A Physical Core-Loss Model for Laminated Magnetic Sheet Steels

A full-frequency instant core-loss equation built from the induction physical model of magnetic materials, where the iron loss, eddy loss, and hysteresis loss no longer have an integral term, and this new equation provides high simulation accuracy and performs dynamic core loss analysis on non-sinusoidal or pulse magnetic fields. The simulation examples use a high-grade electrical steel sheet 65CS400 by Epstein experimental data covering magnetic field 0.1 - 1.8 T and frequency 50 - 5000 Hz, and the average error of the simulated core loss is less than 4%. Since the simulation is converged by magnetic physical parameters, so the physical relevance of the similar laminated materials can be compared with the coefficient results. .

Investigation of Surface Damage in Forming of High Strength and Galvanized Steel Sheets

Powdering/exfoliating of coatings and scratching galvanized steels and high strength steels （HSS）, are the main forms of surface damage in the forming of which result in increased die maintenance cost and scrap rate. In this study, a special rectangular box was developed to investigate the behavior and characteristics of surface damage in sheet metal forming （SMF） processes. U-channel forming tests were conducted to study the effect of tool hardness on surface damage in the forming of high strength steels and galvanized steels （hot-dip galvanized and galvannealed steels）. Experimental results indicate that sheet deformation mode influences the severity of surface damage in SMF and surface damage occurs easily at the regions where sheet specimen deforms under the action of compressive stress. Die corner is the position where surface damage initiates. For HSS sheet, surface damage is of major interest due to high forming pressure. The HSS and hot-dip galvanized steels show improved ability of damage-resistance with increased hardness of the forming tool. However, for galvannealed steel it is not the forming tool with the highest hardness value that performs best.

Analysis of edge microstructural characteristics and stamping formability of low carbon pickled steel sheets

The microstructural characteristics and formability at the edges of low carbon pickled steel sheets have been investigated based on the generation of earing and cracking defects while drawing. The microstructure of the edge features coarse grains and mixed sized grains. The strength of the sheet edge is slightly lower than that at the center. Besides, the formability is obviously worsened. The plastic strain ratios along the longitudinal and transverse orientations are 0.31 and 0.6, respectively, with distinct anisotropy. The plastic strain ratio at the edge is obviously lower than that at the middle of the steel sheet. The observed microstructural characteristics and mechanical properties at the edge of the steel sheet can be attributed to the lower rolling temperature in the two-phase region of pro-eutectoid ferrite and austenite. These differences in microstructure and mechanical properties at the edge of the steel sheet lead to the generation of earing and cracking defects while drawing. The microstructure and mechanical properties at the edge of low carbon pickled steel sheets can be improved via the optimization of the rolling process and the adjustment of chemical composition.

Laser brazing with filler wire for galvanized steel sheets

The process properties and interface behavior of CO_2 laser brazing with automatic wire feed for galvanized steel sheets were investigated, in which the brazing filler metal was CuSi3 and no flux was used. As to the appearance quality of the brazing seams, the roles of the processing parameters, such as brazing speed, wire feeding rate, inclination and feeding direction of the wire, laser power, spot diameter and heating position, were assessed. The further investigation indicates that the behavior of the active elements Si, Mn and Zn are significantly influenced by energy input. At the interface, the microstructure of the base metal was composed of columnar crystals and the acicular α solid solution was found on the filler metal side.

Recent Developments in the Study on Oriented Silicon Steel Sheets

Over the past several decades, the texture, properties and manufacture of quality silicon steels have been investigated for application in magnetic devices requiring magnetically soft materials, such as transformers, inductive devices, etc. Most recently, the factors effecting the texture and magnetic properties, e.g. impurities, rolling process and annealing process, have been greatly studied. The benefits of this study are that low core loss silicon steels with stable high-performance can be obtained through an economic production process. This review is intended to summarize the recent developments in the texture, properties, manufacture and application of oriented silicon steel sheets.

Dynamic simulation of resistance spot welding of zinc-coated steels

A model was developed to simulate the temperature distribution and nugget formation during resistance spot welding （ RS1V） of zinc-coated steels. It employs a coupled thermal-electrical-mechanical analysis simulating the dynamic RSW process. Temperature-dependent thermal-electrical-mechanical material properties were considered including contact-resistance. The contact area was determined from a coupled thermal-mechanical analysis. A layer of transition elements was used to represent the change of contact area by killing or activating elements. The heat generation and temperature field were computed in a coupled thermal-electrical model. All these analyses were solved using the commercial finite element method （FEM） based on ANSYS code, and some advanced functions were used by writing a paragraph of codes by the authors. Compared with the results from only coupled thermal-electrical model in which contact area was uniform during the whole process, the result matches better to the experimental results.

Properties,Microstructures and Precipitate Morphology of Hot-rolled Interstital-Free(IF)Steel Sheets

In order to simplify production process and to decrease production cost of thicker cold-rolled iF steel sheets for deep drawing applications, a new hot-rolled IF steel sheet is developed through hot-rolling in or region. In this paper, properties, microstructures and precipitate morphology of hot-rolled iF steel sheets are described..

Effect of surface roughness on the surface lubrication performance of galvanized steel sheets with a self-lubricated coating

Four kinds of galvanized steel sheets having different surface roughness values were used to prepare the steel sheets with a self-lubricated coating. The effects of surface roughness on the surface lubrication performance of the steel sheets were examined using a friction coefficient tester. Results revealed large dynamic friction coefficients for the galvanized steel sheets, which increased remarkably with surface roughness. Once the self-lubricated coating was applied, significant drops in the dynamic friction coefficients were measured. After the first stage of the friction test,the coefficients were almost unchanged, which reflected a weak dependence on the surface roughness of the self-lubricated steel sheets. However, the dynamic friction coefficients gradually increased as the test progressed, where these increase clearly correlated with the surface roughness of the self-lubricated steel sheets.

Study on the formation of intermetallic phases in the new type of Zn-Mg coatings on steel sheets

Zn-Mg alloy coatings were obtained by physical vapor deposition （PVD） on electroplated steel sheets. Study on the formation of intermetallic phases in the coatings was conducted through the use of X-ray diffraction （XRD） ,scanning electron microscope （SEM） and glow discharge optical emission spectrometry （GDOES）. It is found that MgZn2 is the main Zn-Mg alloy phase formed after heat treatment. The formation of Mg-Zn intermetallic phases is controlled not only by thermodynamics, but also by kinetics. MgZn2 has different morphologies, such as laminar structure,porous structure and floc-like structure,which are mainly determined by the annealing temperature. Obvious diffusion of Mg starts at 350 ℃, and the diffusion of iron increases significantly when the temperature is elevated to 380℃.

Effects of Cover Sheets on the Nugget Growth and Fracture Behavior of Resistance Spot Welded Q&P980 Steel Joints

The resistance spot weldability of galvanized ultra-high-strength steels is not satisfed,the joints are prone to interfacial fracture and the weldable current range is narrow.To solve the problems,a novel method called resistance spot welding with double-sided cover sheets was introduced to weld a galvanized Q&P980 steel with the thickness of 1.2 mm.Two thin SPCC mild steel sheets were chosen as cover sheets and were placed symmetrically at both sides between the Q&P980 steels and the electrodes,then the RSW process was carried out.Compared with the traditional RSW method,the joints obtained by using the novel method achieved larger tensile shear strength and energy absorption,which increased by 26.9%and 52.6%,respectively.With increasing the welding current,the failure mode transferred from interfacial fracture to nugget pull-out fracture or base metal tearing fracture.By contrast,the joints always showed interfacial fracture without cover sheets.The improvement of the joint performance was mainly attributed to the enlargement of the nugget.With the help of fnite element simulation,it was found that the cover sheets helped increase the contact area and reduced the current density during welding,which postponed the expulsion,and a larger area could be evenly heated.The application of the novel method can be easily extended to the resistance spot welding of other ultra-high-strength steels with various thicknesses.

Bonding Characteristics and Flexural Stiffening Effect of Carbon Fibre Reinforced Plastics Strand Sheets Bonded to Steel Beams

Corrosion of steel structures is unavoidable and the structural performance decreases dramatically due to the corrosion. As a repairing method for corroded steel members, bonding carbon fiber sheets with resin had been developed. The purpose of this study is to propose the flexural strengthening method for steel members by using CFRP （carbon fiber reinforced polymer） strand sheets. In order to clarify the stiffening effect and the debonding characteristics of CFRP strand sheets, and to optimize the strengthening design specifications, the flexural tests using high tension steel beams strengthened with CFRP strand sheets are performed. Two cases of experiments are carried out. In Experiment 1, the result from previous research is reflected in the strengthening design. Moreover in Experiment 2, the debonding characteristics obtained from Experiment 1 are reflected. As a result, it was clarified that CFRP strand sheets have stiffening effect equivalent to the theoretical value and its debonding property is practically high enough when FRP （fiber reinforcement polymer） sheets have an appropriate bonding length.

The production and practice of cold-rolled steel sheets for automobile

Shougang Group has carried out a strategic structure adjustment in order to realize the promise of Chinese people to the Olympic Games.Automotive sheets are chosen as a type of strategic product and an engine to upgrade enterprise management,technology and operation to reach the top international level during the transition from long products to steel sheets in Shougang Group.Since 2006,Shougang Group has made an elaborate preparation on steel sheet culture,production line construction,technology import,pilot plant and talent reserve.It lays the foundation for the development of automotive sheets.The developing history of cold rolled automotive sheets is reviewed and the research and development of cold rolled automotive sheets, tackling key problem of defect on surface and the latest progress of automotive sheets construction are described in this paper.The main contents were given as follows:①The products of automotive sheets realize zero breakthrough in Shougang Group.Monthly output was 300 ton in January,2009 and it increased to 48 000 ton in June,2010.The ratio of IF steel sheets increases to 70%from 40%.The proportion of outside panel in automotive sheets occupys more than 15%.②A high emulational pilot plant is used as a product developing platform to develop successfully automotive sheets with 1 000 MPa and below.It guarantees that the industrial development of DP and TRIP sheets gets success at a time.It covers continuous annealing sheets with tensile strength≤780 MPa and galvanizing sheets with tensile strength≤590 MPa.③Individual design is used to meet special requirement of customer.Shougang owns 23 inner brands of LCAK and IF steels.It insures that the grades of yield strength cover whole range from 120 to 270 MPa.It keeps the stabilization of steel performance by means of chemical composition control and high accuracy rolling technology.For example,the strength of soft steel fluctuates within±15 MPa.④The steel sheets with surface grade O5 are produced steadily by solving forming striation of IF steel,grain coarse on surface,edge curling skin and mountains - and - waters painting defects.⑤The safeguard mechanism on quality of products is improved steadily and the output of automotive sheets and outside panel increases greatly by building consistency quality management system、information - system and customer service system.

Dislocation Densites of Deformed Steel Sheets Based on Positron Annihilation

The variation regularity of dislocation densites of some deformed steel sheets under three kinds of strainpaths as uniaxial tension, plane strain and equal biaxial stretching was investigated by means of positron lifetimespectrum and Doppler-broadening techniques. The results show that the increasing rate of dislocation densites isrelated to the plastic strain path. A relationship between the increasing rate of micro-defects, macro-instability andforming limits during the process of steel sheet forming was got based on analyzing the mechanism of dislocationdensity increasing under different stress-strain condihons.

The corrosive behaviors of GI and IF steel sheets in salt water drops

The corrosive behaviors of hot-dip galvanized steel （G I） sheets and the corresponding interstitial free （IF） steel base sheets for use in automobiles were investigated by the classical salt water drop （SWD） test at room temperature. The corrosive processes and products were observed and analyzed through morphological observation, a scanning electronic microscope （SEM） and an energy dispersive spectrum （EDS）. The results show that the anodic and cathode sites can be distinguished clearly during and after the test. The propagation of rusting, and the color, distribution and composition of the final corrosive products of the two kinds of materials are quite different. The SWD corrosive mechanisms of steel with and without galvanized coating are both discussed in this paper.

Characteristics and application of Baosteel's Cr-free ultrathick J coat for non-oriented silicon steel sheets

Baosteel＇ s Cr-free ultrathick J coat for non-oriented silicon steel sheets has excellent insulation performance and has been successfully applied to middle and large scale electric power trains and wind electric power devices, which have stricter requirements than typical for coat insulation. In this paper, the characteristics and application of this type of coating for non-oriented silicon steel sheets were described in detail.

Effect of annealing parameters on mechanical properties of cold-rolled martensitic steel sheets

Cold-rolled martensitic steel sheets produced on continuous annealing lines with water quenching facility,have advantages of high strength and low alloying element contents.These are in good accordance with the trend of light-weighting and fuel saving for automotive steel.In this article,a cold-rolled martensitic steel is studied to investigate the effect of annealing parameters on its mechanical properties.It is found that the quenching temperature and the slow cooling speed as well as the overageing temperature have significant influence on the strength of the experimental steel.The temperature zone at which the austenite decomposition is slow or has not started may be chosen as the quenching temperature to ensure the steel’s strength stability.The slow cooling speed also influences the steel’s strength greatly.A high cooling rate will lead to significantly higher strength.Tempering would decrease the steel’s tensile strength but would increase its yield strength.

Development and application of Baosteel's cold-rolled martensitic steel sheets

Cold-rolled martensitic steel sheets are becoming widely applied in the automotive industry because of their ultra-high strength,which may result in satisfactory weight reduction. The grades of martensitic steel sheets are classified based on their tensile strength,which ranges from 980 to 1 700 MPa. The main applications include a series of structural parts of uniform cross-section or simple shape,such as bumper beams,door beams and door sills,etc. The study and development of cold-rolled martensitic steel sheets date back to 2007 in Baosteel,and some grades became commercially available in 2009. By 2015,Baosteel had commercially supplied thousands of tons of these steel sheets with tensile strength up to 1 400 MPa. Currently,1 500 MPa martensitic steel sheet is commercially available and 1 700 MPa martensitic steel sheet has been successfully produced. The process technology and application guides of Basoteel ＇s cold-rolled martensitic steels are summarized and analyzed in order to assist ongoing research and ensure correct applications of these ultra-high strength steel sheets.

Reinforcing Effect of CFRP Strand Sheets on Steel Members

The steel structure is corroded by various mechanisms, and thus its performance decreases. As a repairing method of the corroded steel member, a method in which carbon fiber sheets is bonded to the steel member with glue has been studied. In recent years, as more efficient repairing method using FRP materials, the strand sheet bonding which has high mass per unit area has been developed. The purpose of this study is to propose the repairing method for corroded steel member by using the strand sheets. In order to confirm a reinforcing effect, the tensile and flexural tests using steel plates and girders reinforced with strand sheets were performed. Test results showed effectiveness of strand sheets for the reinforcement of the steel members.

Biodiesel Resistance of Thin Resin Cr-Free Steel Sheets for Fuel Tank

The content of biodiesel mixed with diesel fuel were compared to inspect the fuel resistance of thin resin Cr-free steel sheets, which are widely used as steel sheets of automobile fuel tank. Some additives which can be presented during the process of biodiesel preparation were added for CCT (Cyclic Corrosion Test). These additives can accelerate the occurrence of corrosion. The corrosion was appeared on the coating and painting layer and in serious cases even substrate material was corroded. For methanol, mixing with blended fuel showed the reduction in corroded area as the additive concentration was reduced in the mixed fuel. Especially the peroxide hydrogen showed the strongest corrosiveness. It is known that formic acid has a tendency of weaker corrosiveness than peroxide hydrogen, but the corrosion is occurred throughout the specimen. Water is not mixed well with fuel, and does not seem to impact on corrosion significantly. However, water is easily mixed with other additives and is considered to facilitate the corrosion by other additives.

Effect of Hot Processing Technology on Mechanical Properties and Structure of Interface of Ti/Steel Composite Sheet

研究了热加工工艺对钛-钢复合板界面力学性能和显微组织的影响。测试了在A，B，C，D4种温度下热轧复合板界面的力学性能，用金相显微镜及扫描电镜观察了界面显微组织并分析了界面的成分。结果表明，在A，B2种温度下轧制的钛-钢复合板界面机械性能良好，延伸率高，其剪切强度不但可保持坯料原有的水平，甚至还略有增加。在C，D2种温度下轧制的钛-钢复合板界面机械性能相对较低，延伸率较高，但剪切强度要比爆炸复合坯料低，尤其是D加热温度，轧制后界面剪切强度急剧下降。热轧的终轧温度也是影响钛-钢复合板界面结合性能的重要因素。在低于相转变温度的合适温区热轧，且终轧温度合适，获得的钛-钢复合板结合界面无爆炸波纹，没有污染，生产的脆性化合物极细小，组织类同于钛材完全退火的等轴组织。