High-rigidity environment-friendly pre-hardened low-crack-sensitivity saw blade steel and manufacturing method thereof

Abstract

The invention belongs to the field of black metal materials, and particularly relates to high-rigidity environment-friendly pre-hardened low-crack-sensitivity saw blade steel and a manufacturing method thereof. The steel comprises the following chemical components: C, Si, Mn, less than or equal to 0.025% of P, less than or equal to 0.010% of S, less than or equal to 0.30% of Cr and Mo, 5.5 to 6.0% of Als, B, Ti, Mg, Ti / (Mg + B), 0.05 to 0.10% of TiB2, 0.01 to 0.02% of B / TiB2, and the balance of Fe and inevitable impurities. According to the saw blade steel, the rigidity is larger than or equal to 8754 N / m, the yield strength is larger than or equal to 1082 MPa, the tensile strength is larger than or equal to 1418 MPa, the ductility is larger than or equal to 23%, the room-temperature impact energy AKV is larger than or equal to 157 J, the hardness is 42-46 HRC, and the tooth top quenching hardness is larger than or equal to 57 HRC.

Description

Technical Field

[0001] The present invention belongs to the field of ferrous metal materials, and in particular relates to a high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity saw blade steel and a manufacturing method thereof. Background Art

[0002] With the rapid development of my country's mining, stone, and construction industries, saw blades are shifting toward larger diameters and higher speeds. Circular saw blades now reach sizes up to 4800mm in diameter and must be delivered pre-hardened. Traditional materials like DJ100 and 65Mn, due to their high carbon content, produce poor flatness when rolled into ultra-wide steel plates exceeding 3000mm, failing to meet users' demand for high flatness. Furthermore, traditional saw blade steel is highly crack-susceptible and prone to water-quenching cracking, making it difficult for steel mills to deliver pre-hardened steel. After hot-rolled steel is delivered, users must re-oil-quench it. This oil quenching process produces significant environmental pollution and carries a risk of quenching cracking. Furthermore, to ensure stable sawing, blades must possess a certain degree of rigidity. Therefore, technological innovation in saw blade steel is urgently needed to meet the industry's demand for high-rigidity, environmentally friendly, pre-hardened, low-crack-susceptibility, and ultra-wide saw blades.

[0003] Patent document CN100366779C discloses a stone cutting saw blade steel and its manufacturing method. The composition, by mass percentage, is as follows: C 0.45-0.60%, Si 0.10-0.60%, Mn 1.3-1.6%, P ≤ 0.02%, S ≤ 0.02%, Cr 0.15-0.30%, N 0.005-0.020%, Ca 0-0.005%, V 0-0.3%, Al 0.005-0.040%, with the balance being Fe and unavoidable impurities. The saw blade manufactured using this technology has a maximum thickness of 10mm and a diameter of only 1800mm. It is oil-quenched, and therefore fails to address the current issues of limited width specifications, quenching cracking, and environmental pollution associated with saw blade steel.

[0004] Patent document CN104532150B discloses an economical, extra-wide saw blade steel and its manufacturing method, the composition of which is calculated by mass percentage: C 0.35-0.45%, Si 0.10-0.50%, Mn 0.60-1.20%, P ≤ 0.030%, S ≤ 0.010%, B 0.0010-0.0040%, Al 0.010-0.080%, Ti 0.060%, Ca 0.0010-0. 0.0080%, N≤0.0080%, O≤0.0080%, H≤0.0004%, and one or more of Nb0.001-0.050%, Cr0.01-0.50%, Mo0.01-0.50%, Ni0.01-0.50%, and V0.01-0.15%, and satisfying 0.15%≤(Cr / 5+Mn / 6+50B)≤0.45%, with the remainder being Fe and unavoidable impurities. This technology can produce steel plates with a thickness of 6-16mm and saw blade diameters of 1700-4500mm. Through online water cooling and tempering, the saw blade steel has a yield strength greater than 850MPa, a tensile strength of 1000-1400MPa, an elongation greater than 10%, and a Charpy V-type longitudinal impact energy of 50-90J. However, this technology has a high carbon content of 0.35-0.45%, making it a medium-carbon alloy steel with high resistance to rolling deformation. In actual production, the shape of the plate cannot be guaranteed when rolling widths exceed 3500mm, making it unworkable. Furthermore, the national standard "GB / T24181 Steel for Diamond Welded Saw Blade Substrates" stipulates that the hardness range of saw blade steel must cover 38-47HRC, while users actually use a hardness of 42-45HRC. However, the maximum hardness of saw blade steel produced by this technology is only 40HRC, which cannot meet the performance requirements of user applications.

[0005] Therefore, the existing technology does not solve the requirements of saw blade steel on stiffness, as well as the problems of environmental pre-hardening, quenching cracking, and ultra-wide high-flatness plate shape. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention aims to provide a high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity saw blade steel and its manufacturing method. By reducing the C content and adding Ti, Mg, and B elements, the Ti-Mg-B composite effect promotes the large-scale generation of intragranular ferrite and refines it into acicular ferrite with good strength and plasticity, inhibiting the formation of pearlite with poor plasticity, thereby ensuring that the steel plate has good ductility during the rolling process and ensuring the smooth rolling of thin-gauge and ultra-wide steel plates; at the same time, the precipitation strengthening, grain refinement, and dispersion strengthening effects of Ti-Mg-B are utilized to ensure the strength and hardness of the steel. The addition of reinforcing phase particles TiB2 plays a role in refining the grains and improving the strength. At the same time, the growth morphology and distribution state of TiB2 are regulated by B to withstand the load of the steel during elastic deformation, so that the effective stress acting on the steel matrix structure is significantly reduced, the elastic modulus of the steel is increased, and thus the rigidity of the steel is improved. Through controlled rolling and controlled cooling process design, the volume fraction of acicular ferrite in the rolled steel plate is controlled to 70% to 75%, and the volume fraction of pearlite is controlled to 25% to 30%, so that the saw blade steel has a good match of strength, plasticity and toughness. At the same time, online pre-hardening is achieved, eliminating offline oil quenching and tempering treatment, and realizing environmentally friendly pre-hardening production of saw blade steel.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity saw blade steel. The chemical composition of the steel is as follows by weight: C: 0.10%-0.20%, Si: 0.3%-0.8%, Mn: 0.9%-1.3%, P≤0.025%, S≤0.010%, Cr: 0.30%-0.50%, Mo≤0.30%, Als: 0.02%-0.08%, B: 0.0008%-0.0020%, Ti: 0.020%-0.035%, Mg: 0.0025%-0.0040%, Ti / (Mg+B): 5.5-6.0, TiB2: 0.05%-0.10%, B / TiB2: 0.01-0.02, and the balance is Fe and unavoidable impurities.

[0009] The reasons for adopting the above components are as follows:

[0010] 1) Carbon: Carbon is an important element for ensuring the wear resistance of saw blade steel and balancing strength and ductility. However, high carbon content leads to increased resistance to rolling deformation, making it difficult to control the rolled plate shape. Furthermore, high carbon content significantly increases the steel's tendency to quench cracking. Therefore, the present invention controls the carbon content in the steel within the range of 0.10% to 0.20%.

[0011] 2) Si: Si is a good deoxidizer that can improve the strength and wear resistance of steel. However, an increase in Si content can reduce the plasticity and toughness of the steel. Therefore, the Si content in the present invention is controlled to 0.3% to 0.8%.

[0012] 3) Mn: Mn can refine the pearlite interlamellar spacing and improve the strength of pearlite. Excessive Mn content will reduce the ductility of the steel. Therefore, the Mn content in the present invention is controlled to 0.9% to 1.3%.

[0013] 4) P: P is a harmful element in steel and can easily cause cold brittleness. However, strict control of P content increases production costs. Therefore, the present invention controls the P content in steel to ≤ 0.025%.

[0014] 5) S: S is a harmful element in steel, causing hot brittleness and reducing its ductility and toughness. Therefore, the present invention requires that the S content in the steel be ≤ 0.010%.

[0015] 6) Cr: Cr can hinder austenite grain growth and significantly reduce the spacing between pearlite lamellae, thereby increasing the strength and hardness of the steel. However, excessive Cr can easily cause element segregation, reducing the steel's plasticity. Therefore, the present invention controls the Cr content in the steel to 0.30% to 0.50%.

[0016] 7) Mo: Mo significantly improves the hardenability of steel, but excessive Mo content increases the steel's resistance to deformation during rolling. Therefore, the present invention controls the Mo content in the steel to ≤ 0.30%.

[0017] 8) Al: Al can improve the purity of steel, refine grains, and enhance wear resistance. However, excessive Al content can affect the hot working properties of steel. Therefore, in the present invention, the Al content is controlled to 0.02% to 0.08%.

[0018] 9) Boron: Boron can segregate at austenite grain boundaries, inhibiting the formation and growth of ferrite there, forming grain boundary precipitates and improving the strength and plasticity of the grain boundaries. However, excessive amounts of boron can easily form hard and brittle compounds at the grain boundaries, impairing the hot workability and plasticity of the steel. Therefore, in the present invention, the boron content is controlled to 0.0008% to 0.0020%.

[0019] 10) Ti: Ti has a strong affinity for O and N in molten steel, deoxidizing and degassing the steel while also contributing to dispersion strengthening. Furthermore, Ti is a ferrite-forming element, promoting the formation of intragranular ferrite. However, Ti increases the viscosity of the molten steel, making it difficult to separate non-metallic inclusions. Therefore, in the present invention, the Ti content is controlled to 0.020% to 0.035%.

[0020] 11) Mg: Mg is a good deoxidizer and desulfurizer, and it also refines ferrite grains. Excessive Mg content can form Mg inclusions. Therefore, in the present invention, the Mg content is controlled to 0.0025% to 0.0040%.

[0021] 12) The present invention controls Ti / (Mg+B) to be 5.5-6.0. Through the composite effect of Ti-Mg-B, the formation of large amounts of intragranular ferrite is promoted and refined into acicular ferrite with good strength and plasticity, and the formation of pearlite with poor plasticity is suppressed, thereby ensuring that the steel plate has good ductility during the rolling process. At the same time, the precipitation strengthening, grain refinement and dispersion strengthening effects of Ti-Mg-B are utilized to ensure the strength and hardness of the steel.

[0022] 13) TiB2: TiB2 has a high elastic modulus and can also refine grains, improving the strength and toughness of steel. However, excessive TiB2 can negatively impact the steel's plasticity. Therefore, the TiB2 content in this invention is controlled to 0.05% to 0.10%.

[0023] 14) The present invention controls the B / TiB2 ratio to 0.01-0.02. B significantly influences the growth morphology and distribution of TiB2 particles in steel. With the relative change in B content, the TiB2 particle size becomes elongated rods or granules distributed along grain boundaries or within grains. By controlling the addition ratio of the two, the present invention limits the TiB2 particle size to ≤5µm and distributes it in granular form at grain boundaries, thereby increasing the elastic deformation limit of the grain boundaries.

[0024] The saw blade steel has a thickness of 5 to 12 mm, a maximum width of 4800 mm, and an unevenness of ≤4 mm / 2 m.

[0025] The stiffness of the saw blade steel is ≥8754N / m, the yield strength is ≥1082MPa, the tensile strength is ≥1418MPa, the elongation is ≥23%, the room temperature impact energy AKV is ≥157J, the hardness is 42~46HRC, and the tooth tip quenching hardness meets ≥57HRC.

[0026] A method for manufacturing high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity saw blade steel, the specific method comprising:

[0027] 1) Use converter slag blocking for steel tapping and control the slag layer thickness to 60-90mm to increase the alloy element recovery rate and reduce the inclusion content; VD refining holding time is controlled at 15-25min to reduce the gas content, and requires [H] ≤ 2ppm, [O] < 20ppm, [N] < 50ppm.

[0028] 2) TiB2 adopts KBF4-K2TiF6 mixed salt powder system, and the mixed salt powder is wrapped in a thin steel strip according to the Ti / B atomic ratio of 1:2-2.5 to make cored wire, which is inserted into the ladle through the wire feeder during the ladle refining process; the calming time before the ladle is put on the machine is controlled at 20-30 minutes to make the molten steel composition uniform; the target superheat of the ladle is controlled at 20-25℃ to ensure the quality of the ingot and production efficiency; the casting is protected throughout and electromagnetic stirring is used in the secondary cooling zone to refine the grains, with a current intensity of 400-600A; in order to eliminate defects such as segregation, looseness and shrinkage cavities of the ingot, light reduction is applied at the end of solidification, with the reduction range at the position of 0.4-0.9 of the central solid phase ratio, the reduction amount is 6.8-7.4mm, the reduction rate is 0.9-1.2mm / min, and the continuous casting process adopts a constant pulling speed of 0.9-1.0m / min.

[0029] 3) The temperature of the second heating section of the slab is 1120-1210°C, the temperature of the soaking section is 1150-1200°C, and the total time in the furnace is 0.8-1.2 min / mm (thickness) to ensure that the alloy elements are fully and evenly dissolved.

[0030] 4) The starting rolling temperature is not less than 1050℃, and the reduction rate of the first three passes is ≥30% to allow the rolling force to penetrate into the core of the billet and improve the uniformity of the structure. The reduction rate of the last two passes is 8% to 10% to improve the rolled plate shape. The final rolling temperature is 840 to 860℃ to refine the grains and improve the plasticity of the steel; the ACC starting cooling temperature is 730 to 760℃, the cooling rate is 10 to 12℃ / s, and the red-return temperature is 620 to 650℃; to inhibit the growth of pearlite, increase the proportion of ferrite, and control the volume fraction of acicular ferrite in the rolled steel plate to 70% to 75%, and the volume fraction of pearlite to 25% to 30%.

[0031] 5) After the steel plate exits the water, it undergoes three passes of hot straightening at a temperature of 540-560°C and a straightening speed of 14-16 m / min to fully release the residual stress of the steel plate and avoid deformation of the steel plate after cooling.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1) By reducing the C content and adding Ti, Mg, and B elements, the Ti-Mg-B composite effect promotes the massive generation of intragranular ferrite and refines it into acicular ferrite with good strength and plasticity, inhibiting the formation of pearlite with poor plasticity, thereby ensuring that the steel plate has good ductility during the rolling process, ensuring the smooth rolling of thin-gauge and ultra-wide steel plates, while reducing crack sensitivity and reducing the risk of quenching cracking; at the same time, the precipitation strengthening, grain refinement, and dispersion strengthening effects of Ti-Mg-B are utilized to ensure the strength and hardness of the steel; the addition of reinforcing phase particles TiB2 plays a role in refining the grains and improving the strength, and at the same time, the growth morphology and distribution state of TiB2 are regulated by B to withstand the load of the steel during elastic deformation, so that the effective stress acting on the steel matrix structure is significantly reduced, thereby improving the elastic modulus of the steel.

[0034] 2) Through controlled rolling and controlled cooling process design, the volume fraction of acicular ferrite in the rolled steel plate is controlled to 70% to 75%, and the volume fraction of pearlite is controlled to 25% to 30%, so that the saw blade steel has a good match of strength, plasticity and toughness. At the same time, online pre-hardening is achieved, eliminating offline oil quenching and tempering treatment, and realizing environmentally friendly pre-hardening production of saw blade steel.

[0035] 3) The saw blade steel of the present invention has a thickness of 5 to 12 mm, a width of ≤4500 mm, an unevenness of ≤4 mm / 2 m, a stiffness of ≥8754 N / m, a yield strength of ≥1082 MPa, a tensile strength of ≥1418 MPa, an elongation of ≥23%, an impact energy AKV of ≥157 J at room temperature, a hardness of 42 to 46 HRC, and a tooth tip quenching hardness of ≥57 HRC. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the specific implementation methods of the present invention are further described below in conjunction with examples. The following examples are used to specifically illustrate the contents of the present invention. These examples are only general descriptions of the contents of the present invention and do not limit the contents of the present invention.

[0037] A high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity saw blade steel and a manufacturing method thereof are described in detail as follows:

[0038] According to the alloy element ratio in Table 1, converter smelting, VD refining, continuous casting, slab heating, controlled rolling, and controlled cooling were carried out. The main process parameters of smelting, heating, controlled rolling, and controlled cooling in each embodiment are shown in Tables 2 to 6, and the mechanical properties are shown in Table 7.

[0039] Table 1 Chemical composition of steel smelting in each example (%)

[0040]

[0041] Table 2 Process parameters of steel in various examples

[0042]

[0043] Table 3 Process parameters of steel in various examples

[0044]

[0045] Table 4 Process parameters of steel in various examples

[0046]

[0047] Table 5 Process parameters of steel in various examples

[0048]

[0049] Table 6 Process parameters of steel in various examples

[0050]

[0051] The structure of the comparative example in Table 6 is blocky, polygonal ferrite + pearlite, without acicular ferrite.

[0052] Table 7 Mechanical properties of various examples

[0053]

[0054] *Test conditions: 1800mm circular saw, chuck diameter 260mm, loading point R=820mm, loading force: 50N.

[0055] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity saw blade steel, characterized in that: The chemical composition of the steel by weight percentage is: C: 0.10%~0.20%, Si: 0.3%~0.8%, Mn: 0.9%~1.3%, P≤0.025%, S≤0.010%, Cr: 0.30%~0.50%, Mo≤0.30%, Als: 0.02%~0.08%, B: 0.0008%~0.0020%, Ti: 0.020%~0.035%, Mg: 0.0025%~0.0040%, Ti / (Mg+B): 5.5~6.0, TiB2: 0.05%~0.10%, B / TiB2: 0.01~0.02, and the balance is Fe and unavoidable impurities.

2. The high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity saw blade steel according to claim 1, characterized in that: The saw blade steel has a thickness of 5 to 12 mm, a maximum width of 4800 mm, and an unevenness of ≤4 mm / 2 m.

3. The high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity saw blade steel according to claim 1, characterized in that: The stiffness of the saw blade steel is ≥8754N / m, the yield strength is ≥1082MPa, the tensile strength is ≥1418MPa, the elongation is ≥23%, the room temperature impact energy AKV is ≥157J, the hardness is 42~46HRC, and the tooth tip quenching hardness meets ≥57HRC.

4. The high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity saw blade steel according to claim 1, characterized in that: The TiB2 particle size is ≤5µm and is distributed in the form of particles at the grain boundaries.

5. A method for manufacturing a high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity saw blade steel according to any one of claims 1 to 4, characterized in that: Specific methods include: 1) Use converter slag blocking for tapping, control the slag layer thickness to 60-90mm, control the VD refining holding time to 15-25min, and require [H]≤2ppm, [O]<20ppm, [N]<50ppm; 2) The cooling time of the ladle before loading is controlled at 20-30 minutes, the target superheat of the tundish is controlled at 20-25°C, the casting is protected throughout, and electromagnetic stirring is applied in the secondary cooling zone with a current intensity of 400-600A; light reduction is applied at the end of solidification, with the reduction range at the center solid phase ratio of 0.4-0.9, the reduction amount is 6.8-7.4mm, the reduction rate is 0.9-1.2mm / min, and a constant pulling speed of 0.9-1.0m / min is adopted during the continuous casting process; 3) The temperature of the second heating section of the slab is 1120-1210°C, the temperature of the soaking section is 1150-1200°C, and the total time in the furnace is 0.8-1.2 min / mm; 4) The starting rolling temperature is not less than 1050℃, the reduction rate of the first three passes is ≥30%, the reduction rate of the last two passes is 8%~10%, the finishing rolling temperature is 840~860℃, the ACC cooling temperature is 730~760℃, the cooling rate is 10~12℃ / s, and the red-return temperature is 620~650℃; 5) After the steel plate comes out of the water, it undergoes three passes of hot straightening at a temperature of 540-560°C and a straightening speed of 14-16 m / min.

6. The method for manufacturing a high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity saw blade steel according to claim 5, characterized in that: The volume fraction of acicular ferrite in the rolled steel plate is 70% to 75%, and the volume fraction of pearlite is 25% to 30%.

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