Coiling temperature impact properties on the strip
After finish rolling the strip, cooling water within the layer to change the coiling temperature range α is significantly suppressed. Under most eutectoid ferrite nucleation and growth in the coiling temperature, following the completion of extremely slow cooling conditions can be considered similar to isothermal transformation process, therefore, affecting the coiling temperature on the microstructure and properties of steel understood as the impact of changes in temperature. So the impact of coiling temperature on microstructure and properties of steel is very significant. When the coiling temperature is high, coarse ferrite grains uniform, which is too low due to the change in the degree of supercooling α, less nucleation points, mainly at the grain boundaries of primary γ grains, the growth velocity than the ferrite fast due. When the coiling temperature is low, α increased the number of nucleation, growth velocity slows ferrite, ferrite grain size becomes smaller, but tends to diffuse fine pearlite. With decreasing coiling temperature ferrite grain refinement, the number of acicular ferrite gradually increased, increasing pearlite content, pearlite lamellar spacing is gradually reduced. Thus, with lower coiling temperature, strength index will increase, while the plasticity index decreased slightly, which is the carbon and ferritic alloy elements due to the γ-α phase transition at lower temperatures obtained when the content of high exigencies. When the end of the cold temperature is too low, the yield ratio improved formability detrimental to, because too many second generation phase, especially coarse bainite steel plasticity index of disadvantage.
Coiling temperature control effect on microstructure
Metallurgical machinery equipment, coiling temperature and finish rolling temperature, as the impact of a large steel microstructure, is one of the determinants of finished steel processing, mechanical properties of the important process parameters. Coiling temperature control is essentially the production of hot-rolled strip steel rolling controlled cooling, and controlled cooling after rolling the main factors affecting the quality of products is the start of cooling (cooling start temperature is basically finishing temperature) and the ending temperature, cooling speed and uniformity of cooling. The coiling temperature should be below 670 ℃, generally 600 ~ 650 ℃. Within this temperature ranges, metallurgical machinery steel microstructure has been finalized, can slow cooling and slow cooling to reduce internal stress of the strip is also beneficial. Coiling temperature is too high, it will result recrystallization and slow cooling after coiling produce tissue accumulation and coarse grain carbides, resulting in deterioration of the mechanical properties and the generation of hard iron skin, so pickling difficult. If the coiling temperature is too low, while the winding difficult, and the presence of residual stress, easy unwinding, affect the quality of the finished strip; other hand, the coiling temperature is not enough to make the supersaturated carbonitrides precipitation, affecting rolled performance. Therefore, the coiling temperature control by the internal microstructure within the scope defined by the steel, is another key control measures Metallurgical Machinery strip quality. Different varieties and specifications of the strip, its tip rolling finishing temperature is generally 800 ℃, highly oriented silicon steel finishing temperature is usually 980 ℃, whereas in the more than 100 m long steel output rollers running time of only 5 to 158 . For in such a short period of time to reduce the strip temperature 200 ~ 350 ℃, heat radiation alone steel output rollers and roller heat to natural cooling method is not possible, the output rollers must be very Setting a long distance high-efficiency water cooling means for the strip, forced cooling of the water surface, and to accurately control the amount of water to meet the requirements of the coiling temperature. Specific implementation coiling temperature control is based metallurgical machinery respective different characteristics of the strip (material, size), and the different states of the same strip point (temperature, speed), the flow through the length of the cooling layer (i.e., open cooling The number of the header) of the dynamic adjustment of the total length of the strips to a certain point from the high precision Qian final rolling temperature to the winding temperature of the rapid cooling required.
Post time: Sep-26-2019