Analysis on composition and inclusions of ballpoint pen tip steel

Ballpoint pen tip steel, a super free-cutting stainless steel, exhibits excellent corrosion resistance and good machining properties. In this study, inductively coupled plasma spectroscopy, metallographic microscopy, and scanning electron microscopy were used to determine the elemental contents in five ballpoint pen tips and their components, morphologies, and inclusion distributions. The results showed that the steels were all S–Pb–Te super free-cutting ferritic stainless steel. The free-cutting phases in the steels were mainly Mn S, Pb, and small amounts of Pb Te. Mn S inclusions were in the form of chain distributions, and the aspect ratio of each size inclusion in the chain was small. The stress concentration effect could substantially reduce the cutting force when the material was machined. Some of the Pb was distributed evenly in the steel matrix as fine particles（1–2 μm）, and the rest of the Pb was distributed at the middle or at both ends of the Mn S inclusions. The Pb plays a role in lubrication and melting embrittlement, which substantially increases the cutting performance. Pb Te was also usually distributed in the middle and at both ends of the Mn S inclusions, and Te could convert the sulfides into spindles, thereby improving the cutting performance of the steel.

Effects of the width and thickness of slabs on broadening in continuous casting

A 3D viscoelastic-plastic thermal-mechanical coupled finite element model was built on the basis of the secondary development of the commercial software MSC.Marc. Numerical simulations were performed to study slab broadening in the secondary cooling zone. The effects of slab width and thickness on slab broadening were considered. The obtained results reveal that the width broadening is noticeable, and the ratio of ultimate broadening slightly increases with the increase of slab width. This agrees well with the measured data in practice. There is no obvious increase in ultimate broadening when the thickness of slabs increases.

Analysis of precipitation behavior of MnS in sulfur-bearing steel system with finite-difference segregation model

To further reveal the influence of micro-segregation on the precipitation behavior of MnS in sulfur-bearing steel system, a coupled model of micro-segregation and MnS precipitation was established by the finite-difference method based on various calculation domains and the solid diffusion degrees, and a new controlled diffusion equation with more stable convergence was also used. 49MnVS3 and 1215 steels were used to analyze the influence of calculation domain, segregation model and S content on the precipitation behavior of MnS. The calculation results were verified by a high- temperature confocal laser scanning microscope （HT-CLSM）. The results show that the domain has little effect on the precipitation temperature, precipitation solid fraction and precipitation amount of MnS, but affects the precipitation location and segregation of the solutes. For low- and medium-sulfur steels, the temperatures calculated by the diffusion control growth （DCG） model and the Lever model were nearly identical, whereas the temperature calculated by the Scheil model was lower. However, for high-sulfur steels, the precipitation temperatures calculated by three segregation models were nearly same. The precipitation solid fraction is more reasonable to describe the precipitation behavior of MnS. The precipitation behavior of MnS, observed by the HT-CLSM, matches well with that in the DCG model.

Application of fractal theory to study morphology of manganese sulfide inclusion in resulfurized free-cutting steels

The morphology and distribution of manganese sulfide(MnS)inclusions have a significant influence on the comprehensive performance,which is an important research field for resulfurized steels.Based on the experiments of non-aqueous electrolyte and scanning electron microscope observation,the fractal theory was employed to study the three-dimensional morphologies of MnS inclusions.The results showed that the edge fractal dimension of MnS inclusions was between 1.59 and 1.88.In addition,similar morphology of MnS inclusions had a close fractal dimension.The MnS edge fractal dimension is highly positively correlated with the morphological parameters.The multifractal spectrums of MnS inclusions on two-dimensional plane of as-cast and as-rolled resulfurized free-cutting steels were calculated.The large-size MnS inclusions belong to large probability subset,while the small-size MnS inclusions belong to small probability subset.The multifractal spectrum can truly and effectively reflect the difference and non-uniformity of distribution of MnS inclusions on 2D plane.On the premise of similar content of MnS,with the refinement of MnS inclusions,the multifractal spectrum width and the multifractal spectrum symmetry parameter were decreased.The multifractal spectrum provides a new method for studying the second phase in materials.

Reaction mechanism between Al_(2)O_(3)–MgO refractory materials and rare earth high-carbon heavy rail steel

Submerged entry nozzle(SEN)clogging is a major problem affecting the production quality of rare earth steel,and finding a suitable refractory outlet can significantly reduce production costs.To explore the relationship between refractory composition and interface interaction,unprotected coated Al_(2)O_(3)–MgO refractories and SiO2-coated Al_(2)O_(3)–MgO refractories were added to rare earth high-carbon heavy rail steel under laboratory conditions,and the Al_(2)O_(3)–MgO refractory was found to be more suitable.The results show that,from the epoxy resin side to the refractory side,the contour of the refractory interface reaction layer can be divided into two main layers:an iron-rich reaction layer and an iron-poor reaction layer.Calculations based on the spherical model suggest that the adhesion force is proportional to the size of the refractory particles and inclusions,and the same result applies to the surface tension.Controlling the inclusions at a smaller size has a specific effect on alleviating the erosion of refractories.Combined with the erosion mechanism of Al_(2)O_(3)–MgO refractories,the interface reaction mechanism between Al_(2)O_(3)–MgO refractories and molten steel was proposed,which provides ideas for solving SEN clogging.

A method for observing tridimensional morphology of sulfide inclusions by non-aqueous solution electrolytic etching

Three-dimensional investigation of sulfides is required in order to improve the mechanical properties of steel by controlling the sulfides in the steel.A method including its principles and device is introduced for the investigation of threedimensional morphology of sulfides.The method is suitable for gear steel,free cutting steel,non-quenched steel,tempered steel(ws≥0.02 wt.%),etc.The influences of current density,time,and temperature on the exposure degree of sulfide inclusions were investigated by using 16MnCrS5 steel.The best parameters of electrolytic etching of sulfur steel,as found by experimentation,are as follows:current density,37.5-52.5 mA/cm2;time,30-35 min;and temperature,—10 to 0℃.Under these conditions,the three-dimensional morphology of sulfide inclusions in sulfur-bearing steel can be exposed effectively.

Application of tellurium in free-cutting steels

Te is widely used in iron and steel industry. After adding a certain amount of Te in the steel, many physical and chemical properties can be improved. As a free-cutting element, a small amount of Te can significantly improve the machinability of steel. The existing form of Te in the steel, the modification law of MnS inclusion by Te and the influence rule and mechanism of Te on the machinability of steel are summarized and expounded in detail, providing a reference for further study and development of Te-containing free-cutting steels.

Carbon Reduction Programs and Key Technologies in Global Steel Industry

Greenhouse gases, particularly the carbon dioxide, cause global warming and extreme weather, which has become a serious threat to human beings. The steel industry creates enormous amounts of carbon emission and has tremendous potential in carbon reduction. Considering the consistently increasing demand of iron and steel, to obtain significant carbon reduction by reducing the steel production is not practical, thus the development and implementa- tion of carbon reduction programs and technologies is important for the steel industry. Despite the significant poten- tial of carbon reduction in the steel industry, ironmaking and steelmaking processes are complex. Therefore, resear- ches and developments for the carbon reduction must focus on key processes. Here, key processes and technologies adopted in ULCOS program in EU, COURSE 50 program in Japan, POSCO program in South Korea, AISI pro- grams in US and other carbon reduction programs are summarized and evaluated, and feasible suggestions for carbon reduction in developing countries are presented. If effective measures can be referred to and taken in developing coun- tries, global carbon emission can be greatly reduced.

Effect of cooling rate on microstructure and inclusion in non-quenched and tempered steel during horizontal directional solidification

In order to investigate the relationship between microstructure and MnS inclusion in non-quenched and tempered steel, and cooling rate during horizontal directional solidification, 49MnVS steel was used to conduct the experiments with a selfdesigned device. The mathematical effect of cooling rate on dendritic arm spacing and mean diameter of MnS particles (dMnS) were determined by using linear regression method. The results show that the length of dendrite from solid–liquid interface to end-solidification decreased with increasing the withdrawal velocity (#). dMnS has a similar value in the area of the steady directional solidification;the value of dMnS was 4.1, 3.6, 3.3, 2.8 and 2.3 lm at withdrawal velocity of 50, 75, 100, 150 and 200 lm/s, respectively. dMnS increased with reducing # or RC (interface cooling rate). MnS precipitated in the gaps between dendrites and was influenced by secondary dendritic arm spacing. Besides, a new concept of the ‘Precipitation Unit Space’(PUS) was proposed and the relationships between dMnS, VPUS (volume of PUS) and RC were obtained.

Influence of on-line tempering parameters on microstructure of medium-carbon steel

A new process involving ultra-fast cooling（UFC）and on-line tempering（OLT）was proposed to displace austempering process,which usually implements in a salt/lead bath and brings out serious pollution in the industrial application.The optimization of the new process,involving the evolution of the microstructure of medium-carbon steel during various cooling paths,was studied.The results show that the cooling path affected the final microstructure in terms of the fraction of pearlite,grain size and distribution of cementite in pearlite.Increasing the cooling rate or decreasing the OLT temperature contributes to restraining the transformation from austenite to ferrite,and simultaneously retains more austenite for the transformation of pearlite.It is also noted that bainite was observed in the microstructure at the cooling rate of 45℃/s and the OLT temperature of 500℃.Through either increasing the cooling rate or decreasing the OLT temperature,the distribution of cementite in pearlite is more dispersed and grain is refined.Taking the possibility of industrial applications into account,the optimal process of cooling at 45℃/s followed by OLT at 600℃ after hot rolling was determined,which achieves a microstructure containing nearly full pearlite with an average grain size of approximately 7μm and a homogeneously dispersed distribution of cementite in pearlite.

Crystal structure and formation mechanism of the secondary phase in Heusler Ni-Mn-Sn-Co materials

In the present work, crystal structure and for- mation mechanism of the secondary phase in Heusler Ni- Mn-Sn-Co materials were investigated using X-ray dif- fraction, scanning/transmission electron microscopy and selected-area electron diffraction techniques. Experimental results showed that the secondary phase presented in both Ni44.1Mn35.1Sn10.8Co10 as-cast bulk alloy and melt-spun ribbon, possessing a face-centered cubic （fcc） NilTSn3-type structure. The secondary phase in the as-cast bulk alloy was resulted from a eutectic reaction after the formation of a primary dendritic flphase during cooling. However in the melt-spun rapidly solidified ribbon, the secondary phase was largely suppressed as nano-precipitates distributed along the grain boundaries, which was attributed to a divorced eutectic reaction. The secondary phase exhibited partial amorphous state due to high local cooling rate.

Thermomechanical analysis of triangular zone cracks in vertical continuous casting slabs based on viscoelastic-plastic model

The triangular zone cracks in 2101 duplex stainless steel produced by the vertical continuous caster have troubled company A for a long time. To simulate the temperature and thermal stress distributions in the solidification process of 2101 duplex stainless steel produced by the vertical continuous caster, a two-dimensional viscoelastic-plastic thermomechanically coupled finite element model was established by the secondary development of the commercial nonlinear finite element analysis software MSC Marc. The results show that the thermal stress on the surface reaches a maximum at the exit of the mould, and the highest thermal stresses at the centre of the wide face and the narrow face are 75 and 115 MPa, respectively. Meanwhile, the internal temperature of slab is still higher than the solidus temperature, resulting in no thermal stress. The slab shows different high-temperature strengths and suffers from different stresses at different positions; thus, the risk of cracking also varies. At a location of 6-8 m from the meniscus, the temperature of the triangular zone is 1270-1360℃ and the corresponding permissible high-temperature strength is about 10-30 MPa, while the thermal stress at this time is 60 MPa, which is higher than the high-temperature strength. As a result, triangular zone cracks form easily.

Dilatometric Analysis of Irreversible Volume Change during Phase Transformation in Pure Iron

One assumption underlying the conventional dilatometric analysis based on the lever rule is that the volume of the specimen changes isotropically during phase transformation,which conflicts with the irreversible length change shown in actual measurements.The contribution of this irreversible effect to the dilation data of pure iron upon heating and cooling was respectively quantified via conversion equations based on lattice parameters.A model considering the elastic strain and creep deformation was established for both the interpretation of the irreversible volume change and the discrepancy between the results measured by a dilatometer and a micrometer.

Effect of Mg-treatment on transformation of oxide inclusions in X80 pipeline steel

In order to investigate the modification behavior and regularity of inclusions in X80 pipeline steel by Mg-treatment, the comparative industrial experiments of Mg-treatment and Ca-treatment in X80 pipeline steel were carried out. Mg and Ca were added to the steel in the form of cored wire after RH (Ruhrstahl-Hereaeus vacuum degassing) process. After adding Ca-containing cored wire, the inclusions were transformed into CaO–Al_(2)O_(3) in the steel. With the progress of smelting, the cleanliness of molten steel became worse, and the equivalent diameter of inclusions was at a higher level. Mg-treatment had a good effect on the modification of inclusions. After Mg-containing cored wire was added to the steel, Al_(2)O_(3) and CaO–Al_(2)O_(3) in the steel were transformed into MgO, MgO·Al_(2)O_(3), and CaO–MgO–Al_(2)O_(3) inclusions, which were basically spherical. The initial precipitated MgO became the core of other inclusions in the steel, which promotes the precipitation of MgO·Al_(2)O_(3). After Mg-treatment, almost no unmodified calcium aluminate inclusions existed in the hot rolled plate, and the cleanliness of the steel was improved. The effect of Ca and Mg on the transformation of inclusions in pipeline steel was studied by thermodynamic calculation, the result of which is consistent with the experimental results.