Ultra-thin frame saw blade with 75cr1 hot-rolled steel strip and its production method

Abstract

The application provides a 75Cr1 hot-rolled steel strip for an ultra-thin frame saw blade and a production method thereof. By adjusting the element components and content in the 75Cr1 hot-rolled steel strip for the ultra-thin frame saw blade, and by using superior process flow and process parameters, the 75Cr1 hot-rolled steel strip for the frame saw blade with excellent tenacity, high fatigue performance and long service life is manufactured. 0.02% to 0.025% Nb element is added in the steel to refine the grain size of the 75Cr1 steel, reduce the surface decarburization, and improve the strength and fatigue performance. The content of P and S is controlled to be low. The 75Cr1 hot-rolled steel strip for the ultra-thin frame saw has the characteristics of high cleanliness of molten steel, low inclusion level, small and uniform microstructure, small fluctuation of mechanical properties, and high size precision.

Description

Technical Field

[0001] This application relates to the field of alloy tool steel manufacturing technology, specifically to 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades and its production method. Background Technology

[0002] Marble slabs are widely used in public building projects such as train stations, airports, squares, and libraries. The most important tool for cutting marble slabs is the frame saw blade, which cuts large blocks of stone into hundreds of slab-shaped pieces. Currently, the mainstream thickness of marble frame saws used in the market is 2.5mm and 2.0mm, and the material is 75Cr1 cold-rolled steel strip, which is produced by hot-rolled steel strip through multiple cold rolling and annealing processes.

[0003] In the process of stone sawing, reducing the thickness of the saw blade is a very effective way to reduce sawing losses and increase the yield of stone, which can bring good economic benefits. However, reducing the thickness of the saw blade means a decrease in the stiffness of the saw blade. During the sawing process, the unit stress that the saw blade is required to withstand increases, and the fatigue performance requirements are relatively higher. This requires the raw materials of the saw blade to have better steel cleanliness, more uniform mechanical properties and microstructure, and higher dimensional accuracy.

[0004] Currently, traditional production methods are insufficient to produce hot-rolled raw materials that meet the requirements. 75Cr1 hot-rolled strip steel materials on the market all have one or more problems such as inclusions, molten steel cleanliness, microstructure uniformity and grain size, mechanical property fluctuations, and dimensional tolerances. These quality defects will be inherited by subsequent cold-rolled steel strips, making it difficult to produce high-quality cold-rolled raw material steel strips. Summary of the Invention

[0005] This application provides a 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades and its production method, aiming to improve the strength, toughness, fatigue performance, and service life of the saw blades.

[0006] In a first aspect, embodiments of this application provide a method for producing 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades, comprising: loading molten iron and scrap steel into a converter, producing the steel using a top-and-bottom combined blowing converter, smelting the steel using a high-pulling carbon process to obtain converter steel, wherein the tapping temperature of the converter steel is 1590–1650°C, the carbon content at the tapping endpoint is 0.20–0.35%, and the oxygen content at the tapping endpoint is 300–600 ppm; when tapping the converter steel, ferrosilicon alloy, ferromanganese alloy, and carbon powder are first added for deoxidation and alloying, and when the steel is tapped to half its length, ferroaluminum alloy is added for deoxidation and ferrochrome alloying;

[0007] The molten steel from the converter is transferred to the LF refining furnace, and limestone is added to form slag with a basicity of 3.0–4.5. Aluminum granules are added to ensure that the acid-soluble aluminum content is between 50 and 200 ppm. Ferromanganese alloy, ferrosilicon alloy, ferrochrome alloy, and ferroniobium alloy are added. The number of heating and power supply operations during the entire smelting process is controlled to within three times. The temperature is adjusted to 1560–1600℃, and soft blowing is performed for 10–15 minutes to obtain the first refined molten steel. The acid-soluble aluminum content of the first refined molten steel leaving the station is below 120 ppm, and the sulfur content is below 30 ppm.

[0008] The first refined molten steel is charged into an RH refining furnace and treated under vacuum for 15-20 minutes to perform dehydrogenation, denitrification and removal of inclusions to obtain the second refined molten steel. The hydrogen content in the second refined molten steel is below 1.0 ppm, the nitrogen content is below 30 ppm and the oxygen content is below 8 ppm.

[0009] The second refined steel is continuously cast to obtain a billet; the billet contains the following components by mass percentage: C: 0.72%–0.80%, Si: 0.20%–0.45%, Mn: 0.60%–0.90%, Cr: 0.30%–0.60%, Nb: 0.02%–0.025%, P: ≤0.015%, S: ≤0.005%; the remainder is Fe and unavoidable impurities;

[0010] The 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades is obtained by heating the billet in a heating furnace, rough rolling, fine rolling, laminar flow cooling, coiling and slow cooling treatment.

[0011] According to an embodiment of the first aspect of this application, in the step of continuously casting the second refined molten steel to obtain a billet, the continuously cast molten steel satisfies the following conditions: hydrogen content is below 1.5 ppm, nitrogen content is below 35 ppm, and oxygen content is below 10 ppm.

[0012] According to the embodiment of the first aspect of this application, in the step of continuously casting the second refined molten steel to obtain a billet, the superheat is 20-35°C and the casting speed is 1.0-1.6 m / min.

[0013] According to an embodiment of the first aspect of this application, the 75Cr1 hot-rolled steel strip used for ultra-thin frame saw blades meets the following requirements: the acid-soluble aluminum content is below 100ppm and the calcium content is below 8ppm.

[0014] According to an embodiment of the first aspect of this application, the heating process in the heating furnace includes: the furnace temperature of the billet entering the heating furnace is above 400°C, the billet is heated to 1180-1250°C in the heating furnace, and the furnace time is 150-300 minutes.

[0015] According to an embodiment of the first aspect of this application, the roughing process includes: performing 7 passes of roughing to obtain an intermediate billet; the finishing process includes: performing 7 passes of finishing, wherein the first to fifth finishing stands adopt CVC roll profiles, and the sixth and seventh finishing stands adopt flat roll profiles for rolling to obtain hot-rolled steel coils; the finishing temperature is controlled at 860 to 920°C.

[0016] According to the embodiments of the first aspect of this application, the thickness of the continuously cast billet is 210mm to 250mm; the thickness of the intermediate billet is 40mm to 50mm; and the thickness of the hot-rolled steel coil is 1.8mm to 5mm.

[0017] According to the embodiment of the first aspect of this application, a front-end cooling mode is adopted to rapidly reduce the temperature of the strip steel to near the coiling temperature, with the coiling temperature controlled at 580-640°C.

[0018] Secondly, embodiments of this application provide a 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades, produced by the above-described production method, comprising the following components by mass percentage: C: 0.72–0.80%, Si: 0.20–0.45%, Mn: 0.60–0.90%, Cr: 0.30–0.60%, Nb: 0.02–0.025%, P: ≤0.015%, S: ≤0.005%; the remainder being Fe and unavoidable impurities.

[0019] According to an embodiment of the second aspect of this application, the 75Cr1 hot-rolled steel strip for the ultra-thin frame saw blade satisfies at least one of the following conditions:

[0020] (1) The acid-soluble aluminum content in the 75Cr1 hot-rolled steel strip used for ultra-thin frame saw blades is below 100ppm and the calcium content is below 8ppm;

[0021] (2) The inclusion levels of A, B, C and D in the 75Cr1 hot-rolled steel strip used for ultra-thin frame saw blades shall not exceed 0.5;

[0022] (3) The ultra-thin frame saw blade uses 75Cr1 hot-rolled steel strip without a fully decarburized layer and the depth of the semi-decarburized layer is less than 10μm;

[0023] (4) The tensile strength of 75Cr1 hot-rolled steel strip used for ultra-thin frame saw blades is 840MPa~940MPa;

[0024] (5) The metallographic structure of 75Cr1 hot-rolled steel strip for ultra-thin frame saw blade is 100% pearlite, and the pearlite cluster size does not exceed 50μm;

[0025] (6) The longitudinal thickness fluctuation of the 75Cr1 hot-rolled steel strip used for ultra-thin frame saw blades is ±30μm, and the convexity C40≤20μm.

[0026] Compared with the prior art, the present invention has at least the following beneficial effects:

[0027] This application manufactures 75Cr1 hot-rolled steel strips for ultra-thin frame saw blades by adjusting the elemental composition and content of the strips, and employing superior process flow and parameters. This allows for the production of 75Cr1 hot-rolled steel strips with excellent strength and toughness, high fatigue performance, and long service life. This application adds 0.02–0.025% Nb to the steel to refine the grain size of the 75Cr1 steel, reduce surface decarburization, and improve strength and fatigue performance. The P and S contents are controlled at a low level. This ultra-thin 75Cr1 hot-rolled steel strip for frame saws features high steel cleanliness, low inclusion level, fine and uniform microstructure, small fluctuations in mechanical properties, and high dimensional accuracy. Attached Figure Description

[0028] The features, advantages, and technical effects of exemplary embodiments of this application will now be described with reference to the accompanying drawings.

[0029] Figure 1 This is a microstructure diagram of the 75Cr1 hot-rolled steel strip used for the ultra-thin frame saw blade of Embodiment 1 of this application;

[0030] Figure 2 This is a microstructure diagram of the 75Cr1 hot-rolled steel strip used for the ultra-thin frame saw blade of Embodiment 2 of this application;

[0031] Figure 3 This is a microstructure diagram of the 75Cr1 hot-rolled steel strip used for the ultra-thin frame saw blade of Embodiment 3 of this application. Detailed Implementation

[0032] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0033] In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicating orientation or positional relationships, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. "Vertical" does not require strict verticality, but may include permissible errors. "Parallel" does not require strict parallelism, but may include permissible errors.

[0034] Currently, 75Cr1 hot-rolled strip steel materials on the market all have one or more problems, such as inclusion level, steel cleanliness, microstructure uniformity and grain size, mechanical property fluctuation, and dimensional tolerance. These quality defects will be inherited by subsequent cold-rolled steel strips, making it difficult to produce high-quality cold-rolled raw material steel strips.

[0035] In view of this, the inventors of this application, through extensive experimental research, provide a 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades and its production method, aiming to improve the strength, toughness, fatigue performance, and service life of the processed saw blades.

[0036] Production method of 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades

[0037] In a first aspect, embodiments of this application provide a method for producing 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades, comprising:

[0038] Molten iron and scrap steel are loaded into a converter and produced using a top-and-bottom blown converter. High-pulling carbon technology is used for smelting to obtain converter steel. The tapping temperature of the converter steel is 1590–1650℃, and the carbon content at the tapping endpoint is 0.20–0.35%, while the oxygen content at the tapping endpoint is 300–600 ppm. When tapping the converter steel, ferrosilicon alloy, ferromanganese alloy, and carbon powder are added first for deoxidation and alloying. When the steel is tapped halfway, ferroaluminum alloy is added for further deoxidation and ferrochrome alloying.

[0039] The molten steel from the converter is transferred to the LF refining furnace, and limestone is added to form slag with a basicity of 3.0–4.5. Aluminum granules are added to ensure that the acid-soluble aluminum content is between 50 and 200 ppm. Ferromanganese alloy, ferrosilicon alloy, ferrochrome alloy, and ferroniobium alloy are added. The number of heating and power supply operations during the entire smelting process is controlled to within three times. The temperature is adjusted to 1560–1600℃, and soft blowing is performed for 10–15 minutes to obtain the first refined molten steel. The acid-soluble aluminum content of the first refined molten steel leaving the station is below 120 ppm, and the sulfur content is below 30 ppm.

[0040] The first refined molten steel is charged into an RH refining furnace and treated under vacuum for 15-20 minutes to perform dehydrogenation, denitrification and removal of inclusions to obtain the second refined molten steel. The hydrogen content in the second refined molten steel is below 1.0 ppm, the nitrogen content is below 30 ppm and the oxygen content is below 8 ppm.

[0041] The second refined steel is continuously cast to obtain a billet; the billet contains the following components by mass percentage: C: 0.72%–0.80%, Si: 0.20%–0.45%, Mn: 0.60%–0.90%, Cr: 0.30%–0.60%, Nb: 0.02%–0.025%, P: ≤0.015%, S: ≤0.005%; the remainder is Fe and unavoidable impurities;

[0042] The 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades is obtained by heating the billet in a heating furnace, rough rolling, fine rolling, laminar flow cooling, coiling and slow cooling treatment.

[0043] The high-carbon process refers to stopping oxygen blowing when the carbon content in the converter reaches the steelmaking requirement. At this time, not only do the sulfur, phosphorus, and temperature in the converter meet the steelmaking temperature requirements, but also, after taking into account the carbon brought into the metal by the ferroalloy, the carbon in the molten steel can meet the specifications of the steel being produced.

[0044] In the converter smelting stage, this application employs a high-carbon extraction process to control the endpoint. This shortens the smelting time and reduces the oxygen content in the molten steel, resulting in a lower oxygen content at the endpoint. Simultaneously, less hydrogen and nitrogen are dissolved in the molten steel, leading to fewer endogenous non-metallic inclusions and a lower level of inclusions, resulting in high-purity molten steel with significantly improved quality. In this application, the tapping temperature during the converter smelting stage is controlled at 1590–1650℃, the carbon content at the tapping endpoint is 0.20–0.35%, and the oxygen content at the tapping endpoint is 300–600 ppm, all of which improve steel quality. For example, the mass percentage of carbon at the end of the steel tapping can be 0.20%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.30%, 0.31%, 0.32%, 0.33%, 0.35%, or a range of any two of the above values.

[0045] To reduce the content of brittle Al2O3 inclusions, ferrosilicon alloy, ferromanganese alloy, and carbon powder are added to the molten steel during tapping for deoxidation and alloying. When the steel is halfway tapped, ferroaluminum alloy is added for further deoxidation and ferrochrome alloying.

[0046] In the refining stage of the LF refining furnace, high-basicity slag with a basicity of 3.0–4.5 is used for smelting to better remove sulfur and oxygen from the molten steel. By controlling the amount of aluminum particles added, the acid-soluble aluminum content in the LF refining furnace is kept between 50 and 200 ppm. Maintaining a certain acid-soluble aluminum content allows for deep deoxidation of the molten steel. For example, the basicity of the high-basicity slag can be 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, or any combination of two of the above values.

[0047] Add ferromanganese alloy, ferrosilicon alloy, ferrochrome alloy, and ferroniobium alloy. Control the number of heating and power supply times during the entire smelting process to within three. Adjust the temperature to 1560-1600℃ and gently blow for 10-15 minutes to fine-tune the composition of the first refined molten steel to the target value.

[0048] Considering that the oxygen content in high-carbon steel is inherently low, the acid-soluble aluminum content at the outlet needs to be controlled below 120 ppm and the sulfur content below 30 ppm, which can further reduce the Al2O3 inclusion content.

[0049] During the refining stage of the RH refining furnace, this treatment mode is adopted, involving dehydrogenation, denitrification, and inclusion removal under vacuum conditions for 15-20 minutes. Considering the delayed cracking effect of hydrogen in steel, the hydrogen content of the second-refined molten steel is below 1.0 ppm, the nitrogen content is below 30 ppm, and the oxygen content is below 8 ppm. Before breaking the vacuum in the RH refining furnace, a sample of molten steel is taken to test the hydrogen, nitrogen, and oxygen content to ensure that the hydrogen, nitrogen, and oxygen contents in the molten steel meet the above requirements; otherwise, the treatment time is extended by 5 minutes. For example, the vacuum condition is 67 Pa.

[0050] During the continuous casting stage, the continuous casting billet is protected throughout the casting process, with the superheat controlled at 20-35℃ and the casting speed at 1.0-1.6m / min, in order to prevent center segregation and billet cracks.

[0051] For example, the superheat can be 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, 35°C or a range of any two of the above values.

[0052] For example, the pulling speed can be 1.0 m / min, 1.1 m / min, 1.2 m / min, 1.3 m / min, 1.4 m / min, 1.5 m / min, 1.6 m / min or any range of two of the above values.

[0053] In some embodiments, the hydrogen content in the continuously cast steel is below 1.5 ppm, the nitrogen content is below 35 ppm, and the oxygen content is below 10 ppm. This results in a high degree of steel cleanliness, thus producing 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades with low inclusion levels, with each type of inclusion—A (sulfides), B (alumina), C (silicates), and D (spheroidal oxides)—not exceeding level 0.5.

[0054] For example, the hydrogen content in the continuously cast steel can be 0.5ppm, 0.6ppm, 0.7ppm, 0.8ppm, 0.9ppm, 1.0ppm, 1.1ppm, 1.2ppm, 1.3ppm, 1.4ppm, 1.5ppm, or any combination of two of the above values; the nitrogen content in the continuously cast steel can be 15ppm, 16ppm, 17ppm, 18ppm, 19ppm, 20ppm, 21ppm, 22ppm, 23ppm, 24ppm, 25ppm, 26ppm, 27ppm, 28ppm, 29ppm, 30ppm, 31ppm, 32ppm, 33ppm, 34ppm, 35ppm, or any combination of two of the above values; and the oxygen content in the continuously cast steel can be 3ppm, 4ppm, 5ppm, 6ppm, 7ppm, 8ppm, 9ppm, 10ppm, or any combination of two of the above values.

[0055] Furthermore, in the embodiments of this application, adding 0.02–0.025% Nb to 75Cr1 can refine the pearlite cluster size in the hot-rolled microstructure, which is inherited by the subsequent cold-rolled and heat-treated steel strip, resulting in a similar refinement of grain size, thereby improving the strength, toughness, and fatigue performance of the saw blade. Adding Nb can form NbC second-phase particles with the carbon in the steel, hindering surface decarburization of the continuously cast billet in the heating furnace and the steel strip during heat treatment, and also playing a role in stabilizing strength and fatigue performance.

[0056] For example, the mass percentage of Nb can be 0.02%, 0.021%, 0.022%, 0.023%, 0.024%, 0.025%, or any range of two of the above values.

[0057] During the heating stage of the heating furnace, the continuous casting billet adopts a hot charging and hot delivery process to ensure that the billet temperature when entering the heating furnace is above 400℃, the billet heating temperature is between 1180 and 1250℃, and the time in the furnace is between 150 and 300 minutes.

[0058] Within this temperature range, the phase structure of the cast billet can be made homogeneous, which is beneficial for fine grains and can, to some extent, eliminate compositional segregation that occurs during the solidification process. For example, the billet heating temperature can be 1180℃, 1190℃, 1200℃, 1210℃, 1220℃, 1230℃, 1240℃, 1250℃, or any combination of two of these values; the furnace time can be 150 min, 160 min, 170 min, 180 min, 190 min, 200 min, 210 min, 220 min, 230 min, 240 min, 250 min, 260 min, 270 min, 280 min, 290 min, or 300 min.

[0059] The rolling stage includes roughing and finishing. Roughing involves seven passes to obtain an intermediate billet. Finishing involves seven passes, where the first to fifth finishing stands use CVC rolls, and the sixth and seventh finishing stands use flat rolls to obtain a hot-rolled steel coil. The finishing temperature is controlled between 860 and 920°C. For example, the finishing temperature can be 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, or any combination of two of these values.

[0060] In some embodiments, the thickness of the slab formed by continuous casting is 210 mm to 250 mm; the thickness of the intermediate slab obtained after rough rolling is 40 mm to 50 mm; and the thickness of the hot-rolled steel strip obtained after finish rolling of the intermediate slab is 1.8 mm to 5 mm. Preferably, the thickness is 2.5 mm to 4.0 mm.

[0061] The above rolling process can be used to develop hot-rolled steel strips of 75Cr1 material for ultra-thin frame saw blades with thicknesses of 1.5mm, 1.2mm, and 1.0mm, thus providing high-quality raw materials for the production of high-quality cold-rolled steel strips.

[0062] During the laminar flow cooling stage, a front-end cooling mode is adopted to rapidly reduce the temperature of the strip steel to near the coiling temperature.

[0063] During the winding stage, low-temperature winding is employed, with the winding temperature controlled between 580 and 640°C. In this application, the winding temperature is controlled between 580 and 640°C because low-to-medium temperature winding can produce a fine and uniform microstructure and suitable hardness. Exemplarily, the winding temperature can be 580°C, 590°C, 600°C, 610°C, 620°C, 630°C, 640°C, or any combination of two of the above values.

[0064] Finally, after rolling, the steel coil is quickly removed from the production line and placed in a slow cooling pit to be slowly cooled to ambient temperature. This slow cooling method helps reduce the internal stress of the 75Cr1 hot-rolled steel strip used in ultra-thin frame saw blades and improves its ductility and toughness.

[0065] In summary, this application, by adjusting the elemental composition and content of 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades and employing superior process flow and parameters, manufactures 75Cr1 hot-rolled steel strip suitable for producing frame saw blades with excellent strength and toughness, high fatigue performance, and long service life. In this application, 0.02–0.025% Nb is added to the steel to refine the grain size of the 75Cr1 steel, reduce surface decarburization, and improve strength and fatigue performance. The P and S contents are controlled at a low level. This ultra-thin 75Cr1 hot-rolled steel strip for frame saws features high steel cleanliness, low inclusion level, fine and uniform microstructure, small fluctuations in mechanical properties, and high dimensional accuracy.

[0066] 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades

[0067] Secondly, embodiments of this application provide a 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades, produced by the above-described production method, comprising the following components by mass percentage: C: 0.72–0.80%, Si: 0.20–0.45%, Mn: 0.60–0.90%, Cr: 0.30–0.60%, Nb: 0.02–0.025%, P: ≤0.015%, S: ≤0.005%; the remainder being Fe and unavoidable impurities.

[0068] In some embodiments, the acid-soluble aluminum content in the 75Cr1 hot-rolled steel strip used for ultra-thin frame saw blades is below 100 ppm, and the calcium content is below 8 ppm.

[0069] The acid-soluble aluminum content in the steel strip is below 100 ppm and the calcium content is below 8 ppm, which can reduce the inclusions in the steel strip and the inclusion level is low.

[0070] In some embodiments, the inclusion levels of categories A, B, C, and D in the 75Cr1 hot-rolled steel strip used for ultra-thin frame saw blades do not exceed level 0.5.

[0071] The molten steel used in this application embodiment has a high degree of cleanliness, so the inclusion level of the 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades is low, with each type of inclusion level, such as A (sulfides), B (alumina), C (silicates), and D (spherical oxides), not exceeding level 0.5.

[0072] In some embodiments, the ultra-thin frame saw blade uses 75Cr1 hot-rolled steel strip without a fully decarburized layer, and the depth of the semi-decarburized layer is less than 10μm.

[0073] The decarburization layer depth refers to the distance from the surface of the decarburized layer to the point where the metallographic differences between the decarburized layer and the matrix are no longer indistinguishable. An excessively deep decarburization layer on the steel surface will reduce the steel's surface hardness, tensile strength, wear resistance, and fatigue limit. The 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades prepared in this application has no fully decarburized layer, and the depth of the semi-decarburized layer is less than 10 μm; therefore, it meets the relevant standards for application in the saw blade field.

[0074] In some embodiments, the tensile strength of the 75Cr1 hot-rolled steel strip used for ultra-thin frame saw blades is 840 MPa to 940 MPa. Exemplarily, the tensile strength is 840 MPa, 850 MPa, 860 MPa, 870 MPa, 880 MPa, 890 MPa, 900 MPa, 910 MPa, 920 MPa, 930 MPa, 940 MPa, or a range consisting of any two of the above values.

[0075] In some embodiments, the microstructure of the 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades is 100% pearlitic by volume percentage.

[0076] In some embodiments, the longitudinal thickness variation of the 75Cr1 hot-rolled steel strip used for ultra-thin frame saw blades is ±30μm, and the convexity C40 ≤ 20μm.

[0077] For example, the hot-rolled steel strip is -30μm, -25μm, -20μm, -15μm, -10μm, -5μm, 0μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm or any range of two of the above values.

[0078] For example, the convexity C40 is 0 μm, 5 μm, 10 μm, 15 μm, 20 μm, or a range of any two of the above values.

[0079] Example

[0080] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all components, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0081] Example 1:

[0082] Molten iron and scrap steel were charged into a converter in a certain proportion and smelted using a top-and-bottom combined blowing converter. The smelting time was 34 minutes, and the high-pulling carbon process was used for smelting. The tapping temperature was 1636℃, and the carbon content at the tapping end was 0.21%, and the oxygen content at the tapping end was 529ppm.

[0083] After the molten steel is tapped, ferrosilicon alloy, ferromanganese alloy, and carbon powder are added for deoxidation and alloying. When the steel is halfway tapped, ferroaluminum alloy is added for further deoxidation and ferrochrome alloying. Limestone is added for slag formation and aluminum particles for deep deoxidation, resulting in a slag basicity of 3.77.

[0084] Ferromanganese, ferrosilicon, ferrochrome, and ferroniobium alloys were added to the LF furnace to fine-tune the composition to the target value. The acid-soluble aluminum content during the LF furnace smelting process ranged from 72 to 183 ppm. The entire process involved three heating and power-on cycles, adjusting the temperature to 1592℃, followed by a 10-minute soft-blowing process before exiting the furnace. The acid-soluble aluminum content at the exiting furnace was 91 ppm, and the sulfur content was 19 ppm. No calcium treatment was performed on the molten steel. The RH treatment mode was: treatment under an ultimate vacuum of 67 Pa for 16 minutes. Before breaking the vacuum in the RH furnace, samples of molten steel were taken to test the hydrogen, nitrogen, and oxygen contents, which were 0.8 ppm, 29 ppm, and 8 ppm, respectively.

[0085] The continuous casting billet was poured under full protection, with superheat controlled at 27℃ and casting speed at 1.25 m / min. The hydrogen content in the molten steel was measured to be 1.1 ppm, nitrogen content to be 32 ppm, and oxygen content to be 9 ppm. The thickness of the continuous casting billet was 230 mm.

[0086] The continuously cast billet adopts a hot charging and hot delivery process. The billet's initial temperature upon entering the heating furnace is 482–556℃, the heating temperature is 1240℃, and the furnace time is 279 minutes. Rough rolling consists of 7 passes, resulting in an intermediate billet thickness of 40mm. Finish rolling also consists of 7 passes, with the final rolling temperature controlled at 910℃. Finish rolling F1–F5 uses CVC rolls, while F6 and F7 use flat rolls on a double-stand setup. The resulting hot-rolled steel coil has a thickness of 2.0mm. Laminar flow cooling employs a front-stage cooling mode to rapidly reduce the strip temperature to near the coiling temperature. Coiling uses a low-temperature mode with a coiling temperature set at 640℃. After rolling, the steel coil is quickly removed from the line and slowly cooled to ambient temperature in a slow cooling pit.

[0087] The 75Cr1 hot-rolled steel strip produced using the above method has an acid-soluble aluminum content of 77 ppm, a calcium content of 6 ppm, and inclusion grades A, B, C, and D of 0, 0.5, 0, and 0.5, respectively. Its decarburized layer is a semi-decarburized layer with an average depth of 8.6 μm. The tensile strength is 932 MPa. The microstructure is a fully pearlitic structure, uniform and fine, with an average grain size of 38 μm and dense carbide lamellar spacing. The longitudinal thickness fluctuation of the hot-rolled steel strip is ±18 μm, and the crown C40 can be controlled within 10.2 μm.

[0088] Example 2:

[0089] Molten iron and scrap steel were charged into a converter in a certain proportion and smelted using a top-and-bottom combined blowing converter. The smelting time was 38 minutes, and the high-pulling carbon process was used for smelting. The tapping temperature was 1622℃, and the carbon content at the tapping end was 0.27%, and the oxygen content at the tapping end was 501ppm.

[0090] After the molten steel is tapped, ferrosilicon alloy, ferromanganese alloy, and carbon powder are added for deoxidation and alloying. When the steel is halfway tapped, ferroaluminum alloy is added for further deoxidation and ferrochrome alloying. Limestone is added for slag formation and aluminum particles for deep deoxidation, resulting in a slag basicity of 4.24. Ferromanganese, ferrosilicon, ferrochrome, and ferroniobium alloys are added to the LF furnace to fine-tune the composition to the target value.

[0091] The acid-soluble aluminum content in the LF furnace smelting process ranges from 97 to 186 ppm. The entire process involves three heating and power-on cycles, adjusting the temperature to 1582℃, followed by 10 minutes of soft blowing before exiting the furnace. The acid-soluble aluminum content at the exit is 86 ppm, and the sulfur content is 22 ppm. The molten steel is not treated with calcium. The RH furnace uses the same treatment mode, undergoing treatment under a 67 Pa ultimate vacuum for 19 minutes. Before breaking the vacuum in the RH furnace, molten steel samples were taken to test the hydrogen, nitrogen, and oxygen contents, which were 1.0 ppm, 31 ppm, and 8 ppm, respectively. Continuous casting of the billet was carried out under full protection, with superheat controlled at 31℃ and a casting speed of 1.20 m / min. The hydrogen content in the continuously cast steel was measured at 1.3 ppm, nitrogen at 33 ppm, and oxygen at 10 ppm. The thickness of the continuously cast billet was 230 mm.

[0092] The continuously cast billet adopts a hot charging and hot delivery process. The billet's initial temperature upon entering the heating furnace is 461–523℃, the heating temperature is 1240℃, and the furnace time is 253 minutes. Rough rolling consists of 7 passes, resulting in an intermediate billet thickness of 45mm. Finish rolling also consists of 7 passes, with the final rolling temperature controlled at 890℃. Finish rolling F1–F5 uses CVC rolls, while F6 and F7 use flat rolls on a double-stand setup. The resulting hot-rolled steel coil has a thickness of 3.5mm. Laminar flow cooling employs a front-stage cooling mode to rapidly reduce the strip temperature to near the coiling temperature. Coiling uses a low-temperature mode with a coiling temperature set at 620℃. After rolling, the steel coil is quickly removed from the line and slowly cooled to ambient temperature in a slow cooling pit.

[0093] The 75Cr1 hot-rolled steel strip produced using the above method has an acid-soluble aluminum content of 71 ppm, a calcium content of 5 ppm, and inclusion grades A, B, C, and D of 0.5, 0.5, 0, and 0.5, respectively. Its decarburized layer is a semi-decarburized layer with an average depth of 7.2 μm. The tensile strength is 903 MPa. The microstructure is a fully pearlitic structure, uniform and fine, with an average grain size of 42 μm and dense carbide lamellar spacing. The longitudinal thickness fluctuation of the hot-rolled steel strip is ±23 μm, and the crown C40 can be controlled within 16 μm.

[0094] Example 3:

[0095] Molten iron and scrap steel were charged into a converter in a specific ratio and smelted using a top-and-bottom blown converter for 38 minutes. A high-pulling carbon process was employed, with a tapping temperature of 1615℃ and a final carbon content of 0.31% and an oxygen content of 494 ppm. After tapping, ferrosilicon alloy, ferromanganese alloy, and carbon powder were added for deoxidation and alloying. Halfway through tapping, ferroaluminum alloy was added for further deoxidation and ferrochrome alloying. Limestone was added for slag formation and aluminum granules for deep deoxidation, resulting in a slag basicity of 4.07. Ferromanganese, ferrosilicon, ferrochrome, and ferroniobium alloys were added to the LF furnace to fine-tune the composition to the target values. The acid-soluble aluminum content during the LF furnace smelting process ranged from 88 to 185 ppm. The entire process involved three temperature increases and power-on cycles, adjusting the temperature to 1590℃, followed by a 10-minute soft-blowing process before exiting the smelting station. The acid-soluble aluminum content at the exit station was 86 ppm, and the sulfur content was 22 ppm. The molten steel underwent no calcium treatment. The RH furnace was treated using this method under an ultimate vacuum of 67 Pa for 18 minutes. Before breaking the vacuum in the RH furnace, steel samples were taken to test the hydrogen, nitrogen, and oxygen contents, which were 0.7 ppm, 31 ppm, and 7 ppm, respectively. The continuous casting billet was poured under full protective conditions, with superheat controlled at 26°C and a casting speed of 1.20 m / min. The hydrogen content in the continuously cast steel was measured to be 0.9 ppm, nitrogen 32 ppm, and oxygen 10 ppm, and the billet thickness was 230 mm.

[0096] The continuously cast billet adopts a hot charging and hot delivery process. The billet's initial temperature upon entering the heating furnace is 440–506℃, the heating temperature is 1220℃, and the furnace time is 255 minutes. Rough rolling consists of 7 passes, resulting in an intermediate billet thickness of 50mm. Finish rolling also consists of 7 passes, with the final rolling temperature controlled at 860℃. Finish rolling F1–F5 uses CVC rolls, while F6 and F7 use flat rolls on a double-stand setup. The resulting hot-rolled steel coil has a thickness of 5.0mm. Laminar flow cooling employs a front-stage cooling mode to rapidly reduce the strip temperature to near the coiling temperature. Coiling uses a low-temperature mode with a coiling temperature set at 580℃. After rolling, the steel coil is quickly removed from the line and slowly cooled to ambient temperature in a slow cooling pit.

[0097] The 75Cr1 hot-rolled steel strip produced using the above method has an acid-soluble aluminum content of 72 ppm, a calcium content of 7 ppm, and inclusion grades A, B, C, and D of 0.5, 0.5, 0, and 0.5, respectively. Its decarburized layer is a semi-decarburized layer with an average depth of 9.1 μm. The tensile strength is 851 MPa. The microstructure is a fully pearlitic structure, uniform and fine, with an average grain size of 48 μm and dense carbide lamellar spacing. The longitudinal thickness fluctuation of the hot-rolled steel strip is ±28 μm, and the crown C40 can be controlled within 19 μm.

[0098] Comparative Example 1

[0099] The production process is similar to that of Example 1, except that Nb is not added and the thickness is 3.5 mm.

[0100] Comparative Example 2

[0101] The production process is similar to that of Example 1, except that the winding temperature is adjusted to 680°C and the thickness is 3.5 mm.

[0102] Comparative Example 3

[0103] The production process is similar to that of Example 1, except that the carbon content at the tapping point is 0.08% and the thickness is 3.5 mm.

[0104] Comparative Example 4

[0105] The production process is similar to that of Example 1, except that the billet is heated in the furnace for 350 minutes and has a thickness of 3.5 mm.

[0106] Comparative Example 5

[0107] Similar to the production process in Example 1, the difference is that the sixth and seventh finishing mill stands did not use flat rolls for rolling, but instead used CVC rolls with a thickness of 3.5 mm.

[0108] The performance of the ultra-thin frame saw blades obtained in Examples 1-4 and Comparative Examples 1-5 was tested according to the test methods in GB / T228.1-2021, GB / T 6394-2017, GB / T 224-2019 and GB / T 10561-2023; the results are shown in Table 1.

[0109] Table 1. Performance test results of Examples 1-3 and Comparative Examples 1-5

[0110]

[0111]

[0112] Figure 1 This is a microstructure diagram of the 75Cr1 hot-rolled steel strip used for the ultra-thin frame saw blade of Embodiment 1 of this application; Figure 2 This is a microstructure diagram of the 75Cr1 hot-rolled steel strip used for the ultra-thin frame saw blade of Embodiment 2 of this application;

[0113] Figure 3 This is a microstructure diagram of the 75Cr1 hot-rolled steel strip used for the ultra-thin frame saw blade of Embodiment 3 of this application. (Combined with...) Figures 1 to 3As shown in Table 1, the 75Cr1 hot-rolled steel strips for ultra-thin frame saw blades in Examples 1-3 have a shallow decarburized layer, small grain size, moderate strength, and few inclusions. This results in the 75Cr1 hot-rolled steel strip of this application exhibiting excellent fatigue resistance while maintaining good plasticity and toughness. This demonstrates that the chemical composition ratio and production process provided in this application effectively enable the resulting 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades to possess good mechanical and fatigue properties.

[0114] Comparative Example 1: The absence of Nb resulted in coarser grain size and a deeper decarburized layer. Comparative Example 2: Excessively high coiling temperature led to coarser grain size, uneven pearlite lamellar spacing, and poor microstructure uniformity. Comparative Example 3: Low carbon content at the tapping endpoint resulted in a higher level of inclusions in the steel. Comparative Example 4: Excessive furnace heating time for the slab resulted in coarser grain size and a deeper decarburized layer. Comparative Example 5: The use of CVC rolls on the sixth and seventh finishing mill stands resulted in reduced edge thickness and a larger crown (C40).

[0115] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for producing 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades, characterized in that, include: Molten iron and scrap steel are loaded into a converter and produced using a top-and-bottom blown converter. High-carbon smelting is employed to obtain converter steel. The tapping temperature of the converter steel is 1590–1650℃, the carbon content at the tapping endpoint is 0.20–0.35%, and the oxygen content at the tapping endpoint is 300–600 ppm. During tapping, ferrosilicon alloy, ferromanganese alloy, and carbon powder are first added for deoxidation and alloying. When the steel is tapped halfway, ferroaluminum alloy is added for further deoxidation and ferrochrome alloying. The molten steel from the converter is transferred to the LF refining furnace, and limestone is added to form slag. The basicity of the slag is 3.0 to 4.

5. Aluminum particles are added to make the acid-soluble aluminum content between 50 and 200 ppm. Ferromanganese alloy, ferrosilicon alloy, ferrochrome alloy, and ferroniobium alloy are added. The number of heating and power supply times during the entire smelting process is controlled to within three times. The temperature is adjusted to 1560 to 1600℃, and soft blowing is performed for 10 to 15 minutes to obtain the first refined molten steel. The acid-soluble aluminum content of the first refined molten steel leaving the station is below 120 ppm, and the sulfur content is below 30 ppm. The first refined molten steel is charged into an RH refining furnace and treated under vacuum for 15 to 20 minutes to perform dehydrogenation, denitrification and inclusion removal treatment to obtain the second refined molten steel. The second refined molten steel has a hydrogen content of less than 1.0 ppm, a nitrogen content of less than 30 ppm and an oxygen content of less than 8 ppm. The second refined steel is continuously cast to obtain a billet; the billet comprises the following components in mass percentage: C: 0.72%~0.80%, Si: 0.20%~0.45%, Mn: 0.60%~0.90%, Cr: 0.30%~0.60%, Nb: 0.02%~0.025%, P: ≤0.015%, S: ≤0.005%; the remainder is Fe and unavoidable impurities; The billet is heated in a furnace, then rough-rolled, finished-rolled, laminar flow cooled, coiled, and slowly cooled to obtain 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades. The furnace heating process includes: the billet entering the furnace at a temperature above 400℃, and being heated to 1180–1250℃ for 150–300 minutes. The rough rolling process includes seven passes to obtain an intermediate billet with a thickness of 40–50 mm. The finish rolling process includes seven passes, with the first to fifth finish stands using CVC rolls, and the sixth and seventh finish stands using flat rolls to obtain a hot-rolled steel coil. The final finishing temperature is controlled at 860–920℃. A front-stage cooling mode is used to rapidly reduce the temperature of the hot-rolled steel coil to near the coiling temperature, which is controlled at 580–640℃.

2. The production method according to claim 1, characterized in that, In the step of continuously casting the second refined molten steel to obtain a billet, the continuously cast molten steel meets the following requirements: hydrogen content below 1.5 ppm, nitrogen content below 35 ppm, and oxygen content below 10 ppm.

3. The production method according to claim 1 or 2, characterized in that, In the step of continuously casting the second refined molten steel to obtain a billet, the superheat is 20-35℃ and the casting speed is 1.0-1.6m / min.

4. The production method according to claim 1, characterized in that, The ultra-thin frame saw blade uses 75Cr1 hot-rolled steel strip that meets the following requirements: acid-soluble aluminum content is below 100ppm and calcium content is below 8ppm.

5. The production method according to claim 1, characterized in that, The thickness of the continuously cast billet is 210mm to 250mm; the thickness of the intermediate billet is 40mm to 50mm; and the thickness of the hot-rolled steel coil is 1.8mm to 5mm.

6. A type of 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades, produced by the production method according to any one of claims 1-5, characterized in that, The components include the following components by mass percentage: C: 0.72%~0.80%, Si: 0.20%~0.45%, Mn: 0.60%~0.90%, Cr: 0.30%~0.60%, Nb: 0.02%~0.025%, P: ≤0.015%, S: ≤0.005%; the remainder is Fe and unavoidable impurities.

7. The 75Cr1 hot-rolled steel strip for ultra-thin frame saw blades according to claim 6, characterized in that, The 75Cr1 hot-rolled steel strip used for the ultra-thin frame saw blade meets at least one of the following conditions: (1) The acid-soluble aluminum content in the 75Cr1 hot-rolled steel strip used for the ultra-thin frame saw blade is below 100ppm and the calcium content is below 8ppm; (2) The inclusion levels of A, B, C and D in the 75Cr1 hot-rolled steel strip used for the ultra-thin frame saw blade shall not exceed 0.5; (3) The ultra-thin frame saw blade is made of 75Cr1 hot-rolled steel strip without a fully decarburized layer and the depth of the semi-decarburized layer is less than 10μm; (4) The tensile strength of the 75Cr1 hot-rolled steel strip used for the ultra-thin frame saw blade is 840MPa~940MPa; (5) The metallographic structure of the 75Cr1 hot-rolled steel strip used for the ultra-thin frame saw blade is 100% pearlite, and the pearlite cluster size does not exceed 50μm; (6) The longitudinal thickness fluctuation of the 75Cr1 hot-rolled steel strip used for the ultra-thin frame saw blade is ±30μm, and the convexity C40≤20μm.

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