CN102212752A - Low-temperature angle steel and manufacturing method thereof - Google Patents

Abstract

The invention relates to a hot-rolled angle steel for low temperature and a manufacturing method thereof, belonging to the field of low temperature steel. The angle steel has excellent low-temperature toughness above -40° C., and the yield strength reaches 350 MPa, and is suitable as a material for transmission iron towers under low-temperature conditions in alpine regions. The proportion by weight of the chemical composition of the angle steel is C: 0.05-0.18%, Mn: 0.5-1.7%, Si: 0.01-0.55%, Ga: 0.005-0.01%, V: 0.01-0.08%, Nb: 0.02-0.02%. 0.08%, Ca: 0.001-0.005%, Ti: 0.005-0.05%, Als: 0.01-0.06%, Cu: 0.15%-0.25%, B: 0.0005-0.002%, P: 0-0.01%, S: 0- 0.005%, the rest is Fe and unavoidable impurities. The invention has the advantages of simple process, pure steel quality, stable structure, yield strength greater than 350MPa, and excellent low-temperature toughness above -40°C, adopts the alloying principle of multiple elements and a small amount, and has low-cost high-low temperature performance.

Description

A kind of angle steel for low temperature and its manufacturing method

technical field

The invention belongs to the field of low-temperature steel, and in particular relates to a hot-rolled angle steel for low-temperature use and a manufacturing method thereof.

Background technique

The problem of low-temperature fracture of materials arose in the 1930s and 1940s with the application of large-scale steel structures. In the 1930s, the Belgian Hasselt Bridge broke and crashed only 14 months after it was built. The temperature at that time was -20°C. The bridge across the highway near Berlin was partially damaged on January 2, 1938 when the temperature dropped sharply to -10°C, and cracks as long as 3m appeared on the bridge. In the 1950s, a bridge in Quebec, Canada, broke and crashed 27 months after it was opened to traffic, when the temperature was -35°C. On December 27, 1965, the derrick of the "Haibao" marine drilling rig in the North Sea gas field collapsed and sank, and the hourly temperature was 3°C. On January 4, 1984, an engineering crane arm brittle fracture accident occurred in Xinjiang, my country, resulting in the death of one person. The working environment temperature at that time was -15°C. Studies have shown that the stress of the material is lower than the yield limit and the required stress of the design. The steel is still brittle and fails.

Our country has a vast territory. In many areas in the north, the temperature in winter is below -20°C, and the extreme temperature is below -40°C. Especially in the northeast region, it belongs to the cold temperate and frigid climate areas, with low temperature, large temperature difference, large snowfall, and air density. Large and other characteristics, and last for a long time, the low temperature generally occurs for more than 3 to 6 months, and the annual average temperature in the Greater and Lesser Khingan Mountains is below 0 °C. The temperature of the coldest month in Northeast China is roughly between -10°C and -30°C, and the multi-year average of the extreme minimum temperature in the Xing'an Mountains is mostly around -40°C, and the extreme value can reach around -45°C. In recent years, the atmosphere and natural environment have undergone drastic changes, and the frequency of extreme weather phenomena has increased. Table 1 shows the calculated low temperature T _j in some areas of China (taken from the heating code, which is the average value of low temperature for 5 consecutive days in 50 years) and historical The lowest temperature T _z that occurs.

Table 1 The calculated low temperature T _j and the lowest temperature T _z in history in some regions of China (℃)

Low-temperature steel should mainly have the following properties: ①The ductile-brittle transition temperature is lower than the service temperature; ②The strength meets the design requirements; ③The structure is stable at the service temperature; The patented technology is as follows:

The authorized publication number is CN101545077A, and the invention title is "a low-temperature steel and its manufacturing method", which discloses a low-temperature steel plate and its manufacturing method, mainly for the development of low-temperature steel plates. It has excellent low-temperature toughness at ℃, and is mainly used for low-temperature steel plates for oil and gas pipelines, low-temperature gas storage tanks for LPG and LNG. The content of noble metal Ni element in the technical scheme is 0.05-0.35%.

The application number is 201010157592.X, and the invention title is "High-strength Low-Temperature Toughness Steel". It discloses a fishplate steel technical solution, which is suitable for construction machinery and railway fittings steel used under low-temperature conditions in alpine regions. , such as joint splints for railway rails, etc., are medium-carbon low-silicon steels, which have an impact energy of 28.6-36J at -40°C and a yield strength of 680-780MPa. The chemical composition of low-temperature steel contains precious metal Ni and Mo elements, which improves the Low temperature steel production costs.

The application number is 200910019494.7, and the invention title is "a kind of -40 ℃ to -60 ℃ low temperature impact toughness hot-rolled H-shaped steel and its preparation method". For the hot-rolled H-shaped steel used under the conditions, the impact energy of the V-shaped sample exceeds 27J at -40°C to -60°C. The content of noble metal Ni element in the chemical composition of H-beam is 0.30-0.90%.

The above-mentioned steel grades all contain noble metal Ni.

In recent years, the brittle fracture of my country's transmission towers at low temperatures has aroused widespread concern from domestic experts. According to my country's power grid planning, multiple transmission lines will be built in Northeast China, North China, and Northwest China. The temperature in these areas is low in winter, and the lowest temperature will reach below -40°C. The transmission towers have large material specifications, heavy loads, and harsh construction conditions. There is a lack of experimental research on the performance difference of existing angle steels at different low temperatures, and there is no relevant experimental data to support the performance of steel used in power grids in alpine regions. The toughness and plasticity of the existing steel types are greatly reduced under the low temperature condition of -40°C. It is not clear whether the existing technical standards can meet the requirements for stable operation of the power grid under severe low temperature conditions.

Transmission line towers are mainly made of Q235 and Q345 hot-rolled angle steel profiles. According to the deployment of the State Grid Corporation of China, Q420B angle steel has been widely used in transmission towers in recent years, and Q460C angle steel has also been used in some pilot projects. In many areas in the north, the winter temperature is below -20°C, and the extreme temperature is below -40°C. The temperature T is used to select its quality grade: -20℃≤T<0℃, select C and D grade steel; when T<-20℃, select D and E grade steel. According to the above regulations, it is necessary to choose D-grade or even E-grade steel to meet the operation requirements of transmission towers.

Due to the limitation of my country's steel production equipment and technical level, the existing profile manufacturers have no actual production experience in producing D-grade or E-grade angle steel, and the market cannot supply a large number of cheap low-temperature angle steel. There are a large number of A-grade and B-grade steels, but with the drastic changes in the atmosphere and natural environment in recent years, the frequency of extreme weather has increased, and low-stress brittle fracture accidents of tower materials have occurred many times. A typical accident occurred on March 12, 2010, when the main material of the iron tower of Changchun Power Supply Company's 66kV Agricultural Development Line A and B broke.

People's daily life and the country's economic development are inseparable from or even heavily dependent on the use of steel. The brittle failure of steel will lead to serious consequences such as water and power outages, traffic jams, collapse of houses and towers, and heavy losses in manpower and material resources. The collapse of the transmission tower, known as the lifeline project, will directly lead to the paralysis of the power supply system, causing fires, and affecting the production and construction of the country and people's lives. Therefore, it is of great significance to develop steel materials specially used for transmission towers in alpine regions. As we all know, there are currently two ways to improve the low-temperature toughness of steel. One is to improve the low-temperature toughness by changing the hot rolling process and heat treatment process to achieve fine grain strengthening; the other is to add a certain amount of alloy components such as Ni and Mo to achieve The purpose of high low temperature toughness. Generally, these two methods are often used in actual production to improve the low temperature toughness of steel, but due to the high cost of Ni and Mo, economical production is difficult to achieve. Therefore, it is of great economic and social benefit to seek a hot-rolled angle steel for transmission towers that can meet the requirements of low-temperature impact toughness at -40°C and has low production costs. .

Contents of the invention

The object of the present invention is to provide a Q350MPa hot-rolled angle steel with excellent low-temperature toughness for power transmission towers and a manufacturing method thereof. The invention mainly adopts the alloying principle of multiple elements and a small amount, combined with multi-pass hot rolling and heat treatment processes, to develop Q350MPa hot-rolled angle steel. The angle steel has excellent low-temperature toughness above -40°C, and is suitable for use under low-temperature conditions in my country's alpine regions. transmission tower.

For realizing above-mentioned purpose of the invention, the technical scheme that the present invention takes is as follows:

An angle steel for low temperature, which is improved in that the weight percent distribution ratio of the chemical components of the angle steel is: C: 0.05-0.18%, Mn: 0.5-1.70%, Si: 0.01-0.55%, Ga: 0.005-0.01% , V: 0.01-0.08%, Nb: 0.02-0.08%, Ca: 0.001-0.005%, Ti: 0.005-0.05%, Als: 0.01-0.06%, Cu: 0.15%-0.25%, B: 0.0005-0.002% , P: 0-0.01%, S: 0-0.005%, and the rest are Fe and unavoidable impurities.

Another preferred technical solution of the present invention is: the weight percent distribution ratio of the chemical components of the angle steel is: C: 0.05-0.18%, Mn: 0.65-1.70%, Si: 0.01-0.55%, Ga: 0.005-0.01%, V: 0.01-0.08%, Nb: 0.02-0.08%, Ca: 0.001-0.005%, Ti: 0.005-0.05%, Als: 0.01-0.06%, Cu: 0.15%-0.25%, B: 0.0005-0.002%, P: 0 to 0.01%, S: 0 to 0.005%, and the rest are Fe and unavoidable impurities.

Another preferred technical solution of the present invention is: at least one of V and Nb is added to the angle steel, and the total content of V and Nb does not exceed 0.12%.

Another preferred technical solution of the present invention is: the manufacturing method includes the following steps:

1) According to the weight percent distribution of chemical components, C: 0.05-0.18%, Mn: 0.5-1.70%, Si: 0.01-0.55%, Ga: 0.005-0.01%, V: 0.01-0.08%, Nb: 0.02- 0.08%, Ca: 0.001-0.005%, Ti: 0.005-0.05%, Als: 0.01-0.06%, Cu: 0.15%-0.25%, B: 0.0005-0.002%, P: 0-0.01%, S: 0- 0.005%, the rest is Fe and unavoidable impurities, of which the total content of V and Nb does not exceed 0.12%;

2) Initial refining: control the tapping temperature at 1630-1660°C;

3) Carry out converter refining, and control the refining time at 15-30 minutes;

4) casting after vacuum deoxidation to obtain a billet;

5) Heating the steel billet described in step 4 to 1190-1290°C for multi-pass hot rolling to obtain angle steel, the final rolling temperature is between 860-940°C, and air-cooled;

Another preferred technical solution of the present invention is: at the beginning of rolling, as the temperature of the billet decreases, the billet is continuously rolled in the austenite zone and ferrite recrystallization temperature zone, with 10 hot rolling passes.

Another preferred technical solution of the present invention is: the angle steel is an equilateral or unequal side hot-rolled angle steel.

Another preferred technical solution of the present invention is: the ferrite grain size of the angle steel after normalizing is not lower than grade 8.

The role and mechanism of each alloying element are as follows:

C: It exists as interstitial atoms in steel, and can also be combined with strong carbon compound elements of steel such as Ti, Nb, V, W, etc. to form fine and dispersed carbides, which can inhibit grain growth and precipitation strengthening It is one of the most effective strengthening elements. However, with the increase of C content, although the hardness of the steel increases, the elongation and impact toughness decrease greatly, and the low temperature toughness decreases even more. Considering the strength and low temperature toughness of the steel, the C content used in the present invention will be in the range of 0.05-0.18%.

Mn: It is a very important beneficial alloying element, which is mainly dissolved in ferrite and has the effect of solid solution strengthening, which can improve the strength and hardness of steel. It is also a good deoxidizer and desulfurizer, containing a certain amount of manganese can eliminate or weaken the brittleness of steel caused by sulfur, thereby improving the toughness of steel at low temperature. Mn is an FCC stabilizing element, which can expand the austenite region, reduce the temperature of A ₁ and A ₃ , and increase the temperature of A ₄ . As the temperature at point _A3 drops, the pro-eutectoid ferrite precipitates at a lower temperature, thereby inhibiting the growth of grains and refining the structure. And at the same time, it also inhibits the precipitation of carbides at the grain boundaries of supercooled austenite, which plays a role in reducing DBTT. Therefore, Mn is the main alloying element in low temperature steel; but when its content is high, due to the superheat sensitivity of steel Increase, in the case of slight overheating, the crystal grains will coarsen and temper brittleness will occur, so the Mn content used in the present invention is in the range of 0.50% to 1.70%.

in:

Ac ₁ : the temperature at which pearlite transforms to austenite when heated;

Ar ₁ : the temperature at which austenite transforms to pearlite during cooling;

Ac ₃ : the final temperature at which proeutectoid ferrite transforms into austenite when heated;

Ar ₃ : the starting temperature of austenite to ferrite transformation during cooling;

Ac ₄ : the final temperature at which the secondary cementite is completely dissolved into austenite during heating;

Ar ₄ : The temperature at which secondary cementite begins to precipitate from austenite during cooling.

Si: It is often added in steel for deoxidation, does not form carbide but dissolves in ferrite, has a strong solid solution effect, and is a strong BCC stabilizing element, so it will increase DBTT and reduce steel Toughness, so the present invention strictly regulates the content of Si element within 0.01-0.55%.

Ga: Gallium is generally added in the form of cheap coarse gallium or iron-gallium compounds. Studies have shown that a small amount of gallium can greatly improve the hardenability of steel; The range of Ga element used in is 0.005-0.01%.

V and Nb: Both are strong carbon compound forming elements. The second phase particles such as VC and NbC formed in the steel can hinder the austenite grain growth of the steel when it is heated, and can inhibit the recrystallization and After recrystallization, the grain grows, which plays the role of refining the grain, thereby improving the strength and low-temperature toughness of the steel; but when Nb and V are excessive, it is easy to generate intergranular cracks and reduce the weldability of the steel, so the two The sum of their content should not exceed 1.2%.

Ca: As a purifying agent for deoxidation and desulfurization, it can purify molten steel, improve the purity of steel, improve the shape of non-metallic inclusions, make MnS in steel spheroidize, and exert the potential of the material. When its content is too high, it is easy to Coarse non-metallic inclusions are formed. The solid Ca content is controlled within the range of 0.001-0.005%.

Ti: is a strong carbide and nitride forming element, easy to form fine particles such as TiC and TiN, TiC and TiN are very stable, can effectively pin the grain boundary, refine the grain, and have stable reheating the role of the organization. A small amount of Ti element can improve the strength and low temperature toughness of steel; but because Ti is a strong BCC (body-centered cubic crystal) stable element, adding Ti will increase DBTT, and excessive Ti will easily form coarse TiN or TiC , so that the pinning effect is weakened, and the toughness of the steel will be damaged. Therefore, the present invention stipulates that the Ti content is 0.005-0.05%.

Al: This element is the main deoxidizing element. A certain amount of Al can form fine and insoluble AlN particles with N in the steel. The dispersed distribution plays a role in refining the grains and improving the strength and toughness of the steel. However, if the amount of aluminum is too high, it is easy to Lead to too many inclusions, which is not good for the low temperature toughness of steel. Therefore, the content range of Al in the present invention is 0.01-0.06%.

Cu: It is a stable element of FCC (face-centered cubic crystal), which plays a role of precipitation strengthening through the precipitation of the second phase during tempering. A small amount of Cu element can reduce DBTT and improve the low-temperature toughness and fatigue crack growth resistance of steel; When the Cu content is high, the toughness of the steel will decrease and the DBTT will directly increase due to the large and uncontrollable second phase amount of precipitation, and excessive Cu will also cause the slab to become brittle during casting and hot rolling, so the present invention The content control range of Cu is 0.15%-0.25%.

B: Adding a very small amount of boron can significantly improve the performance of steel. A small amount of boron can inhibit the segregation and intergranular fracture of harmful elements of phosphorus and sulfur. intergranular fracture, thereby significantly improving the low temperature toughness of steel. Boron can improve the shape and distribution of inclusions. After boron treatment, due to the high surface activity of boron, it can be adsorbed on the surface of sulfides and oxides, preventing further growth of inclusions, making inclusions small, round, Evenly distributed in the grain boundary, strengthen the grain boundary, reduce local stress concentration, inhibit crack initiation and reduce crack growth rate, so as to improve the toughness of the material. When boron is added to niobium steel, boron and niobium can form a compound to refine the grain; and a small amount of boron can greatly improve the hardenability of the steel, and obtain a uniform structure with good comprehensive mechanical properties (lower bainite or tempered sorbite) to improve the toughness of steel; but the boron element must be maintained in a trace range, as the content of boron element increases, coarse inclusions will be formed, which will have an adverse effect on the performance of the steel .

P: It is a harmful element in steel. Due to its serious segregation tendency, it forms a banded structure, which makes the mechanical properties of steel uneven. It is generally believed that phosphorus is the main cause of brittle fracture of steel materials at low temperatures. Therefore, the less the content, the better, and the present invention controls the phosphorus content to below 0.01%.

S: It is a harmful element in most steel types, and has a serious segregation tendency, which can easily cause low-temperature intergranular fracture and high-temperature embrittlement of the steel, and can lead to the disadvantages of low anisotropy and toughness of the steel. Therefore, its content should be strictly controlled, and the present invention controls the sulfur content below 0.005%.

Owing to adopting above-mentioned technical scheme, compared with prior art, the beneficial effect that the present invention obtains comprises:

1) Excellent low temperature toughness at -40°C

According to the requirements of my country on the low-temperature impact toughness of steel products, the impact energy Akv at the corresponding temperature is greater than 27J to meet the low-temperature impact performance index. The impact energy of the hot-rolled angle steel in the present invention is 60-88J at -40°C. It can be seen that this The invented hot-rolled angle steel meets the index of impact toughness at -40°C;

2) Yield strength greater than 350MPa

The low-temperature tensile performance test was carried out using the GB/T13239-2006 low-temperature tensile test method. The results showed that the yield strength of the hot-rolled angle steel was greater than 350MPa, and it had excellent low-temperature toughness and good mechanical properties;

3) Low cost

The low-temperature angle steel uses manganese and gallium instead of nickel, and adopts the principle of alloying with a small amount of multiple elements; at the same time, the content of B element in the steel is changed by adding cheap iron boron during the smelting process; while improving the low-temperature performance of the angle steel, it is greatly reduced. It reduces the cost and is suitable as a transmission tower material under low temperature conditions in alpine regions;

4) The process is simple, the steel is pure, and the structure is stable

The characteristics of the process of its invention are as follows: the primary refining is carried out first, the billet is controlled at a higher temperature and then refined in a converter, the content of S and P is reduced, the gas content in the steel is controlled, and vacuum denitrification and deoxidation are carried out. After vacuum deoxidation, the billet is subjected to 10 passes Secondary hot rolling, continuous hot rolling in the austenite zone and recrystallization temperature zone. The steel billet is soft in the austenite zone and has excellent plasticity. After 4 passes of hot rolling, the steel billet has the shape of an angle steel, and the austenite grains are broken, and after nucleation, they become many fine subgrains. The temperature of the steel billet is lowered, and it is continuously hot-rolled into equilateral or unequal angle steel in the ferrite recrystallization temperature zone. A large amount of deformation causes the deformation of the grain to produce deformation strengthening, and the grain is too late to grow through air cooling, and finally ferrite is obtained. Hot-rolled angle steel with bulk grain size higher than 8. The manufacturing method of the hot-rolled angle steel of the present invention has simple process, and the obtained angle steel has stable structure and stable mechanical properties, and is suitable for large-scale industrial production.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings.

Figure 1 is a standard Charpy V-notch impact specimen;

Figure 2 is a low temperature tensile sample;

Marking unit in the figure: mm.

Detailed ways

Below in conjunction with example the present invention is described in detail.

All implementation modes are all to adopt conventional smelting and rolling equipment, carry out according to the steps described above:

Example 1:

Q350MPa hot-rolled angle steel for transmission towers with excellent low-temperature toughness, the weight percentage of its chemical composition is: C: 0.145%, Mn: 0.65%, Si: 0.21%, Ga: 0.005%, V: 0.025%, Ca: 0.001 %; Ti: 0.005%, Als: 0.02%, Cu: 0.16%, B: 0.0005, P: 0-0.01%, S: 0-0.005%, and the rest are Fe and unavoidable trace impurities.

A method for producing Q350MPa hot-rolled angle steel for low-temperature ductile power transmission towers, the steps of which are:

(1) Primary refining: control the tapping temperature at 1630-1640°C;

(2) Carry out converter refining, control refining time at 15min;

(3) vacuum deoxidation and casting;

(4) Heating the billet to 1195-1130°C for 10 passes of hot rolling, the final rolling temperature is between 860-940°C, and air-cooled.

Example 2:

Q350MPa hot-rolled angle steel for transmission towers with excellent low-temperature toughness, the weight percentage distribution of its chemical composition is: C: 0.16%, Mn: 1.06%, Si: 0.37%, Ga: 0.006%, Nb: 0.045%, Ca: 0.002 %; Ti: 0.01%, Als: 0.032%, Cu: 0.18%, B: 0.0007%, P: 0-0.01%, S: 0-0.005%, and the rest are Fe and unavoidable trace impurities.

A method for producing Q350MPa hot-rolled angle steel for low-temperature ductile power transmission towers, the steps of which are:

(1) Initial refining: control the tapping temperature at 1635-1645°C;

(2) Carry out converter refining, control refining time at 18min;

(3) vacuum deoxidation and casting;

(4) Heating the billet to 1220-1245°C for 10 passes of hot rolling, the final rolling temperature is between 860-940°C, and air cooling.

Example 3:

Q350MPa hot-rolled angle steel for transmission towers with excellent low-temperature toughness, the weight percentage distribution of its chemical composition is: C: 0.16%, Mn: 1.32%, Si: 0.44%, Ga: 0.008%, V: 0.065%, Ca: 0.003%; Ti: 0.025%, Als: 0.045%, Cu: 0.19%, B: 0.001%, P: 0-0.01%, S: 0-0.005%, and the rest is Fe and unavoidable trace impurities.

A method for producing Q350MPa hot-rolled angle steel for low-temperature ductile power transmission towers, the steps of which are:

(1) Primary refining: control the tapping temperature at 1640-1645°C;

(2) Carry out converter refining, control refining time at 20min;

(3) vacuum deoxidation and casting;

(4) Heating the billet to 1230-1250°C for 10 passes of hot rolling, the final rolling temperature is between 860-940°C, and air cooling.

Example 4:

Q350MPa hot-rolled angle steel for transmission towers with excellent low-temperature toughness, the weight percentage of its chemical composition is: C: 0.17%, Mn: 1.58%, Si: 0.55%, Ga: 0.01%, Nb: 0.08%, Ca: 0.004 %; Ti: 0.033%, Als: 0.43%, Cu: 0.18%, B: 0.0012%, P: 0-0.01%, S: 0-0.005%, and the rest are Fe and unavoidable trace impurities.

A method for producing Q350MPa hot-rolled angle steel for low-temperature ductile power transmission towers, the steps of which are:

(1) Initial refining: control the tapping temperature at 1640-1650°C;

(2) Carry out converter refining, control refining time at 15min;

(3) vacuum deoxidation and casting;

(4) Heating the billet to 1245-1265°C for 10 passes of hot rolling, the final rolling temperature is between 860-940°C, and air-cooled.

Example 5:

Q350MPa hot-rolled angle steel for transmission towers with excellent low-temperature toughness, the weight percentage of its chemical composition is: C: 0.175%, Mn: 1.70%, Si: 0.55%, Ga: 0.01%, V: 0.045%, Nb: 0.043 %, Ca: 0.005%; Ti: 0.042%, Als: 0.51%, Cu: 0.2%, B: 0.0015%, P: 0~0.01%, S: 0~0.005%, the rest is Fe and unavoidable trace impurities .

A method for producing Q350MPa hot-rolled angle steel for low-temperature ductile power transmission towers, the steps of which are:

(1) Primary refining: control the tapping temperature at 1640-1655°C;

(2) carry out converter refining, control refining time at 28min;

(3) vacuum deoxidation and casting;

(4) Heating the billet to 1255-1285°C for 10 passes of hot rolling, the final rolling temperature is between 860-940°C, and air-cooled.

Tensile and impact samples are taken along the longitudinal direction of the hot-rolled angle steel, and GB/T3808 is strictly implemented using a pendulum impact testing machine, and the impact test is carried out using the V-shaped notch in the GB/T229-1994 metal Charpy notch impact test method. The low-temperature tensile performance test was carried out using the GB/T13239-2006 low-temperature tensile test method. The sample dimensions are shown in Figures 1 and 2. Table 1 lists the mechanical properties of each example at a temperature of -40°C.

Table 1 Test results of steel performance inspection

example R _el (MPa) R _m (MPa) A(%) Akv(-40℃)(J)longitudinal Grain size (level) Example 1 355 515 32 60 8 Example 2 367 522 29 75 8 Example 3 382 557 31 85 9 Example 4 386 566 27 88 9.5 Example 5 353 517 30 80 8

According to my country's requirements for low-temperature impact toughness of steel, the impact energy AKV greater than 27J at the corresponding temperature meets the low-temperature impact performance index. It can be seen from Table 1 that the hot-rolled angle steel of the present invention meets the impact toughness index at -40°C.

The invention has the advantages of simple process, pure steel, stable structure, yield strength greater than 350MPa, and excellent low-temperature toughness above -40°C, and uses manganese and gallium instead of nickel, and adopts the principle of alloying with a small amount of multiple elements to improve the low temperature of angle steel. The performance is greatly reduced at the same time, and it is suitable as a transmission tower material under low temperature conditions in alpine regions.

The invention has been described herein in terms of specific exemplary embodiments. Appropriate substitutions or modifications will be apparent to those skilled in the art without departing from the scope of the present invention. The exemplary embodiments are illustrative only, and not limiting of the scope of the invention, which is defined by the appended claims.

Claims (7)

1. An angle steel for low temperature, characterized in that the weight percent distribution ratio of the chemical composition of the angle steel is: C: 0.05-0.18%, Mn: 0.5-1.70%, Si: 0.01-0.55%, Ga: 0.005-0.01% , V: 0.01-0.08%, Nb: 0.02-0.08%, Ca: 0.001-0.005%, Ti: 0.005-0.05%, Als: 0.01-0.06%, Cu: 0.15%-0.25%, B: 0.0005-0.002% , P: 0-0.01%, S: 0-0.005%, and the rest are Fe and unavoidable impurities. 2. The steel for low temperature according to claim 1, characterized in that the weight percent distribution ratio of the chemical components of the angle steel is: C: 0.05-0.18%, Mn: 0.65-1.70%, Si: 0.01-0.55%, Ga B : 0.0005-0.002%, P: 0-0.01%, S: 0-0.005%, and the rest are Fe and unavoidable impurities. 3. The steel for low temperature according to claim 1, characterized in that at least one of V and Nb is added to the angle steel, and the total content of V and Nb does not exceed 0.12%. 4. A method for manufacturing low temperature angle steel as claimed in claim 1, characterized in that said method for manufacturing comprises the following steps: 1) According to the weight percent distribution of chemical components, C: 0.05-0.18%, Mn: 0.5-1.70%, Si: 0.01-0.55%, Ga: 0.005-0.01%, V: 0.01-0.08%, Nb: 0.02- 0.08%, Ca: 0.001-0.005%, Ti: 0.005-0.05%, Als: 0.01-0.06%, Cu: 0.15%-0.25%, B: 0.0005-0.002%, P: 0-0.01%, S: 0- 0.005%, the rest is Fe and unavoidable impurities, of which the total content of V and Nb does not exceed 0.12%; 2) Primary refining: control the tapping temperature at 1630-1660°C; 3) Carry out converter refining, and control the refining time at 15-30 minutes; 4) casting after vacuum deoxidation to obtain a billet; 5) Heating the steel slab described in step 4 to 1190-1290° C. and performing multi-pass hot rolling to obtain angle steel, the final rolling temperature is between 860-940° C., and air-cooled. 5. the manufacture method of a kind of low-temperature angle steel as claimed in claim 4, it is characterized in that rolling starts, along with the reduction of steel billet temperature, continuous rolling in the austenite zone and ferrite recrystallization temperature zone of steel billet , hot rolling pass is 10 times. 6. A method for manufacturing low-temperature steel angles as claimed in claim 4, characterized in that said angle steels are equilateral or unequal-edge hot-rolled angle steels. 7. The manufacturing method of a low temperature angle steel as claimed in claim 4, characterized in that the ferrite grain size of the angle steel after normalizing is not lower than grade 8. the

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