阅读说明：本技术 一种优质碳素结构钢的热轧工艺 (Hot rolling process of high-quality carbon structural steel ) 是由 石晨敏 王传森 兰俊 于 2020-05-15 设计创作，主要内容包括：本发明提供了一种优质碳素结构钢的热轧工艺,采用预热、加热、均热、轧制、冷却、精整、检验的工序,控制加热段的温度为1060～1250℃、均热段的温度为1040～1240℃避免加热段以及均热段温度过低而导致轧制力增加、轧机负荷过重,减少了设备损坏的风险；控制终轧温度为900～950℃,使终轧温度接近相变点,加速过冷奥氏体向珠光体+铁素体转变的速率,使优质碳素结构刚的布氏硬度降低,改善后续的冷剪切工艺中容易产生裂纹的现象；控制钢坯成分、冷却方式、卷曲温度等方式,进一步减少碳素结构钢生产过程中边裂现象的发生,控制难度小、可操作性强、方法简单,无需进行控冷工艺的高成本改造,成本低,可适用于各种规格的优质碳素结构钢的生产。(The invention provides a hot rolling process of high-quality carbon structural steel, which adopts the procedures of preheating, heating, soaking, rolling, cooling, finishing and inspection, controls the temperature of a heating section to be 1060-1250 ℃ and the temperature of a soaking section to be 1040-1240 ℃ so as to avoid the increase of rolling force and overload of a rolling mill caused by over-low temperature of the heating section and the soaking section, and reduce the risk of equipment damage; controlling the finish rolling temperature to be 900-950 ℃, enabling the finish rolling temperature to be close to a phase transition point, accelerating the transformation rate of super-cooled austenite to pearlite and ferrite, reducing the Brinell hardness of a high-quality carbon structure steel, and improving the phenomenon that cracks are easy to generate in the subsequent cold shearing process; the method has the advantages of controlling the components of the steel billet, the cooling mode, the curling temperature and other modes, further reducing the edge crack phenomenon in the production process of the carbon structural steel, along with small control difficulty, strong operability, simple method, no need of high-cost modification of a cooling control process, low cost and suitability for the production of high-quality carbon structural steel with various specifications.)

1. The hot rolling process of the high-quality carbon structural steel is characterized by comprising the following steps of:

(1) preheating a high-quality carbon structural steel billet, and controlling the temperature of a preheating section to be less than or equal to 800 ℃;

(2) after preheating, allowing the steel billet to enter a heating section, and controlling the temperature of the heating section to be 1060-1250 ℃;

(3) after heating, the steel billet enters a soaking section, and the temperature of the soaking section is controlled to be 1040-1240 ℃;

(4) rolling a steel billet, wherein the final rolling temperature is controlled to be 900-950 ℃ in the rolling process;

(5) cooling the rolled steel billet;

(6) and finishing and inspecting the steel billet after cooling to finally prepare the high-quality carbon structural steel.

2. The hot rolling process according to claim 1, wherein the high-quality carbon structural steel billet comprises the following chemical components in percentage by weight: c: 0.42 to 0.50%, Si: 0.20 to 0.35%, Mn: 0.10-0.15%, P: 0-0.035%, S: 0-0.035%, Al: 0.005-0.030%, Ti: 0.009-0.015%, Cr: 0.01 to 0.02%, Nb: 0.015-0.019%, and the balance of Fe and inevitable impurities.

3. The hot rolling process according to claim 1, wherein the temperature of the heating section in the step (2) is 1140-1250 ℃; the temperature of the soaking section in the step (3) is 1130-1240 ℃; and (4) controlling the finishing temperature to be 920-940 ℃.

4. The hot rolling process as claimed in claim 1, wherein the heating section is divided into a heating section and a heating section; the temperature of the first heating section is 880-1100 ℃; the temperature of the heating second section is 1060-1250 ℃; the heating time of the heating process is 135-200 min.

5. The hot rolling process of claim 1, wherein the high pressure water descaling is applied to the surface of the slab prior to the slab entering the rolling stage.

6. The hot rolling process according to claim 1, wherein 3 groups of rough rolling mill sets, 2 groups of middle rolling mill sets and 4 groups of finish rolling mill sets are adopted for continuous rolling, the initial rolling temperature is controlled to be 960-980 ℃, the rolling speed is 0.5-3 m/s, the total rolling reduction rate is more than or equal to 30%, and the final rolling reduction rate is less than or equal to 20%; the multiple groups of rough rolling units, the middle rolling units and the finishing rolling units are alternately arranged in a flat-crossed manner.

7. The hot rolling process according to claim 1, wherein the cooling is performed by a water curtain cooling device at a cooling speed of 30-50 ℃/s.

8. The hot rolling process according to claim 1, wherein the finishing comprises coiling the steel slab at a controlled coiling temperature of 500-650 ℃.

Technical Field

The invention relates to the technical field of hot rolled steel, in particular to a hot rolling process of high-quality carbon structural steel.

Background

The carbon steel is an iron-carbon alloy with carbon mass fraction of 0.2-2.06% and containing a small amount of impurities such as Si, Mn, P, S and the like, and can be classified into carbon structural steel, carbon tool steel and carbon cast steel according to the application. The carbon structural steel can be divided into common carbon structural steel and high-quality carbon structural steel according to metallurgical quality. The common carbon structural steel has simple smelting method and contains harmful impurities and nonmetallic inclusions, and the high-quality carbon structural steel refers to carbon steel containing less than 0.8 percent of carbon, less sulfur, phosphorus and nonmetallic inclusions, better uniformity and surface quality and better mechanical property.

At present, in the process of preparing high-quality carbon structural steel, a steel mill can add a trace amount of alloy elements such as Ti, Nb and the like to separate out fine and dispersed carbon and nitrogen compounds, and has good effects on the aspects of grain refinement, precipitation strengthening, recrystallization control and the like, thereby not only effectively improving the strength of the high-quality carbon structural steel, but also improving the ductility and toughness and meeting the requirements of the comprehensive performance of the high-quality carbon structural steel. In order to fully play the roles of grain refinement and precipitation strengthening of alloy elements, a controlled rolling and controlled cooling process is widely adopted in steel mills at present, a cooling bed adopted by a production line is generally a stepping cooling bed, the cooling speed is required to be less than 10 ℃/s so as to ensure that the transformation from austenite to ferrite and pearlite (the structure transformation product of ferrite and pearlite at the temperature of more than 550 ℃) in high-quality carbon structural steel is completely finished in a phase transformation region at the temperature, but a steel billet is required to be rapidly cooled to the coiling temperature condition after finish rolling, the supercooled austenite cannot be transformed to the ferrite and pearlite due to the excessively high cooling speed, an upper bainite structure is generated, the hardness of the upper bainite structure is high, cracks are frequently generated during subsequent cold shearing of the steel billet, and the product performance is influenced, so that the controlled rolling and controlled cooling process can be effectively used for reducing the surface hardness of the high-quality carbon structural, The hot rolling process suitable for producing high-quality carbon structural steel of various specifications is very important.

Disclosure of Invention

The invention aims to provide a hot rolling process of high-quality carbon structural steel, which is used for reducing the surface hardness of a high-quality carbon structural steel billet, improving the problem of billet cracking in cold shearing, avoiding high-cost modification of a controlled cooling process and being suitable for producing high-quality carbon structural steel with various specifications.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a hot rolling process of high-quality carbon structural steel comprises the following steps:

(1) preheating a high-quality carbon structural steel billet, and controlling the temperature of a preheating section to be less than or equal to 800 ℃;

(2) after preheating, allowing the steel billet to enter a heating section, and controlling the temperature of the heating section to be 1060-1250 ℃;

(3) after heating, the steel billet enters a soaking section, and the temperature of the soaking section is controlled to be 1040-1240 ℃;

(4) rolling a steel billet, wherein the final rolling temperature is controlled to be 900-950 ℃ in the rolling process;

(5) cooling the rolled steel billet;

(6) and finishing and inspecting the steel billet after cooling to finally prepare the high-quality carbon structural steel.

Further, the high-quality carbon structural steel billet comprises the following chemical components in percentage by weight: c: 0.42 to 0.50%, Si: 0.20 to 0.35%, Mn: 0.10-0.15%, P: 0-0.035%, S: 0-0.035%, Al: 0.005-0.030%, Ti: 0.009-0.015%, Cr: 0.01 to 0.02%, Nb: 0.015-0.019%, and the balance of Fe and inevitable impurities.

Further, the temperature of the heating section in the step (2) is 1140-1250 ℃; the temperature of the soaking section in the step (3) is 1130-1240 ℃; and (4) controlling the finishing temperature to be 920-940 ℃.

Further, the heating section is divided into a first heating section and a second heating section; the temperature of the first heating section is 880-1100 ℃; the temperature of the heating second section is 1060-1250 ℃; the heating time of the heating process is 135-200 min.

Further, before the billet enters the rolling stage, a high-pressure water descaling procedure needs to be carried out on the surface of the billet.

Further, the rolling is performed by adopting 3 groups of rough rolling units, 2 groups of middle rolling units and 4 groups of finish rolling units, the initial rolling temperature is controlled to be 960-980 ℃, the rolling speed is 0.5-3 m/s, the total rolling reduction rate is more than or equal to 30%, and the final pass reduction rate is less than or equal to 20%; the multiple groups of rough rolling units, the middle rolling units and the finishing rolling units are arranged in a flat-crossed alternative mode.

Further, a water curtain cooling device is adopted for cooling, and the cooling speed is 30-50 ℃/s.

Further, the finishing comprises the step of curling the steel billet, and the curling temperature is controlled to be 500-650 ℃.

The invention has the beneficial effects that:

1. according to the invention, the temperature of the heating section and the temperature of the soaking section are controlled to prevent austenite grains from coarsening, so that the conditions that the rolling force is increased and the load of a rolling mill is too heavy due to too low temperature of the heating section and the temperature of the soaking section are avoided, and the risk of equipment damage is reduced; the finish rolling temperature of the rolling process is controlled to be close to the phase transition point, the phase transition is induced by thermal deformation, the phase transition temperature is increased, the incubation period is shortened, the transformation rate of super-cooled austenite to pearlite + ferrite is accelerated, the rolled steel structure is ensured to be pearlite + ferrite, the Brinell hardness of the high-quality carbon structure steel is reduced, the Brinell hardness is reduced from about 217HBW to about 172HBW, and the phenomenon that cracks are easily generated in the subsequent cold shearing process is improved.

2. The method further reduces the occurrence of edge cracking in the production process of the carbon structural steel by controlling the components of the steel billet, the cooling mode, the curling temperature and the like, has small control difficulty, strong operability, simple method, no need of high-cost transformation of a cooling control process and low cost, and is suitable for producing high-quality carbon structural steel with various specifications.

Drawings

FIG. 1 is a flow chart of a hot rolling process of the high-quality carbon structural steel.

Detailed Description

The invention will be described in further detail below with reference to the drawings, but the scope of the invention is not limited thereto.

The invention provides a hot rolling process of high-quality carbon structural steel, which comprises a heating process and a rolling process, wherein the heating process comprises a heating section and a soaking section; the Brinell hardness of the high-quality carbon structural steel is reduced by controlling the temperature of the heating section to be 1060-1250 ℃, controlling the temperature of the soaking section to be 1040-1240 ℃ and controlling the finish rolling temperature of the rolling process to be 900-950 ℃.