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CN113789475B - Method for producing low-alloy hot-rolled steel strip with yield strength of 355MPa at low cost - Google Patents

Method for producing low-alloy hot-rolled steel strip with yield strength of 355MPa at low cost Download PDF

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CN113789475B
CN113789475B CN202111075290.2A CN202111075290A CN113789475B CN 113789475 B CN113789475 B CN 113789475B CN 202111075290 A CN202111075290 A CN 202111075290A CN 113789475 B CN113789475 B CN 113789475B
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CN113789475A (en
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高磊
李东宇
栗锐
董洋
王洪海
景鹤
王尊呈
马锋
刘志伟
曲帅
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Angang Steel Co Ltd
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    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/02Ferrous alloys, e.g. steel alloys containing silicon
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226Hot rolling
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/04Ferrous alloys, e.g. steel alloys containing manganese
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/06Ferrous alloys, e.g. steel alloys containing aluminium
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/001Austenite
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/005Ferrite

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Abstract

The invention relates to a method for producing low-alloy hot-rolled steel strips with 355 MPa-grade yield strength at low cost, which comprises the following steps of 1) producing steel coils with the thickness H less than or equal to 12 mm; controlling the heating temperature of the smelted plate blank to be 1160-1180 ℃, carrying out 1+5 or 3+3 times of rough rolling, wherein the thickness of the intermediate blank after rough rolling is 13-17% of that of the continuous casting blank, and the temperature of the rough rolling RT2 is 1020-1050 ℃; carrying out finish rolling on the intermediate blank, wherein the finish rolling temperature is 850-890 ℃, carrying out finish rolling, then firstly carrying out ultra-fast cooling, and then carrying out laminar cooling to 590-630 ℃ for coiling; 2) producing a steel coil with the thickness of 12mm and H less than or equal to 20 mm; controlling the heating temperature of the smelted plate blank to be 1130-1160 ℃, carrying out 1+5 or 3+3 times of rough rolling, wherein the thickness of the intermediate blank after rough rolling is 17-22% of that of the continuous casting blank, and the temperature of the rough rolling RT2 is 970-1020 ℃; and (3) carrying out finish rolling on the intermediate blank, wherein the finish rolling temperature is 820-850 ℃, carrying out finish rolling, then firstly carrying out ultra-fast cooling, and then carrying out laminar cooling to 550-590 ℃ for coiling. The product has excellent formability.

Description

Method for producing low-alloy hot-rolled steel strip with yield strength of 355MPa at low cost
Technical Field
The invention relates to the technical field of steel rolling processes. In particular to a method for producing low-alloy hot-rolled steel strip with 355MPa grade yield strength at low cost.
Background
The Q355-grade low alloy variety is a main variety of hot-rolled coils, and the steel is mainly based on carbon-manganese steel, and micro-alloy carbon and nitrogen compounds such as Nb, V, Ti and the like are added into the steel to form elements, so that the strength of the steel plate is improved through solid solution strengthening, precipitation strengthening and fine grain strengthening. Statistically, the yield of such steel plates is about 15% of the total yield of hot rolled coils per year.
In general, alloying elements such as Mn, Nb, V, Ti and the like are added in the smelting process in order to meet the requirement of strength performance of Q355 grade. Mn is dissolved in ferrite to increase the strength of the hot-rolled C-Mn steel, and Nb, V and Ti are combined with C, N elements in the steel to form non-deformable second-phase precipitates such as TiC and TiN to increase the strength of the steel. The existence of these elements also increases the austenite non-recrystallization temperature, increases the amount of deformation in the austenite non-recrystallization region, and achieves fine grain strengthening. The strengthening effect of the alloy elements is obvious, but the dosage and the alloy smelting cost are higher.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for producing a low-alloy hot-rolled steel strip with the yield strength of 355MPa at low cost, reducing alloy addition and improving the product profitability level.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for producing a low-alloy hot-rolled steel strip with 355MPa grade yield strength at low cost comprises the steps of smelting molten iron in a converter, carrying out external refining on the molten iron, pouring into a continuous casting billet, and heating, rough rolling, finish rolling, cooling and coiling the continuous casting billet; the method comprises the following steps:
1) producing a steel coil with the thickness H less than or equal to 12 mm;
a. the chemical components of smelting steel are as follows: 0.15 to 0.20 percent of C, 0.30 to 0.50 percent of Si, 0.80 to 1.00 percent of Mn, less than or equal to 0.050 percent of Als, less than or equal to 0.025 percent of P, less than or equal to 0.015 percent of S, and the balance of Fe and inevitable impurity elements;
b. the heating temperature of the plate blank is controlled to be 1160-1180 ℃, 1+5 or 3+3 passes of rough rolling are adopted for rough rolling, the thickness of the intermediate blank after rough rolling is 13-17% of that of the continuous casting blank, and the temperature of the rough rolling RT2 is 1020-1050 ℃;
c. carrying out finish rolling on the intermediate blank, wherein the finish rolling temperature is 850-890 ℃, carrying out finish rolling, then firstly carrying out ultra-fast cooling, and then carrying out laminar cooling to 590-630 ℃ for coiling;
2) producing the steel coil with the thickness of 12mm and H less than or equal to 20mm
a. The chemical components of smelting steel are as follows: 0.18 to 0.24 percent of C, 0.30 to 0.50 percent of Si, 1.00 to 1.20 percent of Mn, less than or equal to 0.050 percent of Als, less than or equal to 0.025 percent of P, less than or equal to 0.015 percent of S, and the balance of Fe and inevitable impurity elements;
b. the heating temperature of the plate blank is controlled to be 1130-1160 ℃, 1+5 or 3+3 passes of rough rolling are adopted for rough rolling, the thickness of the intermediate blank after rough rolling is 17% -22% of that of the continuous casting blank, and the temperature of the rough rolling RT2 is 970-1020 ℃;
c. and (3) carrying out finish rolling on the intermediate blank, wherein the finish rolling temperature is 820-850 ℃, carrying out finish rolling, then firstly carrying out ultra-fast cooling, and then carrying out laminar cooling to 550-590 ℃ for coiling.
In the step c of the step 1), for the steel coil with the thickness H of less than or equal to 6mm of the finished product, the ultra-fast cold water amount is 2000m 3 /h~3000m 3 H, water pressure of 0.20-0.50 MPa, cooling speed of 20-30 ℃/s, finished product thickness of 6-H, H and H of less than or equal to 12mm, and ultrafast cold water amount of 4000m 3 /h~4500m 3 The water pressure is 0.50-0.75 MPa, and the cooling speed is 30-40 ℃/s.
In step c of step 2), the amount of ultrafast cold water is 4500m 3 ~5000m 3 The water pressure is 0.75-0.90 MPa, and the cooling speed is 35-50 ℃/s.
And controlling rolling and cooling to realize grain refinement and grain strengthening. The control of the hardening state of the austenite is realized by controlling the rolling, namely, a large amount of energy is accumulated in the austenite through deformation, the austenite in the hardening state is obtained in the rolling process, and preparation is made for realizing grain refinement in the subsequent phase transformation process. But hardened austenite has a large number of "defects" that more readily increase the likelihood of ferrite nucleation. And adopting a low-temperature heating and low-temperature rolling strategy. The low temperature is to suppress recrystallization of austenite, to keep austenite in a non-recrystallized region, and to maintain its hardened state. The rolling process then increases the stored deformation of the hardened austenite. The controlled cooling is to control the phase transformation process of the hardened austenite, and further refine ferrite grains by controlling the cooling speed after rolling so as to improve the performance of the material.
Compared with the prior art, the invention has the beneficial effects that:
the 355 MPa-grade low-alloy hot-rolled steel strip does not need to be added with Nb and Ti microalloy elements, the addition amount of Mn alloy can be reduced, the same mechanical property as that of the conventional process is realized, the yield strength ReH is more than or equal to 355MPa, the tensile strength Rm is 470-630 MPa, the elongation (transverse) A after fracture is more than or equal to 20%, and the yield ratio is lower compared with that of the product of the conventional process, the yield ratio of the product of the conventional process is generally more than 0.88, while the yield ratio of the product of the invention is generally less than 0.80 and has excellent formability; compared with the traditional process, the cost of each ton of steel is reduced by 60-100 yuan/ton, and the production cost is greatly reduced. The market competitiveness of the product is improved.
Detailed Description
The invention is further illustrated by the following examples:
the following examples describe the invention in detail. These examples are merely illustrative of the best embodiments of the present invention and do not limit the scope of the invention.
The method for producing the low-alloy hot-rolled steel strip with the yield strength of 355MPa at low cost comprises the steps of smelting molten iron in a converter, carrying out external refining on the molten iron, pouring into a continuous casting billet, and heating, rough rolling, finish rolling, cooling and coiling the continuous casting billet;
examples the thickness and chemical composition of the finished product are shown in table 1.
Table 1: thickness and chemical composition of finished product
Examples Thickness/mm of finished product C/wt% Si/wt% Mn/wt% P/wt% S/wt% Als/wt%
1 2 0.15 0.30 0.80 0.023 0.010 0.050
2 4 0.16 0.44 0.87 0.015 0.008 0.038
3 5 0.17 0.36 0.92 0.020 0.006 0.043
4 6 0.17 0.38 0.91 0.025 0.015 0.030
5 6.5 0.18 0.50 0.86 0.022 0.004 0.025
6 8 0.19 0.46 0.97 0.024 0.012 0.020
7 10 0.18 0.34 0.95 0.021 0.014 0.010
8 12 0.20 0.48 1.00 0.019 0.003 0.047
9 14 0.18 0.46 1.05 0.017 0.005 0.003
10 15 0.20 0.32 1.09 0.013 0.013 0.033
11 16 0.19 0.45 1.13 0.018 0.008 0.025
12 17 0.22 0.39 1.16 0.022 0.009 0.043
13 19 0.23 0.47 1.19 0.020 0.006 0.016
14 20 0.24 0.35 1.20 0.012 0.010 0.024
The production process parameters are shown in the table 2.1 and the table 2.2;
table 2.1:
Figure BDA0003261897480000031
table 2.2:
Figure BDA0003261897480000032
Figure BDA0003261897480000041
the properties of the examples are shown in Table 3.
Table 3: examples mechanical Property test results
Figure BDA0003261897480000042

Claims (1)

1. A method for producing 355MPa grade low alloy hot rolled steel strip of yield strength with low cost, the molten iron is smelted by a converter, the molten steel is refined outside the converter, and is poured into a continuous casting billet, and the continuous casting billet is heated, rough rolled, finish rolled, cooled and coiled; the method is characterized by comprising the following steps:
1) producing a steel coil with the thickness H less than or equal to 12 mm;
a. the chemical components of smelting steel are as follows: 0.15 to 0.20 percent of C, 0.36 to 0.50 percent of Si, 0.86 to 1.00 percent of Mn, less than or equal to 0.050 percent of Als, less than or equal to 0.025 percent of P, less than or equal to 0.015 percent of S, and the balance of Fe and inevitable impurity elements;
b. the heating temperature of the plate blank is controlled to be 1160-1180 ℃, the thickness of the intermediate blank after rough rolling is 13-17% of that of the continuous casting blank, and the finish rolling temperature of the rough rolling is 1020-1050 ℃;
c. carrying out finish rolling on the intermediate blank, wherein the finish rolling temperature is 850-890 ℃, carrying out finish rolling, then firstly carrying out ultra-fast cooling at a cooling speed of 20-35 ℃/s, and then carrying out laminar cooling to 590-630 ℃ for coiling; for the steel coil with the finished product thickness H less than or equal to 6mm and the ultra-fast cold water amount of 2000m 3 /h~3000m 3 H, water pressure of 0.20-0.50 MPa, cooling speed of 20-30 ℃/s, finished product thickness of 6-H, H and H of less than or equal to 12mm, and ultrafast cold water amount of 4000m 3 /h~4500m 3 H, the water pressure is 0.50-0.75 MPa, and the cooling speed is 30-35 ℃/s;
2) producing the steel coil with the thickness of 12mm and H less than or equal to 20mm
a. The smelting steel comprises the following chemical components: 0.18 to 0.24 percent of C, 0.39 to 0.50 percent of Si, 1.00 to 1.20 percent of Mn, less than or equal to 0.050 percent of Als, less than or equal to 0.025 percent of P, less than or equal to 0.015 percent of S, and the balance of Fe and inevitable impurity elements;
b. the heating temperature of the plate blank is controlled to be 1130-1160 ℃, the thickness of the intermediate blank after rough rolling is 17-22% of that of the continuous casting blank, and the finish rolling temperature of the rough rolling is 970-1020 ℃;
c. the intermediate billet is subjected to finish rolling at the finishing temperature of 820-850 ℃, after finish rolling, ultra-fast cooling is firstly adopted, the cooling speed is 35-50 ℃/s, after ultra-fast cooling, laminar cooling is carried out to 550-590 ℃, coiling is carried out, and the amount of ultra-fast cold water is 4500m 3 ~5000m 3 The water pressure is 0.75-0.90 MPa.
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