CN111621716B - Nb-containing low alloy steel rolling process - Google Patents
Nb-containing low alloy steel rolling process Download PDFInfo
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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Abstract
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.
Description
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.
The low-alloy medium and heavy plate produced by the TMCP process in the prior art has the main defects that: the steel plate has low yield strength due to low finish rolling temperature of the steel plate; the sheet finishing temperature is low, the plate shape is difficult to control, and a large amount of rolling waste products are caused; the temperature of the intermediate billet is controlled, and the hourly output of the rolling mill is low; the ACC cooling speed is high, the temperature of red return is low, and the steel plate generates granular bainite structures, so that the elongation rate of the steel plate is unqualified; after the steel plate is straightened out of the ACC, bainite phase change on the surface of the steel plate generates deformation and floats when a cooling bed is carried out; the steel plate has large dislocation density and large thermal stress to cause large internal stress, warpage is generated after cutting processing, and some methods adopt off-line heap cooling to cause complex production procedures and increased cost; the temperature of the straightening steel plate is low, and spare parts of the straightening machine are more in loss; the shape of the steel plate and the warping after cutting generate a large amount of quality objections; many steel mills recover high Mn components to avoid the above problems, resulting in increased costs.
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 steel plate 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, carrying out ultra-fast cold forced cooling on the steel plate 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 |
Example 1
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 high temperature, wherein the charging temperature is 650 ℃, the heating is divided into three heating sections, a soaking section and discharging, the temperature of the heating sections is 1240 ℃, the temperature of the soaking section is 1220 ℃, the temperature of the discharging core is 1190 ℃, the heating speed is 7min/cm, and the total in-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 1170 ℃, and the final rolling temperature is 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 final rolling temperature is 940 ℃;
fourthly, carrying out ultra-fast cold forced cooling on the steel plate rolled in the third step, cooling to 790 ℃ at the opening temperature of 920 ℃ and the cooling speed of 10 ℃/s, and then carrying out air cooling;
fifthly, performance test of the rolled steel plate with the thickness of 40 mm: the yield strength is 378MPa, the tensile strength is 534MPa, the elongation is 30 percent, the cold bending is qualified, and the normal-temperature average impact energy is 258J.
Example 2
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 high temperature, wherein the charging temperature is 640 ℃, the heating is divided into three heating sections, a soaking section and discharging, the temperature of the heating section is 1200 ℃, the temperature of the soaking section is 1180 ℃, the temperature of the discharging core is 1170 ℃, the heating speed is 6min/cm, and the total in-furnace time is 4.5 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 ℃, and the final rolling temperature is 970 ℃; 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 920 ℃;
fourthly, carrying out ultra-fast cold forced cooling on the steel plate rolled in the third step, cooling to 780 ℃ at the opening temperature of 905 ℃ and the cooling speed of 5 ℃/s, and then carrying out air cooling;
fifthly, testing the performance of the rolled steel plate with the thickness of 10 mm: the yield strength 397MPa, the tensile strength 547MPa, the elongation 33 percent, the cold bending qualification and the normal-temperature average impact energy 143J (7.5mm samples).
Example 3
The rolling process comprises the following steps:
firstly, producing qualified plate blanks in a steelmaking process;
directly heating the plate blank in the step one at high temperature, wherein the charging temperature is 630 ℃, the heating is divided into three heating sections, a soaking section and discharging, the temperature of the heating section is 1220 ℃, the temperature of the soaking section is 1200 ℃, the temperature of the discharging core is 1180 ℃, the heating speed is 8min/cm, and the total in-furnace time is 4 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 1160 ℃, and the final rolling temperature is 980 ℃; 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 925 ℃;
fourthly, carrying out ultra-fast cold forced cooling on the steel plate rolled in the third step, cooling to 800 ℃ at the start-cooling temperature of 915 ℃ at the cooling speed of 8 ℃/s, and then carrying out air cooling;
fifthly, performance test of the rolled steel plate with the thickness of 20 mm: the yield strength is 386MPa, the tensile strength is 525MPa, the elongation is 32 percent, the cold bending is qualified, and the normal-temperature average impact energy is 264J.
The tensile property performance and the longitudinal impact property performance of the steel sheets produced in the above embodiments are shown in tables 4 and 5.
TABLE 4 tensile Property Performance of the Steel sheets
TABLE 5 actual performance of 20 ℃ longitudinal impact performance of steel plate
As can be seen from tables 3 and 5, 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 submerged arc welding test is carried out on the Q355B plate produced by the new process, and the result shows that the Q355B plate produced by the new process is welded under the condition that the heat input is 50kJ/cm, the tensile property, the bending property and the impact property of a welding joint are good, and the standard requirements can be met.
The technical principle of the invention is as follows: the invention has the rolling process characteristics of high-temperature austenite fine grain preparation and critical normalizing, all steel rolling production lines can be realized, and the produced Nb-containing low alloy steel has the structure of (F + P). The technical principle is that Nb microalloying treatment is applied, high-temperature rapid reciprocating rolling in a recrystallization zone is used for refining austenite grains, a large amount (more than 52%) of Nb (C, N) is used for pinning austenite grain boundaries, growth of high-temperature austenite grains is inhibited, and a high-temperature austenite single-phase zone is subjected to ultra-rapid cooling to retain a high-temperature refining effect; air cooling is started at the critical temperature of Ar3(Ar3 temperature is about 778 ℃) to form a (P + F) similar balanced structure with extremely fine grains, so that the dislocation density of the steel plate is reduced, the strength and toughness matching of the steel plate are maintained, and the requirement of the steel plate on the strength after rolling mutagenesis precipitation is cancelled is met; the low yield strength of the steel plate caused by low finishing temperature and low water inlet temperature of the thin plate is avoided; the sheet profile is well controlled, and rolling waste products are reduced; granular bainite cannot be generated after the steel plate is air-cooled, and the elongation of the steel plate is high; the high-temperature air cooling process has the advantages that the steel plate is not bent, the internal stress of the steel plate is small, the steel plate is not warped after being cut and processed, and an off-line heap cooling procedure is cancelled; the content of Nb alloy is reduced, and the production cost is reduced.
The embodiments of the present invention are preferred embodiments of the present invention, and the scope of the present invention is not limited by these embodiments, so: all equivalent changes made according to the structure, shape, principle and the like of the invention are covered by the protection scope of the invention.
The ranges for each component of the present invention include any combination of any lower limit and any upper limit mentioned in the specification, and also include any range where the particular amount of the component in each particular embodiment constitutes a combination of the upper or lower limits: all such ranges are intended to be included within the scope of the present invention for brevity and clarity only and are not intended to be exhaustive or to limit the scope of the invention to the precise forms disclosed. Each feature of the invention described in this specification may be combined with any other feature of the invention which combination is not specifically disclosed in the specification for the sake of brevity.
Claims (3)
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, wherein the cooling mode is ultra-fast cold and strong cold, the open cooling temperature is 900-.
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.
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| CN112795755B (en) * | 2020-12-30 | 2022-06-07 | 日照钢铁控股集团有限公司 | Method for flexibly producing low-alloy high-strength hot-rolled H-shaped steel |
| CN114622135B (en) * | 2022-02-21 | 2022-11-18 | 柳州钢铁股份有限公司 | Micro-niobium alloyed Q355B low-alloy high-strength structural steel plate and manufacturing method thereof |
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| CN101871078A (en) * | 2009-04-24 | 2010-10-27 | 宝山钢铁股份有限公司 | Super-high strength cold rolled steel and manufacturing method thereof |
| CN101880824A (en) * | 2010-06-14 | 2010-11-10 | 南阳汉冶特钢有限公司 | Q345q-series super-thick bridge steel plate and production method thereof |
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