300MPa-grade cold-rolled enamel steel and preparation method thereof

Abstract

The invention discloses 300MPa-grade cold-rolled enamel steel and a preparation method thereof, and belongs to the technical field of cold-rolled strip production. The cold-rolled enamel steel comprises the following chemical components in percentage by mass: 0.01%-0.08% of C, less than or equal to 0.10% of Si, 0.10%-0.60% of Mn, less than or equal to 0.030% of P, 0.020%-0.040% of S, 0.010%-0.070% of Als, less than or equal to 0.0050% of N, 0.020%-0.060% of Ti and the balance of Fe and inevitable impurities. The adopted titanium-containing low-carbon steel is low in smelting cost, after a modern continuous annealing furnace is adopted for appropriate annealing process treatment, the cold-rolled enameled steel plate with the yield strength being 300 MPa or above and good fish scaling resistance is obtained, meanwhile, the original thickness specification is thinned by about 15%, and the production cost is greatly reduced. The problem that existing cold-rolled enamel steel cannot meet the requirements for excellent fish scaling resistance and thinning and cost reduction at the same time can be effectively solved.

Description

Technical Field

[0001] The invention belongs to the technical field of cold-rolled plate and strip production, and particularly relates to a 300MPa grade cold-rolled enameled steel and a preparation method thereof. Background Art

[0002] With the technological advancement and innovative development of the home appliance industry, enameled steel, a metal-based composite material widely used in the home appliance industry, is continuously developing and gradually gaining widespread application. Water heater inner tanks are generally produced using hot-rolled enameled steel or cold-rolled B-microalloyed low-carbon aluminum-killed steel DC01EK. However, hot-rolled enameled steel generally has low sensitivity to scale cracking and is prone to scale cracking defects. Due to the pressure resistance and other limitations of water heater inner tanks, DC01EK is difficult to meet the requirements of thinning and cost reduction of inner tanks. This requires the development of a cold-rolled enameled steel with a cost comparable to DC01EK and higher strength for thinning and cost reduction of water heater inner tanks. Therefore, high-strength cold-rolled enameled steel has broad market prospects.

[0003] CN110273106A discloses a 260MPa-grade cold-rolled, continuously annealed, enameled steel and its production method. The 260MPa-grade cold-rolled, continuously annealed, enameled steel comprises the following chemical composition by weight: C: 0.020-0.060%, Si ≤ 0.030%, Mn: 0.020-0.60%, P ≤ 0.020%, S ≤ 0.010%, Al: 0.020-0.060%, B: 0.0015-0.0040%, N: 0.0040-0.0100%, with the remainder being Fe and unavoidable impurities. The steel is produced through thin slab continuous casting and rolling, cold rolling, continuous annealing, and skin-passing. The hot rolling finish temperature is controlled at 860-960°C, and the coiling temperature is controlled at 600-650°C. The cold rolling reduction ratio is ≥70%, and continuous annealing is performed at a temperature of 730-780°C for 90-150 seconds. The resulting cold-rolled steel sheet has a microstructure of ferrite + dispersed carbides, and mechanical properties include a yield strength ≥260 MPa, a tensile strength ≥360 MPa, and an elongation A50 ≥35%. However, this method uses a scale-susceptibility test for enameled steel sheets, which is not sufficiently accurate.

[0004] CN111945059A discloses a method for preparing cold-rolled high-strength, heat-resistant enameled steel. The steel comprises the following chemical composition by weight: C: 0.04-0.07%, Si ≤ 0.03%, Mn: 0.40-0.80%, P ≤ 0.025%, S ≤ 0.020%, Alt ≤ 0.030%, Cr: 0.15-0.40%, Mo: 0.05-0.15%, N: 0.004-0.010%, with the remainder being Fe and unavoidable impurities. The hot rolling finish temperature is controlled between 880-920°C, and the coiling temperature is controlled between 580-640°C. The cold rolling reduction is ≥ 65%, and a bell annealing process is employed, with an annealing temperature of 660-700°C and a holding time of 8-10 hours. This method adds precious metals such as Mo and Cr to the chemical composition and adopts a hood annealing process, resulting in a high production cost. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the existing cold-rolled enameled steel cannot simultaneously meet the requirements of excellent anti-scale performance and thinning and cost reduction.

[0006] The technical solution adopted by the present invention to solve the technical problem is: 300MPa grade cold-rolled enameled steel, whose chemical composition, calculated by mass percentage, is: C 0.01%-0.08%, Si≤0.10%, Mn 0.10%-0.60%, P≤0.030%, S0.020-0.040%, Als 0.010%-0.070%, N≤0.0050%, Ti 0.020%-0.060%, and the rest is Fe and unavoidable impurities.

[0007] Furthermore, the chemical composition is calculated by mass percentage as follows: C 0.03% to 0.06%, Si≤0.10%, Mn0.30% to 0.45%, P≤0.030%, S 0.025 to 0.035%, Als 0.020% to 0.050%, N≤0.0050%, Ti 0.030% to 0.050%, and the rest is Fe and unavoidable impurities.

[0008] The microstructure of the above 300 MPa grade cold-rolled enameled steel consists of ferrite + cementite.

[0009] The yield strength of the 300MPa grade cold-rolled enameled steel is 300-340MPa, the tensile strength is 390-430MPa, the elongation A80 value is 32.0-38.0%, and the number of weld fatigue cycles is greater than 2 million times.

[0010] The anti-scale sensitivity TH value of the above 300MPa grade cold-rolled enameled steel is greater than 20min / mm 2 .

[0011] The preparation method of the above-mentioned 300MPa grade cold-rolled enameled steel is to obtain the 300MPa grade cold-rolled enameled steel through the processes of smelting, hot rolling, pickling, continuous annealing and tempering.

[0012] In the above preparation method, the continuous annealing step is specifically as follows:

[0013] (1) The cold-rolled strip is heated to 300°C at a rate of 10-15°C / s, then heated to 780-820°C at a rate of 1.0-2.0°C / s, and then held at this temperature for 80-120 seconds.

[0014] (2) After holding, cool to 580-620°C at a rate of 3-5°C / s, then cool to 340-380°C at a rate of 45-50°C / s, and hold for 400-480 seconds;

[0015] (3) After keeping warm, cool to 330-360°C at a rate of 45-50°C / s, then cool to 180°C at a rate of 2-4°C / s, and then water-cool to room temperature.

[0016] In the above preparation method, the smelting process is specifically as follows: smelting is performed according to the chemical composition of the above 300MPa grade cold-rolled enameled steel, ferrosulfur and sponge titanium are added in the refining process, and then casting is performed into slabs.

[0017] In the above preparation method, the hot rolling process obtains the hot rolled coil through slab heating, descaling, rough rolling, finish rolling and laminar cooling.

[0018] Furthermore, the slab heating temperature is 1220-1260° C., and the total time in the furnace is 180-280 min.

[0019] Furthermore, the finishing rolling start temperature is 1040-1130° C., the final rolling temperature is 860-930° C., and the hot rolling thickness is 5.0-6.0 mm.

[0020] Furthermore, the laminar cooling adopts a centralized ultra-fast cooling mode, with the upper and lower headers at 90% and 100%, the middle temperature at 720-780°C, and the coiling temperature at 620-680°C.

[0021] Furthermore, high-pressure water descaling treatment is carried out at the roughing and finishing rolling entrances, respectively. The pressure of the high-pressure water is 18-22 MPa, and the descaling water volume at the roughing and finishing rolling entrances is 540 m3 / s. 3 / h and 450m 3 / h, the distances between the nozzle and the slab / strip are 120mm and 90mm respectively.

[0022] In the above preparation method, the hot rolled coil is cold rolled in 5 stands, and the total cold rolling reduction is controlled to be 70-80%.

[0023] In the above preparation method, the flattening elongation is controlled to be 0.6-1.5%.

[0024] The beneficial effects of the present invention are as follows: the present invention adopts titanium microalloying composition design, and produces a cold-rolled enameled steel with a yield strength of 300 MPa through a continuous annealing unit. The alloy of the present invention has low cost and good formability. The yield strength of the cold-rolled enameled steel is 300-340 MPa, the tensile strength is 390-430 MPa, the elongation A80 value is 32.0-38.0%, and the number of weld fatigue cycles is greater than 2 million times; the hydrogen permeation test (EN 10209-2013) is used to test the anti-enameling scale explosion sensitivity (TH value), and the anti-scale explosion performance is evaluated by an electrochemical method, which is accurate and efficient, and the anti-scale explosion sensitivity TH value of the cold-rolled enameled steel is greater than 20 min / mm 2 , excellent anti-scale performance.

[0025] The titanium-containing low-carbon steel used in the present invention has low smelting cost. After being treated with a modern continuous annealing furnace through a suitable annealing process, a cold-rolled enameled steel plate with a yield strength of more than 300 MPa and good anti-scale explosion performance is obtained. It can be used to enhance the strength and reduce the thickness of the water heater tank, and can reduce the original thickness by about 15%. It has good cost-reduction and efficiency-enhancing capabilities and market potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a metallographic image of the 300 MPa grade cold-rolled enameled steel prepared in Example 1;

[0027] Figure 2 This is the metallographic image of the 300MPa grade cold-rolled enameled steel prepared in Example 2. DETAILED DESCRIPTION

[0028] The technical solution of the present invention can be implemented in the following manner.

[0029] The chemical composition of 300MPa grade cold-rolled enameled steel is as follows by mass percentage: C 0.01%~0.08%, Si≤0.10%, Mn0.10%~0.60%, P≤0.030%, S 0.020~0.040%, Als 0.010%~0.070%, N≤0.0050%, Ti0.020%~0.060%, and the rest is Fe and unavoidable impurities.

[0030] Preferably, the chemical composition is calculated by mass percentage as follows: C 0.03% to 0.06%, Si≤0.10%, Mn 0.30% to 0.45%, P≤0.030%, S 0.025 to 0.035%, Als 0.020% to 0.050%, N≤0.0050%, Ti0.030% to 0.050%, and the rest is Fe and unavoidable impurities.

[0031] The alloy composition design principle of the present invention is as follows:

[0032] C: As one of the most important components in steel, C determines the strength, plasticity, and formability of steel plates. Low C content results in low strength, high r-values, and significant anisotropy. Excessive C content impairs weldability and formability. To achieve a low r-value while maintaining good isotropy and balancing weldability and formability, the C content in this invention is 0.01-0.08%, preferably 0.03-0.06%.

[0033] Si: exists in steel as a residual element and is not intentionally added.

[0034] Mn: Mn is a good deoxidizer and desulfurizer. During the continuous casting process, it forms MnS precipitation with S, preventing the formation of FeS and cracks in the corners of the cast billet. Mn is also a commonly used solid solution strengthening element in steel. Increasing the Mn content can reduce the r value, but it significantly reduces the plasticity of the steel. Therefore, the Mn content of the present invention is 0.10-0.60%, preferably 0.30-0.45%.

[0035] Al: Al plays a role in deoxidation and grain refinement in steel. The Al content in the present invention is 0.010-0.070%, preferably 0.020-0.050%.

[0036] Sulfur (S): Predominantly exists in the form of sulfides. Sulfides exhibit beneficial effects within a certain range. Increasing the S content promotes the precipitation of second-phase particles such as TiS and Ti4C2S2, which act as hydrogen traps and enhance scale resistance. Furthermore, increasing the amount of sulfur also improves fatigue performance. The S content in this invention is 0.020-0.040%, preferably 0.025-0.035%.

[0037] Ti: Ti fixes nitrogen in steel, hinders recrystallization, and contributes to fine grain size. Its addition promotes the precipitation of second-phase particles such as TiC, TiS, Ti(C,N), and Ti4C2S2, acting as hydrogen traps and improving fishscale resistance. It also inhibits the precipitation of large-scale MnS, enhancing fatigue performance and formability. The solute drag effect of Ti suppresses the increase in texture strength and improves Δr. The Ti content in the present invention is 0.020-0.060%, preferably 0.030-0.050%.

[0038] The microstructure of the 300MPa grade cold-rolled enameled steel is composed of ferrite + cementite, with a yield strength of 300-340MPa, a tensile strength of 390-430MPa, an elongation A80 value of 32.0-38.0%, a weld fatigue cycle number of more than 2 million times, and an anti-scale sensitivity (test standard EN 10209-2013) TH value of >20min / mm 2 .

[0039] The production steps of the above-mentioned 300MPa grade cold-rolled enameled steel include:

[0040] (a) Smelting process: Smelting is carried out according to the chemical composition designed above, adding ferrosulfur and sponge titanium in the refining process, and then casting into slabs;

[0041] (b) Hot rolling process: The slab is heated, descaled, rough rolled, finish rolled and laminar cooled to obtain a hot rolled coil;

[0042] The heating temperature is 1220-1260℃. In order to ensure uniform chemical composition of each part of the strip, the total time in the furnace is 180-280 minutes.

[0043] In order to obtain good surface quality, high-pressure water descaling treatment is carried out at the roughing and finishing entrances. The pressure of high-pressure water is 18-22 MPa, and the descaling water volume at the roughing and finishing entrances is 540 m3 respectively. 3 / h and 450m 3 / h, the distance between the nozzle and the slab / strip is 120mm and 90mm respectively;

[0044] The starting temperature of the finishing rolling is 1040-1130°C, the final rolling temperature is 860-930°C, and the hot rolling thickness is 5.0-6.0mm;

[0045] In order to ensure the stability of the longitudinal structure and performance of the strip, the hot coil box is used to adjust the strip head and tail before entering the finishing mill;

[0046] Laminar cooling adopts centralized ultra-fast cooling mode, with upper and lower headers at 90% and 100%, and the middle temperature is 720-780℃;

[0047] Coiling temperature is 620~680℃;

[0048] (c) Pickling process: the hot rolled coil is subjected to cold rolling in 5 stands with a total cold rolling reduction of 70% to 80%;

[0049] (d) Continuous annealing process: The cold-rolled steel strip is subjected to continuous annealing to produce 300 MPa grade cold-rolled enameled steel;

[0050] The steel is heated to 300°C and 780-820°C at a rate of 10-15°C / s and 1.0-2.0°C / s respectively, and then kept warm for 80-120s; cooled to 580-620°C at a rate of 3-5°C / s, and then cooled to 330-360°C at a rate of 45-50°C / s, and then kept warm at 340-380°C for 400-480s; cooled to 180°C at a rate of 2-4°C / s, and then water-cooled to room temperature.

[0051] (e) Leveling process: Control the elongation to 0.6-1.5%.

[0052] The technical solutions and effects of the present invention are further illustrated below through practical examples.

[0053] Example

[0054] This embodiment provides two groups of 300MPa grade cold-rolled enameled steels, the chemical compositions of which are shown in Table 1 , with the remainder being Fe;

[0055] Table 1 Chemical composition (wt.%)

[0056] serial number C Si Mn P S Ti Als N Example 1 0.058 0.01 0.38 0.009 0.027 0.035 0.045 0.0045 Example 2 0.036 0.01 0.42 0.007 0.029 0.045 0.033 0.0033

[0057] The preparation method of the above-mentioned 300MPa grade cold-rolled enameled steel is as follows:

[0058] A. Smelting process: After the smelting process, a slab with the chemical composition shown in Table 1 is prepared;

[0059] B. Hot rolling process: The slab is heated, dephosphorized, hot rolled and laminar cooled to obtain a hot rolled coil. The specific hot rolling process parameters are shown in Table 2.

[0060] Table 2 Main process parameters of hot rolling

[0061] serial number Heating temperature Time in the furnace Rolling temperature Finishing temperature Coiling temperature Hot rolled thickness Example 1 1244℃ 200min 1068℃ 884℃ 654℃ 5.0mm Example 2 1250℃ 230 minutes 1066℃ 878℃ 665℃ 6.0mm

[0062] C. Pickling process: After pickling, the hot-rolled coil is cold-rolled into thin strip steel. The thickness of the thin strip steel in Example 1 is 1.5 mm, and the cold rolling reduction ratio is 70.0%; the thickness of the thin strip steel in Example 2 is 1.5 mm, and the cold rolling reduction ratio is 75.0%;

[0063] D. Continuous annealing process: The cold-rolled thin strip steel is processed into the required product through continuous annealing process. The annealing temperature is 780-820℃, the slow cooling end temperature is 580-620℃, the rapid cooling end temperature is 330-360℃, the over-aging stage temperature is 340-400℃, and the flat elongation is 0.6-1.5%. The specific continuous annealing process parameters are shown in Table 3:

[0064] Table 3 Annealing process parameters

[0065]

[0066] The microstructure of the cold-rolled enameled steel with a yield strength of 300 MPa prepared by the above process is shown in Example 1. Figure 1 As shown, Example 2 is organized as Figure 2 As shown, the cold-rolled enameled steel was tested according to GB / T228-2010 "Metallic Materials Room Temperature Tensile Test Methods", and its mechanical properties are shown in Table 4 below. The hydrogen permeation test was carried out using the European standard EN 10209-2013, and the results are shown in Table 5.

[0067] Table 4 Mechanical properties

[0068] serial number Yield strength tensile strength <![CDATA[Elongation A 80 > n value r-value Weld fatigue cycles Example 1 311MPa 398MPa 37.0％ 0.18 1.275 2 million times Example 2 322MPa 413MPa 35.0％ 0.17 1.265 2 million times

[0069] Table 5 Anti-scale burst performance

[0070] serial number Sample thickness (mm) Penetration time (min) <![CDATA[TH value (min / mm 2 )]]> Example 1 1.49 46.99～52.26 21.17～23.54 Example 2 1.48 51.25～52.89 23.40～24.15

[0071] The results show that the microstructure of the cold-rolled enameled steel prepared by the present invention is composed of ferrite and cementite, the yield strength reaches more than 300 MPa, and the anti-scale sensitivity TH value reaches 20 min / mm 2 The above has good forming performance and anti-scale performance.

Claims

1. 300MPa grade cold-rolled enameled steel, characterized in that: Its chemical composition is calculated by mass percentage as follows: C 0.01%-0.08%, Si≤0.10%, Mn 0.10%-0.60%, P≤0.030%, S 0.020-0.040%, Als 0.010%-0.070%, N≤0.0050%, Ti 0.020%-0.060%, and the rest is Fe and unavoidable impurities.

2. The 300MPa grade cold-rolled enameled steel according to claim 1, characterized in that: Its chemical composition is calculated by mass percentage as follows: C 0.03%-0.06%, Si≤0.10%, Mn 0.30%-0.45%, P≤0.030%, S 0.025-0.035%, Als0.020%-0.050%, N≤0.0050%, Ti 0.030%-0.050%, and the rest is Fe and unavoidable impurities.

3. The 300MPa grade cold-rolled enameled steel according to claim 1, characterized in that: Its microstructure is composed of ferrite + cementite.

4. The 300MPa grade cold-rolled enameled steel according to claim 1, characterized in that: Its yield strength is 300-340MPa, tensile strength is 390-430MPa, elongation A80 value is 32.0-38.0%, weld fatigue cycle number is more than 2 million times, anti-scale explosion sensitivity TH value is more than 20min / mm 2 .

5. The method for preparing 300MPa grade cold-rolled enameled steel according to any one of claims 1 to 4, characterized in that: After smelting, hot rolling, pickling, continuous annealing and leveling, 300MPa grade cold-rolled enameled steel is obtained; Among them, the continuous annealing process is specifically as follows: (1) The cold-rolled strip is heated to 300°C at a rate of 10-15°C / s, and then heated to 780-820°C at a rate of 1.0-2.0°C / s, and then heat-equilibrated for 80-120 seconds; (2) After heat preservation, cool to 580-620°C at a rate of 3-5°C / s, then cool to 340-380°C at a rate of 45-50°C / s, and heat preservation for 400-480s; (3) After keeping warm, cool to 330-360°C at a rate of 45-50°C / s, then cool to 180°C at a rate of 2-4°C / s, and then water-cool to room temperature.

6. The method for preparing 300MPa grade cold-rolled enameled steel according to claim 5, characterized in that: The smelting process is specifically as follows: smelting is performed according to the chemical composition described in claim 1, ferrosulphide and sponge titanium are added in the refining process, and then casting is performed into a slab.

7. The method for preparing 300MPa grade cold-rolled enameled steel according to claim 5, characterized in that: The hot rolling process obtains hot rolled coils through slab heating, descaling, rough rolling, finish rolling and laminar cooling, specifically: The slab heating temperature is 1220-1260°C, and the total furnace time is 180-280 minutes; The finishing rolling temperature is 1040-1130°C, the final rolling temperature is 860-930°C, and the hot rolling thickness is 5.0-6.0mm; Laminar cooling adopts centralized ultra-fast cooling mode, with upper and lower headers at 90% and 100%, the middle temperature at 720-780℃, and the coiling temperature at 620-680℃.

8. The method for preparing 300MPa grade cold-rolled enameled steel according to claim 7, characterized in that: High-pressure water descaling treatment was carried out at the roughing and finishing entrances, with the pressure of high-pressure water being 18-22 MPa, and the descaling water volume at the roughing and finishing entrances being 540 m3 respectively. 3 / h and 450m 3 / h, the distances between the nozzle and the slab / strip are 120mm and 90mm respectively.

9. The method for preparing 300MPa grade cold-rolled enameled steel according to claim 5, characterized in that: The specific process of pickling rolling is as follows: the hot rolled coil is cold rolled through 5 stands, and the total cold rolling reduction is controlled to be 70-80%.

10. The method for preparing 300MPa grade cold-rolled enameled steel according to claim 5, characterized in that: The specific leveling process is: controlling the leveling elongation to be 0.6-1.5%.

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