阅读说明：本技术 一种含Nb低合金钢轧制工艺 (Nb-containing low alloy steel rolling process ) 是由 杨云清 郭龙鑫 关秀格 郭恩元 郭延生 陈科晓 庞洪轩 陈建超 郑磊 付中原 左 于 2020-05-14 设计创作，主要内容包括：本发明涉及一种含Nb低合金钢轧制工艺,其化学成分质量百分比为：C=0.17-0.19,Si=0.20-0.40,Mn=0.55-0.65,P≤0.020,S≤0.020,Al=0.003-0.020,Nb=0.008-0.010,CEV≤0.30,其余为Fe和不可避免的杂质元素。轧制工艺包括以下步骤：一、炼钢工序生产合格的板坯；二、将步骤一的板坯采用高温直接加热；三、将步骤二加热后的板坯进行粗轧和精轧；四、对步骤三轧制后的钢板进行冷却。本发明克服已有技术存在的不足,满足低成本低合金钢板轧钢生产的需要；简化部分工序及减少Nb合金含量,降低生产成本。(The invention relates to a rolling process of low alloy steel containing Nb, which comprises the following chemical components in percentage by mass: c =0.17-0.19, Si =0.20-0.40, Mn =0.55-0.65, P ≤ 0.020, S ≤ 0.020, Al =0.003-0.020, Nb =0.008-0.010, CEV ≤ 0.30, and the balance of Fe and unavoidable impurity elements. The rolling process comprises the following steps: firstly, producing qualified plate blanks in a steelmaking process; secondly, directly heating the plate blank in the first step at a high temperature; thirdly, performing rough rolling and finish rolling on the plate blank heated in the second step; fourthly, cooling the steel plate rolled in the third step. The invention overcomes the defects of the prior art and meets the requirements of low-cost and low-alloy steel plate steel rolling production; simplifies part of working procedures, reduces the content of Nb alloy and reduces the production cost.)

1. A rolling process of low alloy steel containing Nb is characterized in that: the steel comprises the following chemical components in percentage by mass: c =0.17-0.19, Si =0.20-0.40, Mn =0.55-0.65, P is less than or equal to 0.020, S is less than or equal to 0.020, Al =0.003-0.020, Nb =0.008-0.010, CEV is less than or equal to 0.30, and the balance is Fe and unavoidable impurity elements; the rolling process comprises the following steps:

firstly, producing qualified plate blanks in a steelmaking process;

secondly, directly heating the plate blank in the first step at a high temperature;

thirdly, performing rough rolling and finish rolling on the plate blank heated in the second step; the rough rolling reduction specification is compiled into the maximum pass reduction, the maximum pass reduction rate is more than 20 percent, the initial rolling temperature of rough rolling is 1150-1170 ℃, and the final rolling temperature is 970-1000 ℃; the accumulated reduction rate of finish rolling is more than 60 percent, the reduction rate of the last three passes is more than 16 percent, and the finish rolling temperature is 900-;

fourthly, cooling the steel plate rolled in the third step.

2. The Nb-containing low alloy steel rolling process according to claim 1, characterized in that: in the second step, the heating is divided into three heating sections, a soaking section and a furnace discharge, wherein the temperature of the heating section is 1240 ℃ for 1200-.

3. The Nb-containing low alloy steel rolling process according to claim 1, characterized in that: and step three, rough rolling is rapid rolling.

4. The Nb-containing low alloy steel rolling process according to claim 1, characterized in that: the cooling mode of the fourth step is ultra-fast cooling and strong cooling, the opening cooling temperature is 900-.

Technical Field

The invention relates to a rolling process of low alloy steel containing Nb, belonging to the technical field of steel making.

Background

The Q355 and Q235 series steel is the most abundant in practical use at present, and particularly, a low alloy steel Q355 series (Q345 series in original GB/T1591-2008) steel mill produces qualified products by using Ti and Nb microalloying in production and assisting a proper rolling process, so that the production cost is greatly reduced.

The main process of rolling the Nb-containing steel is completed by basic processes of heating, rough rolling, finish rolling, controlled cooling and the like.

The data show that the content of niobium dissolved in austenite of the low-alloy carbon manganese steel containing 0.039% of niobium increases along with the increase of temperature. When the coarsening temperature is lower than the coarsening temperature, the niobium-containing second phase particles can effectively prevent the crystal grains from growing; slightly above the coarsening temperature, the second phase particles lose their inhibitory effect on the growth of a portion of the grains, resulting in the appearance of mixed crystals. The inventors have studied the precipitation and solid solution contents of Nb in C — Mn — Nb steels containing 0.020% to 0.040% of niobium at different heating temperatures, and the results are shown in table 1.

TABLE 1 precipitation amount and solid solution amount (%)

The test results in the table show that: the amount of Nb (C, N) in the steel below 900 ℃ is substantially equivalent to the original as-rolled content, while at temperatures above 900 ℃ Nb (C, N) begins to dissolve in small amounts as the temperature increases, and after a temperature above 990 ℃ Nb (C, N) in the steel begins to dissolve in large amounts and Nb (C, N) is sufficiently dissolved into the steel. In C-Mn-Nb steel, the Nb (C, N) precipitate phase in the steel is substantially completely dissolved (about 95%) at 1150 ℃ and dissolved in the steel.

Analysis of the rolling process for Nb-containing low alloy steel in table 1 reveals that: the precipitation amount of Nb at 1150-900 ℃ is almost 52% (94.44-41.66%), and the precipitation amount at 900-840 ℃ is only 5% (41.66-36.11%), so that the precipitation of Nb is in the high-temperature rolling process. The controlled rolling is to form a large amount of deformation zones in a recrystallization zone, 5 percent of Nb (C, N) is formed to precipitate in the deformation zones, and the Nb is changed into a phase change core in the controlled cooling process, so that crystal grains are refined, and the strength and the toughness of the material are improved.

From the foregoing analysis of the Nb solid solution behavior in the steel, it is found that the precipitation amount of Nb (C, N) in the steel is reduced with the increase in the cooling rate, but the relative reduction amount is not large, and thus it appears that the precipitation amount of Nb (C, N) is not significantly increased by the intensive cooling from the precipitation amount of Nb (C, N) alone in the controlled rolling and controlled cooling process, and it is seen that a large amount of Nb (C, N) precipitation occurs under the strain induction of the controlled rolling. Therefore, the research of the controlled rolling process containing Nb is particularly important. The actual production of the Wu steel ship plate is described by data, high-temperature large reduction is adopted in a few passes before controlled rolling of a high-temperature recrystallization zone, the pass reduction is 15-20mm, and the accumulated deformation is more than 60%; the initial rolling temperature is 1150 ℃, and the final rolling temperature is over 980 ℃. About 5% of the Nb (C, N) remains undissolved in the austenite, and this portion of undissolved Nb (C, N) particles prevents the austenite grains from growing large when heated and refines the austenite grains when heated. The rough rolling and the controlled rolling are carried out in a recrystallization zone, and austenite grains are refined in the repeated deformation and recrystallization processes of austenite. And after rough rolling, cooling to 950 ℃ and finishing. The reduction rate of the finish rolling pass is more than 10 percent. The Nb-containing low carbon steel increases the recrystallization temperature to 900-950 ℃. The finish rolling is therefore carried out in the zone of no recrystallization (or of little recrystallization) and consequently deformed austenite is obtained. Due to the deformation induction precipitation of Nb (C, N), the growth of deformed austenite grains is inhibited, a large amount of deformation zones are formed in the deformation process of austenite, nucleation points during gamma → alpha transformation are increased, the gamma → alpha phase transformation refining effect is enhanced, the alpha grains are refined, the steel has high strength and toughness, and meanwhile, the dislocation density in the steel is high.

Chinese patent application numbers 201110041266.7, 201110041878.6, 201110041280.7 and 201110041881.8 are all 'production methods of hot rolled steel coils', and disclose production technologies of Q345B, Q345C, Q345D and Q345E low alloy steel plates respectively. The hot rolled steel coil with the thickness range of less than 16mm is different from a single-piece rolled medium-thickness steel plate. The composition is as shown in Table 2.

Table 2 design range of composition of steel coil in prior art patent (%)

Chinese patent application numbers 201210432438.8, 201210432232.5, 201210432525.3 and 201210432521.5 "a production method of low-alloy medium-thickness steel plates", respectively disclose production technologies of Q345B, Q345C, Q345D and Q345E low-alloy steel plates. The steel comprises the following components in percentage by mass: 0.17-0.19% of C, 0.20-0.40% of Si, 0.55-0.65% of Mn, less than or equal to 0.020% of P, less than or equal to 0.020% of S, 0.003-0.010% of Al, 0.014-0.016% of Nb, less than or equal to 0.30% of CEV, and the balance of Fe and inevitable impurity elements. The production process of the steel plate is TMCP, namely controlled rolling plus ACC.

The 8 patent technologies are applied in production, and the performance of the produced Nb-containing low alloy steel meets the standard requirement. In 2017, the physical requirements of users on the steel plate are improved, the technology has some problems, and some steel mills gradually recover high Mn components to cause cost increase.

Disclosure of Invention

The invention aims to provide a Nb-containing low alloy steel rolling process, in particular to a rolling process for producing a Nb-containing Q355 series low alloy steel plate with the thickness of 10-40 mm, overcomes the defects of the prior art, and meets the requirements of low-cost low alloy steel plate steel rolling production; simplifies part of working procedures, reduces the content of Nb alloy and reduces the production cost.

In order to achieve the purpose, the invention adopts the technical scheme that:

a rolling process of low alloy steel containing Nb comprises the following chemical components in percentage by mass: 0.17-0.19% of C, 0.20-0.40% of Si, 0.55-0.65% of Mn, less than or equal to 0.020% of P, less than or equal to 0.020% of S, 0.003-0.020% of Al, 0.008-0.010% of Nb, less than or equal to 0.30% of CEV, and the balance of Fe and inevitable impurity elements; the rolling process comprises the following steps:

firstly, producing qualified plate blanks in a steelmaking process;

secondly, directly heating the plate blank in the first step at a high temperature;

thirdly, performing rough rolling and finish rolling on the plate blank heated in the second step; the rough rolling reduction specification is compiled into the maximum pass reduction, the maximum pass reduction rate is more than 20 percent, the initial rolling temperature of rough rolling is 1150-1170 ℃, and the final rolling temperature is 970-1000 ℃; the accumulated reduction rate of finish rolling is more than 60 percent, the reduction rate of the last three passes is more than 16 percent, and the finish rolling temperature is 900-;

fourthly, cooling the plate blank rolled in the third step.

The technical scheme of the invention is further improved as follows: in the second step, the heating is divided into three heating sections, a soaking section and a furnace discharge, wherein the temperature of the heating section is 1240 ℃ for 1200-.

The technical scheme of the invention is further improved as follows: and step three, rough rolling is rapid rolling.

The technical scheme of the invention is further improved as follows: the cooling mode of the fourth step is ultra-fast cooling and strong cooling, the opening cooling temperature is 900-.

Due to the adoption of the technical scheme, the invention has the following technical effects:

the Q355B steel plate produced by the process completely meets the requirements of GB/T1591-2018, the CEV of the steel plate is below 0.30%, and the steel plate has good welding performance. The yield strength and the tensile strength have larger margins, and the elongation and the impact toughness are equivalent to those of the steel plate produced by the original TMCP process.

The invention applies a Nb-containing low alloy steel rolling process, and the Nb-containing low alloy steel with high performance and good welding performance is produced by the process. Compared with the prior art, the invention has the following advantages: the high-temperature hot rolling reduces the load of the rolling mill, cancels the temperature control of the intermediate billet and improves the hourly output of the rolling mill; the high-temperature hot-rolled sheet has good plate shape; air cooling is started near the Ar3 temperature, the plasticity of the steel plate is well matched, the steel plate does not generate drift, and off-line stacking slow cooling is cancelled; the internal stress of the steel plate is small, and a user does not warp after cutting, so that quality objections are reduced; the load of high-temperature steel plate straightening equipment is small, and the maintenance cost of a straightening machine is greatly reduced; the steel plate starts to be air-cooled at high temperature, and the performance fluctuation range of the steel plate is small; the content of Nb alloy is reduced, and the production cost is reduced.

Drawings

FIG. 1 is a graph of a process of the present invention;

FIG. 2 is a metallographic structure diagram of a Nb-containing low alloy steel Q355B according to the invention.

Detailed Description

The invention is described in further detail below with reference to the following figures and specific embodiments:

the invention discloses a rolling process of Nb-containing low-alloy steel, aiming at meeting the requirements of low-cost low-alloy steel plate steel rolling production; simplifies part of working procedures, reduces the content of Nb alloy and reduces the production cost. The steel comprises the following chemical components in percentage by mass: 0.17-0.19% of C, 0.20-0.40% of Si, 0.55-0.65% of Mn, less than or equal to 0.020% of P, less than or equal to 0.020% of S, 0.003-0.020% of Al, 0.008-0.010% of Nb, less than or equal to 0.30% of CEV, and the balance of Fe and inevitable impurity elements; as shown in fig. 1, the rolling process includes the following steps:

firstly, producing qualified plate blanks in a steelmaking process;

secondly, directly heating the plate blank in the first step at high temperature, wherein the heating is divided into three heating sections, a soaking section and a furnace discharge, the temperature of the heating section is 1200-1240 ℃, the temperature of the soaking section is 1180-1220 ℃, the temperature of the furnace discharge center is 1170-1190 ℃, the heating speed is 6-8min/cm, and the total furnace time is 3-5 h;

thirdly, performing rapid rough rolling and finish rolling on the plate blank heated in the second step; the rough rolling reduction specification is compiled into the maximum pass reduction, the maximum pass reduction rate is more than 20 percent, the initial rolling temperature of rough rolling is 1150-1170 ℃, and the final rolling temperature is 970-1000 ℃; the accumulated reduction rate of finish rolling is more than 60 percent, the reduction rate of the last three passes is more than 16 percent, and the finish rolling temperature is 900-;

fourthly, performing ultra-fast cold forced cooling on the plate blank rolled in the third step, wherein the cooling temperature is 900-. The metallographic structure of the obtained product was observed by a microscope as shown in FIG. 2.

The invention will be further described with reference to the example of producing the Q355B steel plate. .

The steelmaking process produces a qualified slab with a section of 320X2000 with Q355B, and the steel components are in percentage by mass as shown in Table 3.

Table 3 example Q355B steel billet composition (%)

Composition (I)

C

Si

Mn

P

S

AlT

Nb

Internal control assembly

0.17～0.19

0.20～0.40

0.55～0.65

≤0.020

≤0.020

0.003～0.020

0.008～0.012

Actual composition

0.18

0.35

0.62

0.018

0.016

0.008

0.010