Study on Control Technology of Slag Composition for Low-Sulfur and Low-Oxygen Steel

In order to reduce the content of oxygen and sulfur in steel, and produce low-sulfur and low-oxygen steel, study on slag has been carried out. Refining slag system of CaO-SiO2-Al2O3 is put forward with the consideration of slag amount from converter, oxidizability of slag and activity of oxygen in molten steel. On this basis, refining slagging system for low-sulfur and low-oxygen steel has been developed combined with the modification of slag from converter and composition control of refining slag in LF treatment process. The results show that oxygen content is not more than 15×10-6, as well as sulfur content is as low as 0.005% in tube blank steel. And it achieves the production of low-sulfur and low-oxygen steel.     

Oxygen and Iron-and Steelmaking:Best Friends and Arch-Enemies

Ironmaking is the art of removal the arch-enemy oxygen from iron ore by means of carbon reduction and thus producing hot metal.Steelmaking is the art of removing carbon from liquid hot metal by means of best friend pure oxygen,followed by alloying and deoxidation-where oxygen returns to be the arch-enemy.Non-metallic particles in steel such as oxides can have a detrimental effect on the steel product properties in terms of formability,strength and surface properties.An overview of the battle for clean steel production is given based on the experience of the author in industry as well as university research.     

Effect of Niobium on Transformations From Austenite to Ferrite in Low Carbon Steels

Niobium has an important effect on the transformation behaviour,grain size refinement and precipitation strengthening during hot rolling and subsequent cooling in low carbon steels,with even a low content of niobium having a strong effect on the transformation rate from austenite to ferrite.However,the effects of niobium on transformation behaviour have not been fully characterised and understood to date.This paper examines in detail austenite grain growth as a function of austenitisation time in high strength low alloy (HSLA) steels with three different niobium contents,together with the effect of niobium on the isothermal transformation kinetics from austenite to ferrite as a function of temperature.It is shown that austenite has the slowest grain growth rate in the steel with the highest niobium content.When austenite grain sizes are consistent,the steel with the highest niobium content was found to have the slowest transformation rate from austenite to ferrite.     

Simulation of Case Depth of Cementation Steels According to Fick＇s Laws

 The carburizing process is the enrichment of the depth of low carbon steels with carbon. It leads to samples with a combination of high surface hardness and high core toughness and to an impact strength that is required for many engineering parts. The material studied is a low carbon steel. The carbon content is little in this type of steel (wC=0.2%). The calculation of case depth is very important for cementation steels that are hardened in the carburizing process. The effective case depth is defined as the perpendicular distance from the surface to a place at which the hardness is HV 550. Nowadays, a great number of studies have been carried out on the simulation of effective case depth, but no studies have been conducted to determine the numerical relation between the total case depth on one hand and the carburizing time and the effective case depth on the other hand. The steel specimens were subjected to graphite powder. Then, they were heat treated at 925 ℃ for about 3, 5, 8 and 12 h, respectively. Then, these parts were quenched in oil. To determine the effective case depth, the microhardness test was performed on the cross-section of specimens. Plotting the case depth vs carburizing time, the required conditions for obtaining the specified case depth were determined. Also, the comparison between the case depths in numerical solution and the actual position in pack carburizing was performed.     

HCWCI/Carbon Steel Bimetal Liner by Liquid-Liquid Compound Lost Foam Casting

 Impact, friction and corrosion from the grinding balls and the grinding medium during the mineral processing result in liner breakage. Liner, made from Hadfield steel or alloyed steel, could not have served in wet grinding environment for more than ten months. Composite liner, made from HCWCI (high Cr white cast iron) and carbon steel, has been developed successfully with liquid-liquid composing process based on LFC (lost foam casting). The microstructure of composite was analyzed with optical microscope, SEM (scanning electron microscope)/EDX energy-dispersive X-ray and XRD (X-ray diffraction). According to micrograph, the combination region of two metals was staggered like dogtooth, no mixtures occurred between two liquid metals, and its interface presented excellent metallurgical bonding state. The results of mechanical property test show that, the hardness of HRC, the fracture toughness, and the bending strength are more than 61, 16.5 J/cm2 and 1600 MPa, respectively. Comparison between liners made from bimetal composite and alloyed steel has also been investigated in industrial hematite ball mill. The results of eight months test in wet grinding environment prove that the service life of bimetal composite liner is three times as long as that of one made from alloyed steel.     

Modeling of an Impinging Oxygen Jet on Molten Bath Surface in 150 t EAF

 A transient three-dimensional mathematical model has been developed to analyze the three-phase flow in a 150 t EAF (electric arc furnace) using oxygen. VOF (multiphase volume of fluid) method is used to simulate the behaviors of molten steel and slag. Numerical simulation was conducted to clarify the transient phenomena of oxygen impingement on molten bath. When oxygen jet impinges on the surface of molten bath, the slag layer is broken and the penetrated cavity in molten steel is created. Simultaneously, the wave is formed at the surface of uncovered steel on which the slag layer is pushed away by jet. The result of numerical simulations shows that the area and velocity of uncovered steel created by impingement, jet penetration depth change from 0.10 m2, 0.0125 m/s, 3.58 cm to 0.72 m2, 0.1445 m/s, 11.21 cm, when the flow rate of an oxygen lance varies from 500 to 2000 m3/h. The results have been validated against water model experiments. More specially, the relation between the penetration depth and oxygen flow rate predicted by numerical simulation has been found to agree well with that concluded by water model.     

High-Temperature Mechanical Properties of Shipbuilding Steel BC in Continuous Casting

The mechanical property of shipbuilding steel BC has been studied by means of tensile test at various temperatures from 700 ℃ to 1000℃ with theGleeble-1500D thermo-mechanical simulator.The results indicate that the yield strength and tensile strength of steel have an analogous change pattern as temperature decreasing,and the transition in variation rate of strength occurs at 800℃ in both of them;the hot ductility trough of steel BC is a temperature range from 725℃ to 800℃,while the best hot ductility ranges from 875℃ to 1000℃ with the ductility value over 80%.For the sake of understanding the fracture mechanism of the steel,fracture surface and microstructure of the specimens have been examined by scanning electron microscope and metalloscope correspondingly.The results show that both the second phase particles and the pro-eutectoid ferrite surrounding the austenite boundaries play a significant role to the variation of hot ductility of steel BC.Deservedly,the research is important to the improvement and the further studies on the quality of steel during slab continuous casting process.     

Dry Sliding Oxidative Wear in Plain Carbon Dual Phase Steel

 To investigate the tribological potential of the dual phase (DP) steel as a wear resistant material, the wear and the friction characteristics of this steel, which consists of hard martensite islands embedded in a ductile ferrite matrix, have been investigated and compared with those observed in plain carbon hardened (H) steel that has the same carbon content of 02%. Dry sliding wear tests have been carried out using a pin on disk wear testing machine at different normal loads of 213 N, 285 N, 357 N, and 426 N and at a constant sliding velocity of 120 m/s. The analysis of surface and wear debris of samples showed that the wear mechanism was mainly mild oxidative. The friction and the wear rate of the H steel and the DP steel have been explained with respect to the microstructure and the wear mechanism.     

Turbulent Flow and Transport of Bubbles in Slab Continuous Casting Mold Under Electromagnetic Brake

Large eddy simulation model with magnetohydrodynamics(MHD)is developed to study the effect of electromagnetic braker(EMBr)on molten steel flow and transport of argon bubbles in the continuous casting process.The large eddy simulation with Smagorinsky sub-grid scale model is used to calculate the turbulent variables.The results indicate that the magnetic force can optimize the molten steel flow pattern in the braking area.The flow is asymmetric,especially in the lower of the mold,even if with applied electromagnetic effect.The flow deviation of the molten steel in the mold is inevitable existence.More bubbles tend to release from the top surface with LMF-EMBr,while,FCMF-EMBr has little effect on the overall removal fraction of bubbles,but it affects the trajectory of bubbles.     

Development of Ultra-Low Oxygen Automobile Gear Steel

In view of process conditions of Vanadium Recovery and Steelmaking Plant, PanGang Group Panzhihua steel and Vanadium Co.,Ltd., and on the basis of making choice of a reasonable deoxidization process, some measures have been taken to the development of automobile gear steel (20CrMoH) such as the pre-refining technology during converter tapping, "white slag" refining in LF, RH Vacuum treatment, and even protective casting technology. Also different and suitable models of argon blowing from bottom of ladle were adopted in the platform after converter, LF refining and calcium treatment. Test results show that the high cleanness 20CrMoH gear steel slab with T[O] ≤15×10-6(The average T[O] is 11.8×10-6) could be obtained through all these measures.     

Effect of Microalloying,Principally With Vanadium,Processing Conditions and Microstructure on Resistance to CO₂ Corrosion

One driver for steel development over recent decades has been the engineering requirements of improved strength and toughness,combined with weldability,for the safe and cost effective recovery and transmission of oil and gas.This has been achieved through refinement of grain size by microalloy precipitation and thermomechanical processing.However,little attention has been paid to these significant changes in steel chemistry and processing on corrosion resistance,despite the dominance of economic carbon steel for construction in the oil and gas industries.The more common forms of corrosion are associated with the presence of H 2 S or CO 2.CO 2 in aqueous solution forms a weak acid sufficient to promote significant localized corrosion in transmission gas/oil pipelines and in well-head applications (’down-hole’).Systematic study has identified the influence of a wide range of alloying elements and different processing conditions on the resistance of low-carbon steels to CO 2 corrosion;strong carbide-forming microalloying elements such as Ti,Nb and V,along with Cr additions,and different levels of Mn,Si,Cu,Mo and Ni,have been explored,along with treatments simulating different processing conditions.The present study also emphasizes the role of V and Ti microalloying in improving the resistance of Cr-containing carbon steel to corrosion in carbonic acid and how this is influenced by microstructure and the metallurgical condition of the microalloying addition,in particular,the extent of precipitation.It is noted that some commercially available corrosion inhibitors contain V as a vanadate compound to interfere with the corrosion process and so it is suggested that V microalloying may also be beneficial if present in an appropriate form in the steel.That Ti also seems to play a role in corrosion in the steels studied is judged to be compatible with the thermodynamics of transition metal anions in the Ti-V-Cr group.     

Nitrogen Desorption in Molten Stainless Steel during Immersion Argon Blowing

The behavior of nitrogen desorption reaction in molten stainless steel for AISI 304 and 316 during immersion argon blowing through an immersed alumina nozzle with 3 mm in I.D. has been investigated by sampling method. Some kinetic parameters such as reaction order, rate constant and apparent activation energy of nitrogen desorption reaction for AISI 304 and 316 have been obtained. Results show that nitrogen desorption reaction from molten stainless steel for AISI 304 and 316 is the second order reaction. The rate constant at 1550 ℃ and 1580 ℃ for AISI 316 is 0.08407%-1·min-1 and 0.82370%-1·min-1, respectively. The rate constant at 1550 ℃ for AISI 304 is 0.4166%-1·min-1. The apparent activation energy Ea of nitrogen desorption reaction for AISI 316 is 2136.47 kJ/mol. This huge value of apparent activation energy verifies that the nitrogen desorption reaction has a complex and multistep reaction mechanism. The rate of nitrogen desorption reaction from molten stainless steel is mixed controlled by the desorption reaction of diatomic molecule nitrogen or of monatomic nitrogen from molten metal at the gas-metal interface and the mass transfer of nitrogen in molten metal. The rate equation of process for nitrogen desorption has been deduced.     

Trial Production of Sulphurous Free-Cutting Gear Steel by Convert-Billet Continuous Casting Process

In consideration of the composition characteristics and quality requirements of sulphurous free-cutting gear steel, the rational measures of sulfur control, calcium treatment and key technologies of continuous casting process are applied in the development of a full-line operation of LD-Billet continuous casting on steelmaking with semi-steel, which suggests an economic production of the steel has been realized. Test results show that the average retrieval rate of sulphurous alloy in the process of RH treatment is 95.3% and sulfur content of products is stability. Otherwise, content of T[O] in casting billet is in the range of 11×10-6 ~ 18×10-6 with average value is 14.7×10-6.Based on this, the billets have good surface quality and internal quality.     

Study on the friction and wear properties of the surface nanocrystallized 1.0C-1.5Cr steel induced by the surface mechanical attrition treatment

Nano-structured layers are fabricated on the surface of 1.0C-1.5Cr steel by using the surface mechanical attrition treatment(SMAT)technology,and the microstructures of the surface nano-crystallization layers are characterized by means of X-ray diffraction(XRD)and transmission electron microscopy(TEM).The friction and wear properties are also investigated by a UMT-2 friction and wear tester.Experimental research has indicated that the average diameter of nanocrystalline grains in the surface layer after being treated for 15 min is in the range of 10-20 nm,and ferrite and cementite grains can not be identified by their morphologies.The wear-resistance of the specimen treated for 15 min has been doubled,compared with that of the matrix due to the grain refinement to a nano-sized scale.The lowest friction coefficient is 0.27,which is for the specimen treated for 30 min,resulting from the dissolution of the cementite phase and the formation of a relative homogenous structure.The SMAT technique for enhancing the wear-resistance of the 1.0C-1.5Cr steel has an optimum processing time,which is in the range of 15-30 min.The dominant wear mechanism of the specimen treated for 15 min changes from adhesive wear into particle wear.     

Influence of Nb on Microstructure and Property of Low-Carbon Mn-Series air-cooled Bainitic Steel

 The effect of Nb on the microstructure evolution of low carbon Mn series air cooling bainitic steels has been discussed in this paper by using Gleeble 1500D, SEM, and TEM observation. The results show that: The amount of grain boundary allotriomorphic ferrites is relatively higher in non-Nb bearing steel than Nb-bearing steel under same deformation conditions. And the ferrites in Nb bearing steel are more finer. With the decreasing of finishing rolling temperature (FRT), the particles of Nb(CN) precipitating in Nb bearing steel are smaller and more dispersive. The properties of the Nb bearing steel is higher than that of non-Nb bearing steel at same FRT, and it is suggested that the toughness of Nb Micro-alloyed steel will be improved more effectively than that of non-Nb bearing steel with the decreasing of FRT.     

Influence of V(C,N) Precipitates on Microstructure and Mechanical Properties of Continuous Cooled C-Mn-V

The effect of chemical composition and processing parameters on the formation of acicular ferrite and/or bainite has been investigated.In particular,this paper deals with the influence that N through its combination with V,as V(C,N) precipitates,has on the decomposition of austenite.Likewise,the intragranular nucleation potency of V(C,N) precipitates is analyzed through the continuous cooling transformation diagrams (CCT) of two C-Mn-V steels with different contents of N.Results reported in this work allow us to conclude that acicular ferrite can only be achieved alloying with vanadium and nitrogen,meanwhile bainite is promoted in steels with a low level of nitrogen.It is concluded that higher strength values are obtained in acicular ferrite than in bainitic steel but a similar brittle-ductile transition temperature (BDT),and lower values of impact absorbed energy (KV) has been recorded in nitrogen-rich steel.     

Solidification Structure Refining of 430 Ferrite Stainless Steel With TiN Nucleation

The thermodynamics of TiN precipitation in liquid steel of 430 ferrite stainless steel has been calculated to find out the condition of TiN precipitation during the initial solidification stage. The difference in the solidification structure of 430 ferrite stainless steel has been discussed through comparative tests of vacuum induction furnace melting with different contents of Ti. It has been found that the equiaxed grain proportion can be increased from 20% to 69% as the content of Ti from 0.1% up to 0. 4%. The size of the TiN particles precipitated is 1-3 μm and the number of TiN particles is about （200- 300）/μm^2. It is found that the effect of using TiN to refine the solidification structure has been confirmed under the strict process condition used for 430 ferrite stainless steel.     

Evaluation of Dry Sliding Wear Behaviour of Plasma Transferred Arc Hardfaced Stainless Steel

 The effects of different experimental conditions on the dry sliding wear behavior of stainless steel surface produced by plasma transferred arc (PTA) hardfacing process were studied. The wear test was conducted in a pin on roller wear testing machine, at constant sliding distance of 1 km. Mathematical models were developed to estimate wear rate incorporating with rotational speed, applied load and roller hardness using statistical tools such as design of experiments, regression analysis and analysis of variance. It is found that the wear resistance of the PTA hardfaced stainless steel surface is better than that of the carbon steel substrate.     

Anticorrosion Performance of Carbon Steel in 55% LiBr Solution Containing PMA/SbBr3 Inhibitor

The anticorrosion performance of carbon steel in 55% LiBr solution containing PMA/SbBr3 inhibitor was studied by weight-loss tests, electrochemical measurements and surface analysis. In 55%LiBr PMA/SbBr3 solution, corrosion rates of carbon steel at 145 ℃, 175 ℃, 190 ℃ and 240 ℃ are 18.32 μm·a-1, 27.68 μm·a-1, 53.58 μm·a-1 and 73.78 μm·a-1, respectively. PMA/SbBr3 inhibitor may inhibit the corrosion of carbon steel in 55% LiBr solution effectively. Especially, it shows an excellent corrosion inhibition performance at high temperature. Both anodic and cathodic reactions of carbon steel may be inhibited by PMA/SbBr3 inhibitor, so it may be classified as mixed inhibitor. In 55%LiBr PMA/SbBr3 solution, the apparent activation energy of the corrosion reaction of carbon steel is 29.61 kJ·mol-1. The corrosion inhibition mechanism of PMA/SbBr3 is suggested as follows: PMA has the effect of inhibiting hydrogen evolution and a strong oxidizing property; Sb3 also exhibits oxidizing properties, and can exist stably with PMA in LiBr solutions; the passive film comprising Fe2O3 and antimony formed on carbon steel surface may prevent Br- from diffusing into the metal surface due to the synergistic effect of PMA and Sb3 ; As a result, the anticorrosion performance of carbon steel may be improved by PMA/SbBr3 inhibitor in 55% LiBr solution.     

Overview of Particles and Bubbles in Continuously Cast Steel

This paper gives an overview of phenomena associated with particles and bubbles in continuously cast steel. During steel processing from deoxidation to solidification the inclusion population undergoes changes with opportunities of removal. Flotation is an important separation mechanism. Inclusion particles may accumulate in the solidifying strand, thus forming enriched bands, which depend on the type of casting machine. Bubbles are created during inert gas injection. They also change in size, can float out, but also form accumulation bands. The interaction of bubbles and particles is discussed. Internal structure that recently has been observed on the inner surface of bubbles will be reviewed.