Fracture behavior and mechanism of highly fragmented steel cylindrical shell under explosive loading

An in-depth understanding of the fracture behavior and mechanism of metallic shells under internal explosive loading can help develop material designs for warheads and regulate the quantity and mass distribution of the fragments formed.This study investigated the fragmentation performance of a new high-carbon silicon-manganese(HCSiMn)steel cylindrical shell through fragment recovery experiments.Compared with the conventional 45Cr steel shell,the number of small mass fragments produced by the HCSi Mn steel shell was significantly increased with a scale parameter of 0.57 g fitted by the Weibull distribution model.The fragmentation process of the HCSi Mn shell exhibited more brittle tensile fracture characteristics,with the microcrack damage zone on the outer surface being the direct cause of its high fragmentation.On the one hand,the doping of alloy elements resulted in grain refinement by forming metallographic structure of tempered sorbite,so that microscopic intergranular fracture reduces the characteristic mass of the fragments;on the other hand,the distribution of alloy carbides can exert a"pinning"effect on the substrate grains,causing more initial cracks to form and propagate along the brittle carbides,further improving the shell fragmentation.Although the killing power radius for light armored vehicles was slightly reduced by about 6%,the dense killing radius of HCSiMn steel projectile against personnel can be significantly increased by about 26%based on theoretical assessment.These results provided an experimental basis for high fragmentation warhead design,and to some extent,revealed the correlation mechanism between metallographic structure and shell fragmentation.

ABSTRACTS——From Journal of Iron and Steel Research(in Chinese)

The electrochemical nature of reaction between melt and slag in a closed system was worked out. Experimental results demonstrated that both the rate and reaction extent increase when the electronic conductor or voltage was applied between melt and slag. The bigger the contact area of the conductor with melts is, the faster the reaction rate is. With the increase of applied voltage which is beneficial for electron's migration between metal and slags, the rate and extent of reaction increase.

Discussion of Environmental Problem and Study of Environmental Impact on Steel Industry in China

The environmental conditions in steel industry were discussed in detail.It was also pointed out that it was necessary to reduce the quantity of waste generated and discharged by improving the raw material,energy structure and consumption rate,and reinforcing the waste control and management.At the same time,the relevant mathematical models of environmental impact were set up on the basis of raw material consumption,energy consumption and waste generation and discharge in different technical routes of steelmaking.The result showed that the production route of DR-iron clearly has more environmental advantages over that of BF-hot metal.

The welding application of high strength steels used in engineering machinery

With the rapid development of low alloy steel strength level,more problems caused by welding are exposed day by day.Recently,the efforts have been paid to improve or enchance the low toughness of heated affected zone and welded metal which can enchance the comprehensive mechanical properties that is the core scientific problems of its safe operation by researching crack initiation and crack propragation attracted a rapidly growing interest.This article focuses on the research status and progress of welding technology and joint microstructure and properties of advanced steel materials.The influence of shielding gas on the microstructure evolution of deposited metals,the effect heat input of welded joint performance,interpass temperature and alloy elements on welded joints microstructure and M-A constituent evolution and properties are reviewed in detail.And for the heat affected zone,the grain size and microstructure as well as the shape,size,and distribution of M-A constituent,have a significant impact on the impact toughness.This paper is an attempt to review the effect of different welding process parameters on welded metal and HAZ of HSLA steels.

Study on Direct Reduction Characteristics of Iron Ore Coal Mixed Pellets

In order to get DRI iron ore coal mixed pellets are reduced isothermally. The mechanisms of reduction desulphurization, iron oxide reduction and the structure regenesis of the coal mixed pellets during reduction have been studied. The effect of various processing factors on the quality of DRI and economy technological indices including compression strength, desulphurization rate, recovery rate, reaction fraction, carbon content and metallization are also researched.

A STUDY ON THE MICROSTRUCTURE AND FRACTURE PROCESS OF A PEARLITIC STEEL BY MEANS OF EDC TECHNIQUE

An investigation of the microstructure and the mioroprocess of fracture of an eutectoid pearlitic steel has been carried out by means of electron-diffraction-contrast(EDC) and other analytical techniques. The nature of the dislocations in pro-eutectoid-ferrite and ferrite in pearlite was determined. The character of interface conjunction between ferrite and cementite was discussed. The fracture process of pearlitic steel has been analysed crystallographically.

Simulation of recrystallization based on EBSD data using a modified Monte Carlo model that considers anisotropic effects in cold-rolled ultra-thin grain-oriented silicon steel

A Monte Carlo Potts model was developed to simulate the recrystallization process of a cold-rolled ultra-thin grain-oriented silicon steel.The orientation and image quality data from electron backscatter diffraction measurements were used as input information for simulation.Three types of nucleation mechanisms,namely,random nucleation,high-stored-energy site nucleation(HSEN),and high-angle boundary nucleation(HABN),were considered for simulation.In particular,the nucleation and growth behaviors of Goss-oriented({011}<100>)grains were investigated.Results showed that Goss grains had a nucleation advantage in HSEN and HABN.The amount of Goss grains was the highest according to HABN,and it matched the experimental measurement.However,Goss grains lacked a size advantage across all mechanisms during the recrystallization process.

Thermal expansion behavior of sintered Nd–Fe–B magnets with different Co contents and orientations

The thermal expansion behavior of sintered Nd–Fe–B magnets is a crucial parameter for production and application.However, this aspect has not been thoroughly investigated. In this study, three different sintered Nd–Fe–B magnets with varying Co content(Co = 0, 6, 12 wt%) were prepared using the conventional powder metallurgy method, and four magnets oriented under different magnetic fields were prepared to compare. The thermal expansion behavior for the magnets was investigated using a linear thermal dilatometry in the temperature range of 20℃–500℃. It was found that, the coefficient of thermal expansion(CTE) increases with the increase of Co contents, while the anisotropy of thermal expansion decreases.The introduction of Co leads to continuous changes from negative to positive thermal expansion in the vertically oriented direction, which is important for the development of zero thermal expansion magnets. The thermal expansion of nonoriented magnets was found to be isotropic. Additionally, the anisotropy of thermal expansion increases with the increase of orientation degree. These results have important implications for the development of sintered Nd–Fe–B with controllable CTE.

Catalytic mechanism of in-situ Ni/C co-incorporation for hydrogen absorption of Mg

Ni and carbon materials exhibit remarkable catalysis for the hydriding reaction of Mg.But the underlying mechanism of Ni/C hybrid catalysis is still unclear.In this work,density functional theory(DFT)calculation is applied to investigate the effect of Ni/C co-incorporation on the hydriding reaction of Mg crystal.The morphology and crystal structure of the Ni/C co-incorporated Mg sample show that the coincorporated structure is credible.The transition state searching calculation suggests that both the incorporations of Ni and C are beneficial for the H_(2) dissociation.But Ni atom has a dramatic improvement for H_(2) dissociation and makes the H diffusion become limiting step of the hyriding reaction.The Ni dz_(2)orbit and H s orbit accept the electrons and combine together compactly,while the Ni d_(xy) orbit is half-occupied.The catalytic effect of Ni on H_(2) dissociation can be ascribed to the bridging effect of Ni d_(xy) orbit.The incorporation of C can weaken the over-strong interaction between Ni and H which hindered the H diffusion on Mg(0001).The Ni/C co-incorporated Mg(0001)shows the best performance during hyriding reaction compared with the clean and single incorporated Mg(0001).

Effect of heat treatment on microstructure and mechanical properties of selective laser-melted PH13-8Mo stainless steel

PH13-8Mo stainless steel powder with high sphericity and well fluidity was prepared by the plasma rotating electrode process.The formed parts with ultra-high purity were manufactured by selective laser melting.The tensile and impact mechanical properties of the printed parts under three heat treatment regimes were compared to those without heat treatment.The microstructure,grain orientation and phase composition were characterized by electron-backscatter diffraction,X-ray diffraction and transmission electron microscopy.The characterization results reveal that the addition of heat treatment makes the grains enlarge,and after different heat treatments,the average grain size from 1.51μm in the printed state increases to 2.78,3.09 and 2.06μm,respectively.The formed parts are mainly composed of martensite and retained austenite.Moreover,the NiAl and M23C precipitates form,which are the major strengthening phases of PH13-8Mo stainless steel.The optimal heat treatment process is 925℃×1 h water cooling(WC)+0℃×2 h air cooling(AC)+540℃×4 h AC.Using this heat treatment process,PH13-8Mo formed parts have the optimal comprehensive mechanical properties:the tensile strength,yield strength and impact energy KU2 are 1492 MPa,1432 MPa and 63 J,respectively.The strengthening and toughening via heat treatment are mainly attributed to dislocation strengthening,the formation of NiAl and M23Co precipitates and the change of volume fraction of the retained austenite.

New Duplex Microstructure of Grain Boundary Allotriomorphic Ferrite/Granular Bainite

This was a feasibility study for a modified 304 steel resistant to stress corrosion cracking (SCC) in aqueous environment containing chloride. SCC tests were conducted potentiostaticaly with spot welded specimens, which had both crevice and residual stress, mainly in 3 % NaCl solution at various temperatures to determine the critical temperature for SCC at and below which the steel would not suffer from SCC. The effects of individual alloying element of silicon, manganese and copper on SCC of 18Cr 14Ni steels which phosphor content is 0.002 % and molybdenum content is 0.01 % were examined. Addition of 1 or 2 % of copper has beneficial effect on resistance to SCC, while increasing silicon or manganese content has no significant effect. Critical temperature of the steel with 0.002 % of phosphor and 2 % of copper is 150 ℃, which is markedly higher than 50 ℃ of 304L steel. However, the beneficial effect of copper is reduced with increasing phosphor content. From practical viewpoint, the modified steel with good SCC resistance should have 0.01 %-0.015 % of phosphor and 0.3 % or more of molybdenum, because it is very difficult to reduce phosphor content below 0 008 % industrially and such molybdenum content is inevitably introduced through cost saving melting process using return steel. Aluminium is to be added as another alloying element and 3 % of aluminium combined with 2 % of copper has been found to negate the deleterious effects of increased phosphor and molybdenum content. As a candidate steel at this stage, 14Cr 16Ni 0.013P 2Cu 1Al (0.3 1)Mo steel has critical temperature of 110 ℃.

Grain size based low cycle fatigue life prediction model for nickel-based superalloy

Nickel-based superalloys are easy to produce low cycle fatigue(LCF)damage when they are subjected to high temperature and mechanical stresses.Fatigue life prediction of nickel-based superalloys is of great importance for their reliable practical application.To investigate the effects of total strain and grain size on LCF behavior,the high temperature LCF tests were carried out for a nickel-based superalloy.The results show that the fatigue lives decreased with the increase of strain amplitude and grain size.A new LCF life prediction model was established considering the effect of grain size on fatigue life.Error analyses indicate that the prediction accuracy of the new LCF life model is higher than those of Manson-Coffin relationship and Ostergren energy method.

AXISYMMETRIC CONTACT PROBLEM OF CUBIC QUASICRYSTALLINE MATERIALS

The axisymmetric elasticity theory of cubic quasicrystal was developed in Ref. [1]. The axisymmetric elasticity problem of cubic quasicrystal is reduced to a single higher-order partial differential equation by introducing a displacement function, based on which, the exact analytic solutions for the elastic field of an axisymmetric contact problem of cubic quasicrystalline materials are obtained for universal contact stress or contact displacement. The result shows that if the contact stress has order - 1/2 singularity on the edge of the contact domain, die contact displacement is a constant in the contact domain. Conversely, if the contact displacement is a constant, the contact stress must have order - 1/2 singularity on the edge of die contact domain.

Evolution behavior of γ″ phase of IN718 superalloy in temperature/stress coupled field

The evolution behavior of theγ″phase of IN718 superalloy in a temperature/stress coupled field was investigated.Results showed that the coarsening rate of theγ″phase was significantly accelerated in the temperature/stress coupled field.Based on the detail microstructural and crystal defect analysis,it was found that the coarsening rate of theγ″phase with applied stress was significantly higher than that without stress.The main reasons for the increase in the coarsening rate of theγ″phase are as follows:the vacancy formation energy is decreased by the applied stress,which leads to an increase in the vacancy concentration;in the temperature/stress coupled field,the Nb atoms easily combine with vacancies to form complexes and diffuse with the complexes,resulting in a significant increase in the Nb atom diffusion coefficient;Nb atom diffusion is the key control factor for the coarsening of theγ″phase.

Definition and Verification of Shape Meter Method

Based on quantitative microscopic examinations of welds and welding rate for different steels (40Cr and T10A) joint, which possess the ultra fine microstructure after high frequency hardening (HFH) and salt bath cyclic quenching (SCQ), the suitable defect grey scale threshold value was determined, and the welding rate of superplastic solid state welding of different steels (40Cr and T10A steel) was systematically inspected and analyzed by means of self made ultrasonic imaging inspection system. The experimental results showed that the superplastic solid state weld of different steels can be inspected more accurately, reliably and quickly by this system, and the results were in good accordance with that of metallographic observation. The welding rate of superplastic welding is in linear relation with tensile strength of joint.

Behavior of Mn^(2+) in perovskite manganites with nominal composition La_(0.6-x)Nd_xSr_(0.1)MnO_3

The fact that there are Mn^(2+) at the A sites in the ABO_3 perovskite phase of manganites with the nominal composition La_(0.6-x)Nd_xSr_(0.1)MnO_3 showed by detailed experimental study and theoretical calculations.The magnetic moments of these Mn^(2+) are antiparallel to those of the Mn ions at the B sites.The content of the Mn^(2+) increases as the average ionic radius,<r_A>,of the ions at A sites decreases,resulting in the experimentally observed phenomenon that the content of the Mn_3O_4 phase in the manganites decreases with decreasing <r_A>.

Study on microstructure and properties of 590 MPa class welding wire deposited metal on hull

By means of metallographic microscope(OM),scanning electron microscope(SEM),back scattering electron diffraction(EBSD)and transmission electron microscope(TEM),the effect of Cu on microstructure transformation and mechanical properties of deposited metal of 590MPa class steel welding wire was studied.The results show that the microstructure of deposited metal is composed of acicular ferrite,lamellar bainite,granular bainite and residual austenite.With the increase of Cu content,the phase transition temperature of the deposited metal decreases,making the phase transition region of ferrite and pearlite shift to the right,expanding the phase transition region of bainite and shrinking the phase transition region of ferrite and pearlite.The microstructure of deposited metal changed,the content of M-A elements increased but the size decreased,and the ferrite-bainite biphasic microstructure was matched.The reduction of M-A component content in strips and blocks and the reduction of effective grain size will reduce the nucleation probability of microcracks,increase crack growth resistance,and improve the impact toughness of the deposited metal.

Revealing effect of Al content on oxidation of novel Co-Cr-Nb-W carbide-strengthened superalloy

The high-temperature oxidation behavior of novel Co-Cr-Nb-W carbide-strengthened wear-resistance alloys with different Al contents(1wt%,2wt%and 3wt%)at 950,1000 and 1050℃was thoroughly investigated by scanning electron microscopy,X-ray diffraction,X-ray photoelectron spectroscopy and field emission electron probe analyzer.The porous property of NbC in-situ oxidation products(Nb_(2)O_(5),Co Nb_(2)O_(6)and Co_(4)Nb_(2)O_(9))induces a multi-layered oxide scale with micropores and cracks.Co-Cr-Nb-W alloy with 1 wt%Al undergoes catastrophic oxidation and spalling above 1000℃.The outward transportation of Cr and Co is effectively restrained by a continuous Al_(2)O_(3)scale formed around NbC in-situ oxidation region when Al content reaches 3 wt%.The β-Co Al in Co-Cr-Nb-W alloy with 3 wt%Al has an oxidation priority over eutectic carbides and the alloy matrix which are both enriched with Cr,thereby preventing the formation of Cr-depletion area and improving the self-healing ability of the oxide film.A slight change in Al content has a remarkable influence on the cooperative effect of Al and Cr and multiplies the antioxidant capacity of Co-Cr-Nb-W alloy above 1000℃.

Pr-Tb synergistic strengthening on coercivity of Nd-Ce-Fe-B magnets grain boundary diffused with Pr-Tb-Al-Ga alloys

Sintered Nd-Ce-Fe-B magnets were grain boundary diffused(GBDed) with Pr_(x)Tb_(80-x)Al_(10)Ga_(10)(at%)(x=0,20,40,60,80) alloys.The effect of Pr/Tb content in diffusion source on magnetic properties,microstructure and elements distribution of GBDed magnets was investigated.When Pr is used to substitute for 75% Tb in diffusion source,Tb consumption per unit coercivity improvement of GBDed magnet reduces by 77%,compared with the Tb_(80)Al_(10)Ga_(10) diffused magnet.Tb element diffuses into magnets and then forms Tb-rich shell with high magneto-crystalline anisotropy field surrounding main phase grains,resulting in substantial coercivity improvement.Pr with low melting point diffuses deeply along liquid grain boundary phase during GBD process.It can eliminate some sharp defects of main phase grains and make grain boundaries smooth,which provides diffusion channels for further diffusion of Tb element.Therefore,there are more diffusion channels for Tb and less Tb enriched at surface region,making Tb diffuse more deeply and improving Tb utilization efficiency.This method significantly improves the coercivity,and realizes the green,efficient and high-quality utilization of heavy rare earth(HRE)elements.

Effects of Co and Nb on the Crack of Additive Manufacturing Nickel-Based Superalloys

Increasing the print quality is the critical requirement for the additive manufactured complex part of aero-engines of nickel-based superalloys.A study of the effects of Co and Nb on the crack is performed focusing on the selective laser melting(SLM)nickel-based superalloy.In this paper,the solvus temperature of γ',crack characteristics,microstructure,thermal expansion,and mechanical properties of SLM nickel-based superalloy are investigated by varying the content of Co and Nb.The alloy with 15Co/0Nb shows the highest comprehensive quality.Nb increases the crack risk and thermal deformation,and then Co accelerates the stress release.Therefore,Co is an extremely important alloying element for improving the quality of SLM nickel-based superalloy.Finally,the crack growth kinetics and the strain difference are discussed to reveal the SLM crack regular that is affected by time or temperature.The analysis work on the effect of alloying elements can obtain an effective foundational theory to guide the composition optimization of SLM nickel-based superalloys.