Hot Steel Plate Research Articles

Visual Observation of Circular Water Jet Impingement Boiling on Stationary Hot Steel Plate

The time-and space-resolved water jet impingement heat transfer on stationary hot steel plate was measured by a novel experimental technique that has a function of high-temperature heat flux gauge. The simultaneous visual observation was helpful to understand the complex heat transfer regimes occurring on a stationary hot steel plate cooled from 900°C by a circular water jet. The heat transfer regimes adjacent to a circular water jet impinging on a hot steel plate were known as to be classified into 5 distinct regimes; (I) single phase forced convection, (II) nucleate and transition boiling, (III) forced convection film boiling, (IV) agglomerated pools, (V) radiation and natural convection to surroundings. The observed images of water jet impingement boiling were well agreed with the measured cooling curve and boiling curve, so this study can provide the benchmark data for validating the 5 distinct regimes.

Study on Ultra-fast Cooling Behaviors of Water Spray Cooled Stainless Steel Plates

Spray cooling is an effective tool to dissipate high heat fluxes from hot surfaces. This article thoroughly investigates the effect of thickness of a hot stainless steel plate on the cooling time, cooling rate, heat flux, and heat transfer coefficient under constant mass flow rate maintained at 1 MPa using water as the coolant. Cylindrical samples of stainless steel with constant diameter (D = 25 mm) and thickness (δ = 7.5, 12, 16.5, and 21 mm) were used in the present study. Critical droplet diameter to achieve an ultra-fast cooling rate of 300°C/s was estimated by using an analytical model for samples of varying thicknesses. The analytical model (one side spray cooling) showed good agreement with experimental results with a relative error of 3.2% in the plate thickness range of 1–12 mm. An increasing trend in maximum heat flux was found with increasing thickness of the plate. Maximum heat flux as high as 1,800 kW/m2 was achieved for a 21-mm-thick sample. Heat transfer coefficients in the range 0.092–96.24 kW/m2K, 0.111–98.9 kW/m2K, 0.074–63.4 kW/m2K, and 0.127–55.63 kW/m2K were reported for sample of varying thicknesses in the present study. Limited published work is available with reference to water spray cooling dynamics and thickness of stainless steel plate. Therefore, the present study focuses on the correlation between the thickness of the plate and spray dynamics of water spray cooling.

Welding assessment of a damaged crane pedestal of a container ship

A structural integrity assessment of a damaged crane pedestal/column of a container ship is presented. Crane cabins and pedestal/columns are subjected to fatigue coupled with sudden overloads during cargo operations and corrosion effects due to sea environment. Significant number of surface cracks was detected around the pedestal/column, at inner and outside of the crane foundation, close to the main weld seam and, in consequence, the ship-owner ordered a survey. The main weld seam and the sites where cracks were found are evaluated in the present study. For the purpose, the sample material (hot rolled steel plate and upper ring) of the pedestal was provided by the shipyard and macro and micrographics were observed. Results did not show any cracks, although they have been found by the NDT technical services of the shipyard which have decided to remove them by the grinding process. The weld seam did not also show relevant defects, whereby the replacing of the pedestal/column by a new one would not had been necessary. Regardless of some occasional overloads, the surface cracks found on the pedestal/column could be a consequence of the normal operation conditions of the crane during the last 5 years and also due to poor maintenance.

Toughness improvement in hot rolled HSLA steel plates through asymmetric rolling

Asymmetric hot rolling and conventional hot rolling were applied to a HSLA steel in order to improve the impact toughness of thick-gauge hot rolled plates. The asymmetric rolling condition was introduced by applying mismatched roll diameters. The diameter ratio between big and small rolls was 1.25. The rolling temperatures were between 900°C and 1150°C. The results show that asymmetric rolling produced a smaller average grain size at the centre layer of the hot rolled plate than symmetric rolling and brought a through thickness texture change. The impact toughness was increased and the toughness anisotropy was reduced in the asymmetric hot rolled plate in the ductile to brittle transition temperature range. The improved impact toughness in the asymmetric hot rolled plate is related to the fine grain structure and the lower toughness anisotropy is related to the reduced α-fibre texture.

트랙 이행거리에 따른 SKD61 재질의 레이저 메탈 디포지션 기초 특성 분석

In this study, AISI M2 powder was selected primarily through various literature in order to improve the hardness and wear resistance. Among the laser metal deposition parameters, laser power was studied to improve the deposition efficiency in the laser metal deposition using a diode pumped disk laser. SKD61 hot work steel plate and AISI M2 powder were used as a substrate and powder for laser metal deposition, respectively. Fixed parameters are CTWD, focal position, travel speed, powder feed rate, etc. Experiments for the laser metal deposition were carried out by changing laser power. Through optical micrographs analysis of cross-section in LMD track, effect of the major parameters were predicted by track pitch. As the track pitch increased, so the reheated zone width, the overlap width and the minimum thickness was decreased. The hardness was decreased in the HAZ area, the hardness in the reheated HAZ area was decreased significantly and regularly in particular.

Research on Preventing Copper-Brittleness Process for Hot Rolling Copper-Containing of Atmospheric Corrosion-Resisting Steel Used in Vehicles

Copper in hot rolling copper-containing steel plate can passivate the cathode-anode of corrosion reaction on plate surface and form a dense anti-rusting layer, so the rusting reaction is postponed and prevented, and the corrosion resistance is enhanced. However, copper enrichment around grain boundaries in copper-containing steel plate leads to the formation of net-like surface cracking called copper-brittleness. In this paper, through researching the technologies of smelting, and adding rare earth and heating, a reasonable and feasible production technology is found, which effectively prevents the defect of copper-brittleness.

Effect of Oxide Layer in the Ultra Fast Cooling of a Steel Plate

This study deals with the effect of oxide layer during ultra-fast cooling of a hot plain carbon steel plate. In the current research, the hot plain carbon steel plates were cooled from an initial surface temperature of 900°C by using air atomized spray at different air pressures. The heat transfer analysis illustrates that during high pressure air atomized spray cooling, the average surface temperature is almost unaffected by the presence of an oxide layer. For better understanding, the plain carbon steel cooling data have been compared with the data obtained during the cooling of a stainless-steel plate.

클래드강 맞대기 용접부의 후열처리 유지시간에 따른 델타 페라이트 거동

Recently, in order to enhance the function and usefulness of products, cladding of dissimilar materials that maximizes the performance of the material is being widely used in all areas of industry as an important process. Clad steel plate, produced by cladding stainless steel plate, an anticorrosive material, on carbon steel plate, is being used to produce pressure vessels. Stainless steel plate has good corrosion resistance, and carbon steel plate has good rigidity and strength; clad steel can satisfy all of these qualities at once. This study aims to find the <TEX>${\delta}$</TEX>-ferrite behavior, mechanical properties, structure change, integrity and reliability of clad steel weld on hot rolled steel plates. For this purpose, multi-layer welding, repair welding and post weld heat treatment were implemented according to welding procedure specifications (WPS). In order to observe the mechanical properties and toughness of clad steel weld zone, post weld heat treatment was carried out according to ASME Sec. VIII Div.1 UW-40 procedure for post weld heat treatment. With heat treatment at <TEX>$625^{\circ}C$</TEX>, the hold time was used as the process variable, increased by intervals that were doubled each time, from 80 to 1,280 min. The structure of weld part was typical cast structure; localized primary austenite areas appeared near central vermicular ferrite and fusion line. The heat affected zone showed rough austenite structure created by the weld heat input. Due to annealing effects of heat treatment, the mechanical properties (tensile strength, hardness, impact value) of the heat affected area tended to decrease. From the results of this study, it is possible to conclude the integrity of clad steel welds is not affected much in field welding, repair welding, multi-layer welding, post weld heat treatment, etc.

Experimental Investigation of Effect of Different Types of Surfactants and Jet Height on Cooling of a Hot Steel Plate

Heat transfer studies of a hot AISI 304 stainless steel plate by water jet impingement with different concentrations of three different types of surfactants have been investigated. The study involves a square plate of 100 mm × 100 mm surface area and 6 mm thickness with three subsurface thermocouples positioned at various locations inside the plate. The influence of jet height has been studied by varying the distance between the nozzle and plate from 200 mm to 600 mm. The results show that the heat transfer rate is found to increase with the jet height up to 400 mm and thereafter decreases due to capillary instability of liquid jet. Based on the maximum surface heat flux obtained for a particular nozzle height of 400 mm and an initial surface temperature of 900 °C, further experiments have been carried out with different types of surfactants. The types of surfactants used in the experimental study are anionic surfactant (sodium dodecyl sulphate, SDS), cationic surfactant (cetyltrimethylammonium bromide, CTAB) and nonionic surfactant (Polyoxyethylene 20 sorbitan monolaurate, Tween 20). During cooling, the transient temperature data measured by thermocouples have been analyzed by inverse heat conduction procedure to calculate surface heat flux and surface temperatures. The increase in surface heat flux has been observed with increasing concentration of surfactants and it has been found to be limited to a particular concentration of surfactant after which further increase in concentration leads to decrease in heat flux. Use of surfactant added water minimizes the surface tension and promotes better spreadability of coolant on the test specimen by reducing the solid–liquid contact angle. The maximum heat transfer rate has been found by using nonionic surfactant additive which can primarily be attributed to its lesser foam formability nature.

Mixed-surfactant additives for enhancement of air-atomized spray cooling of a hot steel plate

The current study covers the cooling enhancement of a hot stainless steel plate using mixtures of ionic and nonionic surfactant additives in air-atomized water spray. The surfactant when dissolved in water, exhibits surface activity to influence the atomization process as well as solid–liquid contact by forming a monolayer at air–water interface. The properties of monolayer formed by mixed-surfactant systems depend on the interactions between the surfactants such that the heat transfer rate differs from that of the surface. In this study, sodium dodecyl sulfate (an anionic surfactant), cetrimonium bromide (a cationic surfactant), and polysorbate 20 (Tween 20, a nonionic surfactant) have been used. For detailed analysis on heat transfer performance of mixed-surfactants, the optimum concentration levels of the three surfactants have been considered from the authors’ earlier work. A test plate of AISI 304 designated steel of surface area 100mm×100mm and a thickness of 6mm has been employed with three subsurface thermocouples to collect the transient temperature data during cooling from an initial surface temperature of 900°C. A commercial inverse heat conduction software, INTEMP has been used to estimate the surface heat flux and temperatures such that the cooling rates can be calculated for all the experiments. The results are analyzed to see the effect of mixed-surfactants on cooling performance of the hot plate, which reveal that the mixtures of nonionic and ionic surfactants give higher heat transfer enhancement than those of the individual surfactants in water. However, catanionic surfactant mixture diminishes the heat transfer ability of pure water. Overall, a maximum cooling rate of 240°C/s and heat transfer co-efficient of 20,000W/m2°C can be achieved from this study which is very important for run-out table cooling of a Hot Strip Mill in steel industry.

Experimental investigation of air-atomized spray with aqueous polymer additive for high heat flux applications

The experimental investigation of using a water based polymer additive to enhance the spray cooling performance of hot steel plate, has been carried out in the current research. This is essentially important to produce high-strength steel on the run-out table (ROT) of a Hot Strip Mill. The ultra-high heat flux cooling system has been developed using an air-atomized spray, containing dissolved polyvinylpyrrolidone (PVP) in water at different concentration ranges between 10 and 150ppm and compared with the cooling performance of pure water. To understand the heat transfer mechanism of aqueous polymer solutions, the physical properties such as surface tension, viscosity and thermal conductivity were measured. The cooling experiments were conducted using an AISI 304 stainless steel plate of 6mm thickness initially kept at a temperature above 900°C, where the Leidenfrost effect is predominant. In these experiments, the transient temperature data during cooling has been measured with three subsurface thermocouples and this time-temperature history has been used to estimate the surface temperature and the surface heat flux histories using a commercial inverse heat conduction software namely, INTEMP. The results explain that the polymer solution has a significant effect on the enhancement of surface heat flux, critical heat flux, as well as the cooling rate of the test plate. It was observed that an increase in the polymer concentration increases the heat transfer rate up to an optimal concentration; after which it results in a reduction in the rate. A maximum cooling rate of 253°C/s was obtained with a critical heat flux of 4.212MW/m2, which can be termed as the higher range of an ‘Ultrafast cooling’ process. Overall, the aqueous polymer solution can serve as a better heat transfer fluid for high heat flux applications.

Multi-jet Impingement Cooling of a Hot Flat Steel Plate

One of the most important steps to control the quality in steel hot rolling is the Runout Table (ROT) Cooling. In this investigation, the heat transfer of water jets impinging on a hot flat steel plate was studied under temperatures below the boiling point to understand the convection heat transfer phenomena which is a major step preceding the boiling. Single axisymmetric jet and a pair of interacting jets are simulated using Computational Fluid Dynamics (CFD). The RANS model under steady and transient conditions as well as the k-ɛ turbulence model are used for both 2D axisymmetric and 3D simulations. The water flow rate influence on the jets cooling characteristics is investigated.Two sets of boundary conditions, constant temperature and constant heat flux were applied at the surface of the steel plate and evaluated. The single jet numerical results are successfully compared to published data based on measurements and analytical models. The two jets thermal performance was found to be unaffected because the jets are too far from each other to generate any additional thermal interaction.

Optimization of Mechanical Properties of Low Carbon Bainitic Steel Using TMCP and Accelerated Cooling

The recent increased severity in service conditions, such as frequent earthquakes, have further promoted the development of steel production technologies for many types of microstructural control. In the present paper, two-stage thermomechanical control process (TMCP) combined with accelerated cooling was employed to control the microstructural evolution and to study the microstructure-property relationship of low carbon bainitic steel. The main microstructure of hot rolled steel plates changed from granular bainite to lath bainite (or bainitic ferrite) when the final accelerated cooling temperature decreased from about 530 to 430°C, accompanied with a notable increase in yield strength at the expense of slightly decreasing toughness. The strengthening mechanism was mainly attributed to dislocation strengthening and precipitation strengthening for this low carbon microalloyed steel. In addition, if the strain hardening exponent of hot rolled steel plate with the thickness of 13mm is expected to be higher than 0.1, the final cooling temperature range should be maintained above 500°C.

Enhancement of heat transfer rate in air-atomized spray cooling of a hot steel plate by using an aqueous solution of non-ionic surfactant and ethanol

Air-atomized spray cooling, where compressed air atomizes water into fine droplets, is an efficient alternative to conventional cooling techniques. The present work deals with the air-atomized spray cooling of a 6 mm thick stainless steel plate having an initial surface temperature of 900 °C, using surfactant Tween 20 and ethanol additives. The main difficulty in achieving a high cooling rate at elevated surface temperatures is the Leidenfrost phenomenon. The metallurgical properties of steel are highly affected by the run-out table cooling rate between the temperature range of 900–600 °C. Another important cooling region, particularly to achieve the high strength martensite microstructure in steel, is 900 °C–200 °C. Therefore, in this study, the heat transfer studies have been done over those temperature regions. The physical properties of the coolant mixture were measured to understand the heat transfer enhancement mechanism. The results show that increasing the ethanol fraction in pure water (with or without surfactant) enhances the critical heat flux, heat transfer coefficient and cooling rate of a hot surface in the nucleate and transition boiling regimes. A maximum cooling rate of 183 °C/s has been obtained with the ethanol–water mixture; whereas ethanol–water–surfactant mixture gives a cooling rate of 235 °C/s, both of which lie in ‘ultrafast cooling’ regime.

Ultra fast cooling of hot steel plate by air atomized spray with salt solution

In the present study, the applicability of air atomized spray with the salt added water has been studied for ultra fast cooling (UFC) of a 6 mm thick AISI-304 hot steel plate. The investigation includes the effect of salt (NaCl and MgSO4) concentration and spray mass flux on the cooling rate. The initial temperature of the steel plate before the commencement of cooling is kept at 900 °C or above, which is usually observed as the “finish rolling temperature” in the hot strip mill of a steel plant. The heat transfer analysis shows that air atomized spray with the MgSO4 salt produces 1.5 times higher cooling rate than atomized spray with the pure water, whereas air atomized spray with NaCl produces only 1.2 times higher cooling rate. In transition boiling regime, the salt deposition occurs which causes enhancement in heat transfer rate by conduction. Moreover, surface tension is the governing parameter behind the vapour film instability and this length scale increases with increase in surface tension of coolant. Overall, the achieved cooling rates produced by both types of salt added air atomized spray are found to be in the UFC regime.

Enhancement of Cooling Rate for a Hot Steel Plate using Air-Atomized Spray with Surfactant-Added Water

The objective of the current research deals with the experimental study of an air-atomized spray with surfactant-added water, cooling a 12-mm-thick AISI-1020 stationary steel plate at three different initial surface temperatures (400°C, 600°C, and 900°C). Furthermore, the effects of surfactant concentration and airflow rate on the cooling rate have been investigated. The surface heat flux and surface temperature show a significant improvement in cooling for all three cases of initial surface temperatures when the air-atomized spray was used with surfactant-added water.

Experimental investigation of free-surface jet impingement quenching process

Liquid jet impingement cooling technique is critical in many industrial processes, such as fuel bundle cooling post-loss-of-coolant-accident in nuclear reactors, heat treatment of metal parts post-hot-processing, etc. The ability of liquid jets to extract high heat flux from metal parts, with temperatures as high as 800–1000°C, at moderate flow rates has made them indispensable in these applications. The complex mechanism of flow boiling heat transfer during jet impingement cooling is not been well understood. This study presents a systematic methodology for the measurement and estimation of the temporospatial variation of heat transfer on the impingement surface during jet impingement cooling of extremely hot steel plate. The effect of jet impingement velocity and subcooling variations from 2.5 to 10m/s and 60 to 87K, respectively, on the temporospatial heat transfer variation on the impingement surface is reported.A gradually growing circular wetted region, with its periphery named as the wetting front, forms soon after the cooling starts but its velocity decreases as it grows in diameter. A local maximum in the surface heat flux closely follows the wetting front, with the local maximum heat flux reducing with distance from the stagnation point. The wetting front velocity and local maximum heat flux increase with both the jet velocity and subcooling. The enhancement in the local film velocity and subcooling result in a strong suppression of boiling activity and, resultantly, high heat transfer rates at plate surface temperatures in much excess of the critical temperature of the coolant is achieved. This observation confirms the industrial practice of using impinging jets for accelerated cooling of hot steel plates.

Experimental study of the effect of spray inclination on ultrafast cooling of a hot steel plate

The ultrafast cooling that occurs during high mass flux air-atomized spray impingement on a hot 6 mm thick stainless steel plate has been studied experimentally in terms of the nozzle inclination between 0° and 60°. The average mass flux of water used in the study accounts to 510 kg/m2 s. The coolants used in the study are pure water and surfactant water of 600 ppm concentration. The initial temperature of the plate has been maintained at 900 °C, which is the temperature of a hot strip on run-out table in steel industry. The transient surface heat flux and temperature histories have been estimated by an inverse heat solver using measured temperature input data. Heat transfer results demonstrates that optimum cooling efficiency (~2.76 MW/m2, 194 °C/s) for pure water has been achieved at 30° nozzle orientation. The inclined nozzle has not been found beneficial when surfactant water is used as the coolant.

Achievement of ultrafast cooling rate in a hot steel plate by air-atomized spray with different surfactant additives

Ultrafast cooling of a 6mm thick hot stainless steel plate (AISI 304) has been achieved by high flow conditions of air and water, which is needed at the runout table of a hot strip mill to develop advanced high strength steels. The present study primarily focuses on the effect of adding different types of surfactants at various concentration levels to air atomized water spray for enhancement of ultrafast cooling rate. The anionic, cationic and non-ionic surfactants used have been characterized by measuring their surface tension, contact angle and viscosity. The surfactant enhanced heat transfer experiments have been conducted with a full cone atomizer at a fixed nozzle to surface distance using constant air and water flow rates optimized earlier. The initial surface temperature of the test plate has been maintained at 900°C in each case. The experimental measurements have been applied to a commercial inverse heat conduction solver (INTEMP) to estimate local surface heat flux as well as surface temperature histories. The concentration of all the surfactants has been optimized based on the highest cooling rate. Depending on their spreadability, wetting characteristics and ability to foam formation, the cationic and non-ionic surfactants are found to produce better cooling effects than the anionic surfactant. These enhanced ultrafast cooling rates can be useful to produce advanced high strength steels in the steel industries.

Study on Hot Stamping and Usibor 1500P

Nowadays, automobile industry is under the pressure of market requirements of lightweight and energy-efficient. In order to follow the trend, automobile manufacturers have made their unremitting efforts in diverse aspects of materials research and development, designing and manufacturing. This thesis has explored the hot aspect, mechanical aspect, microscopic structure and the latest status of technical domain of hot stamping. The analysis is made on the main technology of hot stamping forming and its working process, and the application of hot stamping technology on automobile and advantages of this technology are expounded, respectively. This thesis has made a systematic introduction on the core technology of hot stamping and its pros and cons through testing the coating hot stamping steel plates, and pointed out the current status of its application as well as its future prospect.