Rolling method for thick low-alloy high-strength steel

Abstract

The invention discloses a rolling method for thick low-alloy high-strength steel, which belongs to the technical field of steel rolling and comprises the following steps: controlling the heating temperature at 1230 + / -20 DEG C; the rough rolling outlet temperature is controlled to be 1040 + / -30 DEG C, the finish rolling temperature is controlled to be 870 + / -20 DEG C, and the coiling temperature is controlled to be 650 + / -20 DEG C; the same-plate difference temperature of the plate blank is controlled within the range of 35 DEG C, and the deviation between the head temperature and the body temperature of the intermediate blank is smaller than 15 DEG C; the finish rolling speed is increased to 4.9 m / s; the thickness of the intermediate billet is increased to the maximum value of 49 mm; the relative reduction rates of the rolling load of a finish rolling worker and the rolling load of a finishing mill F5-F7 rack are improved to 19.2%, 14.7% and 8.9%, and the finish rolling rack F3 is thrown out; according to the dephosphorization system, rough rolling four-pass dephosphorization is added; according to the finish rolling process water system, reverse water spraying between racks is synchronously started; and according to the laminar cooling system, the cooling configuration is set to be in a 1 / 4 mode, and the plate coil is cooled in the whole length at the rough adjustment section.

Description

Technical Field

[0001] The invention belongs to the technical field of steel rolling, and in particular relates to a method for rolling thick-gauge low-alloy high-strength steel. Background Art

[0002] At present, the design thickness of the plate and coil of the hot rolling mills owned by some enterprises has reached a range of 1.2 mm to 16 mm. With the continuous improvement of the capacity of the downstream leveling machine, there has been a trend in the market that hot coils are increasingly used to replace medium plates in the demand for extremely thick specifications. This trend is not only reflected in the demand for the production of extremely thick specifications, but also in the development trend of research and development of products with thickness exceeding the standard. However, in the thick specifications of 14.0 mm and above produced by the hot rolling mill, there are some problems of abnormal organization, especially the large difference in uniformity between the thickness center and the surface organization, which leads to the product's non-compliance with the standards in terms of elongation, yield strength, tensile strength, impact and other properties. In addition, there are defects in the quality of the surface oxide film of the plate and coil, and these problems urgently need to find effective solutions. Summary of the invention

[0003] The present invention provides a method for rolling low-alloy high-strength steel in thick specifications in order to solve the technical problems existing in the known technology.

[0004] The first object of the present invention is to provide a method for rolling low alloy high strength steel in thick gauge, comprising:

[0005] Temperature control: control the heating temperature at 1230±20℃; the rough rolling outlet temperature at 1040±30℃, the finishing rolling temperature at 870±20℃, and the coiling temperature at 650±20℃; control the slab temperature difference within 35℃, and the temperature deviation between the head of the intermediate slab and the body is less than 15℃;

[0006] Speed ​​control, increasing the finishing rolling speed to 4.9m / s;

[0007] Intermediate billet thickness: transfer the rough rolling load to the finishing rolling, and the intermediate billet thickness is increased to a maximum of 49mm;

[0008] The relative reduction rate of the rolling load of the finishing mill F5-F7 stands was increased to 19.2%, 14.7% and 8.9%, and the finishing rolling was abandoned by the finishing mill stand F3;

[0009] Phosphorus removal system: add four rough rolling passes to remove phosphorus;

[0010] The finishing rolling process water system starts the reverse water spray between the stands simultaneously to blow away the impurities on the strip surface in time;

[0011] Laminar cooling system, cooling configuration is set to 1 / 4 mode, the whole length of the coil is cooled in the coarse adjustment section to reduce the cooling rate.

[0012] Preferably, the low alloy high strength steel is Q355B series steel with a thickness of 14 mm to 20 mm.

[0013] Preferably, the heating temperature is 1210°C, 1230°C, or 1250°C.

[0014] Preferably, the rough rolling outlet temperature is 1010°C, 1040°C or 1070°C.

[0015] Preferably, the finishing rolling temperature is 850°C, 870°C or 890°C.

[0016] Preferably, the coiling temperature is 630°C, 650°C or 670°C.

[0017] Preferably, the intermediate billet is rough rolled using 2 or 4 passes of wandering technology to refine the grain structure.

[0018] The advantages and positive effects of the present invention are:

[0019] The present invention utilizes an advanced low-temperature rolling technology to significantly reduce the temperature during the rolling process, thereby achieving a significant increase in rolling speed. This increase in speed further promotes the increase in rolling reduction rate, effectively breaking up the grains in the material. As the temperature decreases, the energy required for the material to recrystallize is also reduced, which helps to further refine the grain size. In addition, under relatively low temperature conditions, the conditions for the formation of oxide film are significantly reduced, and the time the strip is exposed to the air is also shortened accordingly, which helps to better control the thickness of the oxide scale of the coil.

[0020] In order to further optimize the rolling process, the present invention has studied the load distribution, reduction system, deformation system, temperature system and speed system in the rough rolling and finishing rolling stages of the rolling line. Through careful design and reasonable control of these key parameters, the present invention has successfully improved the internal structure of the coil, thereby significantly improving the mechanical properties of the material. This series of improvement measures not only improves the quality of the product, but also provides new ideas and methods for optimizing the rolling process. DETAILED DESCRIPTION

[0021] In order to make the above-mentioned purpose and design advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0022] The technical solution of the present invention is:

[0023] The present invention aims to solve several key problems often encountered in the process of rolling thick-gauge coils of low-alloy high-strength steel. These problems include elongation, yield strength and tensile strength that cannot meet the predetermined standards, as well as quality problems such as uneven microstructure grains. In order to solve these problems, the present invention proposes a comprehensive control strategy, which mainly focuses on the load distribution, reduction system, deformation system, temperature system and speed system in the rough rolling and finishing rolling stages of the rolling line. By precisely controlling these key parameters, the present invention can effectively improve the internal microstructure of the coil, thereby ensuring that its mechanical properties meet the predetermined standards. This method not only improves product quality, but also optimizes the production process, ensures the performance consistency of the final product, and meets the strict requirements in industrial applications.

[0024] A method for rolling low-alloy high-strength steel of thick specifications, comprising:

[0025] In terms of temperature control, this application adjusts the heating temperature from the conventional 1260°C to 1230±20°C to ensure the accuracy of the heating process. The rough rolling outlet temperature is set to 1040±30°C to meet the temperature requirements of the rough rolling process. The finishing temperature of fine rolling is set to 870±20°C to ensure temperature control of the fine rolling process. The coiling temperature is set to 650±20°C to ensure the temperature stability of the coiling process. At the same time, this application strictly examines that the temperature difference of the same plate of the slab is within 35°C to ensure the consistency of the slab temperature. In addition, this application also strictly examines that the deviation between the head temperature of the intermediate billet and the body temperature is less than 15°C to ensure the uniformity of the intermediate billet temperature.

[0026] In terms of speed control, this application optimizes the rough rolling mill process and increases the finishing rolling speed from 3.5m / s to 4.9m / s to improve production efficiency and product quality.

[0027] In terms of intermediate billet thickness control, the present application transfers the rough rolling load to the finishing rolling, and increases the intermediate billet thickness from 45mm to a maximum of 49mm to optimize the rolling process. At the same time, the present application adopts the 2nd and 4th pass wandering technology of rough rolling to refine the grain structure and improve product quality.

[0028] In terms of rolling load control of the finishing mill, the present application increases the relative reduction rate of the rolling load of the finishing mill F5-F7 frames to 19.2%, 14.7%, and 8.9%, and increases the absolute reduction amount of the last pass of finishing rolling, effectively crushing the grains in the incomplete recrystallization zone, thereby refining the grains.

[0029] In terms of the dephosphorization system, the application guarantees the treatment effect of high-pressure water, strengthens the inspection of dephosphorization nozzles, and replaces them in time if they are blocked or worn. At the same time, the application reduces the rolling speed of odd passes of rough rolling, prolongs the dephosphorization time of slabs, and increases the dephosphorization of the fourth pass of rough rolling to ensure the dephosphorization effect.

[0030] In terms of the finishing rolling process water system, in order to prevent the oxide film of the rolls of the first four rolling mills from peeling off and pressing into the strip to cause surface defects, this application turns on the roll anti-stripping water function. At the same time, this application simultaneously turns on the reverse water spray between the stands to blow away the impurities on the surface of the strip in time to prevent surface defects of the strip.

[0031] In terms of the laminar cooling system, this application sets the cooling configuration to 1 / 4 mode, cools the entire length of the coil in the coarse adjustment section, and further reduces the cooling rate to ensure the uniformity and stability of the cooling process.

[0032] In terms of the rolling process path, this application adopts the process path of heating furnace → roughing mill → finishing mill → laminar cooling → coiling to ensure product quality and production efficiency.

[0033] In terms of temperature control, the present application controls the steel output temperature of the heating furnace in the heating furnace process, controls the temperature of the five rough rolling passes in the rough rolling process, controls the final rolling temperature in the finishing mill process, and controls the coiling temperature in the coiler process to ensure temperature control of the entire rolling process.

[0034] In terms of speed control, the present application is optimized in the roughing mill process to improve production efficiency and product quality.

[0035] In terms of side pressure control, the present application optimizes the roughing mill process to improve product quality.

[0036] In terms of dephosphorization after the heating furnace, the present application performs dephosphorization treatment in the heating furnace process, performs rough rolling dephosphorization treatment in the rough rolling mill process, and performs finishing rolling entrance dephosphorization treatment in the finishing rolling mill process to ensure product quality.

[0037] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are within the scope of the technical solution of the present invention.

Claims

1. A method for rolling thick low-alloy high-strength steel, characterized in that: include: Temperature control: control the heating temperature at 1230±20℃; the rough rolling outlet temperature at 1040±30℃, the finishing rolling temperature at 870±20℃, and the coiling temperature at 650±20℃; control the slab temperature difference within 35℃, and the temperature deviation between the head of the intermediate slab and the body is less than 15℃; Speed ​​control, increasing the finishing rolling speed to 4.9m / s; Intermediate billet thickness: transfer the rough rolling load to the finishing rolling, and the intermediate billet thickness is increased to a maximum of 49mm; The relative reduction rate of the rolling load of the finishing mill F5-F7 stands was increased to 19.2%, 14.7% and 8.9%, and the finishing rolling was abandoned by the finishing mill stand F3; Phosphorus removal system: add four rough rolling passes to remove phosphorus; The finishing rolling process water system starts the reverse water spray between the stands simultaneously to blow away the impurities on the strip surface in time; Laminar cooling system, cooling configuration is set to 1 / 4 mode, the whole length of the coil is cooled in the coarse adjustment section to reduce the cooling rate.

2. The method for rolling thick-gauge low-alloy high-strength steel according to claim 1, characterized in that: The low alloy high strength steel is Q355B series steel with a thickness of 14 mm to 20 mm.

3. The method for rolling thick-gauge low-alloy high-strength steel according to claim 1, characterized in that: The heating temperature is 1210°C, 1230°C or 1250°C.

4. The method for rolling thick-gauge low-alloy high-strength steel according to claim 1, characterized in that: The rough rolling outlet temperature is 1010℃ or 1040℃ or 1070℃.

5. The method for rolling thick-gauge low-alloy high-strength steel according to claim 1, characterized in that: The finishing rolling temperature is 850℃, 870℃ or 890℃.

6. The method for rolling thick-gauge low-alloy high-strength steel according to claim 1, characterized in that: The coiling temperature is 630°C, 650°C or 670°C.

7. The method for rolling thick-gauge low-alloy high-strength steel according to claim 1, characterized in that: The intermediate billet is rough rolled with 2 and 4 passes of wandering technology to refine the grain structure.