阅读说明：本技术 一种含稀土的铌微合金化高强耐候角钢及生产工艺 (Rare earth-containing niobium microalloyed high-strength weather-resistant angle steel and production process thereof ) 是由 周成 贾阳光 王厚昕 郭爱民 高玉含 张乐 刘峻松 玄东坡 周游 于 2019-08-20 设计创作，主要内容包括：本发明涉及钢铁生产技术领域,提供了一种含稀土的铌微合金化高强耐候角钢及生产工艺,其化学成分以质量百分数计：C：0.05-0.12％,Si：0.20-0.65％,Mn≤1.10％,Cu：0.20-0.55％,Cr：0.30-1.25％,Ni：0.12-0.65％,Nb：0.015-0.060％,P≤0.020％,S≤0.020％,RE：0.01-0.04％,Ceq≤0.44,I≥6,余为Fe和杂质,生产工艺包括连铸坯生产、角钢轧制、角钢矫直。本发明添加RE以减少或替代Cr以降低成本,以Nb代V来细化组织增加强韧性,并严控S含量,获得强度级别高、低温韧性好、焊接性能和耐腐蚀性能优良的角钢。(The invention relates to the technical field of steel production, and provides a rare earth-containing niobium microalloyed high-strength weather-resistant angle steel and a production process thereof, wherein the niobium microalloyed high-strength weather-resistant angle steel comprises the following chemical components in percentage by mass: c: 0.05 to 0.12%, Si: 0.20-0.65%, Mn is less than or equal to 1.10%, Cu: 0.20-0.55%, Cr: 0.30-1.25%, Ni: 0.12-0.65%, Nb: 0.015-0.060%, P is less than or equal to 0.020%, S is less than or equal to 0.020%, RE: 0.01-0.04%, Ceq is less than or equal to 0.44, I is more than or equal to 6, and the balance is Fe and impurities. According to the invention, RE is added to reduce or replace Cr to reduce the cost, Nb is used for replacing V to refine the structure and increase the toughness, the S content is strictly controlled, and the angle steel with high strength level, good low-temperature toughness, excellent welding performance and excellent corrosion resistance is obtained.)

1. The niobium microalloyed high-strength weather-resistant angle steel containing rare earth is characterized by comprising the following chemical components in percentage by mass: c: 0.05 to 0.12%, Si: 0.20-0.65%, Mn is less than or equal to 1.10%, Cu: 0.20-0.55%, Cr: 0.30-1.25%, Ni: 0.12-0.65%, Nb: 0.015-0.060%, P is less than or equal to 0.020%, S is less than or equal to 0.020%, RE: 0.01-0.04%, and the balance of Fe and inevitable impurities.

2. The rare-earth-containing niobium microalloyed high-strength weather-resistant angle steel as claimed in claim 1, wherein the yield strength Rel of the angle steel is not less than 460MPa, the tensile strength Rm is not less than 570MPa, the elongation A is not less than 20%, and the impact absorption energy Akv (-20 ℃) is not less than 34J, Akv (-40 ℃) not less than 27J.

3. A process for producing a rare earth-containing niobium microalloyed high strength weathering angle steel as claimed in claim 1 or 2, characterized by comprising, in order: producing a continuous casting blank, rolling angle steel and straightening the angle steel.

4. The production process according to claim 3, wherein in the continuous casting billet production step, molten iron pretreatment is performed to remove impurities in the molten iron, and then converter smelting, LF refining and billet continuous casting are sequentially performed; after the deep desulfurization of the molten iron, the mass percent of sulfur elements is controlled to be below 0.020%, the molten iron is poured into a casting blank with a certain size, and the internal quality of the casting blank is improved through protective casting and electromagnetic stirring.

5. The production process according to claim 3, wherein a heat-accumulating walking-beam type heating furnace is used to heat the continuous casting slab to be rolled in the angle steel rolling process, the rolling process is divided into a rough rolling stage and a finish rolling stage in sequence, and air cooling treatment is performed after the rolling is finished.

6. The production process as claimed in claim 5, wherein the temperature for heating the continuous casting slab to be rolled is controlled to 1180-1210 ℃, the initial rolling temperature in the rolling process is 1050-1150 ℃, and the final rolling temperature is 870-920 ℃.

7. The production process as claimed in claim 3, wherein in the straightening process of the angle steel, the temperature of the upper cooling bed is controlled to be 750-800 ℃, the cooling time is controlled to be within 2.5h, and the angle steel is straightened at the temperature below 50 ℃.

8. The process for producing the niobium microalloyed high-strength high-weather-resistant angle steel as claimed in claim 7, wherein the leveler employs a 9-roll double-support variable-pitch leveler, and the degree of curvature is controlled to be within 0.15%.

9. The process for producing niobium microalloyed high-strength high-weather-resistance angle steel as claimed in claim 3, wherein the angle steel is equilateral hot-rolled angle steel with specification of 16#, 18# or 20#, and the total compression ratio is greater than 6.

Technical Field

The invention relates to the technical field of steel production, in particular to niobium microalloyed high-strength weather-resistant angle steel containing rare earth and a production process thereof.

Background

The power transmission line is exposed in the atmosphere for a long time, the corrosion of tower materials is serious, and although the corrosion hazard of the atmosphere can be relieved by adopting galvanized steel, the problems of high galvanizing cost, environmental pollution caused by a galvanizing process, maintenance needed in the later period of a galvanized iron tower and the like exist. At present, new materials, energy conservation and environmental protection become symbols of development of times, more strict environmental protection policies are gradually implemented in the future countries, and the hot-dip galvanizing process of steel materials is gradually limited and forbidden. The weathering steel is successfully applied to transmission towers in developed countries such as the United states, Italy and Japan, and is widely popularized in industries such as railways, ships and bridges in China, but practical transmission line projects in China are few so far. At present, the application and popularization of weather-resistant angle steel mainly have the following two problems: firstly, the component design is unreasonable, and the alloy cost is expensive; secondly, the production process is not suitable and the mechanical property is poor.

Along with the improvement of voltage grade, the bearing capacity of the iron tower is required to be continuously enhanced, and the tower weight and the occupied area of a corridor are reduced as much as possible. The rare earth elements which are the resources of the characteristics of China can purify a matrix, improve the density of a protective rust layer and reduce or replace Cr to reduce the cost. In recent years, domestic steel mills are used for modifying and upgrading heating devices, refining and rolling equipment and the like, and the Nb strengthening and toughening device has the capability of enabling Nb to exert the optimal strengthening and toughening. Due to the implementation of the policy of environmental protection, the price of ferrovanadium is changed dramatically, which is beneficial to the popularization of microalloying with Nb instead of V. The application of the rare earth-containing niobium microalloyed high-strength weather-resistant angle steel can simplify the structure of a tower, reduce the weight of a single component, correspondingly reduce the cost of transportation, installation and the like, reduce atmospheric corrosion loss and prolong the service life of a power transmission iron tower.

Disclosure of Invention

The technical problem solved is as follows:

for a long time, the steel for the power transmission tower in China uses Q345 as a main material, Q235 as a main material and VN alloying or Nb, V and Ti multi-element micro alloying is adopted to ensure the strength of the steel, hot galvanizing and corrosion prevention are realized, and compared with the international advanced countries, the strength value of the steel for the power transmission tower is lower, so that the steel consumption of the power transmission tower in China is larger than that of other countries, and the material selection margin is smaller. Meanwhile, the price of ferrovanadium is greatly changed due to the implementation of environmental protection policy. And other metal elements are selected to replace V, so that the fluctuation of the vanadium iron price can be effectively avoided.

The invention aims to overcome the defects of the prior art and provides a rare earth-containing niobium microalloyed high-strength weather-resistant angle steel and a production process thereof, wherein the welding performance is improved by adopting low C, the mechanical performance is ensured by Nb microalloying, the design idea of optimizing the corrosion resistance by RE is added, and the production process of adjusting a two-stage rolling temperature system and a reduction rule is adopted to produce the Q460 grade weather-resistant angle steel with the specifications of 16#, 18#, and 20#, so that the problems of unreasonable component design (replacing V) and improper production process in the prior art are solved.

The technical scheme adopted by the rare earth-containing niobium microalloyed high-strength weather-resistant angle steel is characterized in that low-C and low-S, Nb microalloying and RE addition are combined with a two-stage controlled rolling production process.

Nb has obvious grain refinement and precipitation strengthening with medium strength, and Nb microalloying ensures the mechanical property of the angle steel, allows the carbon content to be reduced, and thus improves the welding performance of the weather-resistant angle steel.

The addition of RE can refine the precipitation phase of the microalloy element, increase the precipitation quantity of the precipitation phase and play the roles of fine-grain strengthening and precipitation strengthening. On the other hand, microalloy elements such as Nb and Ni can increase the solid solution amount of rare earth in steel, and the solid-dissolved rare earth has the effects of desulfurization, deoxidation, inclusion denaturation and the like, thereby reducing the occurrence of pitting corrosion and promoting the generation of a protective rust layer.

Nb and RE in the weather-resistant angle steel are both rigid and flexible, and the mechanical property and the corrosion resistance of the angle steel are improved, so that the advantages of native resources are exerted, and the alloy cost is reduced.

The invention adopts the following technical scheme:

the niobium microalloyed high-strength weather-resistant angle steel containing rare earth comprises the following chemical components in percentage by mass: c: 0.05 to 0.12%, Si: 0.20-0.65%, Mn is less than or equal to 1.10%, Cu: 0.20-0.55%, Cr: 0.30-1.25%, Ni: 0.12-0.65%, Nb: 0.015-0.060%, P is less than or equal to 0.020%, S is less than or equal to 0.020%, RE: 0.01-0.04%, and the balance of Fe and inevitable impurities.

Furthermore, the yield strength Rel of the angle steel is more than or equal to 460MPa, the tensile strength Rm is more than or equal to 570MPa, the elongation A is more than or equal to 20 percent, and the impact absorption power Akv (-20 ℃) is more than or equal to 34J, Akv (-40 ℃) and more than or equal to 27J.

According to the phase change theory and the reduction coefficient law under the deformation condition of the disc type pass rolling process of the angle steel, the established rolling temperature system and the reduction rule are adopted, and the rolling is divided into two stages of rough rolling and finish rolling in sequence: roughly rolling in a recrystallization zone, wherein the initial rolling temperature is 1050-1150 ℃, and the multi-pass large reduction deformation is used for accumulating a large amount of dislocation and storage energy in the finish rolling stage; and (3) finish rolling is carried out in a non-recrystallization area, the finish rolling temperature is 870-920 ℃, fine and uniform ferrite and pearlite structures are obtained due to the pinning effect of strain-induced ferrite and precipitated phases, and the comprehensive performance of the angle steel is further improved.

A production process of the niobium microalloyed high-strength weather-resistant angle steel containing rare earth sequentially comprises the following steps: producing a continuous casting blank, rolling angle steel and straightening the angle steel.

Further, in the production step of the continuous casting billet, molten iron pretreatment is firstly carried out, impurities in the molten iron are removed, then converter smelting, LF refining and billet continuous casting are sequentially carried out; after the deep desulfurization of the molten iron, the mass percent of sulfur elements is controlled to be below 0.020%, the molten iron is poured into a casting blank with a certain size, and the internal quality of the casting blank is improved through protective casting and electromagnetic stirring.

Furthermore, in the process of rolling the angle steel, a heat storage walking beam type heating furnace is adopted to heat a continuous casting billet to be rolled, the rolling process is divided into a rough rolling stage and a finish rolling stage in sequence, and air cooling treatment is carried out after the rolling is finished.

Further, the temperature for heating the continuous casting billet to be rolled is controlled to be 1180-1210 ℃, the initial rolling temperature in the rolling process is 1050-1150 ℃, and the final rolling temperature is 870-920 ℃.

Further, in the process of straightening the angle steel, the temperature of an upper cooling bed is controlled to be 750-800 ℃, the cooling time is controlled within 2.5h, and the angle steel is straightened at the temperature below 50 ℃.

Further, the straightener adopts a 9-roller double-support variable-pitch straightener, and the bending degree is controlled to be within 0.15%.

Furthermore, the angle steel is equilateral hot rolled angle steel, the specification of the angle steel is 16#, 18# or 20#, and the total compression ratio is greater than 6.

The invention has the beneficial effects that: through the optimized design and the adjustment of the production process of the components, the RE purification matrix is added to reduce or replace Cr, Nb is used for replacing V to ensure the mechanical property, the content of S element is strictly controlled, the stable production of the product is realized, and the high-strength weather-resistant angle steel with stable mechanical property and good welding property and corrosion resistance is obtained. The yield strength Rel of the high-strength weather-resistant angle steel containing the rare earth is more than or equal to 460MPa, the tensile strength Rm is more than or equal to 570MPa, the elongation A is more than or equal to 20 percent, the impact absorption power Akv (-20 ℃) is more than or equal to 34J, and Akv (-40 ℃) is more than or equal to 27J.

Detailed Description

Hereinafter, specific embodiments of the present invention will be described in detail. It should be noted that technical features or combinations of technical features described in the following embodiments should not be considered as being isolated, and they may be combined with each other to achieve a better technical effect.

In the embodiment of the invention, Nb is used for replacing V; nb has obvious grain refinement and precipitation strengthening with medium strength, and Nb microalloying ensures the mechanical property of the angle steel and allows the carbon content to be reduced, thereby improving the welding property of the weather-resistant angle steel (by accounting for the market price of the raw materials in 3 months in 2019, by adopting the design components of the invention, the alloy cost can be saved by not less than 156 yuan/ton, and the cost for saving later maintenance and the like is not included). According to the invention, Nb is used for replacing V, so that the mechanical property of the steel is improved, the requirement of Q460-level high-strength angle steel is met, the tower structure can be simplified, the weight of a single component is reduced, and the transportation and installation costs are correspondingly reduced.

RE is used as a resource rare earth element with characteristics in China, solid-dissolved rare earth has the effects of desulfurization, deoxidation, inclusion deformability and the like, the occurrence of pitting corrosion is reduced, and the generation of a protective rust layer can be promoted, besides, the cost of Cr corrosion-resistant alloy elements in China is high, and the RE is used for reducing or replacing Cr, so that the atmospheric corrosion loss is reduced, and the service life of the power transmission iron tower is prolonged (in the invention, the contribution of 0.02 wt% of RE element to corrosion resistance is equivalent to that of 0.04 wt% of Cr in the first example, and the contribution of 0.026 wt% of RE element to corrosion resistance is better than that of 0.04 wt% of Cr element in the second example).

In the embodiment of the invention, the function of Nb in steel is played, the heating temperature is controlled to be 1200 ℃, and the growth of austenite grains is controlled by solid solution Nb in the form of Nb (CN). Within the range of equipment capacity and technological parameters, the reduction rate of each pass is matched with the rolling temperature, Nb starts to promote the generation of a flattened austenite structure under the action of solid solution dragging near the lowest temperature of recrystallization, and if the flattened structure at higher temperature (such as 950 ℃ or even 1000 ℃) enters air cooling, abnormal growth of crystal grains is easily caused, coarse and uneven isometric crystals are formed, and finally the coarse of phase-change ferrite crystal grains is caused. When the deformation approaches to or below the recrystallization stop temperature, the flattened austenite is pinned by Nb separated out by strain induction, the effect of refining and homogenizing the phase change structure on the whole section is generated, the tendency of generating granular bainite and weishi is reduced, so two-stage controlled rolling is adopted, the rough rolling process is in a recrystallization zone, the initial rolling temperature is controlled at 1100 ℃, the finish rolling process is in a non-recrystallization zone, the initial rolling temperature is controlled at 940 ℃, the final rolling temperature is controlled at 880 ℃, and the total compression ratio is more than 6. In addition, the Nb in the cooling process after rolling has little influence on the dynamics of the tissue transformation, and air cooling can be adopted to replace water cooling or air cooling, so that the production cost is reduced, and finally, the fine ferrite + pearlite tissue is obtained to ensure the mechanical property.