Papers by Keyword: Finishing Temperature

Abstract: The effect of thermomechanical controlled processing (TMCP) strain and finishing temperature on the microstructure of as-rolled and air-cooled 50mm thick Nb-Ti-V-Ni microalloyed steel plate was investigated through laboratory simulations, incorporating variations in reheating, roughing and finishing practices. Laboratory simulations produced microstructures similar to those observed in industrial rolling owing to comparable total strain in the TMCP region. Larger total strains in the TMCP region promoted sub-grain formation and increased nucleation site density, leading to grain refinement. Recrystallisation was completely suppressed at the commencement of finishing in all TMCP schedules due to sufficiently lower starting temperatures. The extent of recrystallisation during finishing depended on the finishing temperature: i) partial softening after finishing above 910°C and ii) complete recrystallisation below 910°C due to substantial accumulated strain. Finishing below 910°C produced finer polygonal ferrite and pearlite microstructures. Microstructure and mechanical properties were fairly consistent when the finishing temperature was between 925 and 950°C. However, the sub-zero impact toughness can be significantly improved by employing lower finish temperatures or applying larger total TMCP strains. Interrupted accelerated cooling at 5°C/s after finishing significantly refined the microstructure.

Abstract: The thermomechanical control processing (TMCP) was conducted through the adjustment of the rolling technological parameters to the test steel. The influence of the finishing temperature, cooling rate and alloying elements to the microstructure and mechanical properties was investigated by comprehensive utilization of grain refining strengthening and second phase strengthening.The results show that the microstructure was mainly composed of bainite, ferrite and second phase TiC; at the finishing temperature of 870°C, the yield strength was 596.7 MPa, the tensile strength reached 748.5 MPa, the elongation ratio was 20.17%; at high cooling rate of 16°C/s, the yield strength achieved 616.7 MPa, the tensile strength reached 785.5 MPa, the tensile ratio reduced for 0.78, and the elongation ratio enhanced to 20.92%. And the quantity of bainite increased with the raise of finishing temperature from 800°C to 870°C, which improved the hardness and wear resistance of the steel.

Abstract: Hot-rolled low carbon steel strips were produced using two different finishing temperatures at 910 and 820 °C in an industrial hot-rolling line. Mechanical adhesion of scale on the steel substrate at 40 mm from the edge was investigated by tensile test. It was found that the strain initiating the first spallation of scale produced at higher finishing temperature was lower. Spallation ratio which is a spalled area of scale divided by the total area of scale examined under an optical microscope was steeper when the scale was produced at higher finishing temperature. The lower values of strain initiating the first spallation and the higher values of spallation ratio of scale formed both at higher finishing temperature were due to higher thickness of that scale. Pickling behaviour of the hot-rolled steels was investigated by immersing the studied steels in a 10%v/v HCl solution at 80 °C. X-ray diffraction (XRD) peak of hematite relative to that of iron decreased with pickling time and approached zero during pickling periods from 3 to 10 s, while magnetite-and-iron ratio gradually decreased and tended to be zero at longer pickling time. This might indicate the existence of hematite as the outermost layer of scale and subscale containing magnetite as the inner part.

Abstract: 0.2mm-thick high silicon steel thin sheet under 94% cold rolling reductions has been successfully produced by conventional rolling method. Texture evolution during hot rolling, cold rolling and final annealing as well as magnetic properties has been investigated with emphasis on the effect of finishing temperature. It is found that a favorable strong {001}<210> recrystallization texture and evidently improved magnetic properties can be obtained at the finishing temperature of 900°C, which is in contrast with relatively strong detrimental {111}<112> and weak {001}<210> recrystallization texture at the finishing temperature of 700°C. Effects of finishing temperature can be explained in terms of the cold rolling texture due to different texture morphology in hot bands.

Abstract: Microstructures and textures after annealing at 680°C in low carbon Al-killed steels with low finishing temperature and high coiling temperature were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM) and X-Ray Diffractometer (XRD). The results show that higher coiling temperature and lower finishing temperature can both cause the appearance of equiaxed grain and line cementite. The equiaxed grain in 2# steel with higher coiling temperature is the more obvious. Advantage textures are weak in the steels with higher coiling temperature and lower finishing temperature and volume fraction of {111}fiber in 2# steel with higher coiling temperature is only 7.17%, so the stamping property should be worse.

Abstract: The objective of this work was to carry out tensile tests to investigate the effect of finishing temperature on mechanical adhesion of thermal oxide scale on hot-rolled low carbon steel strips. Two hot-rolled low carbon steel strips were produced in an industrial hot rolling line by fixing a coiling temperature at 620 °C and varying finishing temperatures at 820 and 910 °C. Two testing methods were conducted. First, each of a number of samples was subjected to a given imposed strain with ex-situ imaging of scale surface after straining. Second, only one sample was strained in a test with ex-situ imaging of scale surface at every 2 mm elongation of the sample. A spallation ratio, an area where scale was spalled out and normalised by the total area observed by microscope, was plotted as a function of the imposed strain. These two methods gave the same tendency of results as follows. At a given strain, the spallation ratio of scale on steel produced using higher finishing temperature was larger. The gradient of spallation ratio with respect to the imposed strain of that scale was also steeper. This reflects the higher susceptibility of scale to spall out with increasing imposed strain. This behaviour might be related to the larger thickness of scale on steel produced using higher finishing temperature. For the second testing method, lowering the magnification of microscope to observe scale spallation from 50x to 20x increased R2 of the curve of spallation ratio versus the imposed strain, as well as improved the reproducibility of the test.

Abstract: Thermo mechanical processing and controlled rolling of microalloyed steel sheets are affected by several factors. In this investigation, finishing temperature of rolling which is considered as the most effective parameters on the final mechanical properties of hot rolled products has been studied. For this purpose, three different finishing temperatures of 950, 900 and 850 °C below the non-recrystallization temperature and one temperature of 800 °C in the intercritical range were chosen. It is observed that decreasing the finishing temperature causes increase of strength and decrease of total elongation. This is accompanied by more grain refinement of microstructure and the morphology was changed from polygonal ferrite to acicular one. Findings of this research provide suitable connection among finishing temperature, microstructural features, and mechanical properties of hot rolled Nb-microalloyed steel sheets.

Abstract: Based on the character of plate rolling, the temperature model was developed by considering the influence of radiation, convection, water descaling, and roll conductivity and deformation energy. The factors affect the finishing temperature of the plate were analyzed, including the holding time during control rolling, rolling speed, slab temperature and pass number. Holding time, rolling speed and slab temperature have significant influence on finishing temperature, and pass number has great influence on finishing temperature of thick plate, but has little on finishing temperature of media plate.

Abstract: The microstructures of 30Mn20Al3 non-magnetic steel after different finishing temperature and cooling rates have been studied by multi-pass compression test in a thermal-mechanical simulator. The results show that the microstructure of this steel is totally of austenitic with amounts of twins. At the same cooling rate, larger amount of thicker twins appear when lowering finishing temperature. The austenite grain size is related to finishing temperature and cooling rate. The critical temperature of austenite recrystallization is determined as 950~1000°C. When the finishing temperature is about 1000°C and cooling rate higher than 15°C/s, fine and uniform austenite grains can be obtained.