carbonitride is encouraged. This new mechanism for precipitation is particularly significant for medium carbon steels typically used for hot rolled bars and sections. The total carbon content of the steel also contributes to the yield strength by increasing the volume fraction of pearlite. It is shown that the contribution from pearlite is stronger than generally recognised.

High Nitrogen Steels. Structural Control of Stainleaa Steel by Nitrogen Absorption in Solid State.

Nitrogen addition to stainless steels is very effective for improving mechanical properties and corrosion resistance. Powder metallurgy process, which is the sintering of stainless powder in N2 gas atmosphere, has some beneficial points to the production of high nitrogen stainless steels, because a large amount of nitrogen can be absorbed into powder particles in a very short time. In this paper, the behavior of nitrogen absorption into an Fe-23mass%Cr ferritic alloy powder was investigated in association with the structural changes. The results obtained are as follows: (1) Since the amount of nitrogen absorbed is dependent on the surface equilibrium between N2 gas and nitrogen content of steels, the saturation nitrogen content increases with lowed sintering temperature. (2) At 1473 K in 1 atm-N2 gas, the saturation nitrogen content of an Fe-23mass%Cr alloy is about 1 mass%N and the nitrogen absorption causes a structural change of the matrix from ferrite to austenite. The nitrogen content is also enough to give a stable austenitic structure at room temperature for the alloy. (3) The Fe-23mass%Cr-1mass%N alloy developed by the above sintering treatment has a high yield strength and a moderate elongation in spite of containing about 12 vol% of retained pores. Such good mechanical properties are attributed to the solid-solution of a great deal of nitrogen into the steel.

Calibration Method for Determination of Nitrogen Content in Steel by Thermo-Conductimetry after Fusion in the Current of an Inert Gas

A calibration method for determining the nitrogen content in steel by a thermo-conductimetric method after fusion in the current of an inert gas is proposed. In this calibration method, a pure chemical substance whose nitrogen content can be calculated based on its molecular weight is used as a calibrant. The nitrogen recovery and thermostability of 9 chemical substances in the fusion procedure were investigated; it was found that potassium nitrate is the most suitable as a calibrant. The results of analysis of 9 steel samples of certified reference materials demonstrate that the proposed calibration method is applicable to determination of nitrogen contents between 0.001% and 0.5%.

Alloying steel with nitrogen from gas phase in high‐pressure plasma reactor

The paper presents a study of the possibility of saturating austenitic Cr18%–Mn18% steel with nitrogen from the gas phase by use of “low – temperature” thermal plasma. The experimental work was carried out in a DC plasma reactor of the authors' own design working at a total gas pressure of 0.38 MPa on a 20 kg sample. It was evident that it was possible to obtain a very high level of nitrogen saturation close to the level of nitrogen solubility in the metal by the use of plasmogenic gas containing purified nitrogen. The highest content of nitrogen in steel containing 18wt.% chromium and 16.7wt.% manganese was 0.77wt.% at [C] = 0.054. Refining the metal with CaSi additive turned out to have a stabilizing influence, the total amount of oxygen and sulphur being lower than 200 ppm. The material obtained turned out to be also highly homogeneous chemically after solidification.

Determination of Ultra Low Content of Nitrogen in Metal and Slag by Ion-Chromatography

Effects of HCl, Fe, Na, and K in the determination of nitrogen as NH4+ have been studied by the method of ion-chromatography. Analyzed value of nitrogen was reduced in the presence of HCl (≥9×10−5 mol) and K (≥2 μg) in the injected solution, while that was scarcely influenced by 120 μg of Fe or 30 μg of Na. In the analysis of ultra low content of nitrogen in steel or slag, 1 mass ppm of nitrogen sample was determined with CV-value=3.5% by a combination of the steam-distillation method and ion-chromatography.

イオンクロマトグラフィーによる金属およびスラグ中の極微量窒素の定量

Effects of HCl, Fe, Na, and K in the determination of nitrogen as NH 4 + have been studied by the method of ion-chromatography. Analyzed value of nitrogen was reduced in the presence of HCl (≥9×10 -5 mol) and K (≥2 μg) in the injected solution, while that was scarcely influenced by 120 μg of Fe or 30 μg of Na. In the analysis of ultra low content of nitrogen in steel or slag, 1 mass ppm of nitrogen sample was determined with CV-value=3.5% by a combination of the steam-distillation method and ion-chromatography

Quick analyzer with a built-in microcomputer to determine the nitrogen content of steel

Quick analyzer with a built-in microcomputer to determine the nitrogen content of steel

The properties of chromium steels with a high nitrogen content

1. It was found that it is expedient to raise the nitrogen content of stainless and heat-resisting austenitic-ferritic and austenitic steels. Raising the nitrogen content of the steels results in an increase of the strength at room and elevated temperatures without any substantial effect on the plastic characteristics. With a high nitrogen content the austenitic-ferritic steel Kh21·G7AN5 becomes austenitic. 2. Raising the nitrogen content of austenitic-martensitic steel lowers MS, as the result of which the elevated concentration of austenite (not transformed in the course of heat treatment) lowers the strength characteristics.

鋼に対する合金元素としての窒素（第6報）鋼の青熱脆性に及ぼす酸素及び珪素の影響

The present investigation has been carried out to explain the mechanism of blue-brittleness in steels. In the 3rd∼6th reports under this title, it has been shown that the blue-brittleness would not occur in steels free from the nitrogen and that the more the nitrogen content in steels is the more clearly the blue brittleness appears.In present investigation the follwoing experiments were carried out.(A) The effect of the annealing in nitrogen or in hydrogen atmosphere was determined by the tensile test at 0∼350° on the specimens shown in Table 1 and the results of these were plotted in Fig. 1∼5.(B) The effect of cold work on the blue-brittleness was examined on the specimens shown in Table 2, that is tempered for 1 hour at 180° after cold work at room temperature ; the tensile values of these are plotted in Fig. 6∼8.(C) The effect of different testing speed was determined on the specimens shown in Table 3 and the tensile values of these are plotted in Fig. 9,10.(D) The change of specific gravity on the specimens tempered for 1 hour at 0∼350° after cold work at room temperature was measured as shown in Table 4.(E) The figure of stress by Fry’s method were examined on the specimens that had used for the tensile test at each testing temperature. From those experiments the following results were obtained.(F) In accordance with either the increase or decrease of nitrogen content in steels by heating it in nitrogen or in hydrogen atmosphere, the degree of blue brittleness varied.(G) The blue-brittleness decreased on the specimens in which some parts of nitrogen had been precipitated by cold working and tempering.(H) The temperature range of blue brittleness moved to a higher temperature range with the increase of testing speed.(I) There is a clear correlation between the blue brittleness and Fry’s figure of stress.From the present and former investigations authors concluded the mechanism of blue brittleness as follow :The blue brittleness in steel is due to the precipitation of nitride or carbide from α-iron by the existence of working stress : and the brittleness by nitrogen appears much more exactly in lower temperature range than that by carbon.

鋼に対する合金元素としての窒素（第7報）青熱脆性機構の実験的考察

The present investigation has been carried out to ascertain the effect of silicon and oxygen on the blue brittleness in steels.In the 3rd and the 4th reports under this title it has been shown that the blue brittleness would not occur in steels free from the nitrogen and that the more nitrogen content in steels is the more clearly the blue brittleness appears.But, on the other hand, the blue brittleness by carbon would likely to appear more than by nitrogen, as the nitrogen in steel diminished at the upper temperature range.To ascertain the effect of silicon, the short time tensile properties at the temperature range of 0∼320° for steels were determined as shown in Table 1∼2.All specimens employed for this investigation were air cooled from 950°, and then slowly cooled after being tempered for 3 hours at 550°. The tensile value of each steel is plotted in Figs. 1∼14, and the increased percentage of tensile strength and the decreased percentage of elongation or reduction of area at blue brittleness range are plotted in Fig. 7, and the effect of silicon on the tensile strength (σB), elongation (δ), and reduction of area (φ) at room temperature are shown in Fig. 15.To ascertain the effect of oxygen, the short time tensile properties of steels were studied, as shown in Table 3, the result of which are plotted in Figs. 16∼19, and in Fig. 20 is shown the diagram of percentage of blue brittleness versus oxygen percentage.These figures show that the blue brittleness decreases with the increase of silicon content, and by the addition of oxygen in steel the blue brittleness increases a little in the property of elongation.

含硼素鋼の研究（第3報）含硼素中炭素鋼の硬化素，特に窒素含有量の影響について

Dealing boron-treated steels, with the Medium-Carbon (0.3∼0.4%), the maximum hardenability was gained by the addition of an order of about 0.003%B; and with increase of the nitrogen content in steels, the desirable effect of boron on the hardenability decreased sharply, and the effect completely disappeared when the nitrogen content exceeded an order of 0.02%.And when the small amonnt of Al(0.1%) or Ti(0.03%) was added to the steels prior to the addition of boron, the effect of boron usually appeared more sharply, because they acted as the fixers of nitrogen.