阅读说明：本技术 一种管线钢自回火提升强度的方法 (Method for improving strength of pipeline steel through self tempering ) 是由 叶俊文 于 2021-07-01 设计创作，主要内容包括：本申请公开了一种管线钢自回火提升强度的方法,工艺流程为：加热、TMCP轧制、冷却、矫直、温矫矫直、精整剪切；TMCP轧制阶段采用2阶段轧制,分别为再结晶区和非再结晶区轧制；TMCP轧制阶段终轧温度控制在750-800℃,减少先共析铁素体析出；冷却到300-400℃,以350℃为目标实现350℃自回火；温度冷到300℃以下,会造成碳化物析出少,造成屈服强度低,抗拉强度高,通过轧钢控制冷却到350℃左右,在350℃空冷缓慢冷却,可以析出碳化物,提高屈服强度,相当于采用热处理回火的效果；均匀管线钢钢板的整体组织及性能,在轧制生产过程中提升屈服强度,减少了屈服强度不足时添加合金成分和热处理回火挽救的费用。(The application discloses a method for improving strength of pipeline steel through self tempering, which comprises the following process flows of: heating, TMCP rolling, cooling, straightening, temperature straightening, finishing and shearing; the TMCP rolling stage adopts 2-stage rolling, namely rolling in a recrystallization region and a non-recrystallization region respectively; the final rolling temperature in the TMCP rolling stage is controlled at 750-; cooling to 400 ℃ at 300 ℃ to realize 350 ℃ self-tempering by taking 350 ℃ as a target; the cooling to below 300 ℃ causes little carbide precipitation, low yield strength and high tensile strength, the steel is controlled to be cooled to about 350 ℃ through steel rolling, the steel is slowly cooled in air at 350 ℃ to precipitate the carbide, the yield strength is improved, and the effect of tempering by heat treatment is equivalent to the effect of tempering by adopting heat treatment; the overall structure and performance of the steel plate of the pipeline steel are uniform, the yield strength is improved in the rolling production process, and the cost of adding alloy components and heat treatment tempering rescue when the yield strength is insufficient is reduced.)

1. A method for improving the strength of pipeline steel by self tempering is characterized in that: the method for improving the strength of the pipeline steel by self tempering comprises the following process flows: heating, TMCP rolling, cooling, straightening, temperature straightening, finishing and shearing; the TMCP rolling process adopts controlled rolling and controlled cooling, and achieves the performance equivalent to heat treatment tempering by accurately controlling the final cooling temperature to 350-400 ℃ and then performing air cooling on a cooling bed.

2. The method for improving the strength of the pipeline steel by self tempering according to claim 1, wherein the method comprises the following steps: the method for improving the self-tempering strength of the pipeline steel is realized by optimizing TMCP rolling, and specifically comprises the steps of directly cooling a rolled steel plate from 800 ℃ of 750-.

3. The method for improving the strength of the pipeline steel by self-tempering according to claim 2, wherein the TMCP rolling comprises the following specific steps:

the first step is as follows: the TMCP rolling stage adopts 2-stage rolling, namely rolling in a recrystallization region and a non-recrystallization region respectively;

the second step is that: the final rolling temperature in the TMCP rolling stage is controlled at 750-;

the third step: and (3) carrying out water cooling to 350-400 ℃ by adopting ACC (aluminum chloride), and realizing 350 ℃ self-tempering by taking 350 ℃ as a target.

4. The method for improving the strength of the pipeline steel by self tempering according to claim 1, wherein the method comprises the following steps: the heating adopts a stepping heating furnace.

5. The method for improving the strength of the pipeline steel by self tempering according to claim 4, wherein the method comprises the following steps: the heating stage is specifically heating to 1160-1200 ℃ by adopting a stepping heating furnace.

Technical Field

The invention belongs to the technical field of self-tempering of pipeline steel, and particularly relates to a method for improving strength of the pipeline steel through self-tempering.

Background

The pipeline steel plate is a special material, and has strict performance requirements due to complex use background and high reliability requirements. Compared with other steel grades, the pipeline steel has upper and lower limit requirements on tensile strength and yield strength, and API 5L has strict requirements on yield ratio, impact toughness and drop weight crack arrest performance, so the production difficulty is very high.

30 ten thousand tons of pipeline steel are produced in a sand steel wide and thick plate workshop every year, and the pipeline steel is difficult to produce, so that quality problems generated every year are more, and great waste is caused. Through research, cooling is absolutely one of the most main causes of quality fluctuation of pipeline steel. The amount of cooling water required by the laminar flow rapid cooling process adopted in the production process of pipeline steel is large, the change of water temperature and air temperature has great influence on the steel plate with the cooling amplitude of more than 400 ℃, and slight change can cause great fluctuation of the cooling temperature. For pipeline steels, fluctuations in cooling amplitude at 30 ℃ result in completely different yield strength properties.

Chinese patent CN202011333308.X discloses a preparation method of 15MnNiNbDR steel plate for ultra-low temperature storage tank, which is characterized in that through normalizing, slow cooling self-tempering and simulated postweld heat treatment, the precipitation proportion of carbide in steel is about 50%, the reserve energy before simulated welding is large, and the qualified simulated postweld heat treatment performance of the steel plate can be ensured; the steel plate is cooled to 480-. But considering that the 500 ℃ self-tempering is carried out through the slow cooling pit to improve the performance after the simulated postweld heat treatment, the method realizes the self-tempering strength improvement of the low-carbon pipeline steel).

Chinese patent CN202011417523.8 discloses a method for controlling yield strength fluctuation of 420 MPa-level hot-galvanized high-strength steel, which comprises the following steps of self-tempering and slow cooling, placing a hot-rolled coil in a sealed box for slow cooling for 40-48h within 20min after the hot-rolled coil is coiled, promoting the temperature of a coiled core corresponding to a belt head part and the temperature of an outer ring steel plate corresponding to a belt tail part to be increased by utilizing the diffusion of the internal temperature of the hot-rolled coil, promoting the uniform transformation of the through-coil structure of the hot-rolled coil, and enabling 420 MPa-level hot-galvanized products to obtain the through-coil uniform structure and two-phase particle precipitation, wherein the through-coil performance of the products is stable, and the yield strength fluctuation is not more than 20 MPa. But considering that the self-tempering in a sealed box is adopted on the hot coil plate, the method is applied to medium plate pipeline steel, and the specific realization temperature is available).

Chinese patent CN202010270763.3 discloses a cooling method after rolling for improving Rockwell hardness of a steel section, which adopts a pile cooling self-tempering method, namely a plurality of steel materials are piled together to be air-cooled and self-tempered, and when the temperature of a steel billet is less than or equal to 200 ℃, the steel billet is separated to obtain the steel which is non-quenched and tempered steel for direct cutting. The steel has no phase change below 200 ℃ and is not influenced by other factors. And (5) placing the steel materials in a wind-sheltering position for stacking, and naturally cooling. However, the prior art is slightly deficient in view of heat treating a steel slab.

Chinese patent CN202011210520.7 discloses a method for producing a high-toughness, low-stress and high-strength steel plate, which has large structural stress caused by structural change after quenching, and needs to be tempered to eliminate internal stress. The secondary tempering is self-tempering, and internal stress of the structure is eliminated through self-tempering treatment. After the graded tempering treatment, uniform and fine tempered sorbite structure is obtained, the tempered sorbite structure is a mixture of ferrite and granular carbide, the ferrite has basically no carbon supersaturation, the carbide is also stable carbide, and the tempered sorbite structure is a balanced structure at normal temperature. The tissue has good toughness and plasticity and high strength, so that the tissue has good comprehensive mechanical properties. By adopting the graded tempering process, the stress can be released, the toughness can be increased, and the strength can be adjusted. However, the prior art is slightly deficient in consideration of (heat-treated steel sheet, we do not adopt heat treatment to realize heat treatment performance, and cost is saved).

Disclosure of Invention

The technical problem to be solved is as follows: the application mainly provides a method for improving the strength of pipeline steel by self tempering, and solves the technical problems that the yield strength is not enough in the production process of the pipeline steel and the like in the prior art; by the method, when the pipeline steel has the problem of low yield strength, the yield strength is improved in the rolling production process without heat treatment tempering, and the cost for adding alloy components and heat treatment tempering rescue when the yield strength is insufficient is reduced.

The technical scheme is as follows:

a method for improving the strength of pipeline steel by self tempering comprises the following process flows: heating, TMCP rolling, cooling, straightening, temperature straightening, finishing and shearing; the TMCP rolling process adopts controlled rolling and controlled cooling, and achieves the performance equivalent to heat treatment tempering by accurately controlling the final cooling temperature to 350-400 ℃ and then performing air cooling on a cooling bed.

As a preferred technical scheme of the invention: the method for improving the self-tempering strength of the pipeline steel is realized by optimizing TMCP rolling, and specifically comprises the steps of directly cooling a rolled steel plate from 800 ℃ of 750-.

As a preferred technical scheme of the invention: the method for improving the strength of the pipeline steel by self tempering comprises the following steps of:

the first step is as follows: the TMCP rolling stage adopts 2-stage rolling, namely rolling in a recrystallization region and a non-recrystallization region respectively;

the second step is that: the final rolling temperature in the TMCP rolling stage is controlled at 750-;

the third step: and (3) carrying out water cooling to 350-400 ℃ by adopting ACC (aluminum chloride), and realizing 350 ℃ self-tempering by taking 350 ℃ as a target.

As a preferred technical scheme of the invention: the heating adopts a stepping heating furnace.

As a preferred technical scheme of the invention: the heating stage is specifically heating to 1160-1200 ℃ by adopting a stepping heating furnace.

Has the advantages that: compared with the prior art, the method for improving the strength of the pipeline steel through self tempering has the following technical effects:

1. by the method, when the pipeline steel has a low yield strength, the yield strength can be improved in the rolling production process without heat treatment tempering, and the cost for saving by adding alloy components and heat treatment tempering when the yield strength is insufficient is reduced.

2. The method for improving the yield strength and the performance uniformity of the steel plate by the self-tempering of the wide and thick pipe line steel can replace the heat treatment tempering by the self-tempering method, improve the yield strength and the performance uniformity of the steel plate, and solve the problem of abnormal fluctuation of the performance detection performance of the pipe line steel caused by uneven performance.

3. The self-tempering method is equivalent to heat treatment tempering, the overall performance of the pipeline steel plate is uniform, and the problems that the rolled steel plate is uneven in strength, high in tensile strength and low in yield strength and is easy to cause the problem that the standard judgment is not met are solved. Meanwhile, the problem that the uniformity of the performance of the pipeline steel plate at different positions is greatly different is improved by tempering.

4. Heat treatment and tempering are not needed, so that the uniform structure is achieved, the performance uniformity is improved, and the problem of large performance fluctuation is reduced; due to the fact that the structural uniformity of the steel plate is relatively poor in the rolling and cooling processes, the problems of high tensile strength, low yield and the like can be solved, and the problem can be greatly improved due to the fact that carbide is separated out in the tempering process through the self-tempering method.

5. The carbon in the hard phase ferrite can not be separated out when the temperature is cooled to below 300 ℃, the yield strength is low, the tensile strength is high, the carbon can be separated out through self tempering at 350 ℃, the yield strength is improved, the tensile strength is reduced, the effect is equivalent to the effect of adopting heat treatment tempering, the effect is similar to that of adopting heat treatment tempering, and the heat treatment cost is saved by about 200 yuan/ton.

6. The heating is carried out by adopting a stepping heating furnace to 1160-1200 ℃ so as to fully dissolve the Nb compound, but the Nb compound does not grow rapidly due to the characteristics of the Nb compound.

Detailed Description

The invention is further illustrated by the following examples: the invention will be better understood from the following examples. However, those skilled in the art will readily appreciate that the specific process conditions and results described in the examples are merely illustrative of the invention and should not, nor should they, limit the invention as detailed in the claims.

Examples

A method for improving the strength of pipeline steel by self tempering comprises the following process flows: heating, TMCP rolling, cooling, straightening by temperature straightening, finishing and shearing.

The TMCP rolling stages of the X70M and X80M pipeline steel adopt 2-stage rolling to refine grains, namely rolling in a recrystallization region and a non-recrystallization region respectively, the finishing temperature in the TMCP rolling stage is 750-800 ℃, and the precipitation of proeutectoid ferrite is reduced, so that the pipeline steel with an acicular ferrite structure is obtained.

The purposes of replacing alloy to reduce cost and improve strength are achieved by ACC high-speed cooling at the cooling temperature of 300-400 ℃, water is the alloy with the lowest price in the production of the steel plate, the water is good in utilization, the effect of improving the performance of the alloy can be achieved, the alloy is equivalent to the alloy, but the cost is almost ignored, and the alloy cost is high. In the high-speed cooling process, the high-amplitude cooling easily causes the too high strength of the hard phase and the low strength of the soft phase, so that the macroscopic structure causes high tensile strength and low yield strength, and the steel plate can generate violent change of plate shape in the violent cooling process to cause water aggregation, so the performance uniformity is poor. The customer will have different performance results from the steelworks tests. When the pipeline steel plate is used for manufacturing the pipe, the roundness is uneven due to poor performance uniformity and overlarge deviation of tensile strength and yield strength during pipe manufacturing, and the bulge problem is caused during water pressure testing.

The steel plate realizes self-tempering in 350-plus-400 ℃ natural cooling, which is equivalent to heat treatment tempering, saves 200 yuan per ton of steel cost, realizes carbon diffusion, reduces tensile strength, improves yield strength, homogenizes structure and improves the performance uniformity of the whole plate.

The steel plate is cooled by stacking, and can be not used, whether the strength performance after self tempering meets the standard or not is specifically seen, whether the uniformity meets the expectation or not is judged, and if not, the stacking cooling effect is better.

The method for improving the strength of the pipeline steel by self tempering comprises the following steps of:

the first step is as follows: the TMCP rolling stage adopts 2-stage rolling, namely rolling in a recrystallization region and a non-recrystallization region respectively;

the second step is that: the final rolling temperature in the TMCP rolling stage is controlled at 750-;

the third step: and (3) carrying out water cooling to 350-400 ℃ by adopting ACC (aluminum chloride), and realizing 350 ℃ self-tempering by taking 350 ℃ as a target.

The implementation result shows that the invention is greatly debugged and verified to solve the problems in the production process, the performance difference of the same plate is small after being verified, the invention is applied to various pipeline steel such as X70M, X80M and the like, the problems that the tensile strength is high, the yield strength is low and the like do not meet the standard are solved, the uniformity of the performance of the whole plate is obviously improved, and the performance difference between different plates is small after being verified.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to cover the technical scope of the present invention, and the equivalent replacement or modification of the inventive concept according to the technical solution of the present invention within the technical scope of the present invention.