Experimental and numerical study on the influence of shaped charge liner cavity filing on jet penetration characteristics in steel targets

Penetration characteristic(size and shape of penetration craters made in high hardness ARMSTAL 30PM steel) of shaped charge jets formed after detonations of modified PG-7VM warheads was analyzed in the article. Modifications consisted in removing the frontal part of the grenade(fuse, ballistic cap and conductive cone) and introducing of the liner cavity filling made of polyacetal copolymer POM-C. The filings in the form of solid cones with three different heights(33%, 66% and 100% of H-the height of original PG-7VM liner) were placed inside of the hollow cone shaped charge liner. As opposed to the vast majority of previously published works(in which warhead optimization studies were focused on increasing of the depth of penetration in rolled homogeneous armor steel) the main aim of the presented modifications was to maximize the damage ratio(diameters of craters, inlet and outlet holes) of target perforated by shaped charge jet at the cost of the loss of part of the jet penetration capability. According to the best knowledge of the authors such approach to the use of the old PG-7VM warheads has not been analyzed so far. Taking into consideration high stock levels of PG-7VM warheads, and the fact that they are continuously being replaced by more efficient and more sophisticated high-explosive anti-tank warheads, it seems reasonable to look for alternate applications of the warheads withdrawn from the service. Thanks to the introduction of proposed modifications the warheads could be used by special forces or other assault units as directional mines or statically detonated cutting shaped charges as well as by combat engineers as universal charges used in various types of engineering or sapper works. The research included experimental penetration tests and their numerical reproduction in the LS-Dyna software with the simulation methodology defined and validated in previous works of the authors.Small differences(average error = 10-20%) were identified between the experimental and numerical results(dimensions of craters made in steel targets were compared) what confirmed the reliability of the modelling methodology and enabled its use for further optimization of the shapes of fillings. Within the analyzed variants of warheads modifications maximum diameters of penetration craters were obtained for the filling of the height of h = 2/3H. The diameters of holes in individual steel plates were increased by 164%, 70%, 65%(for the first, second and third plate, respectively) in relation to the variant without filling. The results of the study indicated that with the use of different materials of fillings and their various heights it is possible to control the shape of penetration craters pierced in the steel targets.

Finite element analysis of shape control for continuous hot rolling mills of super wide strip steel

The efficacy of shape control is the core of this technology and the main basis of automatic shape control system model designing. This passage constructs the three-dimensional elastic deformation model of CVCplus roll system in 2250 mm hot rolling mill. Comparing and analyzing different influence of working factors on control characteristic, the shape control characteristic of CVCplus roll system in its whole work time is studied, and the cause is analyzed and the difference of the roll gap curve and crown adjustable area in early and latter work time is compared. The outcome has crucial meaning in both theory and production.

Mechanical model for controlling floor heave in deep roadways with U-shaped steel closed support

Open U-shaped steel arch supports are commonly used in large-section static-pressure roadways in coal mines that are more than 900 m deep;however,it is very difficult to control floor heave of roadways.In this paper,a U-shaped steel closed support with an inverted U-shaped steel arch in the floor is proposed as a method for improving the support effect of the surrounding rock during the process of floor heaving.This research established a mechanical model for the U-shaped steel closed support,and determined the reaction forces at the connection of a camber angle.Using the limit load method calculated the critical buckling load of the inverted U-shaped steel arch,and use of a strength check method tested the strength of the U-shaped steel material.A numerical simulation was conducted using the finite difference software FLAC3 D.The simulation results show that the U-shaped steel closed support is able to control the floor heave of roadways,which is successfully used in the West 11-2 development roadway of the Zhuji Mine in the Huainan mining area in China.The cumulative floor heave over two years was less than50 mm.

Research and Development Trend of Shape Control for Cold Rolling Strip

Shape is an important quality index of cold rolling strip. Up to now, many problems in the shape control domain have not been solved satisfactorily, and a review on the research progress in the shape control domain can help to seek new breakthrough directions. In the past 10 years, researches and applications of shape control models, shape control means, shape detection technology, and shape con- trol system have achieved significant progress. In the aspect of shape control models, the researches in the past improve the accuracy, speed and robustness of the models. The intelligentization of shape control models should be strengthened in the future. In the aspect of the shape control means, the researches in the past focus on the roll opti- mization, mill type selection, process optimization, local strip shape control, edge drop control, and so on. In the future, more attention should be paid to the coordination control of both strip shape and other quality indexes, and the refinement of control objective should be strengthened. In the aspects of shape detection technology and shape control system, some new types of shape detection meters and shape control systems are developed and have successfully indus- trial applications. In the future, the standardization of shape detection technology and shape control system should be promoted to solve the problem of compatibility. In general,the four expected development trends of shape control for cold roiling strip in the future are intelligentization, coordi- nation, refinement, and standardization. The proposed research provides new breakthrough directions for improv- ing shape quality.

Warm/cold rolling processes for producing Fe-6.5wt% Si electrical steel with columnar grains

A new technical prototype for producing Fe-6.5wt% Si electrical steel sheets by directional solidification, heat treatment before rolling, warm rolling, and cold rolling was proposed in the present study. The formability of Fe-6.5wt% Si electrical steel before rolling and the reasonable process parameters of this technical prototype were obtained. Experimental results reveal that the formability of Fe-6.5wt% Si electrical steel is improved significantly under the combination of directional solidification and heat treatment before rolling. Fe-6.5wt% Si electrical steel sheets with the thickness of 0.15 ram, bright surface, few edge cracks, and high rolling yield can be successfully fabricated using this technology without any intermediate annealing during the whole rolling. The combination of directional solidification, heat treatment before rolling, warm rolling, and cold rolling can work as a new process for highly efficient and compact fabrication of Fe-6.5wt% Si electrical steel sheets.

Effect of cold rolling on the microstructural, magnetic, mechanical, and corrosion properties of AISI 316L austenitic stainless steel

This study has evaluated the effect of different levels of cold rolling（from 0 to 50%）on the microstructural,magnetic,and mechanical properties and the corrosion behavior of 316L austenitic stainless steel in Na Cl（1 mol/L）＋H_2SO_4（0.5 mol/L）solution.Microstructural examinations using optical microscopy revealed the development of a morphological texture from coaxial to elongated grains during the cold-rolling process.Phase analysis carried out on the basis of X-ray diffraction confirmed the formation of the ferromagneticα′-martensite phase under the stresses applied during cold rolling.This finding is in agreement with magnetic measurements using a vibrating sample magnetometer.Mechanical properties determined by tensile and Vickers microhardness tests demonstrated an upward trend in the hardness-to-yield strength ratio with increasing cold-rolling percentage,representing a reduction in the material’s work-hardening ability.Uniform and localized corrosion parameters were estimated via potentiodynamic polarization corrosion tests and electrochemical impedance spectroscopy.In contrast to the uniform corrosion,wherein the corrosion current density increased with increasing cold-working degree because of the high density of microstructural defects,the passive potential range and breakdown potential increased by cold working,showing greater resistance to pit nucleation.Although pits were formed,the cold-rolled material repassivation tendency decreased because of the broader hysteresis anodic loop,as confirmed experimentally by observation of the microscopic features after electrochemical cyclic polarization evaluations.

Effect of cryogenic rolling and annealing on the microstructure evolution and mechanical properties of 304 stainless steel

Metastable 304 austenitic stainless steel was subjected to rolling at cryogenic and room temperatures, followed by annealing at different temperatures from 500 to 950°C. Phase transition during annealing was studied using X-ray diffractometry. Transmission electron microscopy and electron backscattered diffraction were used to characterize the martensite transformation and the distribution of austenite grain size after annealing. The recrystallization mechanism during cryogenic rolling was a reversal of martensite into austenite and austenite growth. Cryogenic rolling followed by annealing refined grains to 4.7 μm compared with 8.7 μm achieved under room-temperature rolling, as shown by the electron backscattered diffraction images. Tensile tests showed significantly improved mechanical properties after cryogenic rolling as the yield strength was enhanced by 47% compared with room-temperature rolling.

Microstructures and properties of capacitor discharge welded joint of TiNi shape memory alloy and stainless steel

Microstructures and properties of capacitor discharge welded （CDW） joint of TiNi shape memory alloy （ SMA ） and stainless steel （SS） were studied. The fracture characteristics of the joint were analyzed by means of scanning electron microscope （ SEM）. Microstructures of the joint were examined by means of optical microscope and SEM. The results showed that the teusile strength of the inhomogeneous joint （ TiNi-SS joint） was low and the joint was brittle. Because TiNi SMA and SS melted, a brittle as-cast structure and compound were formed in the weld. The tensile strength and the shape memory effect （SME） of TiNi-SS joint were strongly influenced by the changes of composition and structure of the weld. Measures should be taken to prevent defects from forming and extruding excessive molten metal in the weld for improving the properties of TiNi-SS joint.

Microstructure-Properties Correlation of Dual Phase Steels Produced by Controlled Rolling Process

The purpose of this research is to quantify the effects of compositional and processing parameters on the microstruc-ture and properties of dual phase steel produced directly by hot rolling and rapid cooling. Steels with the base composition of 0.1%C, 1.4%Si, and 1.0%Mn with additions of 0.5%Cr to influence hardenability, 0.04%Nb to retard recrystallization in the latter stages of rolling, or 0.02%Ti to inhibit grain growth during and after reheating were investigated. Investigation was made to predict microstructure evolution and to correlate microstructure with processing parameters. The effects of the important microstructure parameters such as ferrite grain size, martensite volume fraction (VM) and morphology (polygonal or fibrous) on the tensile and impact properties are discussed. Multiple linear regression analysis of the ultimate tensile strength has shown that, increasing VM and martensite microhardness and grain refinement of ferrite are the major contributions to increase the strength of the steel. It was found that the dual-phase steel produced by controlled rolling process, with a microstructure which consisted of fine grained ferrite (4 um) and 35%~40% fibrous martensite, presented optimum tensile and impact properties because of enhanced resistance to crack propagation.

Austenite Recrystallization and Controlled Rolling of Low Carbon Steels

The dynamic recrystallization and static recrystallization in a low carbon steel were investigated through single-pass and double-pass experiments. The results indicate that as the deformation temperature increases and the strain rate decreases, the shape of the stress-strain curve is changed from dynamic recovery shape to dynamic recrystallization shape. The austenite could not recrystallize within a few seconds after deformation at temperature below 900 ℃. According to the change in microstructure during deformation, the controlled rolling of low carbon steel can be divided into four stages： dynamic recrystallization, dynamic recovery, strain-induced ferrite transformation, and rolling in two-phase region. According to the microstructure after deformation, the controlled rolling of low carbon steel can be divided into five regions： non-recrystallized austenite, partly-recrystallized austenite, fully-recrystallized austenite, austenite to ferrite transformation, and dual phase.

INFLUENCE OF COLD ROLLING REDUCTION ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF TWIP STEEL

The influence of cold rolling reduction on microstructure and mechanical properties of the TWIP （ttwinning induced plasticity） steel was investigated. The results＇ indicated that the steel had better comprehensive mechanical properties when cold rolling reduction was about 65.0% and the annealing temperature was 1000℃. The tensile strength of the steel is about 640MPa and the yield strength is higher than 255MPa, while the elongation is＇ above 82%. The microstructure is composed of austenitic matrix and annealing twins at room temperature, at the same time, a significant amount of annealing twins and stacking faults＇ are observed by transmission electron microscopy （TEM）. Mechanical twins play a dominant role during deformation, and result in exceUent mechanical properties.

MODELING OF FERRITE GRAIN GROWTH OF LOW CARBON STEELS DURING HOT ROLLING

For most commercial steels the prediction of the final properties depends on accurately calculating the room temperature ferrite grain size. A grain growth model is proposed for low carbon steels Q235B during hot rolling. By using this model, the initial ferrite grain size after continuous cooling and ferrite grain growing in coiling procedure can be predicted. In-plant trials were performed in the hot strip mill of Ansteel. The calculated final ferrite grain sizes are in good agreement with the experimental ones. It is helpful both for simulation of microstructure evolution and prediction of mechanical properties.

Controlled Rolling and Cooling Process for Low Carbon Cold Forging Steel

Effect of controlled rolling and cooling process on the mechanical properties of low carbon cold forging steel was investigated for different processing parameters of a laboratory hot rolling mill. The results show that the specimens with fast cooling after hot rolling exhibit very good mechanical properties, and the improvement of the mechanical properties can be attributed mainly to the ferrite-grain refinement. The mechanical properties increase with decreasing final cooling temperature within the range from 670 ℃ to 570 ℃ due to the finer interlamellar spacing of pearlite colony. The specimen with fast cooling after low temperature rolling shows the highest values of the mechanical properties. The effect of the ferrite grain size on the mechanical properties was greater than that of pearlite morphology in the present study. The mechanical properties of specimens by controlled rolling and cooling process without thermal treatment were greatly superior to that of the same specimens by the conventional rolling, and their tensile strength reached 490 MPa grade even in the case of low temperature rolling without controlled rolling. It might be expected to realize the substitution medium-carbon by low-carbon for 490 MPa grade cold forging steel with controlled rolling and cooling process.

Roll System and Stock's Multi-parameter Coupling Dynamic Modeling Based on the Shape Control of Steel Strip

The existence of rolling deformation area in the rolling mill system is the main characteristic which dis- tinguishes the other machinery. In order to analyze the dynamic property of roll system＇s flexural deformation, it is necessary to consider the transverse periodic movement of stock in the rolling deformation area which is caused by the flexural deformation movement of roll system simul- taneously. Therefore, the displacement field of roll system and flow of metal in the deformation area is described by kinematic analysis in the dynamic system. Through intro- ducing the lateral displacement function of metal in the deformation area, the dynamic variation of per unit width rolling force can be determined at the same time. Then the coupling law caused by the co-effect of rigid movement and flexural deformation of the system structural elements is determined. Furthermore, a multi-parameter coupling dynamic model of the roll system and stock is established by the principle of virtual work. More explicitly, the cou- pled motion modal analysis was made for the roll system. Meanwhile, the analytical solutions for the flexural defor- mation movement＇s mode shape functions of rolls are discussed. In addition, the dynamic characteristic of the lateral flow of metal in the rolling deformation area has been analyzed at the same time. The establishment ofdynamic lateral displacement function of metal in the deformation area makes the foundation for analyzing the coupling law between roll system and rolling deformation area, and provides a theoretical basis for the realization of the dynamic shape control of steel strip.

Test research on sticking mechanism during hot rolling of SUS 430 ferritic stainless steel

The sticking phenomenon during hot rolling of SUS 430 ferritic stainless steel was investigated by means of a two-disc type high-temperature wear tester. The test results indicate that sticking particles on the surfaces of high chromium steel （HiCr） and high-speed steel （HSS） rolls undergo nucleation, growth, and saturation stages. Grooves on the roll surface generated by grinding provide nucleation sites for sticking particles. The number of sticking particles on the HiCr roll surface is greater than that on the HSS roll surface. The average surface roughnesses （Ra） of HiCr and HSS rolls change from 0.502 and 0.493 μm at the initial stage to 0.837 and 0.530 μm at the saturation stage, respectively. The test further proves that the sticking behavior is strongly dependent on roll materials, and the HSS roll is more benefi- cial to prevent particles sticking compared with the HiCr roll under the same hot-rolling conditions.

Static and dynamic finite element analysis of 304 stainless steel rod and wire hot continuous rolling process

Three-dimensional finite element models were developed to analyze 304 stainless steel rod and wire hot continuous rolling process with the help of MSC.Marc software. The entire 30-pass deformation process and the actual parameters of production line were taken into account. Static and dynamic procedures were used to study the continuous rolling process with the aid of the thermo-mechanical coupled FEM of elastic-plasticity. The properties of billets, such as deformation, temperature field and rolling force, were mainly discussed. The simulation results of temperature agree well with the measured values. Comparisons of the analysis results obtained using static implicit method and dynamic implicit method were presented. It is shown that static implicit procedure is more accurate than dynamic implicit procedure and is able to simulate the rolling process with a lower speed, such as a roughing mill. Whereas, dynamic analysis shows a higher efficiency than static analysis and is fit for simulating the rolling process with a higher speed, such as a finishing mill.

Mechanism of hot-rolling crack formation in lean duplex stainless steel 2101

The thermoplasticity of duplex stainless steel 2205（DSS2205） is better than that of lean duplex steel 2101（LDX2101）, which undergoes severe cracking during hot rolling. The microstructure, microhardness, phase ratio, and recrystallization dependence of the deformation compatibility of LDX2101 and DSS2205 were investigated using optical microscopy（OM）, electron backscatter diffraction（EBSD）, Thermo-Calc software, and transmission electron microscopy（TEM）. The results showed that the phase-ratio transformations of LDX2101 and DSS2205 were almost equal under the condition of increasing solution temperature. Thus, the phase transformation was not the main cause for the hot plasticity difference of these two steels. The grain size of LDX2101 was substantially greater than that of DSS2205, and the microhardness difference of LDX2101 was larger than that of DSS2205. This difference hinders the transfer of strain from ferrite to austenite. In the rolling process, the ferrite grains of LDX2101 underwent continuous softening and were substantially refined. However, although little recrystallization occurred at the boundaries of austenite, serious deformation accumulated in the interior of austenite, leading to a substantial increase in hardness. The main cause of crack formation is the microhardness difference between ferrite and austenite.

Mechanical performance and texture characteristic of an IF steel containing Nb and Ti by double cold rolling

Single cold rolling and double cold rolling were applied to hot rolled strips with different reduction ratios. The evolutions of { 100}, { 111} and Goss face texture during double rolling were investigated by comparing the orientation distribution function （ODF） of the double rolled sample with that of the single rolled one. The double cold rolling texture is characterized by a higher γ-texture and a lower α-texture, and the { 111}〈112〉 component is improved remarkably. Based on the TEM observation and mechanical properties test, it is found that the reduction ratio assignment significantly affects the texture variation, as-annealing microstructures, and properties of the double cold rolled samples. These results may provide a theoretical guide for the industrial production of double cold rolled IF steel.

Microstructures and mechanical properties of laser-welded TiNi shape memory alloy and stainless steel wires

The Nd ： YAG laser welding was used to join the TiNi shape memory alloy and AISI304 stainless steel wires. The microstructural features of the dissimilar material joint were analyzed. The tensile and hardness tests were carried out to examine the mechanical properties and microhardness distribution of the welded joint. The results show that the joint has the non-homogeneous microstructure and element distribution. The brittle phases such as Fe2 Ti , Fe Ti , Cr2 Ti , Ti3 Ni4, Feo 2 Ni4.s Ti5 and TiN mainly segregate in rich Ti region of fusion zone. The laser-welded joint has the tensile strength of 298 MPa with the elongation of 3.72 % and exhibits the brittle fracture features on the fracture surfaces. The reasons for low joint strength were discussed in this investigation.

Effect of temper rolling on the bake-hardening behavior of low carbon steel

In a typical process, low carbon steel was annealed at two different temperatures （660℃ and 750℃）, and then was temper rolled to improve the mechanical properties. Pre-straining and baking treatments were subsequently carried out to measure the bake-hardening （BH） values. The influences of annealing temperature and temper rolling on the BH behavior of the steel were investigated. The results indicated that the microstructure evolution during temper rolling was related to carbon atoms and dislocations. After an apparent increase, the BH value of the steel significantly decreased when the temper rolling reduction was increased from 0%to 5%. This was attributed to the increase in solute carbon concentration and dislocation density. The maximum BH values of the steel annealed at 660℃ and 750℃ were 80 MPa and 89 MPa at the reductions of 3%and 4%, respectively. Moreover, increasing the annealing temperature from 660 to 750℃ resulted in an ob-vious increase in the BH value due to carbide dissolution.