A steel strip for garden tools and a method for manufacturing the same

Abstract

This invention discloses a hot-rolled steel strip for garden tools and its manufacturing method. The chemical composition of the hot-rolled steel strip, by mass percentage, is as follows: C: 0.72%–0.79%, Mn: 0.60%–0.80%, Si: 0.18%–0.28%, Cr: 0.50%–0.80%, Mo: 0.10%–0.15%, Nb: 0.015%–0.030%, Ti: 0.010%–0.025%, Alt: 0.010%–0.040%, with the remainder being Fe and unavoidable impurity elements; wherein, Cr:Mo = 5:(1–1.2), 0.03% ≤ Nb + Ti ≤ 0.05%. After quenching, tempering, and high-temperature baking paint treatment, the hardness of the garden tool steel remains above 54 HRC, solving the problems of reduced hardness, decreased wear resistance, and reduced sharpness that occur in conventional carbon tool steel after high-temperature baking paint treatment.

Description

Technical Field

[0001] This invention belongs to the field of tool steel technology, and relates to a hot-rolled steel strip for garden tools and its manufacturing method, specifically to a hot-rolled wide steel strip for garden tools with high tempering stability and its manufacturing method. Background Technology

[0002] Garden tools mainly include garden shears, saw blades, saw strips, and razor blades. With the development of urban construction in China in recent years, urban greening has become a large industry, and daily maintenance relies on these tools. Conventional carbon tool steels such as 55MnB, 75, and SK85 are widely used in the gardening industry due to their high hardness and good wear resistance after quenching, and have broad market application prospects.

[0003] However, in recent years, people have placed higher and higher demands on the aesthetics of garden tools. The baking paint process for garden tools has gradually shifted from low-temperature baking paint at 140-180℃ to high-temperature baking paint at 300-450℃, which has a more uniform, smooth, and richer color. However, conventional carbon tools made of materials such as 55MnB, 75, and SK85 have problems such as unstable tempering performance, reduced hardness, and decreased wear resistance and sharpness after high-temperature baking paint, resulting in a shorter product lifespan and failure to meet the requirements of high-end garden tools.

[0004] Therefore, there is an urgent need to develop a hot-rolled wide steel strip for garden tools that has high tempering stability and excellent hardenability to ensure good hardness and wear resistance after heat treatment. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a hot-rolled steel strip for garden tools and its manufacturing method. After quenching, tempering and high-temperature baking paint treatment, the hardness of the garden tool steel is still maintained above 54HRC, which solves the problems of reduced hardness, wear resistance and sharpness of conventional carbon tool steel after high-temperature baking paint treatment.

[0006] The technical solution adopted in this invention is as follows:

[0007] A hot-rolled steel strip for garden tools, wherein the chemical composition of the hot-rolled steel strip for garden tools, by mass percentage, is: C: 0.72%–0.79%, Mn: 0.60%–0.80%, Si: 0.18%–0.28%, Cr: 0.50%–0.80%, Mo: 0.10%–0.15%, Nb: 0.015%–0.030%, Ti: 0.010%–0.025%, P≤0.020%, S≤0.010%, Alt 0.010%–0.040%, with the remainder being Fe and unavoidable impurity elements; wherein, Cr:Mo = 5:(1-1.2), 0.03%≤Nb+Ti≤0.05%.

[0008] The metallographic structure of the hot-rolled steel strip for garden tools is pearlite.

[0009] After the steel used for garden tools is processed into garden tool scissor blades, and then subjected to quenching, tempering, and high-temperature baking paint treatment, its hardness still remains above 54HRC.

[0010] The quenching temperature is 850–870℃, and the quenching time is 50–70 min; the tempering temperature is 180–200℃, and the tempering time is 80–100 min; the high-temperature baking temperature is 300–450℃, and the baking time is 20–40 min.

[0011] The garden tools, assembled from steel shear blades, were able to cut live tree branches 6,500 times without any chipping or breakage, demonstrating good toughness and sharpness.

[0012] The present invention also provides a method for manufacturing hot-rolled steel strip for garden tools, the method comprising the following steps: molten iron pretreatment - converter smelting - LF refining - continuous casting - heating - rolling - coiling.

[0013] In the converter smelting step, the smelting time is 35-50 minutes, the tapping temperature is 1550-1600℃, and the mass percentage of carbon in the final stage of the primary smelting is controlled to be 0.06-0.20%, and the mass percentage of phosphorus is ≤0.020%.

[0014] In the continuous casting step, the temperature of the molten steel in the tundish is controlled at 1470–1490℃, and the casting speed is 0.90–1.20 m / min.

[0015] In the heating step, the slab is hot-charged with a charging temperature greater than 400°C. The slab is heated to 1200-1260°C and the slab is tapped after being in the furnace for 160-230 minutes.

[0016] In the rolling process, the exit temperature of the hot roughing mill is controlled at 1010-1080℃, and the finishing mill temperature is controlled at 850-900℃.

[0017] In the coiling step, the final rolled steel strip is cooled to 600-680℃ using a layer cooling method before coiling. The coiled steel coil is then placed in an insulation pit for slow cooling for 48-72 hours.

[0018] The width of the hot-rolled steel strip used for garden tools is 800mm to 1450mm.

[0019] Conventional carbon tool steel 75 and SK85 hot-rolled steel strips are mainly composed of C, Mn, Si, P, and S, with the remainder being Fe and impurity elements. This invention incorporates a Cr+Mo+Nb+Ti composition design. The addition of certain amounts of chromium and molybdenum improves the steel's hardenability, wear resistance, and red hardness, resulting in good tempering stability. The addition of trace alloying elements niobium and titanium refines the grain size, improves impact toughness, and meets the requirements for hardness and sharpness.

[0020] The elements contained in the hot-rolled steel strip for garden tools provided by this invention and the reasons for their selection are as follows:

[0021] (1) C: Carbon is the cheapest solid solution strengthening element in quenching heat treatment and can significantly improve hardenability, but if the content is too high, it will reduce toughness. Taking all factors into consideration, the carbon content in this invention is selected to be between 0.72% and 0.79%.

[0022] (2) Si: Silicon mainly improves the strength of steel through solid solution strengthening, and it is also a deoxidizing element in steel. The silicon content should be controlled between 0.18% and 0.28%. Excessive content can easily cause surface problems such as pitting on the steel plate.

[0023] (3) Mn: Manganese is a weak carbide-forming element. In smelting, it plays a role in deoxidation and eliminating the adverse effects of sulfur. It can also lower the austenite transformation temperature, refine ferrite grains, and improve the strength and toughness of steel. Manganese can also dissolve in ferrite, playing a solid solution strengthening role. As the Mn content increases, the strength of the steel increases, but excessive manganese will also reduce the toughness of the steel. In this invention, the manganese content is controlled at 0.60%–0.80%.

[0024] (4) Cr: Chromium is an element in steel that improves hardenability, mainly by forming carbides Cr7C3 or Cr with carbon. 23 C6 can also form complex carbides with carbon, improving the hardness and wear resistance of steel, and providing a certain degree of tempering stability and toughness. However, excessive chromium can also affect the toughness of the steel. In this invention, the chromium content is controlled between 0.50% and 0.80%.

[0025] (5) Mo exists in both the solid solution phase and the carbide phase in steel, and has both solid solution strengthening and carbide dispersion strengthening effects. Molybdenum can also significantly improve the hardenability, wear resistance, and tempering stability of steel. Due to the high price of ferromolybdenum (Mo), a small amount of Mo combined with Cr can achieve good results. In this invention, the chromium content is controlled at 0.10% to 0.15%.

[0026] (6) Nb: The niobium content in this invention is 0.015% to 0.030%. Niobium is a strong carbide and nitride forming element. Even trace amounts of niobium can refine the grains and improve strength and toughness. It can also increase the tempering stability of steel and has a secondary hardening effect.

[0027] (7) Al: Aluminum is added to steel as a deoxidizer or alloying element. Its main role in steel is to refine grains and fix nitrogen in the steel, thereby significantly improving the impact toughness of the steel and reducing its tendency to become brittle and age-related. However, excessive aluminum content can not only form alumina inclusions, affecting the performance of the steel, but may also cause quenching brittleness. In this invention, the aluminum content is controlled at 0.010% to 0.040%.

[0028] (8) The upper limit of impurity elements in steel is controlled as P≤0.020% and S≤0.010% to improve the purity of steel and improve its plasticity and toughness.

[0029] Based on the above, by controlling the synergistic Cr:Mo = 5:(1-1.2) and 0.03≤Nb+Ti≤0.05, the solid solution strengthening, precipitation strengthening and fine grain strengthening of the steel can be guaranteed to achieve good results, ensuring the hardness, toughness, tempering stability and service life of the steel.

[0030] The manufacturing method of hot-rolled steel strip for garden tools provided by this invention is simple.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The hot-rolled steel strip for garden tools provided by this invention has high tempering stability. Garden scissor blades made from this strip, after processing, quenching, tempering, and high-temperature baking paint treatment, achieve a hardness of over 54 HRC and can withstand over 6500 cutting cycles without chipping or burring, significantly improving the service life of garden scissors. This hot-rolled wide steel strip, after high-temperature baking paint treatment, does not exhibit problems such as unstable tempering performance, reduced hardness, or decreased wear resistance and sharpness. Attached Figure Description

[0033] Figure 1 The image shows the metallographic structure of the hot-rolled steel strip for garden tools in Example 1.

[0034] Figure 2 The image shows the metallographic structure of the hot-rolled steel strip for garden tools in Example 2.

[0035] Figure 3 The image shows the metallographic structure of the hot-rolled steel strip for garden tools in Example 1 after quenching, tempering, and baking paint treatment at 300℃.

[0036] Figure 4 The image shows the metallographic structure of the hot-rolled steel strip for garden tools in Example 2 after quenching, tempering, and baking paint treatment at 300℃.

[0037] Figure 5The image shows the metallographic structure of the hot-rolled steel strip for garden tools in Example 1 after quenching, tempering, and baking paint treatment at 450℃.

[0038] Figure 6 The image shows the metallographic structure of the hot-rolled steel strip for garden tools in Example 2 after quenching, tempering, and baking paint treatment at 450℃. Detailed Implementation

[0039] The chemical composition of the hot-rolled steel strip for garden tools provided by this invention, by mass percentage, is as follows: C: 0.72%–0.79%, Mn: 0.60%–0.80%, Si: 0.18%–0.28%, Cr: 0.50%–0.80%, Mo: 0.10%–0.15%, Nb: 0.015%–0.030%, Ti: 0.010%–0.025%, P≤0.020%, S≤0.010%, Alt 0.010%–0.040%, with the remainder being Fe and unavoidable impurity elements; wherein, Cr:Mo = 5:(1-1.2), 0.03%≤Nb+Ti≤0.05%.

[0040] The manufacturing method of the hot-rolled steel strip for garden tools includes the following steps: molten iron pretreatment - converter smelting - LF refining - continuous casting - heating - rolling - coiling, specifically:

[0041] (1) Hot metal pretreatment: The hot metal is pretreated by the KR desulfurization process. After desulfurization, the hot metal [S] is ≤0.010%. Slag is strictly removed. After slag removal, there are no obvious residues on the surface of the hot metal. Slag is removed until more than 90% of the metal surface is bright.

[0042] (2) Converter smelting process: A top-and-bottom blown oxygen converter is used for smelting, with molten iron and scrap steel as raw materials. The smelting time is 35-50 minutes, and the tapping temperature is 1550-1600℃. The mass percentage of carbon in the initial smelting of molten steel is controlled at 0.06-0.20%, and the mass percentage of phosphorus is ≤0.020%. During tapping, ferrosilicon alloy, ferromanganese alloy, and aluminum blocks are added to the molten steel in the ladle for deoxidation, so that the mass percentage of silicon, manganese, and aluminum in the molten steel is close to or equal to the designed content in the finished product.

[0043] (3) LF refining process: After the molten steel is sent to the LF refining station, lime, refining slag, and fluorite are added to the molten steel. After slag is formed by electrolysis, aluminum particles are added to deoxidize and create white slag. The white slag in the LF furnace is maintained for ≥10 minutes. Ferrochrome alloy, ferroniobium alloy, and ferrotitanium alloy are added to the ladle to further adjust the mass percentage content of C, Si, Mn, Cr, Nb, Ti, and Al elements in the molten steel so that the composition of the molten steel reaches the target content. Then, calcium wire is fed at a rate of 1.2-1.5m per ton of steel, and argon is blown softly for 12-18 minutes. After that, the molten steel is sent to the continuous casting workshop for continuous casting.

[0044] (4) Slab continuous casting process: Molten steel is cast into slabs with a thickness of 230mm by a slab continuous casting machine. During continuous casting, the temperature of molten steel in the tundish is controlled at 1470~1490℃, and the casting speed is 0.90~1.20m / min. After the slab exits the continuous casting horizontal section, it is flame-cut.

[0045] (5) Heating process: The slab is hot-charged with a charging temperature of more than 400℃. The slab is heated to 1200-1260℃ and the slab is tapped after being in the furnace for 160-230 minutes.

[0046] (6) Rolling process: The heated slab is rolled using a hot continuous rolling mill and coiled into steel strip. The exit temperature of the hot roughing mill is controlled at 1010-1080℃, and the finishing mill temperature is controlled at 850-900℃.

[0047] (7) The strip after final rolling is cooled by layer cooling and the strip is coiled into a coil. The coiling temperature is controlled at 600-680℃. After coiling, the coil is quickly removed from the production line and placed in the heat preservation pit for slow cooling for 48-72 hours.

[0048] The present invention will now be described in detail with reference to the embodiments.

[0049] Example 1

[0050] A hot-rolled wide steel strip for garden tools with high tempering stability has the following composition and mass percentages: C 0.75%, Mn 0.72%, Si 0.23%, Cr 0.55%, Mo 0.13%, Nb 0.019%, Ti 0.015%, P 0.013%, S 0.004%, Alt 0.023%, with the remainder being iron (Fe) and unavoidable impurity elements, wherein Cr:Mo = 5:1.18 and Nb+Ti = 0.034%.

[0051] The manufacturing process of the hot-rolled wide steel strip for garden tools with high tempering stability is as follows:

[0052] (1) Hot metal pretreatment: The hot metal is pretreated by the KR desulfurization process. After desulfurization, the hot metal [S] = 0.004%. Slag is strictly removed. After slag removal, there are no obvious residues on the surface of the hot metal. Slag is removed until more than 90% of the metal surface is bright.

[0053] (2) Converter smelting process: A top-and-bottom combined blowing oxygen converter was used for smelting. 204 tons of molten iron and 35 tons of scrap steel were charged into the converter for smelting. The smelting time was 38 minutes, and the tapping temperature was 1586℃. The carbon content at the end of the initial smelting was controlled at 0.13%, and the phosphorus content was controlled at 0.013%. 1600 kg of silicon-manganese alloy and 290 kg of aluminum blocks were added to the molten steel in the ladle for deoxidation and alloying.

[0054] (3) LF refining process: After the molten steel is sent to the LF refining station, 800 kg of lime, 400 kg of refining slag and 150 kg of fluorite are added to the molten steel. After the slag is turned on by electricity, 60 kg of aluminum particles are added to deoxidize and make white slag. The white slag in the LF furnace is maintained for 13 minutes. High-carbon ferrochrome, ferromolybdenum, ferroniobium, ferrosilicon, ferrotitanium, carbon raisers, and aluminum blocks are added to the ladle to further adjust the mass percentage content of C, Si, Mn, Cr, Ti, and Al elements in the molten steel, so that the steel composition reaches the following: C: 0.72%–0.79%, Mn: 0.60%–0.80%, Si: 0.18%–0.28%, Cr: 0.50%–0.80%, Mo: 0.10%–0.15%, Nb: 0.015%–0.030%, Ti: 0.010%–0.025%, P≤0.020%, S≤0.010%, Alt 0.010%–0.040%, with the remainder being iron (Fe) and unavoidable impurity elements. After achieving the above target range, 230 meters of calcium wire are fed, and soft argon blowing time is 15 minutes. Then, the molten steel is sent to the continuous casting workshop for casting.

[0055] (4) Slab continuous casting process: Molten steel is cast into slabs with a thickness of 230 mm and a width of 1200 mm using a slab continuous casting machine. During continuous casting, the temperature of the molten steel in the tundish is controlled at 1478-1488℃, and the casting speed is 1.05 m / min. After the slab exits the continuous casting horizontal section, it is flame-cut into steel billets with a length of 9.1 m. At the same time, during the casting process, the molten steel is sampled for composition analysis. The specific smelting composition by mass percentage is: C 0.75%, Mn 0.72%, Si 0.23%, Cr 0.55%, Mo 0.13%, Nb 0.019%, Ti 0.015%, P 0.013%, S 0.004%, Alt 0.023%, with the remainder being iron (Fe) and unavoidable impurity elements, of which Cr:Mo = 5:1.18, and Nb+Ti = 0.034%.

[0056] (5) Heating process: The slab loading temperature is 480~530℃. The slab is heated to 1230℃ and the slab is tapped after 175 minutes in the furnace.

[0057] (6) Rolling process: Hot rolling adopts a 1580mm hot continuous rolling production line. First, the slab is rough rolled to an intermediate slab thickness of 43mm. The average exit temperature of the last rough rolling pass is controlled at 1040℃. Then, it is rolled to a finished product thickness of 3.2mm by a 7-stand finishing mill. The average temperature of the final finishing rolling is controlled at 880℃.

[0058] (8) The strip after final rolling is cooled by layer cooling, and then the strip is coiled into a coil. The average coiling temperature is controlled at 680℃. After coiling, the coil is quickly removed from the production line and placed in the heat preservation pit for slow cooling for 48 hours.

[0059] Through the above steps, a steel coil with a thickness * width * length = 3.2mm * 1200mm * L was obtained. After further processing and quenching + tempering + high-temperature baking paint treatment, it was made into garden shear blades.

[0060] Example 2

[0061] A hot-rolled wide steel strip for garden tools with high tempering stability has the following composition and mass percentages: C 0.76%, Mn 0.75%, Si 0.21%, Cr 0.65%, Mo 0.15%, Nb 0.018%, Ti 0.019%, P 0.014%, S 0.005%, Alt 0.022%, with the remainder being iron (Fe) and unavoidable impurity elements, wherein Cr:Mo = 5:1.15 and Nb+Ti = 0.037%.

[0062] The manufacturing process of the hot-rolled wide steel strip for garden tools with high tempering stability is as follows:

[0063] (1) Hot metal pretreatment: The hot metal is pretreated by the KR desulfurization process. After desulfurization, the hot metal [S] = 0.006%. Slag is strictly removed. After slag removal, there are no obvious residues on the surface of the hot metal. Slag is removed until more than 90% of the metal surface is bright.

[0064] (2) Converter smelting process: A top-and-bottom combined blowing oxygen converter is used for smelting. 200 tons of molten iron and 36 tons of scrap steel are charged into the converter for smelting. The smelting time is 42 minutes, and the tapping temperature is 1591℃. The carbon content at the end of the initial smelting is controlled at 0.11%, and the phosphorus content is controlled at 0.011%. 1550 kg of silicon-manganese alloy and 300 kg of aluminum blocks are added to the molten steel in the ladle for deoxidation and alloying.

[0065] (3) LF refining process: After the molten steel is sent to the LF refining station, 750kg lime, 420kg refining slag and 120kg fluorite are added to the molten steel. After the slag is turned on by electricity, 70kg aluminum particles are added to deoxidize and make white slag. The white slag in the LF furnace is maintained for 12 minutes. High-carbon ferrochrome, ferroniobium, ferrosilicon, ferrotitanium, carbon raisers, and aluminum blocks are added to the ladle to further adjust the mass percentage of C, Si, Mn, Cr, Ti, and Al elements in the molten steel, so that the steel composition reaches the following: C: 0.72%–0.79%, Mn: 0.60%–0.80%, Si: 0.18%–0.28%, Cr: 0.50%–0.80%, Mo: 0.10%–0.15%, Nb: 0.015%–0.030%, Ti: 0.010%–0.025%, P≤0.020%, S≤0.010%, Alt 0.010%–0.040%, with the remainder being iron (Fe) and unavoidable impurity elements. After reaching the above target range, 210 meters of calcium wire are fed, and the soft blowing argon time is 14 minutes. Then, the molten steel is sent to the continuous casting workshop for casting.

[0066] (4) Slab continuous casting process: Molten steel is cast into slabs with a thickness of 230 mm and a width of 1250 mm using a slab continuous casting machine. During continuous casting, the temperature of the molten steel in the tundish is controlled at 1480-1490℃, and the casting speed is 1.0 m / min. After the slab exits the continuous casting horizontal section, it is flame-cut into steel billets with a length of 9.1 m. At the same time, during the casting process, the molten steel is sampled for composition analysis. The specific smelting composition by mass percentage is: C 0.76%, Mn 0.75%, Si 0.21%, Cr 0.65%, Mo 0.15%, Nb 0.018%, Ti 0.019%, P 0.014%, S 0.005%, Alt 0.022%, with the remainder being iron (Fe) and unavoidable impurity elements, of which Cr:Mo = 5:1.15 and Nb+Ti = 0.037%.

[0067] (5) Heating process: The slab loading temperature is 460-510℃. The slab is heated to 1230℃ and the slab is tapped after 180 minutes in the furnace.

[0068] (6) Rolling process: Hot rolling adopts a 1580mm hot continuous rolling production line. First, the slab is rough rolled to an intermediate slab thickness of 45mm. The average exit temperature of the last rough rolling pass is controlled at 1060℃. Then, it is rolled to a finished product thickness of 5.0mm by a 7-stand finishing mill. The average temperature of the final finishing rolling is controlled at 860℃.

[0069] (9) The strip after final rolling is cooled by layer cooling, and then the strip is coiled into a coil. The average coiling temperature is controlled at 620℃. After coiling, the coil is quickly removed from the production line and placed in the heat preservation pit for slow cooling for 72 hours.

[0070] Through the above steps, a steel coil with a thickness * width * length = 5.0mm * 1250mm * L was obtained. After further processing and quenching + tempering + high-temperature baking paint treatment, it was made into garden shear blades.

[0071] Comparative Example 1

[0072] Comparative Example 1 uses SK85 steel strip produced in the same manner as Example 1, with the main difference being the chemical composition and element content. The chemical composition of Comparative Example 1, by mass percentage, is: C 0.83%, Mn 0.43%, Si 0.21%, P 0.012%, S 0.003%, Alt 0.022%, with the remainder being iron (Fe) and unavoidable impurities. A steel coil with dimensions of thickness * width * length = 3.2 mm * 1200 mm * L was produced through smelting and hot rolling processes.

[0073] Comparative Example 2

[0074] Comparative Example 2 uses 55MnB steel strip produced in the same manner as Example 2, with the main difference being the chemical composition and element content. The chemical composition of Comparative Example 1, by mass percentage, is: C 0.56%, Mn 0.67%, Si 0.24%, P 0.015%, S 0.003%, B 0.0020%, Alt 0.019%, with the remainder being iron (Fe) and unavoidable impurities. A steel coil with dimensions of thickness * width * length = 5.0 mm * 1250 mm * L was produced through smelting and hot rolling processes.

[0075] Comparative Example 3

[0076] Comparative Example 3 uses steel strip produced in the same manner as in Example 1, with the main difference being the content of chemical components. The mass percentages of each chemical component in Comparative Example 3 are: C 0.75%, Mn 0.72%, Si 0.22%, Cr 0.40%, Mo 0.10%, Nb 0.020%, Ti 0.014%, P 0.012%, S 0.004%, Alt 0.024%, with the remainder being iron (Fe) and unavoidable impurity elements, where Cr:Mo = 5:1.25 and Nb+Ti = 0.034%. A steel coil with a thickness * width * length = 3.2 mm * 1200 mm * L was produced through smelting, hot rolling, and other processes.

[0077] Comparative Example 4

[0078] Comparative Example 4 was produced using the same method as Example 2, with the main difference being the chemical composition. The mass percentages of each chemical component in Comparative Example 4 were: C 0.77%, Mn 0.74%, Si 0.21%, Cr 0.64%, Mo 0.15%, Nb 0.009%, Ti 0.009%, P 0.013%, S 0.005%, Alt 0.021%, with the remainder being iron (Fe) and unavoidable impurities. The Cr:Mo ratio was 5:1.17, and the Nb+Ti ratio was 0.018%. A steel coil with dimensions of 5.0 mm * 1250 mm * L was produced through smelting and hot rolling processes.

[0079] The hot-rolled steel strips obtained in each embodiment and comparative example were processed into identical garden tool scissor blades, and then subjected to quenching, tempering, and high-temperature baking paint treatment. The treatment conditions for Embodiment 1, Comparative Example 1, and Comparative Example 3 were: quenching temperature 850℃, quenching time 50 min, tempering temperature 190℃, tempering time 90 min, and high-temperature baking paint temperatures of 300℃ and 450℃, respectively, with a baking time of 30 min. The treatment conditions for Embodiment 2, Comparative Example 2, and Comparative Example 4 were: quenching temperature 860℃, quenching time 60 min, tempering temperature 190℃, tempering time 100 min, and high-temperature baking paint temperatures of 300℃ and 450℃, respectively, with a baking time of 35 min.

[0080] The hardness of the shear blades after quenching, tempering and high-temperature baking paint treatment was tested. At the same time, after being assembled into shears, the number of times live tree branches were cut was tested. The results are shown in Table 1.

[0081] Table 1. Test results of scissor blades after quenching, tempering, and high-temperature baking paint treatment.

[0082]

[0083] As shown in Example 1 and Comparative Example 1, and Example 2 and Comparative Example 2, the scissor blades made from the steel strip of this invention, after quenching, tempering, and baking paint treatment at 450℃, still maintain a hardness of over 54 HRC, which is 8-10 HRC higher than SK85 and 55MnB treated with the same process, demonstrating high resistance to tempering. Furthermore, the scissor blades did not exhibit chipping or blistering after cutting live tree branches for up to 6500 cycles, demonstrating good toughness and sharpness. Compared to conventional tool steels SK85 and 55MnB, they have better cutting ability and service life.

[0084] As shown in Example 1 and Comparative Example 3, after quenching, tempering, and baking paint at 300℃ / 450℃, the hardness of Comparative Example 3 was 8-9 HRC lower than that of Example 1, and the number of live tree branch shearings was also significantly worse. This was mainly due to the low Cr and Mo content, with Cr:Mo = 5:1.25, which does not meet the requirement of Cr:Mo = 5:(1-1.2) of this invention. Compared with Comparative Example 4, after quenching, tempering, and baking paint at 300℃ / 450℃, the hardness of Example 2 was not significantly different, but the number of live tree branch shearings of Comparative Example 4 was significantly worse, indicating insufficient toughness of the shear blade. This was mainly due to the low Nb and Ti content, with Nb+Ti = 0.018%, which does not meet the requirement of 0.03% ≤ Nb+Ti ≤ 0.05% of this invention. In summary, Comparative Examples 3 and 4, due to variations in the content of Cr, Mo, Nb, and Ti, do not meet the synergistic control requirements of this invention, namely Cr:Mo = 5:(1-1.2) and 0.03≤Nb+Ti≤0.05. Consequently, they fail to guarantee the solid solution strengthening, precipitation strengthening, and fine grain strengthening effects of the steel, resulting in inferior hardness, toughness, tempering stability, and service life of the shear blades compared to those of this invention.

[0085] The above detailed description of a hot-rolled steel strip for garden tools and its manufacturing method, with reference to the embodiments, is illustrative rather than limiting. Several embodiments can be listed according to the defined scope. Therefore, variations and modifications without departing from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A hot-rolled steel strip for garden tools, characterized in that, The chemical composition of the hot-rolled steel strip for garden tools, by mass percentage, is as follows: C: 0.72%~0.79%, Mn: 0.60%~0.80%, Si: 0.18%~0.28%, Cr: 0.50%~0.80%, Mo: 0.10%~0.15%, Nb: 0.015%~0.030%, Ti: 0.010%~0.025%, P≤0.020%, S≤0.010%, Alt 0.010%~0.040%, with the remainder being Fe and unavoidable impurity elements; wherein, Cr:Mo=5:(1-1.2), 0.03%≤Nb+Ti≤0.05%; The hot-rolled steel strip for garden tools, after being quenched, tempered, and baked at high temperature, still maintains a hardness of over 54 HRC. The manufacturing method of the hot-rolled steel strip for garden tools includes the following steps: hot iron pretreatment - converter smelting - LF refining - continuous casting - heating - rolling - coiling; In the heating step, the slab is hot-charged with a charging temperature of over 400°C. The slab is heated to 1200-1260°C and the slab is tapped after being in the furnace for 160-230 minutes. In the rolling process, the exit temperature of the hot roughing mill is controlled at 1010-1080℃, and the finishing mill temperature is controlled at 850-900℃. In the coiling step, the final rolled steel strip is cooled to 600-680℃ using a layer cooling method before coiling, and the coiled steel coil is slowly cooled for 48-72 hours.

2. The hot-rolled steel strip for garden tools according to claim 1, characterized in that, The metallographic structure of the hot-rolled steel strip for garden tools is pearlite.

3. The method for manufacturing hot-rolled steel strip for garden tools as described in claim 1, characterized in that, The manufacturing method includes the following steps: molten iron pretreatment - converter smelting - LF refining - continuous casting - heating - rolling - coiling.

4. The manufacturing method according to claim 3, characterized in that, In the converter smelting step, the smelting time is 35-50 minutes, the tapping temperature is 1550-1600℃, and the mass percentage of carbon in the final stage of the primary smelting is controlled to be 0.06-0.20%, and the mass percentage of phosphorus is ≤0.020%.

5. The manufacturing method according to claim 3, characterized in that, In the continuous casting step, the temperature of the molten steel in the tundish is controlled at 1470–1490℃, and the casting speed is 0.90–1.20 m / min.

6. The manufacturing method according to claim 3, characterized in that, The width of the hot-rolled steel strip used for garden tools is 800mm~1450mm.

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