45 steel plate for punch forming of high-strength chain wheel and preparation method of 45 steel plate

Abstract

The invention relates to a 45 steel plate for punch forming of a high-strength chain wheel and a preparation method of the 45 steel plate. The steel comprises the following chemical components: 0.42%-0.48% of C, 0.20%-0.30% of Si, 0.55%-0.65% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, 0.015%-0.025% of V, 0.15%-0.20% of Cr and the balance of Fe and impurities. The metallographic structure of the finished steel plate is a ferrite and pearlite mixed structure, and the volume fraction ratio of ferrite to pearlite is (45%-55%): (55%-45%); and the grain size grade is 8.0-10.0 grade. On the basis of traditional 45 steel components, a small amount of V and Cr elements are added, a specific controlled rolling and controlled cooling process is combined, under the condition that follow-up heat treatment is not carried out, hot-rolled strip steel which is small in grain size, uniform in structure and excellent in obdurability matching is directly obtained, and the finished steel product is particularly suitable for punch forming of chain wheels.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of special steel, and particularly relates to a 45 steel plate for high-strength sprocket stamping forming and a preparation method thereof. BACKGROUND

[0002] 45 steel is a common medium carbon steel, and is widely used for manufacturing mechanical parts, including sprocket, due to good comprehensive mechanical properties and low cost. Traditional sprocket manufacturing processes mostly adopt round steel cutting processing, and the material utilization rate is low and the production cost is high. The sprocket produced by using the strip steel stamping forming process has the advantages of high efficiency, low cost and high material utilization rate, and is the development trend of the industry in the future.

[0003] However, the production of the sprocket with a complex tooth shape by using the stamping forming method puts high requirements on the strength, toughness and uniformity of the material. For the above requirements, the conventional 45 steel has the following problems: (1) In the traditional hot-rolled or normalized state, the strength of the 45 steel is sufficient and the toughness is insufficient, and micro-cracks are easily generated at the stress concentration during stamping; (2) The uniformity of the steel strip is poor, the grain size fluctuates greatly, and there is a mixed crystal phenomenon, which leads to inconsistent stamping deformation, poor product size precision and high scrap rate; (3) The proportion of ferrite and pearlite in the steel material is improper, if the pearlite is too much, the material is too brittle, which will cause stamping tearing, tooth breaking and the like; and if the ferrite is too much, the material strength is insufficient, and cannot meet the use conditions of the sprocket.

[0004] In order to solve the above problems, the industry usually adopts the method of adding a heat treatment process before stamping, but the production cost and energy consumption are increased accordingly. Therefore, how to make the hot-rolled steel material have high strength, high toughness and uniform structure on the basis of the existing 45 steel composition by low-cost micro-alloying and optimization of rolling process to meet the needs of high-efficiency stamping forming of the sprocket has become a problem to be solved at the present stage. SUMMARY

[0005] The present application provides a 45 steel plate for high-strength sprocket stamping forming and a preparation method thereof. On the basis of the traditional 45 steel composition, a small amount of V and Cr elements are added, and a specific controlled rolling and controlled cooling process is combined, so that a hot-rolled strip steel with fine grains, uniform structure and excellent strength and toughness matching is directly obtained without subsequent heat treatment, and the finished steel material is particularly suitable for stamping forming of the sprocket.

[0006] In order to achieve the above purpose, the present application adopts the following technical scheme: The high-strength chain wheel stamping forming 45 steel plate provided by the application has the following chemical components in percentage by weight: C: 0.42% to 0.48%, Si: 0.20% to 0.30%, Mn: 0.55% to 0.65%, P: ≤0.015%, S: ≤0.010%, V: 0.015% to 0.025%, Cr: 0.15% to 0.20%, and the rest is Fe and inevitable impurities; the metallographic structure of the finished steel plate is a mixed structure of ferrite and pearlite, and the volume fraction ratio of the ferrite and the pearlite is 45% to 55%: 55% to 45%; the grain size level is 8.0 to 10.0.

[0007] The yield strength of the finished steel plate is ≥400 MPa, the tensile strength is ≥650 MPa, and the elongation is ≥20%.

[0008] The thickness of the finished steel plate is 4.0 to 12.0 mm, and the width is 580 to 760 mm.

[0009] A preparation method of the high-strength chain wheel stamping forming 45 steel plate comprises the following processes: 1) smelting: after pre-desulfurization of the molten iron, the molten iron is smelted by a converter, and then refined by an LF furnace, and the LF refining is performed to remove sulfur, finely adjust alloy components, and purify the molten iron; 2) continuous casting: the superheat degree of the molten iron is controlled to be 10 to 25 ℃, the drawing speed is controlled to be 1.50 to 1.80 m / min, the specific water consumption of the secondary cooling water is 0.8 to 1.0 L / kg, and the thickness of the continuous casting slab is 180 to 220 mm and the width is 500 to 750 mm; 3) heating: the continuous casting slab is directly heated in the furnace by using a hot delivery and direct loading mode, the heating temperature is 1200 to 1250 ℃, and the soaking time is not less than 120 min; 4) controlled rolling: coarse rolling: the coarse rolling inlet temperature is 1080 to 1120 ℃, large reduction is adopted for rolling, the first pass reduction of the coarse rolling is ≥25%, and the total reduction is ≥85%, and the coarse rolling outlet temperature is controlled to be 980 to 1020 ℃; finish rolling: the finish rolling opening rolling temperature is 880 to 920 ℃, and the finish rolling is performed in the non-recrystallization zone by using multi-pass rolling, and the finish rolling final rolling temperature is controlled to be 850 to 880 ℃; 5) controlled cooling: the steel plate is immediately subjected to laminar cooling after rolling, and the front concentrated cooling mode is adopted; the initial cooling temperature is controlled to be 800 to 830 ℃, and the cooling speed is 15 to 25 ℃ / s; 6) coiling: the coiling temperature is 670 to 700 ℃.

[0010] In the continuous casting process, the taper of the crystallizer is 1.05% to 1.15%, the vibration parameters are: amplitude A=2.82+3.2v, frequency f=120+22v, the drawing speed v>1.0m / min, and the deflection rate a is set to 9% to 11%.

[0011] In the heating process, the continuous casting slab is sent into the walking beam furnace for heating.

[0012] Compared with the prior art, the beneficial effects of the present application are: The present application forms a complete preparation method of 45 steel for high-strength sprocket through the synergistic effect of chemical composition design and controlled cooling and rolling process, and the innovation points are as follows: 1) Chemical composition design: based on the traditional 45 steel, trace amounts of V (0.015% to 0.025%) and Cr (0.15% to 0.20%) are added. Among them, V element can form fine V(C, N) precipitated phase, produce strong precipitation strengthening and fine grain strengthening effect, and significantly improve the strength. Cr element can improve the hardenability of the steel, refine the structure, and solid solution strengthen the ferrite, while improving the wear resistance of the steel. The combined addition of the two can significantly improve the strength of the steel under the premise of low cost, while maintaining good toughness.

[0013] 2) Uniformization of structure: in the rough rolling stage, large reduction is adopted (total reduction rate is not less than 85%), which greatly fragments the original coarse grain structure and eliminates composition segregation, obtaining uniform and fine recrystallized austenite structure, which provides a fundamental guarantee for realizing the uniformity of the final product structure.

[0014] 3) Fine structure and proportion control: by accurately controlling the finish rolling temperature and the start cooling (initial cooling) temperature (800 to 830℃) and cooling speed (15 to 25℃ / s) of laminar cooling, the phase change process is accurately controlled; the appropriate start cooling temperature ensures that the phase change occurs in the best temperature range, and finally a fine grain structure with a grain size of 8.0 to 10.0 is obtained. At the same time, the proportion of ferrite and pearlite is controlled at the best proportion of approximately 1:1, so that the material has high strength and excellent plasticity, the yield strength is more than 400MPa, the tensile strength is more than 650MPa, and the elongation is not less than 20%, which fully meets the stringent requirements of sprocket stamping on material plasticity and toughness.

[0015] 4) The problems of tearing and tooth breaking in the stamping process caused by insufficient toughness and plasticity of raw materials, grain size difference, and non-uniform structure are effectively solved, the raw material annealing process is saved, the energy consumption is reduced, the production and processing cost is greatly reduced, and significant economic benefits are obtained. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1This is a flowchart of the production process control for the 45 steel plate used in the high-strength sprocket stamping of the present invention.

[0017] Figure 2 This is a metallographic photograph of the 45 steel plate used for stamping high-strength sprockets according to the present invention. Detailed Implementation

[0018] The present invention discloses a high-strength 45 steel plate for stamping sprockets. The chemical composition of the steel, by weight percentage, is: C: 0.42%–0.48%, Si: 0.20%–0.30%, Mn: 0.55%–0.65%, P≤0.015%, S≤0.010%, V: 0.015%–0.025%, Cr: 0.15%–0.20%, with the remainder being Fe and unavoidable impurities.

[0019] The roles of the various chemical components in steel are as follows: C element: can improve the strength and hardness of steel plates and promote the formation of high-hardness martensite structure in steel plates during heat treatment (such as quenching).

[0020] Mn element: can improve the strength and hardenability of steel plates, improve the hot working performance of steel, and make the quenched and tempered structure of steel more uniform and refined.

[0021] Si element: Improves the strength of steel while enhancing hardenability and tempering resistance.

[0022] V element: can form stable and refractory carbides, allowing the steel plate to maintain a fine-grained structure at high temperatures and reducing the steel's overheating sensitivity.

[0023] Cr element: can improve the hardenability of steel and has a secondary hardening effect, thereby improving the hardness and wear resistance of steel plates.

[0024] S and P elements: harmful elements in steel, which have an adverse effect on the plasticity and toughness of steel. The lower the content, the better.

[0025] like Figure 1 As shown, the method for preparing a high-strength 45 steel plate for stamping sprockets according to the present invention includes the following process: 1) Smelting: After pre-desulfurization, the molten iron is smelted in a converter and then refined in an LF furnace. The LF refining process completes desulfurization, fine-tuning of alloy composition and purification of molten steel.

[0026] 2) Continuous casting: The superheat of molten steel is controlled at 10-25℃, and the casting speed is controlled at 1.50-1.80 m / min; the secondary cooling water ratio is 0.8-1.0 L / kg; the crystallizer taper is 1.05%-1.15%, and the vibration parameters are: amplitude A=2.82+3.2v, frequency f=120+22v, casting speed v>1.0 m / min, and skewness a is set at 9%-11%. The thickness of the continuously cast slab is 180-220 mm, and the width is 500-750 mm.

[0027] 3) Heating: The continuously cast slab is fed into a walking beam furnace for heating using a hot-feeding direct loading mode. The heating temperature is 1200-1250℃, and the heat soaking time is not less than 120 minutes. The purpose is to allow the V and Cr elements added to the steel to be fully dissolved into the austenite and to reserve sufficient deformation energy for subsequent rolling.

[0028] 4) Controlled rolling: Rough rolling: The entry temperature of the rough rolling mill is 1080–1120℃, using a large reduction rolling process. The reduction rate of the first pass in the rough rolling mill is ≥25%, and the total reduction rate is ≥85%. Through intense plastic deformation, the coarse original cast structure is fully broken down, and austenite recrystallization is repeatedly induced to refine the austenite grains, laying the foundation for the refinement of the final microstructure. The exit temperature of the rough rolling mill is controlled at 980–1020℃.

[0029] Finishing rolling: The initial rolling temperature of finishing rolling is 880-920℃. Multiple rolling passes are performed in the non-recrystallization zone to flatten and elongate the austenite grains, generate a large number of deformation bands in the grains, and increase the phase deformation nucleation points. The final rolling temperature of finishing rolling is controlled at 850-880℃.

[0030] 7) Controlled cooling: The rolled steel plate is immediately subjected to laminar flow cooling, and a centralized cooling method is adopted in the front section; the initial cooling temperature is controlled at 800-830℃, and the cooling rate is 15-25℃ / s; controlled cooling suppresses the precipitation of coarse ferrite and promotes a large number of nucleations at the grain boundaries and intragranular defects of deformed austenite, forming fine ferrite grains.

[0031] 8) Coiling: The coiling temperature is 670-700℃. At this temperature, the spacing between pearlite lamellars is moderate, which can ensure the strength of the steel plate while giving it good plasticity.

[0032] The thickness of the finished steel plate is 4.0 to 12.0 mm, and the width is 580 to 760 mm.

[0033] like Figure 2 As shown, the metallographic structure of the finished steel plate is a mixed structure of ferrite and pearlite, with a volume fraction ratio of ferrite to pearlite of 45% to 55%: 55% to 45%; the grain size is 8.0 to 10.0.

[0034] The yield strength of the finished steel plate is ≥400 MPa, the tensile strength is ≥650 MPa, and the elongation is ≥20%.

[0035] In order to more intuitively embody the present application, the embodiments of the present application are further described in combination with examples. The following examples are only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any skilled person in the art can obtain the technical solutions within the technical range disclosed by the present application, including simple changes or equivalent replacements, which are within the protection scope of the present application.

[0036] Example 1 In the present example, the chemical composition and main process parameters are intermediate values, which ensure balanced performance, make the production process easy to control, reduce the scrap rate, and are suitable for large-scale production of sprockets.

[0037] 1. Chemical composition The chemical composition in the steel is C: 0.45%, Si: 0.25%, Mn: 0.60%, P: 0.010%, S: 0.005%, V: 0.020%, Cr: 0.18%, and the rest is Fe and unavoidable impurities, in terms of weight percentage.

[0038] 2. Preparation process (1) Smelting: After pre-desulfurization of molten iron, the molten iron is smelted in a converter and then enters an LF furnace for refining, to complete desulfurization, fine adjustment of alloy composition, and purification of molten steel.

[0039] (2) Continuous casting: The thickness of the continuous casting billet is 180 mm, and the width is 600 mm. The superheat of the molten steel is controlled at 20℃, the withdrawal speed is controlled at 1.65 m / min, and the specific water quantity of the secondary cooling water is 0.89 L / kg.

[0040] (3) Heating: The continuous casting slab is sent to a walking beam heating furnace in a hot charging mode, heated to 1225℃, and kept at temperature for 120 min, so that the V and Cr elements are fully solid-solved in the austenite.

[0041] (4) Controlled rolling: Coarse rolling: The coarse rolling inlet temperature is 1106℃, the first pass reduction is 25%, the total reduction is 85%, and the coarse rolling outlet temperature is 980℃.

[0042] Finish rolling: The finish rolling opening temperature is 880℃, and the finish rolling final rolling temperature is 850℃.

[0043] (5) Controlled cooling: The laminar cooling is adopted, the cooling speed is 15℃ / s, and the cooling start temperature is 800℃.

[0044] (6) Coiling: The coiling temperature is 670℃.

[0045] The finished steel plate has a thickness of 7.0 mm and a width of 740 mm.

[0046] 3. Performance test results of finished product The finished steel plate has a microstructure of ferrite and pearlite uniformly distributed in the steel, with a volume fraction ratio of 48%:52%. The grain size is 9.0 grade.

[0047] The finished steel plate has a mechanical property of yield strength 435 MPa, tensile strength 672 MPa, and elongation 22%.

[0048] Conclusion: The performance of the finished steel plate fully meets the requirements of chain wheel stamping forming.

[0049]

Example 2

[0050] 1. Chemical composition The chemical composition of the steel is C: 0.42%, Si: 0.20%, Mn: 0.55%, P: 0.015%, S: 0.010%, V: 0.015%, Cr: 0.15%, and the rest is Fe and unavoidable impurities, by weight percentage.

[0051] 2. Preparation process (1) Smelting: After pre-desulfurization of molten iron, the molten iron is smelted in a converter and then refined in an LF furnace to complete desulfurization, alloy composition fine adjustment, and molten steel purification.

[0052] (2) Continuous casting: The thickness of the continuous casting billet is 180 mm, and the width is 500 mm. The superheat of the molten steel is controlled at 16℃, the withdrawal speed is controlled at 1.75 m / min, and the specific water consumption of the secondary cooling water is 0.75 L / kg.

[0053] (3) Heating: The continuous casting slab is sent to the walking beam heating furnace in a hot charging mode, heated to 1200℃, and kept at temperature for 120 min to make V and Cr elements fully solid-solute in austenite.

[0054] (4) Controlled rolling: Coarse rolling: The coarse rolling inlet temperature is 1095℃, the first pass reduction is 25%, the total reduction is 85%, and the coarse rolling outlet temperature is 980℃.

[0055] Finish rolling: The finish rolling opening temperature is 900℃, and the finish rolling final rolling temperature is 870℃.

[0056] (5) Controlled cooling: The laminar cooling is adopted, the cooling speed is 20℃ / s, and the cooling start temperature is 815℃.

[0057] (6) Winding: Winding temperature 680℃.

[0058] The finished steel plate is 7.9mm thick and 725mm wide.

[0059] 3. Finished product performance test results Metallographic structure of finished steel plate: Ferrite and pearlite are uniformly distributed in the steel, with a volume fraction ratio of ferrite to pearlite of 45%:55%. Grain size is grade 9.0.

[0060] Mechanical properties of finished steel plates: yield strength 413MPa, tensile strength 661MPa, elongation 21%.

[0061] Conclusion: Finished steel plates are suitable for stamping sprockets where high toughness is required.

[0062]

Example 3

[0063] 1. Chemical composition By weight percentage, the chemical composition of the steel is C: 0.48%, Si: 0.30%, Mn: 0.65%, P: 0.010%, S: 0.005%, V: 0.025%, Cr: 0.20%, with the remainder being Fe and unavoidable impurities.

[0064] 2. Preparation process (1) Smelting: After pre-desulfurization, the molten iron is smelted in a converter and then refined in an LF furnace to complete desulfurization, fine-tuning of alloy composition and purification of molten steel.

[0065] (2) Continuous casting: The thickness of the continuous casting billet is 180 mm and the width is 705 mm. The superheat of the molten steel is controlled at 23℃, the casting speed is controlled at 1.50 m / min, and the secondary cooling water ratio is 0.89 L / kg.

[0066] (3) Heating: The continuous casting slab is fed into the walking beam furnace in a hot delivery mode and heated to 1250℃. It is then kept at the temperature for 120 minutes to allow V and Cr elements to be fully dissolved in the austenite.

[0067] (4) Controlled rolling: Roughing: The inlet temperature of the roughing mill is 1115℃, the first pass reduction rate is 35%, the total reduction rate is 90%, and the outlet temperature of the roughing mill is 1020℃.

[0068] Finishing rolling: The initial rolling temperature is 920℃, and the final rolling temperature is 880℃.

[0069] (5) Controlled cooling: Laminar flow cooling is adopted, the cooling rate is 25℃ / s, and the start-up cooling temperature is 830℃.

[0070] (6) Winding: Winding temperature 700℃.

[0071] The finished steel plate is 8.5mm thick and 635mm wide.

[0072] 3. Finished product performance test results Metallographic structure of finished steel plate: Ferrite and pearlite are uniformly distributed in the steel, with a volume fraction ratio of ferrite to pearlite of 53%:47%. Grain size is grade 10.0.

[0073] Mechanical properties of finished steel plates: yield strength 442MPa, tensile strength 698MPa, elongation 21%.

[0074] Conclusion: Finished steel plates are suitable for stamping high-strength, high-wear-resistant sprockets.

[0075] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A 45 steel plate for high-strength sprocket press forming, characterized by, The chemical composition in the steel is C: 0.42%~0.48%, Si: 0.20%~0.30%, Mn: 0.55%~0.65%, P≤0.015%, S≤0.010%, V: 0.015%~0.025%, Cr: 0.15%~0.20%, the rest is Fe and inevitable impurities; the metallographic structure of the finished steel plate is ferrite+pearlite mixed structure, the volume fraction ratio of ferrite and pearlite is 45%~55%: 55%~45%; the grain size level is 8.0~10.0 level.

2. The 45 steel plate for press forming of a high-strength chain wheel according to claim 1, characterized by The yield strength of the finished steel plate is ≥400 MPa, the tensile strength is ≥650 MPa, and the elongation is ≥20%.

3. The 45 steel plate for press forming of a high-strength chain wheel according to claim 1, characterized by The thickness of the finished steel plate is 4.0~12.0 mm, and the width is 580~760 mm.

4. A method of producing a 45 steel plate for press forming a high-strength chain wheel according to any one of claims 1 to 3, characterized by, It comprises the following processes: 1) smelting: after pre-desulfurization of molten iron, converter smelting is adopted, then LF refining is carried out, and desulfurization, alloy component fine adjustment and molten steel purification are completed after LF refining; 2) continuous casting: the superheat degree of molten steel is controlled at 10~25 ℃, the drawing speed is controlled at 1.50~1.80 m / min; the specific water quantity of the secondary cooling water is 0.8~1.0 L / kg; the thickness of the continuous casting slab is 180~220 mm, and the width is 500~750 mm; 3) heating: the continuous casting slab is directly heated in the furnace in the hot delivery and direct loading mode, the heating temperature is 1200~1250 ℃, and the soaking time is not less than 120 min; 4) controlled rolling: coarse rolling: the coarse rolling inlet temperature is 1080~1120 ℃, large reduction is adopted for rolling, the first pass reduction of coarse rolling is ≥25%, and the total reduction is ≥85%; the coarse rolling outlet temperature is controlled at 980~1020 ℃; finish rolling: the finish rolling opening rolling temperature is 880~920 ℃, multi-pass rolling is carried out in the unrecrystallization zone, and the finish rolling final rolling temperature is controlled at 850~880 ℃; 5) controlled cooling: the steel plate is immediately subjected to laminar cooling after rolling, and the front concentrated cooling mode is adopted; the initial cooling temperature is controlled at 800~830 ℃, and the cooling speed is 15~25 ℃ / s; 6) coiling: the coiling temperature is 670~700 ℃.

5. The method of producing a 45 steel plate for high-strength sprocket press forming according to claim 4, characterized in that, In the continuous casting process, the mold taper is 1.05%~1.15%, the vibration parameters are: amplitude A=2.82+3.2v, frequency f=120+22v, the drawing speed v>1.0 m / min, and the skew rate a is set to 9%~11%.

6. The method of producing a 45 steel plate for high-strength sprocket press forming according to claim 4, characterized in that, In the heating process, the continuous casting slab is sent into the walking beam furnace for heating.

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