Production process of spring flat steel with long fatigue life

Abstract

The invention discloses a production process of spring flat steel with long fatigue life, and relates to the field of spring flat steel production, the production process comprises the following steps: step 1, blank preparation: preparing a 60Si2Mn or 50CrVA steel blank; 2, preprocessing is conducted, specifically, the steel billet is smelted and remanufactured; 3, surface treatment is conducted, specifically, the surface of the steel blank preprocessed in the step 2 is treated; fourthly, machining treatment is conducted, and rolling and heat treatment are conducted on the steel blank treated in the third step; 5, quality detection and control, wherein dimensional precision, surface quality and mechanical property inspection is conducted on a finished product; and 6, packaging and warehousing. The content of harmful impurities such as sulfur and phosphorus is effectively reduced, so that the purity of the steel is remarkably improved, the strength, toughness, fatigue life and other mechanical properties of the spring flat steel are enhanced, the surface quality is optimized, abrasion in the using process is reduced, the comprehensive mechanical properties of the flat steel are further optimized, the working efficiency of the spring is improved, the service life of the spring is prolonged, and the product quality is improved.

Description

Technical Field

[0001] The invention relates to the field of spring flat steel production, in particular to a production process of spring flat steel with high fatigue life. Background Art

[0002] With the rapid development of modern industry, spring flat steel has extensive and important applications in many key fields, such as automobile manufacturing, mechanical equipment, aerospace and other industries. In the automobile suspension system, springs made of spring flat steel need to withstand repeated tensile and compressive loads for a long time; various elastic components in mechanical equipment also rely on spring flat steel to ensure stable mechanical properties; and the aerospace field has extremely high requirements for the reliability of parts and components, and parts made of spring flat steel must serve for a long time under complex and harsh working conditions. These application scenarios urgently require spring flat steel to have a high fatigue life to ensure the safe and stable operation of the entire system.

[0003] The traditional production process of spring flat steel often has many shortcomings. In terms of raw material selection, the purity of the raw materials is not controlled finely enough, and the impurity content may be too high, which lays hidden dangers for defects in subsequent products. In the steelmaking process, the refining process is not perfect, and the harmful elements cannot be fully removed and the composition of the molten steel cannot be homogenized. These will affect the purity of the steel and reduce the mechanical properties of the spring flat steel, such as strength, toughness, and fatigue life. Summary of the invention

[0004] In view of the deficiencies of the prior art, the present invention provides a production process for spring flat steel with high fatigue life, which solves the problems raised in the above-mentioned background technology.

[0005] To achieve the above objectives, the present invention is implemented by the following technical scheme: A production process of spring flat steel with high fatigue life, comprising the following steps:

[0006] Step 1: Billet preparation: prepare 60Si2Mn or 50CrVA steel billet;

[0007] Step 2: Pre-processing, melting and remaking the steel billet;

[0008] Step 3: Surface treatment, treating the surface of the steel blank pre-processed in step 2;

[0009] Step 4: Processing, rolling and heat treating the steel billet after the processing in step 3;

[0010] Step 5: Quality inspection and control, testing the dimensional accuracy, surface quality and mechanical properties of the finished product;

[0011] Step 6: Packing and storage.

[0012] According to the above technical solution, during the blank preparation process described in step 1, each batch of blanks is sampled and inspected, and its chemical composition is required to meet the requirements of carbon steel 60%-80%, alloy elements 5%-15%, nickel 1%~5%, and molybdenum 1%~5%.

[0013] According to the above technical solution, during the pre-processing process of step 2, the temperature is controlled at about 1500°C-1550°C, the steel billet is smelted and remade, and ferrosilicon is added at a ratio of 10kg / ton for deoxidation, and lime is added at a ratio of 20kg / ton for slag making.

[0014] According to the above technical solution, in the surface treatment process of step 3, the pressure is selected to be 15-20MPa and the flow rate is 50-100m 3 / h high-pressure water dephosphorization device makes the flat steel pass through the high-pressure water jet area at a speed of 1-3m / min. After dephosphorization is completed, coarse grinding and fine grinding are carried out in turn.

[0015] According to the above technical solution, the processing step in step 4 includes the following processes:

[0016] S1, rough rolling: horizontal and vertical alternating rolling process;

[0017] S2, medium-strengthening: further grain refinement;

[0018] S3, finishing rolling: final dimensional accuracy and surface quality control;

[0019] S4, quenching: the heating temperature is controlled within the range of 830℃-880℃, and after heat preservation, water quenching is used for cooling, the water temperature is controlled within the range of 15℃-30℃, and proper stirring is performed to ensure uniform cooling;

[0020] S5, tempering: the heating temperature is controlled at 550°C-650°C to obtain a tempered troostite structure, and after 30-60 minutes of heat preservation, air cooling is used for cooling.

[0021] According to the above technical scheme, during the quality inspection and control process of step five, calipers and micrometers are used to accurately measure the length, width and thickness of the spring flat steel, and the allowable error is strictly controlled within the range of ±1mm. The surface finish reaches Ra0.8-Ra1.6μm, the tensile strength reaches 1275MPa-1570MPa, the yield strength is around 1100MPa, and the elongation is not less than 10%.

[0022] According to the above technical solution, in the quality inspection and control process of step five, after the defects inside the flat steel are detected, the process parameters are adjusted in time, and an accurate fatigue life prediction model is constructed based on big data and material performance tests.

[0023] According to the above technical solution, during the packaging and warehousing process in step six, the products are wrapped, and after the wrapping is completed, multiple groups of products are bundled and finally put into storage.

[0024] The present invention provides a production process for spring flat steel with high fatigue life, which has the following beneficial effects:

[0025] (1) The production process of spring flat steel with high fatigue life can significantly reduce the content of harmful impurities such as sulfur and phosphorus, significantly improve the purity of steel, and further enhance the mechanical properties such as strength, toughness, fatigue life of spring flat steel, optimize surface quality, reduce wear during use, and improve the working efficiency and service life of the spring.

[0026] (2) The production process of spring flat steel with high fatigue life can more accurately achieve the transition from steel blank to finished product size, which helps to ensure product dimensional accuracy, avoid dimensional deviation caused by unreasonable deformation, and further optimize the comprehensive mechanical properties of the flat steel, such as toughness and plasticity, so that the product performance is more in line with the high standard requirements of spring flat steel in actual use.

[0027] (3) The production process of spring flat steel with high fatigue life can more accurately detect tiny, deep internal defects, prevent defective products from entering the market, improve the stability of product quality and performance, reduce product quality problems caused by unreasonable process parameters, effectively improve the quality and reliability of spring flat steel, and extend its service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the overall steps of the present invention;

[0029] Figure 2 This is a schematic diagram of the process flow of step four of the present invention. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] See also Figure 1-Figure 2 The present invention specifically provides a process for producing spring flat steel with high fatigue life, comprising the following steps:

[0032] Step 1: Billet preparation: prepare 60Si2Mn or 50CrVA steel billets to ensure that their chemical composition meets the requirements of carbon steel (60%-80%), alloy elements (5%-15%), nickel (1%-5%), and molybdenum (1%-5%). Inspect the billets to ensure that the content of each element is within the specified standard range and that there is no obvious deviation in composition.

[0033] Step 2: Pre-processing, melting and remaking the steel billet to improve the purity of the molten steel, controlling the temperature at about 1500℃-1550℃, melting and remaking the steel billet, adding ferrosilicon at a ratio of 10kg / ton for deoxidation, and adding lime at a ratio of 20kg / ton for slagging;

[0034] Step 3: Surface treatment: treat the surface of the steel billet after pre-processing in step 2, using a pressure of 15-20MPa and a flow rate of 50-100m 3 / h high-pressure water dephosphorization device, so that the flat steel at a stable speed, usually controlled at 1-3m / min, through the high-pressure water jet area, after the completion of dephosphorization, first use coarse grain size, such as 80-120 mesh sandpaper or grinding wheel for rough grinding, and then replace with fine grain size, such as 200-400 mesh sandpaper or grinding wheel for fine grinding, after grinding, the flat steel and the polishing wheel with appropriate contact pressure, usually controlled between 0.1-0.3MPa, and the relative speed of about 10-20m / min for contact polishing, so that the surface roughness of the flat steel is reduced to about Ra0.8-Ra1.6μm;

[0035] Step 4: Processing: rolling and heat treating the steel billet after the processing in step 3, transferring the steel billet after smelting and reprocessing and passing the inspection from the smelting workshop to the rolling workshop, sending it to the heating furnace for reheating, and the heating temperature is controlled between 1100℃ and 1200℃. The spring flat steel after rolling and cooling is heat treated again;

[0036] Step 5: Quality inspection and control, carry out dimensional accuracy inspection on the finished product, control the allowable error within the range of ±1mm, surface quality inspection, ensure that the surface finish reaches Ra0.8-Ra1.6μm, and use mechanical property testing equipment to test the tensile strength, yield strength, elongation and other mechanical indicators of the spring flat steel to ensure that the tensile strength of the spring reaches 1275MPa-1570MPa, the yield strength is around 1100MPa, and the elongation is not less than 10%;

[0037] Step 6: Packing and warehousing: Wrap with moisture-proof paper and plastic film, bundle the packaged spring flat steel with steel belt and nylon belt, and confirm by counting and weighing to ensure the quantity in storage is accurate.

[0038] In the process of preparing the blanks in step 1, each batch of blanks is sampled and inspected. In the process of pre-processing in step 2, the temperature is controlled at about 1500℃-1550℃, the steel blanks are melted and remade, and ferrosilicon is added at a ratio of 10kg / ton for deoxidation, and lime is added at a ratio of 20kg / ton for slag making. In the process of surface treatment in step 3, the pressure is selected to be 15-20MPa and the flow rate is 50-100m 3 / h high-pressure water dephosphorization device makes the flat steel pass through the high-pressure water jet area at a speed of 1-3m / min. After dephosphorization is completed, coarse grinding and fine grinding are carried out in turn.

[0039] The processing step in step 4 includes the following processes:

[0040] S1, rough rolling: adopt horizontal and vertical alternating rolling process, the total deformation is 30%-60%, the rolling passes are determined according to the initial size of the steel billet and the target size of the finished spring flat steel, usually about 5-10 passes, the first pass pressure can be controlled at about 20-30mm, and the pressure is gradually reduced as the number of rolling passes increases. The rolling speed is set in the range of 0.5-1.5m / s according to the capacity of the rolling mill;

[0041] S2, medium rolling: further refine the grains, the total deformation is 20%-50%, usually using a continuous rolling mill to further refine the size of the billet, the rolling passes are about 3-6 passes, the pressure of each pass is further reduced compared to the rough rolling stage, controlled between 5-15mm, and the rolling speed is appropriately increased to about 1.5-2.5m / s;

[0042] S3, finishing rolling: the final dimensional accuracy and surface quality control is carried out, the deformation is 5%-10%, the temperature is controlled at 800℃-950℃, and the final dimensional accuracy and surface quality of the flat steel are strictly controlled. The number of finishing passes is relatively small, mostly 2-4 passes, the pressure is usually in the range of 1-5mm, and the rolling speed can reach 2-3m / s;

[0043] S4, quenching: control the heating temperature within the range of 830℃-880℃, keep warm and then cool by water quenching, the water temperature is controlled within the range of 15℃-30℃, and stir appropriately to ensure uniform cooling;

[0044] S5, tempering: the heating temperature is controlled at 550℃-650℃ to obtain tempered bainite structure. After 30-60 minutes of heat preservation, air cooling is used for cooling. These processes can more accurately achieve the transition from steel billet to finished product size, help to ensure product dimensional accuracy, avoid dimensional deviation caused by unreasonable deformation and other problems, and further optimize the comprehensive mechanical properties of flat steel such as toughness and plasticity, so that the performance of the product is more in line with the high standards of spring flat steel in actual use.

[0045] In the quality inspection and control process described in step five, an ultrasonic flaw detection device is introduced to inspect the inside of the spring flat steel. In the quality inspection and control process described in step five, after the defects inside the flat steel are detected, the process parameters are adjusted in time, and an accurate fatigue life prediction model is constructed based on big data and material performance tests. In the packaging and warehousing process described in step six, the products are wrapped, and after the wrapping is completed, multiple groups of products are bundled and finally put into storage.

[0046] The object of the present invention is achieved in that:

[0047] Purchase blanks from regular and reliable suppliers, check their quality certification documents to ensure that the marked chemical composition can match the 60Si2Mn and 50CrVA steel grades, sample each batch of blanks, and use a spectrometer to accurately detect the content of key elements such as carbon, silicon, manganese, chromium, vanadium, as well as phosphorus and sulfur to ensure that the carbon steel content is 60%-80%, the alloy element content is 5%-15%, the nickel content is 1%-5%, and the molybdenum content is 1%-5%. In addition, test blank samples at different locations to check whether the chemical composition is uniform and consistent to avoid excessive deviation in local composition, otherwise it will affect the stability of subsequent spring flat steel performance.

[0048] Start the smelting furnace and adjust the temperature to about 1500℃-1550℃ to gradually melt the selected steel billets. During the smelting period, closely monitor the temperature in the furnace and the smelting time to ensure that the molten steel is fully melted and has a uniform composition. At the same time, add ferrosilicon at a ratio of 10kg / ton to deoxidize the molten steel, and add lime at a ratio of 20kg / ton to make slag to remove impurities and gases in the molten steel and improve the purity of the molten steel. After the smelting, deoxidation and slag making are completed, perform the steel tapping operation to smoothly guide the molten steel into the casting ladle, preheat the casting ladle before pouring, and install a suitable casting mold to ensure a smooth subsequent casting process.

[0049] The selected pressure is 15-20MPa and the flow rate is 50-100m 3 / h high-pressure water dephosphorization device, the spring flat steel billet that has been smelted, remade and initially formed is transported to the working area of ​​the high-pressure water dephosphorization device, so that the flat steel passes through the high-pressure water jet area at a stable speed, usually controlled at 1-3m / min. In this process, according to the thickness and adhesion of the iron oxide scale on the surface of the flat steel, the pressure, flow rate of the high-pressure water and the distance between the nozzle and the flat steel are adjusted in time. After the dephosphorization is completed, a coarser grain size, such as 80-120 mesh sandpaper or grinding wheel, is first used for rough grinding to quickly remove the tiny bumps, scratches and other defects remaining on the surface, and avoid surface unevenness caused by local excessive grinding. Then, replace it with finer-grained sandpaper or grinding wheel such as 200-400 mesh for fine grinding. After grinding, make the flat steel and the polishing wheel have appropriate contact pressure, usually controlled between 0.1-0.3MPa, to further refine the surface texture and reduce the surface roughness. The flat steel after grinding is polished with the polishing wheel, and the relative speed is about 10-20m / min for contact polishing. The gloss and roughness changes of the flat steel surface are observed in real time. According to the actual situation, the polishing paste is supplemented in time to reduce the surface roughness of the flat steel to about Ra0.8-Ra1.6μm, ensuring that the polishing effect meets the expected requirements.

[0050] Use calipers and micrometers to accurately measure the length, width and thickness of spring flat steel, strictly control the allowable error within the range of ±1mm, ensure that the size of each spring flat steel meets the production requirements, and mark and record the finished products that exceed the tolerance range in time to facilitate subsequent tracing and analysis of the reasons. At the same time, optimize the frequency and method of measurement to improve detection efficiency and accuracy. Through visual observation and the use of flaw detection equipment, carefully check whether there are cracks, scratches, pits, rust and other defects on the surface of the spring flat steel to ensure that the surface finish reaches Ra0.8-Ra1 .6μm, and pay special attention to minor defects that may affect the performance of the spring. Products with substandard surface quality should be classified and processed. Mechanical performance testing equipment should be used to ensure that the tensile strength of the spring reaches 1275MPa-1570MPa, the yield strength is around 1100MPa, and the elongation is not less than 10%. Each batch of products should be sampled and tested to ensure that the overall mechanical properties are stable and reliable. At the same time, the testing technology and methods are continuously updated and improved to meet higher quality production needs, strengthen the analysis and application of test data, and help the continuous improvement of production processes.

[0051] Before packaging, use wiping and blowing methods to carefully clean the surface of the spring flat steel, remove oil, debris and other impurities remaining in the production process, ensure the appearance of the product is clean and tidy, avoid impurities from contaminating the packaging materials or affecting the subsequent storage quality, and choose moisture-proof paper and plastic film to wrap the spring flat steel according to the specifications and quantity of the spring flat steel to provide moisture-proof and rust-proof protection. The interfaces are sealed to prevent the intrusion of outside air and moisture. Use steel belts and nylon belts to bundle the packaged spring flat steel. According to the weight and length of the product, the position and quantity of the bundling are reasonably determined to ensure that the product will not be loose or shifted during transportation and storage, and the bundling force should be moderate to avoid damaging the surface of the flat steel. The packaged spring flat steel is transported to the warehouse and confirmed by counting and weighing to ensure that the quantity entering the warehouse is accurate. If the quantity does not match, find the cause and solve it in time.

[0052] The purpose of step 4 is achieved as follows:

[0053] After arriving at the rolling workshop, the steel billet is sent to the corresponding heating furnace for reheating according to its specific material and size specifications. The heating temperature is controlled between 1100℃-1200℃. The heating speed needs to be reasonably adjusted according to the weight of the steel billet and the furnace type to avoid thermal stress caused by excessive temperature difference between the inside and outside of the steel billet due to too rapid heating. During the heating process, the temperature in the furnace should be monitored in real time by temperature monitoring equipment, and the operation should be carried out strictly in accordance with the predetermined heating system to ensure that the overall steel billet is heated evenly and reaches a good plastic state suitable for rolling.

[0054] Rough rolling stage: Take out the heated steel billet from the heating furnace and quickly send it to the rough rolling mill for rolling. The rough rolling mill uses a reversible rolling mill or a continuous rough rolling mill, and adopts a horizontal and vertical alternating rolling process. The total deformation is 30%-60%. The rolling passes are determined according to the initial size of the steel billet and the target size of the finished spring flat steel, usually about 5-10 passes. The pressure in the first pass can be controlled at about 20-30mm. As the number of rolling passes increases, the pressure is gradually reduced. The rolling speed is set in the range of 0.5-1.5m / s according to the capacity of the rolling mill. At the same time, the gap and rolling force of the rollers are continuously adjusted through the automatic control system of the rolling mill, so that the steel billet is gradually rolled into an intermediate billet close to the width and thickness specifications of the finished product, and the dimensional accuracy and surface quality of the billet are guaranteed, and defects such as iron oxide that may appear on the surface are removed in time.

[0055] Intermediate rolling stage: After rough rolling, the intermediate billet enters the intermediate rolling stage to further refine the grains. The total deformation is 20%-50%. Continuous rolling mills are usually used to further refine the size of the billet. The rolling passes are about 3-6 passes. The pressure of each pass is further reduced compared to the rough rolling stage and is controlled between 5-15mm. The rolling speed is appropriately increased to about 1.5-2.5m / s, so that the size accuracy, flatness and surface quality of the billet are better improved.

[0056] Finishing rolling stage: After intermediate rolling, the billet enters the finishing rolling stage for final dimensional accuracy and surface quality control. The deformation is 5%-10%, and the temperature is controlled at 800℃-950℃. The final dimensional accuracy and surface quality of the flat steel are strictly controlled. The number of finishing passes is relatively small, mostly 2-4 passes. The downward pressure is usually in the range of 1-5mm, and the rolling speed can reach 2-3m / s. The finishing mill is generally equipped with high-precision rollers and advanced automation control systems to strictly control the final dimensional accuracy and surface quality of the flat steel, ensuring a smooth surface without obvious rolling defects such as folds and cracks.

[0057] Quenching treatment: control the heating temperature within the range of 830℃-880℃, calculate the time based on 1-2 minutes of insulation per millimeter thickness to ensure that the internal structure of the flat steel is fully austenitized. After the insulation is completed, use water quenching to cool, control the water temperature at 15℃-30℃, and stir appropriately to ensure uniform cooling, quickly immerse the flat steel in water to ensure that the flat steel can obtain sufficient cooling speed during the quenching process to form the required martensitic structure, while avoiding defects such as quenching cracks caused by excessive cooling speed.

[0058] Tempering treatment: Control the heating temperature at 550℃-650℃ to obtain tempered bainite structure. After 30-60 minutes of insulation, the uniformity of the furnace temperature must be strictly controlled during the tempering process. The temperature monitoring and adjustment system in the furnace is used to ensure that the performance of the flat steel after tempering is uniform and consistent, so as to eliminate quenching stress, stabilize the structure and adjust the hardness.

[0059] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A process for producing spring flat steel with high fatigue life, characterized in that: The following steps are involved: Step 1: Billet preparation: prepare 60Si2Mn or 50CrVA steel billet; Step 2: Pre-processing, melting and remaking the steel billet; Step 3: Surface treatment, treating the surface of the steel blank pre-processed in step 2; Step 4: Processing, rolling and heat treating the steel billet after the processing in step 3; Step 5: Quality inspection and control, testing the dimensional accuracy, surface quality and mechanical properties of the finished product; Step 6: Packing and storage.

2. A process for producing spring flat steel with high fatigue life according to claim 1, characterized in that: During the step 1 blank preparation process, each batch of blanks is sampled and inspected, and the chemical composition thereof is required to meet the requirements of 60% to 80% carbon steel, 5% to 15% alloying elements, 1% to 5% nickel, and 1% to 5% molybdenum.

3. A process for producing a spring flat steel with a long fatigue life according to claim 2, characterized in that: During the pre-processing of step 2, the temperature is controlled at about 1500°C-1550°C, the steel billet is smelted and re-processed, and ferrosilicon is added at a ratio of 10kg / ton for deoxidation, and lime is added at a ratio of 20kg / ton for slagging.

4. A process for producing a spring flat steel with a high fatigue life according to claim 3, characterized in that: In the surface treatment process of step 3, the pressure is selected to be 15-20MPa and the flow rate is 50-100m 3 / h high-pressure water dephosphorization device makes the flat steel pass through the high-pressure water jet area at a speed of 1-3m / min. After dephosphorization is completed, coarse grinding and fine grinding are carried out in turn.

5. A process for producing a spring flat steel with a long fatigue life according to claim 4, characterized in that: The fourth processing step includes the following processes: S1, rough rolling: horizontal and vertical alternating rolling process; S2, medium-strengthening: further grain refinement; S3, finishing rolling: final dimensional accuracy and surface quality control; S4, quenching: the heating temperature is controlled within the range of 830℃-880℃, and after heat preservation, the water quenching method is used for cooling, the water temperature is controlled within the range of 15℃-30℃, and proper stirring is performed; S5, tempering: the heating temperature is controlled at 550°C-650°C to obtain a tempered troostite structure, and after 30 to 60 minutes of heat preservation, air cooling is used for cooling.

6. A process for producing a spring flat steel with a long fatigue life according to claim 5, characterized in that: During the quality inspection and control process in step five, calipers and micrometers are used to accurately measure the length, width and thickness of the spring flat steel, and the allowable error is strictly controlled within the range of ±1mm. The surface finish reaches Ra0.8-Ra1.6μm, the tensile strength reaches 1275MPa-1570MPa, the yield strength is around 1100MPa, and the elongation is not less than 10%.

7. A process for producing a spring flat steel with a high fatigue life according to claim 6, characterized in that: In the quality inspection and control process of step five, after the defects inside the flat steel are detected, the process parameters are adjusted in time, and an accurate fatigue life prediction model is constructed based on big data and material performance tests.

8. A process for producing a spring flat steel with a long fatigue life according to claim 7, characterized in that: In the step six packaging and warehousing process, the products are wrapped, and after the wrapping is completed, multiple groups of products are bundled and finally put into storage.

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