阅读说明：本技术 一种提高钢筋强度及其断裂韧性的热轧工艺 (Hot rolling process for improving strength and fracture toughness of steel bar ) 是由 赵小军 刘芳 马正洪 于 2020-05-22 设计创作，主要内容包括：本发明属于炼钢技术领域,涉及一种提高钢筋强度及其断裂韧性的热轧工艺；设计钢坯的组分,然后将钢坯送入加热炉加热；粗轧之前开启高压水除磷；粗轧3～6个道次；再进行精轧,精轧前配有穿水冷却装置,采用KOCKS三辊减定径机组轧制,盘卷冷却,卷取后缓慢冷却；精轧过后的钢筋进行预水冷,冷却表面温度在表面的奥氏体短时间内会发生相变；其余部分快速返红仍保持奥氏体组织；在空冷过程中,首先析出V的析出物,钉扎住奥氏体晶界,阻止晶粒长大,之后到达相变点,从表层到芯部先后进行了奥氏体向铁素体和珠光体的转变,形成高强度的细晶组织,最后收集打捆；本发明工艺能提高钢筋性能和稳定性,使得钢筋的强度级别、韧性级别均大幅度提高。(The invention belongs to the technical field of steel making, and relates to a hot rolling process for improving the strength and the fracture toughness of a steel bar; designing components of a steel billet, and then conveying the steel billet into a heating furnace for heating; starting high-pressure water to remove phosphorus before rough rolling; rough rolling for 3-6 passes; performing finish rolling, wherein a water cooling device is arranged before finish rolling, a KOCKS three-roller reducing sizing mill set is adopted for rolling, coiling and cooling are performed, and the coiling and cooling are performed slowly; pre-cooling the finish-rolled steel bar by water, wherein the surface temperature of the steel bar is cooled to generate phase change in austenite on the surface in a short time; the other part is rapidly reddened and still keeps the austenite structure; in the air cooling process, firstly precipitating V precipitates, pinning austenite crystal boundaries, preventing grains from growing up, then reaching a phase transformation point, sequentially carrying out transformation from austenite to ferrite and pearlite from a surface layer to a core part to form a high-strength fine crystal structure, and finally collecting and bundling; the process can improve the performance and stability of the steel bar, and greatly improve the strength grade and the toughness grade of the steel bar.)

1. A hot rolling process for improving the strength and the fracture toughness of a steel bar is characterized by comprising the following steps:

(1) the steel billet comprises the following chemical components in percentage by weight: 0.03-0.15%, Si: 0.25 to 0.45%, Mn: 1.4-1.5%, V: 0.01 to 0.05%, Nb: 0.015 to 0.025%, Cr: 0.10-0.20%, B: 0.001-0.0015%, Ti: 0.001-0.005%, less than or equal to 0.025% of S, less than or equal to 0.03% of P, and the balance of Fe and inevitable impurities;

(2) feeding the steel billets obtained in the step (1) into a heating furnace, wherein the preheating section is 800-900 ℃, the initial rolling temperature is 1050-1080 ℃, the furnace temperature of the soaking section is 1150-1800 ℃, and the total heating time is 80-85 minutes;

(3) rough rolling: starting high-pressure water to remove phosphorus before rough rolling; then, roughly rolling for 3-6 passes under the rolling condition that the speed is 0.8-1.1 m/s, controlling the final rolling temperature to be 950-960 ℃, and controlling the reduction rate;

(4) finish rolling: a water cooling device is arranged before finish rolling, the temperature of entering KOCKS is controlled, a KOCKS three-roller reducing sizing mill set is adopted for rolling, a coil is cooled, and a slow cooling mode is adopted for cooling after coiling; the finish rolling deformation is controlled to be less than or equal to 30 percent,

(5) pre-cooling the finish-rolled steel bar by water, and cooling the surface temperature to a certain temperature to ensure that the austenite on the surface can generate phase change in a short time; the rest part rapidly returns to above 900 ℃, and the austenite structure is still maintained; in the subsequent air cooling process, V precipitates are precipitated firstly, austenite crystal boundaries are pinned, grain growth is prevented, then the crystal grains reach a phase transformation point, austenite is transformed into ferrite and pearlite from the surface layer to the core part in sequence, the strength and the fracture toughness of the steel bar are improved, and finally the steel bar is collected and bundled.

2. The hot rolling process for improving the strength and fracture toughness of steel bars according to claim 1, wherein in the step (1), the hot pressing furnace adopts a high-efficiency walking beam type heating furnace, and a control system consisting of an industrial microcomputer and a PLC can realize automatic combustion according to set parameters.

3. The hot rolling process for improving the strength and the fracture toughness of the steel bar according to claim 1, wherein in the step (3), the dephosphorization pressure is 16-18 MPa.

4. The hot rolling process for improving the strength and the fracture toughness of the steel bar according to the claim 1, characterized in that in the step (3), the reduction rate is controlled to be below 40%; and the rolling of the first 2 passes in the rough rolling is smaller than that of the subsequent passes.

5. The hot rolling process for improving the strength and the fracture toughness of the steel bar according to claim 1, wherein in the step (3), the KOCKS entering temperature is 900-920 ℃; the finish rolling speed of the finishing mill group is 8-10 m/s, the rolling speed is controlled, and the problems of surface quality and structural strength of a rolled piece caused by too high speed are avoided.

6. The hot rolling process for improving the strength and fracture toughness of steel bars according to claim 1, wherein in the step (4), the slow cooling is cooling the coils with cooling water for 3-5 min.

7. The hot rolling process for improving the strength and the fracture toughness of the steel bar according to claim 1, wherein in the step (5), the temperature of the cooling surface is 550-580 ℃.

Technical Field

The invention belongs to the technical field of steel making, and particularly relates to a hot rolling process for improving the strength and the fracture toughness of a steel bar.

Background

China has already entered a new normal state of medium-high speed development and the largest market of reinforcing steel consumption, and in the total amount of steel production and consumption, the construction reinforcing steel occupies a great proportion, and along with the rapid development of the construction industry, the requirement on the performance of hot rolled reinforcing steel is higher and higher; in recent years, the green development of the construction industry is advocated, and the requirements on the strength and the toughness of the steel bar are higher for saving steel and improving the safety of a building structure.

At present, the domestic process for producing the steel bars generally adds a large amount of trace alloy elements, such as carbonitrides formed and precipitated in steel by using V elements, and plays roles of precipitation, strengthening and grain refinement, thereby further improving the strength of the steel; but generally the strength and toughness of steel is a pair of spearheads; the strength of the steel bar is increased and the fracture toughness is deteriorated.

Therefore, how to control and improve the strength of steel and improve the fracture toughness of the steel is a key problem to be solved urgently in the process of mass production of steel.

Disclosure of Invention

The invention aims to overcome the technical defects in the prior art and provide a hot rolling process which is simple to operate and can improve the strength and the fracture toughness of a steel bar.

In order to achieve the above object, the hot rolling process for improving the strength and fracture toughness of the steel bar comprises the following steps:

(1) the steel billet comprises the following chemical components in percentage by weight: 0.03-0.15%, Si: 0.25 to 0.45%, Mn: 1.4-1.5%, V: 0.01 to 0.05%, Nb: 0.015 to 0.025%, Cr: 0.10-0.20%, B: 0.001-0.0015%, Ti: 0.001-0.005%, less than or equal to 0.025% of S, less than or equal to 0.03% of P, and the balance of Fe and inevitable impurities;

(2) feeding the steel billets obtained in the step (1) into a heating furnace, wherein the preheating section is 800-900 ℃, the initial rolling temperature is 1050-1080 ℃, the furnace temperature of the soaking section is 1150-1800 ℃, and the total heating time is 80-85 minutes;

(3) rough rolling: starting high-pressure water to remove phosphorus before rough rolling; roughly rolling for 3-6 passes under the rolling condition of the speed of 0.8-1.1 m/s, controlling the final rolling temperature to be 950-960 ℃, and controlling the reduction rate;

(4) finish rolling: a water cooling device is arranged before finish rolling, the temperature of entering KOCKS is controlled, a KOCKS three-roller reducing sizing mill set is adopted for rolling, a coil is cooled, and a slow cooling mode is adopted for cooling after coiling; the finish rolling deformation is controlled to be less than or equal to 30 percent,

(5) pre-cooling the finish-rolled steel bar by water, and cooling the surface temperature to a certain temperature to ensure that the austenite on the surface can generate phase change in a short time; the rest part rapidly returns to above 900 ℃, and the austenite structure is still maintained; in the subsequent air cooling process, V precipitates are precipitated firstly, austenite crystal boundaries are pinned, grain growth is prevented, then the crystal grains reach a phase transformation point, austenite is transformed into ferrite and pearlite from the surface layer to the core part in sequence, the strength and the fracture toughness of the steel bar are improved, and finally the steel bar is collected and bundled.

Preferably, in the step (1), the hot-pressing furnace adopts a high-efficiency walking beam type heating furnace, a control system is formed by an industrial microcomputer and a PLC, and automatic combustion can be realized according to set parameters.

Preferably, in the step (3), the dephosphorization pressure is 16-18 MPa.

Preferably, in the step (3), the reduction rate is controlled to be below 40%; and the rolling of the first 2 passes in the rough rolling is smaller than that of the subsequent passes.

Preferably, in the step (4), the KOCKS feeding temperature is 900-920 ℃; the finish rolling speed of the finishing mill group is 8-10 m/s, the rolling speed is controlled, and the problems of surface quality and structural strength of a rolled piece caused by too high speed are avoided.

Preferably, in the step (4), the slow cooling is cooling the coil for 3-5min by cooling water.

Preferably, in the step (5), the temperature of the cooling surface is 550 to 580 ℃.

The invention has the advantages and technical effects that:

(1) the invention controls the initial rolling temperature, the final rolling temperature, the rolling speed, the rolling pass and time and the rapid cooling and cooling control after rolling through the steel rolling process, so that the dual functions of Nb and B microalloy strengthening and cooling control fine grain strengthening can be fully exerted, the strength of the steel bar is obviously improved, and better plastic toughness is kept; meanwhile, in the air cooling process after the finish rolling, V precipitates are precipitated firstly, austenite crystal boundaries are pinned, grains are prevented from growing up, then the austenite crystal boundaries reach a phase transformation point, and the austenite is transformed into ferrite and pearlite from the surface layer to the core part in sequence to form a high-strength fine crystal structure.

(2) The invention adopts the KOCKS rolling mill to move the assembly of the frame guide, the replacement preparation of the roll collar guide, the adjustment of the roll and the guide and the like to the offline for completion, thereby reducing the shutdown time of the rolling line and improving the operating rate of the production line; the high-efficiency walking beam type heating furnace is adopted, a control system is formed by an industrial microcomputer and a PLC, automatic combustion can be realized according to set parameters, and the high-efficiency walking beam type heating furnace has the advantages of flexible production operation, uniform heating of steel billets, less oxidation burning loss, energy conservation and the like.

(3) Because the combined control is carried out on the initial rolling temperature, the finish rolling deformation and the rapid cooling process with smaller cooling strength after rolling, compared with the rapid cooling process which only depends on the smaller cooling strength after rolling, the process has the advantages that the performance is improved, and the stability of the performance, the strength level and the toughness level are greatly improved; meanwhile, the elongation is higher, and the impact performance is better, so that the possibility of fracture of steel due to plastic deformation under severe deformation load is reduced.

Detailed Description

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.