Round steel for high-pressure common-rail diesel engine injector and manufacturing method of round steel

Abstract

The invention relates to round steel for a high-pressure common-rail diesel engine injector and a manufacturing method of the round steel. The round steel comprises the following chemical components: 0.17 to 0.22 percent of C, 0.15 to 0.40 percent of Si, 1.10 to 1.40 percent of Mn, 1.00 to 1.30 percent of Cr, 0.10 to 0.20 percent of Ni, 0.010 to 0.020 percent of S, less than or equal to 0.025 percent of P, 0.020 to 0.040 percent of Al, 0.0005 to 0.0010 percent of Ca and the balance of Fe and inevitable impurities. According to the ultra-pure round bar steel manufactured through the method of molten steel primary smelting, molten steel refining, vacuum degassing, continuous casting, rolling, skin turning, flaw detection, detection, packaging and warehousing, T.O. (total oxygen) is smaller than or equal to 0.0010%, macroscopic inclusions do not exist, microscopic inclusion oxides do not exceed the 1.0 level, sulfides do not exceed the 1.5 level, ultrasonic flaw detection meets the AAA level requirement of the GB / T 4162 standard, the hardenability J3 is 43-48 HRC, the hardenability J5 is 40-46 HRC, the hardenability J9 is 34-40 HRC, the surface is free of decarburization and defects, and the service life of the round bar steel is prolonged. And the dimensional deviation meets the h9-level requirement of the GB / T 3207 standard, and the method is suitable for manufacturing the high-pressure common-rail diesel engine fuel injector.

Description

Technical Field

[0001] The invention belongs to the technical field of special steel smelting, and in particular relates to round steel for a high-pressure common rail diesel engine injector and a manufacturing method thereof. Background Art

[0002] Fuel injection pressure is an important indicator of diesel engines, which is closely related to the engine's power, fuel consumption, emissions, etc. The higher the injection pressure, the better the combustion characteristics. For axial piston engines driven and controlled by the camshaft, the fuel system pressure is linearly related to the engine speed. There is a problem of insufficient fuel pressure at low engine speeds, while the high-pressure common rail engine can obtain very high fuel pressure in all engine speed ranges. It completely separates the generation of injection pressure and the injection process from each other, and accurately controls the injector pressure through the high-pressure oil pump, high-pressure oil rail, and electronic control unit, so that the injector pressure is independent of the engine speed, greatly reducing the degree of change of the diesel engine fuel supply pressure with the engine speed, and achieving complete combustion and high torque even under low-speed conditions.

[0003] The injector is one of the four important components of the high-pressure common rail system. Its function is to atomize the fuel and distribute it in the engine combustion chamber. It has been facing the harsh working conditions of high temperature, high pressure and high-speed fuel flushing for a long time. The fuel pressure of the high-pressure common rail diesel engine injection system is as high as 2000-3000bar, which puts extremely high requirements on the materials used for the injector, especially the purity of the material. Any small inclusions may cause the parts to fail. In addition, the injector is also one of the precision parts of the engine, requiring the material to have good plasticity, high dimensional accuracy, and easy chip breaking during the drilling process.

[0004] The patent with publication number CN112375985B proposes a steel for needle valve body of ultra-high pressure common rail fuel injection system for diesel engine under harsh working conditions, with the composition of C: 0.3-0.5%, Si: 0.8-1.2%, Mn: 0.4-0.6%, S: ≤0.03%, P: ≤0.022%, Cr: 5.0-6.0%, V: 0.9-1.2%, Mo: 0.35-0.4%, Ti: 0.09-0.11%, N: 0.020-0.050%, and the balance is Fe. The patent lacks description of the material purity control method, making it difficult to mass produce.

[0005] The patent with publication number CN116607082A discloses a steel for automobile engine fuel injection nozzle and its manufacturing method, the composition is C: 0.47-0.54%, Si: 0.10-0.37%, Mn: 0.55-0.85%, Cr: 1.00-1.30%, P: ≤0.020%, S: 0.009-0.015%, Ni: ≤0.10%, Mo: 0.16-0.26%, Al: 0.012-0.038%, N: 0.0025-0.0065%, Ti: ≤0.0020%, and the balance is Fe. The steel is medium carbon steel, which needs to add a large amount of precious alloy Mo, and the production cost is high. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a round steel for a high-pressure common rail diesel engine injector and a manufacturing method thereof in view of the above-mentioned prior art.

[0007] The technical solution adopted by the present invention to solve the above problems is: a round steel for a high-pressure common rail diesel engine injector, wherein the chemical composition and mass percentage of the steel are: C: 0.17-0.22%, Si: 0.15-0.40%, Mn: 1.10-1.40%, Cr: 1.00-1.30%, Ni: 0.10-0.20%, S: 0.010-0.020%, P≤0.025%, Al: 0.020-0.040%, Ca≤0.0010%, and the balance is Fe and unavoidable impurities.

[0008] The round steel for high-pressure common rail diesel engine injector of the present invention has high material purity and zero surface decarburization and zero defects through means such as source control of oxidizability, deep deoxidation in the refining process, secondary oxidation prevention in the continuous casting process, flame cleaning of the surface of the ingot, and rolling wagon. The fluctuation of hardenability between different heats is controlled within 4HRC through precise control of the components in the refining process. High-precision control of the rolled material size is achieved through KOCKS finishing rolling.

[0009] The main functions and design basis of each element in the chemical composition of the steel of the present invention are: C is the most basic element in steel and also the most economical strengthening element. In order to ensure that the parts produced by the steel have high surface hardness and good toughness in the core after quenching and tempering, the C content of the steel of the present invention is determined to be in the range of 0.17-0.22%.

[0010] Si plays a major role in deoxidation in steel and can also improve the surface hardness of steel after quenching and tempering and improve wear resistance. However, excessive Si content will lead to poor cold extrusion performance, so the Si content is designed to be in the range of 0.15-0.40% in the present invention.

[0011] Mn has a solid solution strengthening effect on steel. On the one hand, it can strongly improve the hardenability of steel. On the other hand, it combines with S in steel to form sulfides with good plasticity, improve cutting performance and reduce tool loss. According to the hardenability requirements of parts, the Mn content of the steel of the present invention is determined to be in the range of 1.10-1.40%.

[0012] Cr has a solid solution strengthening effect on steel, which is beneficial to improving the hardenability of the core. According to the hardenability requirements of parts, the Cr content of the steel of the present invention is determined to be in the range of 1.00-1.30%.

[0013] Ni in the steel of the invention plays a role in improving strength and impact toughness, and also plays a role in improving post-hardenability. Considering that Ni is a precious alloy, in order to control production costs, the Ni content of the steel of the invention is in the range of 0.10-0.20%.

[0014] P is an impurity element and a harmful element, which is harmful to the mechanical properties and hot working properties of steel, and is prone to forming defects such as segregation, causing a significant decrease in plasticity and impact toughness, and its content should be reduced as much as possible. In the present invention, P is controlled to be ≤0.025%.

[0015] S is a free-cutting element. It forms MnS plastic inclusions with Mn in steel to improve the cutting performance of the material and reduce the cutting cost. However, too high S content will not only deteriorate the castability of molten steel, but also deteriorate the purity of molten steel. Under the principle of improving cutting performance without deteriorating the purity of molten steel, the S content in the steel of the present invention is controlled in the range of 0.010-0.020%.

[0016] Al is a strong deoxidizing element, but too high Al content will cause the molten steel to be easily secondary oxidized, and the purity of the molten steel will decrease instead of increase. Therefore, the Al content in the steel of the present invention is controlled in the range of 0.020-0.040%.

[0017] Ca is a strong oxide-forming element. Adding an appropriate amount of Ca into the molten steel will transform the solid Al2O3 inclusions into liquid CaO-Al2O3 inclusions, thereby facilitating the floating and removal of the inclusions. Combined with the thermodynamic calculation results of inclusion transformation, the Ca content in the steel of the present invention is controlled in the range of 0.0005-0.0010%.

[0018] Another object of the present invention is to provide a method for manufacturing round steel for the above-mentioned high-pressure common rail diesel engine injector, comprising the following process: molten iron pretreatment - molten steel primary refining - molten steel refining - continuous casting - continuous rolling - car body - flaw detection - testing, packaging, and warehousing.

[0019] Furthermore, the specific production process of the steel of the present invention is: 100t converter-LF refining outside the furnace-RH vacuum degassing-continuous casting (390×510mm 2 )-heating of ingot-flame cleaning-rolling into finished products-car skin-flaw detection-inspection, packaging and warehousing.

[0020] The above production process specifically includes the following steps: In the initial steelmaking stage, the C content of steel is in the range of 0.05-0.10% to control the oxidizability of the initial steel and aluminum iron is added for pre-deoxidation during the steelmaking process. The amount of aluminum iron added is 100-400kg per 100t of steel to reduce oxide inclusions from the source. After the initial steelmaking is completed, Mn and Cr alloys are added during the steelmaking process. In order to melt all the alloys, the steelmaking temperature is ≥1620℃.

[0021] During the LF refining stage of molten steel, aluminum wire precipitation deoxidation, silicon carbide bleaching and aluminum particle diffusion deoxidation are fed in batches for multiple times, and the LF refining time is controlled at 40-60 minutes. During this period, samples are taken for rapid component testing 2 or more times to achieve precise control of all chemical components. The deviation of Mn, Cr, and Ni between different furnaces is ≤0.05%, the deviation of C is ≤0.02%, and the deviation of Al, P, and S is ≤0.01%.

[0022] During the RH vacuum degassing stage, the adsorption of inclusions by refined slag is accelerated by mixing steel slag, and the time is controlled to be more than 15-30 minutes. Immediately after breaking the air, the carbonized rice husk is evenly spread on the surface of the molten steel to prevent secondary oxidation, and the silicon-calcium wire is fed to transform the solid phase inclusions into calcium-containing liquid phase inclusions. The Ca content needs to be controlled in the range of 0.005-0.0010%. Before the molten steel is continuously cast into billets, it needs to be left to stand for 20-40 minutes to ensure that the residual inclusions in the molten steel have sufficient time to float up and be removed.

[0023] During continuous casting, the superheat of the molten steel in the tundish is controlled in the range of 15-30℃, and the technology of electromagnetic induction heating of the tundish + automatic addition of protective slag to the crystallizer + automatic control of the crystallizer liquid level + electromagnetic stirring of the crystallizer + electromagnetic stirring at the end is adopted.

[0024] The continuous casting billet is heated in a walking beam heating furnace. The billet temperature does not exceed 200°C before entering the furnace. The temperature of the preheating section is controlled at 500-750°C, the temperature of the heating section is controlled at 1150-1250°C, the temperature of the soaking section is controlled at 1200-1260°C, and the total heating time is 3.5 hours or more.

[0025] The ingot is descaled with high-pressure water before rolling. It is flame cleaned before rolling. The surface metal of the ingot is cleaned with a high-pressure oxygen flame to a depth of 0.5 to 3 mm to remove surface cracks, subcutaneous inclusions and other defects. The starting rolling temperature is 1050 to 1100°C, and the final rolling temperature is above 950°C. 12 two-roll mills + 5 KOCKS three-roll mills are used to ensure that the dimensional accuracy of the rolled material is controlled within ±0.15mm.

[0026] After rolling, the surface defects of the car skin are removed and polished. The depth of the car skin is 0.4-0.7mm. The product surface has zero decarburization and zero defects. The diameter deviation meets the requirements of GB / T 3207 standard h9 level to remove surface defects.

[0027] Ultrasonic flaw detection meets the AAA level requirement of GB / T 4162. According to GB / T 10561 standard, the microscopic oxide inclusions are ≤1.0 level and the sulfide inclusions are ≤1.5 level.

[0028] Compared with the prior art, the advantages of the present invention are: The steel manufactured by the present invention has TO (total oxygen) ≤ 0.0010%, no macroscopic inclusions, microscopic oxide inclusions not exceeding level 1.0, sulfide inclusions not exceeding level 1.5, ultrasonic flaw detection meets the AAA level requirement of GB / T 4162 standard, hardenability J3=43-48HRC, J5=40-46HRC, J9=34-40HRC, zero decarburization and zero defects on the surface, and dimensional deviation meets the h9 level requirement of GB / T 3207 standard. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of product size and deviation detection in Example 1 of the present invention.

[0030] Figure 2 This is a schematic diagram of product size and deviation detection in Example 2 of the present invention.

[0031] Figure 3 This is a physical picture of a product according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is described in more detail in conjunction with the preferred embodiments of the present invention. However, these embodiments are only descriptions of the preferred implementation methods of the present invention and cannot impose any limitation on the scope of the present invention.

[0033] Example 1 and Example 2 A method for manufacturing a high-pressure common rail diesel engine injector steel according to the embodiment: 100t molten iron primary refining in a converter → LF refining → RH vacuum degassing → continuous casting (390×510mm 2 )→slow cooling→high temperature heating of continuous casting billet→flame cleaning→continuous rolling→cooling→car skin→flaw detection→inspection, packaging, warehousing.

[0034] The molten iron is poured into the converter for oxygen blowing and decarburization. After the initial refining, the sample rapid analysis shows that the end carbon is 0.07% and 0.06% respectively, and the temperature is 1630℃ and 1640℃ respectively, which meets the conditions for steel discharge. The furnace is shaken, the steel discharge port is opened, and the molten steel flows quickly into the ladle. When the ladle is 1 / 3 full, the weighed manganese ferroalloy and ferrochrome alloy are added from the high-level silo. After the molten steel is discharged, 200kg of aluminum iron is added to each furnace of steel for pre-deoxidation.

[0035] The molten steel was transferred to the LF furnace station for refining. After the ladle was seated, the first sampling and analysis of the composition was carried out, and the appropriate amount of alloy was added according to the results. During this period, deep deoxidation was carried out by feeding aluminum wire, scattering silicon carbide and aluminum particles. The second sampling and analysis of the composition was carried out 5 minutes before the end of refining. After all the components entered the internal control, the molten steel could be transferred to the RH station for vacuum degassing. The refining time of the two furnaces LF was 53 minutes and 55 minutes respectively. After 23 minutes and 22 minutes of vacuum degassing respectively, the pre-prepared silicon carbide rice husk was immediately thrown into the ladle to prevent secondary oxidation, and then silicon calcium wire was fed for inclusion modification. The third sampling and analysis was carried out to check the composition of the molten steel. In order to make the residual inclusions in the molten steel fully deteriorate and have sufficient time to float up, grow and be removed, the two furnaces of molten steel were left to stand for 32 minutes and 34 minutes respectively before continuous casting.

[0036] The molten steel is transferred to the continuous casting platform and flows into the tundish through the long nozzle. The tundish is heated by electromagnetic induction. The superheat of the molten steel in the two furnaces is 20℃ and 22℃ respectively. The molten steel in the tundish then flows into the lower crystallizer through the immersion nozzle and is cast into 390×510mm 2 For large square blooms, the liquid level in the crystallizer is automatically adjusted during the casting process, the protective slag is automatically sprayed on the surface of the molten steel, and the molten steel is electromagnetically stirred in the crystallizer.

[0037] The blank is heated in a walking beam heating furnace, with the preheating section temperature at 500-750°C, the heating section temperature at 1190-1250°C, the soaking section temperature at 1210-1260°C, and the total heating time at 4.0-4.5 hours.

[0038] The ingot is descaled by high-pressure water and the surface metal of the ingot is cleaned by flame before rolling. The depth is 1.0mm, and the rolling temperature is 1050-1080℃. 12 two-roll rolling mills + 5 KOCKS three-roll rolling mills are used for rolling. The dimensional accuracy of the rolled material is ±0.15mm. No water is penetrated during the rolling process, and the final rolling temperature is above 960-985℃. The rolled material is pile-cooled after being put down from the cooling bed.

[0039] The hot-rolled black leather material is used for lathe, and the lathe depth is 0.5-0.6mm. After lathe, ultrasonic flaw detection is carried out according to the AAA standard in GB / T 4162, and the qualified products are packed and stored.

[0040] The results of the smelting composition test of the above embodiment are shown in Table 1.

[0041] Table 1 Melting composition (wt%) Steel Type C Si Mn P S Cr Ni Al TO Example 1 0.20 0.20 1.31 0.020 0.018 1.15 0.14 0.025 0.0007 Example 2 0.21 0.21 1.33 0.019 0.017 1.17 0.15 0.028 0.0005 The results of the inclusion detection in the above embodiment according to GB / T 10561 are shown in Table 2.

[0042] Table 2 Inclusion detection results

[0043] The hardenability test results of the above implementation cases are shown in Table 3.

[0044] Table 3 Hardenability test results Detection point J3 J5 J9 Example 1 Detection value 45HRC 43.5HRC 38HRC Example 2 Detection value 44HRC 42HRC 37HRC Although the preferred embodiments of the present invention are described in detail above, it should be clearly understood that various modifications and variations are possible for those skilled in the art. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A round steel for a high pressure common rail diesel engine injector, characterized in that The chemical composition of the steel is as follows by mass percentage: C: 0.17~0.22%, Si: 0.15~0.40%, Mn: 1.10~1.40%, Cr: 1.00~1.30%, Ni: 0.10~0.20%, S: 0.010~0.020%, P≤0.025%, Al: 0.020-0.040%, Ca: 0.005-0.0010%, and the balance is Fe and unavoidable impurities.

2. The round steel for a high-pressure common rail diesel engine injector according to claim 1, characterized in that: The round steel has a total oxygen content of ≤0.0010%, no macroscopic inclusions, microscopic oxide inclusions of no more than level 1.0, and sulfides of no more than level 1.

5. Ultrasonic flaw detection meets the AAA level requirement of GB / T 4162 standard, hardenability J3=43-48HRC, J5=40-46HRC, J9=34-40HRC, zero decarburization and zero defects on the surface, and dimensional deviation meets the h9 level requirement of GB / T 3207 standard.

3. A method for manufacturing round steel for high pressure common rail diesel engine injector according to claim 1, characterized in that: The method comprises the following steps: 1) The primary steelmaking furnace is a BOF converter, and aluminum and iron are added for pre-deoxidation during the steel discharge process in the converter to reduce the subsequent steel refining and deoxidation tasks; 2) During the LF refining stage of molten steel, aluminum wire is fed in batches for precipitation deoxidation, silicon carbide is sprinkled, and aluminum particles are diffused for deoxidation. The LF refining time is controlled at 40-60 minutes; 3) During the RH vacuum degassing stage, the adsorption of inclusions by refined slag is accelerated by mixing steel slag, and the time is controlled to be more than 15-30 minutes; 4) During continuous casting, the superheat of molten steel in the tundish is controlled within the range of 15-30℃; 5) The continuous casting billet is heated in a walking beam heating furnace. The billet temperature before entering the furnace shall not exceed 200°C, the preheating section temperature shall be controlled at 500-750°C, the heating section temperature shall be controlled at 1150-1250°C, the soaking section temperature shall be controlled at 1200-1260°C, and the total heating time shall be 3.5 hours or more; 6) The ingot is rolled after being descaled by high-pressure water. Before rolling, it is flame cleaned. The surface metal of the ingot is cleaned by high-pressure oxygen flame with a depth of 0.5 to 3 mm to remove surface cracks, subcutaneous inclusions and other defects of the ingot. The starting rolling temperature is 1050 to 1100 ° C, the final rolling temperature is above 950 ° C, and 12 two-roll rolling mills + 5 KOCKS three-roll rolling mills are used to ensure that the dimensional accuracy of the rolled material is controlled within ± 0.15 mm. 7) After rolling, the surface defects of the car skin are removed and polished. The depth of the car skin is 0.4-0.7mm. The product surface has zero decarburization and zero defects. The diameter deviation meets the h9 level requirements of GB / T 3207 standard to remove surface defects; 8) Ultrasonic testing meets the AAA level requirements of GB / T 4162, and the microscopic oxide inclusions are ≤1.0 level and the sulfide inclusions are ≤1.5 level according to GB / T 10561 standard.

4. The method for manufacturing round steel for high-pressure common rail diesel engine injector according to claim 3, characterized in that: In step (1), the amount of steel C is controlled within the range of 0.05-0.10% to prevent overoxidation of the primary molten steel. The amount of aluminum and iron added per 100t of molten steel is 100-400kg. The alloy containing Mn and Cr is added during the steel discharging process after the primary molten steel is completed. In order to melt the alloy completely, the steel discharging temperature is ≥1620°C.

5. The method for manufacturing round steel for high-pressure common rail diesel engine injector according to claim 3, characterized in that: During LF refining in step (2), samples are taken 2 or more times for rapid composition testing to achieve accurate control of all chemical compositions. The deviation of Mn, Cr and Ni between different heats is ≤0.05%, the deviation of C is ≤0.02%, and the deviation of Al, P and S is ≤0.01%. The hardenability bandwidth calculated according to the SEP 1664 formula is ≤4HRC.

6. The method for manufacturing round steel for high-pressure common rail diesel engine injector according to claim 3, characterized in that: In step (3), immediately after the air is broken, the carbonized rice husk is evenly spread on the surface of the molten steel to prevent secondary oxidation, and the silicon-calcium wire is fed to transform the solid phase inclusions into calcium-containing liquid phase inclusions, and the Ca content is controlled in the range of 0.005-0.0010%. Before the molten steel is continuously cast into billets, it needs to be left to stand for 20-40 minutes to ensure that the residual inclusions in the molten steel have sufficient time to float up and be removed.

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