Low-cost hot-rolled steel plate for high temperature enameling, and manufacturing method theefor

Abstract

A low-cost hot-rolled steel plate for high temperature enameling. The chemical composition in mass percentage of the plate contains mainly: C: 0.03-0.12%, Si: 0.1-0.5%, Mn: 0.3-1.5%, P: 0.03-0.10%, Al: 0.02-0.10%, Cr: 0.01-0.20%, Cu: 0.01-0.30%, N: 0.007-0.020%, and B: 0.0006-0.003%, and further satisfies: P(N14B/11)10.sup.3>0.3. A manufacturing method for manufacturing such low-cost hot-rolled steel plate.

Claims

1. A low-cost hot-rolled steel plate for high temperature enameling consisting of the following chemical composition in mass percentage: C: 0.03-0.12%, Si: 0.1-0.5%, Mn: 0.3-1.5%, P: 0.03-0.10%, Al: 0.02-0.10%, Cr: 0.01-0.20%, Cu: 0.01-0.30%, N: 0.007-0.020%, B: 0.0006-0.003%, and the balance being Fe and other inevitable impurities; wherein the chemical composition further satisfies the condition: P(N14B/11)10.sup.3>0.3; and in the calculation, P, N, and B are respectively substituted with the numerical value before the percent sign in the mass percentage of the corresponding chemical element; and wherein the hot-rolled steel plate has a microstructure of ferrite and pearlite, and the ferrite has an average grain size at grade 10-12, as determined in accordance with GB/T 6394-2017.

2. The low-cost hot-rolled steel plate for high temperature enameling of claim 1, wherein a thickness of the hot-rolled steel plate is 1.5-3.5 mm.

3. The low-cost hot-rolled steel plate for high temperature enameling of claim 1, wherein a yield strength of the hot-rolled steel plate in its hot-rolled state is 364-410 MPa, a decrease in yield strength measured after high temperature enameling within a temperature range of 870-950 C. for 10 minutes and air cooling is within 10% relative to the yield strength of the hot-rolled steel plate, and a value of the yield strength of the steel plate after the high temperature enameling is greater than or equal to 342 MPa.

4. A manufacturing method for the low-cost hot-rolled steel plate for high temperature enameling of claim 1, comprising the following steps: (1) smelting and casting; (2) heating; (3) hot rolling: controlling a rough rolling temperature at above 850 C., a finish rolling start temperature at 900-1050 C., and a finish rolling end temperature at 840-900 C.; (4) laminar cooling: controlling a cooling rate at 10-35 C./s; and (5) coiling.

5. The manufacturing method of claim 4, wherein in step (2), a heating temperature is controlled at 1150-1260 C.

6. The manufacturing method of claim 4, wherein in step (5), a coiling temperature is controlled at 550-680 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a relationship between the defined chemical element synergy M* and the yield strength of the low-cost hot-rolled steel plate for high temperature enameling after enameling, in the present invention; and

(2) FIG. 2 is a photo of the microstructure of the low-cost hot-rolled steel plate for high temperature enameling in Example 1 of the present invention.

DETAILED DESCRIPTION

(3) The low-cost hot-rolled steel plate for high temperature enameling, and the manufacturing method therefor in the present invention will be further explained and described below in conjunction with the accompanying drawings and specific embodiments. However, the explanation and description do not constitute improper limitations on the technical solutions of the present invention.

Examples 1-6 and Comparative Examples 1-3

(4) The low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6 and comparative steel plates in Comparative Examples 1-3 are prepared according to the following steps: (1) Smelting and Casting: Performing smelting and casting according to chemical compositions shown in Table 1 below. The smelted molten steel is then subjected to vacuum degassing and continuous casting to obtain a continuous cast slab; (2) Heating: The obtained continuous cast slab is heated, and the heating temperature is controlled at 1150-1260 C.; (3) Hot rolling: Controlling the rough rolling temperature at above 850 C., the finish rolling start temperature at 900-1050 C., and the finish rolling end temperature at 840-900 C.; (4) Laminar cooling: Performing laminar water cooling, and controlling the cooling rate at 10-35 C./s; and (5) Coiling: Controlling the coiling temperature at 550-680 C.

(5) Table 1 presents the mass percentages of various chemical elements in the low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6 and the comparative steel plates in Comparative Examples 1-3.

(6) TABLE-US-00001 TABLE 1 (the balance being Fe and other inevitable impurities) Serial C Si Mn P Al Cr Cu N B Number (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) M* Example 1 0.06 0.21 1.2 0.06 0.035 0.06 0.1 0.012 0.0012 0.63 Example 2 0.05 0.38 1.4 0.05 0.05 0.02 0.12 0.017 0.0015 0.75 Example 3 0.04 0.13 0.9 0.03 0.04 0.08 0.11 0.012 0.0015 0.30 Example 4 0.08 0.22 0.76 0.08 0.06 0.07 0.06 0.008 0.0022 0.42 Example 5 0.09 0.25 0.8 0.07 0.06 0.05 0.055 0.013 0.0028 0.66 Example 6 0.11 0.45 0.52 0.04 0.09 0.19 0.28 0.015 0.0008 0.56 Comparative 0.06 0.15 0.65 0.04 0.032 0.06 0.07 0.005 0.001 0.15 Example 1 Comparative 0.05 0.2 0.72 0.02 0.025 0.05 0.05 0.004 0.0015 0.04 Example 2 Comparative 0.07 0.35 0.68 0.03 0.041 0.07 0.08 0.01 0.002 0.22 Example 3 Note: M* = P (N 14 B/11) 10.sup.3, and in the calculation, P, N, and B in the formula are respectively substituted with the numerical value before the percent sign in the mass percentage of the corresponding chemical element.

(7) Table 2 presents the specific process parameters of the low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6 and the comparative steel plates in Comparative Examples 1-3 in the above-mentioned manufacturing steps.

(8) TABLE-US-00002 TABLE 2 Step (3) Step (2) Rough Finish rolling Finish rolling Step (4) Step (5) Heating rolling start end Cooling Coiling Serial Thickness t temperature temperature temperature temperature rate temperature Number (mm) ( C.) ( C.) ( C.) ( C.) ( C./s) ( C.) Example 1 2.5 1230 1050 1000 855 20 610 Example 2 1.5 1220 880 910 860 32 680 Example 3 2.5 1230 1060 1020 850 12 560 Example 4 2.0 1180 1050 1030 880 12 640 Example 5 3.0 1230 1080 1050 860 25 580 Example 6 3.5 1150 920 960 840 13 600 Comparative 2.5 1200 1050 1000 845 10 610 Example 1 Comparative 2.0 1230 1050 1030 850 8 620 Example 2 Comparative 1.5 1220 1010 1000 860 11 620 Example 3

(9) The obtained low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6 and the comparative steel plates in Comparative Examples 1-3 are respectively sampled, properties of the steel plates in the Examples and comparative examples are tested to obtain test results which are listed in Table 3, and the relevant performance testing methods and procedures are described as follows: Tensile test: an SCL233 normal-temperature tensile test machine is utilized for test based on GB/T 228.1-2010 Metallic Materials-Tensile TestingPart 1: Method of test at room temperature, the test was conducted at a tensile speed of 3 mm/min with a JIS5 tensile test specimen. Hole expanding test: an SCL250 cupping test machine is utilized for test based on GB/T 24524-2009 Metallic materials-Sheet and strip-Hole expanding test, wherein the test speed is 6 mm/min. Drop-weight test: a corresponding drop-weight test apparatus is adopted for testing adhesion of enamel based on a drop-weight test method described in European standard BS EN 10209-1996; and Average grain size of ferrite: the average grain size is determined by comparing with a standard series grading chart by adopting a comparison method with the aid of a metallographic microscope, based on GB/T 6394-2017 Determination of estimating the average grain size of metal.

(10) Table 3 presents the performance test results, microstructures and grain sizes of ferrite of the low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6 and the comparative steel plates in Comparative Examples 1-3.

(11) TABLE-US-00003 TABLE 3 Yield Tensile Elongation Hole Average Serial strength strength A50 expanding grain size of Number (MPa) (MPa) (%) rate (%) Microstructure ferrite Example 1 390 458 29 85 ferrite + pearlite Grade 10 Example 2 410 512 27 82 ferrite + pearlite Grade 12 Example 3 368 466 28 92 ferrite + pearlite Grade 10 Example 4 364 460 29 90 ferrite + pearlite Grade 10 Example 5 385 464 28 80 ferrite + pearlite Grade 11 Example 6 372 456 31 88 ferrite + pearlite Grade 10 Comparative 346 410 30 91 ferrite + pearlite Grade 9 Example 1 Comparative 320 385 33 98 ferrite + pearlite Grade 8 Example 2 Comparative 355 391 32 96 ferrite + pearlite Grade 9 Example 3

(12) To further demonstrate the performance of the low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6 and the comparative steel plates in Comparative Examples 1-3 after enameling, it is necessary to enamel the steel plates in the Examples and the comparative examples:

(13) Specifically, a Ferro EMP6515 high-temperature glaze is adopted to perform single-sided wet-process enameling on the steel plates in the Examples and the Comparative Examples. The enameling process was controlled at an enameling temperature of 870-950 C. with a holding time of 10 minutes, followed by air cooling to obtain the enameled steel plates in Examples 1-6 and Comparative Examples 1-3.

(14) After the above-mentioned operations are completed, the enameled hot-rolled steel plates in Examples 1-6 and the enameled comparative steel plates in Comparative Examples 1-3 were observed and tested. After enameling, the steel plates were enabled to stand for 48 hours, no fish scaling phenomenon was observed on surfaces of the steel plates. The adhesion performance between the steel plates and enamel was verified by the drop-weight test, and the adhesion was excellent. Tensile tests were conducted to determine the yield strength of the enameled steel plates of each example and comparative sample. The test results are listed in Table 4.

(15) Table 4 presents the performance test results of the low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6 and the comparative steel plates in Comparative Examples 1-3 after enameling.

(16) TABLE-US-00004 TABLE 4 Yield strength Decrease in yield Fish scaling Adhesion Serial Number (MPa) strength (%) resistance performance Example 1 369 5.4 No fish scaling Excellent phenomenon occurs Example 2 385 6.1 No fish scaling Excellent phenomenon occurs Example 3 342 7.1 No fish scaling Excellent phenomenon occurs Example 4 348 4.4 No fish scaling Excellent phenomenon occurs Example 5 363 5.7 No fish scaling Excellent phenomenon occurs Example 6 355 4.6 No fish scaling Excellent phenomenon occurs Comparative 270 22.0 No fish scaling Excellent Example 1 phenomenon occurs Comparative 220 31.3 No fish scaling Excellent Example 2 phenomenon occurs Comparative 290 18.3 No fish scaling Excellent Example 3 phenomenon occurs

(17) It can be seen from Table 4 in conjunction with Tables 1-3 that the low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6 have the thickness within a range of 1.5-3.5 mm, the yield strength in the hot-rolled state of 364-410 MPa, the tensile strength of 456-512 MPa, the elongation of 27-31%, and the hole expanding rate of 80-92%. After high temperature enameling within a temperature range of 870-950 C., the decrease in the yield strength of the steel plates in Examples 1-6 is within 10%, and the yield strength is still greater than or equal to 342 MPa. This indicates the steel plates have excellent high temperature enameling resistance. After the enameled steel plates finally obtained in Examples 1-6 were enabled to stand for 48 h, no fish scaling phenomenon was observed on the enamel surfaces. The drop-weight test confirmed the excellent adhesion between the steel plates and an enamel layer, fully meeting user requirements.

(18) In contrast, the performance of the comparative steel plates in Comparative Examples 1-3 are significantly inferior to those of the low-cost hot-rolled steel plates for high temperature enameling in Examples 1-6. In Comparative Examples 1-3, the content of the P, N, and B elements in the steel does not satisfy the condition P(N14B/11)10.sup.3>0.3. After high temperature enameling within the temperature range of 870-950 C., the decrease in the yield strength reaches 18% or above, and the value of the yield strength is within 220-290 MPa.

(19) FIG. 1 shows the relationship between the defined chemical element synergy M* and the yield strength of the low-cost hot-rolled steel plate for high temperature enameling after enameling, in the present invention, where M*=P(N14B/11)10.sup.3.

(20) It can be seen from FIG. 1 that in the present invention, there is an obvious correlation between the yield strength of the steel plate after enameling and the value of M*. When the value of M* is greater than 0.3, it can be ensured that the yield strength is 342 MPa or above, which satisfies the design target requirements of the product.

(21) FIG. 2 is a photo of a microstructure of the low-cost hot-rolled steel plate for high temperature enameling in Example 1.

(22) As shown in FIG. 2, the microstructure of the low-cost hot-rolled steel plate for high temperature enameling in Example 1 is ferrite and pearlite, and the average grain size of ferrite is at grade 10.

(23) It should be noted that combination manners of technical features in this case are not limited to combination manners recorded in the claims of this case or combination manners recorded in the specific embodiments, and all the technical features recorded in this case can be freely combined or incorporated in any manners unless there are conflicts between them.

(24) It should be further noted that the embodiments listed above are merely the specific embodiments of the present invention. The present invention is not limited to the above-mentioned embodiments, similar changes or variants made therewith can be directly obtained or readily envisioned from the content disclosed by the present invention by those skilled in the art so as to fall within the protection scope of the present invention.