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This report summaries the work within the project ”Effect of spatial-temporal behavior of a newly developed cooling system on carbon and stainless-steel bar properties”. The project was conducted from 2020-01-01 to 2022-12-31 and was co-produced by SSAB, Outokumpu and University of Gävle (UoG). The Knowledge Foundation, SSAB, Outokumpu and UoG financed the project. For the Swedish steel companies SSAB and Outokumpu producing special steels, it is very important to be able to control the cooling process in order to produce steel bars with excellent properties. Both steel companies also want to be able to control the cooling process so that the excellent steel properties become even over the bars’ spatial configuration. The aim of the present project is to reveal the spatial-temporal behavior of a newly developed cooling technology in order to produce steel bars with excellent properties and to control the phase transformation to achieve optimal performance of the steel bars. By using the special test rig at the UoG, detail temperature measurement mapping, invers solution and direct numerical simulation, the present project has identified and quantified several important aspects related to the quenching process, operating conditions, and temperature field development within the investigated products. The result from the proposed cooling process provides an outstanding cooling rate that is very crucial to obtain the required steel phase and thus the correct properties of the bar with different sizes. Results from this study have also shown that the cost per kg product can be reduced by tunning the process parameters such as soaking time and bar temperature before starting the cooling process. In addition, both experimental and numerical results of the material investigation show that the cooling technology has resulted in the desired phase transformation and subsequently the desired steel phases and material properties. The results show that the cooling technology and, Funding: The Knowledge Foundation, SSAB, Outokumpu and University of Gävle, Effect of spatial-temporal behavior of a newly developed cooling system on carbon and stainless steel bar properties

The worldwide competitive market on metal products with higher quality in industry has increased the need to implement more advanced and controllable quenching techniques in the hardening stage of the heat treatment process. Moreover, sustainability and energy efficiency are key factors to consider in the development of advanced quenching techniques. Among various cooling methods that are used in industry, a water impinging jet quenching system is one of the few that offers wide flexibility to adjust cooling rate based on the chemical composition and proper phase transformation in the continuous cooling transformation diagram (CCT) to achieve desired material properties. On an industrial scale, a large number of water impinging jets are placed in the cooling configuration introducing multiple array of jets in the quenching system. In the literature study by the author, there has been interest to study the quenching heat transfer by single water jet in various applications. Even so, little scientific attention has been paid to the multiple array of water impinging jets and the importance of various quenching parameters on the quenching heat transfer with multiple array of jets. This thesis deals with a study of quenching rotary hot hollow cylinder with multiple configurations of water impinging jets. The aim of this investigation is to obtain better understanding of boiling heat transfer phenomena in application of multiple array of water impinging jets and quenching parameters. An experimental test rig was designed to control most influential parameters in quenching experiments. The results of experimental study contained recorded temperature data beneath the quenching surface of a hollow cylinder. A heat conduction inverse solution based on the GMRES method was developed for application of quenching hollow cylinder. This model used the recorded temperature data of quenching experiments to predict surface temperature and heat flux. A thorough parametric study inves, Den världsomspännande konkurrenskraftiga marknaden för metallprodukter med högre kvalitet i branschen har ökat behovet av att implementera mer avancerade och kontrollerbara kylningstekniker i härdningsfasen av värmebehandlingsprocessen. Dessutom är hållbarhet och energieffektivitet nyckelfaktorer att beakta vid utvecklingen av avancerade kylningstekniker. Bland de olika kylmetoderna som används i industrin är kylningssystem med impinging jetstrålar ett av få som erbjuder bred flexibilitet för att justera kylhastigheten baserat på den kemiska sammansättningen och korrekt fasomvandling i CCT diagrammet (continues cooling transformation) för att uppnå önskade materialegenskaper. I industriell skala placeras ett stort antal impinging jetstrålar för vatten i kylkonfigurationen, vilket introducerar matriser av jetstrålar i kylningssystemet. I författarens litteraturstudier har det funnits intresse för att studera värmeöverföringen med en impinging jetstråle i olika applikationer. Trots det har föga vetenskaplig uppmärksamhet ägnats åt matriser av impinging jetstrålar och vikten av olika kylningsparametrar för denna kylteknik. Denna avhandling behandlar studier av härdning av en roterande varm ihålig cylinder med flera konfigurationer av impinging jetstrålar. Syftet med undersökningen är att få bättre förståelse för värmeöverföringsfenomen p.g.a. kokning vid användning av matriser av vattenstrålar med impinging jettekniken och olika härdningsparametrar. En experimentell testrigg utformades för att undersöka de mest påverkande parametrarna i härdnings-experimentet. Resultaten av de experimentella studierna innehöll mättade temperaturdata under den ihåliga cylindersytan. En inversvärmeledningslösning baserad på GMRES-metoden utvecklades för applicering vid kylning av en ihålig cylinder. Denna modell använde mättade temperaturdata från härdningsexperimentet för att förutsäga yttemperatur och värmeflöde. Vid en grundlig parametrisk studie undersöktes effekten av olika härdning

Experimental study has been carried out to investigate transient quenching of rotary hollow cylinder by subcooled water impinging jets (∆Tsub= 55-85K) in 1-row and 2-row inline array. The flow rate of water jets varied from 2.7 to 10.9 L/min, impinging on hot rotary cylinder (Ti =600℃) with rotation speed 10-50 rpm and different curvature ratio (Do/d = 12, 19 and 24). The local average and maximum boiling heat transfer at water jet’s stagnation point revealed effect of studied quenching parameters and multiple jet arrays in the boiling heat transfer. The result showed among the studied parameters, jet’s flow rate and curvature ratio influenced heat transfer in all the boiling regimes. Rotation speed was effective in film and transition boiling regime and strong effect of subcooling was captured in the transition boiling regime. The characteristics of maximum heat flux point in the boiling curve were found to be dependent on the studied quenching parameters as well as array of nozzles. Multiple jet arrays had effect on the spatial variation and rate of boiling heat transfer on quenching surface. The heat transfer enhancement by larger number of rows, i.e. 2-row array, was studied based on two approaches of constant single jet’s flow rate and array’s total flow rate. The result shown better heat transfer performance is achieved by increasing number of row in the array while the total flow rate is constant. It was found that by impinging constant water flow rate into the jets, 2-row array with twice the number of impinging jets enhanced heat transfer significantly in film and transition boiling regime in combination with other quenching parameters.

Transient heat transfer studies of quenching rotary hollow cylinders with in-line and staggered multiple arrays of jets have been carried out experimentally. The study involves three hollow cylinders (Do/d = 12 to 24) with rotation speed 10 to 50 rpm, quenched by subcooled water jets (∆Tsub=50-80 K) with jet flow rate 2.7 to 10.9 L/min. The increase in area-averaged and maximum heat flux over quenching surface (Af ) has been observed in the studied multiple arrays with constant Qtotal compared to previous studies. Investigation of radial temperature distribution at stagnation point of jet reveals that the footprint of configuration of 4-row array is highlighted in radial distances near the outer surface and vanishes further down toward the inner surface. The influence of the main quenching parameters on local average surface heat flux at stagnation point is addressed in all the boiling regimes where the result indicates jet flow rate provides strongest effect in all the boiling regimes. Effectiveness of magnitude of maximum heat flux in the boiling curve for the studied parameters is reported. The result of spatial and temporal heat flux by radial conduction in the solid presents projection depth of cyclic variation of surface heat flux in the radial axis as it disappears near inner surface of hollow cylinder. In addition, correlations are proposed for area- averaged Nusselt number as well as average and maximum local heat flux at stagnation point of jet for the in-line and staggered multiple arrays.

A rotating steel cylinder has been heated up to 600ºC in order to be the cooled down seconds later so that desired material properties are obtained or improved. This process is done by the innovative method of multiple water impinging jets. The aim of this project is to develop a better understanding of the advantages of the multiple water impinging jets quenching method and its flexibility to control the cooling rate. The experimental process has been measured and monitored with measurement instruments such as embedded thermocouples, DAQ system and LabVIEW program. In this way, the curve of temperature drop vs time (among others) has been drawn and analyzed. Numerous tests, focused in different parameters of impinging jets setup, have been carried out in order to study the boiling heat transfer and achieve an optimized cooling setup by water impinging jets technique. Jet’s flow rate was varied between 5.6 and 16.7 l/min, as well as cylinder rotation speed (10 - 50 rpm), initial quenching temperature (300 – 600 ºC), jet-to-jet spacing in the jets configuration (S/d = 4 and 6) and the configuration of multiple array of nozzles (staggered and in-line). The results showed that higher cooling rates are obtained by higher jet’s flow rate, but higher temperature difference was also created in material from center to outer point during cooling process. Higher initial temperature resulted in higher cooling rate in onset of quenching. Results revealed that the footprint caused by rotation speed was captured only in very low rotation speed, creating a cyclic oscillation in the temperature history at the beginning of the quenching process. In comparison of multiple arrays, lower cooling rate was obtained in the fountain points between neighbor jets in the in-line array than in the staggered. More uniform cooling rate was found in the footprint of cooling rate in 3-D counter plot in staggered array. Higher cooling rate was achieved with larger jet-to-jet spacing (S/d), but less