Cold rolling processing technology of medium carbon alloy structural steel for diaphragm spring

Abstract

The invention relates to a cold rolling processing technology of medium carbon alloy structural steel for a diaphragm spring, which comprises the following steps: selecting a hot-rolled pickled steel coil with the mark of 51CrV4, and carrying out stress relief annealing on the hot-rolled pickled steel coil to obtain a stress-relieved annealed steel coil; the annealed steel coil is subjected to longitudinal shearing and slitting, and a longitudinal shearing narrow strip steel coil is obtained; transferring the longitudinally-sheared narrow strip steel coil to a pickling production line through a crane device, and pickling the longitudinally-sheared narrow strip steel coil to prepare a pickling coil plate with no oxide scale on the surface and a passive film on the surface; carrying out softening annealing on the acid-pickled coiled plate to prepare a softened and annealed steel coil; and repeatedly rolling the softened and annealed steel coil to obtain a rolled steel coil. The method has the beneficial effects that the hot-rolled and pickled steel coil raw material is adopted for large-coil softening annealing, the internal stress of the hot-rolled coil is eliminated through annealing, edge notches are not affected by shearing stress during longitudinal shearing and splitting, and the edge cracks are avoided in the rolling and bending process.

Description

Technical Field

[0001] The invention relates to the technical field of strip steel production and processing, in particular to a cold rolling processing technology of medium carbon alloy structural steel for diaphragm springs. Background Art

[0002] Diaphragm spring is a special form of spring, which is widely used in various mechanical and industrial equipment, especially in the fields of automobile clutch, etc.

[0003] Cold-rolled steel is the main type of steel used in the manufacture of automotive clutch diaphragm springs. The manufacturing process of diaphragm springs is relatively complex, and has high requirements for raw material quality and dimensional accuracy. As the market gradually increases quality requirements, the metallographic structure, mechanical properties and surface state requirements of the cold-rolled raw materials are also getting higher and higher. Therefore, the cold rolling process must keep pace with changes in market demand and be updated and optimized to manufacture high-quality cold-rolled products that better meet market requirements. Summary of the invention

[0004] The purpose of the present invention is to provide a cold rolling process for medium carbon alloy structural steel for diaphragm springs to solve the above problems existing in the prior art.

[0005] The technical solution of the present invention to solve the above technical problems is as follows:

[0006] A cold rolling process for medium carbon alloy structural steel for diaphragm springs comprises the following steps:

[0007] Step S01, selecting a hot-rolled pickled steel coil with a grade of 51CrV4, and performing stress relief annealing on the hot-rolled pickled steel coil to obtain a stress relief annealed steel coil;

[0008] Step S02, slitting the annealed steel coil into strips to obtain slitting narrow strip steel coils;

[0009] Step S03, transferring the slit narrow strip steel coil to a pickling production line through a crane device, pickling the slit narrow strip steel coil to obtain a pickled coil with no iron oxide scale on the surface and a passivation film formed on the surface;

[0010] Step S04, performing soft annealing on the pickled coil to obtain a soft annealed steel coil;

[0011] Step S05, repeatedly rolling the softened annealed steel coil to obtain a rolled steel coil;

[0012] Step S06, performing isothermal spheroidizing annealing on the rolled steel coil to obtain a spheroidizing annealed steel coil;

[0013] Step S07, performing finish rolling on the spheroidizing annealed steel coil to obtain a finish rolled steel coil;

[0014] Step S08, performing precision longitudinal shearing and slitting on the finish-rolled steel coil to obtain a finished slitting cold-rolled steel coil;

[0015] Step S09: packing the stripped cold-rolled steel coils.

[0016] The beneficial effects of the present invention are as follows: hot-rolled pickled steel coil raw materials are used for large coil softening annealing, and the internal stress of the hot-rolled coil is eliminated through annealing, the edge cut is not affected by the shear stress during longitudinal shearing and stripping, and cracks are not generated at the edge during the coiling and bending process; the surface oxide scale and oxygen molecules on the surface of the matrix are removed through the pickling process, so that they lose the opportunity to combine with oxygen molecules during the subsequent full hydrogen furnace spheroidizing annealing, and the decarburization tendency during the subsequent high-temperature annealing is significantly improved; through the subsequent isothermal spheroidizing annealing, the structure, mechanical properties and hardness of the head, middle and tail of the steel coil are uniformized, and the internal stress distribution of the steel coil during finish rolling is relatively uniform, so as to obtain a good rolled plate shape, thereby significantly improving the quality of the produced products.

[0017] Based on the above technical solution, the present invention can also be improved as follows.

[0018] Further, the step S01 specifically includes the following steps:

[0019] Step S011, during the soft annealing, the annealing furnace is heated to 200° C. at full speed;

[0020] Step S012, setting the time to 4h and heating to 420°C;

[0021] Step S013, set the temperature to 500°C for 6 hours and keep it at this temperature for 2 hours;

[0022] Step S014, set the temperature to 530°C for 1 hour and keep it at this temperature for 14 hours;

[0023] Step S015, after the heat preservation is completed, the annealing furnace is hooded and air-cooled to reduce the temperature of the annealing furnace to 320°C;

[0024] Step S016, after the temperature of the annealing furnace drops to 320°C, the temperature of the annealing furnace is lowered from 320°C to 120°C by water cooling outside the hood, and the steel coil is taken out of the furnace to obtain a stress-relieved annealed steel coil.

[0025] Furthermore, the pickling production line in step S03 is provided with two pickling tanks, a passivation tank and a neutralization tank, the pickling concentrations of the two pickling tanks are set to 18% to 22% and 15% to 18% respectively, the acid position in the two pickling tanks is 380mm to 420mm, and the acid solution temperature is 45°C to 60°C, the pH value in the neutralization tank is 11 to 13, the pH value in the passivation tank is 7 to 8, the temperature value of the passivation tank is 40°C to 50°C, and the cleaning speed of the pickling production line is 5m / min to 15m / min.

[0026] Furthermore, it is characterized in that the step S04 specifically comprises the following steps:

[0027] Step S041, firstly, the annealing furnace is heated to 200° C. at full speed;

[0028] Step S042, setting the time to 4h and heating to 420°C;

[0029] Step S043, set the temperature to 690°C for 6 hours and keep it at this temperature for 2 hours;

[0030] Step S044, set the temperature to 720°C for 1 hour and keep it at that temperature for 12 hours;

[0031] Step S045, after the heat preservation is completed, the furnace is cooled to 650°C;

[0032] Step S046, the annealing furnace is hooded and air-cooled, and the temperature is reduced to 320° C.;

[0033] Step S047, after the temperature of the annealing furnace drops to 320°C, the inner cover is cooled by spraying water to reduce the temperature of the annealing furnace to 120°C before being taken out of the furnace to obtain a softened annealed steel coil.

[0034] Further, the step S06 specifically includes the following steps:

[0035] Step S061, firstly, the annealing furnace is heated to 200° C. at full speed;

[0036] Step S062, setting the time to 4h and heating to 420°C;

[0037] Step S063, set the temperature to 720°C for 6 hours and keep it at this temperature for 2 hours;

[0038] Step S064, set the temperature to 750°C for 1 hour and keep it at this temperature for 12 hours;

[0039] Step S065, cooling to 680°C with the furnace and keeping the temperature for 8 hours;

[0040] Step S066, after the heat preservation is completed, the furnace is cooled to 650°C; the annealing furnace is hooded and air-cooled, and the temperature drops to 320°C;

[0041] Step S067, after the temperature of the annealing furnace drops to 320°C, the inner cover is cooled by spraying water to reduce the temperature of the annealing furnace to 80°C before being taken out of the furnace to obtain a spheroidized annealed steel coil.

[0042] Furthermore, in the step S05, when rolling the softened annealed steel coil, a rolling work roll with a roll curvature of 0.05 mm is selected to perform reciprocating rolling multiple times to obtain a rolled steel coil.

[0043] Furthermore, the step S01 further includes: detecting the thickness and width of the selected hot-rolled pickled steel coils, and performing stress relief annealing on the hot-rolled pickled steel coils that meet the standards.

[0044] Furthermore, the step S08 also includes: before the precision longitudinal shearing and slitting, the metallographic spheroidizing structure, surface decarburization, grain boundary oxidation and mechanical properties of the finished steel coil are tested by a metallographic microscope, a universal testing machine and a hardness tester, and the precision longitudinal shearing and slitting are performed on the finished steel coil with qualified indicators. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a processing flow chart of the present invention;

[0046] Figure 2 It is a stress relief annealing curve diagram in the processing technology of the present invention;

[0047] Figure 3 It is a softening annealing curve diagram in the processing technology of the present invention;

[0048] Figure 4 It is a spheroidizing annealing curve diagram in the processing technology of the present invention. DETAILED DESCRIPTION

[0049] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0050] Combination Figures 1 to 4 As shown, in embodiment 1 of the present invention, a cold rolling process of a medium carbon alloy structural steel for a diaphragm spring is characterized by comprising the following steps:

[0051] Step S01, selecting a hot-rolled pickled steel coil with a grade of 51CrV4, the specification of the hot-rolled pickled steel coil is 7.9*1280mm, transferring the hot-rolled pickled steel coil to a bell-type annealing furnace through a crane device, and performing stress relief annealing on the hot-rolled pickled steel coil to obtain an annealed steel coil with internal stress removed;

[0052] Step S02, longitudinally cutting the annealed steel coil into strips to obtain longitudinally cut narrow strip steel coils;

[0053] Step S03, transferring the slit narrow strip steel coil to the pickling production line through a crane device, pickling the slit narrow strip steel coil to obtain a pickled coil with no iron oxide scale on the surface and a passivation film formed on the surface;

[0054] Step S04, performing soft annealing on the pickled coil to obtain a soft annealed steel coil;

[0055] Step S05: transfer the softened annealed steel coil to the AGC reversible rolling mill production line through a crane device, and repeatedly roll the softened annealed steel coil to obtain a rolled steel coil; and roll the thickness of the steel coil from 7.9 mm to 5.3 mm.

[0056] Step S06, transferring the rolled steel coil to a bell-type annealing furnace through a crane device, and performing isothermal spheroidizing annealing on the rolled steel coil to obtain a spheroidizing annealed steel coil;

[0057] Step S07, the spheroidizing annealing steel coil is transferred to a finishing mill, and the spheroidizing annealing steel coil is finish-rolled to obtain a finish-rolled steel coil; the thickness of the steel coil is rolled from 5.3 mm to 5.25 mm.

[0058] Step S08, perform precision longitudinal shearing and slitting on the finished rolled steel coil to obtain finished slit cold rolled steel coil; perform precision longitudinal shearing on the steel coil with specifications from 5.25*415mm to 5.25*405*Cmm.

[0059] Step S09: packing the stripped cold-rolled steel coils.

[0060] Hot-rolled pickled steel coils are used as raw materials for large coil softening annealing. Annealing eliminates the internal stress of the hot-rolled coils. The edge cuts are not affected by shear stress during longitudinal shearing and stripping, and cracks are not generated on the edges during coiling and bending. The pickling process removes the surface oxide scale and oxygen molecules on the surface of the matrix, which makes them lose the opportunity to combine with oxygen molecules during the subsequent full hydrogen furnace spheroidizing annealing, significantly improving the decarburization tendency during the subsequent high-temperature annealing. The subsequent isothermal spheroidizing annealing makes the structure, mechanical properties and hardness of the head, middle and tail of the steel coils tend to be uniform, so that the internal stress distribution of the steel coils during finish rolling is relatively uniform, so as to obtain a good rolled plate shape, thereby significantly improving the quality of the products produced.

[0061] Embodiment 2 of the present invention is a cold rolling process for a medium carbon alloy structural steel for a diaphragm spring. Based on Embodiment 1, step S01 specifically includes the following steps:

[0062] Step S011, during the soft annealing, the annealing furnace is heated to 200° C. at full speed;

[0063] Step S012, setting the time to 4h and heating to 420°C;

[0064] Step S013, set the temperature to 500°C for 6 hours and keep it at this temperature for 2 hours;

[0065] Step S014, set the temperature to 530°C for 1 hour and keep it at this temperature for 14 hours;

[0066] Step S015, after the heat preservation is completed, the annealing furnace is hooded and air-cooled to reduce the temperature of the annealing furnace to 320°C;

[0067] Step S016, after the temperature of the annealing furnace drops to 320°C, the temperature of the annealing furnace is lowered from 320°C to 120°C by water cooling outside the hood, and the steel coil is taken out of the furnace to obtain an annealed steel coil with internal stress removed.

[0068] Before the pickling process, annealing is performed at a temperature slightly lower than the critical point of decarburization of steel ≥550 degrees. To a certain extent, it not only ensures the quality of longitudinal shearing, but also effectively inhibits the tendency of subsequent decarburization and grain boundary oxidation. Low-temperature annealing does not affect the removal of surface oxide scale and residual oxygen molecules by pickling, which leads to annealing decarburization.

[0069] Embodiment 3 of the present invention is a cold rolling processing technology for medium carbon alloy structural steel for diaphragm springs. On the basis of Embodiment 1, the pickling production line in step S03 is provided with two pickling tanks, a passivation tank and a neutralization tank. The pickling concentrations of the two pickling tanks are set to 18% to 22% and 15% to 18% respectively. The acid position in the two pickling tanks is 380mm to 420mm, and the acid solution temperature is 45°C to 60°C. The pH value in the neutralization tank is 11 to 13, the pH value in the passivation tank is 7 to 8, the temperature value of the passivation tank is 40°C to 50°C, and the cleaning speed of the pickling production line is 5m / min to 15m / min.

[0070] The pickling process has been refined, which can effectively remove the oxide scale of hot-rolled coils while improving the pickling production efficiency.

[0071] Embodiment 4 of the present invention is a cold rolling process of a medium carbon alloy structural steel for a diaphragm spring. Based on Embodiment 1, step S04 specifically includes the following steps:

[0072] Step S041, firstly, the annealing furnace is heated to 200° C. at full speed;

[0073] Step S042, setting the time to 4h and heating to 420°C;

[0074] Step S043, set the temperature to 690°C for 6 hours and keep it at this temperature for 2 hours;

[0075] Step S044, set the temperature to 720°C for 1 hour and keep it at that temperature for 12 hours;

[0076] Step S045, after the heat preservation is completed, the furnace is cooled to 650°C;

[0077] Step S046, the annealing furnace is hooded and air-cooled, and the temperature is reduced to 320° C.;

[0078] Step S047, after the temperature of the annealing furnace drops to 320°C, the inner cover is cooled by spraying water to reduce the temperature of the annealing furnace to 120°C before being taken out of the furnace to obtain a softened annealed steel coil.

[0079] The high-temperature holding time has been shortened (from the conventional 14 hours to 12 hours), and the stress at the edges of the longitudinally sheared steel coils can still be effectively removed and the internal grain structure can be restored, which can save 2 hours of annealing time and slightly improve production efficiency.

[0080] Embodiment 5 of the present invention is a cold rolling process of a medium carbon alloy structural steel for a diaphragm spring. Based on Embodiment 1, step S06 specifically includes the following steps:

[0081] Step S061, firstly, the annealing furnace is heated to 200° C. at full speed;

[0082] Step S062, setting the time to 4h and heating to 420°C;

[0083] Step S063, set the temperature to 720°C for 6 hours and keep it at this temperature for 2 hours;

[0084] Step S064, set the temperature to 750°C for 1 hour and keep it at this temperature for 12 hours;

[0085] Step S065, cooling to 680°C with the furnace and keeping the temperature for 8 hours;

[0086] Step S066, after the heat preservation is completed, the furnace is cooled to 650°C; the annealing furnace is hooded and air-cooled, and the temperature drops to 320°C;

[0087] Step S067, after the temperature of the annealing furnace drops to 320°C, the inner cover is cooled by spraying water to reduce the temperature of the annealing furnace to 80°C before being taken out of the furnace to obtain a spheroidized annealed steel coil.

[0088] Embodiment 6 of the present invention is a cold rolling process for a medium carbon alloy structural steel for a diaphragm spring. Based on Embodiment 1, in step S05, when rolling the softened annealed steel coil, a rolling working roll with a roller curvature of 0.05 mm is selected to perform reciprocating rolling multiple times to obtain a rolled steel coil.

[0089] Increase the curvature of the working roll to offset the rolling disturbance, so as to obtain a smaller lateral three-point difference and a flatter plate shape, providing better quality assurance for the thickness accuracy of the finishing rolling process.

[0090] Embodiment 7 of the present invention is a cold rolling processing technology for medium carbon alloy structural steel for diaphragm springs. Based on Embodiment 1, step S01 also includes: testing the thickness and width dimensions of the selected hot-rolled pickled steel coils, and performing stress relief annealing on the hot-rolled pickled steel coils that meet the standards.

[0091] Embodiment 8 of the present invention is a cold rolling processing technology for medium carbon alloy structural steel for diaphragm springs. Based on Embodiment 1, step S08 also includes: before precision longitudinal shearing and slitting, the metallographic spheroidizing structure, surface decarburization, grain boundary oxidation and mechanical properties of the finished steel coil are tested by a metallographic microscope, a universal testing machine and a hardness tester, and the finished steel coil with qualified indicators is precisely longitudinally sheared and slid.

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A cold rolling process for medium carbon alloy structural steel for diaphragm springs, characterized in that: The following steps are involved: Step S01, selecting a hot-rolled pickled steel coil with a grade of 51CrV4, and performing stress relief annealing on the hot-rolled pickled steel coil to obtain a stress relief annealed steel coil; Step S02, slitting the annealed steel coil into strips to obtain slitting narrow strip steel coils; Step S03, transferring the slit narrow strip steel coil to a pickling production line through a crane device, pickling the slit narrow strip steel coil to obtain a pickled coil with no iron oxide scale on the surface and a passivation film formed on the surface; Step S04, performing soft annealing on the pickled coil to obtain a soft annealed steel coil; Step S05, repeatedly rolling the softened annealed steel coil to obtain a rolled steel coil; Step S06, performing isothermal spheroidizing annealing on the rolled steel coil to obtain a spheroidizing annealed steel coil; Step S07, performing finish rolling on the spheroidizing annealed steel coil to obtain a finish rolled steel coil; Step S08, performing precision longitudinal shearing and slitting on the finish-rolled steel coil to obtain a finished slitting cold-rolled steel coil; Step S09: packing the stripped cold-rolled steel coils.

2. According to claim 1, a cold rolling process of a medium carbon alloy structural steel for a diaphragm spring is characterized in that: The step S01 specifically includes the following steps: Step S011, during the soft annealing, the annealing furnace is heated to 200° C. at full speed; Step S012, setting the time to 4h and heating to 420°C; Step S013, set the temperature to 500°C for 6 hours and keep it at this temperature for 2 hours; Step S014, set the temperature to 530°C for 1 hour and keep it at this temperature for 14 hours; Step S015, after the heat preservation is completed, the annealing furnace is hooded and air-cooled to reduce the temperature of the annealing furnace to 320°C; Step S016, after the temperature of the annealing furnace drops to 320°C, the temperature of the annealing furnace is lowered from 320°C to 120°C by water cooling outside the hood, and the steel coil is taken out of the furnace to obtain a stress-relieved annealed steel coil.

3. According to claim 1, a cold rolling process of a medium carbon alloy structural steel for a diaphragm spring is characterized in that: The pickling production line in step S03 is provided with two pickling tanks, a passivation tank and a neutralization tank, the pickling concentrations of the two pickling tanks are set to 18% to 22% and 15% to 18% respectively, the acid position in the two pickling tanks is 380mm to 420mm, and the acid solution temperature is 45°C to 60°C, the pH value in the neutralization tank is 11 to 13, the pH value in the passivation tank is 7 to 8, the temperature value of the passivation tank is 40°C to 50°C, and the cleaning speed of the pickling production line is 5m / min to 15m / min.

4. According to claim 1, a cold rolling process of a medium carbon alloy structural steel for a diaphragm spring is characterized in that: The step S04 specifically includes the following steps: Step S041, firstly, the annealing furnace is heated to 200° C. at full speed; Step S042, setting the time to 4h and heating to 420°C; Step S043, set the temperature to 690°C for 6 hours and keep it at this temperature for 2 hours; Step S044, set the temperature to 720°C for 1 hour and keep it at that temperature for 12 hours; Step S045, after the heat preservation is completed, the furnace is cooled to 650°C; Step S046, the annealing furnace is hooded and air-cooled, and the temperature is reduced to 320° C.; Step S047, after the temperature of the annealing furnace drops to 320°C, the inner cover is cooled by spraying water to reduce the temperature of the annealing furnace to 120°C before being taken out of the furnace to obtain a softened annealed steel coil.

5. The cold rolling process of the medium carbon alloy structural steel for diaphragm spring according to claim 1, characterized in that: The step S06 specifically includes the following steps: Step S061, firstly, the annealing furnace is heated to 200° C. at full speed; Step S062, setting the time to 4h and heating to 420°C; Step S063, set the temperature to 720°C for 6 hours and keep it at this temperature for 2 hours; Step S064, set the temperature to 750°C for 1 hour and keep it at this temperature for 12 hours; Step S065, cooling to 680°C with the furnace and keeping the temperature for 8 hours; Step S066, after the heat preservation is completed, the furnace is cooled to 650°C; the annealing furnace is hooded and air-cooled, and the temperature drops to 320°C; Step S067, after the temperature of the annealing furnace drops to 320°C, the inner cover is cooled by spraying water to reduce the temperature of the annealing furnace to 80°C before being taken out of the furnace to obtain a spheroidized annealed steel coil.

6. The cold rolling process of the medium carbon alloy structural steel for diaphragm spring according to claim 1, characterized in that: In the step S05, when rolling the softened annealed steel coil, a rolling work roll with a roll curvature of 0.05 mm is selected to perform reciprocating rolling multiple times to obtain a rolled steel coil.

7. The cold rolling process of the medium carbon alloy structural steel for diaphragm spring according to claim 1, characterized in that: The step S01 further includes: detecting the thickness and width of the selected hot-rolled pickled steel coils, and performing stress relief annealing on the hot-rolled pickled steel coils that meet the standards.

8. The cold rolling process of the medium carbon alloy structural steel for diaphragm spring according to claim 1, characterized in that: The step S08 also includes: before the precision longitudinal shearing and slitting, the metallographic spheroidizing structure, surface decarburization, grain boundary oxidation and mechanical properties of the finished rolled steel coil are tested by a metallographic microscope, a universal testing machine and a hardness tester, and the precision longitudinal shearing and slitting are performed on the finished rolled steel coil with qualified indicators.

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