HOT-ROLLED STEEL FOR ENAMELING HAVING ENAMELING AND FIRING STRENGTHENING PROPERTY, AND MANUFACTURING METHOD THEREFOR

Abstract

Disclosed is a hot-rolled steel for enameling having an enameling and firing strengthening property, comprising, in addition to Fe and inevitable impurities, the following chemical elements in mass percent: C: 0.03-0.07%, Si0.05%, Mn: 1.5-2.5%, Al: 0.01-0.05%, Cr: 0.25-0.65%, Cu: 0.02-0.20%, Ti: 0.01-0.08%, V: 0.01-0.10%, and Mo: 0.01-0.10%. Accordingly, further disclosed is a manufacturing method for the hot-rolled steel for enameling, comprising the steps of: (1) smelting and casting; (2) heating; (3) hot rolling, the temperature of rough rolling being controlled to be greater than 850 C., the start temperature of finish rolling being controlled to be 900-1050 C., and the final temperature of finish rolling being controlled to be 840-900 C.; (4) laminar cooling, the cooling speed being controlled to be 10-35 C./s; and (5) coiling. The hot-rolled steel for enameling provided by the present invention has low strength and good formability in a hot-rolled state, and after high-temperature enameling and firing, the yield strength of the hot-rolled steel for enameling is not decreased but increased, such that the strength of a final enamel product can be effectively improved.

Claims

1. A hot-rolled steel for enameling having enamel firing strengthening properties, wherein, in addition to Fe and unavoidable impurities, it further comprises the following chemical elements in mass percentages: C: 0.030.07%, Si0.05%, Mn: 1.52.5%, Al: 0.010.05%, Cr: 0.250.65%, Cu: 0.020.20%, Ti: 0.010.08%, V: 0.010.10%, Mo: 0.010.10%.

2. The hot-rolled steel for enameling according to claim 1, wherein it comprises the following chemical elements in mass percentages: C: 0.030.07%, Si0.05%, Mn: 1.52.5%, Al: 0.010.05%, Cr: 0.250.65%, Cu: 0.020.20%, Ti: 0.010.08%, V: 0.010.10%, Mo: 0.010.10%, with a balance of Fe and other unavoidable impurities.

3. The hot-rolled steel for enameling according to claim 1, wherein it further comprises B: 0.00060.003%.

4. The hot-rolled steel for enameling according to claim 1, wherein each chemical element satisfies: (CTi/4V/4.25)(Mn+Cr)>0.05; wherein each of C, Ti, V, Cr and Mn represents the value of mass percentage of the corresponding element.

5. The hot-rolled steel for enameling according to claim 1, wherein it has a microstructure of ferrite+pearlite.

6. The hot-rolled steel for enameling according to claim 5, wherein it has a ferrite grain size of Grade 810.

7. The hot-rolled steel for enameling according to claim 1, wherein it has a thickness of 1.5-3.5 mm.

8. The hot-rolled steel for enameling according to claim 1, wherein it has a yield strength of 345389 MPa in a hot-rolled state, and a yield strength of 402439 Mpa after high temperature enamel firing at a temperature in a range of 870950 C.

9. An enameled steel comprising a substrate and an enamel layer on one or two surfaces of the substrate, wherein the substrate is the hot-rolled steel for enameling according to claim 1.

10. The enameled steel according to claim 9, wherein the enameled steel has a yield strength of 400450 MPa, a tensile strength of 610660 MPa, an elongation A.sub.50 of 18%; and/or, the substrate has a microstructure of ferrite+bainite.

11. A manufacturing method for the hot-rolled steel for enameling according to claim 1, comprising steps of: (1) smelting and casting; (2) heating; (3) hot-rolling: wherein a rough rolling temperature is controlled at more than 850 C., an initial finish rolling temperature is controlled at 9001050 C., and a final finish rolling temperature is controlled at 840900 C.; (4) laminar flow cooling: wherein a cooling rate is controlled at 1035 C./s; (5) coiling.

12. The manufacturing method according to claim 9, wherein, in step (2), a heating temperature is 11501260 C.

13. The manufacturing method according to claim 9, wherein, in step (5), a coiling temperature is controlled at 550680 C.

14. A manufacturing method for the enameled steel according to claim 9, comprising a step of manufacturing the hot-rolled steel for enameling by the method comprising: (1) smelting and casting; (2) heating: (3) hot-rolling: wherein a rough rolling temperature is controlled at more than 850 C., an initial finish rolling temperature is controlled at 9001050 C., and a final finish rolling temperature is controlled at 840900 C.; (4) laminar flow cooling: wherein a cooling rate is controlled at 1035 C./s; (5) coiling, and a step of enamel firing the hot-rolled steel for enameling as a substrate.

15. The manufacturing method according to claim 14, wherein, in the step of enamel firing, the steel is enamel-fired at 870950 C. for 515 min.

16. The hot-rolled steel for enameling according to claim 2, wherein it further comprises B: 0.00060.003%.

17. The hot-rolled steel for enameling according to claim 2, wherein each chemical element satisfies: (CTi/4V/4.25)(Mn+Cr)>0.05; wherein each of C, Ti, V, Cr and Mn represents the value of mass percentage of the corresponding element.

18. The hot-rolled steel for enameling according to claim 5, wherein the proportion of pearlite is 1045% by area ratio.

19. The enameled steel according to claim 10, wherein the proportion of bainite is 1040% by area ratio.

20. The manufacturing method according to claim 15, wherein the method further comprises a shot blasting treatment for the hot-rolled steel for enameling before the step of enamel firing, and/or the enamel firing treatment is carried out by one enamel coating/one firing or two enamel coatings/two firings.

Description

DESCRIPTION OF THE DRAWINGS

[0056] FIG. 1 shows the effect of different enamel firing temperatures on the yield strength performance of the steel of Example 1 of the present disclosure and Comparative Example 1 (Comp. Ex. 1) after enamel firing.

[0057] FIG. 2 shows the metallographic structure of the hot-rolled steel for enameling of Example 1 in a hot-rolled state.

[0058] FIG. 3 shows the metallographic structure of the hot-rolled steel for enameling of Example 1 after it is subjected to high temperature enamel firing at 870 C. and kept for 10 min and air-cooled.

DETAILED DESCRIPTION

[0059] The hot-rolled steel for enameling and the manufacturing method therefor will be further interpreted and explained below in combination with specific embodiments and figures, but the interpretation and explanation do not constitute an undue limitation to the technical solution of the present disclosure.

Example 1-7 and Comparative Example 1-2

[0060] The hot-rolled steels for enameling of Examples 1-7 and the comparative steels of Comparative Examples 1-2 were prepared by the following steps: [0061] (1) Smelting and casting were performed according to the chemical compositions shown in Table 1: The molten steel after the completion of smelting was subjected to continuous casting after vacuum degassing treatment to obtain a continuous casting slab. [0062] (2) heating: the continuous casting slab was heated and the heating temperature was controlled at 11501260 C. [0063] (3) hot-rolling: the rough rolling temperature was controlled at higher than 850 C., the initial finish rolling temperature was controlled at 9001050 C., and the final finish rolling temperature was controlled at 840900 C. [0064] (4) laminar flow cooling: the steel was subjected to laminar flow cooling and the cooling rate was controlled at 1035 C./s. [0065] (5) coiling: the coiling temperature was controlled at 550680 C.

[0066] The hot-rolled steels for enameling of Examples 1-7 according to the present disclosure was prepared by the above steps, and its chemical composition and related process parameters all met the control requirements of the design specification of the present disclosure.

[0067] It should be noted that, different from the above hot-rolled steels for enameling of Examples 1-7, although the comparative steels of Comparative Examples 1-2 were also prepared by the above steps (1)-(5), there were parameters in the chemical composition that did not meet the design requirements of the present disclosure.

[0068] Table 1 lists the mass percentages of various chemical elements in the hot-rolled steels for enameling of Examples 1-7 and the comparative steels of Comparative Examples 1-2.

TABLE-US-00001 TABLE 1 (a balance of Fe and other unavoidable impurities) C Si Mn Al Cr Cu Ti V Mo B No. (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) M* Ex. 1 0.052 0.008 1.9 0.032 0.53 0.05 0.04 0.04 0.05 0.079 Ex. 2 0.057 0.015 1.5 0.03 0.52 0.2 0.05 0.056 0.01 0.063 Ex. 3 0.066 0.042 2.5 0.01 0.65 0.16 0.07 0.09 0.045 0.086 Ex. 4 0.07 0.035 2.1 0.025 0.39 0.09 0.08 0.06 0.07 0.0015 0.089 Ex. 5 0.04 0.048 2.3 0.05 0.48 0.11 0.045 0.01 0.1 0.073 Ex. 6 0.042 0.019 2.2 0.038 0.25 0.02 0.02 0.055 0.053 0.0025 0.059 Ex. 7 0.032 0.026 2.1 0.02 0.6 0.08 0.022 0.025 0.06 0.0008 0.056 Comp. 0.058 0.032 0.32 0.033 0.04 0.06 0.16 0.0018 0.006 Ex. 1 Comp. 0.06 0.016 0.65 0.018 0.03 0.01 0.12 0.020 Ex. 2 Note: M* = (C Ti/4 V/4.25) (Mn + Cr); wherein each of C, Ti, V, Cr and Mn represents the value of mass percentage of the corresponding element.

[0069] Note: M*=(CTi/4V/4.25)(Mn+Cr); wherein each of C, Ti, V, Cr and Mn represents the value of mass percentage of the corresponding element.

[0070] Table 2 lists the specific process parameters of the hot-rolled steels for enameling of Examples 1-7 and the control steels of Comparative Examples 1-2.

TABLE-US-00002 TABLE 2 Step (3) Step (2) Rough Initial finish Final finish Step (4) Step (5) Thickness Heating rolling rolling rolling Cooling Coiling t temperature temperature temperature temperature rate temperature No. (mm) ( C.) ( C.) ( C.) ( C.) ( C./s) ( C.) Ex. 1 2.5 1230 1050 1000 855 20 610 Ex. 2 1.5 1220 880 910 860 32 680 Ex. 3 2 1230 1060 1020 850 12 560 Ex. 4 3.5 1180 1050 1030 880 12 640 Ex. 5 3 1230 1080 1050 860 25 580 Ex. 6 4 1150 920 960 840 13 600 Ex. 7 2.5 1200 1050 1020 850 30 630 Comp. Ex. 1 2.5 1200 1050 1000 845 10 610 Comp. Ex. 2 1.8 1230 1050 1030 850 15 620

[0071] The hot-rolled steels for enameling in the hot-rolled state of Examples 1-7 and the control steels of Comparative Examples 1-2 were sampled and tested for its performance in the hot-rolled state and the test results were recorded in the following Table 3. The test method and technical means for relevant performance were as follows: Tensile test: according to GB/T 228.1-2010 Metallic material-Tensile testing-Method of test at room temperature, the samples were tested by SCL233 room temperature tensile testing machine, wherein the tensile speed was 3 mm/min and the tensile specimen was JIS5 tensile specimen, so as to obtain the yield strength, tensile strength and elongation A.sub.50 of the hot-rolled steels of Examples 1-7 and Comparative Examples 1-2.

TABLE-US-00003 TABLE 3 Yield strength Tensile strength Elongation A.sub.50 No. (MPa) (MPa) (%) Ex. 1 352 561 30 Ex. 2 345 558 32 Ex. 3 380 606 28 Ex. 4 389 625 28 Ex. 5 376 582 30 Ex. 6 364 570 29 Ex. 7 370 575 31 Comp. Ex. 1 537 594 24 Comp. Ex. 2 456 535 30

[0072] As shown in Table 3, in the present disclosure, the hot-rolled steels for enameling of Examples 1-7 in the hot-rolled state had lower yield strength and good forming performance. The yield strength was 345-389 MPa, the tensile strength was 558-625 MPa and A.sub.50 was 28-32%.

[0073] The lower yield strength was conducive to the stamping and cold-bending formation processing of the steel plate in use by the user. For example, in the processing of the inner barrel body of the water heater, it can avoid resilience after cold-bending and edge coiling, which was conducive to the welding process. Compared with Examples 1-7, the yield strength of the control steels of Comparative Examples 1-2 was higher, which was not conducive to the processing in use by the user.

[0074] In order to further verify the properties of the hot-rolled steels for enameling of Examples 1-7 of the present disclosure and the control steels of Comparative Examples 1-2 after enameling, it is necessary to perform enamel treatment for the steel plate of each Example and Comparative Example: The steel plate of each Example and Comparative Example was subjected to wet double-sided enamel coating with a high-temperature glaze of FULU EMP6515 type. The enamel firing process was controlled as follows: the enamel firing temperature was controlled at 870950 C. and hold for 10 min, then the steel plates were air cooled to obtain the steel plates of Examples 1-7 and Comparative Examples 1-2 after enameling.

[0075] It should be noted that, in the present embodiment, Examples 1-7 and Comparative Examples 1-2 were all controlled to be subjected to enamel firing at high temperature in the range of 870950 C. and kept for 10 minutes. In the present disclosure, the specific enamel firing temperature of each Example and Comparative Example is listed in Table 4 below.

TABLE-US-00004 TABLE 4 No. High temperature enamel firing temperature ( C.) Ex. 1 870 Ex. 2 890 Ex. 3 870 Ex. 4 950 Ex. 5 900 Ex. 6 910 Ex. 7 920 Comp. Ex. 1 870 Comp. Ex. 2 870

[0076] After the completion of the above high-temperature enameling, the hot-rolled steels for enameling in Examples 1-7 and the control steels of Comparative Examples 1-2 that were treated by high-temperature enameling were further observed, analyzed and tested: After standing for 48 hours, the steel plates of Examples 1-7 and the steel plates of Comparative Examples 1-2 were observed to determine whether the fish-scaling phenomenon occurs on the surface. The adhesion between the steel plate and the enamel glaze was tested by the drop weight test. The yield strength, tensile strength and elongation A.sub.50 of the steel plate in each Example and Comparative Example after enameling were determined by the tensile test, and the results of the test were listed in Table 5.

[0077] Table 5 lists the mechanical property and enameling performance test results of the hot-rolled steels for enameling of Examples 1-7 and the control steels of Comparative Examples 1-2 after enameling.

TABLE-US-00005 TABLE 5 Yield Tensile strength strength Elongation Fish-scaling Adhesion No. (MPa) (MPa) A.sub.50 (%) resistance performance Ex. 1 410 621 20 No fish- good scaling Ex. 2 402 610 22 No fish- good scaling Ex. 3 436 657 18 No fish- good scaling Ex. 4 439 660 19 No fish- good scaling Ex. 5 415 633 20 No fish- good scaling Ex. 6 417 632 19 No fish- good scaling Ex. 7 420 640 20 No fish- good scaling Comp. Ex. 1 396 430 32 No fish- good scaling Comp. Ex. 2 300 372 33 Fish- good scaling

[0078] As shown in Table 4 in combination with Table 1-3, it can be seen that the thickness range of the hot-rolled steels for enameling of Example 1-7 may be between 1.5 mm and 3.5 mm, and the strength of the steel plates of Example 1-7 did not decrease but increased after high-temperature enamel firing treatment at a temperature in the range of 870950 C. Its yield strength increased to 402439 MPa, the tensile strength increased to 610660 MPa, and the elongation A.sub.50 was 18-22%.

[0079] The finally obtained enameled steel plate of Examples 1-7 was observed after 48 hours, and no fish-scaling phenomenon occurred on the enamel surface. After the drop weight test, the adhesion performance between the steel plate and the glaze layer was excellent, which fully met the use requirements of the users.

[0080] Correspondingly, the performance of the control steel plates of Comparative Examples 1-2 was significantly worse than the hot-rolled steels for enameling of Examples 1-7. With respect to Comparative Examples 1-2, after high temperature enamel firing, the yield strength of the steels of Comparative Examples 1-2 decreased dramatically. The large decrease in the yield strength of the steel plate before and after enamel firing will lead to problems such as bending and deformation of the steel plate, which was not conducive to the processing and use by the users. At the same time, the fish-scaling defect appeared after Comparative Example 2 was subjected to double-sided enameling, which could not meet the requirements of the fish-scaling resistance of double-sided enameling.

[0081] FIG. 1 shows the effect of different enamel firing temperatures on the yield strength performance of the steel of Example 1 of the present disclosure and Comparative Example 1 after enamel firing.

[0082] As shown in FIG. 1, with the increase of the enamel firing temperature, the yield strength of the steel in Example 1 showed an increasing trend. When the enamel firing temperature was 930 C., the yield strength may be up to 425 MPa. With the increase of the enamel firing temperature, the yield strength of the steel in Comparative Example 1 showed a decreasing trend. When the enamel firing temperature was 930 C., the yield strength of the steel in Comparative Example 1 decreased to 289 MPa.

[0083] FIG. 2 shows the metallographic structure of the hot-rolled steel for enameling of Example 1 in a hot-rolled state.

[0084] FIG. 3 shows the metallographic structure of the hot-rolled steel for enameling of Example 1 after it is subjected to high temperature enamel firing at 870 C. and kept for 10 min and air-cooled.

[0085] As shown in FIGS. 2 and 3, in the present disclosure, the hot-rolled steel for enameling of Example 1 has a microstructure of ferrite+pearlite, which was transformed into ferrite+bainite after high-temperature enamel firing.

[0086] It should be noted that the combination of the technical features in the present disclosure is not limited to the combination described in the claims or the specific embodiments, and all the technical features recorded herein may be freely combined or combined in any way, unless there is a contradiction between them.

[0087] It should also be noted that the examples listed above are only specific embodiments of the present disclosure. Obviously, the present disclosure is not limited to the above embodiments, and similar changes can be made thereby. All the modifications directly derived from the contents disclosed in the present disclosure or easily envisaged by those skilled in the art shall fall within the protection scope of the present disclosure.