TWI472624B - Method for manufacturing low carbon steel material - Google Patents

Description

Method for manufacturing low carbon steel

The present invention relates to a method of producing a steel material, and more particularly to a method of manufacturing a low carbon steel material.

In the rolling process, the hot rolled steel coil containing bismuth is prone to red rust defects, which not only causes the steel to be unsightly, but also causes the surface quality of the steel after downstream processing to be poor. Therefore, in order to improve the quality of hot-rolled steel containing niobium, it is necessary to improve the red rust problem caused by hot rolling of niobium-containing steel.

Traditionally, when the problem of red rust in hot-rolled steel is improved, most of the furnace atmosphere is controlled to bias the furnace atmosphere to a reducing atmosphere, thereby reducing the formation of red rust. Another way to improve the hot rolling red rust problem is to remove the red rust on the surface of the steel blast by high pressure water jet after the steel blast out of the heating furnace, thereby reducing the chance of red rust defects on the steel surface.

However, both of the above methods can only reduce the occurrence of red rust on the surface of the hot-rolled steel containing bismuth by controlling the external environment. Therefore, although the implementation of these two methods is effective, the improvement effect is limited, and the quality of the hot rolled steel containing bismuth cannot be effectively improved.

Accordingly, an aspect of the present invention provides a method for producing a low carbon steel which can greatly improve the surface quality of a low carbon steel by simultaneously controlling the composition of the steel and the process conditions.

Another aspect of the present invention provides a method for producing a low carbon steel which can change the structure of a tantalum iron layer in a scale by adjusting the content of niobium and a chromium alloy element in the steel material, thereby During the heating process, the bonding force between the scale and the base material is reduced. Therefore, the formation of hot rolling red rust defects can be effectively suppressed, and the claim and reprocessing cost caused by the hot rolling red rust defects of the steel can be greatly reduced.

Still another aspect of the present invention is to provide a method of producing a low carbon steel which can be carried out without a controlled heating atmosphere.

According to the above object of the present invention, a method for producing a low carbon steel material comprising the following steps is proposed. A low carbon steel embryo is provided. The composition of the low carbon steel preform includes a carbon (C) content of 0.20 wt% or less, a bismuth (Si) content of 0.2 wt% to 2.0 wt%, a manganese (Mn) content of 2.0 wt% or less, and a phosphorus (P) content of 0.10 wt% or less. The sulfur (S) content is 0.10% by weight or less, the copper (Cu) content is 1.0% by weight or less, the chromium (Cr) content is 1.0% by weight or less, the nickel (Ni) content is 1.0% by weight or less, and the titanium (Ti) content is 0.10% by weight or less. The aluminum (Al) content is 1.0 wt% or less, the nitrogen (N) content is 200 ppm or less, and iron (Fe). The low carbon steel embryo is subjected to repeated heat treatment. The process temperature of this reheating treatment is controlled to be below 1150 ° C or above 1200 ° C. A low-temperature steel embryo is subjected to a cooling and descaling treatment. A low-carbon steel preform is subjected to a hot rolling process to obtain a finished steel. The finished steel is subjected to a one-stage flow cooling treatment. A coiling step is performed on the finished steel to obtain a steel coil. The steel coil is subjected to a pickling treatment to remove the scale of the steel coil.

According to an embodiment of the present invention, when the reheating treatment is performed, the process temperature is maintained for 1 hour or longer.

According to another embodiment of the present invention, the temperature-lowering and rust-removing treatment lowers the temperature of the low carbon steel embryo to below 1100 °C.

According to still another embodiment of the present invention, the rolling temperature of the hot rolling process is controlled to be 950 ° C or lower.

According to still another embodiment of the present invention, the coiling step described above is carried out at a temperature below 700 °C.

According to still another embodiment of the present invention, the process temperature of the reheating treatment is 1100 ° C or more, and the process temperature is maintained for 1 hour or more. According to an example, after the reheating treatment described above, a surface of the low carbon steel embryo is formed with a scale layer. The composition of the scale layer is from the surface of the scale layer to the surface of the low carbon steel embryo, followed by ferric oxide (Fe ₂ O ₃ ), ferroferric oxide (Fe ₃ O ₄ ), ferrous oxide (FeO), and A combination of ferrous oxide and iron citrate (Fe ₂ SiO ₄ ).

Please refer to FIG. 1 , which is a flow chart showing a method for manufacturing a low carbon steel according to an embodiment of the present invention. The method 100 of the present embodiment can produce a low carbon steel material under the effective control of the scale layer of the steel material. When the low carbon steel is produced by the method 100, a low carbon steel blank is first provided as described in step 102. In one embodiment, the composition of the low carbon steel preform comprises a carbon content of 0.20 wt% or less, a niobium content of 0.2 wt% to 2.0 wt%, a manganese content of 2.0 wt% or less, a phosphorus content of 0.10 wt% or less, and a sulfur content of 0.10 wt%. Hereinafter, the copper content is 1.0 wt% or less, the chromium content is 1.0 wt% or less, the nickel content is 1.0 wt% or less, the titanium content is 0.10 wt% or less, the aluminum content is 1.0 wt% or less, the nitrogen content is 200 ppm or less, and iron. In general, low carbon steel embryos also contain insignificant impurities.

Next, as described in step 104, the low carbon steel embryo is reheated. In one embodiment, the process temperature can be controlled below 1150 ° C or above 1200 ° C during reheat processing. In addition, this process temperature can be maintained 1 The low carbon steel embryo is reheated for more than one hour at this process temperature for more than one hour. In an exemplary embodiment, when the temperature of the reheating treatment is 1100 ° C or more and the temperature is maintained for 1 hour or more, a surface of the low carbon steel embryo after the reheating treatment is formed with a scale layer. The composition of the scale layer is from the surface of the scale layer to the surface of the low carbon steel embryo, which may be a composition of ferric oxide, triiron tetroxide, ferrous oxide, and ferrous oxide and iron citrate.

After the reheating treatment, as described in step 106, the low carbon steel embryo may be subjected to a temperature and derusting treatment by, for example, spraying low pressure steel embryos with high pressure water. In one embodiment, the temperature reduction rusting treatment may, for example, reduce the temperature of the low carbon steel blank to below 1100 °C. By this cooling and rust removal treatment, the chance of red rust defects on the surface of the low carbon steel embryo can be reduced.

Next, as described in step 108, the low carbon steel embryo is subjected to a hot rolling process to obtain a rolled steel. In an exemplary embodiment, the finishing temperature of the hot rolling pass can be controlled, for example, below 950 °C. Then, as described in step 110, the finished steel is subjected to a laminar cooling treatment to reduce the temperature of the rolled steel to facilitate the subsequent coiling step. In an exemplary embodiment, the laminar cooling treatment may, for example, cool the temperature of the finished steel to below 700 °C.

Next, as described in step 112, the rolled steel may be coiled, for example, at a temperature below 700 °C. After the rolled steel is coiled, a steel coil is obtained. Then, as described in step 114, the steel coil may be pickled with an acid solution to remove the scale formed on the surface of the coil, thereby substantially completing the production of the low carbon steel.

In the present embodiment, by adjusting the content of the bismuth and chromium alloy elements in the low carbon steel, the knot of the bismuth silicate layer in the scale can be changed during the heating process. Structure to reduce the structural density of the iron silicate layer. Since the iron silicate layer in the scale is an interface layer bonded to the base material of the low carbon steel, the reduction in the structural density of the iron silicate layer allows the bonding between the scale and the base material of the low carbon steel embryo. The force is weakened, and the scale is peeled off from the base material. Further, since in the present embodiment, the low carbon steel embryo is cooled and derusted by high pressure water after the reheating treatment. Therefore, the scale can be peeled off from the base material because the thermal stress during the heating and then cooling is excessive. Therefore, with the present embodiment, the quality of the surface of the low carbon steel can be greatly improved.

The technical contents and effects of the present embodiment will be more specifically described below using a plurality of embodiments and comparative examples. Please refer to Table 1 below and Table 2 below. Table 1 lists the alloy composition and content (wt%) of several comparative examples and examples of steel, while Table 2 lists several process control conditions.

Steels were prepared using the steel components listed in Table 1 above and the process conditions listed in Table 2 above. The relationship between the composition of the obtained steel, the process conditions and the characteristics of the scale layer is shown in Table 3 below. The steel embryos containing the alloy composition and content as shown in Table 1 can be used, and the steel embryos are sequentially subjected to reheating treatment, cooling and descaling treatment, hot rolling, hot rolling cooling, coiling and pickling.

First, the low carbon steel embryo is reheated, and the process temperature is controlled at 1150 ° C ~ 1350 ° C, and the temperature is maintained for more than 1 hour. Next, high-pressure water is used to cool and derust the low-carbon steel, and the temperature of the low-carbon steel is lowered to below 1100 °C. Next, the low carbon steel embryo is subjected to a hot rolling process to obtain a rolled steel, and the finish rolling temperature is controlled to be below 950 °C. Subsequently, the rolled steel is subjected to laminar cooling treatment. Next, the rolled steel is coiled to obtain a steel coil, and the temperature at the time of coiling is controlled to be below 700 °C. Then, the steel coil is subjected to pickling treatment.

In Table 3, the total thickness of the scale layer is ferric oxide, triiron tetroxide, The sum of the layers of ferrous oxide, ferrous oxide and iron citrate. In addition, in the evaluation of the composition of the scale layer and the structural compactness, the observation and analysis of the surface structure of the low carbon steel surface by optical and electron microscopy were carried out, and the interface structure compactness of the scale layer and the base material of the low carbon steel was evaluated. Among them, "◎" indicates that the interface structure between the scale layer and the base material of the low carbon steel is dense, and "X" indicates that the interface structure between the scale layer and the base material of the low carbon steel is not dense. In addition, when assessing the adhesion of the scale layer, the surface of the low-carbon steel surface was observed by optical and electron microscopy to confirm that the scale on the high-temperature surface of the low-carbon steel was cooled by high-pressure water spray, and the mother of the low-carbon steel. The adhesion of the material. Among them, "X" indicates that the scale layer has been completely separated from the base material of the low carbon steel, and "△" indicates that the surface of the base material still has a rust layer.

According to the experimental results in Table 3, in the comparative example, when the cerium content is less than 0.1% by weight and the temperature of the reheating treatment is 1501150 ° C, when the temperature of the water spray cooling treatment (1100 ° C) and the temperature of the reheating treatment are between If the temperature difference is too small, even if the interface structure between the scale layer and the base metal is not dense, it is not easy to completely separate the scale layer from the base material. Therefore, in these comparative examples, the surface of the formed low carbon steel material still has a red rust problem. However, as the temperature difference between the temperature of the water spray cooling treatment and the temperature of the reheating treatment is expanded, the increase in thermal stress contributes to the separation of the scale layer from the base material, and the red rust problem on the surface of the steel material can be reduced.

In addition, in the case where the cerium content is less than 0.1% by weight and the temperature of the reheating treatment is 1501150 ° C, when the content of the chromium element exceeds 1.0% by weight, the rust layer may be made tighter due to the chromium element, which is disadvantageous for cooling and rust removal. The treated water vapor of the sprayed water penetrates into the scale layer. Therefore, even if the temperature difference between the temperature of the water spray cooling treatment and the temperature of the reheat treatment is increased, it does not help to improve the red color of the steel surface. Rust problem.

In the case where the niobium content is less than 0.1% by weight, if the temperature of the reheating treatment is increased to more than 1200 ° C, the thickening speed of the scale layer is accelerated (thickness of 50 μm or more), and the scale layer may be increased due to thermal stress. Separated from the base metal. Therefore, the occurrence of red rust on the surface of the steel can be reduced.

In the embodiment of the present invention, when the bismuth content of the alloy component of the low carbon steel blast is 0.3 wt%, and the temperature of the reheating treatment is 1501150 ° C, the interface structure of the rust layer/base material which is not dense may be obtained. Due to the formation of solid iron silicate at the interface between the rust layer and the base material, the adhesion of the interface structure between the rust layer and the base material is further deteriorated. Therefore, in the case where the temperature difference between the temperature of the water spray cooling treatment (for example, 1100 ° C) and the temperature of the reheat treatment (for example, 1150 ° C) is not large, the scale layer can be easily separated from the base material.

In addition, with the increase of the cerium content in the composition of the low carbon steel and the reheating treatment, for example, the cerium content ≧1.2 wt% and the reheating treatment temperature ≧1200 ° C, the oxidized rust layer melts the ferrous silicate and the ferrous oxide. The eutectic compound will enter the interface between the rust layer and the base material along the crack, and the interface between the rust layer and the base material will have significantly larger holes or cracks after cooling. Moreover, in the process of cooling and descaling of high-pressure water spray, the interface structure of iron silicate between the rust layer and the base metal is changed from a liquid state to a solid state, and the volume of the interface structure of iron citrate is significantly contracted. In this way, the adhesion between the scale layer and the base metal can be reduced, and the quality of the surface of the low carbon steel can be greatly improved.

Based on the above experimental results and description, it can be seen that by controlling the content of bismuth and chromium in the composition of low carbon steel, and controlling the temperature of reheating treatment and the temperature of cooling and rust removal treatment, the scale and the mother of low carbon steel can be obtained. The iron-clad iron coating at the interface of the material is reheated at a temperature of 1501150 ° C If the compactness of the structure is poor, or the reheating treatment temperature is 1200 ° C, the thermal stress is too large to be separated from the base material. Therefore, the use of the present invention can greatly improve the surface quality of the low carbon steel, and can reduce the cost of the steel due to hot rolling red rust and reprocessing costs.

It is apparent from the above embodiments that one of the advantages of the present invention is that the surface quality of the low carbon steel can be greatly improved by simultaneously controlling the composition of the steel and the process conditions.

It can be seen from the above embodiments that another advantage of the present invention is that the structure of the iron silicate layer in the scale can be changed by adjusting the content of bismuth and chromium alloy elements in the steel material, thereby being able to heat the steel during the heating process. Reduce the adhesion of the scale to the base metal. Therefore, the formation of hot rolling red rust defects can be effectively suppressed, and the claim and reprocessing cost caused by the hot rolling red rust defects of the steel can be greatly reduced.

According to the above embodiments, another advantage of the present invention is that the method for producing a low carbon steel according to the present invention can be carried out without controlling the heating atmosphere.

While the present invention has been described above by way of example, it is not intended to be construed as a limitation of the scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

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The above and other objects, features, advantages and embodiments of the present invention will become more <RTIgt; Flow chart of the manufacturing method of the material.

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Claims (7)

A method for manufacturing a low carbon steel, comprising: providing a low carbon steel embryo, wherein the low carbon steel embryo comprises a carbon content of 0.20 wt% or less, a niobium content of 0.2 wt% to 2.0 wt%, and a manganese content of 2.0 wt% or less. Phosphorus content of 0.10 wt% or less, sulfur content of 0.10 wt% or less, copper content of 1.0 wt% or less, chromium content of 1.0 wt% or less, nickel content of 1.0 wt% or less, titanium content of 0.10 wt% or less, aluminum content of 1.0 wt% or less, nitrogen a content of less than 200 ppm, and iron; performing a derusting process, comprising: reheating the low carbon steel embryo, wherein one of the reheating processes is controlled to be above 1200 ° C; and the low carbon steel embryo is subjected to a process Cooling and descaling treatment; performing a hot rolling process on the low carbon steel embryo to obtain a finished steel; performing a one-stage cooling treatment on the finished steel; performing a coiling step on the finished steel to obtain a steel Rolling; and pickling the steel coil to remove the scale of the steel coil. The method for producing a low carbon steel material according to claim 1, wherein the process temperature is maintained for 1 hour or more when the reheating treatment is performed. The method for producing a low carbon steel material according to claim 1, wherein the temperature lowering and rust removing treatment lowers the temperature of the low carbon steel embryo to 1100 ° C or lower. The method for producing a low carbon steel material according to claim 1, wherein the heat The rolling temperature of the rolling pass is controlled below 950 °C. The method for producing a low carbon steel material according to claim 1, wherein the coiling step is carried out at a temperature of 700 ° C or lower. The method for producing a low carbon steel according to claim 1, wherein the process temperature of the reheating treatment is 1100 ° C or more, and the process temperature is maintained for 1 hour or more. The method for producing a low carbon steel according to claim 6, wherein after the reheating treatment, a surface of the low carbon steel embryo is formed with a scale layer, and the composition of the scale layer is from the surface of the scale layer to the low carbon The surface of the steel blank is sequentially composed of ferric oxide, triiron tetroxide, ferrous oxide, and a combination of ferrous oxide and iron citrate.