INTRODUCTION (MOTIVATION)
The idea of hot deformation of blooms with the presence of the liquid core is known for a long time. It was widely tested in steel blooms. In this case, according to various researchers, the compression bars in the presence of liquid phase provides a significant reduction in axial porosity and increases the homogeneity of internal structure. However, due to some technological and technical considerations for the use of blooms was quite problematic.
The steady improvement of the quality requirements of continuous casting blooms in the axial zone in the last decade has stimulated the development of the principles of its "soft" compression at the end of solidification in order to suppress the axial porosity and segregation. "Soft" compression (in the UK. Literature - soft reduction or mechanical soft reduction) is one of the most effective ways to improve the quality of the inner layers of continuously cast blooms. In this central part of the bloom is in liquid or semisolid (in England. Literature - mushy zone) condition. However, in practice there is now, at least some original technical solutions to implement this method.
In general, the following basic directions of improvement of the classical scheme of "soft" compression bloom.
First, changes in the cross-section of cast blooms.
At some smelters in Japan and Germany using an improved scheme of soft compression blooms that, in order to create favorable conditions for application of force and control the degree of compression on the faces of large blooms include special trapezoidal tides thickness of 5 ... 12 mm.
These tides further pressed into inside two or three stages. However, such a scheme involves changing the geometric shape of the mold, as well as shape and size of the tides, depending on the location of application of compression, steels, cooling conditions, the location of the hole liquid phase and so on. In turn, the paper presents the data in the development of optimal modes of breakdown of continuously cast blooms of various shapes with a large ratio of width to height. Laboratory experiments were carried out mainly on clay physical models of two types: with a rectangular cross-section with grooves in the widest part of the bloom. Check-developed regimes implemented on existing caster with a block of soft reduction.
Second, the improvement of geometry tool ..
Assessment of quality of continuously cast blooms exposed the "soft" compression showed that in some cases the end product had a fairly large number of internal cracks. It is this fact prompted the company Nippon Steel Corp (Japan) to perform complex studies to assess the influence of the geometry of the working rolls and applied modes of "soft" compression on the process of internal cracks. In particular, the studies varied in width of flat land, the size of compression and the ratio of one-time compression critical with. It was found that with decreasing length of the straight section from 200 to 0 mm total length of internal cracks at the same value? Rc increases. Furthermore, it was also revealed that a growing proportion of equiaxed crystals, the number of internal cracks decreases. Practical implementation of results of completed studies is reflected in the fact that since 1993 the factory of the Nippon Kokan (Japan) for soft-compression, blum cut 400x520 mm using rolls with the length of the barrel 250 ... 300 mm. This allowed ease phase separation and exclude the appearance of internal cracks.
Third, the change in direction of the applied external strain effects.
Traditionally, the implementation of technology "soft" compression involves compression of the blooms in the horizontal rolls, ie through the application of strain effects in the vertical plane to a wide verge bloom. However, the literature contains reports of the research process of "soft" compression, when the strain was applied in the horizontal plane, ie by a narrow verge of bloom.
In the framework of the invention by the task by increasing the homogeneity of deformation to reduce the axial porosity and phase separation and to reduce the number of cracks, which will improve the quality of continuous blooms and billets.
The task is achieved by way of compression of continuously cast blooms and billets in the liquid-solid state includes compression of blooms in the stands, sequentially arranged along the length of the ingot in the zone of final solidification of two phases, respectively, the invention of the first stage compresses ingots shifted one relative to the second in horizontal plane at an angle of 2-6 ° rolls.
The method, which is claimed is as follows. Continuously cast bloom gets in the deformation zone of final solidification, when he is in a two-phase state, in crimp cages located along the ingot in this area in several stages. During the compression of the ingot in such a state is the displacement of the liquid core of the zone final hardening. Also offset shrinkage of the metal. In consequence, a decrease in porosity and axial segregation.
The proposed method provides compression in each of the crimp cages block "soft" compression divided into two interrelated stages. In the first phase ingots obtiskuyut shifted one relative to the second in a horizontal plane at an angle of 2-6 ° rollers of the first series to do with the central part on the width of which is equal to the width of the liquid phase with the degree of deformation of 0,6-1,2% and end sections with the degree of strain not less than 50% of the central.
PARAMETERS OF THE NEW WAY
1. Cut of a workpiece - 335х400 мм
2. Roll diameter - 400 мм
3. Angle Crossing - 1, 2, 4, 6, 8°
4. Rolling speed - 0,01 м/с
5. Degree of deformation - 0,5, 0,6, 0,9, 1,2, 1,5 %
The use of shaped rolls that are displaced one relative to the horizontal plane Drugova cause one side features the crystallization of continuously cast blooms of rectangular or square cross-section, on the other side - the current fluctuations of process parameters and the pouring of multiphase cooling.
In that case, as a result of more intense cooling corners of the ingot, and metal edges that are adjacent to them will have an enhanced level of mechanical properties, and above all strength. As a result of increasing the elastic component in the overall deformation of the ingot. However, giving special crimp rolls profiling will facilitate a more complete penetration of the strain inside the ingot. In addition, the implementation in this case, the uneven compression on the entire width of the verge of contacting the ingot, which compresses it would be advisable because it would assist the overall reduction of tensile stresses in the corners of the ingot.
Additional introduction in the manufacturing process possible, on the shift in the horizontal plane relative to one another compressing rolls is advisable as well allows to vary the width of the central section, which should equal the width of the liquid component. Such a possibility is due to the presence of fluctuations of process parameters rozlivki, which in turn leads to fluctuations in thickness of crust vertical faces of the ingot. However, the production schedules of continuous pouring process does not allow the parameters vary within more than 2%. In that case, a crossing of the rolls at an angle of 2-6% will guarantee the possibility of compression of the central parts in width which equals the width of a liquid phase. Reducing the angle of the intersection at an angle of less than 2% will result in that part of the lateral line that had already crystallized get compression with a high level than desired. Consequently, in these areas arise Annex stretching tension. Increased perekreschivaniyaniya rolls at an angle of more than 6% is also undesirable, since in this case has eroded the quality of processing of the ingot because of compression will not get the boundary areas of an ingot due to the fact that the width of the actual center of the strain will be less than the actual width of the liquid phase.
CONCLUSIONS
For research purposes, and work has been formulated the following tasks:
1. Clarification of existing approaches for further improvement of the technological scheme of deformation of Continuously cast blooms
2. Analysis of existing approaches physical and mathematical modeling
3. Developing a new method of deformation of continuously cast blooms
4. Development of mathematical model of deformation of continuously cast blooms
5. The study VAT metal during physical strain on the conditions of the new method.
BIBLIOGRAPHY
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