Comparison between the surface defects caused by Al_2O_3 and TiN inclusions in interstitial-free steel auto sheets

Al_2O_3 and TiN inclusions in interstitial-free(IF) steel deteriorate the properties of the steel. To decrease the defects of cold-rolled sheet, it is important to clearly distinguish between the degrees of damage caused by these two inclusions on the surface quality of the steel. In this study, a nanoindenter was used to test the mechanical properties of the inclusions, and the distribution and size of the inclusions were obtained by scanning electron microscopy(SEM). It was found that when only mechanical properties are considered, TiN inclusions are more likely to cause defects than Al_2O_3 inclusions of the same size during the rolling process. However, Al_2O_3 inclusions are generally more inclined to cause defects in the rolling process than TiN inclusions because of their distribution characteristic in the thickness direction. The precipitation of Al_2O_3 and TiN was obtained through thermodynamical calculations. The growth laws of inclusions at different cooling rates were calculated by solidification and segregation models. The results show that the precipitation regularity is closely related to the distribution law of the inclusions in IF slabs along the thickness direction.

Effect of continuous annealing temperature on microstructure and properties of ferritic rolled interstitial-free steel

In this report,the microstructure,mechanical properties,and textures of warm rolled interstitial-free steel annealed at four different temperatures(730,760,790,and 820°C)were studied.The overall structural features of specimens were investigated by optical microscopy,and the textures were measured by X-ray diffraction(XRD).Nano-sized precipitates were then observed by a transmission electron microscope(TEM)on carbon extraction replicas.According to the results,with increased annealing temperatures,the ferrite grains grew;in addition,the sizes of Ti_4C_2S_2 and Ti C precipitates also increased.Additionally,the sizes of Ti N and Ti S precipitates slightly changed.When the annealing temperature increased from 730 to 820°C,the yield strength(YS)and the ultimate tensile strength(UTS)showed a decreasing trend.Meanwhile,elongation and the strain harden exponent(n value)increased to 49.6%and 0.34,respectively.By comparing textures annealed at different temperatures,the intensity of{111}texture annealed at 820°C was the largest,while the difference between the intensity of{111}<110>and{111}<112>was the smallest when the annealing temperature was 820°C.Therefore,the plastic strain ratio(r value)annealed at 820°C was the highest.

Study on grain refinement of interstitial-free steel during continuous frictional angular extrusion

To explore the application of severe plastic deformation for grain refinement in steel production, a new method called continuous frictional angular extrusion （CFAE） was applied to refine the grain of interstitial-free steel. The deformation was carried out at room temperature and individual sheet specimens were processed in different number of passes. An overall grain size of 200nm was achieved after 8 passes and the proportion of high-angle boundaries to the total boundaries was more than 60%. Through the characterization of high resolution EBSD, X-ray diffraction （XRD） and hardness testing,this paper discussed the evolution of microstructures and textures during deformation and explored the development direction of the method.

Microstructure and Property Relationships in Resistance Spot Weld between 7114 Interstitial Free Steel and 304 Austenitic Stainless Steel

Due to the differences in physical, chemical and mechanical properties of the base metals, the resistance spot welding of dissimilar materials is generally more challenging than that of similar materials. The influence of the primary welding parameters affecting the heat input such as peak current on the morphology, microhardness, and tensile shear load bearing capacity of dissimilar welds between 304 grades austenitic and 7114 grade interstitial free steel has been investigated in this study. The optimum welding parameters producing maximum joint strength were established at a peak current of 9 kA, where the electrode force is kept 6×10^-5 Pa and weld time is kept constant 17 cycles, respectively. The primary cause of weakening the weldment is identified as the excessive grain growing region of heat affected zone （HAZ） in case of 7114 grade interstitial free steel.

Texture evolution during semicontinuous equal-channel angular extrusion process of interstitial-free steel

Semicontinuous equal-channel angular extrusion（ SC-ECAE） is a novel severe plastic deformation technique that has been developed to produce ultrafine-grain steels. Instead of external forces being exerted on specimens in the conventional ECAE,driving forces are applied to dies in SC-EACE. The deformation of interstitial-free（ IF） steel w as performed at room temperature,and individual specimens w ere repeatedly processed at various passes. An overall grain size of 0. 55 μm w as achieved after 10 passes. During SC-ECAE,the main textures of IF steel included { 111} ,{ 110} ,{ 112} ,{ 110} ,and { 110} At an early stage,increasing dislocations induce new textures and increase intensity. When the deformation continues,low-angle boundaries are formed betw een dislocation cell bands,w hich cause some dislocation cell bands to change their orientation,and therefore,the intensity of the textures begins to decrease. After more passes,the intensity of textures continues to decrease w ith high-angle boundaries,and the sub-grains in dislocation cell bands continuously increase. The present study reports the evolution of textures during deformation; these w ere examined and characterized using high-resolution electron backscattered diffraction（ EBSD） in a field emission scanning electron microscope. The mechanisms of texture evolution are discussed.

Process for improving the ladle free- opening rate for high aluminum steel in continuous casting

Steel 20Mn23AlV is a type of high aluminum steel with a very low ladle free-opening rate. The aluminum composition of 20Mn23AlV ranges from 1.6% to 2.45% ,which is significantly higher than other types of steel. According to the real condition of 40 t ladle in steel-making plant of Baosteel Special Steel Company, previous works show that the key factors affecting the ladle free-opening rate of high aluminum steel in continuous casting are：sand material, accessories baking, ladle nozzle cleaning, the process and amount of adding sand, and the rate of argon stirring during refining. Therefore, improving the ladle filler sand quality, baking all of the raw materials, controlling the addition of ladle filler sand, cleaning the ladle nozzle, and optimizing argon stirring during the refining process can resolve the problem of a low ladle free-opening rate of high aluminum steel caused by the long ladle time of liquid steel.

Chrome free surface treatments for galvanized steels—present and future

As the galvanized steels used for electrical and office appliances has achieved a complete chrome-free production worldwide,surface treatment technologies have entered a new phase of development.Grenter effort will be made in exploring new frontier for future surface treatment technologies.A greater contribution will be made for environmental protection,energy-saving and resource-saving,to prevent globalwarming.

Nickel-free Stainless Steel for Medical Applications

BIOSS4 steel is essentially a nickel-free austenitic stainless steel developed by the Institute of Metal Research, Chinese Academy of Sciences, in response to nickel allergy problems associated with nickel-containing stainless steels that are widely used in medical applications. The high nitrogen content of this steel effectively maintains the austenitic stability and also contributes to the high levels of corrosion resistance and strength. BIOSS4 steel possesses a good combination of high strength and toughness, better corrosion resistance, and better blood compatibility, in comparison with the medical 316L stainless steel. Potential applications of BIOSS4 steel can include medical implantation material and orthodontic or orthopedic devices, as well as jewelries and other decorations.

Simulation of the continuous casting process in a mold of free-cutting steel 38MnVS based on a MiLE method

A new method called mixed Lagrangian and Eulerian （MiLE） method was used to simulate the continuous casting process in a mold of free-cutting steel 38MnVS.The simulation results are basically in agreement with experimental data in the literature,achieving the three-dimensional visualization of temperature distribution,melt flow,shell thickness,and stress distribution of blooms in a mold.It is shown that the flow velocity of steel melt becomes smaller gradually as the casting proceeds.When the flow reaches a certain depth,two types of flow patterns can be observed in the upper zone of the mold.The first flow pattern is to flow downwards,and the second one is to flow upwards to the meniscus.The corner temperature is higher,and the thickness is thinner than those in the mid-face.The effective stress in the corner area is much bigger than that in the mid-face,indicating that the corner area is the dangerous zone of cracking.

Analysis of free vibration characteristic of steel-concrete composite box-girder considering shear lag and slip

Based on Hamilton principle,the governing differential equations and the corresponding boundary conditions of steel-concrete composite box girder with consideration of the shear lag effect meeting self equilibrated stress,shear deformation,slip,as well as rotational inertia were induced.Therefore,natural frequency equations were obtained for the boundary types,such as simple support,cantilever,continuous girder and fixed support at two ends.The ANSYS finite element solutions were compared with the analytical solutions by calculation examples and the validity of the proposed approach was verified,which also shows the correctness of longitudinal warping displacement functions.Some meaningful conclusions for engineering design were obtained.The decrease extent of each order natural frequency of the steel-concrete composite box-girder is great under action of the shear lag effect.The shear-lag effect of steel-concrete composite box girder increases when frequency order rises,and increases while span-width ratio decreases.The proposed approach provides theoretical basis for further research of free vibration characteristics of steel-concrete composite box-girder.

Strain rate and cold rolling dependence of tensile strength and ductility in high nitrogen nickel-free austenitic stainless steel

The tensile strength and ductility of a high nitrogen nickel-free austenitic stainless steel with solution and cold rolling treatment were investigated by performing tensile tests at different strain rates and at room temperature. The tensile tests demonstrated that this steel exhibits a significant strain rate and cold rolling dependence of the tensile strength and ductility.With the increase of the strain rate from 10^-4s^-1to 1 s^-1, the yield strength and ultimate tensile strength increase and the uniform elongation and total elongation decrease. The analysis of the double logarithmic stress–strain curves showed that this steel exhibits a two-stage strain hardening behavior, which can be well examined and analyzed by using the Ludwigson equation. The strain hardening exponents at low and high strain regions（n2and n1） and the transition strain（εL） decrease with increasing strain rate and the increase of cold rolling RA. Based on the analysis results of the stress–strain curves, the transmission electron microscopy characterization of the microstructure and the scanning electron microscopy observation of the deformation surfaces, the significant strain rate and cold rolling dependence of the strength and ductility of this steel were discussed and connected with the variation in the work hardening and dislocation activity with strain rate and cold rolling.

Influence of Ca/S and Rolling Reduction on Shape of Sulphide in Free-cutting Steel 5NiSCa

1.IntroductionThe shape of sulphide has a great influ-ence on machinability and transverse prop-erty of steel.It is very important to obtainoval sulphide instead of elongated one forimproving machinability and transverseproperties[1,2].

Experimental Study and Thermodynamical Calculation on the Formation of Eutectic Phase of MnS-RE_2S_3 and(Mn,Ca)S-RE_2S_3 in Sulfur-Containing Free-Cutting Steel

The free-cutting phase in RE or Ca-RE treated sulfur-containing free-cutting steel is the eutectic phases of MnS-RE_2S_3 and (Mn,Ca)S-RE_2S_3,respectively.The atomic ratio of RE/S needed to modify all the MnS into the eutectic phase is higher than 1.48 or 1.41-1.37 Ca/S,when RE or Ca-RE is used as the modifiz- er in the sulfur-containing free-cutting steel.Moreover,the thermodynamical calculation shows that the eutectic temperature is lower than the solidifying temperature,which is the key condition for the eutectic phase to keep globual during solidifying.

Information Construction Technology of Free-Form Surface Steel Grid

Taking the construction project of National Network Security Talents and Innovation Base Exhibition Center as an example,the application of building information model in the construction process of free-form surface steel structure is analyzed in this paper.The results show that the application of Building Information Modeling(BIM)technology to the construction of free-form surface structure improves the work efficiency of the construction team in multi-disciplinary collaboration,surface component manufacturing,and construction process design,and subsequently improves the construction speed and construction quality.

Manufacture and application of a Cr-free insulation coat for non-oriented silicon steel sheets

The manufacturing techniques of a Cr-free coat for non-oriented silicon steel sheets with excellent magnetic properties were developed. The ingredients of the coat mainly include phosphate, epoxy resin, an amine solidified agent and water. Through the adjustment of ingredients, superior adhesiveness, corrosion-resistance performance, welding performance and stamping preformance have been obtained. Thus ,the non-oriented silicon steel sheets with the above Cr-free coat have been used successfully in the fields of compressors ,transformers, and small and medium motors.

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.

Development and application of fluorine-free mold powder for low carbon steel

Fluorine in mold powder is known as harmful to human health and the environment. Being the advocate of green production, Baosteel developed an environmentally friendly mold powder without fluorine. The main problem of fluorine-free flux film is small heat resistance and thus the heat transfer intensity of the mold is too large, which to some extent hinders the increase of the casting speed. With the heat flow simulation equipment, controlling precipitation of crystal in flux and solidification temperature properly, fluorine-free mold powder for low carbon steel,which substitutes F with B203 ,was successfully developed and applied in industrial production. The production results show that, by using boronic fluorine-free mold powder,the boron increment in molten steel is less than 1.3ppm for conventional aluminium killed low carbon steel.

Manufacturing of T300 cobalt-free maraging steel and its tensile property

The 18Ni 300 grade cobalt-free maraging steel T300 was successfully manufactured on an industrial scale by application of vacuum induction melting （VIM） and vacuum arc remelting （VAR） process at Baosteel. With the content of O and N less than 15 ppm and 10 ppm respectively （ 1 ppm = 10 -6 ） ,the T300 steel produced by Baosteel obtained a high degree of purity and a good combination of ultra-high strength and fracture toughness. The effects of solution temperature and ageing temperature on tensile property of solution-treated and aged T300 steel were investigated. The results show that the solution temperature slightly influences the strength of the solution-treated steel, indicating that the solution strengthening rather than the grain boundary strengthening is more important to the solution-treated steel. For the solution-treated T300, the elongation and reduction of area don＇t change much with a rising solution temperature, and remain above 17% and 70% respectively at the solution temperature ranging from 800℃ to 1200℃. For the aged T300 steel,the strength and elongation are reduced with an increasing solution temperature, and the solution temperature has a greater effect on the reduction of area than that on the elongation. The reduction of area of the aged steel reaches a high peak when the solution temperature reaches 920℃. The experimental data indicates that precipitation strengthening makes a contribution of l 100 MPa to the tensile strength of the aged steel. The ageing temperature exerts a greater effect on the strength than on the elongation and reduction of area. The steel achieves a better combination of strength and toughness at the peak ageing temperature of 500℃.

Growth of Free-Standing Diamond Films on Stainless Steel

Free-standing diamond films have been successfully deposited on stainless steel substrates using microwave plasma-assisted chemical vapor deposition. Although iron, which is the main element of stainless steel, is known to inhibit the nucleation of diamond and enhance the formation of graphite, we were able to grow relatively thick films （-1.2 mm）. The films were easily detachable from the substrates. The poor adhesion made it possible to obtain free-standing diamond films without chemical etching. Raman spectroscopy showed the 1332 cm^-1 characteristic Raman peak of diamond and the 1580 cm^-1, 1350 cm^-1 bands of graphite on the growth surface and backside of the films, respectively. By energy dispersive X-ray spectroscopy it was only possible to detect iron on the back of the films, but not on the surface. The role of iron in the film growth is discussed.

Influence of cold deformation on microstructure,mechanical properties,and corrosion resistance of high-sulfur free-cutting 316LS stainless steel

In this study,the influence of plastic deformation produced by cold rolling at reduction ratios ranging from 10% to 80% on the microstructure,mechanical properties,and pitting corrosion behavior of high-sulfur freecutting 316 LS austenitic stainless steel was investigated. The results indicate that slipping is the predominant effect and that sulfide inclusions extend along the rolling direction during the cold deformation of 316 LS. The strong austenite stability of 316 LS results in the formation of only a small quantity of deformation-induced martensite. The experimental results reveal that the strength,hardness,and yield ratio increased with increases in the reduction ratio,mainly due to work hardening,whereas the elongation decreased drastically,due to the combined effect of the work hardening and brittleness caused by the numerous sulfide inclusions. Electrochemically active sites on the surface of316 LS increased with an increased reduction ratio,which caused an increased current fluctuation in the passive zone. This also caused the breakdown potential（ E_b） near the pitting zone to exhibit a gradual increase in the zigzag current shift to the left on the polarization curves. The E_b of 316 LS decreased with increases in the reduction ratio,mainly due to the extended sulfide inclusions,the increased dislocation density,and the deformation-induced martensite content.