阅读说明：本技术 一种焊网使用的高延性冷轧钢筋用钢及其生产方法 (Steel for high-ductility cold-rolled steel bar for welded mesh and production method thereof ) 是由 姜婷 汪开忠 于同仁 郭湛 余良其 张晓瑞 何峰 吴建曦 丁新军 葛晴晴 于 2020-06-28 设计创作，主要内容包括：本发明的一种焊网使用的高延性冷轧钢筋用钢及其生产方法,属于建筑用钢技术领域,焊网使用的高延性冷轧钢筋用钢其主要化学成份组成及质量百分比含量为：C：0.10％～0.20％、Si：0.15％～0.30％、Mn：0.60％～0.90％、Cr：0.10％～0.50％、Nb：0.010％～0.040％、V：0.020％～0.050％、N：0.009％～0.012％、P≤0.025％、S≤0.020％,其余为Fe和其它不可避免的杂质。生产的钢筋,无需回火,强度和延伸率达到CRB630H级别,满足焊网用高延性冷轧钢筋要求。(The invention relates to a steel for high-ductility cold-rolled steel bars used for welding nets and a production method thereof, belonging to the technical field of steel for buildings, wherein the steel for high-ductility cold-rolled steel bars used for welding nets comprises the following main chemical components in percentage by mass: c: 0.10% -0.20%, Si: 0.15% -0.30%, Mn: 0.60-0.90%, Cr: 0.10% -0.50%, Nb: 0.010% -0.040%, V: 0.020-0.050%, N: 0.009-0.012 percent, less than or equal to 0.025 percent of P, less than or equal to 0.020 percent of S, and the balance of Fe and other inevitable impurities. The produced steel bar does not need tempering, the strength and the elongation rate reach the level of CRB630H, and the requirement of high-ductility cold-rolled steel bar for mesh welding is met.)

1. The steel for the high-ductility cold-rolled steel bar used for welding the net is characterized by comprising the following main chemical components in percentage by mass: c: 0.10% -0.20%, Si: 0.15% -0.30%, Mn: 0.60-0.90%, Cr: 0.10% -0.50%, Nb: 0.010% -0.040%, V: 0.020-0.050%, N: 0.009-0.012 percent, less than or equal to 0.025 percent of P, less than or equal to 0.020 percent of S, and the balance of Fe and other inevitable impurities.

2. The steel for the high-ductility cold-rolled steel bar for the welded mesh as claimed in claim 1, wherein the steel for the high-ductility cold-rolled steel bar for the welded mesh comprises the following main chemical components in percentage by mass: c: 0.12% -0.18%, Si: 0.19-0.25%, Mn: 0.72% -0.83%, Cr: 0.24% -0.36%, Nb: 0.015% -0.035%, V: 0.025% -0.045%, N: 0.010-0.011 percent, less than or equal to 0.025 percent of P, less than or equal to 0.020 percent of S, and the balance of Fe and other inevitable impurities.

3. The steel for high-ductility cold-rolled steel bars for mesh welding according to claim 1 or 2, wherein the chemical composition satisfies the following carbon equivalent calculation formula:

carbon equivalent Ceq ═ C + (% Mn)/6+ (% Cr +% Mo +% V)/5+ (% Ni +% Cu)/15 ≦ 0.47.

4. The steel for high-ductility cold-rolled steel bars for mesh welding according to claim 1 or 2, wherein the chemical composition satisfies the following relation: (% N)/7: (% Nb)/41+ (% V)/23) ≥ 0.50.

5. A production process of steel for high-ductility cold-rolled steel bars used for welding nets is characterized by comprising the following steps of:

s1, heating the square billet produced by the converter;

s2, controlled rolling and controlled cooling rolling of the high-speed wire rod;

s3, hot rolling steel bar coils;

and S4, cold rolling to obtain the finished product of the steel bar.

6. The process for producing a steel for a high ductility cold rolled steel bar for a mesh welding according to claim 5, wherein the high speed wire controlled rolling and controlled cooling rolling in step S2 includes:

a. in the square billet rolling stage, the finish rolling temperature is controlled to be 760-800 ℃;

b. in the spinning stage, the spinning temperature is controlled to be 740-780 ℃;

c. and in the controlled cooling stage after rolling, phase change is completed on a stelmor line.

7. The process for producing a steel for a high-ductility cold-rolled steel bar for a welded mesh according to claim 6, wherein in the step c, the heat-insulating cover is fully opened in the heat-insulating stage.

8. The process for producing a steel for a high ductility cold rolled steel bar for a mesh welding according to claim 5, wherein the reduction ratio of the cold rolled steel bar is controlled to be 28% to 35% in the step S4.

Technical Field

The invention belongs to the technical field of building steel, and particularly relates to high-ductility steel for cold-rolled steel bars for welded mesh and a production method thereof.

Background

The welded reinforcing mesh is welded mesh steel welded by cold rolled steel bars, and is a good and efficient material for concrete distribution. The hot rolled disc using the steel grades such as Q215 and Q235 is usually welded after being cold rolled and reduced in diameter, and since the plasticity of the traditional steel grades is deteriorated after being cold rolled and the strength is increased in a limited way, the elongation and the strength need to be increased through the online tempering heat treatment to ensure the service performance. The online tempering line has the advantages of high equipment cost, greatly reduced production efficiency, increased energy consumption and frequent occurrence of the problem of unstable quality of the steel bars due to insufficient heat treatment.

At present, the steel for the high-ductility cold-rolled steel bar for the welded mesh in China mainly uses the national standard, the British standard and other standard medium-grade marks, the steel bar needs to be subjected to heat treatment after being subjected to cold rolling, and the research on new steel types is less. Along with the development of the building industry, the use quality of building materials is required to be more and more stable, quality fluctuation caused by the heat treatment process is required to be eliminated, and meanwhile, along with the more and more strict requirement on environmental protection, the development of novel steel for mesh welding free of tempering heat treatment is urgently needed.

The Chinese patent application numbers are: 201110114872.7, publication date is: 2011-10-12 "production process of high ductility cold-rolled ribbed steel bar", the production process comprises the following steps: (1) reducing the diameter of the disc by a rolling mill with the reducing ratio of 0.79-0.87; (2) reducing the diameter of the steel bar subjected to the diameter reduction by the first rolling mill in the step (1) by a second rolling mill and simultaneously scoring, wherein the diameter reduction ratio is 0.59-0.88; (3) carrying out heat treatment on the steel bars subjected to diameter reduction and scoring of the rolling mill in the step (2) at the temperature of 550-670 ℃ for 1-3 s; (4) and (4) naturally cooling the steel bars subjected to the heat treatment in the step (3) in the air. After the ordinary I, II-grade steel bar is treated by the process, the internal structure and the grain size of the steel bar are changed, so that the strength and the elongation of the steel bar are improved and are close to IV-grade steel bars over III-grade steel; however, this invention requires heat treatment, which increases the cost and energy consumption.

The Chinese patent application numbers are: 201910234085.2, publication date is: 2019-06-14, which discloses a production process of a high-ductility cold-rolled ribbed steel bar, comprising a feeding procedure, steel bar processing and finished product collection, wherein the steel bar processing comprises the following steps: a first rolling procedure: the steel bar passes through a first rolling mill, the rolling mill reduces the diameter of the steel bar and flattens the steel bar, and a second rolling process comprises the following steps: the reinforcing steel bar subjected to the first rolling treatment passes through a second rolling mill, the second rolling mill rolls the reinforcing steel bar subjected to the first rolling treatment into a round and reduces the diameter, the diameter reduction ratio is 0.6-0.8, and the heat treatment process comprises the following steps: tempering the steel bars treated by the two-rolling procedure, carrying out heat treatment at the temperature of 580-650 ℃ for 0.8-2s, and naturally cooling the treated steel bars in the air. The steel bar is not reduced in diameter, the steel bar is flattened, and the strength of the steel bar is improved by flattening the steel bar; but the tempering treatment is needed, the treatment cost is higher, and the energy consumption is increased.

Disclosure of Invention

1. Problems to be solved

Aiming at the problems that the existing steel for the high-ductility cold-rolled steel bar needs tempering treatment and increases energy consumption, the steel for the high-ductility cold-rolled steel bar used for welding the net and the production method thereof are provided, the produced steel bar does not need tempering, the strength and the elongation rate reach the level of CRB630H, and the requirement of the high-ductility cold-rolled steel bar for welding the net is met.

2. Technical scheme

In order to solve the problems, the technical scheme adopted by the invention is as follows:

the invention relates to a steel for high-ductility cold-rolled steel bars used for welding nets, which mainly comprises the following chemical components in percentage by mass: c: 0.10% -0.20%, Si: 0.15% -0.30%, Mn: 0.60-0.90%, Cr: 0.10% -0.50%, Nb: 0.010% -0.040%, V: 0.020-0.050%, N: 0.009-0.012 percent, less than or equal to 0.025 percent of P, less than or equal to 0.020 percent of S, and the balance of Fe and other inevitable impurities.

As a further description of the invention, the steel for the high-ductility cold-rolled steel bar used for the welded mesh comprises the following main chemical components in percentage by mass: c: 0.12% -0.18%, Si: 0.19-0.25%, Mn: 0.72% -0.83%, Cr: 0.24% -0.36%, Nb: 0.015% -0.035%, V: 0.025% -0.045%, N: 0.010-0.011 percent, less than or equal to 0.025 percent of P, less than or equal to 0.020 percent of S, and the balance of Fe and other inevitable impurities.

As a further illustration of the present invention, the chemical composition is required to satisfy the following carbon equivalent calculation relationship:

carbon equivalent Ceq ═ C + (% Mn)/6+ (% Cr +% Mo +% V)/5+ (% Ni +% Cu)/15 ≦ 0.47.

As a further illustration of the present invention, the chemical composition should satisfy the following relationship:

(％N)/7：((％Nb)/41+(％V)/23)≥0.50。

the invention relates to a production process of steel for high-ductility cold-rolled steel bars for welded meshes, which comprises the following steps of:

s1, heating the square billet produced by the converter;

s2, controlled rolling and controlled cooling rolling of the high-speed wire rod;

s3, hot rolling steel bar coils;

and S4, cold rolling to obtain the finished product of the steel bar.

As a further explanation of the present invention, in step S2, the high-speed wire controlled rolling and controlled cooling rolling includes:

a. in the square billet rolling stage, the finish rolling temperature is controlled to be 760-800 ℃;

b. in the spinning stage, the spinning temperature is controlled to be 740-780 ℃;

c. and in the controlled cooling stage after rolling, phase change is completed on a stelmor line.

As a further explanation of the present invention, in the step c, the heat-preserving cover is fully opened in the heat-preserving stage.

As a further explanation of the present invention, in step S4, the reduction ratio of the cold-rolled steel bar is controlled to be 28% to 35%.

3. Advantageous effects

Compared with the prior art, the invention has the beneficial effects that:

(1) the high-ductility steel for the cold-rolled steel bar used for the welded mesh has the grain size of the hot-rolled steel bar of more than or equal to 10 grade and R grade under the condition of meeting the strength and high ductility of the steel bar_el≥430MPa，R_mMore than or equal to 570MPa, and A more than or equal to 32 percent; after the produced hot rolled steel bar is processed into a cold rolled steel bar by 28-35% of surface reduction rate, tempering is not needed, the strength and the elongation rate reach the CRB630H level, and the requirement of the high-ductility cold rolled steel bar for welding a net is met;

(2) the production process of the steel for the high-ductility cold-rolled steel bar used for the welded mesh controls the finish rolling temperature to be 760-800 ℃, and controls the finish rolling temperature to be A by utilizing the severe thermal deformation of the large reduction of an austenite region_C3The transformation of pro-eutectoid ferrite occurs in a temperature range of 20 to 60 ℃ above the point (the steel A of the invention)_C3740 ℃), and combining deformation, the obtained deformation-induced ferrite phase change has strong refined grains, and the steel with deformation-induced ferrite phase change has higher yield strength, tensile strength and good plasticity, and the effect can not be achieved at the temperature higher than or lower than the temperature;

(3) according to the production process of the steel for the high-ductility cold-rolled steel bar used for the welded mesh, the spinning temperature is 740-780 ℃, and if the spinning temperature is lower than 740 ℃, the steel enters a pearlite phase transformation stage before entering a heat-preservation cover; if the temperature is higher than 780 ℃, the phase transition temperature is not reached before the heat preservation cover enters, and the complete phase transition on a stelmor line is difficult to complete, so that the crystal grains grow;

(4) the invention relates to a production process of steel for high-ductility cold-rolled steel bars used for welded meshes, which is characterized in that a stelmor line heat-preserving cover is fully opened, and 10-12 fans are arranged; obtaining an ultra-fine grain ideal structure of ferrite and fine pearlite, wherein if the number of the fans is too large, abnormal structures are easy to generate, and if the number is too small, the grain size is coarsened;

(5) according to the production process of the steel for the high-ductility cold-rolled steel bar used for the welded mesh, the surface reduction rate is controlled to be 28% -35% during cold rolling, if the surface reduction rate is lower than 28%, the cold work hardening rate is insufficient, the steel bar after cold rolling cannot reach 630MPa, and if the surface reduction rate is higher than 35%, the reduction amount is too large, and the plasticity of the cold-rolled steel bar cannot be guaranteed.

Detailed Description

Exemplary embodiments of the present invention are described in detail below. Although these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that various changes to the invention may be made without departing from the spirit and scope of the present invention. The following more detailed description of the embodiments of the invention is not intended to limit the scope of the invention, as claimed, but is presented for purposes of illustration only and not limitation to describe the features and characteristics of the invention, to set forth the best mode of carrying out the invention, and to sufficiently enable one skilled in the art to practice the invention. Accordingly, the scope of the invention is to be limited only by the following claims.

The following detailed description and example embodiments of the invention are set forth.

The main chemical composition, mass percentage content and carbon equivalent of the steel for the high-ductility cold-rolled steel bar used for the welded mesh are shown in table 1:

TABLE 1 chemical compositions and mass percent contents and carbon equivalents of examples and comparative examples

(mass%, the balance being Fe and unavoidable impurities)

	C	Si	Mn	Cr	Nb	V	N	Ni	Cu	Mo	P	S	Ceq
														Example 1	0.10	0.30	0.90	0.50	0.010	0.050	0.0120	0.008	0.007	0.005	0.018	0.005	0.36
Example 2	0.20	0.15	0.60	0.36	0.040	0.020	0.0098	0.007	0.008	0.006	0.016	0.002	0.38
														Example 3	0.16	0.25	0.83	0.10	0.035	0.033	0.0090	0.005	0.007	0.004	0.016	0.004	0.33
Example 4	0.12	0.19	0.72	0.24	0.031	0.045	0.0103	0.006	0.006	0.004	0.015	0.005	0.30
														Example 5	0.18	0.22	0.79	0.31	0.015	0.025	0.0100	0.005	0.005	0.005	0.013	0.004	0.38
Example 6	0.17	0.23	0.75	0.31	0.023	0.031	0.0110	0.005	0.007	0.004	0.014	0.005	0.36
														Comparative example 1	0.23	0.24	0.9	0.5	0.025	0.037	0.011	0.008	0.007	0.005	0.017	0.006	0.49
Comparative example 2	0.22	0.21	0.88	0.005	0.001	0.005	0.0069	0.006	0.005	0.005	0.016	0.005	0.37

The contents of the elements in the above examples all satisfy the following ranges:

c: 0.10% -0.20%, Si: 0.15% -0.30%, Mn: 0.60-0.90%, Cr: 0.10% -0.50%, Nb: 0.010% -0.040%, V: 0.020-0.050%, N: 0.009-0.012 percent, less than or equal to 0.025 percent of P, less than or equal to 0.020 percent of S, and the balance of Fe and other inevitable impurities.

Preferred ranges are: c: 0.12% -0.18%, Si: 0.19-0.25%, Mn: 0.72% -0.83%, Cr: 0.24% -0.36%, Nb: 0.015% -0.035%, V: 0.025% -0.045%, N: 0.010-0.011 percent, less than or equal to 0.025 percent of P, less than or equal to 0.020 percent of S, and the balance of Fe and other inevitable impurities.

The Ni element, Cu element and Mo element in table 1 are impurity elements in steel, and several elements are listed only for convenience of calculating carbon equivalent.

The specific effects of the element composition in the scheme are as follows:

c: c is the most basic effective strengthening element in steel, but as its content increases, the ductility and weldability of the steel decrease. The steel for high-ductility cold-rolled steel bars used for the welded mesh of the present invention has a C content of 0.10 to 0.20%, and preferably 0.12 to 0.18%.

Si: si is an important element for strengthening steel, and increases the strength and hardness of steel by solid solution, but too high Si content deteriorates cold workability of steel. For the steel for high-ductility cold-rolled steel bar used for the welded mesh of the present invention, the Si content is controlled to 0.15% to 0.30%, and more preferably, the Si content is controlled to 0.19% to 0.25%.

Mn: mn and Fe form a solid solution, increasing the hardness and strength of ferrite and austenite in steel, but excessive Mn reduces the plasticity and cold workability of steel, and deteriorates the weldability. In the steel for high-ductility cold-rolled steel bars used for mesh welding according to the present invention, the Mn content is controlled to 0.60% to 0.90%, and more preferably, the Mn content is controlled to 0.72% to 0.83%.

Cr: cr element and carbon form carbide, the toughness of the steel can be effectively improved while the strength of the steel is obviously improved, but the excessive Cr has no obvious effect any more, and the welding performance of the welded mesh steel is deteriorated. For the steel for high-ductility cold-rolled steel bar used for the welded mesh of the present invention, the Cr content is controlled to 0.10% to 0.50%, and more preferably, the Cr content is controlled to 0.24% to 0.36%.

Nb: nb in steel can form fine carbonitride with C, N atoms, and austenite recrystallization is suppressed, and austenite grain growth is promoted. And Nb (CN) can be precipitated not only in the austenite non-recrystallization deformation-removal induction precipitation but also in the ferrite after the phase transformation, and the fine precipitated phases improve the strength and the toughness of the steel, greatly improve the strength in the cold rolling process and keep a higher elongation value. However, excess Nb contributes too much to the yield strength, resulting in an inadequate yield ratio. For the steel for the high-ductility cold-rolled steel bar used for the welding mesh, the Nb content is controlled to be 0.010-0.040%, and the Nb content is further preferably controlled to be 0.015-0.035%.

V: v is an excellent deoxidizer of steel, vanadium is added into the steel to form carbonitride with C, N, the structure grains can be refined, the strength and the toughness are improved, when Nb and V are added in a composite mode, part of vanadium is combined into (NbV) CN which is smaller than respective carbonitride of Nb and V, the precipitation temperature is wider, therefore, austenite grains can be effectively prevented from growing and recrystallizing, and finally the strength and the ductility of the steel are improved. For the steel for the high-ductility cold-rolled steel bar used for the welding mesh, the content of V is controlled to be 0.020-0.050%, and the content of Nb is further preferably controlled to be 0.025-0.045%.

N: n mainly forms precipitation phase with vanadium and niobium in steel to improve the strength and toughness of the steel, but excessive N precipitates Fe in the steel₄N, the diffusion speed is slow, and the steel has timeliness. The content of N in the steel for high-ductility cold-rolled steel bars used for the welded mesh of the present invention is controlled to be 0.009% -0.012%, and more preferably 0.010% -0.011%.

S and P: the sulfur is easy to form MnS inclusion with manganese in the steel and is harmful to the processing deformation of the material; p is an element with a strong segregation tendency and usually also causes co-segregation of sulphur and manganese, which is detrimental to the homogeneity of the product structure and properties. For the steel for the high-ductility cold-rolled steel bar used for the welded mesh, P is controlled to be less than or equal to 0.025 percent, and S is controlled to be less than or equal to 0.020 percent.

The above elements also need to satisfy the following:

the carbon equivalent Ceq ═ C + (% Mn)/6+ (% Cr +% Mo +% V)/5+ (% Ni +% Cu)/15 ≦ 0.47 to meet the welding performance when the cold-rolled steel bar is made into a welding net.

In addition, in order to ensure sufficient precipitation of niobium vanadium carbonitride, it is also necessary to ensure that the ratio (% N)/7: (% Nb)/41+ (% V)/23) ≥ 0.50. Because the addition of carbon is high enough, the ratio is not considered, the atomic ratio of the three elements of N, Nb and V (7, 41 and 23 are the relative atomic mass of N, Nb and V respectively) is mainly considered, and under the condition that the atomic ratio is more than or equal to 0.50, the niobium-vanadium-carbonitride can be ensured to be fully precipitated, the grain refinement is realized, and the strength and the ductility of the steel are comprehensively improved.

The invention relates to a production process of steel for high-ductility cold-rolled steel bars for welded meshes, which comprises the following steps of:

s1, heating the square billet produced by the converter;

s2, high-speed wire controlled rolling and controlled cooling rolling, wherein the high-speed wire controlled rolling and controlled cooling rolling comprises the following steps:

a. in the square billet rolling stage, the finish rolling temperature is controlled to be 760-800 ℃; controlling the finishing temperature to be 760-800 ℃, and controlling the finishing temperature to be A by utilizing the severe thermal deformation of the austenite area under the large reduction_C3The transformation of pro-eutectoid ferrite occurs in a temperature range of 20 to 60 ℃ above the point (the steel A of the invention)_C3The point is 740 ℃), and deformation is combined, so that the obtained deformation-induced ferrite phase change has strong refined grains, and the steel with the deformation-induced ferrite phase change has higher yield strength, tensile strength and good plasticity, and the effect cannot be achieved at the temperature higher than or lower than the temperature.

b. In the spinning stage, the spinning temperature is controlled to be 740-780 ℃; if the spinning temperature is lower than 740 ℃, the spinning enters a pearlite phase transformation stage before entering the heat-preserving cover; if the temperature is higher than 780 ℃, the phase transition temperature is not reached before entering the heat-preserving cover, and the complete phase transition on a stelmor line is difficult to complete, so that the crystal grains grow up.

c. In the controlled cooling stage after rolling, the stelmor line heat preservation cover is fully opened, and 10-12 fans are opened; an ideal ultrafine grain structure of ferrite and fine pearlite is obtained, if the number of the fans is too large, abnormal structures are easy to generate, and if the number is too small, the grain size is coarsened.

S3, hot rolling steel bar coils;

s4, cold rolling to obtain the finished product of the steel bar, and controlling the surface reduction rate of the cold rolled steel bar to be 28-35%. The surface reduction rate is controlled to be 28-35% during cold rolling, if the surface reduction rate is lower than 28%, the cold work hardening rate is insufficient, the steel bar after cold rolling does not reach 630MPa, and if the surface reduction rate is higher than 35%, the reducing amount is too large, and the plasticity of the cold-rolled steel bar cannot be guaranteed.