Concentration gradients of inclusions during inductive and gas stirring of AISI H13 tool steel in... more Concentration gradients of inclusions during inductive and gas stirring of AISI H13 tool steel in a ladle have been studied using a unique experimental technique at Uddeholm Tooling AB in Sweden. A specially designed sampling equipment , which allows five samples to be taken at the same time and at different depths was used. The aim was to experimentally quantify the existence of inclusion size population gradients in different positions of the steel melt. One experiment was carried out using induction stirring and one using gas stirring. The main findings from the induction stirring experiment was that i) concentration gradients of inclusions exist, ii) the number of inclusions decreases with stirring time in all positions, and iii) that the superficial positions show a more rapid decrease than the deeper ones. The main findings from the gas stirring experiment are that i) concentration gradients of inclusions exist, ii) the superficial positions are mostly affected by the gas plumes, and show a very pronounced decrease of the number of inclusions with stirring time, and iii) the deeper positions and also one of the superficial position (no "3") shows no decreasing trend.
A static modelling approach was used to studythe growth and removal of inclusions during gas stir... more A static modelling approach was used to studythe growth and removal of inclusions during gas stirring in a ladle. A mathematical model of a gas-stirred ladle was used to predict the data necessary to calculate growth and removal of inclusions. Results indicated that inclusion growth resulting from laminar shear collisions is negligible incomparison with growth from turbulent and Stokes collisions. Furthermore, the need fora model describing inclusion flotation byspherical-cap bubbles was identified. Sincethe existing models presented inthe literature are only valid forspherical bubbles, a model forthe removal of inclusions byspherical-cap bubbles was developed. Inclusion removal to the slag, refractory and by bubble flotation was compared. The mechanism determined to be responsible for the removal of the majority of inclusions largerthan 25 urn was Stokes flotation and forthe majority ofthe smaller inclusions, bubble flotation byspherical-cap bubbles (assuming plane contact between the inclusion and the bubble).
Mathematical CFD simulations of inclusion growth and removal in stirred ladles have shown that si... more Mathematical CFD simulations of inclusion growth and removal in stirred ladles have shown that size distribution gradients exist during different parts of stirring. Therefore, special plant experim ...
The purpose of this study has been to theoretically evaluate which inclusion growth mechanisms ar... more The purpose of this study has been to theoretically evaluate which inclusion growth mechanisms are important in an inductively stirred ladle. This has been done using data from a computational fluid dynamics model of a real ladle. The data was utilized as the input to the different collision equations. It was concluded that diffusion of oxygen and deoxidant to the inclusion surface, diffusion coalescence and Brownian motion collisions contribute very little to growth of inclusions during the stirring period in the ladle. This was in accordance with earlier findings in the literature. This study also showed that laminar shear collisions could be excluded from a growth model. The major growth mechanism is turbulent collisions. It was also shown that a 700-A stirring current leads to more growth due to turbulent collisions than a 500-A stirring current.
The overall purpose of this thesis work has been to further our understanding of the growth and r... more The overall purpose of this thesis work has been to further our understanding of the growth and removal of inclusions in gas- and induction-stirred ladles. The primary focus has been on alumina inclusions.Growth mechanisms were studied using data from fundamental mathematical models of gas- and induction-stirred ladles. The results showed the turbulence mechanism to be the most dominant in alumina inclusion growth. The dynamic growth and removal of inclusions in a gas-stirred ladle was studied using mathematical modelling. The model results showed concentration gradients of inclusions. The effect was most obvious in the steel flow past the removal sites: top slag, ladle refractory, and gas plume (bubble flotation). A new removal model was developed for large spherical caps bubbles.In order to verify the predicted concentration gradients for the size population of inclusions, three experiments were carried out in production. The sampling equipment enabled sampling at five different positions and different locations at the same time. The results showed that concentration gradients of inclusions do exist both in induction-stirred and gas-stirred ladles. A theoretical analysis showed that the drag force on the inclusions to be the dominating force and that therefore inclusions follow the fluid flow.The cluster behaviour of alumina inclusions were examined on steel samples taken in an industrial-scale deoxidation experiment in a ladle. The samples were examined by microscope and the results used to study cluster growth. It was found that there was rapid cluster growth due to collision during stirring and that at the end of the deoxidation experiment a majority of the small inclusions were bound in clusters. The cluster growth data determined using the microscopic results were compared with predicted cluster-growth data. A method was developed for converting the experimental data observed per unit area into data given per unit volume and vice versa. An expression for the collision diameter of the cluster was also developed. The results showed that the predicted cluster growth agreed well with the microscopic observations for the assumptions made in the growth model.
The ever increasing demand of high performance rolls in the late finishing stands (F5-F7) for hot... more The ever increasing demand of high performance rolls in the late finishing stands (F5-F7) for hot strip mills (HSM) requires better product solutions from roll suppliers. Roll development activities never stop at Union Electric Åkers (UEÅ) in order to meet the requirement. The HYBRID STEEL, a new concept of roll materials especially for the late finishing stands in the HSM, is successfully developed in UEÅ. This paper reviewed the development of previous ICDP as well as enhanced ICDP (eICDP) roll materials, and, the novel HYBRID STEEL roll grade. Rolls manufactured by this new grade have been used in several European mills. A significant improvement over the enhanced ICDP rolls has been observed.
Concentration gradients of inclusions during inductive and gas stirring of AISI H13 tool steel in... more Concentration gradients of inclusions during inductive and gas stirring of AISI H13 tool steel in a ladle have been studied using a unique experimental technique at Uddeholm Tooling AB in Sweden. A specially designed sampling equipment , which allows five samples to be taken at the same time and at different depths was used. The aim was to experimentally quantify the existence of inclusion size population gradients in different positions of the steel melt. One experiment was carried out using induction stirring and one using gas stirring. The main findings from the induction stirring experiment was that i) concentration gradients of inclusions exist, ii) the number of inclusions decreases with stirring time in all positions, and iii) that the superficial positions show a more rapid decrease than the deeper ones. The main findings from the gas stirring experiment are that i) concentration gradients of inclusions exist, ii) the superficial positions are mostly affected by the gas plumes, and show a very pronounced decrease of the number of inclusions with stirring time, and iii) the deeper positions and also one of the superficial position (no "3") shows no decreasing trend.
A static modelling approach was used to studythe growth and removal of inclusions during gas stir... more A static modelling approach was used to studythe growth and removal of inclusions during gas stirring in a ladle. A mathematical model of a gas-stirred ladle was used to predict the data necessary to calculate growth and removal of inclusions. Results indicated that inclusion growth resulting from laminar shear collisions is negligible incomparison with growth from turbulent and Stokes collisions. Furthermore, the need fora model describing inclusion flotation byspherical-cap bubbles was identified. Sincethe existing models presented inthe literature are only valid forspherical bubbles, a model forthe removal of inclusions byspherical-cap bubbles was developed. Inclusion removal to the slag, refractory and by bubble flotation was compared. The mechanism determined to be responsible for the removal of the majority of inclusions largerthan 25 urn was Stokes flotation and forthe majority ofthe smaller inclusions, bubble flotation byspherical-cap bubbles (assuming plane contact between the inclusion and the bubble).
Mathematical CFD simulations of inclusion growth and removal in stirred ladles have shown that si... more Mathematical CFD simulations of inclusion growth and removal in stirred ladles have shown that size distribution gradients exist during different parts of stirring. Therefore, special plant experim ...
The purpose of this study has been to theoretically evaluate which inclusion growth mechanisms ar... more The purpose of this study has been to theoretically evaluate which inclusion growth mechanisms are important in an inductively stirred ladle. This has been done using data from a computational fluid dynamics model of a real ladle. The data was utilized as the input to the different collision equations. It was concluded that diffusion of oxygen and deoxidant to the inclusion surface, diffusion coalescence and Brownian motion collisions contribute very little to growth of inclusions during the stirring period in the ladle. This was in accordance with earlier findings in the literature. This study also showed that laminar shear collisions could be excluded from a growth model. The major growth mechanism is turbulent collisions. It was also shown that a 700-A stirring current leads to more growth due to turbulent collisions than a 500-A stirring current.
The overall purpose of this thesis work has been to further our understanding of the growth and r... more The overall purpose of this thesis work has been to further our understanding of the growth and removal of inclusions in gas- and induction-stirred ladles. The primary focus has been on alumina inclusions.Growth mechanisms were studied using data from fundamental mathematical models of gas- and induction-stirred ladles. The results showed the turbulence mechanism to be the most dominant in alumina inclusion growth. The dynamic growth and removal of inclusions in a gas-stirred ladle was studied using mathematical modelling. The model results showed concentration gradients of inclusions. The effect was most obvious in the steel flow past the removal sites: top slag, ladle refractory, and gas plume (bubble flotation). A new removal model was developed for large spherical caps bubbles.In order to verify the predicted concentration gradients for the size population of inclusions, three experiments were carried out in production. The sampling equipment enabled sampling at five different positions and different locations at the same time. The results showed that concentration gradients of inclusions do exist both in induction-stirred and gas-stirred ladles. A theoretical analysis showed that the drag force on the inclusions to be the dominating force and that therefore inclusions follow the fluid flow.The cluster behaviour of alumina inclusions were examined on steel samples taken in an industrial-scale deoxidation experiment in a ladle. The samples were examined by microscope and the results used to study cluster growth. It was found that there was rapid cluster growth due to collision during stirring and that at the end of the deoxidation experiment a majority of the small inclusions were bound in clusters. The cluster growth data determined using the microscopic results were compared with predicted cluster-growth data. A method was developed for converting the experimental data observed per unit area into data given per unit volume and vice versa. An expression for the collision diameter of the cluster was also developed. The results showed that the predicted cluster growth agreed well with the microscopic observations for the assumptions made in the growth model.
The ever increasing demand of high performance rolls in the late finishing stands (F5-F7) for hot... more The ever increasing demand of high performance rolls in the late finishing stands (F5-F7) for hot strip mills (HSM) requires better product solutions from roll suppliers. Roll development activities never stop at Union Electric Åkers (UEÅ) in order to meet the requirement. The HYBRID STEEL, a new concept of roll materials especially for the late finishing stands in the HSM, is successfully developed in UEÅ. This paper reviewed the development of previous ICDP as well as enhanced ICDP (eICDP) roll materials, and, the novel HYBRID STEEL roll grade. Rolls manufactured by this new grade have been used in several European mills. A significant improvement over the enhanced ICDP rolls has been observed.
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