Discussion on Gas Safety Protection Management in Steel Plants

The necessity of establishing gas protection station in iron and steel works is demonstrated,issues of strengthening the management of gas safety protection,studying new technology of gas protection,adapting to the needs of modernization and building large scale and intelligent iron and steel works are discussed.Relevant sug-gestions are also put forward.

Optimization for vehicle scheduling in iron and steel works based on semi-trailer swap transport

In order to solve internal logistics problems of iron and steel works,such as low transportation efficiency of vehicles and high transportation cost,the production process and traditional transportation style of iron and steel works were introduced.The internal transport tasks of iron and steel works were grouped based on cluster analysis according to demand time of the transportation.An improved vehicle scheduling model of semi-trailer swap transport among loading nodes and unloading nodes in one task group was set up.The algorithm was designed to solve the vehicle routing problem with simultaneous pick-up and delivery(VRPSPD) problem based on semi-trailer swap transport.A solving program was written by MATLAB software and the method to figure out the optimal path of each grouping was obtained.The dropping and pulling transportation plan of the tractor was designed.And an example of semi-trailer swap transport in iron and steel works was given.The results indicate that semi-trailer swap transport can decrease the numbers of vehicles and drivers by 54.5% and 88.6% respectively compared with decentralized scheduling in iron and steel works,and the total distance traveled reduces by 43.5%.The semi-trailer swap transport can help the iron and steel works develop the production in intension.

FEM simulation and experimental verification of temperature field and phase transformation in deep cryogenic treatment

Combining with the low temperature material properties and the boiling heat transfer coefficient of specimen immersed in the liquid nitrogen, a numerical model based on metallo-thermo-mechanical couple theory was established to reproduce the deep cryogenic treatment （DCT） process of a newly developed cold work die steel Cr8Mo2SiV （SDC99）. Moreover, an experimental setup for rapid temperature measurement was designed to validate the simulation results. The investigation suggests that the differences in temperature and cooling rate between the surface and core of specimen are very significant. However, it should be emphasized that the acute temperature and cooling rate changes during DCT are mainly concentrated on the specimen surface region about 1/3 of the sample thickness. Subjected to DCT, the retained austenite of quenched specimen continues to transform to martensite and finally its phase volume fraction reduces to 2.3%. The predicted results are coincident well with the experimental data, which demonstrates that the numerical model employed in this study can accurately capture the variation characteristics of temperature and microstructure fields during DCT and provide a theoretical guidance for making the reasonable DCT procedure.

Multi-energy synergistic optimization in steelmaking process based on energy hub concept

The production process of iron and steel is accompanied by a large amount of energy production and consumption. Optimal scheduling and utilization of these energies within energy systems are crucial to realize a reduction in the cost, energy use, and CO_2 emissions.However, it is difficult to model and schedule energy usage within steel works because different types of energy and devices are involved. The energy hub(EH), as a universal modeling frame, is widely used in multi-energy systems to improve its efficiency, flexibility, and reliability.This paper proposed an efficient multi-layer model based on the EH concept, which is designed to systematically model the energy system and schedule energy within steelworks to meet the energy demand. Besides, to simulate the actual working conditions of the energy devices, the method of fitting the curve is used to describe the efficiency of the energy devices. Moreover, to evaluate the applicability of the proposed model, a case study is conducted to minimize both the economic operation cost and CO_2 emissions. The optimal results demonstrated that the model is suitable for energy systems within steel works. Further, the economic operation cost decreased by 3.41%, and CO_2 emissions decreased by approximately 3.67%.

Research on Optimum Operation and Structure of Tundish

With the technical progress of metallurgical industry, more excess gas will be produced in steel works. The feasibility of producing dimethyl ether by gas synthesis was discussed, which focused on marketing, energy balance, process design, economic evaluation, and environmental protection etc. DME was considered to be a new way to utilize excess coal gas in steel works.

Prediction and Analysis on Oxidation of H13 Hot Work Steel

The understanding of oxidation behaviors on H13 steel was helpful to improve the service life and performance of hot work moulds and dies. Thermal-Calc Software was performed to calculate the oxidation phases on H13 steel along with different partial oxygen pressures in the interesting temperature range of 500-700 ℃. In this range H13 steel samples were treated respectively in different atmosphere including flowing water vapor （0.2 MPa）, normal pressure air （0.1 MPa） and low pressure air （0. 001 MPa）. The different oxidation films were detected with optical microscopy and X-ray diffraction. The microstructures and phase constitutions of the films formed in low pressure air were similar to those of the films formed in water vapor, and obviously different to those of the films formed in normal pressure air. The oxidation mechanisms of H13 steel in different atmosphere were also discussed.

Effect of Rare Earth Composite Modification on Microstructure and Properties of a New Cast Hot-Work Die Steel

The effects of RE modification on structure and the properties of a new cast hot work die (CHD) steel were investigated. The grains of the CHD steel are refined by RE modification. With the increase of RE addition, both grain size and inclusion amount are reduced. Appropriate amount of RE results in decrease in inclusion amount and formation of spheroidal inclusions uniformly-distributed in steel, so that the morphology and distribution of inclusions are improved. RE composite modification favors the formation of bainite, austenite and fine lath martensite with dense dislocation. When the residual RE content reaches 0.02%, no obvious changes in strength and hardness are found, while fracture toughness and threshold of fatigue crack growth are increased. The impact toughness, elongation and reduction of cross sectional area are increased by a factor of two, and thermal fatigue resistance is also improved.

Calculation and Analysis of Valence Electron Structure of Mo_2C and V_4C_3 in Hot Working Die Steel

Taking the hot working die steel （HWDS） 4Cr3Mo2NbVNi as an example, the phase electron structures （PES） and the biphase interface electron structures （BIES） of Mo2C and V4 C3 , which are two kinds of important carbides precipitated during tempering in steel were calculated, on the basis of the empirical electron theory of solids and molecules and the improved TFD theory. The influence of Mo2 C and V4 C3 on the mechanical properties of HWDS has been analyzed at electron structure level, and the fundamental reason that the characteristic of the PES and the BIES of carbides decides the behavior of them has been revealed.

Repair Effect of Hot Work Tool Steel by Laser-Melting Process

Both wear and crack due to heat checking in hot work tool steel are major failure modes.It is desirable to find amethod to lengthen the tool life while reducing manufacturing cost.This paper suggests a method to improve toollife for hot work tool steel(SKD6)with crack by laser-melting process.The method has been evaluated using theimpact and fatigue test results.It is demonstrated that a repair of the crack by a laser-melting process is effectivefor life extension of the damaged tool.

CYCLIC SOFTENING IN HOT-WORKING DIE STEELS DURING LOW-CYCLE FATIGUE

The characteristics and microstructural changes of cyclic softening in hot-working die steels 5CrNiMo and 5Cr2NiMoVSi were studied under strain controlled low-cycle fatigue.The re- sults show that the cyclic softening is featured in both steels hardened in different conditions under the strain controlled amplitude range of Δε_t/2=0.6-1.8×10^(-2).The softening effect mainly occurs in some initial cycles and the stress amplitude varies slightly in the sequential cycles,i.e.the softening effect is minified.No obvious stress saturation phenomenon was ob- served during the whole cyclic deformation.The TEM analysis shows that the cyclic softening is related to heterogenity of plastic deformation.The softening of the tested steels is caused by the formation of the dislocation cell structure with low density and low internal stress,and by the fragmentation and redissolution of fine carbides into matrix.

Application of Mini Mills in China

The COREX(coal reduction process),EOF(energy optimizing furnace)andRCC-DR(rotary continuous casting-directreduction)process have been operatingcommercially in south Africa,Brazil andAustria respectively.The linkage of theseprocesses,the COREX-EOF-RCC-DRprocess,will be suited to small and medium-sized local steel plants in China,whereless scrap is available,electrical poweris expensive and resources of natural gasare scarce.

FLOW STRESS MODEL FOR HARD MACHINING OF AISI H13 WORK TOOL STEEL

An approach is presented to characterize the stress response of workpiece in hard machining, accounted for the effect of the initial workpiece hardness, temperature, strain and strain rate on flow stress. AISI H13 work tool steel was chosen to verify this methodology. The proposed flow stress model demonstrates a good agreement with data collected from published experiments. Therefore, the proposed model can be used to predict the corresponding flow stress-strain response of AISI H13 work tool steel with variation of the initial workpiece hardness in hard machining.

Investigation into microstructure of spray formed V4 cold working mould steel and its roiling and annealing

The material selected for this work was the spray formed Vanadis4 high alloy cold working mould steel （abbreviated to V4 steel）. Its microstructure, hot rolling process, and annealing treatment have been investigated. Observed from the optical and electron microscopes, the as-sprayed V4 steel had the finer microstructure of uniform and equiaxial grains ,while after hot rolling for densification and spheroidized annealing, the V4 steel obtained an excellent spheroidized structure that is favorable to subsequent quenching and tempering treatment. The spheroidized structure and level of annealed hardness of the V4 steel are almost the same as expensive imported powder metallurgy the V4 steel. It is difficult to produce V4 steel with the conventional ingot metallurgical technique, so the multi-step and high-cost powder metallurgy method is generally used at present. Compared to the powder metallurgy technique, using the spray forming technique to produce the V4 steel has obvious advantages and potential market competitiveness in reducing production costs, simplifying working process, and shortening the production cycle.

Effect of Niobium on Microstructure of Cast AISI H13 Hot Work Tool Steel

The effect of niobium addition on the microstructure of cast AISI H13 hot work tool steel was evaluated by using EDX analyzer attached to the scanning electron microscope. The volume percent of eutectic area and eutectic cell size and also volume percent of different carbides of new steel, which is heat treated under different conditions, are also determined. The results show that the a niobium addition modifies the cast structure of Nb-alloyed hot work tool steel, and reduces the size and volume of eutectic cells, and increases the maximum hardness of the steel.

Microstructure and Properties of Hot Working Die Steel H13MOD

Compared with H13 steel, the influences of different heat treatment process on the microstructure and properties of the new type of hot working die steel H13MOD were studied. The results show that the complete aus tenitizing temperature of H13MOD is around 1030 ℃ and the quenching hardness achieves the maximum value at this temperature. While for H13, the complete austenitizing temperature is above 1100 ℃ and the quenching hardness rise constantly with the quenching temperature increasing. In quenching process, the undissolved MC carbides can prevent the coarsening of grain in both steels. With the rise of quenching temperature, when MC carbides dissolve completely, the grain grows quickly. The hardness and strength of H13MOD at higher tempering temperature （above 570 ℃） are nearly the same as those of H13, but its toughness is higher than that of H13. Mo2C carbide is the main strengthening phase in H13MOD, which is attributed to the higher content of Mo. The quantity of VC eutectic car- bides is reduced because of lower content of V in H13MOD, which plays an important role in enhancing the impact toughness of H13MOD. Under a certain strength condition, H13MOD steel can be used in the environment that higher toughness is required and the service life of die casting mold can be improved.

Effect of Heat Treatment on Microstructure of Modified Cast AISI D3 Cold Work Tool Steel

The effects of heat treatment on the microstructure of modified cast high chromium high carbon AISI D3 steel were studied. The modified AISI D3 steel was developed by replacing part of chromium with niobium and titanium, in which chromium carbide was partially replaced with MC carbides. The cast samples produced by investment casting were heat treated under different conditions. The microstructures of the samples were studied by optical microscope and scanning electron microscope equipped with EDS analyzer. To determine the optimized homogenizing process, the effects of homogenizing treatment on the microstructure and the morphology of carbides were also studied. The results show that the MC carbides are not changed in shape and amounts during high temperature homogenizing, whereas the M3C carbides are reduced in amount and become semiglobular in shape, and the homogeneity of microstructure is improved.

Effect of Cryogenic Treatment on Properties of Cr8-Type Cold Work Die Steel

The effect of cryogenic treatment on the properties of Cr8-type cold work die steel was investigated. The results show that cryogenic treatment increases hardness by decreasing retained austenite, but the degree depends on the austenitizing temperature. When quenching at lower austenitizing temperature, the steel can obtain higher tough- ness by cryogenic treatment substituting conventional treatment process. Cryogenic time has little effect on cryogenic treatment. Conversely, cryogenic temperature has a great effect on cryogenic treatment and the effect of cryogenic treatment is more obvious with decreasing cryogenic temperature. In addition, deep cryogenic treatment improves the wear resistance by precipitating more homogeneous specific carbides.

Oxidation and Thermal Fatigue Behaviors of Two Type Hot Work Steels During Thermal Cycling

Thermal fatigue test has been carried out on widely used hot work steel 4Cr5MoSiV1 and a low alloyed steel 3Cr3MoV in temperature range of 200 to 700 ℃. Tempering resistance, as well as high temperature hardness/ strength of steel specimens, works as a dominating material parameter on thermal fatigue resistance. During the heating period, high hardness can depress the inelastic deformation. This deformation is the origination of tensile stress, which acts as the driving [orce o{ heat checking during the cooling period. The cyclic strain-oxidation interac- tion can speed up the damage on surface defects, which plays an obvious role in initiation of thermal cracks. On 4CrSMoSiV1 steel specimens, borders between the matrix and inclusions such as titanium compounds, or lager car- bides such as primary carbides, are focused by strain and attacked by oxidation, and are main initiating places of cracks. While on 3Cr3MoV steel specimens, larger strain causes plastic deformation concentrating around grain boundaries. Then the following oxidation accelerates this grain boundary damage and creates cracks.

Influence of Chemical Composition on Phase Transformation Temperature and Thermal Expansion Coefficient of Hot Work Die Steel

On the basis of the uniform design method, six kinds of martensitic hot work die steels were designed. The phase transformation temperatures including Ac1 , Ac3 , and Ms were measured by DIL805A quenching dilatometer. The influences of the main elements on phase transformation temperatures were analyzed by quadratic stepwise regression analysis, and three corresponding equations were obtained. These equations, in which the interactions of the elements were considered, showed more effectiveness than the traditional ones. In addition, the thermal expansion coefficients of these steels in annealed state and quenched state were also obtained during the tests. The influences of chemical composition and temperature on the thermal expansion coefficient were analyzed; the equations obtained were verified by using several kinds of steels. The predicted values were in accordance with the results of the experiments.

Inclusion Variations of Hot Working Die Steel H13 in Refining Process

Inclusion variations of die steel H13, including changes of species, morphologies, compositions, amounts and sizes, in the production of EAF-LF--VD-ingot casting-electro slag refining （ESR） procedure, were investi- gated by systematic sampling, and analyzed with scanning electron microscope （SEM）, energy dispersive spectrum （EDS） , and metallographic microscope. The variation mechanism was studied by comprehensive analysis of total oxygen, nitrogen, and acid soluble aluminum as well as chemical test of refining slag. Based on the investigations, technical measures for cleanness improvement were discussed. The resuhs show that oxide inclusions in H13 steel change from irregular Al2O3- near globular CaO-MgO-Al2O3 and CaO-Al2O3-SiO2 complex inclusions-finer CaO- Al2O3-SiO2 inclusions with higher CaO content-CaO-Al2O3-SiO2 inclusions with higher Al2O3 content and irregular MgO-AI203 inclusions--fine irregular MgO-Al2O3-CaS inclusions in various steps of the production; the variations are related with changes of acid soluble aluminum content, reactions between slag and steel, re-oxidation of liquid steel during casting, and refining of ESR. It is also found that Al2O3 inclusions are modified by refining slag in LF and VD refining~ and ESR plays a good role in inclusion removal, especially in controlling the large linear VC-CrC- MoC inclusions distributed in grain boundaries. It is suggested that casting protection should be improved, and the basicity of refining slag and acid soluble aluminum content in steel should be raised.