The paper presents a detailed analysis of split end and cracking problems that occurred during hot rolling of thermomechanically treated (TMT) grade steel bars. The major analytical tool was a multiscan computer-controlled ultrasonic image analysis system for analysis of the defects observed on transverse cut slices of the billets under investigation. The possible reasons for billet cracking during hot rolling such as a low Mn/S ratio, high casting speed, high degree of superheat, and high inclusion content in steel were analyzed. Additionally in the process parameters such as low roll diameter, high friction, and low reduction ratio were also analyzed. The cracking appeared to be associated with large surface/internal defects, axial porosity, off-centered cavities/porosities, off-centered cracks, and inclusion bands. The analysis results suggested methods to prevent such defects in continuously cast steel billets and to reduce/eliminate split end problems. The casting parameters should include: (a) Mn/S ratio [35, (b) degree of superheat \60°C, and (c) casting speed: \3.0 m/min, where roll radius and initial thickness of the workpiece should be optimized.
The present paper presents the analysis of ultrasonic C-scan images obtained through an automatic computerised multiscan immersion system, to obtain optimum current and frequency of an electromagnetic stirrer (EMS), installed at Billet Caster-1 of LD Shop-1 of M/s Tata Steel Ltd, Jamshedpur. The purpose was to achieve minimum defects and maximum equiaxed zones in the continuously cast steel billets. The amplitudes and positional data were integrated and controlled by a PC based ultrasonic equipment. The defect size and area in C-scan image was calculated automatically by a labelling and clustering algorithm, which showed a good correlation to the condition of actual defects. One low carbon steel Grade-A and one high carbon Grade-A were selected for experimental trials. The experiments conducted with various current and frequency combinations revealed that in general, quality of continuously cast steel billets improved with increasing EMS current in both grades of steel considered in the present work. The most significant improvement was found at 280 A EMS current and frequency 3.5 Hz. Beyond this there was only a marginal improvement in the billet quality as well as equiaxed zone. Based on the experimental observations, it is recommended to operate EMS at 280 A current and EMS frequency at 3.5 Hz in the plant.
The paper presents an attempt to find the possibility of measuring high temperature properties of mould powder slags such as viscosity, break temperature, liquidus temperature during heating as well as solidification start and solidification end temperatures during cooing using ultrasonics. These powders are used in continuous casting of steel and the abnormality in their properties can impact the productivity and quality of the steel products. These properties are in general measured by high temperature rotational viscometers, hot stage microscopes and DTA instruments. Here, the fundamental flexural guided wave mode F(1,1) in a ceramic buffer rod was employed in experiments. The results show the possibility of measuring all the above properties in single experiment by measuring ultrasonic reflection factors during continuous heating and cooling of the mould powders. The advantage of the ultrasonic system is that it can be installed in the plant for online monitoring of these properties. The ultrasonically measured properties of the mould powders supplied by five different suppliers were compared with those measured by rotational viscometers and estimated by mathematical models.
The present paper highlights the potential of high intensity power ultrasound in iron ore beneficiation in reducing alumina, silica and phosphorous from Noamundi as well as Joda iron ores of M/s Tata Steel Ltd. This will ultimately lead to improve productivity and reduce coke rate of blast furnaces/sinter plants. It has been experimentally observed that applying 20 kHz frequency ultrasound for 5 min can bring down the percentage of alumina and phosphorous content from 1?720 and 0?050% to 1?120 and 0?048% respectively in the case of Noamundi iron ores; whereas in Joda iron ores, alumina was reduced from 2?25 to 1?65% and phosphorous from 0?089 to 0?05%.
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