CN114507818A - Thick normalizing ocean engineering structural steel and manufacturing method thereof - Google Patents

Thick normalizing ocean engineering structural steel and manufacturing method thereof Download PDF

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CN114507818A
CN114507818A CN202210093263.6A CN202210093263A CN114507818A CN 114507818 A CN114507818 A CN 114507818A CN 202210093263 A CN202210093263 A CN 202210093263A CN 114507818 A CN114507818 A CN 114507818A
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cooling
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杨志强
李伟
冯仰峰
杨清山
马林
许继勇
张德勇
马鑫
李新宇
于涛
欧阳宇
邴纯
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Rizhao Steel Yingkou Medium Plate Co Ltd
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Rizhao Steel Yingkou Medium Plate Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C21D1/28—Normalising
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/009—Pearlite

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  • Heat Treatment Of Steel (AREA)

Abstract

A thick normalized ocean engineering structural steel comprises the following chemical components: 0.14-0.18%; mn: 1.40-1.60%; nb: 0.020-0.050%; v: 0.020-0.050%; elements such as Ni, Cr, Mo, Cu and the like are not added; carbon equivalent Ceq: 0.41-0.45%, complete austenitizing temperature AC3The range is 840-852 ℃. After controlled rolling and normalizing, the steel plate has higher strength and toughness and excellent internal quality. Wherein, the normalized mechanical properties are as follows: yield strength Rt0.5 more than or equal to 365MPa and less than or equal to 410MPa, tensile strength Rm more than or equal to 520MPa and less than or equal to 560MPa, and longitudinal impact energy Akv2 more than or equal to-40 ℃ and less than or equal to 300J. The flaw detection result meets the requirement of 'NB/T47013.3 standard TI grade'. The normal microstructure after heat treatment is ferrite + pearlite.

Description

Thick normalizing ocean engineering structural steel and manufacturing method thereof
Technical Field
The invention belongs to the technical field of metal materials, and particularly relates to a process for normalizing heat treatment by adopting controlled rolling plus UFC water cooling and simultaneously normalizing (more than or equal to A)c3Complete austenitizing temperature) heat treatment, can manufacture high-toughness ocean engineering structural steel with the thickness specification of 60-100mm, the yield strength of more than or equal to 355MPa after normalizing heat treatment, the tensile strength of more than or equal to 490MPa and the impact energy of more than or equal to 200J at minus 40 ℃.
Background
With the development of offshore wind power in China, large-scale development conditions are basically met at present on the aspects of developable resource quantity and technical policy. China has abundant offshore wind power resources, and the survey data of the wind energy resources of the China meteorological office shows that China has continental coastlines over 1.8 km, and the amount of developable resources of offshore wind power with the sea area over 300 km2, the water depth of 5-50 m and the height of 70m is about 5 hundred million kW; considering the technical development capability of more than 70m, the actual developable resource amount is more. The offshore wind speed is high, the single fan capacity is large, the annual operation hours can reach more than 4000 hours, the offshore wind efficiency is 20-40% more than the annual power generation of onshore wind power, and the energy efficiency is higher; the offshore wind power plant is far away from the land, is not influenced by city planning, and does not need to worry about the influence of noise, electromagnetic waves and the like on residents.
The offshore wind power steel has the characteristics of large thickness, large unit weight, high surface quality and high flaw detection requirement. The method has high requirements on tooling equipment, quality management, technical development and the like of manufacturers. Particularly, the normalized large-thickness marine wind power steel has the characteristic influence, the yield is not downshifted, the performance is higher than that of Q370R, Q390ND and the like, and the normalized large-thickness marine wind power steel is the normalized steel with the same grade as that of Q420 ND; the method can be used for the first-level flaw detection, and needs very strict steel-making technology, equipment, casting blank quality, management level and the like; the normalizing delivery has long process flow, great difficulty in controlling surface defects and high requirement on refined management and control; the technical requirements such as comprehensive performance, flaw detection requirement, surface quality and the like are strict.
The patent "a low carbon equivalent extra thick specification offshore wind power steel DH36 steel sheet and its production method" (application number CN 112176248A), adopts "C: 0.14-15%, Si: 0.43 to 0.46%, Mn: 1.35-1.45%, P: less than or equal to 0.020%, S: less than or equal to 0.003 percent, Alt: 0.030 to 0.040%, Ceq: 0.38-0.40% "component design. The thickness of the steel plate produced by the TMCP process is 50-100mm, the yield strength is more than or equal to 355Mpa, the tensile strength is more than or equal to 520Mpa, the elongation is more than or equal to 25 percent, and the single value of the transverse impact energy at the temperature of minus 20 ℃ is more than or equal to 150J. In terms of composition design, this patent requires ultra low S control without Nb addition. The cost is obviously increased, the difficulty of controlling the steel making is increased, and the smelting difficulty is also increased. In addition, the impact temperature is only-20 ℃, the low-temperature toughness index is slightly low, and the-40 ℃ impact performance of the EH36 steel cannot be ensured.
The patent "a thick specification marine steel and production method" (application number CN 107779764A), adopts "C: less than or equal to 18 percent, Si: 0.10% -0.45%, Mn: 1.30% -1.65%, P: less than or equal to 0.014%, S: less than or equal to 0.003 percent, Cu: 0.02% -0.20%, Nb: 0.010% -0.060%, Ni: 0.01% -0.15%, Ti: 0.001% -0.015%, V: 0.03% -0.08%, Als: less than or equal to 0.045%, Cr: less than or equal to 0.02 percent, Mo: less than or equal to 0.1 percent. The patent produces the low-carbon equivalent heavy gauge marine steel with the thickness of 60-100mm by the normalizing process, and typical performance data are as follows: the yield strength is 370 plus 410MPa, the tensile strength is 520 plus 550MPa, and the average value of longitudinal impact energy at the temperature of-20 ℃ is 200 plus 260J. In the aspect of component design, the patent adds more Cu: 0.02-0.20%, Ni: 0.01-0.15%, the alloy cost is obviously increased, and the crack defect on the surface of the blank is easy to generate. The addition of the noble alloys Cu and Ni causes the Ceq to rise by about 0.02 percent, the total Ceq reaches 0.45 to 0.47 percent, the Ceq exceeds the range of low carbon equivalent, and the use process is not beneficial to the welding and the forming of the steel plate.
Disclosure of Invention
The invention aims to provide thick-specification normalizing marine engineering structural steel and a manufacturing method thereof, which are used for developing the thick-specification normalizing marine engineering structural steel by adopting reasonable rolling and cooling control processes and an optimized normalizing heat treatment process system on the basis of simple component design and solving the problems of complex component design, low yield strength qualified rate, strict process requirement, high production cost, insufficient toughness index and the like of the conventional heat treatment normalizing wind power steel.
The invention is realized by the following technical scheme:
the utility model provides a thick specification normalizing ocean engineering structural steel which characterized in that: the paint comprises the following components in percentage by mass: c: 0.14-0.18%; si: 0.20-0.40%; mn: 1.40-1.60%; p: less than or equal to 0.020%; s: less than or equal to 0.005 percent; and (3) Als: 0.015-0.050%; nb: 0.020-0.050%; ti: 0.006-0.020%; v: 0.020-0.050%; n: 0.0035 to 0.0080 percent; o: less than or equal to 0.0050 percent; h: less than or equal to 0.0003 percent; the balance of Fe and inevitable impurities, and the carbon equivalent Ceq ranges from 0.41 to 0.45 percent.
The invention also discloses a manufacturing method of the thick normalized ocean engineering structural steel, which comprises a molten steel smelting process, a slab casting process, a rolling process and a normalizing heat treatment process; the method is characterized in that:
in the process of smelting molten steel, molten iron is desulfurized and deslagged, enters a converter for smelting, and is refined and subjected to vacuum treatment by an LF furnace and an RH furnace; controlling the content of P, S, N, H and O in the smelting process, wherein C: 0.14-0.18%, P is less than or equal to 0.020%, S is less than or equal to 0.005%, N: less than or equal to 0.0045-0.0080%, less than or equal to 0.0003% of H, O: less than or equal to 0.0050 percent; the vacuum treatment time is 12min-15 min;
in the slab casting process, a continuous casting billet with the specification of 330-475mm is used, the constant drawing speed is kept in the casting process, the drawing speed range is 0.60-0.80 m/min, and the condition that the C class of the center segregation of the slab is less than or equal to 1.0 level is ensured; heating a slab: the plate blank is heated to the set soaking temperature 1180-: wherein the temperature of the first heating section is 950-;
in the rolling process, a two-stage controlled rolling and controlled cooling process is adopted, the rolling starting temperature of the first stage is ensured to be more than or equal to 1100 ℃, the total rolling reduction rate is 50-70%, at least the final 2-3 single-pass rolling reduction of the first stage is ensured to be more than 30mm, and the thickness of the steel plate is 1.8-2.0 times of the thickness of the finished steel plate; the rolling start temperature of the second stage is 850-; in the water cooling process, a 'DQ + ACC' cooling system is utilized, the initial cooling temperature is more than or equal to 800 ℃, the red returning temperature is 600-660 ℃, and the cooling speed is 10-20 ℃/s; after cooling, the off-line stack is slowly cooled, the stack slow cooling temperature is 450-;
the normalizing heat treatment adopts a temperature Ac3 slightly higher than the complete austenitizing temperature to carry out low-temperature normalizing treatment, wherein the normalizing temperature is 880-900 ℃, the total furnace time in the normalizing process is = the temperature-rise heating time + the heat preservation time, the temperature-rise heating time is 2.0-2.5min/mm, and the heat preservation time is more than or equal to 10 min;
further: the normalized marine engineering structural steel with the thick specification has normalized mechanical properties as follows: yield strength Rt0.5 not less than 365MPa and not more than 410MPa, tensile strength Rm not less than 520MPa and not more than 560MPa, elongation A50 after fracture not less than 25% and not more than 36%, and longitudinal impact energy Akv2 not less than 300J at-40 ℃.
Further: the flaw detection result of the thick normalized ocean engineering structural steel meets the requirement of 'NB/T47013.3 standard TI level'; the normal microstructure after normalizing heat treatment is ferrite + pearlite.
The invention has the advantages that: by means of proper economic component system design, proper C, a small amount of micro-alloy elements Nb and Ti and on the premise of not adding any noble alloy Ni, Cr, Mo and Cu, the steel plate can be stably produced in high-strength and high-toughness normalizing or wind power steel plate through a controlled rolling and controlled cooling process and an optimized normalizing process. The internal quality is excellent, and the flaw detection level can reach NB/47013 standard TI level. The alloy has low cost and simple process, has batch industrial production and application conditions, and has better application prospect in the field of ocean engineering structural steel.
Drawings
FIG. 1 shows a microstructure 1 of a steel sheet of an example after normalization.
FIG. 2 shows a microstructure 2 of the steel sheet of the example after the normalization.
Detailed Description
The invention discloses thick normalizing marine engineering structural steel which comprises the following chemical components in percentage by weight: 0.14-0.18%; si: 0.20-0.40%; mn: 1.40-1.60%; nb: 0.020-0.050%; ti: 0.006-0.020%; and Als: 0.015-0.050%; n: 0.0035 to 0.0090 percent; p: less than or equal to 0.020%; s: less than or equal to 0.005 percent; o: less than or equal to 0.0050 percent; h: less than or equal to 0.0003 percent; ni, Cr, Mo, Cu and other elements are not added intentionally; the balance of Fe and inevitable impurities, and the carbon equivalent Ceq (%) ranges from 0.41 to 0.45 percent. Complete austenitizing temperature Ac3The temperature ranges from 910-.
A thick normalized ocean engineering structural steel basically comprises the following manufacturing processes: the method comprises the following steps of molten iron desulphurization and slagging-off, converter smelting, LF furnace refining, RH vacuum treatment, slab casting, casting and heating, steel plate rolling, DQ/ACC cooling, normalizing heat treatment and mechanical property inspection.
The thick normalizing ocean engineering structural steel comprises the following specific steps and parameters:
(1) in the molten steel smelting process, molten iron is desulfurized and deslagged, enters a converter for smelting, and is refined and subjected to vacuum treatment through an LF furnace and an RH furnace. In the smelting process, the contents of C, P, S, N and H are strictly controlled, and the corresponding weight percentage ranges are respectively-C: 0.14 to 0.18 percent of the total weight of the alloy, less than or equal to 0.020 percent of P, less than or equal to 0.005 percent of S and less than or equal to 0.0060 percent of N; h is less than or equal to 0.00015 percent; the vacuum treatment time is 12min-15 min.
(2) Slab casting: and (3) using a continuous casting billet with the specification of 330 plus 475mm, keeping a constant drawing speed in the casting process, wherein the drawing speed range is 0.60-0.80 m/min, and ensuring that the C class of the center segregation of the slab is less than or equal to 1.0 so as to produce the continuous casting billet with good internal quality.
(3) Heating the plate blank: the slab is heated in sections to the set soaking temperature 1180-1220 ℃ by adopting a walking beam type heating furnace. Wherein the temperature of the first heating section is 950-.
(4) Rolling a steel plate: in the rolling process, a two-stage controlled rolling and controlled cooling process is adopted, the rolling starting temperature of the first stage is ensured to be more than or equal to 1100 ℃, the total rolling reduction rate is 50-70%, and the single-pass reduction of the last 2-3 passes of the first stage is at least ensured to be more than 30 mm; the thickness of the steel plate is 1.8-2.0 times of the thickness of the finished steel plate. The rolling start temperature at the second stage is 850-800 ℃, the finishing temperature is 850-800 ℃, and the total reduction rate is 50-80%.
(5) Water cooling of DQ + ACC: the cooling process is accurately controlled by using a 'DQ + ACC' cooling system, so that low final cooling and high cooling speed are realized, and the requirements of a new generation TMCP (thermal mechanical control processing) process are met; the initial cooling temperature is more than or equal to 800 ℃, the temperature of red returning is 600 ℃ and 660 ℃, and the cooling speed is 10-20 ℃/s. After cooling, the stack is quickly taken off line for slow cooling, the temperature of slow cooling of the stack is 450-. The cooling effect is shown in figure 1. Through the cooling mode of 'DQ + ACC', the surface color of the steel plate is uniform, the cooling effect is good, and the phenomenon of non-uniform cooling is avoided.
(6) Normalizing heat treatment: in order to ensure the strength and toughness after normalizing, a temperature A slightly higher than the complete austenitizing temperature is adoptedc3Performing low-temperature normalizing treatment at the normalizing temperature of 860 ℃ and 870 ℃, wherein the total in-furnace time of the normalizing process is = the heating time (2.0-2.5 min/mm) and the heat preservation time is more than or equal to 10 min;
(7) and (4) mechanical property inspection, sampling and preparing a sample on a normalized steel plate, and inspecting the properties such as stretching, impact, cold bending and the like according to GB/T228, GB/T229 and GB/T232.
The thick normalized ocean engineering structural steel produced by the process flow has stable heat treatment mechanical property, higher strength and toughness and excellent internal quality of the steel plate. Wherein, the normalized mechanical property is as follows: yield strength Rt0.5 not less than 365MPa and not more than 410MPa, tensile strength Rm not less than 520MPa and not more than 560MPa, elongation A50 after fracture not less than 25% and not more than 36%, and longitudinal impact energy Akv2 not less than 300J at-40 ℃. The flaw detection result meets the requirement of 'NB/T47013.3 standard TI grade'. The normal microstructure after normalizing was ferrite + pearlite (see figures 1 and 2).
As can be seen from the figure, the metallographic structure is ferrite/pearlite structure, the structure is uniform and has high refinement degree, and the grain size reaches more than 9.0 grade.
The present invention will be specifically described below with reference to specific examples.
According to the chemical component requirements of the thick normalizing marine engineering structural steel and the manufacturing method thereof, molten steel smelting, slab casting and steel plate rolling are completed. Slab gauge (thickness, width, length) 328mm, 2030mm, 4670mm, rolled steel sheet size (thickness, width, length): 70.4mm 3360mm 13350 mm.
In the process of smelting molten steel, the RH vacuum pressure maintaining time is 14 min. In the casting process, the drawing speed is constant, the drawing speed is 0.75m/min, and the center segregation C class is 0.5.
The actual chemical composition in this example is shown in Table 1, the composition meets the design requirements, the carbon equivalent is 0.42-0.44, Ac3Is 853 ℃.
TABLE 1 chemical composition (wt%)
Element(s) C Si Mn P S Als N Nb Ti V Ceq
Example 1 0.16 0.30 1.52 0.018 0.003 0.029 0.0036 0.031 0.011 0.037 0.43
Example 2 0.16 0.37 1.55 0.017 0.002 0.029 0.0044 0.032 0.014 0.036 0.44
Example 3 0.17 0.26 1.54 0.016 0.003 0.031 0.0048 0.035 0.014 0.037 0.44
Example 4 0.15 0.24 1.54 0.017 0.004 0.028 0.0038 0.032 0.014 0.036 0.42
Example 5 0.16 0.25 1.57 0.015 0.002 0.031 0.0043 0.033 0.013 0.036 0.44
Comparative example 1 0.17 0.24 1.49 0.019 0.002 0.027 0.0031 0.013 0.032 0.038 0.44
Comparative example 2 0.17 0.21 1.50 0.017 0.003 0.026 0.0038 0.011 0.032 0.037 0.44
Comparative example 3 0.16 0.23 1.52 0.017 0.002 0.031 0.0033 0.013 0.033 0.038 0.43
Parameters of the rolling process: the slab soaking temperature is 1214 ℃. Wherein the temperature of the first heating section is 950-. The rolling start temperature of the first stage is 1196-1212 ℃, and the thickness to be heated is 141-159 mm. The rolling start temperature 818 and 833 ℃ and the rolling finish temperature 825 and 835 ℃ in the second stage. The temperature of the red returning after the water cooling of the steel plate is 636-. The steel rolling process parameters emphasized in the rolling process of this embodiment are as follows in table 2.
TABLE 2 Steel Rolling Process parameters
Figure 601330DEST_PATH_IMAGE002
In the cooling process, the starting cooling temperature is more than or equal to 820 ℃, the temperature of red return is 630 +/-30 ℃, and the cooling speed is 11 +/-2 ℃/s; the slow cooling temperature of the stack is 474 ℃, and the stacking time is 74 h.
In the normalizing process, the normalizing temperature is 885 ℃, the total furnace time in the normalizing process is 154min, the heating time is 142min, and the heat preservation time is 12 min.
The steel plate of this example has the comprehensive mechanical properties shown in Table 3. The normalized strength, toughness, cold bending and hardness indexes are good, and the standard requirements are completely met.
TABLE 3 mechanical Properties
Figure 315208DEST_PATH_IMAGE004
The yield strength and the tensile strength of the normalized steel plate are stable, the yield strength and the tensile strength are higher than the standard stability by more than 15MPa, and the impact energy is stable and both reach more than 200J.
The flaw detection results of the steel sheet of this example are shown in Table 4.
TABLE 4 results of flaw detection
Type of probe Coupling agent Flaw detection standard and grade Thickness of Detecting frequency Probe frequency Flaw detection results
Single crystal straight probe Water (W) NB/47013、TI 90 1-6MHz 5MHz Qualified
The flaw detection result of the steel plate is good, and the specification of the thickness of 90mm reaches the standard TI level.
In conclusion, the thick normalized ocean engineering structural steel produced by the method has stable heat treatment mechanical property, higher strength and toughness and excellent internal quality of the steel plate. Wherein, the normalized mechanical property is as follows: yield strength Rt0.5 not less than 365MPa and not more than 410MPa, tensile strength Rm not less than 520MPa and not more than 560MPa, elongation A50 after fracture not less than 25% and not more than 36%, and longitudinal impact energy Akv2 not less than 300J at-40 ℃. The flaw detection result meets the requirement of 'NB/T47013.3 standard TI grade'. The normal microstructure after normalizing is ferrite + pearlite. The microstructure of the microscopic electron microscope is a ferrite/pearlite structure, the microstructure is uniform and has high refinement degree, and the grain size reaches over 9.0 grade.
The above examples are merely illustrative of the best mode of carrying out the invention and do not limit the scope of the invention in any way.

Claims (4)

1. The utility model provides a thick specification normalizing ocean engineering structural steel which characterized in that: the paint comprises the following components in percentage by mass: c: 0.14-0.18%; si: 0.20-0.40%; mn: 1.40-1.60%; p: less than or equal to 0.020%; s: less than or equal to 0.005 percent; and Als: 0.015-0.050%; nb: 0.020-0.050%; ti: 0.006-0.020%; v: 0.020-0.050%; n: 0.0035 to 0.0080 percent; o: less than or equal to 0.0050 percent; h: less than or equal to 0.0003 percent; the balance of Fe and inevitable impurities, and the carbon equivalent Ceq ranges from 0.41 to 0.45.
2. A manufacturing method of thick normalizing ocean engineering structural steel comprises a molten steel smelting process, a slab casting process, a rolling process and a normalizing heat treatment process; the method is characterized in that:
in the process of smelting molten steel, molten iron is desulfurized and deslagged, enters a converter for smelting, and is refined and subjected to vacuum treatment by an LF furnace and an RH furnace; controlling the content of P, S, N, H and O in the smelting process, wherein C: 0.14-0.18%, P is less than or equal to 0.020%, S is less than or equal to 0.005%, N: less than or equal to 0.0045-0.0080%, less than or equal to 0.0003% of H, O: less than or equal to 0.0050 percent; the vacuum treatment time is 12min-15 min;
in the slab casting process, a continuous casting billet with the specification of 330-475mm is used, the constant drawing speed is kept in the casting process, the drawing speed range is 0.60-0.80 m/min, and the condition that the C class of the center segregation of the slab is less than or equal to 1.0 level is ensured; heating a plate blank: the plate blank is heated to the set soaking temperature 1180-: wherein the temperature of the first heating section is 950-;
in the rolling process, a two-stage controlled rolling and controlled cooling process is adopted, the rolling starting temperature of the first stage is ensured to be more than or equal to 1100 ℃, the total rolling reduction rate is 50-70%, at least the final 2-3 single-pass rolling reduction of the first stage is ensured to be more than 30mm, and the thickness of the steel plate is 1.8-2.0 times of the thickness of the finished steel plate; the rolling start temperature of the second stage is 850-; in the water cooling process, a 'DQ + ACC' cooling system is utilized, the initial cooling temperature is more than or equal to 800 ℃, the red returning temperature is 600-660 ℃, and the cooling speed is 10-20 ℃/s; after cooling, the off-line stack is slowly cooled, the stack slow cooling temperature is 450-;
the normalizing heat treatment adopts a temperature Ac3 slightly higher than the complete austenitizing temperature to carry out low-temperature normalizing treatment, wherein the normalizing temperature is 880-900 ℃, the total furnace time in the normalizing process is = the temperature-rise heating time + the heat preservation time, the temperature-rise heating time is 2.0-2.5min/mm, and the heat preservation time is more than or equal to 10 min.
3. The method of claim 2, wherein: the normalized marine engineering structural steel with the thick specification has normalized mechanical properties as follows: yield strength Rt0.5 not less than 365MPa and not more than 410MPa, tensile strength Rm not less than 520MPa and not more than 560MPa, elongation A50 after fracture not less than 25% and not more than 36%, and longitudinal impact energy Akv2 not less than 300J at-40 ℃.
4. The method of claim 2, wherein: the flaw detection result of the thick normalized ocean engineering structural steel meets the requirement of 'NB/T47013.3 standard TI level'; the normal microstructure after normalizing heat treatment is ferrite + pearlite.
CN202210093263.6A 2022-01-26 2022-01-26 Thick normalizing ocean engineering structural steel and manufacturing method thereof Pending CN114507818A (en)

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Application publication date: 20220517