Formation and control of the surface defect in hypo-peritectic steel during continuous casting:A review

Hypo-peritectic steels are widely used in various industrial fields because of their high strength,high toughness,high processability,high weldability,and low material cost.However,surface defects are liable to occur during continuous casting,which includes depression,longitudinal cracks,deep oscillation marks,and severe level fluctuation with slag entrapment.The high-efficiency production of hypo-peritectic steels by continuous casting is still a great challenge due to the limited understanding of the mechanism of peritectic solidification.This work reviews the definition and classification of hypo-peritectic steels and introduces the formation tendency of common surface defects related to peritectic solidification.New achievements in the mechanism of peritectic reaction and transformation have been listed.Finally,countermeasures to avoiding surface defects of hypo-peritectic steels duiring continuous casting are summarized.Enlightening certain points in the continuous casting of hypo-peritectic steels and the development of new techniques to overcome the present problems will be a great aid to researchers.

Study on Key Joining Technology and Test Method of Steel/Al Hybrid Structure Body-in-White

Green and low carbon promote the application and development of light-weight materials in body-in-white. Large-scale die-casting Al alloy (DCAA) and high-strength thermo-formed steel sheet (TFSS) have put forward higher requirements for the application of joining technology of high-strength steel/Al dissimilar materials. Taking the new die-casting Al alloy body as an example, this paper systematically studies the progress of the latest joining methods of steel/Al dissimilar material with combination of two-layer plate and three-layer plate. By analyzing the joining technologies such as FSPR, RES, FDS and SPR, the technology and process characteristics of steel/Al dissimilar material joining are studied, and the joining technical feasibility and realization means of different material combination of the body are analyzed. The conditions of material combination, material thickness, material strength, flange height, preformed holes and joint spacing for achieving high-quality joining are given. The FSPR joining technology is developed and tested in order to meet with the joining of parts with DCAA and TFSS, especially for the joining of three-layer plates with them. It finds the method and technical basis for the realization of high quality joining of dissimilar materials, provides the early conditions for the application of large DCAA and TFSS parts in body-in-white, and meets the design requirements of new energy body. .

Research on the Landscape Utilization and Renovation of Industrial Wasteland in Panzhihua Steel-casting Factory

Renovation design of wasteland on the original Quarter A of Panzhihua Nongnongping Steelcasting Factory was taken for example in this study, natural conditions and biological landscapes in the study area were investigated. Principles and theories of the renovation design were introduced, it was proposed that protection and landscape renovation of industrial heritage had to be insisted to make regular and unique overall spatial layouts. On this basis, design approaches for the wasteland landscape renovation of the steel-casting factory were proposed as "maintaining original images, realizing the functional substitution; optimizing spatial structure; updating seriously-damaged industrial facilities with insignificant functionality; improving and recovering landscape soil; recovering and reconstructing vegetation".

Mechanical Properties of V-,Nb-,and Ti-bearing As-cast Microalloyed Steels

The influence of microalloying additions on the mechanical properties of a low-carbon cast steel containing combinations of V, Nb, and Ti in the as-cast condition was evaluated. Tensile and hardness test results indicated that good combinations of strength and ductility could be achieved by V and Nb additions. While the yield strength and UTS （ultimate tensile strength） increased up to the range of 378-435 MPa and 579- 590 MPa, respectively in the microalloyed heats, their total elongation ranged from 18% to 23%. The presence of Ti, however, led to some reduction in the strength. Microstructural studies including scanning electron microscopy （SEM） and optical microscopy revealed that coarse TiN particles were responsible for this behavior. The Charpy impact values of all compositions indicated that microalloying additions significantly decreased the impact energy and led to the dominance of cleavage facets on the fracture surfaces. It seems that the increase in the hardness of coarse ferrite grains due to the precipitation hardening is the main reason for brittle fracture.

Effects of Rare Earths on Toughness of 31Mn2SiRE Wear- Resistance Cast Steel

The toughness of 31Mn2SiRE wear-resistance cast steel were increased by means of RE compound modification and high temperature austenitizing. The results show that the microstructures can be refined, needle and network ferrite are eliminated, the dislocation density and the quantity of dislocated martensite are increased remarkably, and the shape and distribution of inclusions are improved by the addition of RE. Therefore, the mechanical properties of the modified steel can be greatly increased, especially the toughness (αK) by 44%, yield strength (σs) by 10%, and elongation (δ5) by 42%.

Effect of melting temperature on microstructural evolutions, behavior and corrosion morphology of Hadfield austenitic manganese steel in the casting process

In this study, the effect of melting temperature on the microstructural evolutions, behavior, and corrosion morphology of Hadfield steel in the casting process is investigated. The mold was prepared by the sodium silicate/CO_2 method, using a blind riser, and then the desired molten steel was obtained using a coreless induction furnace. The casting was performed at melting temperatures of 1350, 1400, 1450, and 1500°C, and the cast blocks were immediately quenched in water. Optical microscopy was used to analyze the microstructure, and scanning electron microscopy(SEM) and X-ray diffractrometry(XRD) were used to analyze the corrosion morphology and phase formation in the microstructure, respectively. The corrosion behavior of the samples was analyzed using a potentiodynamic polarization test and electrochemical impedance spectroscopy(EIS) in 3.5 wt% NaCl. The optical microscopy observations and XRD patterns show that the increase in melting temperature led to a decrease of carbides and an increase in the austenite grain size in the Hadfield steel microstructure. The corrosion tests results show that with increasing melting temperature in the casting process, Hadfield steel shows a higher corrosion resistance. The SEM images of the corrosion morphologies show that the reduction of melting temperature in the Hadfield steel casting process induced micro-galvanic corrosion conditions.

Effect of Alloying Elements on Thermal Wear of Cast Hot-Forging Die Steels

The effect of main alloying elements on thermal wear of cast hot-forging die steels was studied. The wear mechanism was discussed. The results show that alloying elements have significant influences on the thermal wear of cast hot-forging die steels. The wear rates decrease with an increase in chromium content from 3% to 4% and molybdenum content from 2% to 3%, respectively. With further increase of chromium and molybdenum contents, chromium slightly reduces the wear resistance and molybdenum severely deteriorates the wear resistance with high wear rate. Lower vanadium/carbon ratio （1.5-2.5） leads to a lower wear resistance with higher wear rate. With an increase in vanadium/carbon ratio, the wear resistance of the cast steel substantially increases. When vanadium/carbon ratio is 3, the wear rate reaches the lowest value. The predominant mechanism of thermal wear of cast hot-forging die steels are oxidation wear and fatigue delamination. The Fe2O3 and Fe3O4 or lumps of brittle wear debris are formed on the wear surface.

Solidification Structure of Low Carbon Steel Strips with Different Phosphorus Contents Produced by Strip Casting

In the present paper, low carbon steel strips with different phosphorus contents were produced using a twin roll strip casting process. The solidification structure was studied and its features were analyzed in detail. It was found that the strips possessed a fine microstructure compared with the mould cast steels. With increasing phosphorus content more ferrite has been formed with finer grains.

Analysis of cracking phenomena in continuous casting of 1Cr13 stainless steel billets with final electromagnetic stirring

Solidification cracking that occurs during continuous casting of 1Cr13 stainless steel was investigated with and without final elec- tromagnetic stirring （F-EMS）. The results show that cracks initiates and propagates along the grain boundaries where the elements of carbon and sulfur are enriched. The final stirrer should be appropriately placed at a location that is 7.5 m away from the meniscus, and the appropri- ate thickness of the liquid core in the stirring zone is 50 ram. As a stirring current of 250 A is imposed, it can promote colurnnar-equiaxed transition, decrease the secondary dendrite arm spacing, and reduce the segregation of both carbon and sulfur. F-EMS can effectively de- crease the amount of cracks in 1Cr13 stainless steel.

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.

Research on Thermal Wear of Cast Hot Forging Die Steel Modified by Rare Earths

Thermal wear of cast hot-forging die steel modified by rare earths（RE） was studied and compared with commercially used die steels. The function of RE and the mechanism of thermal wear of cast steel modified by RE were discussed. The results showed that with increasing content of RE, the wear rate of cast steel reduced at first and then increased. By adding 0.05% （mass fraction） RE, the cast hot-forging die steel with optimum thermal wear resistance was obtained, which was better than that of H13 and 3Cr2WSV. The large amount of coarse inclusions, （RE）2O2S, resulted from excessive RE, which obviously deteriorated thermal wear resistance. The mechanism of thermal wear of the modified cast die steel is oxidation wear and oxide fatigue delamination. The wear debris are lumps of Fe2O3 and Fe3O4.

Simulation Using Realistic Spray Cooling for the Continuous Casting of Multi-component Steel

A three-dimensional heat transfer model for continuous steel slab casting has been developed with realistic spray cooling patterns and a coupled microsegregation solidification model that calculates the solidification path for multi-component steels. Temperature and composition dependent properties are implemented in a database for 15 chemical species. Considerable effort is made to accurately model the spray cooling heat transfer. Each spray nozzle position and distribution is considered, including variations of the spray patterns with flow rate, and spray overlap. Nozzle type, layout, nozzle-to-slab distance, and spray span and flux are variable. Natural convection, thermal radiation and contact cooling of individual rolls are computed. The present model provides more comprehensive information and realistic slab surface temperatures than results from a model using the 'averaged' treatment of boundary conditions. Cooling operating conditions and parameters of individual spray nozzles can be analyzed to optimize nozzle spray distribution, improve product quality, and troubleshoot issues such as nozzle clogging that may arise during production. One spray cooling correlation is used for the entire machine, achieving as good or better agreement with surface temperature measurements than was found previously for the model using an 'averaged' treatment of boundary conditions and using three machine-segment-dependent correlations.

Spheroidization and Ostwald Growth of Carbide in Isothermal Process of Hot-Deformed High Carbon Chromium Cast Steel

In isothermal spheroidizing process,the spheroidization and growth of the carbide formed in hot-deformed high-carbon chromium cast steel at high temperature were investigated.The results showed that the spheroidizing growth of carbide proceeds in such a way that the bigger carbide particles swallow the smaller ones,and the short rhabdoid carbides dissolve and are spheroidized by itself.When the samples were held at 720℃ for more than 3 h,the spheroidization is not obvious.The feature of the process is the size increment and the amount decrement of carbide particles.The empirical equation for growth rate of carbides was obtained.The volume fraction of carbides keeps constant.The growth process agrees well with Ostwald Ripening Law.

Solidification microstructure of M2 high speed steel by different casting technologies

The present work investigated the solidification microstructure of AISI M2 high speed steel manufactured by different casting technologies, namely iron mould casting and continuous casting. The results revealed that the as-cast structure of the steel was composed of the iron matrix and the M2C eutectic carbide networks, which were greatly refined in the ingot made by continuous casting process, compared with that by the iron mould casting process. M2C eutectic carbides presented variation in their morphologies and growth characteristics in the ingots by both casting methods. In the ingot by iron mould casting, they have a plate-like morphology and grow anisotropically. However, in the ingot made by continuous casting, the carbides evolved into the fiber-like shape that exhibited little characteristics of anisotropic growth. It was noticed that the fiber-like M2C was much easier to decompose and spheroidize after heated, as a result, the carbides refined remarkably, compared with the case of plate-like carbides in the iron mould casting ingot.

Study on Heterogeneous Nuclei in Cast H13 Steel Modified by Rare Earth

The dendrite segregation in cast H13 steel was weakened with RE modification treatment. Grain boundary carbide during quenching was also under control and impact toughness was improved greatly. By thermodynamic calculation, analysis of two-dimensional lattice misfitting and electron probe analysis, it is found that Ce2O3 may act as the heterogeneous nuclei of modified cast H13 steel.

Centrifugal Casting of High Speed Steel/Nodular Cast Iron Compound Roll Collar

The centrifugal casting of compound HSS/nodular cast iron roll collar was studied,and the factors affecting transition zone quality were analyzed.The pouring temperature and interval in pouring are the main factors affecting transition zone quality.By controlling process parameter and flux adding during casting,high quality roll collar was obtained.The cause,why in the casting of HSS part,segregation appears easily,was analyzed and the countermeasure eliminating segregation was put forward,the measure eliminating heat treatment crackling was also put forward.

Teeming stream protection using an argon shroud during casting of steel ingots

Two kinds of argon shroud protection devices with two different basic structures were designed and investigated. Industrial experiments and numerical simulations were used to examine the protection effect, and the mechanism of air entrapment during the casting of steel ingots was analyzed. The influence of the structure of the argon shroud protection device on the protection effect was investigated. An argon shroud protection device mounted to the nozzle holder on the bottom of the ladle does not provide a good protection effect because air can easily flow into the teeming system and cause reoxidation of molten steel during teeming. By contrast, an argon shroud protection device seated on the top of the central trumpet provides an excellent protection effect, where air has little chance of flowing into the teeming system during casting. The feasibilities of the argon shroud protection devices are discussed.

Influence of Adding Ti Powder in Preform on Microstructure and Mechanical Properties of Al_2O_3p/Steel Composites by Squeeze Casting

To improve the mechanical properties of alumina particulates reinforced steel matrix composite, Ti powder was added into the alumina preform, a 5140 steel matrix composite was fabricated by squeeze casting, and the influences of Ti powder on the microstructure, hardness and bending strength of the composite were investigated, compared with the composite without adding Ti powder. Applied Ti powder and alumina particulates were 10-25 μm and 100-180 μm in size, respectively. Both composites were successfully fabricated, however Ti powder addition increased the infiltration thickness of the composite. In the Ti contained composite, a TiC film in micron scale is formed on the surface of alumina particles, many TiC aggregates are dispersed in the steel matrix without obvious remaining Ti powder. The hardness and the three-point bending strength of the composite reach 49.5 HRC and 1 018 MPa, respectively, which are 17.9% and 52.4% higher than those of the composite in the absence of Ti addition. Fracture morphology shows that the debonding of alumina particulates is eliminated for the composite in the presence of Ti addition. Sessile drop test shows the average wetting angle between 5140 steel and that of Ti coated Al2O3 is about 82.15°, much lower than the wetting angle 150° between steel and pure Al2O3. Therefore, the increase in the mechanical properties of the composite is attributed to the improvement of Al2O3 p/steel interface wetting and bonding by adding Ti powder in the preform.

3D stress simulation and parameter design during twin-roll casting of 304 stainless steel based on the Anand model

This study first investigated cracks on the surface of an actual steel strip. Formulating the Anand model in ANSYS software, we then simulated the stress field in the molten pool of type 304 stainless steel during the twin-roll casting process. Parameters affecting the stress distribution in the molten pool were analyzed in detail and optimized. After twin-roll casting, a large number of transgranular and intergranular cracks resided on the surface of the thin steel strip, and followed a tortuous path. In the molten pool, stress was enhanced at the exit and at the roller contact positions. The stress at the exit decreased with increasing casting speed and pouring temperature. To ensure high quality of the fabricated strips, the casting speed and pouring temperature should be controlled above 0.7 m/s and 1520℃, respectively.

Flow of Steel in Mold Region During Continuous Casting

The particle image velocimetry （PIV） technique was used to study the fluid flow phenomena that occurred during continuous casting, using a water model with dimensions of 1 840mm× 280 mm. Two types of solidified shells, i. e. , the smooth type and the coarse type, were used to characterize the dendrite in order to simulate different liquid-solid interfacial conditions. The influence of the nozzle angle and the immersion depth of nozzle, as well as the casting speed on the flow behavior was investigated quantitatively. The results were as follows： （1） There are two large recirculations above and below the fluid jet in the mold, respectively, under the smooth interface condition. However, in the case of the dendrite solidified shell, it was found that the flow velocity of the fluid decreased and more smaller vortices appeared in the upper region of the mold. （2） The angle and the immersion depth of nozzle are two important factors affecting the flow pattern, and they are also capable of bringing about the change in the flow direction. （3） The higher the casting speed, the higher are the jet stream and the impacting point on the narrow face. However, the high casting speed causes serious fluctuation of the meniscus, and correspondingly leads to various defects.