EP4253586A1

EP4253586A1 - Preparation method for low-temperature impact toughness-resistant wind power steel

Info

Publication number: EP4253586A1
Application number: EP21896486.4A
Authority: EP
Inventors: Zhongxue WANG; Yan Li; Heng Ma; Wei NING; Wenqiang Li; Changhong Zhang; Kai NI; Tengfei WANG; Kang HE; Yang Cao
Original assignee: Laiwu Steel Group Yinshan Section Steel Co Ltd
Current assignee: Laiwu Steel Group Yinshan Section Steel Co Ltd
Priority date: 2020-11-24
Filing date: 2021-09-14
Publication date: 2023-10-04
Also published as: CN112662933A; WO2022110982A1

Abstract

The present disclosure provides a preparation method for toughness wind power steel with low-temperature impact resistance, comprising the following steps of: pretreating, a desulfurization of molten steel; smelting: pretreated molten steel; refining, being divided into LF refining and RH refining; continuous casting, being adopted whole-process protection casting; and rolling, being adopted two-stage rolling comprising rough rolling and finish rolling. In the preparation method for the toughness wind power steel with low-temperature impact resistance disclosed in the present disclosure, it provides a normalizing-rolled toughness wind power steel with low-temperature impact resistance plate with low cost, excellent low-temperature impact toughness, and good comprehensive performance such as product strength, percentage elongation after fracture, and cold bending performance and the like; and by adding and controlling various alloy elements, and directly using the normalizing rolling process, the production cost is low, the production cycle is short, and the normalizing rolling low-temperature impact toughness wind power steel plate with a thickness of 6mm to 63mm can be produced to obtain the toughness wind power steel with low-temperature impact resistance.

Description

FIELD OF INVENTION

The present disclosure relates to the field of steel smelting, in particular to a preparation method for toughness wind power steel with low-temperature impact resistance.

BACKGROUND OF THE INVENTION

Wind power is a clean and stable new energy, and the wind power generation can effectively slow down climate change, improve energy safety, and promote low-carbon economic growth, thereby the wind power becomes one of the fastest growing energy sources in the world in recent years, and the market demand of wind power steel is also increasing. In China, eight thousands of kilowatt stages of wind power bases will be constructed in seven provincial areas such as Gansu, Mongolia, Xinjiang and the like, and the minimum temperature of the use environment is close to -20°C, so that the requirement on low-temperature impact toughness is high.

The national standard: GB/T1591-2018 provides chemical components and mechanical and process performance requirements of Q355ND steel, as shown in Table 1 and Table 2.

Table 1: Chemical Composition (wt%)

C	Si	Mn	P	S	Nb	Ti	Als
≤0.20	≤0.50	0.90-1.65	≤0.030	≤0.025	0.005-0.05	0.006-0.05	≥0.015

Table 2: Q355ND Mechanical and Process Performance Requirement

Marks	Upper Yield Strength ReH (MPa)			Tensile Strength Rm (MPa)	Percentage Elongation after Fracture A (%)		Impact Power (-20°C Longitudinal) Akv (1)	180° Bended
Marks	Steel Plate Thickness (mm)
	≤16	> 16-40	>40-63	≤63	≤40	>40-63	≤63	≤16	> 16-63
Q355ND	≥355	≥345	≥335	470-630	≥20	≥19	≥34	d=2a	d= 3a

In Table 2, d is diameter of the bend center, and a is thickness of the sample.
In practical applications, various additional requirements are often proposed due to different use conditions and application fields, which require further improvement of product performance on the basis of national standards.
At present, there are many methods for manufacturing wind power steel plates with low-temperature impact toughness, from the perspective of composition, alloy elements are added more, Nb, V and Ti composition system is adopted, and most noble metals such as Ni, Cr and the like are added, thereby increasing the production cost of the steel. Although Ni and Cr component systems are not adopted, controlled rolling and controlled cooling processes are used, and the product obtained by the technology is low in low-temperature impact toughness qualification rate.
In view of the characteristics of the production process, at present, controlling the rolling and normalizing processes are adopted by most of the development and production of low-temperature impact toughness wind power steel plate to obtain the performance requirements of the low-temperature impact-toughness wind power steel plate. Although the structure can be uniform and the low-temperature impact toughness can be improved by adopting the method, the production cycle is longer, the cost is increased, and the production efficiency is lower by adopting the heat treatment process.

SUMMARY

An object of the present disclosure is to provide a preparation method for toughness wind power steel with low-temperature impact resistance to solve at least one of the above-mentioned problems. The present disclosure provides a normalizing-rolled toughness wind power steel with low-temperature impact resistance plate with low cost, excellent low-temperature impact toughness, and good comprehensive performance such as product strength, percentage elongation after fracture, and cold bending performance and the like; and by adding and controlling various alloy elements, and directly using the normalizing rolling process, the production cost is low, the production cycle is short, and the normalizing rolling low-temperature impact toughness wind power steel plate with a thickness of 6mm to 63mm can be produced to obtain the toughness wind power steel with low-temperature impact resistance.
In order to achieve the above-mentioned objects, the present disclosure provides the following technical solutions:
A preparation method for toughness wind power steel with low-temperature impact resistance, comprising the following steps of: pretreating, a desulfurization of molten steel; smelting, pretreated molten steel; refining, being divided into LF refining and RH refining; continuous casting, being adopted whole-process protection casting; and rolling, being adopted two-stage rolling comprising rough rolling and finish rolling.
Further, in the above-mentioned preparation method for toughness wind power steel with low-temperature impact resistance, wherein in the pretreating step, sulfur content in the molten steel is controlled to be below 0.010% by mass percentage; preferably, desulfurization temperature is 1250°C-1320°C.
Further, in the above-mentioned preparation method for toughness wind power steel with low-temperature impact resistance, wherein in the smelting step, the pretreated molten steel enters a converter for smelting, a slagging material is added within 1min-5min before the molten steel enters an end point of the converter, and alkalinity of an final slag is controlled at R=3.0-4.0; preferably, an end point gun pressing time is 65s-120s; preferably, aluminum manganese iron is used for deoxidation, addition amount of the aluminum manganese iron is 2.0kg/t-3.5kg/t, when the molten steel is discharged to one fourth, silicon manganese, silicon iron and niobium iron are added in batches, and finish adding when the molten steel is discharged to three fourths; preferably, the silicon manganese is an iron alloy containing 13%-25% by weight of silicon and 55%-75% by weight of manganese, and addition amount of the silicon manganese is 20kg/t-30kg/t; the silicon iron is an iron alloy containing 70%-78% by weight of silicon, and addition amount of silicon iron is 0.5kg/t-2kg/t; the niobium iron is an iron alloy containing 50%-65% by weight of niobium, and addition amount of the niobium iron is 0.1kg/t-0.8kg/t.
Further, in the above-mentioned preparation method for toughness wind power steel with low-temperature impact resistance, wherein in the refining step, the LF refining adopts a whole-process bottom argon blowing and stirring, an soft argon blowing is performed for 10min-15min, lime is added for slagging, and aluminum particle deoxidizer is used for deoxidation; preferably, yellow and white slag or white slag is kept for 10min-30min, and the alkalinity of the final slag is controlled at R=3.0-4.0.
Further, in the above-mentioned preparation method for toughness wind power steel with low-temperature impact resistance, wherein in the refining step, vacuum degree in the RH refining process is controlled at 10 Pa-30 Pa, and vacuum time is 15min-25min; preferably, pure degassing time is not less than 5min, and soft blowing time is not less than 12min; preferably, a cycle of the RH refining is controlled at 40min-60min, addition amount of an aluminum wire is 0m/t-3.3m/t, and addition amount of a titanium wire is 0.8m/t-3.3m/t.
Further, in the above-mentioned preparation method for toughness wind power steel with low-temperature impact resistance, wherein in the continuous casting step, the whole-process protection casting refers to that from a large ladle to a tundish adopts a long water nozzle and perform argon sealing protection; the tundish adopts a covering agent in combination with carbonized rice husks for covering; from the tundish to crystallizer adopts a submerged nozzle and perform argon sealing protection; and liquid level of the crystallizer adopts peritectic steel protecting slag; preferably, the composition of the peritectic steel protecting slag is 25% <_ SiO₂≤ 35%, 35% <_ CaO <_ 45%, 1.90% <_ MgO <_ 3.00%, and 3.00% <_ Al₂O₃≤ 4.00%.
Further, in the above-mentioned preparation method for toughness wind power steel with low-temperature impact resistance, in the continuous casting step, pulling speed is stabilized to 0.80m/min-1.40m/min; preferably, section 175: pulling speed is stabilized to 1.2-1.35m/min, section 200: pulling speed is stabilized to 1.3-1.4m/min, section 250: pulling speed is stabilized to 1.1-1.3m/min, section 300: pulling speed is stabilized to 0.8-0.9m/min.
Further, in the above-mentioned preparation method for toughness wind power steel with low-temperature impact resistance, wherein in the continuous casting step, casting superheat degree is controlled below 20°C; preferably, height of liquid level of the tundish is controlled, the height of the liquid level of the tundish during pouring is not lower than 600mm, and the height of the liquid level during normal pouring is between 800mm-1000mm; preferably, the casting blank straightening temperature is controlled above 900°C.
Further, in the above preparation method for toughness wind power steel with low-temperature impact resistance, wherein in the rolling step, steel blank tapping temperature is controlled at 1170°C-1280°C; rough rolling starting temperature is 1130°C-1190°C, and rough rolling final temperature is 1050°C-1120°C; rough rolling total compression ratio is more than 50%; finish rolling starting temperature is 850°C-1070°C, and finish rolling final temperature is 830°C-960°C.
Further, in the above-mentioned preparation method for toughness wind power steel with low-temperature impact resistance, wherein the composition of the wind power steel is 0.13% <_ C <_ 0.17%, 0.20% <_ Si ≤ 0.50%, 0.90% <_ Mn ≤ 1.65%, 0 ≤ S ≤ 0.010%, 0 ≤ P ≤ 0.030%, 0.010% ≤ Nb ≤ 0.040%, 0.010% < Ti ≤ 0.030%, 0.015% <_ Als <_ 0.050% in percentage by weight, and the rest are iron and inevitable impurities, Als is acid-soluble aluminum.
It can be seen from the analysis that In the preparation method for the toughness wind power steel with low-temperature impact resistance disclosed in the present disclosure, it provides a normalizing-rolled toughness wind power steel with low-temperature impact resistance plate with low cost, excellent low-temperature impact toughness, and good comprehensive performance such as product strength, percentage elongation after fracture, and cold bending performance and the like; and by adding and controlling various alloy elements, and directly using the normalizing rolling process, the production cost is low, the production cycle is short, and the normalizing rolling low-temperature impact toughness wind power steel plate with a thickness of 6mm to 63mm can be produced to obtain the toughness wind power steel with low-temperature impact resistance.

DETAILED SPECIFICATION OF THE EMBODIMENT

The present disclosure will be described in detail below with reference to embodiments. Each example is provided by way of explanation of the present disclosure, not limitation of the present disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the present disclosure. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present disclosure encompass such modifications and variations as come within the scope of the appended claims and their equivalents.
According to an embodiment of the present disclosure, a preparation method for toughness wind power steel with low-temperature impact resistance is provided. The composition of the wind power steel is 0.13% <_ C <_ 0.17%, 0.20% ≤ Si ≤ 0.50%, 0.90% ≤ Mn ≤ 1.65%, 0 ≤ S < 0.010%, 0 ≤ P ≤ 0.030%, 0.010% ≤ Nb <_ 0.040%, 0.010% <_ Ti ≤ 0.030%, 0.015% <_ Als <_ 0.050% in percentage by weight, and the rest are iron and inevitable impurities, Als is acid-soluble aluminum. At a temperature of -20°C, the minimum value of the impact toughness is greater than or equal to 100J. The wind power steel is low in cost, excellent in low-temperature impact toughness and excellent in comprehensive performance such as product strength, percentage elongation after fracture and cold bending performance. The design of low C+Nb and Ti microalloying components is adopted, and it is guaranteed that the steel plate is easy to weld.
The component content control and effect of the toughness wind power steel with low-temperature impact resistance of the present disclosure are further described below.
On the basis of Q355ND steel provided by GB /T1591-2018, the contents of Nb, Ti and Al are reasonably designed. Nb: the fine grain strengthening effect of Nb is fully exerted, and it is ensured that the steel plate has sufficient strength; Ti: on one hand, the free nitrogen in the steel is eliminated, and the aging resistance is improved; on the other hand, the grains are refined, the segregation is reduced, the banded structure level is reduced, and the toughness is improved; Al: on one hand, the grains can be refined, and the strength is improved; and on the other hand, Al is combined with N, and the strain aging can be prevented.
On the other hand, the present disclosure also provides a preparation method of the toughness wind power steel with low-temperature impact resistance, and the preparation method comprises the following steps: pretreating, smelting, refining, continuous casting and rolling.
In order to ensure the low-temperature impact toughness requirement of the wind power steel, on one hand, the addition amount of each alloy element is fully considered in the component design, and on the other hand, a normalizing rolling process is adopted in the rolling process to meet the requirement for the product performance.
Pretreating refers to a desulfurization of molten steel, and the desulfurization of the molten steel strictly executes the process procedures, and the sulfur content in the molten steel is controlled to be below 0.010% (for example, 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, 0.006%, 0.007%, 0.008%, 0.009%, and 0.010%), by mass percentage, the desulfurization temperature is 1250°C-1320°C (for example, 1250°C, 1255°C, 1258°C, 1260°C, 1263°C, 1267°C, 1270°C, 1275°C, 1280°C, 1290°C, 1300°C, 1305°C, 1310°C, 1315°C, and 1320°C), picking out the slag on the surface of the molten steel when the desulfurization is completed. Generally, the sulfur is a harmful element, which causes hot brittleness of the steel, reduces ductility and toughness of the steel, causes cracks during rolling, and is detrimental to welding performance. According to the present disclosure, during pretreating, KR method is adopted for desulfurization to control the desulfurization temperature, the sulfur content in molten steel is effectively reduced to be below 0.010%, desulfurization is thorough, and the steel purity is ensured.
Smelting, the pretreated molten steel enters a converter for smelting, the slagging material is added within 1min-5min before the molten steel enters the end point of the converter, the alkalinity of the final slag is controlled at R=3.0-4.0, the end point gun pressing time is 65s-120s (such as 65s, 70s, 75s, 80s, 85s, 90s, 95s, 100s, 105s, 110s, 115s, 120s and the range between any two values), the end point gun pressing time is 65s-120s, and the chemical reaction of the added alloy components in the molten steel is just completed to achieve complete homogenization of the components. If the time is shorter than 65s, the reaction cannot be fully completed; if the time is longer than 120s, the production efficiency is affected without any effect on the components.
Aluminum manganese iron is used for deoxidation, the adding amount of aluminum manganese iron is 2.0kg/t-3.5kg/t. When the molten steel is discharged to one fourth, silicon manganese, silicon iron and niobium iron are added in batches, and finish adding when the molten steel is discharged to three fourths. The key point of converter smelting control is to reduce the end point phosphorus and sulfur content as much as possible, reasonably control the carbon content, and ensure the purity of steel.
Silicon manganese is an iron alloy containing 13%-25% by weight of silicon and 55%-75% by weight of manganese, and the addition amount of silicon manganese is 20kg/t-30kg/t; the silicon iron is an iron alloy containing 70%-78% by weight of silicon, and the addition amount of silicon iron is 0.5kg/t-2kg/t; the niobium iron is an iron alloy containing 50%-65% by weight of niobium, and the addition amount of niobium iron is 0.1kg/t-0.8kg/t.
Refining is divided into LF refining and RH refining.
The LF refining adopts a whole-process bottom argon blowing and stirring, the soft argon blowing is performed for 10min-15min, lime is added for slagging, aluminum particle deoxidizer is used for deoxidation, yellow and white slag or white slag is kept for 10min-30min (such as 10min, 12min, 17min, 19min, 20min, 22min, 25min, 27min, 29min and 30min), the yellow and white slag or white slag is kept for too short time, and the final slag has not been completely melted; the yellow and white slag or white slag is kept for too long, and the production efficiency is affected. The alkalinity of the final slag is controlled at R=3.0-4.0, the components are finely adjusted by adopting niobium iron, the aluminum wire is feeded to increase aluminum, and the titanium wire is feeded to increase titanium. The LF refining can further desulfurize, deoxidize and remove impurities, adjust the composition and temperature of the molten steel, and obtain a good refining effect.
The RH refining adopts a deep treatment mode, the vacuum degree is controlled to be 10-30 Pa, and the smaller the vacuum degree is, the smaller the content of gas inclusions such as nitrogen, hydrogen and oxygen in the molten steel is, namely the clean steel smelting. The value of the vacuum degree in an ideal state is 0 Pa, but it is not very realistic to reach, the present disclosure controls the vacuum degree at 10Pa-30Pa, which indicates that the content of gas inclusions such as nitrogen, hydrogen and oxygen in the molten steel is very small and is close to the clean steel smelting. The vacuum time is controlled at 15min-25min (such as 15min, 17min, 19min, 20min, 22min, and 25min). The vacuum degree is kept too short, and the gas inclusion is not clean; the vacuum degree is too long, it will no longer work and the production efficiency is not affected. The pure degassing time was controlled to be not less than 5min, and the soft blowing time was not less than 12min. The cycle of RH refining is controlled at 40min-60min, the addition amount of the aluminum wire is 0m/t-3.3m/t (when the addition amount of the aluminum particles is sufficient to achieve the deoxidation effect during LF refining, the aluminum wire can be no longer added during RH refining), and the addition amount of the titanium wire is 0.8m/t-3.3m/t. The main purpose of RH refining is to perform vacuum degassing, reduce the gas content in the steel, reduce the defects caused by gas inside the steel plate, and improve the purity and alloying and homogenization of the molten steel.
In the continuous casting process of the plate blank, the whole-course protective casting is adopted, that is, a long water nozzle is adopted from a large ladle to a tundish, and argon sealing protection is carried out; the tundish is covered with a covering agent in combination with carbonized rice husks, so that the liquid level is well covered, the molten steel is isolated from air, and secondary oxidation is avoided; a submerged water nozzle is adopted from the tundish to a crystallizer, and the argon sealing protection is adopted; and the liquid level of the crystallizer adopts peritectic steel protecting slag, so that the pulling speed is stable. The main composition of the peritectic steel protecting slag is 25% <_ SiO₂≤ 35%, 35% <_ CaO <_ 45%, 1.90% <_ MgO <_ 3.00%, and 3.00% <_ Al₂O₃ ≤ 4.00% in percentage by weight.
In the continuous casting process, the casting speed is slowly and the pulling speed is uniformly increased, the automatic control is carried out after the pulling speed is increased to the target pulling speed, meanwhile, the liquid level fluctuation condition of the crystallizer is closely observed, and the pulling speed is gradually stabilized to 0.80m/min-1.40m/min. According to the size of section, the pulling speed is also different, and the size of the section refers to the thickness specification of the casting blank. Specifically, it is shown below.

section 175: pulling speed is stabilized to 1.2-1.35m/min;
section 200: pulling speed is stabilized to 1.3-1.4m/min;
section 250: pulling speed is stabilized to 1.1-1.3m/min;
section 300: pulling speed is stabilized to 0.8-0.9m/min.

Generally, the width of the casting blank is 1800mm and 2200mm, and 2400mm is a special width specification for rolling ultra-wide steel plates. Wherein the 2400mm width section (the width of the casting blank) is controlled at 1.0-1.1m/min.
When the casting temperature and the superheat degree are constant, the above-mentioned speed set according to the section can make the liquid more fully solidified, more non-uniform nucleation cores are reserved in the liquid, the nucleation rate is improved, the development of a columnar crystal region is prevented, more equiaxed crystals are obtained, and the effect of refining grains is achieved.
The determination of the pulling speed depends on the casting blank section size. According to the speed increase curve, the speed is increased in a step mode, the speed is increased by 0.05m every 30s, the speed is increased to a value and then kept for a certain time. The specific operation is that the speed is kept for 1minute at 0.4m/min, the speed is kept for 2minutes at 0.6m/min, so that the required pulling speed is finally increased. The dulling speed is large, the section is small, and the dulling speed is small, the section is large, this is determined according to the casting period and the solidification law, and internal defects of the casting blank are avoided. If the section is large, the pulling speed is large, steel leakage will also occur when the molten steel is directly pulled without solidification.
The continuous casting process mainly reduces the central segregation degree of the casting blank by controlling the casting superheat degree and reduces or avoids surface cracks of the continuous casting blank by reasonably controlling the cooling water and the straightening temperature, thereby improving the surface and internal quality of the casting blank and providing powerful guarantee for the quality of the final product. The casting superheat degree is determined by the difference between the tundish temperature and the liquidus temperature, and the goal is to control below 20°C. The height of the liquid level of the tundish is controlled, the height of the liquid level of the tundish is not lower than 600mm during pouring, the height of the liquid level in the normal pouring process is between 800mm and 1000mm, low liquid level pouring is strictly forbidden, so that slag rolling is prevented. On one hand, through water cooling, the casting temperature is reduced, and fine grain size is obtained; and on the other hand, grains are refined by adopting crystallizer vibration and dynamic light pressure. The casting blank straightening temperature is controlled above 900°C.
In the rolling process, adopting two-stage rolling for wide and thick plate rolling, the two-stage rolling is divided into rough rolling and finish rolling, and a four-roller reversible rolling mill is adopted for rough rolling and finish rolling. The steel blank is heated before rolling, and the steel blank tapping temperature is controlled at 1170°C-1280°C (for example, 1170°C, 1175°C, 1180°C, 1190°C, 1200°C, 1205°C, 1210°C, 1215°C, 1220°C, 1225°C, 1230°C, 1235°C, 1240°C, 1245°C, 1250°C, 1255°C, 1260°C, 1265°C, 1270°C, 1275°C, 1280°C and a range between any two values), the purpose of heating the steel blank is to increase the plasticity of the steel, reduce the deformation resistance and improve the internal organization and properties of the metal. Generally, the steel is heated to a temperature range of an austenite single-phase solid solution structure, and a relatively high temperature and sufficient time are ensured to homogenize the structure and dissolve carbides, but the temperature cannot be too high. When the heating temperature is too high, on one hand, the defects of strong oxidation, decarburization, overheating, overburning and the like of the steel will be caused; the viscosity of the iron oxide scale in contact with the matrix of the casting blank will also be increased, which affects the descaling effect; on the other hand, the original austenite grains will be too coarse, and according to the grain genetic principle, the grains of the finished product will also be relatively coarse, which is not conducive to the performance of the finished product. If the heating temperature is too low, the rolling final temperature is reduced, the rolling passes are increased, the rolling force is increased, the control of the rolling rhythm and the shape of the final finished product is affected, the quality of steel is reduced, and even waste products are caused.
After the steel blank is taken out of the furnace, high-pressure water descaling is carried out before rough rolling, that is, iron oxide scale on the surface of the casting blank is removed, and guarantee is provided for subsequently obtaining high surface quality. Therefore, the rough rolling starting temperature of the steel blank is reduced compared with the steel blank tapping temperature. The rough rolling starting temperature of the steel blank is 1130°C to 1190°C (for example, 1130°C, 1135°C, 1140°C, 1145°C, 1150°C, 1155°C, 1160°C, 1165°C, 1170°C, 1175°C, 1180°C, 1185°C, 1190°C and a range between any two values), and the rough rolling final temperature is 1050°C to 1120°C (for example, 1050°C, 1055°C, 1060°C, 1065°C, 1070°C, 1075°C, 1080°C, 1085°C, 1090°C, 1095°C, 1000°C, 1005°C, 1010°C, 1015°C, 1020°C and a range between any two values), higher rolling temperature can provide good temperature conditions for the occurrence of recrystallization, and can reduce the rolling process deformation resistance, reducing the damage to the rolling mill equipment, conducive to the implementation of high temperature and low speed under large pressure process, and conducive to the elimination of defects such as cracks, sparse, porosity and spheroidization of inclusions, conducive to the penetration of deformation to the center, so that the deformation is more uniform, improving the plasticity of the plate blank, which is conducive to rolling to ensure the total compression ratio in the rough rolling stage.
The rough rolling total compression ratio is greater than 50%; the finish rolling starting temperature is 850°C-1070°C (for example, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, 990°C, 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, 1060°C, and 1070°C); and the finish rolling final temperature is 830°C-960°C (for example, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, and 960°C). The normalizing rolling mainly depends on the temperature of the rolling final stage, and the rolling final temperature is 830°C-960°C, which can ensure that the rolling is normalizing rolling.
The control of each parameter in the above-mentioned rolling process can refine the structure grains and improve the structure of the core part of the steel plate to the maximum extent, and the steel plate can be obtained with the final thickness, performance and surface quality meeting the requirements.
In the present disclosure, normalizing rolling is adopted, and both rough rolling and finish rolling are normalizing rolling, wherein normalizing rolling refers to high-temperature rolling performed above the normalizing temperature, and the steel plate after rolling is above the critical temperature A_c3 to simulate the normalizing heat treatment state to obtain the expected structural morphology. A_c3 is the critical temperature of austenitization of the sub-eutectic steel and is the final temperature at which ferrite is transformed to austenite. By adopting normalizing rolling, the normalizing procedure can be omitted to shorten the delivery period and reduce the production cost.
The process or parameters not described in detail in the process of the present disclosure are conventional techniques for wind power steel in the art.

Embodiment 1

The composition of the wind power steel is C: 0.146%, Si: 0.28%, Mn: 1.32%, P: 0.017%, S: 0.004%, Nb: 0.012%, Ti: 0.019%, Als: 0.032% in percentage by weight, and the rest are iron and inevitable impurities.
A manufacturing method of a wind power steel containing the above-mentioned components includes the following steps:

1) Pretreating: the process procedure is strictly executed for molten steel desulfurization, the molten steel sulfur is controlled at 0.008%, the temperature is controlled at 1250°C, and the slag on the surface of molten steel is removed after desulfurization.
2) Smelting: the pretreated molten steel enters a converter for smelting, the slagging material is added 3min before the end point, the alkalinity of the final slag is controlled at R=3.0, and the end point gun pressing time is 65s. Aluminum ferromanganese is adopted for deoxidation, and the addition amount of aluminum ferromanganese 2.5kg/t is added. When the molten steel is discharged to one fourth, silicon manganese, silicon iron and niobium iron are added in batches, and finish adding when the molten steel is discharged to three fourths.
3) Refining: feeding the molten steel smelted by a converter into an LF refining furnace, adding lime for slagging according to actual conditions, keeping the time of yellow and white slag or white slag for 13min, adopting whole-process bottom argon blowing and stirring, and soft argon blowing is performed for 11min.

It enters the RH refining furnace after LF refining, the vacuum degree is controlled at 10 Pa, the vacuum time is controlled at 18min, the pure degassing time is controlled at 10min, the soft blowing time is controlled at 15min, the RH refining period is controlled at 43min, and the addition amount of the titanium wire is 0.8m/t.
4) Continuous casting: adopting whole-process protection casting, the protecting slag adopts peritectic steel protecting slag, a casting blank with section 175 is adopted, and the stable period pulling speed is set as 1.20m/min.
5) Rolling: controlling the rolling temperature, and ensuring rolling in a specified temperature interval, wherein (1) the steel blank tapping temperature is 1230-1280°C; (2) the steel blank rough rolling starting average temperature is 1130-1180°C, the rolling final average temperature is greater than or equal to 1050°C, and the rough rolling total compression ratio is greater than 50%; (3) the finish rolling starting temperature is 1010-1070°C, and the rolling final temperature is 920°C-960°C.
The performance of the steel plate in this embodiment is listed in Table 3, and the performance test method adopts an international universal method.

Embodiment 2

The composition of the wind power steel is C: 0.146%, Si: 0.28%, Mn: 1.34%, P: 0.015%, S: 0.008%, Nb: 0.011%, Ti: 0.018%, Als: 0.039% in percentage by weight, and the rest are iron and inevitable impurities.
The manufacturing method of the wind power steel containing the above-mentioned components is the same as that in embodiment 1.
The performance of the steel plate in this embodiment is listed in Table 3, and the performance test method adopts an international universal method.

Embodiment 3

The composition of the wind power steel is C: 0.142%, Si: 0.30%, Mn: 1.34%, P: 0.013%, S: 0.008%, Nb: 0.037%, Ti: 0.018%, Als: 0.032% in percentage by weight, and the rest are iron and inevitable impurities.
A manufacturing method of the wind power steel containing the above-mentioned components includes the following steps:

1) Pretreating: the process procedure is strictly executed for molten steel desulfurization, the molten steel sulfur is controlled at 0.005%, the temperature 1290°C, and the slag on the surface of molten steel is removed after desulfurization.
2) Smelting: the pretreated molten steel enters a converter for smelting, the slagging material is added 3min before the end point, the alkalinity of the final slag is controlled at R=3.5, and the end point gun pressing time is 100s. Aluminum ferromanganese is adopted for deoxidation, and the addition amount of aluminum ferromanganese 3.0kg/t is adopted. When the molten steel is discharged to one fourth, silicon manganese, silicon iron and niobium iron are added in batches, and finish adding when the molten steel is discharged to three fourths.
3) Refining: feeding the molten steel smelted by a converter into an LF refining furnace, adding lime for slagging according to actual conditions, keeping the time of yellow and white slag or white slag for 13min, adopting whole-process bottom argon blowing and stirring, and soft argon blowing is performed for 15min. Aluminum particle deoxidizer is used for deoxidation. The compositions are finely adjusted by adopting niobium iron, feeding aluminum wire to increase aluminum and feeding titanium wire to increase titanium.

It enters the RH refining furnace after LF refining, the vacuum degree is controlled at 20 Pa, the vacuum time is controlled at 25min, the pure degassing time is controlled at 15min, the soft blowing time is controlled at 20min, the RH refining period is controlled at 60min, and the addition amount of the titanium wire is 1.5m/t, the addition amount of the titanium wire is 2.0m/t.
4) Continuous casting: adopting whole-process protection casting, the protecting slag adopts peritectic steel protecting slag, a casting blank with section 300 is adopted, and the stable period pulling speed is set as 0.85m/min.
5) Rolling: controlling the rolling temperature, and ensuring rolling in a specified temperature interval, wherein (1) the steel blank tapping temperature is 1170-1220°C; (2) the steel blank rough rolling starting average temperature is 1160-1190°C, the rolling final average temperature is 1100-1130°C, and the rough rolling total compression ratio is greater than 50%; (3) the finish rolling starting temperature is 860-900°C, and the rolling final temperature is 830°C-860°C.

The performance of the steel plate in this embodiment is listed in Table 3, and the performance test method adopts an international universal method. In Table 3, d is diameter of the bend center, and a is thickness of the sample.

Table 3: The performance of the steel plate in Embodiments 1-3

Embodiment	Thickness (mm)	Yield Strength (MPa)	Tensile Strength (MPa)	Percentage Elongation after Fracture A (%)	Impact Power (-20°C longitudinal) Akv/J			Bend Test
1	6	420	519	29	156	155	154	d=2a	Qualified
2	25	487	598	25	239	271	243	d=3a	Qualified
3	63	420	552	28	271	273	225	d=3a	Qualified

The production process steps in embodiment 4 and comparative examples 1-3 are the same as in embodiment 1 except that the composition of the wind power steel is different from that of embodiment 1. The composition of the wind power steel in embodiment 4 and comparative examples 1-3 is specified in Table 4. The performance of the steel plates of embodiment 4 and comparative examples 1-3 are listed in Table 5, and the performance test method is adopted by the international universal method. In Table 5, d is diameter of the bending center, a is thickness of the sample.

Table 4: The components of the wind power steel in embodiment 4 and comparative embodiments 1-3

Numbers	C	Si	Mn	P	S	Nb	Ti	Als
Embodiment 4	0.17	0.5	1.6	0.015	0.007	0.035	0.03	0.05
Comparative Example 1	0.14	0.3	1.43	0.011	0.008	0.005	0.04	0.07
Comparative Example 2	0.16	0.4	1.6	0.012	0.005	0.05	0.05	0.03
Comparative Example 3	0.13	0.45	1.65	0.010	0.006	0.05	0.006	0.05

Table 5: The performance of the steel plates in embodiment 4 and comparative examples 1-3

Numbers	Thickness (mm)	Yield Strength (MPa)	Tensile Strength (MPa)	Percentage Elongation after Fracture (%)	Impact Power (-20°C longitudinal) Akv/J			Bend Test
Embodiment 4	6	455	545	28	184	196	172	d=2a	Qualified
Comparative Example 1	6	375	500	25	96.5	144	142	d=2a	Qualified
Comparative Example 2	6	424	527	27	95	93	96	d=2a	Qualified
Comparative Example 3	6	400	516	26	127	125	174	d=2a	Qualified

In comparative examples 4-7, the composition of the wind power steel and other production process steps are the same as in embodiment 3, except that the temperature of Step 5) rolling is different from that of embodiment 3. The rolling temperature of Step 5) in comparative examples 4-7 is specified in Table 6. Comparative example 7 uses the method of using controlled rolling + normalizing process as described in the background technology part, and the performance of the steel plates before the un-normalized heat treatment. The performance of the steel plates of comparative examples 4-7 are listed in Table 7, and the performance test method adopts an international universal method. In Table 7, d is diameter of the bend center, and a is thickness of the sample.

Table 6: The performance of the steel plates in embodiment 4 and Comparative Examples 1-3

Numbers	Thickness (mm)	steel blank tapping temperature	rough rolling starting temperature	rough rolling final temperature	finish rolling starting temperature	finish rolling final temperature
Comparative Example 4	63	1150	1140	990	850	825
Comparative Example 5	63	1140	1130	970	820	800
Comparative Example 6	63	1130	1120	970	800	780
Comparative Example 7	63	1120	1100	960	790	765

Table 7: The performance of the steel plates in comparative examples 4-6

Numbers	Thickne ss(mm)	Yield Strength(M Pa)	Tensile Strength(M Pa)	Percentage Elongation after Fracture (%)	Impact Power (-20°C longitudinal) Akv/J			Bend Test
Comparative Example 4	63	346	426	21	189	178	218	d=3a	Qualifie d
Comparative Example 5	63	340	413	20.5	162	70.1	178	d=3a	Unquali fied
Comparative Example 6	63	326	405	20	40.7	84.6	66.7	d=3a	Unquali fied
Comparative Example 7	63	300	390	16	426	68	93.5	d=3a	Unquali fied

It can be seen from Table 6 and Table 7 that, since the rolling temperature in step 5) is different from that in embodiment 3, the performance of the steel plate obtained in Comparative Examples 4 to 6 is far lower than that of the steel plate obtained in embodiment 3. The comparative example 7 adopts the method of controlling the rolling and normalizing process described in the background section, and the performance of the steel plate is poor before the un-normalized heat treatment, so the rolling process of the present disclosure has the normalizing treatment effect. In comparative examples 4 to 7, (1) the steel blank tapping temperature; (2) the rough rolling starting average temperature and rolling final average temperature of the steel blank being greater than or equal to 1050°C; and (3) finish rolling starting temperature and rolling final temperature being equal temperature values, which are lower than the rolling temperature in step 5) of this application; due to the low temperature, uneven heating, insufficient deformation during rolling, uneven deformation of intermediate structure, most of the performance will be unqualified.
According to the exemplary embodiment of the present disclosure, by adjusting the components and the manufacturing process of the steel, accurate control over the structure transformation and each of the comparative embodiments is realized, and finally the normalizing rolling low-temperature impact toughness wind power steel with special mechanical properties is obtained; the normalizing rolling low-temperature impact toughness wind power steel provided by the present disclosure provides relatively accurate control ranges of C, S and P, the control ranges of Mn, Nb and Ti are given, the production cost of steelmaking is low, the production process is easy to stably control, the chemical components are easy to stably control, the alloy components are controlled through LF refining and RH refining, the low-temperature impact toughness requirement can be met by adopting the normalizing rolling process, and other comprehensive performance (such as cold bending property, elongation rate, yield strength and tensile strength) of the steel plate are excellent. Therefore, the exemplary embodiments of the present disclosure can provide a normalizing rolling low-temperature impact toughness wind power steel without adopting expensive Ni, Cr, and V, thereby significantly reducing production cost.
According to an exemplary embodiment of the present disclosure, a normalizing rolling toughness wind power steel with low-temperature impact resistance having a thickness of 6 mm to 63 mm can be provided, so that the production process of the toughness wind power steel with low-temperature impact resistance can be simplified, and a normalizing rolling toughness wind power steel with low-temperature impact resistance plate having a larger thickness can be provided. The present disclosure relates to an economical wind power steel, which is suitable for wind power towers with normalizing rolling and low-temperature impact toughness requirements, at low temperatures up to -20°C, the minimum value of impact toughness is≥100J.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present disclosure shall fall within the protection scope of the present disclosure.

Claims

A preparation method for toughness wind power steel with low-temperature impact resistance, comprising the following steps of:
pretreating, a desulfurization of molten steel;

smelting, pretreated molten steel;

refining, being divided into LF refining and RH refining;

continuous casting, being adopted whole-process protection casting; and

rolling, being adopted two-stage rolling comprising rough rolling and finish rolling.
The preparation method for toughness wind power steel with low-temperature impact resistance according to claim 1, wherein
in the pretreating step, sulfur content in the molten steel is controlled to be below 0.010% by mass percentage,

specifically, desulfurization temperature is 1250°C-1320°C.
The preparation method for toughness wind power steel with low-temperature impact resistance according to claim 1, wherein
in the smelting step, the pretreated molten steel enters a converter for smelting, a slagging material is added within 1min-5min before the molten steel enters an end point of the converter, and alkalinity of a final slag is controlled at R=3.0-4.0,

specifically, an end point gun pressing time is 65s-120s;

specifically, aluminum manganese iron is used for deoxidation, addition amount of the aluminum manganese iron is 2.0kg/t-3.5kg/t, when the molten steel is discharged to one fourth, silicon manganese, silicon iron and niobium iron are added in batches, and finish adding when the molten steel is discharged to three fourths;

specifically, the silicon manganese is an iron alloy containing 13%-25% by weight of silicon and 55%-75% by weight of manganese, and addition amount of the silicon manganese is 20kg/t-30kg/t;

the silicon iron is an iron alloy containing 70%-78% by weight of silicon, and addition amount of the silicon iron is 0.5kg/t-2kg/t;

the niobium iron is an iron alloy containing 50%-65% by weight of niobium, and addition amount of the niobium iron is 0.1kg/t-0.8kg/t.
The preparation method for toughness wind power steel with low-temperature impact resistance according to claim 1, wherein
in the refining step, the LF refining adopts a whole-process bottom argon blowing and stirring, an soft argon blowing is performed for 10min-15min, lime is added for slagging, and aluminum particle deoxidizer is used for deoxidation;

specifically, yellow and white slag or white slag is kept for 10min-30min, and the alkalinity of the final slag is controlled at R=3.0-4.0.
The preparation method for toughness wind power steel with low-temperature impact resistance according to claim 1, wherein
in the refining step, vacuum degree in the RH refining process is controlled at 10 Pa-30 Pa, and vacuum time is 15min-25min;

specifically, pure degassing time is less than 5min, and soft blowing time is less than 12min;

specifically, a cycle of the RH refining is controlled at 40min-60min, addition amount of an aluminum wire is 0m/t-3.3m/t, and addition amount of a titanium wire is 0.8m/t-3.3m/t.
The preparation method for toughness wind power steel with low-temperature impact resistance according to claim 1, wherein
in the continuous casting step, the whole-process protection casting refers to that from a large ladle to a tundish adopts a long water nozzle and perform argon sealing protection; the tundish is covered with a covering agent in combination with carbonized rice husks; from the tundish to a crystallizer adopts a submerged nozzle and perform argon sealing protection; and liquid level of the crystallizer adopts peritectic steel protecting slag;

specifically, the composition of the peritectic steel protecting slag is 25% <_ SiO₂≤ 35%, 35% < CaO < 45%, 1.90% ≤ MgO < 3.00%, and 3.00% < Al₂O₃≤ 4.00% in percentage by weight.
The preparation method for toughness wind power steel with low-temperature impact resistance according to claim 1, wherein
in the continuous casting step, pulling speed is stabilized to 0.80m/min-1 .40m/min;

specifically,

section 175: pulling speed is stabilized to 1.2-1.35m/min;

section 200: pulling speed is stabilized to 1.3-1.4m/min;

section 250: pulling speed is stabilized to 1.1-1.3m/min;

section 300: pulling speed is stabilized to 0.8-0.9m/min.
The preparation method for toughness wind power steel with low-temperature impact resistance according to claim 1, wherein
in the continuous casting step, casting superheat degree is controlled below 20°C;

specifically, height of liquid level of the tundish is controlled, the height of the liquid level of the tundish during pouring is not lower than 600mm, and the height of the liquid level during normal pouring is between 800mm-1000mm;

specifically, casting blank straightening temperature is controlled above 900°C.
The preparation method for toughness wind power steel with low-temperature impact resistance according to claim 1, wherein
in the rolling step, steel blank tapping temperature is controlled at 1170°C-1280°C;

rough rolling starting temperature is 1130°C-1190°C, and rough rolling final temperature is 1050°C-1120°C;

rough rolling total compression ratio is more than 50%;

finish rolling starting temperature is 850°C-1070°C, and finish rolling final temperature is 830°C-960°C.
The preparation method for toughness wind power steel with low-temperature impact resistance according to claim 1, wherein
the composition of the wind power steel is 0.13% < C < 0.17%, 0.20% < Si ≤ 0.50%, 0.90% ≤ Mn ≤ 1.65%, 0 ≤ S < 0.010%, 0 ≤ P ≤ 0.030%, 0.010% < Nb < 0.040%, 0.010% < Ti ≤ 0.030%, 0.015% < Als < 0.050% in percentage by weight, and the rest are iron and inevitable impurities, Als is acid-soluble aluminum.