Preparation method of lightweight high-strength fine grain steel piston

Abstract

The invention discloses a preparation process of a light-weight high-strength fine-grain steel piston, and belongs to the technical field of preparation of light-weight high-strength materials. According to the high-strength light-weight steel piston, 38MnVS6 steel is adopted as a finished product material, and the preparation method comprises the steps of sample upsetting and blank finish forging; carrying out friction welding treatment; performing multi-stage rapid heating and cooling heat treatment; and a tempering treatment process. The steel comprises the following chemical components in percentage by weight: 0.3 to 0.45 percent of C, 1.4 to 1.6 percent of Mn, 0.18 to 0.26 percent of Si, 0.01 to 0.015 percent of P, 0.04 to 0.05 percent of S, 0.12 to 0.2 percent of Cr, 0.08 to 0.1 percent of Cu, 0.018 to 0.026 percent of Al, 0.06 to 0.09 percent of V, 0.02 to 0.04 percent of La, 0.03 to 0.05 percent of Ce, 0.01 to 0.02 percent of Y and the balance of Fe. And finally, the lightweight piston with high tensile strength, yield strength, fatigue strength and the like is prepared, a workpiece of the lightweight piston can be used for a high-performance diesel engine or a ship engine, and the lightweight piston has a good industrial application prospect.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a light-weight high-strength fine-grain steel piston and belongs to the technical field of light-weight high-strength steel material preparation. BACKGROUND

[0002] 38MnVS6 steel is a kind of high-strength and high-toughness alloy structural steel, which has good hardenability, cutting performance and wear resistance. It is widely used in the fields of automobiles, mechanical manufacturing and aerospace, and is suitable for manufacturing high-load and high-precision parts; the manufacturing and processing technology of 38MnVS6 steel has always been a hot spot in the research of material science.

[0003] Chinese invention patent CN120332001A introduces a high-performance heterogeneous welded special-shaped combustion chamber piston and a preparation method thereof, in which a special-pot-shaped combustion chamber and an oil channel structure are directly formed through a rolling process, and the nitrogen protection friction welding technology is combined to realize the heterogeneous connection of the piston head and the skirt; thus, the weight of the material is reduced to a certain extent, but due to the long production cycle of the piston, the high cost and the difficulty in post-processing, the method is not conducive to actual application and production. SUMMARY

[0004] The application aims to provide a preparation method of a light-weight high-strength fine-grain steel piston, in which rare earth elements are added, and a required strong and tough texture is obtained through the cooperation of a friction welding technology, a multi-stage heat treatment and a tempering process, so that the grain size in the steel is greatly refined, and the overall comprehensive performance of the steel piston is improved; through multi-stage rapid heating and cooling heat treatment, the content of pearlite and ferrite structures in the material can be effectively reduced, and more sheet-shaped martensite and twinned martensite can be obtained, so that high strength and high hardness performance are obtained; the application of the steel piston material in the fields of high-performance diesel engines and marine engines is further expanded, and specifically includes the following steps: (1) a blank is initially prepared by using a pre-alloying method; (2) the upset treatment is performed on the forged blank of the piston head area in the upper part and the piston skirt area in the lower part of the steel piston in step (1); (3) the final forging treatment is performed on the steel piston forged blank obtained in step (2); (4) the friction welding treatment is performed on the steel piston obtained in step (3); (5) the multi-stage heat treatment and the tempering treatment are sequentially performed on the steel piston obtained in step (4).

[0005] Preferably, the chemical composition of the steel piston of the present application and the mass percentage thereof are as follows: C is 0.3-0.45%, Mn is 1.4-1.6%, Si is 0.18-0.26%, P is 0.01-0.015%, S is 0.04-0.05%, Cr is 0.12-0.2%, Cu is 0.08-0.1%, Al is 0.018-0.026%, V is 0.06-0.09%, La is 0.02-0.04%, Ce is 0.03-0.05%, Y is 0.01-0.02%, and the balance is Fe.

[0006] Preferably, the preheating temperature of the upsetting treatment in step (2) of the present application is 1150°C - 1250°C, and the preheating time is 0.5-1h.

[0007] Preferably, in step (3) of the present application, the final forging temperature is 850°C - 950°C, the holding time is 0.5-1h, and the final forging strain rate is 100-150s -1 .

[0008] Preferably, in step (4) of the present application, the flash of the outer circle of the weld is removed using a lathe to obtain a smooth appearance of the workpiece.

[0009] Preferably, in step (5) of the present application, the conditions of the multi-stage heat treatment are as follows: the first stage heating rate is 45-55°C / min, the solution temperature is 920°C, the holding time is 2h, and then water quenching; the second stage heating rate is 25-35°C / min, the solution temperature is 870°C, the holding time is 1h, and then water quenching; the third stage heating rate is 15-25°C / min, the solution temperature is 820°C, the holding time is 2h, and then water quenching.

[0010] Preferably, in step (5) of the present application, the forged piece after the three-stage quenching treatment is subjected to low-temperature tempering at a temperature of 550°C - 600°C for 1.5h, and then air-cooled to room temperature.

[0011] The beneficial effects of the present application are as follows: (1) The present application can form a dense oxide film on the surface of the steel by adding rare earth elements in the steel, which has good adhesion and stability, can effectively prevent the penetration of corrosive media such as oxygen and moisture into the steel, thereby improving the corrosion resistance of the steel; during the subsequent forging forming process, the melt can solidify more uniformly, forming finer and purer grain structures; after adding rare earth elements, the grain size is significantly reduced after forging, and the grain distribution is more uniform, reducing the stress concentration points between grains and improving the strength and toughness of the alloy.

[0012] (2) The present invention provides a better microstructure and phase transformation control capability for the alloy by adding rare earth elements, and the forging and pressing form the alloy to obtain a good shape and preliminary microstructure optimization. Heat treatment further improves the microstructure and performance of the alloy. The three synergistic effects make the alloy significantly improved in terms of strength, toughness, hardness, fatigue resistance and creep resistance. The purification effect of rare earth elements and the microstructure stability after heat treatment make the alloy better able to resist the adverse effects of corrosion, wear and high temperature oxidation during use. The good microstructure uniformity and residual stress elimination after forging and pressing also reduce stress concentration and crack initiation during use. The three synergistic effects greatly extend the service life of the alloy, reduce the material replacement cost, and improve the economy and reliability of the material.

[0013] (3) This invention reduces the content of pearlite and ferrite better through the synergistic effect of adding rare earth elements and heat treatment; rare earth elements can change the phase diagram of the alloy and affect the phase transformation process of the alloy during heat treatment; after adding rare earth elements to steel, the transformation temperature and transformation rate of austenite to pearlite or martensite can be changed; during heat treatment, by reasonably controlling the temperature and time, the phase transformation regulation effect of rare earth elements can be utilized to obtain the desired microstructure; after adding rare earth elements to steel, finer martensite and dispersed carbides can be obtained during heat treatment, thereby improving the hardness and wear resistance of steel.

[0014] (4) The preparation method of the present invention has strong controllability and relatively simple process, making it suitable for industrial promotion and application. Attached Figure Description

[0015] Figure 1 This is a cross-sectional view of the lightweight high-strength steel piston of the present invention, (a) is the piston head and (b) is the piston skirt.

[0016] Figure 2 This is a flowchart of the heat treatment process for the lightweight high-strength steel piston of the present invention. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0018] Example 1 The lightweight, high-strength fine-grained steel piston of this invention has the following chemical composition by weight percentage: C 0.37%, Mn 1.43%, Si 0.21%, P 0.012%, S 0.042%, Cr 0.15%, Cu 0.08%, Al 0.021%, V 0.08%, La 0.03%, Ce 0.05%, Y 0.01%, with the balance being Fe.

[0019] The method for preparing the lightweight, high-strength, fine-grained steel piston described in this embodiment specifically includes the following steps: (1) Use a plasma melting furnace to melt the steel according to the composition in Table 1. At the same time, add rare earth alloys according to the required composition ratio, introduce protective gas argon, the gas flow rate is 20 L / min, the melting temperature is 1750℃, and after melting, turn off the plasma furnace and let the metal cool naturally in the crucible.

[0020] (2) The billet obtained in step (1) is placed in a hot forging press for upsetting. The preheating temperature is 1150°C and the preheating time is 1h. The heated billet is taken out of the furnace, the billet is upset, the metal volume is initially distributed, and the oxide scale on the surface of the billet is broken.

[0021] (3) Perform final forging on the steel piston forging billet in step (2); hold the forging billet at 850°C for 0.5 hours, and then perform final forging on the upset billet. The strain rate of the forging is 120s. -1 This process then forms the final shape of the piston.

[0022] (4) The steel piston forging in step (3) is subjected to friction welding; then the flash of the outer ring of the weld is removed by a lathe at a speed of 2000 rpm, thereby obtaining a smooth workpiece appearance.

[0023] (5) The steel piston in step (4) is placed in a discharge plasma sintering furnace for multi-stage heat treatment: the first stage has a heating rate of 45-55℃ / min, a solution temperature of 920℃, a holding time of 2 hours, and is rapidly cooled by running water; the second stage has a heating rate of 25-35℃ / min, a solution temperature of 870℃, a holding time of 2 hours, and is rapidly cooled by running water; the third stage has a heating rate of 15-25℃ / min, a solution temperature of 820℃, a holding time of 2 hours, and is rapidly cooled by running water.

[0024] (6) The steel piston sample was taken out from the spark plasma sintering furnace and air-cooled to 550°C. Then the alloy sample was placed in the heating furnace and kept at the temperature for 1.5h. After that, the alloy sample was taken out and air-cooled to room temperature to obtain the finished steel piston part. The yield strength of the steel was measured to be 890.8MPa, the tensile strength was 995.6MPa, and the elongation was 13.4%.

[0025] Example 2 The lightweight, high-strength fine-grained steel piston of this invention has the following chemical composition by weight percentage: C 0.42%, Mn 1.45%, Si 0.24%, P 0.015%, S 0.044%, Cr 0.13%, Cu 0.09%, Al 0.023%, V 0.08%, La 0.02%, Ce 0.04%, Y 0.02%, with the balance being Fe.

[0026] The method for preparing the lightweight, high-strength, fine-grained steel piston described in this embodiment specifically includes the following steps: (1) Use a plasma melting furnace to melt the steel according to the composition in Table 1. At the same time, add rare earth alloys according to the required composition ratio, introduce protective gas argon, the gas flow rate is 20 L / min, the melting temperature is 1750℃, and after melting, turn off the plasma furnace and let the metal cool naturally in the crucible.

[0027] (2) The billet obtained in step (1) is placed in a hot forging press for upsetting; the preheating temperature is 1150°C and the preheating time is 1h. The heated billet is taken out of the furnace, the billet is upset, the metal volume is initially distributed, and the oxide scale on the surface of the billet is broken.

[0028] (3) Perform final forging on the steel piston forging billet in step (2); hold the forging billet at 850°C for 0.5 hours, and then perform final forging on the upset billet. The strain rate of the forging is 100s. -1 This process then forms the final shape of the piston.

[0029] (4) The steel piston forging in step (3) is subjected to friction welding; then the flash of the outer ring of the weld is removed by a lathe at a speed of 2000 rpm, thereby obtaining a smooth workpiece appearance.

[0030] (5) The steel piston in step (4) is placed in a discharge plasma sintering furnace for multi-stage heat treatment: the first stage has a heating rate of 45℃ / min, a solution temperature of 920℃, a holding time of 2 hours, and is rapidly cooled by running water; the second stage has a heating rate of 25℃ / min, a solution temperature of 870℃, a holding time of 2 hours, and is rapidly cooled by running water; the third stage has a heating rate of 15℃ / min, a solution temperature of 820℃, a holding time of 2 hours, and is rapidly cooled by running water.

[0031] (6) The steel piston sample was removed from the spark plasma sintering furnace and air-cooled to 550°C. Then, the alloy sample was placed in a heating furnace and held for 1.5 hours. After that, the alloy sample was removed and air-cooled to room temperature to obtain the finished steel piston part. The yield strength of the steel was measured to be 884.2 MPa, the tensile strength to be 1013.2 MPa, and the elongation to be 14.2%.

[0032] Example 3 The lightweight, high-strength fine-grained steel piston of this invention has the following chemical composition by weight percentage: C 0.31%, Mn 1.52%, Si 0.26%, P 0.014%, S 0.048%, Cr 0.18%, Cu 0.1%, Al 0.02%, V 0.09%, La 0.03%, Ce 0.03%, Y 0.02%, with the balance being Fe.

[0033] The method for preparing the lightweight, high-strength, fine-grained steel piston described in this embodiment specifically includes the following steps: (1) Use a plasma melting furnace to melt the steel according to the composition in Table 1. At the same time, add rare earth alloys according to the required composition ratio and introduce protective gas argon. The gas flow rate is 20 L / min and the melting temperature is 1750℃. After melting, turn off the plasma furnace and let the metal cool naturally in the crucible.

[0034] (2) The billet obtained in step (1) is placed in a hot forging press for upsetting. The preheating temperature is 1150°C and the preheating time is 1h. The heated billet is taken out of the furnace, the billet is upset, the metal volume is initially distributed, and the oxide scale on the surface of the billet is broken.

[0035] (3) Perform final forging on the steel piston forging billet in step (2); hold the forging billet at 850°C for 0.5 hours, and then perform final forging on the upset billet. The strain rate of the forging is 150 s. -1 This process then forms the final shape of the piston.

[0036] (4) The steel piston forging in step (3) is subjected to friction welding; then the flash of the outer ring of the weld is removed by a lathe at a speed of 2000 rpm, thereby obtaining a smooth workpiece appearance.

[0037] (5) The steel piston in step (4) is placed in a discharge plasma sintering furnace for multi-stage heat treatment: the first stage has a heating rate of 55℃ / min, a solution temperature of 920℃, a holding time of 2 hours, and is rapidly cooled by running water; the second stage has a heating rate of 35℃ / min, a solution temperature of 870℃, a holding time of 2 hours, and is rapidly cooled by running water; the third stage has a heating rate of 25℃ / min, a solution temperature of 820℃, a holding time of 2 hours, and is rapidly cooled by running water.

[0038] (6) The steel piston sample was taken out from the spark plasma sintering furnace and air-cooled to 550°C. Then the alloy sample was placed in the heating furnace and kept at the temperature for 1.5h. After that, the alloy sample was taken out and air-cooled to room temperature to obtain the finished steel piston part. The yield strength of the steel was measured to be 902.3MPa, the tensile strength was 1024.4MPa, and the elongation was 12.5%.

[0039] Comparative Example 1 The heat treatment process for the lightweight, high-strength fine-grained steel piston described in this embodiment is the same as that in Embodiment 1, except that rare earth elements (La, Ce, and Y) are not added.

[0040] The measured yield strength of the alloy was 786.5 MPa, the tensile strength was 812.6 MPa, and the elongation was 10.3%.

[0041] The comparison shows that the strength of 38MnVS6 steel is significantly reduced. This may be because the solid solution of rare earth elements in the alloy can increase the resistance to dislocation movement, thereby increasing the strength of the material. When rare earth elements are not added, this solid solution strengthening effect may be weakened.

[0042] Comparative Example 2 The heat treatment process for the lightweight, high-strength, fine-grained steel piston described in this embodiment is the same as that in Embodiment 1, except that... The key is that only 0.01% La and 0.02% Ce are added for rare earth elements.

[0043] The measured yield strength of the alloy was 812.3 MPa, the tensile strength was 876.3 MPa, and the elongation was 11.2%.

[0044] The comparison shows that rare earth elements La and Ce have little effect on the strength improvement of 38MnVS6 steel. The reason may be that rare earth elements La and Ce can act as grain refiners in steel, promoting the uniform refinement of grains. La and Ce elements usually have low solid solubility in alloys, and they tend to form compounds or accumulate near grain boundaries, thereby reducing the strength of the alloy.

[0045] Comparative Example 3 The heat treatment process of the lightweight high-strength fine-grained steel piston described in this embodiment is the same as that in Embodiment 1, except that: the heat treatment in step 5 is replaced with conventional heat treatment; the solution temperature is 850℃, held for 3 hours, and then quenched; the tempering temperature is 650℃, held for 1.5 hours, and then air-cooled to room temperature.

[0046] The measured yield strength of the alloy was 776.3 MPa, the tensile strength was 803.2 MPa, and the elongation was 9.6%.

[0047] The comparison shows that conventional heat treatment has a relatively small effect on improving the strength of steel. Due to the versatility of the process, conventional heat treatment has limited effect on improving the performance of alloys and is difficult to meet the needs of high-end applications. Special heat treatment, through precise control of process parameters, can obtain a more uniform microstructure. Special heat treatment processes are designed according to the specific composition and performance requirements of the alloy. The process of combining solution treatment and tempering can give full play to the strengthening mechanism of the alloy and obtain high strength and high oxidation resistance.

[0048] Table 1 Performance Comparison Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a lightweight, high-strength, fine-grained steel piston, characterized in that: Specifically, the following steps are included: (1) The billet was initially prepared by pre-alloying method; (2) Upsetting the forgings of the piston head area at the top and the piston skirt area at the bottom of the steel piston in step (1); (3) Perform final forging on the steel piston forging billet obtained in step (2); (4) The steel piston parts obtained in step (3) are subjected to friction welding. (5) The steel piston obtained in step (4) is subjected to multi-stage heat treatment and tempering treatment in sequence.

2. The method for preparing the lightweight, high-strength, fine-grained steel piston according to claim 1, characterized in that: The chemical composition and mass percentage of the steel piston are as follows: C 0.3-0.45%, Mn 1.4-1.6%, Si 0.18-0.26%, P 0.01-0.015%, S 0.04-0.05%, Cr 0.12-0.2%, Cu 0.08-0.1%, Al 0.018-0.026%, V 0.06-0.09%, La 0.02-0.04%, Ce 0.03-0.05%, Y 0.01-0.02%, balance Fe.

3. The method for preparing the lightweight, high-strength, fine-grained steel piston according to claim 1, characterized in that: In step (2), the preheating temperature for upsetting is 1150°C - 1250°C, and the preheating time is 0.5-1h.

4. The method for preparing the lightweight, high-strength, fine-grained steel piston according to claim 1, characterized in that: In step (3), the final forging temperature is 850°C - 950°C, the holding time is 0.5-1h, and the final forging strain rate is 100-150s. -1 .

5. The method for preparing the lightweight, high-strength, fine-grained steel piston according to claim 1, characterized in that: In step (5), the conditions for multi-stage heat treatment are as follows: the first stage has a heating rate of 45-55℃ / min, a solution temperature of 920℃, a holding time of 2h, and then water quenching; the second stage has a heating rate of 25-35℃ / min, a solution temperature of 870℃, a holding time of 1h, and then water quenching; the third stage has a heating rate of 15-25℃ / min, a solution temperature of 820℃, a holding time of 2h, and then water quenching.

6. The method for preparing the lightweight, high-strength, fine-grained steel piston according to claim 1, characterized in that: In step (5), the forgings after the three-stage quenching treatment are subjected to low-temperature tempering at a temperature of 550°C - 600°C, held for 1.5 hours, and then air-cooled to room temperature.

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