It is important to clarify the characteristic of wear and surface deterioration of the work roll that affected by severe and complex heat and load cycles in the hot strip rolling. To investigate characteristic of wear twin-disc-type high temperature wear testing machine is used. However, specifications of the testing machine vary each institution. We compared the specifications and designed and fabricated a testing machine. High temperature friction and a wear property of High-nickel grain (HiGr) and high speed steel (HSS) were investigated. The amount of wear loss of HSS was about one third of HiGr. The wear rate is defined as a wear loss per unit sliding distance on test discs. Comparing the wear rates with the past literature, it was confirmed that the influence of the temperature is larger than the contact load and the rolling speed.
Finite element analysis of 3D hot rolling wear test was performed. This test consists of two disks, one of which is Material disk made of hot rolled material and another is Roll disk made of the material for roll for hot rolling. These two disks contacts with certain load, and the certain relative sliding velocity is given by rotating each disk with prescribed rotation speed. Firstly, axisymmetric heating process of Material disk was performed in order that heated disk with appropriate distribution of temperature as well as deformation was prepared for 3D hot rolling wear test simulation. Although the induction heating is used in the actual setup, radiant heating process was applied in the simulation. Then, the 3D hot rolling wear test was performed. Heating of Material disk and cooling of Roll disk by water was calculated by heat transfer process between two objects. Wear depth of two disks was estimated by using Archard’s model-based equation. As a result, the change in temperature of Roll disk with contacting with Material disk and cooling by water was evaluated appropriately. For the wear depth, the value was around 100 times larger than that obtained by the corresponding experiment. That was due to incorrect parameter used in wear estimation equation. It was revealed that the comparison to the corresponding experiment was inevitable for further precise simulation.
In hot rolling processes, an accurate prediction of thermal expansion of work rolls is necessary because it affects profile of strips. A precise calculation of thermal expansion requires an accurate heat transfer coefficient between the roll and the strip, and the oxide scale on the surface of the work roll (mill scale) is one of the important factor that affects the heat transfer coefficient. Although clear relation between the mill scale and the heat transfer coefficient is required, it has not clarified because forming mill scale in a laboratory is difficult. In this study, first, we developed a generating method of the mill scale of hot rolling mill in a laboratory. Uniaxial compression contact experiments are used to simulate the contact between the work roll and the strip during the hot rolling. An oxide scale layer that simulates the mill scale was obtained on the surface of punch. The thickness of mill scale which was generated from the different kinds of strips material was measured. Second, the interface heat transfer coefficient for various thickness of mill scale are measured. Heat transfer coefficient is obtained from comparing the measured temperature of punch and the results of computer simulation by FEM. From these results, the relation between the thickness of mill scale and the heat resistance is clarified.
In hot sheet rolling, the sheet end often snakes, contacts the side guide, buckles, and goes into the roll gap, while the overlapped sheet end is squeezed. Although many simulations on sheet snaking are reported, very few researches have been performed to simulate both the sheet snaking and sheet buckling. In this study, we proposed a combined method to simultaneously simulate the sheet snaking through the rigid-plastic FEM and to analyze the sheet buckling by the elementary theory of buckling. The in-plane lateral load and the in-plane bending moment were assumed at the surface of the region for the simulation by the rigid-plastic FEM. The amount of snaking at the sheet end simulated by the rigid-plastic FEM agreed with that calculated from the analysis by the elementary theory. Finally, we clarified the effects of rolling conditions on the occurrence of squeezing, such as the difference in the sheet thickness in the roll axis direction, the difference in the roll gap in the roll axis direction, and the amount of the off-center.
In this study, multi-component white cast irons containing various the amount and combination of MC, M2C and M7C3 carbides were heat treated by hardening and tempering, and their abrasive wear behavior was investigated using Suga type abrasion wear tester.
The wear rate (Rw) decreased greatly with an increase in macro-hardness and slightly with volume fraction of retained austenite (Vγ) regardless of the kinds of carbide or heat treatment conditions. In order to clarify the effect of carbide types on the abrasive wear resistance, the subzero treatment was conducted to get the specimens with very low Vγ and adjusted to almost the same hardness. It was found that in spite of a decrease in total amount of carbides, the specimen containing only MC carbide showed almost same Rw as the basic alloy specimen in which MC and M2C carbides coexisted. On the other hand, Rw increased as the M2C carbide amount increased from that of basic alloy specimen.
This paper discussed reaction on thermal decomposition of limestone and Boudouard reaction.
Thermogravimetric analysis of mixed powder samples of limestone and carbonaceous material was carried out. The ratio of the sequential reaction, αc was 0.65 when limestone powder with large particle size and graphite powder with small particle size were used. It was found that the reactivity varies depending on the states of dispersion and mutual coating of the powder particles. Deep learning by recurrent neural network (RNN) and convolutional neural network (CNN) was applied to calibrate weight loss curve of TG analysis and predict reactivity of samples. The TG curve corrected by RNN was almost equivalent to that processed manually. CNN required more learning to evaluate the reactivity of the sample more accurately in the present conditions. We presented that the constructed models are extremely powerful tool for evaluation of metallurgical reactions.
Pulverized coal injection into blast furnace is the precious technology to decrease the iron making cost. To inject more pulverized coal, it is necessary to investigate the combustion behavior of pulverized coal around the tuyere and many numerical simulations as well as experiments have been carried out. In this paper, by using Extended CPD model which is new devolatilization model and Large Eddy Simulation model, the combustion behavior of individual pulverized coal particles was investigated. The volume fraction of CO+CO2 which is the indicator of how much carbon included in pulverized coal changed to gas phase was reasonably predicted by new simulation model. It is suggested the devolatilization processes of pulverized coals under 40 µm varied widely between individual particles.
In the connection of crack formation in continuously cast slabs, brittleness of ultra low carbon steels caused by sulphur (S) and its recovery by titanium (Ti) addition were evaluated by the reduction area of samples pulled apart in high temperature tensile test and the followings were found: (1) In the case of without Ti addition, brittleness appears in the steels with S content more than around 0.01% due to formation of liquid iron sulphide (FeS) and brittleness does not appear at all with the S content less than 0.003%. (2) In the case of Ti addition, the brittleness in the steels with S content more than 0.009% is improved at the temperature higher than 1323 K but appears sometime at lower than 1273 K. (3) The above mentioned improvement is considered to be due to the shift from the liquid FeS to following precipitated solid titanium sulphide (TiS) and above mentioned appearance of the brittleness is considered to be due to TiS and titanium nitrides (TiN) precipitated along gamma grain boundary, which are based on the precipitate analysis in Ti added steels. (4) In the case of thermal history, cooling and reheating, in continuous casting, it is considered that the brittleness does not appears in the steels with Ti content over 0.016% and that it appears in the steels with S content over 0.011% without Ti addition.
The signal of acoustically stimulated electromagnetic (ASEM) response have been investigated in steel. In the ASEM method, ultrasonic and electromagnetic techniques are used. Magnetization is modulated with the radio frequency (RF) of irradiated ultrasonic waves through magnetomechanical coupling. The signal amplitude of ASEM waves is determined by the magnitude of piezomagnetic phenomenon which is acoustically excited locally. The induced RF magnetic fields are detected by a resonant coil antenna. Here, we applied the ASEM method to detect defects on thin steel sheets. If there is a defect in a steel sheet at a constant magnetization, magnetic flux density distribution around the defect is different from that of sound area. This difference can be detected through the ASEM method. Using a small antenna, 5 mm in diameter and 10 mm at liftoff, we can detect a 0.1 mm through hole in a steel sheet at 0.16 mm in thickness.
Effects of hydrogen sulfide (H2S) on behavior of hydrogen entering into low alloy steel were investigated using electrochemical hydrogen permeation technique. In this study, hydrogen entry sides were charged galvanostatically to control rate of hydrogen evolution reaction.
In pH 3.0 acetic buffer solution with 0.1 MPa H2S or N2, potential, charging current density and permeation current density were measured.
Hydrogen permeation current density had a linear relation to second root of hydrogen charging current density, which means hydrogen evolution reaction proceeds under Volmer-Tafel mechanism.
For analyzing the results of this study, the efficiency of hydrogen entry were calculated from the relationships among hydrogen charging current density, hydrogen permeation current density and hydrogen overpotential. It was found that the efficiency of hydrogen entry was drastically higher in H2S environment than in N2 environment.
On the other hand, the coverage of hydrogen atoms adsorbed on hydrogen entry side did not change in H2S environment.
All these results suggested that, although hydrogen coverage was not changed, hydrogen entry was accelerated in H2S environment.