High-impact-toughness non-quenched and tempered steel crankshaft and process

Abstract

The application discloses a high-impact-toughness non-quenched and tempered steel crankshaft and a process, and solves the problem that the chemical components of the non-quenched and tempered steel crankshaft are not reasonably set in the prior art, which influences the impact toughness of the crankshaft, has the beneficial effect of guaranteeing the forged crankshaft to have excellent strength and high toughness, and specifically has the following technical scheme: a high-impact-toughness non-quenched and tempered steel crankshaft, the mass percentage of the chemical components of the crankshaft is as follows: C 0.36-0.50%, Si 0.24-0.61%, Mn 1.24-1.86%, V 0.08-0.25%, and P and S are less than 0.1%.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of engine crankshafts, in particular to a high-impact-toughness non-quenched and tempered steel crankshaft and process. BACKGROUND

[0002] The statements in this section merely provide background information related to the present application and do not necessarily constitute the prior art.

[0003] Micro-alloyed non-quenched and tempered steel can achieve the performance of quenched and tempered steel after controlled rolling and controlled cooling or controlled forging and controlled cooling, simplifying the process and reducing energy consumption, and is widely used in the petroleum, automobile, machinery and other industries, such as engine crankshafts, connecting rods and other parts. Ferrite-pearlite type non-quenched and tempered steel is a micro-alloyed non-quenched and tempered steel that has been researched and developed for a long time. However, such non-quenched and tempered steel is prone to pro-eutectoid ferrite precipitation along the original austenite grain boundary, resulting in coarse ferrite-pearlite structure, and compared with quenched and tempered steel, it has the problem of excessive strength and insufficient toughness.

[0004] As a moving part, the crankshaft bears periodic bending moment force when the engine is working, and good strength and toughness matching can maximize its fatigue resistance. However, the chemical composition of the existing non-quenched and tempered steel crankshaft is not reasonable, resulting in coarse ferrite-pearlite structure, thereby affecting the impact toughness of the crankshaft.

[0005] In the prior art, the crankshaft is prone to the following problems during forging:

[0006] The final forging temperature is high, which leads to the mixed crystal phenomenon of the crankshaft during forging, and increases the crack tendency;

[0007] The cooling method after forging directly uses air cooling or air cooling, and the cooling speed is low, which leads to the appearance of pro-eutectoid ferrite along the grain boundary in the matrix structure, greatly destroying the continuity of the intragranular ferrite-pearlite structure, and reducing the toughness of the material. SUMMARY

[0008] In view of the deficiencies in the prior art, the purpose of the present application is to provide a high-impact-toughness non-quenched and tempered steel crankshaft, which has a reasonable chemical composition and a low final forging temperature to refine the grain size after austenite deformation recrystallization, thereby directly improving the impact toughness.

[0009] In order to achieve the above-mentioned purpose, the present application is realized by the following technical scheme:

[0010] In the first aspect, the present application provides a high impact toughness non-quenched and tempered steel crankshaft, the chemical composition of the crankshaft is as follows: C 0.36-0.50%, Si 0.24-0.61%, Mn 1.24-1.86%, V 0.08-0.25%, P and S 0.1% or less. The chemical composition of the steel is selected according to the performance requirements of the material in use.

[0011] In the design of the high impact toughness non-quenched and tempered steel crankshaft, the following factors are considered: 1) tensile strength and hardness: the content of C, Si, Mn and other elements is selected to ensure that the crankshaft will not produce plastic deformation or damage under load. 2) impact toughness: the content of carbon and other suitable alloying elements is selected to improve the impact toughness of the crankshaft. 3) wear resistance: the steel is adjusted within the appropriate content range of Mn and other elements to improve the wear resistance of the crankshaft. 4) fatigue resistance: the quality and composition of the steel have a great influence on the fatigue resistance of the crankshaft, so the chemical composition selection needs to consider the stress cycle fatigue life of the crankshaft to prevent early failure. 5) easy processability: the composition content selection also needs to consider the processability of the steel to facilitate mass production. Based on the above factors, the content range of C, Si, Mn, V, P, S and other elements is selected to ensure that the crankshaft has high impact toughness, excellent mechanical properties and wear resistance, while ensuring the processability and fatigue resistance of the crankshaft.

[0012] In the non-quenched and tempered steel, carbon is one of the most important elements, and the content is usually between 0.25%-0.65%; with the increase of C content, the hardness and strength of the steel increase, but the toughness and plasticity decrease. Within a certain range, appropriately increasing the carbon content can increase the strength and plasticity at the same time, and achieve better comprehensive performance. The content of C in the chemical composition in the application is moderate. The Si content in the non-quenched and tempered steel is usually between 0.15%-0.40%, and the Si element can form a solid solution with iron atoms, and through processes such as extrusion, fracture and movement, the binding ability of the grain boundary is enhanced, thereby improving the strength and hardness of the steel. The Si composition in the application ensures the strength of the crankshaft. Mn is one of the important elements affecting the pearlite phase change, and the content is usually between 0.20%-1.50%, and the purpose of designing the Mn content is to control the pearlite. Generally, with the increase of the Mn content, the solid solubility of carbon, chromium and other elements can be promoted, the formation of recrystallization nucleus is reduced, the generation and growth of austenite is inhibited, which is beneficial to the formation and stability of fine pearlite, and the toughness of the crankshaft is improved. Adding an appropriate amount of manganese can also promote grain refinement, form a more uniform microstructure, and improve the toughness of the crankshaft. At the same time, manganese can also reduce the sulfur content in the steel, reduce the brittleness of the crankshaft, and further improve the toughness of the crankshaft. The content of vanadium V is usually between 0.05%-0.20%, and the vanadium element can form block, point or rod-shaped carbides with carbon and other elements, thereby improving the strength and hardness of the crankshaft. In addition, vanadium can effectively refine the grains of the crankshaft, improve the uniformity of its microstructure, and reduce the number and size of its internal defects, thereby improving the tensile strength, yield strength and impact toughness of the crankshaft. In the application, a high vanadium V content is designed, and the main purpose is that the VC (vanadium carbide) particles are partially insoluble in austenite, and the austenite growth is inhibited.

[0013] In a second aspect, the application provides a forging process of a non-quenched and tempered steel crankshaft with high impact toughness, comprising the following contents:

[0014] The non-quenched and tempered steel material is placed in a heating furnace for heating, and the heating time is set;

[0015] After the heating time is set, the heated material is taken out of the heating furnace, and pre-forging and finish-forging are performed;

[0016] After the finish-forging is completed, the material after the finish-forging is controlled to cool until room temperature;

[0017] Pre-forging temperature is higher than finish-forging temperature, and lower finish-forging temperature makes the grains of austenite after deformation recrystallization refined, directly improving the impact performance of the crankshaft.

[0018] The forging process of the non-quenched and tempered steel crankshaft with high impact toughness as described above, wherein the non-quenched and tempered steel material is a vanadium-containing micro-alloy non-quenched and tempered steel.

[0019] The forging process of the high impact toughness non-quenched and tempered steel crankshaft as described above, the chemical composition of the non-quenched and tempered steel material is as follows: C 0.36-0.50%, Si 0.24-0.61%, Mn 1.24-1.86%, V 0.08-0.25%, P and S 0.1% or less.

[0020] The forging process of the high impact toughness non-quenched and tempered steel crankshaft as described above, the non-quenched and tempered steel material is heated in a heating furnace, and the heating temperature is 1130-1220℃.

[0021] The forging process of the high impact toughness non-quenched and tempered steel crankshaft as described above, the non-quenched and tempered steel material is heated in a heating furnace, and the heating time is 60-180min.

[0022] The forging process of the high impact toughness non-quenched and tempered steel crankshaft as described above, the temperature of the pre-forging is greater than 1050℃.

[0023] The forging process of the high impact toughness non-quenched and tempered steel crankshaft as described above, the temperature range of the finish forging is 820℃≤T≤880℃; during the finish forging, 820℃ is the temperature at which the austenite begins to transform into pearlite, and 880℃ is the recrystallization temperature, the pre-forging and the finish forging are combined, the finish forging temperature is low, which can effectively recrystallize the austenite and form a flat austenite grain structure, so that when the phase changes into ferrite, the ferrite structure is significantly refined; and the finish forging temperature is in the ferrite transformation temperature range, which promotes the formation of fine ferrite and changes the precipitation tendency of proeutectoid ferrite at the grain boundary, which is beneficial to improve the strength and toughness of the crankshaft.

[0024] The forging process of the high impact toughness non-quenched and tempered steel crankshaft as described above, the controlled cooling of the material after the finish forging until room temperature includes the following:

[0025] Air cooling the material after the finish forging to the pearlite transformation temperature range;

[0026] Air cooling the material to 480-520℃;

[0027] Air cooling the material until room temperature, thereby air cooling, then air cooling, and finally air cooling the material after the finish forging, through multiple stages of cooling, rather than direct air cooling or air cooling, effectively ensuring the cooling rate and avoiding the appearance of proeutectoid ferrite along the grain boundary in the matrix structure, further ensuring the toughness of the material.

[0028] The forging process of the high impact toughness non-quenched and tempered steel crankshaft as described above, the air cooling of the material is to 500℃.

[0029] The beneficial effects of the present application are as follows:

[0030] 1) The present application proposes the chemical composition of the crankshaft, and the mass percentage of each main component is properly matched, so that the forged crankshaft has excellent strength and high toughness, and the impact performance of the crankshaft is ensured.

[0031] 2) In the forging process, the temperature of the pre-forging is higher than that of the final forging, so that there are more dislocations in the deformed austenite, the grain of the recrystallized austenite is refined, the mixed crystal phenomenon is avoided, the crack tendency is reduced, and the impact toughness of the crankshaft is directly improved.

[0032] 3) The final forging temperature is set to 820℃≤T≤880℃, 820℃ is the temperature at which austenite begins to transform into pearlite, and the fast cooling in the pearlite temperature transformation region promotes the reduction of the pearlite layer spacing; the final forging temperature is in the ferrite transformation temperature region, which changes the precipitation tendency of proeutectoid ferrite at the grain boundary, and is beneficial to improve the strength and toughness of the crankshaft.

[0033] 4) After final forging, through multi-stage controlled cooling, the cooling speed can be adjusted, the phase change behavior of the supercooled austenite is further controlled, and the final organization of fine ferrite + fine lamellar pearlite is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0034] The drawings accompanying the specification of the present application form a part thereof and serve to provide further understanding of the present application, the exemplary embodiments of the present application and its description are used to explain the present application, and do not constitute improper limitation on the present application.

[0035] Figure 1 is a metallographic structure schematic diagram of a high-impact toughness non-quenched and tempered steel crankshaft according to one or more embodiments of the present application.

[0036] In the figure: the mutual distance or size is exaggerated to show the position of each part, and the schematic diagram is only schematic. DETAILED DESCRIPTION

[0037] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise indicated, all technical and scientific terms used in the present application have the same meaning as generally understood by those skilled in the art to which the present application belongs.

[0038] It should be noted that the terms used herein are only for the purpose of describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless otherwise explicitly indicated by the present application, the singular form is also intended to include the plural form, and in addition, it should be understood that when the terms "comprise" and / or "include" are used in the present specification, they mean the presence of a feature, step, operation, device, component and / or combination thereof;

[0039] As introduced in the background technology, there is a problem in the prior art that the unreasonable setting of the chemical components of non-quenched and tempered steel crankshafts affects the impact toughness of the crankshafts. In order to solve the above technical problems, the present invention proposes a non-quenched and tempered steel crankshaft with high impact toughness.

[0040] Example 1

[0041] In a typical embodiment of the present invention, a high impact toughness non-quenched and tempered steel crankshaft has the following chemical composition by weight percentage: carbon C 0.36-0.50%, silicon Si 0.24-0.61%, manganese Mn 1.24-1.86%, vanadium V0.08-0.25%, phosphorus P, and sulfur S less than 0.1%.

[0042] In some examples, the crankshaft's chemical composition by weight is: carbon (C) 0.36%, silicon (Si) 0.24%, manganese (Mn) 1.24%, vanadium (V) 0.08%, phosphorus (P) 0.07%, and sulfur (S) 0.05%. This composition provides high impact toughness for the crankshaft, but average strength and wear resistance, meeting operational requirements.

[0043] In another example, the crankshaft's chemical composition by weight is: carbon (C) 0.45%, silicon (Si) 0.40%, manganese (Mn) 1.50%, vanadium (V) 0.12%, phosphorus (P) 0.05%, and sulfur (S) 0.03%. This crankshaft has improved strength and wear resistance while still maintaining high impact toughness.

[0044] In other examples, the crankshaft's chemical composition by weight is: carbon (C) 0.50%, silicon (Si) 0.61%, manganese (Mn) 1.86%, vanadium (V) 0.25%, phosphorus (P) 0.03%, and sulfur (S) 0.02%. This crankshaft exhibits further improved strength and wear resistance while maintaining excellent impact toughness, making it suitable for applications requiring high strength and wear resistance.

[0045] Specifically, a carbon content between 0.36% and 0.50% ensures the crankshaft's hardness and strength. A silicon content between 0.24% and 0.61% synergizes with carbon to improve the material's strength, toughness, and impact toughness, while also enhancing the toughness of the crankshaft's internal grain boundaries. A manganese content between 1.24% and 1.86% provides excellent fatigue resistance and hardenability, improving the crankshaft's wear resistance and strength. A vanadium content between 0.08% and 0.25% enhances the crankshaft's hardness and toughness, while also improving its stability at high temperatures and resisting high-temperature creep. Meanwhile, phosphorus and sulfur contents should be controlled below 0.1%, minimizing the loss of fatigue strength and toughness, thereby effectively extending the crankshaft's service life. Therefore, this composition range addresses the various requirements of the crankshaft, ensuring its durability and reliability.

[0046] Example 2

[0047] This embodiment provides a forging process for a non-quenched and tempered steel crankshaft with high impact toughness, including the following contents:

[0048] Place the non-quenched and tempered steel material (bar) in a heating furnace and heat it for a set time;

[0049] After heating for the set time, the heated material is taken out of the heating furnace and subjected to pre-forging and final forging;

[0050] After the final forging is completed, the material is cooled to room temperature;

[0051] Among them, the temperature of pre-forging is higher than the temperature of final forging. The lower final forging temperature refines the grains after austenite deformation and recrystallization, directly improving the impact toughness of the final non-quenched and tempered steel and meeting the use requirements of the crankshaft.

[0052] Specifically, the non-quenched and tempered steel material is vanadium-containing microalloyed non-quenched and tempered steel.

[0053] In this embodiment, the chemical composition of the non-quenched and tempered steel material is as follows: C 0.36-0.50%, Si 0.24-0.61%, Mn 1.24-1.86%, V 0.08-0.25%, and P and S 0.1% or less. The C content is moderate, the Si content ensures the strength of the crankshaft, and the Mn content reduces the content of the eutectoid component C in the crankshaft, which is beneficial to increasing the amount of pearlite. Overall, the amount of ferrite is reduced, and the amount of pearlite is increased, which is beneficial to improving the impact toughness of the crankshaft.

[0054] Regarding the heating temperature and heating time, the non-quenched and tempered steel material is placed in a heating furnace (electric furnace) and heated at a temperature of 1130-1220°C; the quenched and tempered steel material is placed in a heating furnace and heated for 60-180 minutes.

[0055] In addition, the pre-forging temperature is greater than 1050℃; the final forging temperature range is 820℃≤T≤880℃; during the final forging process, 820℃ is the temperature at which austenite begins to transform into pearlite, and 880℃ is the recrystallization temperature. The combination of pre-forging and final forging, with a lower final forging temperature, can avoid cracks in the crankshaft during forging; and the final forging temperature is in the ferrite transformation temperature region, which promotes the formation of fine ferrite and changes the precipitation tendency of proeutectoid ferrite at the grain boundaries, which is beneficial to improving the strength and toughness of the crankshaft.

[0056] In addition, the controlled cooling of the material after final forging to room temperature includes the following:

[0057] The material after finish forging is air-cooled to pearlite transformation temperature region, specifically to 780-820℃, and the fast cooling in the pearlite transformation temperature region promotes the reduction of pearlite lamellar spacing;

[0058] The material is air-cooled to 480-520℃.

[0059] The material is air-cooled to room temperature, so that the material after finish forging is first air-cooled, then air-cooled, and finally air-cooled, through multiple stages of cooling, rather than direct air-cooling or air-cooling, effectively ensuring the cooling rate, avoiding the appearance of pro-eutectoid ferrite along the grain boundary in the matrix structure, further controlling the phase transformation behavior of the undercooled austenite, obtaining the final structure of fine ferrite + fine lamellar pearlite, and ensuring the toughness of the material.

[0060] In the above cooling process, the material is air-cooled to 500℃.

[0061] As a ferrite-pearlite type non-quenched and tempered steel, the factors that determine its strength and toughness include grain size, pearlite lamellar spacing, ferrite morphology and distribution; the process provided in the embodiment increases the temperature of pre-forging higher than that of finish forging, deforms austenite, and makes the deformed austenite have more dislocations, forming smaller grains in the subsequent recrystallization process, directly improving the impact toughness of the crankshaft; the finish forging temperature is in the ferrite transformation temperature region, promoting the formation of fine ferrite and changing the precipitation tendency of pro-eutectoid ferrite at the grain boundary; through multi-stage controlled cooling, the cooling rate is adjusted to control the phase transformation behavior of the undercooled austenite, and the final structure of fine ferrite + fine lamellar pearlite is obtained.

[0062] Specifically, in some examples, the non-quenched and tempered steel material (bar) is placed in a heating furnace for heating, the heating temperature is 1200℃, the heating time is 120min, the finish forging temperature is 840℃, and in the controlled cooling process, the material after finish forging is air-cooled to 800℃, then air-cooled to 500℃, and finally air-cooled to room temperature. The transverse impact and tensile samples of the crankshaft have a tensile strength of 985MPa, an impact energy of 17J, a hardness of 320HV, and a metallographic structure as shown in Figure 1 From the metallographic structure as shown in Figure 1 From the metallographic structure as shown in

[0063] 1) Uniform distribution of pearlite: pearlite has a certain hardness and brittleness, but at the same time it can also elastically deform when subjected to impact load, thereby absorbing part of the energy. Therefore, uniform and discontinuous distribution of pearlite can effectively buffer and absorb impact load, improving the impact resistance of the crankshaft.

[0064] 2) The ferrite is distributed reasonably: the ferrite is more flexible than the pearlite, and has higher ductility and deformation capacity. Therefore, the ferrite in the structure is distributed reasonably in the pearlite, which can play a role in buffering and absorbing impact load, and improve the impact resistance and toughness of the crankshaft.

[0065] 3) The size of the pearlite is small: the smaller the size of the pearlite, the closer the distance between the particles, and the greater the interface force, and the stronger the ability to resist micro-cracks. Therefore, the small size of the pearlite has a certain promoting effect on the impact toughness of the crankshaft.

[0066] 4) The content of carbide is moderate: the metallographic structure contains a certain amount of Fe3C carbide, which can limit and prevent the expansion of the cracks generated when the pearlite deforms, thereby improving the toughness and impact load resistance of the crankshaft.

[0067] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A high-impact-toughness non-quenched and tempered steel crankshaft, characterized by, The chemical composition of the crankshaft has the following mass percentage: C 0.36-0.50%, Si 0.24-0.61%, Mn 1.24-1.86%, V 0.08-0.25%, P less than 0.1%, S less than 0.1%, and the balance of Fe; The forging process of the high-impact toughness non-quenched and tempered steel crankshaft comprises the following steps: The non-quenched and tempered steel material is placed in a heating furnace for heating, and the heating time is 60-180 min; The heated material is taken out from the heating furnace and subjected to pre-forging and finish-forging; The temperature range of the finish-forging is 820℃≤T≤880℃; during the finish-forging, 820℃ is the temperature at which austenite starts to transform into pearlite, and 880℃ is the recrystallization temperature; After the finish-forging, the material after the finish-forging is subjected to controlled cooling until room temperature; The controlled cooling of the material after the finish-forging until room temperature comprises the following steps: The material after the finish-forging is subjected to air cooling until the pearlite transformation temperature range; Then, air cooling is performed until 480-520℃; Finally, air cooling is performed until room temperature.

2. The high-impact-toughness non-quenched tempered steel crankshaft according to claim 1, characterized in that, The chemical composition of the non-quenched and tempered steel material has the following mass percentage: C 0.36-0.50%, Si 0.24-0.61%, Mn 1.24-1.86%, V 0.08-0.25%, P less than 0.1%, S less than 0.1%, and the balance of Fe.

3. The high-impact-toughness non-quenched tempered steel crankshaft according to claim 1, wherein The non-quenched and tempered steel material is placed in a heating furnace for heating, and the heating temperature is 1130-1220℃.

4. The high-impact-toughness non-quenched tempered steel crankshaft of claim 1, wherein The temperature of the pre-forging is greater than 1050℃.

5. The high-impact-toughness non-quenched tempered steel crankshaft of claim 1, wherein The air cooling is performed until 500℃.

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