Properties Of High-nitrogen Steels Research Articles

Tailoring of the Microstructure and Mechanical Properties of High Nitrogen Steel Repaired by Underwater Laser Direct Metal Deposition

Tailoring of the Microstructure and Mechanical Properties of High Nitrogen Steel Repaired by Underwater Laser Direct Metal Deposition

Microstructure and mechanical properties of high nitrogen steel – high strength steel bimetallic multi-layered steels fabricated by plasma-arc additive manufacturing

Three bimetallic multi-layered steel samples with different structures as well as a pure high nitrogen steel (HNS) sample and a pure high strength steel (HSS) sample were fabricated by plasma-arc additive manufacturing. The microstructure and mechanical properties of the samples were characterized by various methods. The results indicated that the microstructures of HNS and HSS are mainly austenite and martensite, respectively, and the grains in the interface area of HNS and HSS grew orderly compared with the inner area. The microhardness of the HSS sample (480.7 HV-499.2 HV) is higher than that of HNS (326.4–345.1 HV), and that of the bimetallic multilayered steels is consistent with the structure distribution. The bimetallic multi-layered steels combined the tensile property advantages of HNS and HSS well, and steels with both high strength and toughness were obtained.

Mechanical properties of pre-cracked high nitrogen steel under dynamic composite loading

In this paper, the mechanical properties of pre-cracked high nitrogen steel specimens with different loading angles of 30°, 45° and 60° were studied by using Hopkinson tension bar. The corresponding force-displacement curves under different loading angles were obtained. It was found that with the decrease of the pre-crack loading angle, the proportion of the shear stress on the specimens in the composite loading gradually increased, and the stress concentration appeared during the composite loading process, the fracture strength of the specimens decreased significantly. At the same time, however, the dispersion of the experimental results decreased, and the fracture morphology tended to be consistent with the elongation at break. The obtained mechanical properties of high nitrogen steel under combined loading can provide reference and basis for its technological improvement, safe production and reliable application

Influence mechanisms of underwater hyperbaric environment on nitrogen behavior, phase evolution, and mechanical properties of high nitrogen steel repaired by underwater laser direct metal deposition

Nitrogen outgassing and nitrogen pore formation are tricky problems inherent in the fabrication/repair of high nitrogen steel (HNS). In the current research, HNS powder with a nitrogen content of 0.42 wt% was used to repair damaged HNS plates by the underwater laser direct metal deposition (UDMD) technique at an ambient pressure of 0.3 MPa (sample U1). Under the same process parameters, the DMD repaired sample (sample A1) in the ground environment served as a comparison. The influence mechanisms of the underwater hyperbaric environment on the nitrogen behavior, interface crystallographic characteristics, and mechanical properties were clarified. Results showed that nitrogen outgassing and nitrogen pore formation occurred in sample A1. In sample U1, the elevated ambient pressure increased the nitrogen solubility in the molten pool from 0.628 wt% to 1.088 wt%, thus eliminating porosity defects. In addition, there was a higher content of Kurdjumov-Sachs (KS) and Nishiyama-Wassermann (NW) interfaces (95%) in sample A1. Conversely, the water cooling inhibited the austenite shear transformation period at the relatively low temperature of sample U1. Hence, lower KS/NW interfaces (56%) were obtained due to the changed austenite nucleation and growth mechanism. Benefitting from the denser dislocation density and finer grain size caused by the underwater environment, the comprehensive mechanical properties of defect-free sample U1 were superior to those of sample A1. The nitrogen pores in sample A1 did not weaken the tensile strength but did seriously impair the impact toughness and ductility.

Effect of interstitial nitrogen on bonding characteristics and electronic structure of high nitrogen steel

Interstitial nitrogen can significantly change the electronic structure and bonding characteristics of austenite, and has an important influence on the properties of austenite. The bonding properties and properties of high nitrogen steel with different nitrogen element ratios were calculated. The alloy model with different nitrogen content is established, and the properties of energy, density of states and elastic constant are calculated. Increasing the nitrogen content will reduce the density of states and energy, significantly improving the stability of the cell. The crystal cells with different nitrogen content meet the mechanical stability. With the increase of nitrogen content, the elastic modulus, Poisson’s ratio gradually decreases, strength, shear strain and deformation resistance increase, and plasticity and ductility decrease.

First principle study on the effect of Cr, Mn and Ni on electronic structure and mechanical properties of high nitrogen steel

First principle study on the effect of Cr, Mn and Ni on electronic structure and mechanical properties of high nitrogen steel

Experimental Study on Dynamic Tensile Properties and Ballistic Performance of Different Armor Materials

Hopkinson bar system was used to test the dynamic tensile properties of high nitrogen steel, 685 armor steel, 603 armor steel and 316 stainless steel by adjusting loading pressure, the strain rate and dynamic tensile strength of different armor materials were obtained. Under the experimental conditions in this paper, the dynamic tensile strength of the high-nitrogen steel is 1883 MPa which is the maximum of the four materials. At the same time, by using 12.7 mm armor-piercing projectiles, the ballistic tests of semi-infinite targets of different armor materials were carried out. Penetration depth of high-nitrogen steel is 25.5 mm which is the smallest of the four materials. The standard penetration depths of armor materials decrease with the increase of dynamic tensile strengths, and tensile strength increases under the test conditions in this paper. Therefore, the material with high dynamic tensile strength should be selected as the ballistic component in armor design.

Dynamic Mechanical Properties of High Nitrogen Steel under Combined Loading

High speed collision is the main feature of armored service environment. It is very important for armor structure design to study the dynamic response of armor material under high strain rate loading. Based on Hopkinson bar techniques, dynamic performance experiments of high-nitrogen steel under combined loading were carried out in this paper. The stress-strain curves of high nitrogen steel under different loading conditions were obtained. The results show that with the increase of shear stress ratio, the anti-failure ability of high nitrogen steel decreases significantly. When the loading angle was 90° and 60°, the fracture surfaces and stress-strain curves of the samples were significantly different under the same loading conditions. With the decrease of the loading angle, the fracture surface and the stress-strain curve of the sample under the same loading condition tend to be the same. In the process of combined loading, with the reduction of the loading angle, the tensile force of the sample at the yield stage decreases gradually.

Влияние фазовых превращений в процессе электронно-лучевой 3D-печати и последующей термической обработки на закономерности пластической деформации и разрушение образцов высокоазотистой Cr-Mn-стали

We investigated the phase composition, plastic deformation and fracture micromechanisms of Fe-(25-26)Cr-(5-12)Mn-0.15C-0.55N (wt. %) high-nitrogen chromium-manganese steel. Obtained by the method of electron-beam 3D-printing (additive manufacturing) and subjected to a heat treatment (at a temperature of 1150°C following by quenching). To establish the effect of the electron-beam 3D-printing process on the phase composition, microstructure and mechanical properties of high-nitrogen steel, a comparison was made with the data for Fe-21Cr-22Mn-0.15C-0.53N austenitic steel (wt. %) obtained by traditional methods (casting and heat treatment) and used as a raw material for additive manufacturing. It was experimentally established that in the specimens obtained by additive manufacturing method, depletion of the steel composition by manganese in the electron-beam 3D-printing and post-built heat treatment contributes to the formation of a macroscopically and microscopically inhomogeneous two-phase structure. In the steel specimens, macroscopic regions of irregular shape with large ferrite grains or a two-phase austenite-ferrite structure (microscopic inhomogeneity) were observed. Despite the change in the concentration of the basic elements (chromium and manganese) in additive manufacturing, a high concentration of interstitial atoms (nitrogen and carbon) remains in steel. This contributes to the macroscopically heterogeneous distribution of interstitial atoms in the specimens - the formation of a supersaturated interstitial solid solution in the austenitic regions due to the low solubility of nitrogen and carbon in the ferrite regions. This inhomogeneous heterophase (ferrite-austenite) structure has high strength properties, good ductility and work hardening, which are close to those of the specimens of the initial high-nitrogen austenitic steel used as the raw material for additive manufacturing.

Wear resistance of hydrogenated high nitrogen steel at dry and solid state lubricants assistant friction

Purpose: This paper is devoted the investigation hydrogen influence on of wear resistance of high nitrogen steel (HNS) at dry and solid state lubricants assistant friction. It has been established that after hydrogenation at 250 N loading the wear rate increased by 2.9 ... 4.1 times. Microhardness of hydrogenated layer was 7.6 ... 8.2 GPa, that is increased after hydrogenation in two times. After adding the (GaSe)xIn1-x compounds to the tribo conjugates by X-ray diffraction analysis it has been established the appearance of new phases which formed during the friction process and detected on the friction surface. Design/methodology/approach: This work presents research results concerning the comparative tests of high nitrogen steels in the circumstances of dry rolling friction. It was conducted the experiments to determine the tribological properties of high-nitrogen steels under rolling friction. The test pieces were manufactured in the form of rollers, and rotated with a linear velocity 2.27 m/s (upper roller), 3.08 m/s (bottom roller). Upper roller is made from HNS was subjected for hydrogenation. Analysis of friction surfaces indicates the complex mechanism of fracture surfaces. The results of the local X-ray analysis and X-ray diffraction analysis has been established the appearance of new phases and elements on the friction surface. Findings: It has been found that the level of wear resistance of the investigated materials under hydrogenation. Compounds realize chemisorption, tribochemical mechanisms of the formation of thin protective (anti-wear, antifriction) layers on metal surfaces. Research limitations/implications: An essential problem is the verification of the results obtained using the standard mechanical tests, computer-based image analysis and other methods. Practical implications: The observed phenomena can be regarded as the basic explanation of reduces the plasticity characteristics after hydrogenation. Applying the (GaSe)xIn1-x compounds as a lubricant will allow the formation of films on friction surfaces that can minimize surface wear, which will contribute to the transition to a wear-free friction mode. The protective film is a barrier to high shear and normal loads, preserving the base metal of the part and providing reduced wear and friction. Originality/value: The value of this work is that conducted experiments permit to determine the tribological properties of high nitrogen steels under rolling friction after hydrogenation. After adding (GaSe)xIn1-x compounds to the tribo conjugates after due to X-ray diffraction analysis it has been established the appearance of new phases which formed during the friction process and detected on the friction surface.

High-Nitrogen Steel

The properties of high-nitrogen steels are briefly reviewed, along with their production technologies. High-nitrogen steels are preferable to traditional steels in many respects: specifically, their yield point is four times higher, with a distinctive combination of other properties; expensive alloying elements such as Ni, Mo, Co, and W are required in smaller quantities, if at all; and effective alloying with nontraditional elements (such as Ca, Zn, and Pb) is possible. The influence of the nitrogen content on the properties of such steels is considered. The production technologies for ferritic–pearlitic, martensitic, and austenitic steels are described, along with their applications. For ferritic–pearlitic steels, more careful maintenance of the chemical composition is required in alloying with nitrogen, which is more soluble than carbon, so as to prevent the formation of nitrides, which are insoluble on heat treatment. On tempering martensitic steels, nitrides and carbonitrides may be formed. The influence of nitrogen in those alloys may be associated with decrease in size of the nitride particles relative to the carbide particles. The increased thermal stability of nitrides and carbonitrides improves the mechanical and physical properties of the steel. Because nitrogen is closely equivalent to nickel in terms of the formation of γ phase, it may be used to replace nickel in austenitic steels, in the following proportions: 1 kg nitrogen to around 6–39 kg of nickel. In austenitic–martensitic steels, the main role is played by thermal martensite; stable austenite is formed on aging at the working temperatures. Examples of the effective use of high-nitrogen steels in machine parts are presented.

Study on dynamic mechanical properties of high nitrogen steels

Abstract Reliable dynamic mechanical properties of high nitrogen steels are necessary for the design and assessment of armor structures subject to impact and blast. A series of experiments, based on Hopkinson bar techniques, were conducted and described in this study. The dynamic compression, tensile and shear properties of high nitrogen steel had been tested, and the stress-strain curves under high strain rates were obtained. The results have been showed as follows: High nitrogen steel has a remarkable strain rate strengthening effect. Compared to the static curves, the constitutive curves of dynamic tension and compression move upper. The dynamic compressive yield strength of high nitrogen steel increases first and then decreases with the increase of strain rate, and the yield strength varies in the range of 1465–1549 MPa within the range of 1147–2042 s−1 strain rate; The tensile strength of high nitrogen steel increases with the increase of strain rate. When the strain rate is greater than 1341 s−1, the tensile strength will not increase and the curve tends to be gentle. The pure shear yield strength of the high nitrogen steel is above 800 MPa.

Shock compression response of α″-Fe16N2 nanoparticles

The shock compression response of α''-Fe16N2 nanoparticles is studied in order to evaluate the thermo-mechanical stability of the α'' phase under shock loading. Shock compression experiments were performed using the parallel plate impact gas gun set up at velocities near 850 m/s. The experiments were performed at −21 °C and −126 °C in order to minimize temperature excursions and thereby determine the thermal effects on the phase stability. The α''-Fe16N2 phase is observed to partially decompose into α-Fe and γ'-Fe4N in both samples, as detected by the XRD analysis. The lower temperature produces a higher percentage of γ' phase in addition to the γ''-Fe50N50 phase. The pressure-volume-temperature response of the material is modeled using the dynamic mechanical properties of high nitrogen steel. The model is then used to evaluate the temperature excursions and their effect on the phase transitions observed.

Mechanical Properties of Ni-Free High-Nitrogen Austenitic Stainless Steel Made by Metal Injection Molding with Nitrogen Absorption Method

Microstructure and mechanical properties of high nitrogen steels containing 17Cr-12Mn-3Mo produced by means of metal injection moulding and nitrogen absorption methods were examined. The compacts were sintered at 1300°C, then furnace-cooled to 1200°C and were held at that temperature for 2 to 20 hrs. Subsequently, they were furnace-cooled. Thereafter, solution treatment was done at 1200°C. The solution treated compacts held at 1200°C for above 5 hrs had homogeneous microstructure. Increasing the holding time at 1200°C, ferrite phase disappeared due to the increment of nitrogen content and grain size became larger. Lattice constant of austenite phase also increased. Yield and tensile strength increased with increasing nitrogen content. Yield and tensile strength of the compact held at 1200°C for 10 hrs were 758 MPa, 1172 MPa respectively and elongation was 41 %. However, ductile-brittle transition (DBT) behaviour was seen, and the DBT temperature of every compact was about -20°C. From the fracture surface analysis, brittle fracture surface was identified as (111).

Metal Injection Molding Method of Ni-Free Austenitic Stainless Steel II - Microstructure and Mechanical Properties

Microstructure and mechanical properties of high nitrogen steels whose chemical composition were Fe-17Cr-12Mn-3Mo and that was produced by using metal injection molding method and nitrogen absorption methods were examined. A compact which is furnace cooled from 1573 K has a brittle surface layer with high chromium and nitrogen contents but the surface layer disappears when the compact is held at 1473 K. The compact which is furnace cooled at 1473 K is observed precipitates in the grains and the grain boundary, while the compact which is quenched at 1473 K shows homogeneous microstructure. In the heat treatments at 1473 K for 2, 5, and 10 h, the nitrogen content becomes higher with increasing of holding time. In the holding times of 5 and 10 h, the microstructure is austenite. In the tensile tests, tensile strength becomes larger with increasing of nitrogen content. In the specimen which is conducted the heat treatment at 1473 K for 10 h, tensile strength is about 1,000 MPa and elongation is 80 %, which shows better balance of strength and elongation than SUS304 and SUS316 steels.

Progress in the study of high-nitrogen corrosion-resistant aging nonmagnetic vanadium steels

Studies of the structure and properties of high-nitrogen corrosion-resistant aging nonmagnetic vanadium steels have been analyzed. The hardening of these steels by fine vanadium nitride and carbonitride particles is considered. The mechanisms of the discontinuous decomposition of austenite supersaturated by nitrogen upon heat treatment are described. Methods for the removal of the negative effect of the discontinuous decomposition on the mechanical properties of high-nitrogen steels have been found. Steels with an overequilibrium nitrogen content are shown to exhibit superplasticity. The dependences of the microstructure and properties of high-nitrogen vanadium austenitic steels on their alloying and the conditions of thermal and thermoplastic treatments are considered.