CN112662933A

CN112662933A - Preparation method of low-temperature impact toughness-resistant wind power steel

Info

Publication number: CN112662933A
Application number: CN202011334962.2A
Authority: CN
Inventors: 李艳; 王中学; 麻衡; 宁伟; 李文强; 张长宏; 倪凯; 王腾飞; 何康; 曹阳
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: 2020-11-24
Publication date: 2021-04-16
Also published as: EP4253586A1; WO2022110982A1

Abstract

The invention provides a preparation method of low-temperature impact toughness-resistant wind power steel, which comprises the following steps: pretreating, namely desulfurizing molten iron; smelting, namely smelting the pretreated molten iron; refining, namely LF refining and RH refining; continuous casting, which adopts full-process protection casting; and rolling, namely adopting two-stage rolling, and performing rough rolling and finish rolling. The invention discloses a preparation method of low-temperature impact toughness resistant wind power steel, and provides a normalizing rolling low-temperature impact toughness wind power steel plate which is low in cost, excellent in low-temperature impact toughness and excellent in comprehensive performances such as product strength, elongation after fracture, cold bending performance and the like, and the normalizing rolling low-temperature impact toughness wind power steel plate which is low in production cost, short in production period and capable of producing the thickness of 6mm to 63mm is obtained by adding and controlling various alloy elements and directly adopting a normalizing rolling process.

Description

Preparation method of low-temperature impact toughness-resistant wind power steel

Technical Field

The invention relates to the field of steel smelting, in particular to a preparation method of low-temperature impact toughness-resistant wind power steel.

Background

Wind energy 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, so that 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 increased more and more. In China, 8 million kilowatt-level wind power bases are built in 7 provinces such as Gansu, inner Mongolia, Xinjiang and the like, the lowest temperature of the use environment is close to-20 ℃, and therefore, the requirement on low-temperature impact toughness is high.

The national standard is as follows: GB/T1591-2018 provides the chemical components and mechanical and technological performance requirements of Q355ND steel, as shown in tables 1 and 2.

TABLE 1Q 355ND 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 2Q 355ND mechanical and Process Property requirements

In Table 2, d is the radius of the bend and a is the thickness of the sample.

In practical application, various additional requirements are provided due to different use conditions and application fields, so that the product performance needs to be further improved on the basis of national standards.

At present, a plurality of manufacturing methods of low-temperature impact toughness wind power steel plates are available, from the component point of view, more alloy elements are added, Nb, V and Ti component systems are adopted, and most of noble metals such as Ni, Cr and the like are added, so that the production cost of the steel is increased. Although Ni and Cr component systems are not adopted, the controlled rolling and the controlled cooling process are adopted, and the low-temperature impact toughness yield of the product obtained by the technology is lower.

From the characteristics of the production process, the majority of the current research and production of the low-temperature impact toughness wind power steel plate adopts a method of controlling rolling and normalizing processes to obtain the performance requirements of the low-temperature impact toughness wind power steel plate. Although the above method can make the structure uniform and improve the low-temperature impact toughness, the use of the heat treatment process results in a longer production period, an increase in cost and a lower production efficiency.

Disclosure of Invention

The invention aims to provide a preparation method of low-temperature impact toughness-resistant wind power steel, which aims to solve at least one of the problems. The invention provides a normalizing rolling low-temperature impact toughness wind power steel plate which is low in cost, excellent in low-temperature impact toughness and excellent in comprehensive performances such as product strength, elongation after fracture, cold bending performance and the like, and the normalizing rolling technology is adopted to add and control various alloy elements, so that the production cost is low, the production period is short, and the normalizing rolling low-temperature impact toughness wind power steel plate with the thickness of 6mm to 63mm can be produced to obtain the low-temperature impact toughness wind power steel.

In order to achieve the above purpose, the invention provides the following technical scheme:

a preparation method of low-temperature impact toughness-resistant wind power steel comprises the following steps: pretreating, namely desulfurizing molten iron; smelting, namely smelting the pretreated molten iron; refining, namely LF refining and RH refining; continuous casting, which adopts full-process protection casting; and rolling, namely performing two-stage rolling, namely rough rolling and finish rolling.

Further, in the preparation method of the low-temperature impact toughness resistant wind power steel, in the pretreatment step, the sulfur content in molten iron is controlled to be below 0.010% by mass; preferably, the desulfurization temperature is 1250 ℃ to 1320 ℃.

Further, in the preparation method of the wind power steel with low temperature impact toughness, in the smelting step, pretreated molten iron enters a converter for smelting, slagging materials are added within 1-5 min before the molten iron enters the converter, and the alkalinity of final slag is controlled to be 3.0-4.0; preferably, the terminal gun pressure time is 65s-120 s; preferably, aluminum manganese iron is adopted for deoxidation, the adding amount of the aluminum manganese iron is 2.0kg/t-3.5kg/t, when the molten steel is discharged to one fourth, silicon manganese, ferrosilicon and ferrocolumbium are added in batches, and when the molten steel is discharged to three fourths, the adding is finished; preferably, the silicon and manganese are ferroalloy containing 13 to 25 weight percent of silicon and 55 to 75 weight percent of manganese, and the addition amount of the silicon and manganese is 20 to 30 kg/t; the ferrosilicon is ferroalloy containing 70-78 wt% of silicon, and the adding amount of the ferrosilicon is 0.5-2 kg/t; the ferrocolumbium is an iron alloy containing 50-65 wt% of niobium, and the addition amount of the ferrocolumbium is 0.1kg/t-0.8 kg/t.

Further, in the preparation method of the low-temperature impact toughness resistant wind power steel, in the refining step, bottom argon blowing and stirring are adopted in the LF refining process in the whole process, argon is blown softly for 10-15 min, lime is added for slagging, and an aluminum particle deoxidizer is adopted for deoxidation; preferably, the retention time of the yellow and white slag or the white slag is 10min to 30min, and the alkalinity of the final slag is controlled to be 3.0 to 4.0.

Further, in the preparation method of the low-temperature impact toughness resistant wind power steel, in the refining step, the vacuum degree in the RH refining process is controlled to be 10Pa-30Pa, and the vacuum time is 15min-25 min; preferably, the pure degassing time is not less than 5min, and the soft blowing time is not less than 12 min; preferably, the period of RH refining is controlled to be 40min-60min, the adding amount of the aluminum wire is 0m/t-3.3m/t, and the adding amount of the titanium wire is 0.8m/t-3.3 m/t.

Further, in the preparation method of the low-temperature impact toughness resistant wind power steel, in the continuous casting step, the whole-process protective casting means that a ladle to a tundish adopt a long nozzle and argon sealing protection is performed; the tundish is covered by a covering agent combined with the carbonized rice hulls; the tundish to the crystallizer adopts an immersion type water gap and adopts argon seal protection; the liquid level of the crystallizer adopts peritectic steel covering slag; preferably, the peritectic steel casting powder comprises SiO with the weight percentage of more than or equal to 25 percent₂≤35％、35％≤CaO≤45％、1.90％≤MgO≤3.00％、3.00％≤Al₂O₃≤4.00％。

Further, in the preparation method of the wind power steel with low temperature impact toughness, in the continuous casting step, the casting speed is stabilized to 0.80-1.40 m/min; preferably, section 175: the pulling speed is stabilized to 1.2-1.35m/min, and the section of 200 is as follows: the pulling speed is stabilized to 1.3-1.4m/min, and the section is 250: the pulling speed is stabilized to 1.1-1.3m/min, and the section of 300 is as follows: the pulling speed is stabilized to 0.8-0.9 m/min.

Further, in the preparation method of the wind power steel with low-temperature impact toughness, in the continuous casting step, the casting superheat degree is controlled below 20 ℃; preferably, the height of the liquid level of the tundish is controlled, the height of the liquid level of the tundish is not less than 600mm during casting, and the height of the liquid level is between 800mm and 1000mm during normal casting; preferably, the straightening temperature of the casting blank is controlled to be above 900 ℃.

Further, in the preparation method of the low-temperature impact toughness resistant wind power steel, in the rolling step, the tapping temperature of the steel billet is controlled to be 1170-1280 ℃; the initial rolling temperature of rough rolling is 1130-1190 ℃, and the final rolling temperature of rough rolling is 1050-1120 ℃; the rough rolling total compression ratio is more than 50%; the initial rolling temperature of the finish rolling is 850-1070 ℃, and the final rolling temperature of the finish rolling is 830-960 ℃.

Further, in the preparation method of the wind power steel with low temperature impact toughness, the wind power steel comprises the following components in percentage by weight: c is more than or equal to 0.13 percent and less than or equal to 0.17 percent, Si is more than or equal to 0.50 percent and less than or equal to 0.50 percent, Mn is more than or equal to 0.65 percent and less than or equal to 0.010 percent, P is more than or equal to 0.030 percent and less than or equal to 0.030 percent, Nb is more than or equal to 0.010 percent and less than or equal to 0.040 percent, Ti is more than or equal to 0.030 percent and less than or equal to 0.015 percent and less than or equal to 0.050 percent, and the balance.

Analysis shows that the preparation method of the low-temperature impact toughness resistant wind power steel disclosed by the invention provides the normalizing rolling low-temperature impact toughness wind power steel plate which is low in cost, excellent in low-temperature impact toughness and excellent in comprehensive performances such as product strength, elongation after fracture, cold bending performance and the like, and the normalizing rolling low-temperature impact toughness wind power steel plate which is low in production cost, short in production period and capable of producing the thickness of 6mm to 63mm is obtained by adding and controlling various alloy elements and directly performing a normalizing rolling process.

Detailed Description

The present invention will be described in detail with reference to examples. The various examples are provided by way of explanation of the invention, and not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. It is therefore intended that the present invention encompass such modifications and variations as fall within the scope of the appended claims and equivalents thereof.

According to the embodiment of the invention, the preparation method of the low-temperature impact toughness-resistant wind power steel is provided. The wind power steel comprises the following components in percentage by weight: c is more than or equal to 0.13 percent and less than or equal to 0.17 percent, Si is more than or equal to 0.50 percent and less than or equal to 0.50 percent, Mn is more than or equal to 0.65 percent and less than or equal to 0.010 percent, P is more than or equal to 0.030 percent and less than or equal to 0.030 percent, Nb is more than or equal to 0.010 percent and less than or equal to 0.040 percent, Ti is more than or equal to 0.030 percent and less than or equal to 0.015 percent and less than or equal to 0.050 percent, and the balance. The minimum value of the impact toughness is more than or equal to 100J at the temperature of minus 20 ℃. The wind power steel has low cost, excellent low-temperature impact toughness and excellent comprehensive properties such as product strength, elongation after fracture, cold bending property and the like. And the steel plate is designed by adopting low C + Nb and Ti microalloying components, so that the steel plate is ensured to have easy weldability.

The control of the component content and the function of the low temperature impact toughness resistant wind power steel of the present invention will be further described below.

Based on 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 the steel plate is ensured to have enough strength; ti: on one hand, free nitrogen in steel is eliminated, the anti-aging performance is improved, on the other hand, crystal grains are refined, segregation is reduced, the level of a banded structure is reduced, and the toughness is improved; al: on one hand, the crystal grains can be refined, the strength is improved, and on the other hand, the combination of Al and N can prevent strain aging.

On the other hand, the invention also provides a preparation method of the low-temperature impact toughness resistant wind power steel, which comprises the following steps: pretreatment, 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 during component design, and on the other hand, a normalizing rolling process is adopted in the rolling process so as to meet the requirement on the product performance.

The pretreatment refers to molten iron desulphurization, and the process procedures are strictly executed in the molten iron desulphurization, the sulfur content in the molten iron is controlled to be below 0.010 percent (such as 0.001 percent, 0.002 percent, 0.003 percent, 0.004 percent, 0.005 percent, 0.006 percent, 0.007 percent, 0.008 percent, 0.009 percent and 0.010 percent) according to the mass percentage, the desulphurization temperature is 1250 ℃ -1320 ℃ (such as 1250 ℃, 1255 ℃, 1258 ℃, 1260 ℃, 1263 ℃, 1267 ℃, 1270 ℃, 1275 ℃, 1280 ℃, 1290 ℃, 1300 ℃, 1305 ℃, 1310 ℃, 1315 ℃ and 1320 ℃), and the slag on the molten iron surface is completely removed after the desulphurization. In general, sulfur is a harmful element, causes hot brittleness of steel, reduces ductility and toughness of steel, causes cracks at the time of rolling, and is disadvantageous in welding performance. In the invention, KR method desulfurization is adopted to control the desulfurization temperature during pretreatment, and the sulfur content in the molten iron is effectively reduced to be below 0.010 percent, so that the desulfurization is thorough, and the purity of steel is ensured.

Smelting, the pretreated molten iron enters a converter for smelting, the addition of slag forming materials is finished within 1-5 min before the molten iron enters the end point of the converter, the alkalinity of the final slag is controlled to be 3.0-4.0, the end point gun pressing time is 65-120 s (such as 65s, 70s, 75s, 80s, 85s, 90s, 95s, 100s, 105s, 110s, 115s, 120s and the range between any two numerical values), the end point gun pressing time is within 65s-120s, the chemical reaction of the added alloy components in the molten steel is exactly finished, and the complete homogenization of the components is achieved. If the time is shorter than 65s, the reaction is not sufficiently completed; if the time is longer than 120s, no effect on the components is exerted, and the production efficiency is adversely affected.

And (3) deoxidizing by adopting aluminum-manganese-iron, wherein the adding amount of the aluminum-manganese-iron is 2.0kg/t-3.5kg/t, when the molten steel is discharged to one fourth, adding silicon-manganese, ferrosilicon and ferrocolumbium in batches, and when the molten steel is discharged to three quarters, finishing adding. The key points of converter smelting control are to reduce the phosphorus and sulfur content at the end point as much as possible, reasonably control the carbon content and ensure the purity of steel.

The silicon and manganese are iron alloy containing 13-25% of silicon and 55-75% of manganese by weight, and the addition amount of the silicon and manganese is 20-30 kg/t; the ferrosilicon is ferroalloy containing 70-78 wt% of silicon, and the adding amount of the ferrosilicon is 0.5-2 kg/t; the ferrocolumbium is an iron alloy containing 50-65 wt% of niobium, and the addition amount of the ferrocolumbium is 0.1kg/t-0.8 kg/t.

And refining, namely LF refining and RH refining.

Wherein, LF refining adopts bottom argon blowing and stirring in the whole process, argon is blown softly for 10min-15min, lime is added for slagging, aluminum grain deoxidizer is adopted for deoxidation, yellow and 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 is kept for too short time, and the final slag is not melted; the retention time of the yellow and white slag or the white slag is too long, which affects the production efficiency. Controlling the alkalinity of the final slag to be 3.0-4.0, finely adjusting the components by adopting ferrocolumbium, feeding an aluminum wire for increasing aluminum, and feeding a titanium wire for increasing titanium. The LF refining can further perform desulfurization, deoxidation and inclusion removal, and adjust the components and temperature of molten steel to obtain a good refining effect.

The RH refining adopts a deep processing mode, the vacuum degree is controlled to be 10Pa-30Pa, and the smaller the vacuum degree is, the smaller the content of gaseous inclusions such as nitrogen, hydrogen, oxygen and the like in the molten steel is, namely clean steel smelting is carried out. The value of the ideal state vacuum degree is 0Pa, but the vacuum degree is controlled to be 10Pa-30Pa to achieve unrealistic, which shows that the content of gaseous inclusions such as nitrogen, hydrogen, oxygen and the like in the molten steel is very small and is close to clean steel smelting. The vacuum time is controlled at 15min-25min (such as 15min, 17min, 19min, 20min, 22min, 25min), the vacuum degree retention time is too short, and gas impurities cannot be removed; and the production efficiency is influenced on the contrary because the product is not used any longer. The pure degassing time is controlled to be not less than 5min, and the soft blowing time is not less than 12 min. The RH refining period is controlled to be 40min-60min, the adding amount of the aluminum wire is 0m/t-3.3m/t (when the adding amount of aluminum particles is enough to achieve the deoxidation effect in LF refining, the aluminum wire can not be added in RH refining), and the adding amount of the titanium wire is 0.8m/t-3.3 m/t. The main purposes of RH refining are to perform vacuum degassing, reduce the gas content in steel, reduce the defects caused by gas in the steel plate, and improve the purity, alloying and homogenization of molten steel.

Continuous casting, wherein in the slab continuous casting process, whole-process protective casting is adopted, namely, a long water gap is adopted from a large ladle to a middle ladle, and argon sealing protection is carried out; the tundish is covered by combining a covering agent with the carbonized rice hulls, so that the liquid level is well covered, the molten steel is isolated from air, and secondary oxidation is avoided; the tundish to the crystallizer adopts an immersion type water gap and adopts argon seal protection; the liquid level of the crystallizer adopts peritectic steel covering slag, so that the pulling speed is stable. According to weight percentage, the peritectic steel casting powder mainly comprises SiO with the content of more than or equal to 25 percent₂≤35％、35％≤CaO≤45％、1.90％≤MgO≤3.00％、3.00％≤Al₂O₃≤4.00％。

In the continuous casting process, the casting is slowly and uniformly improved, after the casting speed is improved to the target casting speed, automatic control is carried out, and the fluctuation condition of the liquid level of the crystallizer is closely observed, so that the casting speed is gradually stabilized to 0.80m/min-1.40 m/min. The drawing speed is different according to the size of the cross section, which refers to the thickness specification of the casting blank. In particular, the amount of the solvent to be used,

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

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

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

section 300: the pulling speed is stabilized to 0.8-0.9 m/min.

The width of a general casting blank is 1800mm and 2200mm, and 2400mm is a special width specification and is used for rolling an ultra-wide specification steel plate. Wherein the width section (width of casting blank) of 2400mm is controlled at 1.0-1.1 m/min.

When the casting temperature and the superheat degree are fixed, the liquid can be more fully solidified according to the speed set by the section, more non-uniform nucleation cores are reserved in the liquid, the nucleation rate is improved, and the development of a columnar crystal area is prevented, so that more equiaxial crystals are obtained, and the effect of refining the crystal grains is achieved.

The drawing speed is determined according to the section size of the casting blank. According to the speed increasing curve, the speed is increased in a step mode, the speed is increased by 0.05m every 30s, the speed is maintained for a certain time after the speed is increased to a numerical value, the specific operation is that the speed is maintained for 1 minute at 0.4m/min, the speed is maintained for 2 minutes at 0.6m/min, and the speed is increased to the required pulling speed finally in the mode. The large section drawing speed is small, the small section drawing speed is large, and the casting blank drawing speed is determined according to the casting period and the solidification law, so that the internal defects of the casting blank are avoided. If the section is large and the drawing speed is high, the steel is directly drawn without solidification of the molten steel, and steel leakage is also generated.

The continuous casting process mainly reduces the central segregation degree of the casting blank through controlling the casting superheat degree, reduces or avoids surface cracks of the continuous casting blank through 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 a final product. The casting superheat degree is determined by the difference between the tundish temperature and the liquidus temperature, and the target is controlled below 20 ℃. Controlling the height of the liquid level of the tundish, wherein the height of the liquid level of the tundish is not less than 600mm when casting is started, the height of the liquid level of the tundish is between 800mm and 1000mm in the normal casting process, and strictly prohibiting low-liquid-level casting to prevent slag entrapment. On one hand, the casting temperature is reduced by water cooling to obtain fine grain size; on one hand, the vibration of a crystallizer and dynamic soft pressure are adopted to refine grains. The straightening temperature of the casting blank is controlled to be above 900 ℃.

And rolling, wherein in the rolling process, the wide and thick plate rolling adopts two-stage rolling, the two-stage rolling is divided into rough rolling and finish rolling, and the rough rolling and the finish rolling adopt a four-roller reversing mill. The billet is heated before rolling, the tapping temperature of the billet is controlled to 1170-1280 ℃ (such as 1170 ℃, 1175 ℃, 1180 ℃, 1190 ℃, 1200 ℃, 1205 ℃, 1210 ℃, 1215 ℃, 1220 ℃, 1225 ℃, 1230 ℃, 1235 ℃, 1240 ℃, 1245 ℃, 1250 ℃, 1255 ℃, 1260 ℃, 1265 ℃, 1270 ℃, 1275 ℃, 1280 ℃ and the range between any two values), and the purpose of heating the billet is to improve the plasticity of the steel, reduce the deformation resistance and improve the internal structure and performance of the metal. The steel is generally heated to a temperature within the range of the 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 should not be too high. The heating temperature is too high, so that on one hand, the defects of strong oxidation, decarburization, overheating, overburning and the like of the steel can be caused; the viscosity of iron scale contacted with a casting blank matrix is increased, and the descaling effect is influenced; on the other hand, the prior austenite grains are too coarse, and the grains of the finished product are also coarse according to the grain inheritance principle, so that the performance of the finished product is not facilitated. If the heating temperature is too low, the final rolling temperature is reduced, the rolling passes are increased, the rolling force is increased, the rolling rhythm and the control of the final finished product plate shape are influenced, the quality of steel is reduced, and even waste products can be caused.

After the billet is taken out of the furnace and before rough rolling, high-pressure water descaling is carried out, namely, the iron oxide scale on the surface of the casting blank is removed, so that the follow-up high surface quality is ensured. Therefore, the slab roughing start temperature is lowered as compared with the slab tapping temperature. The initial rolling temperature of the rough rolling of the billet is 1130-1190 ℃ (such as 1130 ℃, 1135 ℃, 1140 ℃, 1145 ℃, 1150 ℃, 1155 ℃, 1160 ℃, 1165 ℃, 1170 ℃, 1175 ℃, 1180 ℃, 1185 ℃, 1190 ℃ and the range between any two values), the final rolling temperature of the rough rolling is 1050-1120 ℃ (such as 1050 ℃, 1055 ℃, 1060 ℃, 1065 ℃, 1070 ℃, 1075 ℃, 1080 ℃, 1085 ℃, 1090 ℃, 1095 ℃, 1000 ℃, 1005 ℃, 1010 ℃, 1015 ℃, 1020 ℃ and the range between any two values), the higher rolling temperature can provide good temperature conditions for recrystallization, reduce deformation resistance in the rolling process, reduce damage to rolling mill equipment, facilitate implementation of high-temperature low-speed high-pressure processes, further facilitate elimination of defects such as cracks, looseness, pores and the like and spheroidization of inclusions, facilitate deformation to penetrate to the center, enable deformation to be more uniform, and improve the plasticity of the slab, is beneficial to rolling so as to ensure the total compression ratio in the rough rolling stage.

The rough rolling total compression ratio is more than 50%; the finish rolling temperature is 850 ℃ to 1070 ℃ (e.g., 850 ℃, 860 ℃, 870 ℃, 880 ℃, 890 ℃, 900 ℃, 910 ℃, 920 ℃, 930 ℃, 940 ℃, 950 ℃, 960 ℃, 970 ℃, 980 ℃, 990 ℃, 1000 ℃, 1010 ℃, 1020 ℃, 1030 ℃, 1040 ℃, 1050 ℃, 1060 ℃, 1070 ℃), and the finish rolling temperature is 830 ℃ to 960 ℃ (e.g., 830 ℃, 840 ℃, 850 ℃, 860 ℃, 870 ℃, 880 ℃, 890 ℃, 900 ℃, 910 ℃, 930 ℃, 940 ℃, 950 ℃, 960 ℃). The normalizing rolling mainly depends on the temperature of the final rolling stage, and the final rolling temperature is 830-960 ℃, so that the normalizing rolling can be ensured.

The control of each parameter in the rolling process can refine the structure grains to the maximum extent and improve the structure of the core of the steel plate, and the steel plate with the final thickness, performance and surface quality meeting the requirements can be obtained.

The invention adopts normalizing rolling, wherein the rough rolling and the finish rolling are both normalizing rolling, the normalizing rolling refers to high-temperature rolling carried out at a normalizing temperature, and a rolled steel plate is at a critical temperature A_c3In the above, the normalized heat treatment state was simulated to obtain a desired morphology. A. the_c3Is the critical temperature for austenitizing the hypoeutectoid steel and is the final temperature for transforming ferrite into austenite. By adopting the normalizing rolling, the normalizing process can be saved, the delivery cycle can be shortened, and the production cost can be reduced.

The processes or parameters which are not described in detail in the process of the invention are conventional techniques for wind power steel in the field.

Example 1:

the wind power steel comprises the following components in percentage by weight: c: 0.146%, Si: 0.28%, Mn: 1.32%, P: 0.017%, S: 0.004%, Nb: 0.012%, Ti: 0.019%, Als: 0.032%, and the balance of iron and inevitable impurities.

The manufacturing method of the wind power steel containing the components comprises the following steps:

1) and (3) preprocessing, strictly executing the technological process of molten iron desulphurization, controlling the sulfur content of the molten iron to be 0.008 percent and the temperature to be 1250 ℃, and completely skimming the slag on the surface of the molten iron after the desulphurization is finished.

2) Smelting, wherein the pretreated molten iron enters a converter for smelting, the slag forming materials are added 3min before the end point, the alkalinity of the final slag is controlled to be 3.0, and the end point gun pressing time is 65 s. The aluminum manganese iron is adopted for deoxidation, and the adding amount of the aluminum manganese iron is 2.5 kg/t. When the molten steel is discharged to one fourth, adding the silicomanganese, the ferrosilicon and the ferroniobium in batches, and finishing the addition when the molten steel is discharged to three fourths.

3) Refining, wherein molten steel smelted in the converter enters an LF refining furnace, lime is added according to actual conditions for slagging, yellow and white slag or white slag is kept for 13min, bottom argon blowing stirring is adopted in the whole process, and argon is blown softly for 11 min.

And (3) after LF refining, feeding the molten titanium into an RH refining furnace, controlling the vacuum degree to be 10Pa, the vacuum time to be 18min, the pure degassing time to be 10min, the soft blowing time to be 15min, the RH refining period to be 43min, and controlling the adding amount of the titanium wires to be 0.8 m/t.

4) And continuous casting, wherein the whole-process protective pouring is adopted, peritectic steel protective slag is adopted as the protective slag, a 175-section casting blank is adopted, and the casting speed in the stationary period is set to be 1.20 m/min.

5) Rolling, wherein the rolling temperature is controlled to ensure that rolling is carried out in a specified temperature range, (1) the billet tapping temperature is 1230-; (2) the average temperature of the rough rolling of the billet at the beginning is 1130-1180 ℃, the average temperature of the final rolling is not less than 1050 ℃, and the total compression ratio of the rough rolling is more than 50 percent; (3) the rolling temperature of the finish rolling is 1010-.

The properties of the steel sheet of this example are shown in Table 3, and the property test method was carried out by the International general method.

Example 2:

the wind power steel comprises the following components in percentage by weight: c: 0.146%, Si: 0.28%, Mn: 1.34%, P: 0.015%, S: 0.008%, Nb: 0.011%, Ti: 0.018%, Als: 0.039%, the balance being iron and unavoidable impurities.

The production process of the wind power steel containing the components has the same operation steps as the example 1.

Example 3:

the wind power steel comprises the following components in percentage by weight: c: 0.142%, Si: 0.30%, Mn: 1.34%, P: 0.013%, S: 0.008%, Nb: 0.037%, Ti: 0.018%, Als: 0.032%, and the balance of iron and inevitable impurities.

1) and (3) preprocessing, strictly executing the technological process of molten iron desulphurization, controlling the sulfur content of the molten iron to be 0.005 percent and the temperature to be 1290 ℃, and completely removing slag on the surface of the molten iron after the desulphurization is finished.

2) Smelting, wherein the pretreated molten iron enters a converter for smelting, the addition of a slagging material is finished 3min before the end point, the alkalinity of the final slag is controlled to be 3.5, and the end point gun pressing time is 100 s. The aluminum manganese iron is adopted for deoxidation, and the adding amount of the aluminum manganese iron is 3.0 kg/t. When the molten steel is discharged to one fourth, adding the silicomanganese, the ferrosilicon and the ferroniobium in batches, and finishing the addition when the molten steel is discharged to three fourths.

3) Refining, wherein molten steel smelted in the converter enters an LF refining furnace, lime is added according to actual conditions for slagging, yellow and white slag or white slag is kept for 13min, bottom argon blowing stirring is adopted in the whole process, and argon is blown softly for 15 min. Deoxidizing by using aluminium particle deoxidant. The components are finely adjusted by adopting ferrocolumbium, aluminum wire is fed for increasing aluminum, and titanium wire is fed for increasing titanium.

And (3) after LF refining, feeding the molten aluminum into an RH refining furnace, controlling the vacuum degree to be 20Pa, the vacuum time to be 25min, the pure degassing time to be 15min, the soft blowing time to be 20min, and the RH refining period to be 60min, wherein the adding amount of the aluminum wire is 1.5m/t, and the adding amount of the titanium wire is 2.0 m/t.

4) And continuous casting, wherein the whole-process protective pouring is adopted, peritectic steel protective slag is adopted as the protective slag, a casting blank with a 300-section is adopted, and the casting speed in the stationary period is set to be 0.85 m/min.

5) Rolling, controlling the rolling temperature to ensure that rolling is carried out in a specified temperature range, (1) the tapping temperature of the billet is 1170-1220 ℃; (2) the average temperature for rough rolling of the billet is 1160-1190 ℃, the average temperature for final rolling is 1100-1130 ℃, and the total compression ratio of rough rolling is more than 50 percent; (3) the initial rolling temperature of finish rolling is 860 ℃ to 900 ℃, and the final rolling temperature is 830 ℃ to 860 ℃.

The properties of the steel sheet of this example are shown in Table 3, and the property test method was carried out by the International general method. In Table 3, d is the radius of the bend and a is the thickness of the sample.

Table 3: steel sheet Properties in examples 1 to 3

In example 4 and comparative examples 1 to 3, the steps of the production process flow are the same as those of example 1 except that the components of the wind power steel are different from those of example 1, and the components of the wind power steel in example 4 and comparative examples 1 to 3 are specifically shown in table 4. The properties of the steel sheets of example 4 and comparative examples 1 to 3 are shown in Table 5, and the properties were measured by the International general method. In Table 5, d is the radius of the bend and a is the thickness of the sample.

Table 4: composition of wind power steel in example 4 and comparative examples 1 to 3

Numbering	C	Si	Mn	P	S	Nb	Ti	Als
									Example 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: steel sheet Properties in example 4 and comparative examples 1 to 3

In comparative examples 4 to 7, the composition and other steps of the production process of the wind power steel are the same as those in example 3 except that the rolling temperature in step 5) is different from that in example 3, and the rolling temperature in step 5) in comparative examples 4 to 7 is specifically shown in table 6. Comparative example 7 properties of the steel sheet before unnormalized heat treatment using the method of controlling rolling + normalizing process described in the background section. The properties of the steel sheets of comparative examples 4 to 7 are shown in Table 7, and the property test method was carried out by the International general method. In Table 7, d is the radius of the center of curvature and a is the thickness of the sample.

Table 6: steel sheet Properties in example 4 and comparative examples 1 to 3

Table 7: steel sheet Properties in comparative examples 4 to 6

As is apparent from tables 6 and 7, since the temperature of the rolling in step 5) is different from that of example 3, the properties of the steel sheets obtained in comparative examples 4 to 6 are far inferior to those of the steel sheets obtained in example 3. Comparative example 7 the performance of the steel sheet before the normalizing heat treatment was not good by the method of controlling the rolling + normalizing process described in the background section, and thus the rolling process of the present invention has the normalizing heat treatment effect. In comparative examples 4 to 7, (1) the tapping temperature of the billet; (2) the average temperature of the rough rolling and the initial rolling of the billet is more than or equal to 1050 ℃; (3) the initial rolling temperature of finish rolling and the final rolling temperature are equal temperature values which are lower than the rolling temperature in the step 5) of the method, and the temperature is low, so that the heating is not uniform, the deformation is insufficient during steel rolling, the deformation of an intermediate structure is not uniform, and the majority of performances have the defect.

According to the normalizing rolling low-temperature impact toughness wind power steel, the structure transformation and the phase proportion are accurately controlled by adjusting the steel components and the manufacturing process, and finally the normalizing rolling low-temperature impact toughness wind power steel with special mechanical properties is obtained. Accordingly, exemplary embodiments of the present invention can provide a normalized-rolled low-temperature impact toughness wind power steel without using expensive Ni, Cr, V, and thus can significantly reduce production costs.

According to the exemplary embodiments of the present invention, it is possible to provide the normalized-rolled low-temperature impact toughness-resistant wind power steel having a thickness of 6mm to 63mm, and thus it is possible to simplify the production process of the low-temperature impact toughness wind power steel, and to provide the normalized-rolled low-temperature impact toughness wind power steel plate having a greater thickness. The invention relates to economic wind power steel which is suitable for wind power towers with normalizing rolling and low-temperature impact toughness requirements, and the minimum value of the impact toughness is more than or equal to 100J when the low temperature reaches-20 ℃.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The preparation method of the low-temperature impact toughness-resistant wind power steel is characterized by comprising the following steps of:

pretreating, namely desulfurizing molten iron;

smelting, namely smelting the pretreated molten iron;

refining, namely LF refining and RH refining;

continuous casting, which adopts full-process protection casting;

and rolling, namely performing two-stage rolling, namely rough rolling and finish rolling.

2. The method for preparing the low temperature impact toughness wind power steel according to claim 1,

in the pretreatment step, the sulfur content in the molten iron is controlled to be below 0.010 percent by mass;

preferably, the desulfurization temperature is 1250 ℃ to 1320 ℃.

3. The method for preparing the low temperature impact toughness wind power steel according to claim 1,

in the smelting step, the pretreated molten iron enters a converter for smelting, the slag-forming materials are added within 1-5 min before the molten iron enters the end point of the converter, and the alkalinity of the final slag is controlled to be 3.0-4.0;

preferably, the terminal gun pressure time is 65s-120 s;

preferably, aluminum manganese iron is adopted for deoxidation, the adding amount of the aluminum manganese iron is 2.0kg/t-3.5kg/t, when the molten steel is discharged to one fourth, silicon manganese, ferrosilicon and ferrocolumbium are added in batches, and when the molten steel is discharged to three fourths, the adding is finished;

preferably, the silicon and manganese are ferroalloy containing 13 to 25 weight percent of silicon and 55 to 75 weight percent of manganese, and the addition amount of the silicon and manganese is 20 to 30 kg/t;

the ferrosilicon is ferroalloy containing 70-78 wt% of silicon, and the adding amount of the ferrosilicon is 0.5-2 kg/t;

the ferrocolumbium is an iron alloy containing 50-65 wt% of niobium, and the addition amount of the ferrocolumbium is 0.1kg/t-0.8 kg/t.

4. The method for preparing the low temperature impact toughness wind power steel according to claim 1,

in the refining step, the LF refining is carried out by bottom argon blowing and stirring in the whole process, argon is blown softly for 10-15 min, lime is added for slagging, and an aluminum particle deoxidizer is used for deoxidizing;

preferably, the retention time of the yellow and white slag or the white slag is 10min to 30min, and the alkalinity of the final slag is controlled to be 3.0 to 4.0.

5. The method for preparing the low temperature impact toughness wind power steel according to claim 1,

in the refining step, the vacuum degree in the RH refining process is controlled to be 10Pa-30Pa, and the vacuum time is 15min-25 min;

preferably, the pure degassing time is not less than 5min, and the soft blowing time is not less than 12 min;

preferably, the period of RH refining is controlled to be 40min-60min, the adding amount of the aluminum wire is 0m/t-3.3m/t, and the adding amount of the titanium wire is 0.8m/t-3.3 m/t.

6. The method for preparing the low temperature impact toughness wind power steel according to claim 1,

in the continuous casting step, the whole-process protective casting means that a long water gap is adopted from a large ladle to a middle ladle and argon sealing protection is carried out; the tundish is covered by a covering agent combined with the carbonized rice hulls; the tundish to the crystallizer adopts an immersion type water gap and adopts argon seal protection; the liquid level of the crystallizer adopts peritectic steel covering slag;

preferably, the peritectic steel casting powder comprises SiO with the weight percentage of more than or equal to 25 percent₂≤35％、35％≤CaO≤45％、1.90％≤MgO≤3.00％、3.00％≤Al₂O₃≤4.00％。

7. The method for preparing the low temperature impact toughness wind power steel according to claim 1,

in the continuous casting step, the drawing speed is stabilized to 0.80m/min-1.40 m/min;

preferably, section 175: the pulling speed is stabilized to 1.2-1.35m/min,

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

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

section 300: the pulling speed is stabilized to 0.8-0.9 m/min.

8. The method for preparing the low temperature impact toughness wind power steel according to claim 1,

in the continuous casting step, the casting superheat degree is controlled below 20 ℃;

preferably, the height of the liquid level of the tundish is controlled, the height of the liquid level of the tundish is not less than 600mm during casting, and the height of the liquid level is between 800mm and 1000mm during normal casting;

preferably, the straightening temperature of the casting blank is controlled to be above 900 ℃.

9. The method for preparing the low temperature impact toughness wind power steel according to claim 1,

in the rolling step, the tapping temperature of the billet is controlled to be 1170-1280 ℃;

the initial rolling temperature of rough rolling is 1130-1190 ℃, and the final rolling temperature of rough rolling is 1050-1120 ℃;

the rough rolling total compression ratio is more than 50%;

the initial rolling temperature of the finish rolling is 850-1070 ℃, and the final rolling temperature of the finish rolling is 830-960 ℃.

10. The preparation method of the low temperature impact toughness wind power steel according to claim 1, wherein the wind power steel comprises the following components in percentage by weight: c is more than or equal to 0.13 percent and less than or equal to 0.17 percent, Si is more than or equal to 0.50 percent and less than or equal to 0.50 percent, Mn is more than or equal to 0.65 percent and less than or equal to 0.010 percent, P is more than or equal to 0.030 percent and less than or equal to 0.030 percent, Nb is more than or equal to 0.010 percent and less than or equal to 0.040 percent, Ti is more than or equal to 0.030 percent and less than or equal to 0.015 percent and less than or equal to 0.050 percent, and the balance.