Hot-rolled pickled steel plate for refrigerator compressor shell and manufacturing method of hot-rolled pickled steel plate

Abstract

The invention discloses a hot-rolled pickled steel plate for a refrigerator compressor shell and a manufacturing method of the hot-rolled pickled steel plate, and belongs to the field of manufacturing of hot-rolled pickled steel plates. The performance of the steel plate can meet the use requirement of stamping a refrigerator compression shell, and the steel plate comprises, by weight, 0.02%-0.08% of C, smaller than or equal to 0.034% of Si, 0.1%-0.5% of Mn, smaller than or equal to 0.02% of P, smaller than or equal to 0.01% of S, 0.025%-0.05% of Al, smaller than or equal to 0.0028% of N, 0.0008%-0.005% of B and the balance iron and inevitable impurities. The manufacturing method comprises the following steps: (1) carrying out argon blowing stirring on molten steel in a steel ladle, and carrying out continuous casting to form a continuous casting billet; (2) the continuous casting billet or the steel billet is heated at the temperature of 1120-1260 DEG C and then subjected to multi-pass rolling, and the total reduction rate is not lower than 90%; the finish rolling temperature is not lower than 835 DEG C, then cooling to the coiling temperature, and the coiling temperature is 540-640 DEG C; and (4) the hot-rolled coil is subjected to acid pickling with the free acid concentration being 130-200 g / L and the bath solution temperature being 60-90 DEG C to remove scale on the surface. The steel plate which contains the components and is manufactured by the process is suitable for punching the refrigerator compressor main shell with a complex shape.

Description

Technical Field

[0001] This invention relates to the manufacture of hot-rolled pickled steel sheets, and more particularly to a hot-rolled pickled steel sheet for refrigerator compressor housings and its manufacturing method. Background Technology

[0002] Hot-rolled pickled steel sheets are widely used in the automotive, home appliance, and construction machinery industries due to their excellent surface quality and high sheet precision. In the home appliance industry, they are mainly used to manufacture compressor housings, brackets, or liquid storage tanks, commonly using the low-carbon mild steel grade SPHC. When users slit thin strips (≤3.0mm), the edges of the hot-rolled pickled low-carbon mild steel strips used for stamping liquid storage tank housings or compressor brackets often exhibit edge binding. In 2018, a steel mill received three such complaints. Therefore, there is an urgent need to develop new production processes to improve the edge structure.

[0003] The above-mentioned reasons are easily observed in hot-rolled pickled steel sheets used for compressor housings with thin specifications (≤3.0mm). During the finishing rolling process, the thin strip heats up quickly, resulting in a temperature drop at the edges. The edge temperature of the strip is even lower than the AR3 temperature of the steel grade itself. Rolling in the two-phase region leads to mixed crystals at the edges. The greater the temperature difference between the strip edge and the AR3 temperature of the steel grade, the more severe the mixed crystals and the wider the mixed crystal area at the edge of the strip.

[0004] Studies have shown that Ar3 = 910 - 730[C] - 73[Mn] - 16000[B]. This formula indicates that increasing C and MN, or adding B, can lower the Ar3 temperature, with the effect of adding B being particularly significant. Lowering the Ar3 temperature of the steel grade itself reduces the actual edge temperature during production from being lower than the steel grade's Ar3 temperature, and may even result in the edge temperature being higher than the steel grade's Ar3 temperature, thus improving the edge microstructure of low-carbon mild steel. The preferential precipitation of coarse boron nitride particles in the high-temperature austenite inhibits the precipitation of fine aluminum nitride, weakening the pinning effect of aluminum nitride at grain boundaries and its precipitation strengthening effect on the matrix. The segregation of boron at austenite grain boundaries inhibits ferrite nucleation, leading to grain coarsening in hot-rolled plates and reduced strength. To ensure strength, the composition must consider the C and MN contents when adding B. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a hot-rolled pickled steel plate for refrigerator compressor housing and its manufacturing method, so as to provide deep drawing capability, excellent resistance to lugs and cracking when manufacturing refrigerator compressor housing parts, and to meet the processing requirements of refrigerator compressor housing parts.

[0006] Technical solution: A hot-rolled pickled steel sheet for a refrigerator compressor housing, the composition by weight percentage is as follows:

[0007] C: 0.02-0.08%; Si ≤ 0.034%; Mn: 0.1-0.5%; P ≤ 0.02%; S ≤ 0.01%; Al: 0.025-0.05%; N ≤ 0.0028%; B: 0.0015-0.005%; balance is iron and unavoidable impurities.

[0008] Preferably, the weight percentage of component C is 0.03-0.055%.

[0009] Preferably, the weight percentage of Mn is 0.17-0.27%.

[0010] Preferably, the weight percentage of component B is 0.0015-0.0025%.

[0011] Preferably, the microstructure of the steel plate consists of ferrite and pearlite. The average grain diameter of the ferrite is not greater than 15 μm.

[0012] Carbon is a key element for ensuring the specified strength of steel plates. Increasing the carbon content increases strength, but decreases plasticity, failing to meet the requirement of deep drawing without cracking. Therefore, the carbon content is controlled at C: 0.02-0.08%, with an optimal range of 0.03-0.055%.

[0013] The addition of manganese is used to improve the strength of steel. The amount of manganese added is mainly determined by the strength structure of the steel, but too much manganese will reduce the plasticity of the steel and fail to meet the requirements of deep drawing. Therefore, the manganese content is controlled at 0.1-0.5%, with an optimal range of 0.17-0.27%.

[0014] The AR3 temperature calculation for low-carbon mild steel is AR3 = 910-730[C]-73[Mn]-16000[B]. Adding boron can significantly reduce the AR3 temperature of AR3 steel. In actual production, the final rolling temperature of thin strip (≤2.0mm) can reach about 830℃. Depending on the amount of C and Mn added and to ensure that the AR3 temperature of the steel is higher than the actual control temperature, the amount of boron added needs to be controlled between 0.0015-0.005%. The segregation of boron at the austenite grain boundaries inhibits ferrite nucleation, resulting in coarse grains in hot-rolled plates. Excessive boron content leads to larger and even uneven grain size, which is not conducive to deep drawing. The preferred range is 0.0015-0.025%.

[0015] In non-titanium alloy carbon-manganese steels, sulfur usually combines with manganese to form MnS, which is an inclusion with excellent plasticity. It will extend with the deformation of the steel billet and eventually seriously impair the transverse plasticity of the steel plate. Therefore, sulfur in non-titanium alloy steels should be kept as low as possible to avoid the formation of MnS inclusions. In order to balance manufacturing costs, the sulfur content should be controlled within the range of S≤0.01%.

[0016] Aluminum is a strong deoxidizing element. To ensure that the oxygen content in steel is as low as possible, the aluminum content is controlled at 0.025-0.05%. Aluminum reacts with nitrogen to form AlN compounds, and the fine AlN particles also help to improve the plasticity of the steel plate.

[0017] To achieve the aforementioned performance requirements of the steel grade, the present invention also provides a method for manufacturing hot-rolled pickled steel sheet for refrigerator compressor housings, the method comprising the following steps:

[0018] S1. Converter smelting, secondary refining, and argon blowing and stirring in the ladle to form a continuous casting billet.

[0019] S2. After continuous casting billet or steel billet is heated to 1120-1260℃, it is rolled in multiple passes with a total reduction of not less than 90%; the final rolling temperature is not less than 835℃, and then cooled to the coiling temperature of 540-640℃.

[0020] S3. Hot-rolled coils are pickled to remove surface iron oxide scale with a free acid concentration of 130-200g / L and a bath temperature of 60-90℃.

[0021] Converter blowing and secondary refining aim to ensure the basic composition requirements of the molten steel by adding alloying elements such as manganese and boron to adjust the alloy composition. Secondary refining homogenizes the temperature of the molten steel, allowing inclusions to float to the surface and ensuring the purity of the steel.

[0022] Continuous casting: ensures uniform internal composition and structure of the billet and good surface quality.

[0023] Hot rolling and cooling: The billet is heated at 1120-1260℃ to obtain a uniform austenitic structure. The final rolling temperature is not lower than 830℃ to avoid edge temperature drop below the AR3 steel grade, which would lead to edge mixed grains. Then it is cooled to the coiling temperature of 540-640℃. During the rolling and cooling process, aluminum reacts with nitrogen to form AlN. These particles are finely dispersed and uniformly distributed in the steel. At the same time, the ferrite structure in the steel is refined, with an average grain diameter of no more than 15μm, thereby improving the strength and plasticity of the steel plate.

[0024] Beneficial effects: This invention addresses the comprehensive performance requirements of hot-rolled pickled steel sheets for refrigerator compressor housings. By adding an appropriate amount of boron to low-carbon steel, the temperature of grade AR3 steel is significantly reduced, and the temperature control window for hot rolling is increased. Even when the hot rolling process cannot increase the final rolling temperature due to the lack of edge heating function in the production of thin-gauge low-carbon mild steel, the degree and range of edge mixing can still be controlled. The edge microstructure is significantly improved compared to non-boron-containing low-carbon mild steel, making it more suitable for the production of refrigerator compressor housing parts. Attached Figure Description

[0025] Figure 1aThe metallographic structure of the steel plate surface layer at the outermost edge according to Embodiment 1 of the present invention is uniform in ferrite and no mixed crystal phenomenon is observed on the surface.

[0026] Figure 1b The metallographic structure of the steel plate surface layer in Embodiment 1 of the present invention is located in the middle of the width, and the ferrite therein is uniform, with no mixed crystal phenomenon observed on the surface. Detailed Implementation

[0027] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] Example

[0029] The chemical composition of the steel plate by weight percentage is as follows: C: 0.03, Si: 0.0052, MN: 0.199, P: 0.0136, S: 0.0113, Al: 0.0396, N: 0.0025, B: 0.002, with the remainder being Fe and unavoidable impurities.

[0030] The molten steel with the above-mentioned chemical composition and specific gravity is continuously cast after secondary refining. The thickness of the continuously cast billet is 225-230mm. The resulting continuously cast billet is heated to 1224℃ and then hot-rolled to 2.5-6.35mm. The actual final rolling temperature used is 896℃ and the coiling temperature is 609℃, as shown in Table 3.

[0031] Using the above-mentioned composition and process parameters, the steel plate exhibits a yield strength of 207 MPa, a tensile strength of 320 MPa, and an elongation of 46.8%. The steel plate is used for stamping processes such as refrigerator compressor housings or bases, without cracking or ear-making phenomena. This demonstrates excellent deep-drawing performance, as shown in Table 2.

[0032] In Example 1, the ferrite in the width-direction edges and middle of the steel plate surface layer was uniform, and no mixed grain phenomenon was observed. Figure 1a and Figure 1b The average grain diameter is approximately 10 μm, which meets the control target of no more than 15 μm. The smaller the average grain diameter, the larger the grain boundary area.

[0033] For the specific chemical composition (wt%) of other embodiments 2-13, please refer to Table 1, and for the properties of the steel plate, please refer to Table 2.

[0034] Table 1 Chemical composition (wt%) of the examples

[0035] C Si MN P S Al N B Example 1 0.0302 0.0052 0.199 0.0136 0.0113 0.0396 0.0025 0.002 Example 2 0.032 0.005 0.194 0.0061 0.007 0.0403 0.0021 0.0018 Example 3 0.034 0.007 0.212 0.0128 0.0048 0.0379 0.0018 0.0024 Example 4 0.036 0.0171 0.208 0.019 0.0048 0.0461 0.0024 0.002 Example 5 0.038 0.0082 0.192 0.0098 0.0035 0.0416 0.0038 0.002 Example 6 0.04 0.0117 0.246 0.0138 0.0074 0.0432 0.0026 0.0025 Example 7 0.042 0.0073 0.215 0.0128 0.0081 0.0419 0.0022 0.0023 Example 8 0.044 0.0051 0.205 0.0153 0.0083 0.0386 0.0022 0.0021 Example 9 0.046 0.0059 0.223 0.0126 0.0065 0.036 0.0016 0.0021 Example 10 0.048 0.0066 0.196 0.0116 0.0071 0.0345 0.0017 0.0021 Example 11 0.05 0.0188 0.226 0.0115 0.0045 0.0403 0.002 0.0021 Example 12 0.0522 0.0088 0.213 0.0145 0.0085 0.0393 0.0027 0.0021 Example 13 0.0536 0.0205 0.214 0.0164 0.0043 0.0418 0.0025 0.002

[0036] Table 2 Process parameters and performance of the embodiments

[0037] Heating temperature Final rolling temperature winding temperature Yield strength RP02_N Tensile strength TS_N Elongation at break (BREAK_EL_N) User stamping situation Example 1 1224 896 609 207 320 46.8 excellent Example 2 1223 883 609 189 314 48.4 excellent Example 3 1202 891 602 201 326 46.7 excellent Example 4 1216 865 600 206 340 46 excellent Example 5 1209 878 603 205 332 46.2 excellent Example 6 1203 901 571 213 333 44 excellent Example 7 1168 883 599 193 324 47.8 excellent Example 8 1195 876 601 217 337 44.4 excellent Example 9 1217 887 601 212 333 45.6 excellent Example 10 1212 905 590 195 306 51.7 excellent Example 11 1207 878 602 239 354 42.7 excellent Example 12 1194 891 602 207 332 46.2 excellent Example 13 1210 892 602 221 345 43.7 excellent

[0038] As can be seen from the above embodiments, the finished steel plate processed using the above-mentioned composition and process parameters has a hot-rolled thickness between 2.5-6.35 mm, a yield strength greater than or equal to 189 MPa, and an elongation of not less than 42.7%, with a maximum of 51.7%, exhibiting high tensile strength. After being stamped by the user, no cracking or ear-making problems were observed, indicating that the material is suitable for processing refrigerator compressor housings, and the implementation effect is good.

[0039] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A hot-rolled pickled steel sheet for a refrigerator compressor housing, characterized by, The weight percentage of the components is: C: 0.02-0.08%; Si≤0.034%; Mn: 0.1-0.5%; P≤0.02%; S≤0.01%; Al: 0.025-0.05%; N≤0.0028%; B: 0.0015-0.005%; the balance being iron and unavoidable impurities.

2. The hot-rolled pickled steel plate for a refrigerator compressor housing according to claim 1, characterized by, The weight percentage of the component C is: 0.03-0.055%.

3. The hot-rolled pickled steel plate for a refrigerator compressor housing according to claim 1, characterized by, The weight percentage of the component Mn is: 0.17-0.27%.

4. The hot-rolled pickled steel plate for a refrigerator compressor housing according to claim 1, characterized by, The weight percentage of the component B is: 0.0015-0.0025%.

5. The hot-rolled pickled steel plate for a refrigerator compressor housing according to claim 1, characterized by, The microstructure of the steel plate is composed of ferrite and pearlite.

6. The hot-rolled pickled steel plate for a refrigerator compressor housing according to claim 5, characterized by, The average grain diameter of the ferrite is not more than 15 um.

7. A method of manufacturing a hot-rolled pickled steel sheet for a refrigerator compressor case according to any one of claims 1 to 6, characterized by, The method comprises the following steps: S1, converter smelting, secondary refining, after argon stirring in the ladle, continuous casting to form a continuous casting billet; S2, after heating at 1120-1260℃, the continuous casting billet or the steel billet is subjected to multi-pass rolling, the total reduction is not less than 90%; the finish rolling temperature is not less than 835℃, then cooled to the coiling temperature, and the coiling temperature is 540-640℃; S3, the hot-rolled coil is subjected to pickling to remove the surface iron oxide scale, the pickling bath has a free acid concentration of 130-200g / L, and the bath temperature is 60-90℃.

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