Materials Science Forum Vol. 762

Abstract: Some surface defects on hot rolled steels arise due to poor descaling. Generally reheated slabs are efficiently descaled but, now and then, residual scale remains on the slab after primary descaling. Commonly it is difficult to trace the few poorly descaled slabs since there often is no scale monitoring system. In the work presented here an image based primary scale monitoring-and evaluation system is presented. It is a stand-alone online vision system consisting of a camera connected to a computer. The camera is located directly after the descaling unit and the computer in the control room. The program automatically locates the boundaries of the top surface of a slab and calculates the quantity of residual scale on the top surface. The quantity of residual scale is logged and can afterwards be evaluated together with process parameters and downstream surface defects to identify problem areas. The system has been tested in industrial scale in the Ruukki plate mill. This work is a cooperation between Swerea MEFOS and Ruukki. The result of the test demonstrated the feasibility of using vision system for detection of residual scale. Some problems were identified and suggestions for solving them are reported. If the suggested modifications are carried out, it is believed that the vision system can be an on-line tool for the operator and also be an off-line resource for the ongoing quality work at the hot rolling mill.

Abstract: Optical emission spectrometry, OES, has been used widely to define the chemical element analysis. The possibility to use OES-PDA-data to identify the amount of inclusions in steel has been studied to get a quick knowledge about inclusions during the process. From the histogram of intensity levels the amount of chemical element being in steel matrix and in inclusions can be observed. The inclusions are observed to be in the tail of histogram. The setting of a correct threshold to divide the histogram into steel matrix and inclusions parts isproblematic. In this research some statistical methods and a histogram threshold method are tested for OES-PDA-data from steel samples.The research discussed in this paper has been carried out in co-operation with Ruukki Metal, at their Raahe Works in Finland. Steel samples were taken from different process stages and different process routes. The objective was to examine the amounts of inclusions at different process stages and how they differ during the process. The research was focused on the chemical elements that are most common in the inclusions. From the results it is observed that calcium and aluminium are identified pretty well, but for other elements both correct and incorrect results are obtained. This method shows a potential to identify the amount of inclusions, though further research is needed.

Abstract: In the signal processing method, envelope analysis is a useful method to evaluate the rolling element bearing problems and Wavelet transform is a powerful method to detect faults occurred on gearboxes. However, exact method for AE signal is not developed yet. Therefore, in this paper, two methods, which are Hilbert Transform (HT) and Hilbert-Huang transforms (HHT), will be compared for development a signal processing method for early fault detection system by using AE. HHT has better advantages than HT because HHT can show the time-frequency domain result. But, HHT needs long time to process a signal, which has a lot of data, and has a disadvantage in de-noising filter.

Abstract: Efficiency improvements in ships lead often to increased size and speed. However, due to the increase in the agency's output, the weight of the propeller, propulsion shaft, vane pitch and the number is increased. Simultaneously, various. vibrations occur in the shaft. Thus, the design of shaft, and vibration analysis has become a challenging matter. In this study the vibration analysis of ship propulsion shaft has been performed, considering the stern bearing characteristics, and established the measures for shaft vibration with suggestion for shaft design method.

Abstract: The demand and importance of vacuum pumps are increasing, because the necessity of dry vacuum pump is proven in semiconductor industry. Various types of vacuum pumps have been developed, and in this research a roots type vacuum pump has been analyzed with a variety of mathematical analysis. Analysis of eigenvalue by FEM analysis and Modal Test were performed through the Roots type vacuum pump and using the results of irregular vibration and instability an assessment has been performed.

Abstract: Fatigue is a common phenomenon in welded structures. Prediction of fatigue life of welded joints in-service is still an unsolved puzzle by the conventional linear ultrasonic testing method. However, the nonlinear ultrasonic waves or the acoustic nonlinear signal can provide clear signs of the accumulative fatigue damage in materials, as reported by a number of researchers. Hence, the nonlinear ultrasonic testing method has revealed a tremendous potential for fatigue damage evaluation. This paper presents a study to characterize the fatigue damage using the analysis of the signal characteristics and a new nonlinear parameter. Based on the very high-cycle fatigue testing results for a 6N01 aluminum alloy welded joint, the relationship between the amplitude of the second-order harmonic and fatigue cycling has been established. The nonlinear ultrasonic system test results show that the amplitude of the second-order harmonic increases at the early fatigue stage, with further increase in cyclic loading until reaching a peak. Metallographic examinations show that a fatigue crack will nucleate in the weld joint in the stage as the amplitude reaches the peak value. Finally, theoretical and experimental results confirm that the amplitude of the second-order harmonic is useful for assessing the fatigue life of a 6N01 aluminum alloy welded joint.

Abstract: In this paper, fatigue damage and life prediction of laser lap joints were investigated based on natural frequency as the damage variable. At each fatigue stage, damage degree of laser welded specimen was monitored by the fatigue test and dynamic response tests. The results show that in the fatigue process during the increase in the number of fatigue cycles, each order natural frequency of test specimen decreased at different rate. There was almost no damage before the number of cycles reached 60% of the fatigue life, and then cracks began to initiate. When the number of cycles reaches 80% of the life, macroscopic cracks appeared and the predicted damage degree reached to 50%. Based on relation between the change rate of the natural frequency and the fatigue damage, a new fatigue life prediction model was established. The results from experimental tests were consistent with the fatigue life prediction model.

Abstract: Numerical models of steelmaking processes are essential tools for process development and optimisation. A usable model is detailed enough to provide reliable results and not to slow to run. In order to make a fast and accurate model of a single process, all model parameters must be known well. This can be achieved by first simulating detailed models from which the parameters are obtained.In many converter processes oxygen is delivered into melt by supersonic top lance blowing. When such process is modeled, a model describing mass transfer from the lance into melt surface is needed.This paper describes numerical modeling of mass transfer by supersonic lances. Lance flow CFD models are used to determine mass transfer coefficients for typical lance applications. Models are validated with supersonic nozzle data and wall impinging jet mass transfer data from literature. The results are later used in fast process simulation models.

Abstract: Research group of Metallurgy at Aalto University has been developing simulation models and tools for continuous casting since from the early 80s. The main models developed are the heat transfer model, DYN3D, and the solidification and microstructure model IDS. The models have been further developed and integrated to a continuous casting simulator and to a slab simulator. The continuous casting simulator calculates the important phenomena taking place in the strand during casting and the slab simulator calculates the phenomena taking place in the slabs when they are transferred from caster to reheating furnace. The numerical solution algorithms in the simulators are so fast that they can be used in on-line applications. The simulators have today many new options as hydrogen removal and quality prediction modules. In this paper, the simulators and their modules are presented.

Abstract: Modeling of the transformation of the starting ferritic-pearlitic microstructure into austenite during heating in continuous annealing process was the objective of the work. Kinetics of this transformation was predicted by solving Avrami equation as well as carbon diffusion equation with a moving boundary. Mathematical and numerical models describing austenitic phase transformation were created for the 1D and 2D domains. Developed models were solved using the Finite Difference, as well as the Finite Element Method. Results of the numerical simulations include austenite volume fraction and carbon segregation profiles in the austenite. The former were compared with the experimental data obtained in laboratory simulations of the continuous annealing. Developed and validated model was applied to simulation of the austenitic transformation during annealing of DP steels.