590MPa-grade low-cost high-yield-ratio high-drawing cold-rolled high-strength steel and production method thereof

Abstract

The invention discloses 590MPa-grade low-cost high-yield-ratio high-drawing cold-rolled high-strength steel and a production method thereof. The high-strength steel comprises the following chemical components in percentage by weight: 0.070 to 0.13 percent of C, 0.61 to 1.31 percent of Si, 1.31 to 2.01 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, 0.005 to 0.300 percent of Al, less than or equal to 0.004 percent of N, 0.0002 to 0.0008 percent of B and the balance of Fe and inevitable impurities. The production method comprises the following steps of steel making, refining, continuous casting blank forming, plate blank cooling, plate blank heating, hot rolling, pickling cold rolling, continuous annealing galvanizing and finishing. According to the high-strength steel obtained through the method, the yield strength is larger than or equal to 360 MPa, the tensile strength is larger than or equal to 590 MPa, the elongation A50 is larger than or equal to 32%, the uniform elongation is larger than or equal to 20%, the yield ratio is larger than or equal to 0.65, the hole expansion rate is larger than or equal to 50%, the high-strength steel is suitable for manufacturing parts with the high yield ratio and the high drawing percentage, and a product has good corrosion resistance, surface quality and plate shape, low in cost and good in manufacturability; the product can be widely used in the industries of automobiles, buildings, machinery and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of cold-rolled high-strength steel manufacturing, and in particular to a 590MPa-grade low-cost, high-yield-to-tensile ratio, high-drawn cold-rolled high-strength steel and a production method thereof. Background Art

[0002] In recent years, in the process of producing galvanized ultra-high strength steel, in order to ensure the strength of ultra-high strength steel, higher levels of alloy elements such as Cr, Mo, Nb, Al, etc. are usually added. The addition of these alloy elements leads to a significant increase in the cost of steel and a significant decrease in the product's market competitiveness. High-strength steel with low alloy content has significant market prospects.

[0003] In the existing production technology of 590MPa grade cold-rolled hot-dip galvanized high-strength steel, the product has a relatively low yield strength, low elongation, and especially low uniform elongation. When designing products, it is usually considered to add higher alloy elements such as Cr, Mo, V, and Al, which is costly. In addition, when producing products containing high Si, the surface quality and plate shape are poor due to unreasonable composition design and process control. The Chinese patent application with application number CN202010671820.9 discloses a low-cost, high-plasticity cold-rolled galvanized steel sheet and its preparation method, and the steel sheet involved has a main chemical composition of C: 0.10-0.15%, Mn: 1.10%-1.70%, Si: 0.30-0.60%, P: ≤0.010%, S: ≤0.005%, Als: 0.30-0.60%, N: ≤0.004%, and the rest is Fe and unavoidable impurity elements. The metallographic structure of the steel plate is composed of 50-75% ferrite, 20%-40% bainite + martensite, and 3%-8% residual austenite. The main processes include: the manufacturing method includes hot rolling, acid rolling, annealing and galvanizing, heating temperature 1250-1300℃, soaking time 30-100min, final rolling temperature 860-900℃, coiling temperature 640-680℃, annealing preheating temperature 200-240℃, insulation temperature 750-810℃, slow cooling section outlet temperature 650-720℃, fast cooling outlet temperature 450-470℃, galvanizing temperature 450-470℃, strip running speed 60m / min-110m / min, dew point controlled at -30--10℃. Yield strength 386MPa-401MPa, tensile strength 627MPa-648MPa, elongation after fracture A 8030.5-33%. The Chinese invention patent with application number CN202010928567.0 discloses a cold-rolled hot-dip galvanized DH590 steel with excellent surface quality and its production method. The steel plate involved has the following main chemical components: C: 0.10-0.15%, Mn: 1.30%-1.90%, Si: ≤0.40%, P: ≤0.03%, S: ≤0.030%, Als: 0.02-0.75%, Cr≤0.20%, Mo≤0.40%, V≤0.040%, Ti≤0.03%, N: ≤0.004%, and the rest are Fe and unavoidable impurity elements. The mechanical properties of the products produced by this method reach: yield strength 360-430MPa, tensile strength ≥600MPa, elongation 30-34%, and product yield strength ratio below 0.65. The preparation method includes: steelmaking → converter smelting → LF furnace refining → continuous casting → hot rolling → pickling cold rolling → intermediate annealing → cold rolling → continuous annealing → finished product. The hot rolling heating temperature is 1150-1250°C, the carrying temperature is 1000-1120°C, the final rolling temperature is above 880°C, the coiling temperature is 500-650°C, and the cold rolling reduction rate is 40%-75%. The acid solution temperature is controlled at 60-95°C, the acid solution concentration is controlled at 50-250g / L, the strip annealing temperature is 750-850°C, the annealing time is 30-300s, the galvanizing temperature is 450-470°C, and then it is quickly cooled to 400-420°C, and finally air-cooled to 250-300°C. The flat elongation is between 0.20% and 0.5%. The metallographic structure of the steel plate is composed of 40-70% ferrite, 20-40% pearlite, 5-20% bainite, and 1-5% cementite. The Chinese patent application with application number CN201910253132.8 discloses a production process of low-cost hot-dip galvanized dual-phase steel DP590. The main chemical composition of the steel plate involved is C: 0.065-0.08%, Mn: 1.48%-1.60%, Si: 0-0.050%, Cr: 0.35-0.50%, Mo: 0.14-0.20%, Nb: 0.008-0.018%, Al: 0.030-0.060%, P: ≤0.025%, S: ≤0.010%, N: ≤0.005%, and the rest is Fe and unavoidable impurity elements. The mechanical properties of the product produced by the method are as follows: yield strength 340-380MPa, tensile strength 590-630MPa, yield strength ratio ≤0.65, elongation 15-20%. The preparation method includes: steelmaking → hot rolling → acid continuous → continuous annealing → finished product. The hot rolling heating temperature is 1185-1260℃, the final rolling temperature is 860-900℃, the continuous annealing temperature is 830℃, and the galvanizing temperature is 460℃.The Chinese invention application with application number CN201610440085.4 discloses a cold-rolled hot-dip galvanized dual-phase steel with enhanced plasticity and a production method thereof, the main chemical components of which are C: 0.12-0.18%, Si: 0.30-0.60%, Mn: 1.30-2.30%, P: ≤0.01%, S: ≤0.01%, Al: 0.4-0.9%, and the rest are Fe and unavoidable impurity elements. Its metallographic structure includes ferrite, martensite and 3% to 7% of residual austenite. The manufacturing method includes converter steelmaking, refining outside the furnace, continuous casting, hot rolling, cold acid rolling, annealing galvanizing, and hot dip galvanizing. The heating temperature is 1210 to 1300°C, the final rolling temperature is 850 to 890°C, the coiling temperature is 620 to 680°C, the annealing preheating temperature is 200 to 240°C, the holding temperature is 770 to 810°C, the slow cooling section outlet temperature is 680 to 710°C, the rapid cooling outlet temperature is 450 to 470°C, the galvanizing temperature is 450 to 470°C, the skin-clearing elongation is 0.2 to 0.5%, and the dew point is controlled below -20 to -10°C. The performance of 600MPa products reaches a tensile strength of 600-640MPa, a yield ratio of ≤0.65, and an elongation at break A80: 23-30%. The performance of 800MPa products is a tensile strength of ≥800MPa, and an elongation A80 of 14%-20%. The Chinese invention patent with application number CN201410389404.4 discloses a cold-rolled hot-dip galvanized dual-phase steel sheet with flanging characteristics and a manufacturing method, the main chemical composition of which is C: 0.06-0.095%, Si: 0.30-0.60%, Mn: 1.40-1.80%, P: ≤0.02%, S: ≤0.01%, Al: 0.02-0.05%, Cr: 0.35-0.55%, Nb: 0.02-0.04%, N: ≤0.005%, and the rest is Fe and unavoidable impurity elements. The manufacturing method comprises converter steelmaking, refining outside the furnace, continuous casting, hot rolling, cold acid rolling, annealing galvanizing and hot dip galvanizing, wherein the heating temperature is 1200-1300°C, the heat preservation is 120-180min, the finishing rolling start temperature is 1000-1100°C, the final rolling temperature is 890-950°C, the coiling temperature is 560-650°C, the cold rolling reduction rate is 60-80%, the thickness of the cold rolled coil is 0.8-2.5mm, the annealing heating temperature is 780-840°C, the heat preservation temperature is 780-840°C, the heat preservation time is 30-90s, and pre-oxidation treatment is carried out in the heating section of the hot dip galvanizing annealing furnace. The pre-oxidation method is to blow nitrogen and air mixed gas into the annealing furnace to make the dew point in the annealing furnace reach -15--20°C, increase the oxygen partial pressure in the furnace, and realize the internal oxidation of Si and Mn elements.After annealing, the steel plate is cooled in the furnace from the soaking temperature to 460-520°C, with a cooling rate of 16-60°C / s. During hot dip galvanizing, the zinc pool temperature is 450-470°C, and the galvanizing time is 2-5s. After galvanizing, it is cooled to 260-300°C, with a cooling rate of 9-25°C / s, and then water-cooled to below 40°C. The product performance reaches a yield strength of 340-391MPa, a tensile strength of 590-631MPa, a yield strength ratio of ≤0.63, a break elongation of ≥21%, and a hole expansion rate of 45-50%.

[0004] In the existing production technology of 590MPa grade cold-rolled hot-dip galvanized high-strength steel, the yield strength and elongation of the product are low, especially the uniform elongation is low, which makes it difficult to meet the demand for parts with high requirements for drawing performance. In addition, the existing products have increased product costs due to the addition of high levels of alloy elements such as Al, Cr, Mo, and V. In summary, it is difficult to obtain low-cost, high-draw 590MPa grade hot-dip galvanized products with existing technology. Summary of the invention

[0005] In order to overcome the shortcomings of the above-mentioned technology, the purpose of the present invention is to provide a 590MPa grade low-cost, high-yield ratio, high-drawn cold-rolled high-strength steel and a production method thereof, so as to solve the problem that high-strength steel in the prior art is difficult to meet the requirements of low cost, high drawing and high yield ratio.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A 590MPa grade low-cost high-yield ratio high-drawn cold-rolled high-strength steel comprises the following chemical components by weight percentage: C: 0.070-0.13%, Si: 0.61-1.31%, Mn: 1.31%-2.01%, P: ≤0.015%, S: ≤0.005%, Al: 0.005-0.300%, N: ≤0.004%, B: 0.0002-0.0008%, and the rest is Fe and unavoidable impurities.

[0008] Preferably, the weight percentage of Mn is 1.40-1.90%, the weight percentage of Si is 0.70-1.20%, and the weight percentage of Al is 0.035-0.25%.

[0009] Preferably, the high-strength steel further includes one or more of the following chemical components by weight percentage: Cr: 0.001-0.095%, Cu: 0.001-0.095%, Nb: 0.001-0.0099%, Ti: 0.0001-0.0099%, V: 0.0001-0.0099%, Mo: 0.001-0.05%.

[0010] Preferably, the weight percentage ratio of Si to Mn is Si / Mn≥0.38.

[0011] Preferably, the high-strength steel has a yield strength of ≥360 MPa, a tensile strength of ≥590 MPa, a yield strength ratio of ≥0.65, an elongation A50 of ≥32%, and a uniform elongation of ≥20%.

[0012] Further preferably, the yield strength of the high-strength steel is 360-500 MPa, and the tensile strength is 590-700 MPa.

[0013] The production method of the above-mentioned 590MPa grade low-cost, high-yield ratio, high-drawn cold-rolled high-strength steel comprises the following steps: steelmaking → refining → continuous casting into billets → slab cooling → slab heating → hot rolling → pickling and cold rolling → continuous annealing and galvanizing → skin passing. During the slab heating process, the slab heating temperature is 1280-1340°C, and the heating time above the heating temperature of 1280°C is 30-59 minutes.

[0014] Preferably, during the hot rolling process, the final rolling temperature is 910-960°C; after hot rolling, three-stage cooling is adopted, the cooling rate of the first stage is 60-200°C / s, the cooling time is 0.5-5s, the cooling rate of the second stage is 2-20°C / s, the cooling time is 3-15s, the cooling rate of the third stage is 10-60°C / s, the cooling time is 3-20s, and the coiling temperature is 450-580°C.

[0015] Preferably, in the continuous annealing galvanizing process, the soaking temperature is 800-880°C, the soaking time is 25-120s, one-stage rapid cooling is carried out after soaking, the rapid cooling cooling rate is 10-40°C / s, the rapid cooling terminal temperature is 380-460°C, and the rapid cooling is kept warm for 30-70s. Galvanizing is carried out after rapid cooling and heat preservation, and cooling is carried out after galvanizing, and the final cooling temperature is ≤230°C; wherein the dew point of the heating section and the dew point of the soaking section are both -40--5°C.

[0016] Preferably, during the galvanizing process, the dew point of the galvanizing furnace nose is -35 to -50°C, and the temperature of the zinc liquid is 450 to 470°C.

[0017] Preferably, during the continuous annealing and galvanizing process, the rapid cooling endpoint temperature is controlled to be lower than the temperature of the zinc solution for galvanizing.

[0018] Preferably, the above production method comprises the following steps:

[0019] 1) Smelt and continuously cast high-strength steel into billets according to its composition, and then cool them.

[0020] 2) The cooled slab is heated at a temperature of 1280 to 1340° C., and the heating time at a temperature above 1280° C. is 30 to 59 minutes.

[0021] 3) Hot rolling: After the slab is descaled, it is hot rolled to descale it and then hot rolled. The final hot rolling temperature is 910-960°C.

[0022] 4) Cooling: After hot rolling, three-stage cooling is adopted. The cooling rate of the first stage is 60-200℃ / s, the cooling time is 0.5-5s, the cooling rate of the second stage is 2-20℃ / s, the cooling time is 3-15s, and the cooling rate of the third stage is 10-60℃ / s, and the cooling time is 3-20s.

[0023] 5) Coiling: Coiling temperature 450~580℃.

[0024] 6) Pickling.

[0025] 7) Cold rolling.

[0026] 8) Continuous annealing and galvanizing: anneal the cold-rolled strip with a soaking temperature of 800-880°C and a soaking time of 25-120s. After soaking, perform one-stage rapid cooling with a cooling rate of 10-40°C / s and a rapid cooling endpoint temperature of 380-460°C. Keep warm for 30-70s after rapid cooling. After keeping warm, galvanize with a zinc liquid temperature of 450-470°C. Cool after galvanizing with a final cooling temperature ≤230°C. The dew point of the heating section and the soaking section is -40--5°C, and the dew point of the furnace nose is -35--50°C.

[0027] The functions of each element and main process in the present invention are:

[0028] C: It plays a role of solid solution strengthening in steel, improves yield strength and yield strength ratio, and is easy to gather in the retained austenite to improve the stability of austenite and improve the drawing performance. Too high C reduces welding performance and easily forms more martensite, reducing the elongation and other properties of the product. Therefore, the C content in the present invention is selected to be 0.070% to 0.13%.

[0029] Mn: Mn plays a role in solid solution strengthening and stabilizing austenite in steel, and plays a role in improving yield strength and drawing properties. A high Mn content increases the cost, so in the present invention, Mn is selected to be 1.31-2.01%.

[0030] Si: Si plays a role of solid solution strengthening in steel, improving strength and yield strength ratio. On the other hand, it inhibits the formation of carbides such as Fe3C during phase transformation, thereby facilitating bainite transformation in steel, increasing the amount of retained austenite and carbon concentration, and improving drawing performance. Therefore, the Si content in the present invention is 0.61-1.31%.

[0031] Al: Combines with N, S, etc. in steel to form AlN, AlS and other substances, reducing the segregation of N, S, etc. at the grain boundaries and improving the elongation performance of the product. However, too high Al content increases the alloy cost and easily leads to problems such as nodules in the steelmaking nozzle.

[0032] B: B plays a role in reducing the formation of ferrite and increasing the martensite content in the steel, which can reduce the amount of alloy elements and reduce costs. However, too much B is not good for elongation. Therefore, in the present invention, B is controlled at 0.0002-0.0008%.

[0033] Cu: A trace amount of Cu is beneficial to improving the stability of the retained austenite, improving the elongation and uniform elongation, while a high Cu content is detrimental to the surface quality. Therefore, the present invention controls the Cu content to be 0.001-0.095%.

[0034] Cr: A trace amount of Cr can effectively reduce the formation of surface oxides and improve surface quality. Too much Cr will form Cr-containing oxides, which is not conducive to surface quality control. Therefore, the present invention controls the Cr content to 0.001-0.095%.

[0035] Nb: Nb forms NbN precipitates with N in steel, reduces the segregation of solid solution N at grain boundaries, plays a role in precipitation strengthening and grain refinement, improves drawing performance, and increases yield strength and yield strength ratio. Too high Nb content increases costs, therefore, the present invention controls the Nb content to 0.001-0.0099%.

[0036] Ti: Ti can form TiN and TiO with harmful elements N and O in steel, reduce the influence of solid solution N and O on the ductility of steel, improve the ductility, and increase the yield strength and yield strength ratio. Too much Ti forms too much TiN, which is not conducive to the improvement of ductility. Therefore, the Ti content of the present invention is 0.0001-0.0099%.

[0037] V: V can form VN with harmful element N in steel, reduce the influence of solid solution N on the drawing performance of steel, and improve yield strength and yield strength ratio. Too much V forms too much VN, which is not conducive to improving the drawing performance. Therefore, the Ti content of the present invention is 0.0001-0.0099%.

[0038] Mo: Mo in steel inhibits the formation of carbides such as Fe3C, which is conducive to the formation of more low-temperature bainite and improves the yield strength ratio. Too high Mo content increases the cost and is not conducive to the improvement of drawing performance. The Mo content of the present invention is 0.001-0.05%.

[0039] Si / Mn: A higher Si / Mn is conducive to obtaining a high yield strength ratio and improving the uniform elongation. If Si / Mn is too low, the product's yield strength is relatively low, and both the elongation and uniform elongation are low.

[0040] The main process reasons in the present invention are analyzed as follows:

[0041] In the slab heating step, the slab heating temperature is 1280-1340°C, and the heating time above 1280°C is 30-59 minutes. High temperature and long heating time are conducive to obtaining uniform structure in the thickness direction of the slab and improving the drawing performance and hole expansion performance of the product. In addition, high temperature and long heating time can increase the stress between the surface iron oxide scale and the matrix, which is conducive to removing the surface iron oxide scale and obtaining good surface quality.

[0042] In the hot rolling step, the hot rolling final rolling temperature is 910-960°C, and three-stage cooling is adopted after hot rolling. The first stage cooling rate is 60-200°C / s, the cooling time is 0.5-5s, the second stage cooling rate is 2-20°C / s, the cooling time is 3-15s, the third stage cooling rate is 10-60°C / s, the cooling time is 3-20s, and the coiling temperature is 450-580°C. The use of a high final rolling temperature is conducive to improving the hot rolling phase change rate and organizational uniformity, which is conducive to improving the elongation and improving the plate shape quality. By adopting three-stage cooling, it is conducive to improving the organizational uniformity of hot rolling in the thickness and width directions, reducing the phase change stress, and improving the plate shape quality.

[0043] During the coiling process, if the coiling temperature is too high, the grains will be coarse, which is not conducive to the improvement of elongation. In addition, high temperature will easily cause the oxide of MnSi to be enriched on the surface, reducing the quality of the plate surface. If the coiling temperature is too low, it will lead to uneven phase change, reduce elongation, and cause poor plate shape.

[0044] During the continuous annealing galvanizing process, if the soaking temperature is too low and the time is too short, the degree of structural recrystallization and austenitization is low, and the structural uniformity is poor, which is not conducive to the improvement of elongation and uniform elongation. If the soaking temperature is too high, it is easy to cause coarse grains, resulting in reduced strength and elongation. Moreover, since the Si / Mn of the present invention is relatively high, higher temperatures are likely to cause surface oxidation and deterioration of surface quality. Therefore, the soaking temperature is controlled at a soaking temperature of 800 to 880°C, and the soaking time is controlled at 25 to 120s. After soaking, one-stage cooling and cooling rate are controlled at 10 to 40°C / s, which can reduce the phase transformation ferrite during the cooling process and help improve the hole expansion rate of the material. Controlling the rapid cooling temperature below the zinc liquid temperature and controlling the holding time after rapid cooling is conducive to promoting the transformation of B and improving the amount and stability of residual austenite. Too low or too high temperature is prone to produce martensite structure. If the holding time is too short, the transformation of austenite to B is insufficient, and it is not easy to produce C enrichment in austenite, which is not conducive to the improvement of elongation and hole expansion rate. If the holding time is too long, more B is generated, which is easy to lead to low tensile strength. Controlling the dew point of the heating section and the soaking section at -40 to -5°C, and the dew point of the furnace nose at -35 to -50°C can reduce the enrichment of Si oxides on the surface, which is conducive to obtaining good surface quality.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] The present invention proposes a 590MPa grade low-cost high-yield ratio high-drawn cold-rolled high-strength steel and a production method thereof. The yield strength of the product of the present invention is ≥360MPa, the tensile strength is ≥590MPa, and the elongation is A 50 ≥32%, uniform elongation ≥20%, yield ratio ≥0.65, hole expansion rate ≥50%, suitable for the manufacture of high yield ratio and high drawable parts, and the product has good corrosion resistance, surface quality and plate shape, low product cost, good manufacturability, the product can be widely used in automobile, construction, machinery and other industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is the microstructure diagram of the galvanized sheet in Example 1 of the present invention. DETAILED DESCRIPTION

[0048] In order to better explain the present invention, the main contents of the present invention are further explained below in combination with the accompanying drawings and Examples 1 to 9 and Comparative Examples 1 to 2, but the contents of the present invention are not limited to the following examples.

[0049] The chemical composition of the high-strength steel in Examples 1 to 9 and Comparative Examples 1 to 2 is shown in Table 1.

[0050] Table 1: Chemical composition of high strength steel in Examples 1 to 9 and Comparative Examples 1 to 2

[0051] C Si Mn Al P S N Cr Mo B Si / Mn Example 1 0.11 0.61 1.42 0.025 0.013 0.002 0.003 0.05 0.01 0.0003 0.44 Example 2 0.092 0.86 1.72 0.018 0.014 0.0015 0.004 0.02 0.02 0.0004 0.50 Example 3 0.096 0.95 1.56 0.022 0.011 0.0012 0.003 0.04 0.008 0.0002 0.61 Example 4 0.090 1.05 1.45 0.020 0.012 0.0013 0.0023 0.01 0.03 0.0003 0.72 Example 5 0.087 1.18 1.50 0.026 0.013 0.0016 0.004 0.02 0.04 0.0005 0.79 Example 6 0.080 1.10 1.80 0.020 0.012 0.002 0.003 0.03 0.03 0.0007 0.61 Example 7 0.10 0.75 1.96 0.15 0.010 0.0001 0.002 0.02 0.01 0.0003 0.38 Example 8 0.12 0.83 1.62 0.20 0.013 0.0011 0.003 0.01 0.02 0.0002 0.51 Example 9 0.075 1.00 1.63 0.05 0.008 0.0012 0.001 0.02 0.02 0.0004 0.61 Comparative Example 1 0.086 0.45 1.60 0.012 0.020 0.003 0.004 0.15 0.13 0.0009 0.28 Comparative Example 2 0.09 0.10 1.95 0.035 0.025 0.004 0.0035 0.20 0.16 0.0005 0.05

[0052] The high-strength steel in Examples 1 to 9 is produced according to the following steps (steelmaking → refining → continuous casting → slab cooling → slab heating → hot rolling → pickling and cold rolling → continuous annealing and galvanizing → skin passing):

[0053] 1) Smelt and continuously cast into billets according to the composition in Table 1, and cool.

[0054] 2) The slab is heated at a temperature of 1280 to 1340° C. The heating time at a temperature above 1280° C. is 30 to 59 minutes.

[0055] 3) Hot rolling: After the slab is descaled, it is hot rolled to descale it and then hot rolled. The final hot rolling temperature is 910-960°C.

[0056] 4) Cooling: After hot rolling, three-stage cooling is adopted. The cooling rate of the first stage is 60-200℃ / s, the cooling time is 0.5-5s, the cooling rate of the second stage is 2-20℃ / s, the cooling time is 3-15s, and the cooling rate of the third stage is 10-60℃ / s, and the cooling time is 3-20s.

[0057] 5) Coiling: The coiling temperature is 450-580°C.

[0058] 6) Pickling.

[0059] 7) Cold rolling.

[0060] 8) Continuous annealing and galvanizing: anneal the cold-rolled strip with a soaking temperature of 800-880°C and a soaking time of 25-120s. After soaking, perform one-stage rapid cooling with a cooling rate of 10-40°C / s and a rapid cooling endpoint temperature of 380-460°C. Keep warm for 30-70s after rapid cooling, and galvanize after keeping warm with a zinc liquid temperature of 450-470°C. Cool after galvanizing with a final cooling temperature ≤230°C; the dew point of the heating section and the soaking section is -40--5°C, and the dew point of the furnace nose is -35--50°C.

[0061] 9) Polishing.

[0062] The specific process parameters in Examples 1 to 9 are shown in Tables 2 to 5. The difference between the production processes of Comparative Examples 1 to 2 and Examples 1 to 9 lies in the difference in related parameters. The specific process parameters are shown in Tables 2 to 5.

[0063] Table 2: Some process parameters of Examples 1 to 9 and Comparative Examples 1 to 2

[0064]

[0065] Table 3: Some process parameters of Examples 1 to 9 and Comparative Examples 1 to 2

[0066]

[0067] Table 4: Some process parameters of Examples 1 to 9 and Comparative Examples 1 to 2

[0068]

[0069] Table 5: Some process parameters of Examples 1 to 9 and Comparative Examples 1 to 2

[0070]

[0071] Table 6: Performance parameters of high-strength steel of Examples 1 to 9 and Comparative Examples 1 to 2

[0072]

[0073] The product performance parameters of Comparative Examples 1-2 and Examples 1-9 are shown in Table 6.

[0074] In the comparative examples 1 to 2, Si / Mn is less than 0.38, Si content is low, and a certain amount of Cr and Mo need to be added to improve strength, resulting in high cost, and the yield strength ratio, elongation, and uniform elongation of the product are low. In the comparative example, the hot rolling heating temperature and heating time are short, the coiling temperature is high, the dew point control temperature during continuous galvanizing is high, and the hot rolling cooling adopts one-stage cooling, and the soaking temperature is low, the surface quality of the final product is poor, that is, the plate quality is poor.

[0075] like Figure 1 As shown, the microstructure of the galvanized sheet in Example 1 of the present invention is fine and uniform, and the fine structure is beneficial to improving the yield strength of the material, improving the yield strength ratio, and improving the uniform elongation and hole expansion rate of the product.

[0076] The components and processes of Examples 1 to 9 of the present invention are all implemented in accordance with the content of the invention, and the properties such as strength, yield strength ratio, uniform elongation and hole expansion rate are good, and the surface quality is good. The yield strength of the product of the present invention is ≥360MPa, the tensile strength is ≥590MPa, the elongation A50 is ≥32%, the uniform elongation is ≥20%, the yield strength ratio is ≥0.65, and the hole expansion rate is ≥50%. It is suitable for the manufacture of high yield strength ratio and high ductility parts, and the product has good corrosion resistance, surface quality and plate shape, low product cost, good manufacturability, and the product can be widely used in the automotive, construction, machinery and other industries.

Claims

1. A 590MPa grade low-cost high-yield ratio high-drawn cold-rolled high-strength steel, characterized by: The chemical composition includes the following by weight percentage: C: 0.070-0.13%, Si: 0.61-1.31%, Mn: 1.31%-2.01%, P: ≤0.015%, S: ≤0.005%, Al: 0.005-0.300%, N: ≤0.004%, B: 0.0002-0.0008%, and the rest is Fe and unavoidable impurities.

2. The 590MPa grade low-cost, high-yield ratio, high-drawn cold-rolled high-strength steel according to claim 1, characterized in that: The weight percentage of the Mn is 1.40-1.90%, the weight percentage of the Si is 0.70-1.20%, and the weight percentage of the Al is 0.035-0.25%.

3. The 590MPa grade low-cost, high-yield ratio, high-drawn cold-rolled high-strength steel according to claim 1, characterized in that: The alloy further includes one or more of the following chemical components by weight percentage: Cr: 0.001-0.095%, Cu: 0.001-0.095%, Nb: 0.001-0.0099%, Ti: 0.0001-0.0099%, V: 0.0001-0.0099%, Mo: 0.001-0.05%.

4. The 590MPa grade low-cost, high-yield ratio, high-drawn cold-rolled high-strength steel according to claim 1, characterized in that: The weight percentage ratio of Si to Mn is Si / Mn≥0.

38.

5. The 590 MPa grade low-cost, high-yield ratio, high-drawn cold-rolled high-strength steel according to any one of claims 1 to 4, characterized in that: The high-strength steel has a yield strength of ≥360 MPa, a tensile strength of ≥590 MPa, a yield strength ratio of ≥0.65, an elongation A50 of ≥32%, and a uniform elongation of ≥20%.

6. The method for producing 590 MPa grade low-cost high yield ratio high-drawn cold-rolled high-strength steel according to any one of claims 1 to 5, comprising the following steps: steelmaking → refining → continuous casting into billets → slab cooling → slab heating → hot rolling → pickling and cold rolling → continuous annealing and galvanizing → skin passing, characterized in that: During the slab heating process, the slab heating temperature is 1280-1340° C., and the heating time above the heating temperature of 1280° C. is 30-59 minutes.

7. The production method according to claim 6, characterized in that: During the hot rolling process, the final rolling temperature is 910-960°C; after hot rolling, three-stage cooling is adopted, the cooling rate of the first stage is 60-200°C / s, the cooling time is 0.5-5s, the cooling rate of the second stage is 2-20°C / s, the cooling time is 3-15s, the cooling rate of the third stage is 10-60°C / s, the cooling time is 3-20s, and the coiling temperature is 450-580°C.

8. The production method according to claim 6, characterized in that: In the continuous annealing galvanizing process, the soaking temperature is 800-880°C, the soaking time is 25-120s, one-stage rapid cooling is performed after soaking, the rapid cooling cooling rate is 10-40°C / s, the rapid cooling terminal temperature is 380-460°C, the rapid cooling is kept for 30-70s, galvanizing is performed after rapid cooling and keeping, and cooling is performed after galvanizing, and the final cooling temperature is ≤230°C; wherein the dew point of the heating section and the dew point of the soaking section are both -40--5°C.

9. The production method according to claim 8, characterized in that: During the galvanizing process, the dew point of the galvanizing furnace nose is -35 to -50°C, and the temperature of the zinc liquid is 450 to 470°C.

10. The production method according to claim 8 or 9, characterized in that: During the continuous annealing and galvanizing process, the rapid cooling endpoint temperature is controlled to be lower than the temperature of the zinc solution for galvanizing.

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