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

Abstract

The present application belongs to the field of ferrous materials, and particularly relates to a high-rigidity, environmentally-friendly, pre-hardened, low-crack-sensitivity saw blade steel and a manufacturing method thereof. The chemical composition of the steel comprises C, Si, Mn, P≤0.025%, S≤0.010%, Cr, Mo≤0.30%, Als, B, Ti, Mg, Ti / (Mg+B): 5.5-6.0, TiB2: 0.05%-0.10%, B / TiB2: 0.01-0.02, and the balance of Fe and inevitable impurities. The rigidity of the saw blade steel is ≥8754 N / m, the yield strength is ≥1082 MPa, the tensile strength is ≥1418 MPa, the elongation is ≥23%, the room temperature impact energy AKV is ≥157 J, the hardness is 42-46 HRC, and the tooth tip quenching hardness satisfies ≥57 HRC.

Description

Technical Field

[0001] This invention belongs to the field of ferrous metal materials, and particularly relates to a high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity saw blade steel and its manufacturing method. Background Technology

[0002] With the rapid development of my country's mining, stone processing, and construction industries, saw blades are shifting towards larger diameters and higher speeds. The largest circular saw blade size has reached φ4800mm, and pre-hardened delivery is required. Traditional materials like DJ100 and 65Mn, due to their high carbon content, result in poor sheet shape when rolling ultra-wide steel plates exceeding 3000mm, failing to meet users' requirements for high flatness. Furthermore, traditional saw blade steel plates are highly susceptible to cracking and prone to water quenching cracking, making pre-hardened delivery difficult for steel mills. After hot-rolled delivery, users need to re-oil quench the steel plates, but the resulting oil fumes cause significant environmental pollution and also pose a risk of quenching cracking. Additionally, to ensure saw blade stability during sawing, a certain level of rigidity is required. Therefore, there is an urgent need for technological innovation in saw blade steel to meet the industry's demand for high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity, and ultra-wide saw blade steel plates.

[0003] Patent document CN100366779C discloses a type of stone cutting saw blade steel and its manufacturing method. The composition, by mass percentage, is: 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 10 mm and a diameter of only 1800 mm, and employs oil quenching. Therefore, it fails to solve the problems of limited width specifications, quenching cracking, and environmental pollution inherent in current saw blade steel.

[0004] Patent document CN104532150B discloses an economical, ultra-wide saw blade steel and its manufacturing method. The composition, by mass percentage, is: 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 0.0010-0.0040%. The saw blade contains 0.0080% N, ≤0.0080% O, ≤0.0080% H, and one or more of the following: Nb 0.001~0.050%, Cr 0.01~0.50%, Mo 0.01~0.50%, Ni 0.01~0.50%, and V 0.01~0.15%, with the condition that 0.15% ≤ (Cr / 5 + Mn / 6 + 50B) ≤ 0.45%, and 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-shaped longitudinal impact energy of 50-90J. However, this technology involves a high carbon content of 0.35–0.45%, classifying it as medium-carbon alloy steel. This results in high resistance to rolling deformation, making it difficult to guarantee the shape of plates with rolling widths exceeding 3500 mm in actual production. Therefore, it is not feasible for production. Furthermore, the national standard GB / T24181, "Steel for Diamond Welded Saw Blades," specifies that saw blade steel should cover a hardness range of 38–47 HRC, while users typically require a hardness of 42–45 HRC. However, the saw blade steel produced by this technology has a maximum hardness of only 40 HRC, failing to meet the performance requirements of user applications.

[0005] Therefore, existing technologies have not solved the rigidity requirements of saw blade steel, as well as the problems of environmentally friendly pre-hardening, quenching cracking, and ultra-wide, high-flatness plate shape. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, 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 carbon content and adding Ti, Mg, and B elements, the Ti-Mg-B composite effect promotes the formation and refinement of intragranular ferrite into highly ductile acicular ferrite, while inhibiting the formation of less ductile pearlite. This ensures good ductility of the steel plate during rolling, facilitating the smooth rolling of thin, ultra-wide steel plates. Simultaneously, the precipitation strengthening, grain refinement strengthening, and dispersion strengthening effects of Ti-Mg-B guarantee the steel's strength and hardness. The addition of reinforcing phase particles TiB2 refines the grains and improves strength. Furthermore, the growth morphology and distribution of TiB2 are controlled by B to withstand the loads during elastic deformation, significantly reducing the effective stress acting on the steel matrix and increasing the steel's elastic modulus, thereby improving its stiffness. By designing a controlled rolling and cooling process, the volume fraction of acicular ferrite in the rolled steel plate is controlled to be 70%–75%, and the volume fraction of pearlite is controlled to be 25%–30%, giving the saw blade steel a good balance of strength, plasticity, and toughness. At the same time, online pre-hardening is achieved, eliminating the need for offline oil quenching and tempering, and realizing environmentally friendly pre-hardening production of saw blade steel.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] A high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity saw blade steel, the chemical composition of which, by weight percentage, is as follows: 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, with the balance being Fe and unavoidable impurities.

[0009] The reasons for using the above-mentioned components are as follows:

[0010] 1) Carbon (C): Carbon is an important element for ensuring the wear resistance of saw blade steel and balancing its strength and toughness. However, high C content leads to greater resistance to rolling deformation and makes it difficult to control the rolled plate shape. At the same time, high C content significantly increases the tendency of steel to crack during quenching. Therefore, this invention controls the C 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, but an increase in Si content will reduce the plasticity and toughness of steel. Therefore, the Si content in this invention is controlled at 0.3% to 0.8%.

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

[0013] 4) P: P is a harmful element in steel, which easily causes cold brittleness. However, strict control of P content will increase production costs. Therefore, this 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, this 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 interlamellar spacing of pearlite, thereby improving the strength and hardness of steel. However, excessive Cr can easily lead to elemental segregation and reduce the plasticity of steel. Therefore, this invention controls the Cr content in the steel to be 0.30% to 0.50%.

[0016] 7) Mo: Mo can significantly improve the hardenability of steel, but excessive Mo content will increase the resistance to deformation during steel rolling. Therefore, this invention controls the Mo content in the steel to ≤0.30%.

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

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

[0019] 10) Ti: Ti has a strong affinity for O and N in molten steel, and plays a role in deoxidation and degassing in steel. It can also play a role in dispersion strengthening. In addition, Ti is a ferrite-forming element and can promote the formation of intragranular ferrite. However, Ti will increase the viscosity of molten steel, making it difficult to separate non-metallic inclusions in the steel. Therefore, the Ti content in this invention is controlled at 0.020% to 0.035%.

[0020] 11) Mg: Mg is a good deoxidizing and desulfurizing agent, and it can also refine ferrite grains. However, excessive Mg content will form Mg inclusions. Therefore, the Mg content in this invention is controlled at 0.0025% to 0.0040%.

[0021] 12) This invention controls the Ti / (Mg+B) ratio to be 5.5 to 6.0. Through the Ti-Mg-B composite effect, it promotes the formation of a large amount of intragranular ferrite and refines it into acicular ferrite with good strength and plasticity, inhibits the formation of pearlite with poor plasticity, and ensures that the steel plate has good ductility during rolling. At the same time, it utilizes the precipitation strengthening, grain refinement strengthening and dispersion strengthening effects of Ti-Mg-B 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 is detrimental to the plasticity of steel. Therefore, the TiB2 content in this invention is controlled at 0.05% to 0.10%.

[0023] 14) This invention controls the B / TiB2 ratio to be 0.01–0.02. B has a significant impact on the growth morphology and distribution of TiB2 particles in steel. With the relative change of B content, the particle size of TiB2 is distributed along grain boundaries or within grains in the form of long rods or granules. This invention, by controlling the addition ratio of the two, limits the TiB2 particle size to ≤5µm and makes it distributed in granular form at grain boundaries, thereby improving the elastic deformation limit of grain boundaries.

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

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

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

[0027] 1) Use converter slag-blocking for steel tapping, and control the slag layer thickness to 60-90mm to improve the recovery rate of alloying elements and reduce the content of inclusions; control the holding time of VD refining to 15-25min to reduce the gas content, and require [H]≤2ppm, [O]<20ppm, [N]<50ppm.

[0028] 2) TiB2 adopts a KBF4-K2TiF6 mixed salt powder system, with a Ti / B atomic ratio of 1:2 to 2.5. The mixed salt powder is wrapped in a thin steel strip to form a cored wire, which is fed into the ladle through a wire feeder during the ladle refining process. The pre-ladle settling time is controlled at 20 to 30 minutes to ensure uniform steel composition. The target superheat of the tundish is controlled at 20 to 25°C to ensure billet quality and production efficiency. The entire casting process is protected and electromagnetic stirring in the secondary cooling zone is used to refine the grains, with a current intensity of 400 to 600 A. To eliminate defects such as billet segregation, porosity, and shrinkage cavities, a light reduction is applied at the end of solidification. The reduction range is at the central solid fraction of 0.4 to 0.9, with a reduction of 6.8 to 7.4 mm and a reduction rate of 0.9 to 1.2 mm / min. The continuous casting process adopts a constant casting speed of 0.9 to 1.0 m / min.

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

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

[0031] 5) After the steel plate comes out of the water, it undergoes three rounds of hot straightening at a temperature of 540-560℃ and a straightening speed of 14-16m / min to fully release the residual stress of the steel plate and prevent deformation after cooling.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] 1) By reducing the C content and adding Ti, Mg, and B elements, the Ti-Mg-B composite effect promotes the formation and refinement of intragranular ferrite into acicular ferrite with good strength and plasticity, while inhibiting the formation of pearlite with poor plasticity. This ensures that the steel plate has good ductility during rolling, ensuring the smooth rolling of thin-gauge ultra-wide steel plates, while reducing crack sensitivity and the risk of quenching cracking. At the same time, the precipitation strengthening, grain refinement strengthening, 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 strength. Meanwhile, the growth morphology and distribution of TiB2 are controlled by B to withstand the load during the elastic deformation of the steel, which significantly reduces the effective stress acting on the steel matrix, thereby improving the elastic modulus of the steel.

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

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

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the specific implementation methods of this invention will be further described below in conjunction with the embodiments. The following embodiments are used to specifically illustrate the content of this invention. These embodiments are only general descriptions of the content of this invention and do not limit the content of this invention.

[0037] The specific implementation method of a high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity saw blade steel and its manufacturing method is as follows:

[0038] The alloy element ratios in Table 1 are used for converter smelting, VD refining, continuous casting, slab heating, controlled rolling, and controlled cooling. The main process parameters for 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 embodiment

[0040]

[0041] Table 2 Steelmaking process parameters for each embodiment

[0042]

[0043] Table 3 Steelmaking process parameters for each embodiment

[0044]

[0045] Table 4 Steelmaking process parameters for each embodiment

[0046]

[0047] Table 5 Steel Process Parameters for Each Example

[0048]

[0049] Table 6 Steelmaking process parameters for each embodiment

[0050]

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

[0052] Table 7 Mechanical properties of each embodiment

[0053]

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

[0055] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within 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 as follows: 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, with the balance being Fe and unavoidable impurities; A method for manufacturing high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity saw blade steel, specifically including: 1) Use converter slag-blocking tapping, control the slag layer thickness to 60-90mm, control the VD refining pressure holding time to 15-25min, and require [H]≤2ppm, [O]<20ppm, [N]<50ppm; 2) The quenching time before the ladle is placed on the machine is controlled at 20-30 minutes. The target superheat of the tundish is controlled at 20-25℃. The entire process is protected during casting and electromagnetic stirring is carried out in the secondary cooling zone with a current intensity of 400-600A. Light reduction is carried out at the end of solidification, with the reduction interval at the position of 0.4-0.9 in the center of the solid fraction, the reduction amount is 6.8-7.4mm, and the reduction rate is 0.9-1.2mm / min. The continuous casting process adopts a constant casting speed of 0.9-1.0m / min. 3) The temperature of the second heating section of the slab is 1120~1210℃, the temperature of the soaking section is 1150~1200℃, and the total time in the furnace is 0.8~1.2min / mm; 4) The initial 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 final rolling temperature is 840~860℃, the ACC cooling temperature is 730~760℃, the cooling rate is 10~12℃ / s, and the reddening temperature is 620~650℃. 5) After the steel plate comes out of the water, it undergoes three rounds of hot straightening at a temperature of 540-560℃ and a straightening speed of 14-16m / min.

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 5-12mm, a maximum width of 4800mm, and an unevenness of ≤4mm / 2m.

3. The high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity saw blade steel according to claim 1, characterized in that, Saw blade steel has the following properties: stiffness ≥ 8754 N / m, yield strength ≥ 1082 MPa, tensile strength ≥ 1418 MPa, elongation ≥ 23%, and room temperature impact energy A. KV ≥157J, hardness 42~46HRC, 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, TiB2 particles have a diameter of ≤5µm and are distributed in granular form at the grain boundaries.

5. A method for manufacturing high-rigidity, environmentally friendly, pre-hardened, low-crack-sensitivity saw blade steel as described in any one of claims 1-4, characterized in that, Specific methods include: 1) Use converter slag-blocking tapping, control the slag layer thickness to 60-90mm, control the VD refining pressure holding time to 15-25min, and require [H]≤2ppm, [O]<20ppm, [N]<50ppm; 2) The quenching time before the ladle is placed on the machine is controlled at 20-30 minutes. The target superheat of the tundish is controlled at 20-25℃. The entire process is protected during casting and electromagnetic stirring is carried out in the secondary cooling zone with a current intensity of 400-600A. Light reduction is carried out at the end of solidification, with the reduction interval at the position of 0.4-0.9 in the center of the solid fraction, the reduction amount is 6.8-7.4mm, and the reduction rate is 0.9-1.2mm / min. The continuous casting process adopts a constant casting speed of 0.9-1.0m / min. 3) The temperature of the second heating section of the slab is 1120~1210℃, the temperature of the soaking section is 1150~1200℃, and the total time in the furnace is 0.8~1.2min / mm; 4) The initial 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 final rolling temperature is 840~860℃, the ACC cooling temperature is 730~760℃, the cooling rate is 10~12℃ / s, and the reddening temperature is 620~650℃. 5) After the steel plate comes out of the water, it undergoes three rounds of hot straightening at a temperature of 540-560℃ and a straightening speed of 14-16m / 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 sheet is 70%–75%, and the volume fraction of pearlite is 25%–30%.

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