Casting method of copper-steel bimetallic cylinder body

Abstract

The invention provides a casting method of a copper-steel double-metal cylinder body, and belongs to the technical field of pump body part machining, the casting method comprises the following steps: pre-treating a steel substrate and a copper alloy, and then heating and preserving heat together; cooling is conducted, cooling is conducted in four stages, the blowing direction of the first stage cooling, the blowing direction of the third stage cooling and the blowing direction of the fourth stage cooling are all from bottom to top, the blowing direction of the second stage cooling is from top to bottom, and solidification of the molten copper is completed after the third stage cooling; and after cooling is completed, tempering treatment is conducted, and the copper-steel double-alloy cylinder body is obtained. In the cylinder body casting process, the heated cylinder body is subjected to multi-stage cooling, the gas blowing directions of different cooling stages are controlled, rapid solidification of molten copper can be achieved, the situation that the molten copper fluctuates is avoided, the solidification defect is effectively controlled, and a compact copper layer is obtained; and through the final-stage cooling and tempering process control, the matrix structure of the steel matrix is regulated and controlled, tempered sorbite is formed, and the mechanical property of the cylinder body is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of pump body part processing, and relates to a melting and casting method for a copper-steel bimetallic cylinder block. Background Art

[0002] As one of the most widely used metal materials at present, steel can form different types of composite materials when combined with different materials. For example, the combination of steel and copper and copper alloys can obtain copper-steel composite materials. Based on the properties of steel materials, it also has the ductility, antifriction property, electrical conductivity, and thermal conductivity of copper itself. The two complement each other and have good application prospects. Copper-steel bimetallic composite materials can be widely used in wear-resistant and impact-resistant application scenarios due to their unique material characteristics. A typical application scenario is for hydraulic cylinder blocks. As one of the key core parts of a piston pump, the performance and quality of the cylinder block will directly affect the transmission efficiency and service life of the piston pump.

[0003] At present, one of the common methods for producing copper-steel bimetallic cylinder blocks is the melting and casting method. Utilizing the melting point difference between copper and steel, with steel materials as the matrix, copper is cladded on the surface of the steel matrix. During operation, a melting pool groove needs to be processed first, and then the copper alloy is placed in the melting pool groove. The workpiece is placed in a sintering furnace and heated. After the copper alloy melts, it spreads on the surface of the steel matrix and forms a bimetallic cylinder block after cooling. It has the advantages of high production efficiency and low production cost. According to the processing process of the copper-steel bimetallic cylinder block, the volume of the steel matrix is much larger than that of the copper layer. During the solidification process, the copper liquid at the copper-steel interface is affected by the heat of the steel matrix, resulting in slow solidification of the copper liquid and poor compactness, and defects such as pores and looseness are likely to occur at the interface. In addition, the matrix structure of the cylinder block after the traditional melting and casting process is pearlite-ferrite, and its performance cannot meet the requirements of future high-pressure hydraulic systems.

[0004] CN 110434315A discloses a heating and cooling method for melting and casting a steel-copper bimetallic cylinder block. The method includes steps such as surface treatment of the steel matrix for melting and casting, preheating, staged heating, variable-speed cooling, and auxiliary crystallization. After the surface treatment of the steel matrix for melting and casting, the copper alloy is placed at the copper water tank, a capping device is installed, and then it is sent to the preheating zone of the melting furnace. After preheating, it is moved to the heating zone for staged heating and heat preservation, and finally variable-speed cooling is carried out. The variable-speed cooling is divided into cooling methods such as rapid cooling, medium-speed cooling, and slow cooling through different cooling media or combinations. The focus of this patent is to install a cap to form a temperature gradient for the copper liquid, so that the solidification of the copper liquid occurs preferentially at the interface, eliminating solidification defects. However, during cooling, the cooling medium needs to act on the steel matrix part, and the heat needs to be conducted to the copper layer, resulting in a slow cooling speed, unable to achieve the purpose of rapid solidification, and easily causing a decrease in the density of the copper layer and poor consistency of the melting and casting quality.

[0005] CN 119140794 A discloses a method for preparing a cast cylinder block and a cast cylinder block. The method includes: sealing the bottom of the plunger hole on the cylinder block, and sintering the copper alloy and the cast cylinder block; cooling the cast cylinder block; performing finish machining on the cooled cast cylinder block; wherein, the cooling adopts air cooling and liquid cooling in a segmented manner, specifically including: first cooling in the air, then placing it in the coolant, the coolant does not completely submerge the cast cylinder block, then lifting the cylinder block from the coolant above the coolant and cooling in the air, and finally immersing it in the coolant again until the local part of the cylinder block turns black, and the cooling ends. Although the cooling process in this method is divided into multiple stages of cooling, it still acts on the lower substrate part, and cools the molten copper through heat conduction, and cannot control the solidification of the molten copper at the interface first, and the solidification defects cannot be effectively controlled.

[0006] In summary, for the casting process of the copper-steel bimetallic cylinder block, especially the process improvement of the solidification process of the molten copper is required, so that the rapid solidification of the molten copper can be realized, the solidification defects can be effectively controlled, the density of the copper layer can be improved, and at the same time, the microstructure of the copper substrate can be improved, and the mechanical properties of the cast cylinder block can be improved. Summary of the Invention

[0007] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a casting method for a copper-steel bimetallic cylinder block. During the casting process of the cylinder block, the heated cylinder block is cooled in multiple stages to realize the rapid cooling and solidification of the molten copper, the solidification defects are effectively controlled, a dense copper layer is obtained, the matrix structure of the steel matrix is adjusted, its mechanical properties are improved, and the yield rate of the cylinder block casting process is high.

[0008] To achieve this purpose, the present invention adopts the following technical solutions:

[0009] The present invention provides a casting method for a copper-steel bimetallic cylinder block, and the casting method includes the following steps:

[0010] (1) Pretreat the steel matrix and the copper alloy, then put them together into the casting equipment, heat and keep warm;

[0011] (2) After the heating and heat preservation in step (1) are completed, perform cooling. The cooling is divided into four-stage cooling. The purging directions in the first stage, the third stage and the fourth stage of cooling are all from bottom to top, and the purging direction in the second stage of cooling is from top to bottom. After the third stage of cooling, the molten liquid of the copper alloy has completed solidification;

[0012] (3) After the cooling in step (2) is completed, perform tempering treatment to obtain a copper-steel bimetallic cylinder block.

[0013] In the present invention, for the melting and casting process of the copper-steel bimetallic cylinder block, using a steel substrate and a copper alloy as raw materials, the copper alloy is melted through a heating process, and by controlling the cooling process, the copper layer and the steel substrate are combined to obtain the cylinder block; according to the positional relationship and volume ratio of the steel substrate and the copper layer, the cooling is divided into a multi-stage cooling process, and the gas blowing direction in different cooling stages is controlled, which can not only achieve the rapid solidification of the copper liquid, but also avoid the formation of undulations in the copper liquid, effectively control the solidification defects, and obtain a dense copper layer; then through the control of the last-stage cooling and the tempering process, the matrix structure of the steel substrate is regulated to form tempered sorbite, improving the mechanical properties of the cylinder block, and the yield rate of the cylinder block is high; the operation design of the method is reasonable, the production efficiency is high, the processing time can be effectively shortened, and the production cost is reduced.

[0014] The following are the preferred technical solutions of the present invention, but not the limitations of the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0015] As a preferred technical solution of the present invention, the material of the steel substrate in step (1) is alloy steel, including chromium molybdenum steel or chromium steel.

[0016] Preferably, the chromium molybdenum steel includes 42CrMoS4 or 30CrMo, and the chromium steel includes 40Cr;

[0017] Preferably, the metallographic structure of the 42CrMoS4 is pearlite + ferrite.

[0018] In the present invention, when 42CrMoS4 is selected as the chromium molybdenum steel, its elemental composition by mass fraction includes C 0.40 - 0.45%, such as 0.40%, 0.41%, 0.42%, 0.43%, 0.44%, 0.45% or 0.46%, etc., Si ≤ 0.40%, such as 0.40%, 0.38%, 0.35%, 0.32%, 0.30%, 0.25% or 0.20%, etc., Mn 0.60 - 0.90%, such as 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85% or 0.90%, etc., P ≤ 0.025%, such as 0.025%, 0.022%, 0.020%, 0.018%, 0.015% or 0.010%, etc., S 0.010 - 0.018%, such as 0.010%, 0.012%, 0.014%, 0.015%, 0.016% or 0.018%, etc., Cr 0.90 - 1.20%, such as 0.90%, 0.95%, 1.00%, 1.05%, 1.10%, 1.15% or 1.20%, etc., Mo 0.19 - 0.30%, such as 0.19%, 0.20%, 0.22%, 0.25%, 0.27% or 0.30%, etc., Cu ≤ 0.20%, such as 0.20%, 0.18%, 0.15%, 0.12%, 0.10% or 0.05%, etc., Ni ≤ 0.30%, such as 0.30%, 0.27%, 0.25%, 0.22%, 0.20%, 0.18%, 0.15% or 0.10%, etc.; however, it is not limited to the listed values, and other unlisted values within their respective numerical ranges are equally applicable.

[0019] Preferably, a molten pool groove and a boss are provided at the upper end of the steel substrate in step (1), the boss is located at the middle position, and the molten pool groove is arranged around the boss.

[0020] Preferably, a central hole is provided at the center of the steel substrate, the central hole is divided into upper and lower sections with different diameters, the diameter of the upper central hole is smaller than that of the lower central hole, and the upper central hole longitudinally penetrates the boss.

[0021] In the present invention, the boss in the steel substrate plays a role of a hot spot during the solidification stage of the copper liquid, so that the solidification direction of the copper liquid is from outside to inside, and the last solidification area is gathered around the boss, effectively controlling solidification defects such as porosity and shrinkage cavity.

[0022] As a preferred technical solution of the present invention, the copper alloy in step (1) includes any one or a combination of at least two of tin-lead bronze, tin bronze, bismuth bronze, aluminum bronze or silicon bronze. Typical but non-limiting examples of the combination are: the combination of tin-lead bronze and bismuth bronze, the combination of tin bronze and aluminum bronze, the combination of aluminum bronze and silicon bronze, the combination of tin-lead bronze, tin bronze and bismuth bronze, etc.

[0023] Preferably, the tin-lead bronze is CuSn10Pb10 or CuSn7Pb15, and its metallographic structure is α-Cu + rod-shaped Pb.

[0024] In the present invention, the elemental chemical composition of the CuSn10Pb10, by mass fraction, includes Sn 9.35 - 10.95%, such as 9.35%, 9.50%, 9.75%, 10.00%, 10.20%, 10.50%, 10.75% or 10.95%, etc., Pb 9.21 - 11.58%, such as 9.21%, 9.50%, 9.75%, 10.00%, 10.50%, 11.00% or 11.58%, etc., Ni 1.24 - 1.86%, such as 1.24%, 1.30%, 1.40%, 1.50%, 1.60%, 1.70%, 1.80% or 1.86%, etc., Zn 0.01 - 0.05%, such as 0.01%, 0.02%, 0.03%, 0.04% or 0.05%, etc., P below 0.1%, such as 0.1%, 0.09%, 0.08%, 0.07%, 0.06% or 0.05%, etc.; however, it is not limited to the listed values, and other unlisted values within their respective value ranges are equally applicable.

[0025] Preferably, the copper alloy is placed in the molten pool tank of the steel matrix.

[0026] As a preferred technical solution of the present invention, the pretreatment of the steel matrix and the copper alloy in step (1) is to clean them with an alkaline cleaning agent.

[0027] Preferably, the composition of the alkaline cleaning agent includes amines, organic acids, surfactants and water.

[0028] In the present invention, in the composition of the alkaline cleaning agent, the amines include ethanolamine, diethanolamine, triethanolamine, cyclohexylamine, etc., the organic acids can be citric acid, oxalic acid, ethylenediaminetetraacetic acid, etc., and the surfactants can be sodium dodecylbenzenesulfonate, sodium lauryl polyether sulfate, coconut oil amide propyl betaine, etc.; the amines are alkaline, and the function of the organic acids is to buffer to achieve a stable pH value of the cleaning agent.

[0029] Preferably, the concentration of the alkaline cleaning agent is 1 - 3 wt%, such as 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.5 wt%, 2.7 wt% or 3 wt%, etc., but it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0030] Preferably, the temperature of the cleaning is 50 - 70°C, such as 50°C, 52°C, 55°C, 58°C, 60°C, 62°C, 65°C, 68°C or 70°C, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable; the time is 20 - 30 min, such as 20 min, 22 min, 24 min, 25 min, 27 min, 28 min or 30 min, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0031] As a preferred technical solution of the present invention, the melting and casting equipment in step (1) includes a melting and casting furnace. After the copper alloy is placed in the molten pool of the steel matrix, the two are jointly placed in the melting and casting furnace.

[0032] Preferably, the heating in step (1) is divided into two-stage heating. The temperature of the first-stage heating is 790 - 980°C, such as 790°C, 800°C, 820°C, 850°C, 880°C, 900°C, 920°C, 940°C, 960°C or 980°C, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable; the temperature of the second-stage heating is 1020 - 1040°C, such as 1020°C, 1022°C, 1025°C, 1028°C, 1030°C, 1032°C, 1035°C, 1038°C or 1040°C, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0033] Preferably, the heat preservation time of the first-stage heating is 60 - 100 min, such as 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, 95 min or 100 min, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable; the heat preservation time of the second-stage heating is 50 - 80 min, such as 50 min, 55 min, 60 min, 65 min, 70 min, 75 min or 80 min, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0034] As a preferred technical solution of the present invention, the cooling in step (2) is carried out in a cooling furnace, and the heated steel matrix and molten copper liquid are jointly transferred from the melting and casting furnace to the cooling furnace.

[0035] In the present invention, the melting and casting furnace and the cooling furnace belong to different regions of the same equipment, and after the heating is completed, they can be automatically transferred without manual operation.

[0036] Preferably, the medium used for cooling in step (2) is liquid nitrogen, and blowing is carried out during the process of liquid nitrogen gasifying into nitrogen, and the blowing direction of the gas is controlled.

[0037] Preferably, the blowing direction is realized by fans arranged at the top and bottom inside the cooling furnace, and the gas flow rate is controlled by the rotational speed of the fans.

[0038] In the present invention, during the cooling process after the cylinder block is heated, it can be mainly divided into the process of copper liquid solidification and the process of the cylinder block cooling down after solidification, which is realized by changing the liquid nitrogen flow rate, the blowing direction and the gas flow velocity. Among them, the liquid nitrogen flow rate is realized by adjusting the pressure inside the furnace, the blowing direction is realized by opening and closing the fans arranged at the top and bottom inside the furnace, and the gas flow velocity is realized by adjusting the rotational speed of the fans.

[0039] As a preferred technical solution of the present invention, during the first-stage cooling in step (2), the blowing direction is vertically upward from the bottom of the steel matrix, the nitrogen pressure is 1000 - 4000 mbar, such as 1000 mbar, 1500 mbar, 2000 mbar, 2500 mbar, 3000 mbar, 3500 mbar or 4000 mbar, etc., the rotational speed of the fan is 800 - 1200 rpm, such as 800 rpm, 850 rpm, 900 rpm, 950 rpm, 1000 rpm, 1050 rpm, 1100 rpm, 1150 rpm or 1200 rpm, etc., and the cooling time is 2 - 6 s, such as 2 s, 3 s, 4 s, 5 s or 6 s, etc.; however, it is not limited to the listed values, and other unlisted values within their respective value ranges are equally applicable.

[0040] Preferably, during the second-stage cooling in step (2), the blowing direction is vertically downward from the upper end face of the steel matrix, the nitrogen pressure is 1000 - 4000 mbar, such as 1000 mbar, 1500 mbar, 2000 mbar, 2500 mbar, 3000 mbar, 3500 mbar or 4000 mbar, etc., the rotational speed of the fan is 1500 - 2500 rpm, such as 1500 rpm, 1600 rpm, 1800 rpm, 2000 rpm, 2200 rpm, 2400 rpm or 2500 rpm, etc., and the cooling time is 2 - 6 s, such as 2 s, 3 s, 4 s, 5 s or 6 s, etc.; however, it is not limited to the listed values, and other unlisted values within their respective value ranges are equally applicable.

[0041] Preferably, during the cooling in the third stage in step (3), the blowing direction is vertically upward from the bottom surface of the steel matrix, the nitrogen pressure is 1000 - 4000 mbar, such as 1000 mbar, 1500 mbar, 2000 mbar, 2500 mbar, 3000 mbar, 3500 mbar or 4000 mbar, etc., the fan speed is 2500 - 3500 rpm, such as 2500 rpm, 2600 rpm, 2800 rpm, 3000 rpm, 3200 rpm, 3400 rpm or 3500 rpm, etc., and the cooling time is 2 - 6 s, such as 2 s, 3 s, 4 s, 5 s or 6 s, etc.; however, it is not limited to the listed values, and other unlisted values within their respective value ranges are equally applicable.

[0042] Preferably, after the three-stage cooling, the copper liquid has completely solidified, and the temperature of the cylinder block at this time is 880 - 950 °C, such as 880 °C, 890 °C, 900 °C, 910 °C, 920 °C, 930 °C, 940 °C or 950 °C, etc.; however, it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0043] In the present invention, the cooling in the first three stages uses liquid nitrogen with a small flow rate, and the gas flow rate is increased step by step. The cooling in the first stage forms a shell-like paste on the surface of the copper liquid. The direct cooling of the copper liquid in the second stage can avoid the dynamic fluctuations caused by direct purging of the copper liquid. In this process, most of the copper liquid is solidified. The cooling in the third stage cools from the lower steel matrix again, so that the copper liquid near the middle boss at the upper end of the steel matrix is solidified. That is, the cooling in the first three stages can achieve the complete solidification of the copper liquid and keep the overall temperature of the cylinder block above the austenite temperature of this alloy steel.

[0044] As a preferred technical solution of the present invention, during the cooling in the fourth stage, the blowing direction is vertically upward from the bottom of the steel matrix, and the liquid nitrogen flow rate is increased for rapid cooling. At this time, the cooling rate is 1.2 - 5 °C / s, such as 1.2 °C / s, 1.5 °C / s, 2 °C / s, 2.5 °C / s, 3 °C / s, 3.5 °C / s, 4 °C / s, 4.5 °C / s or 5 °C / s, etc.; however, it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0045] Preferably, the nitrogen pressure during the fourth-stage cooling is 8000 - 14000 mbar, such as 8000 mbar, 9000 mbar, 10000 mbar, 11000 mbar, 12000 mbar, 13000 mbar or 14000 mbar, etc., the fan speed is 2500 - 3500 rpm, such as 2500 rpm, 2600 rpm, 2800 rpm, 3000 rpm, 3200 rpm, 3400 rpm or 3500 rpm, etc., and the final cooling temperature is below 80 °C, such as 80 °C, 75 °C, 70 °C, 65 °C or 60 °C, etc.; however, it is not limited to the listed values, and other unlisted values within each value range are equally applicable.

[0046] Preferably, after the fourth-stage cooling is completed, the cylinder block is taken out and air-cooled to room temperature.

[0047] In the present invention, the cooling in the fourth stage is rapid cooling, using a large flow rate of liquid nitrogen and a relatively large gas flow velocity, so that the metallographic structure of the steel matrix is transformed into martensite.

[0048] As a preferred technical solution of the present invention, the temperature of the tempering treatment in step (3) is 560 - 630 °C, such as 560 °C, 570 °C, 580 °C, 590 °C, 600 °C, 610 °C, 620 °C or 630 °C, etc., however, it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0049] Preferably, the holding time of the tempering treatment in step (3) is 120 - 180 min, such as 120 min, 130 min, 140 min, 150 min, 160 min, 170 min or 180 min, etc., however, it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0050] Preferably, the cooling method after the tempering treatment in step (3) is to directly take it out of the furnace and air-cool it to room temperature or cool it in the furnace to below 150 °C and then take it out of the furnace and air-cool it to room temperature, such as 150 °C, 145 °C, 140 °C, 135 °C, 130 °C, 125 °C or 120 °C, etc., however, it is not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0051] Preferably, the metallographic structure of the steel matrix after the tempering treatment in step (3) is tempered sorbite.

[0052] In the present invention, after the intense cooling in the fourth stage, the steel matrix part is further subjected to high-temperature tempering treatment, which can transform the metallographic structure of the steel matrix from martensite to tempered sorbite, having excellent strength and toughness and excellent mechanical properties. This is required based on the application of the cylinder block. As a key component in a piston pump or motor, the dual-metal cylinder block functions to cooperate with the piston and the valve plate to form a sealed volume, achieving the purpose of suction and oil discharge to provide power. During service, it is subjected to the impact of hydraulic oil and the friction of the mating pair, so it needs to have good strength and excellent fatigue resistance, which is related to the strength and toughness of the steel matrix and the compactness of the copper layer.

[0053] As a preferred technical solution of the present invention, the casting method includes the following steps:

[0054] (1) Pretreat the steel matrix and the copper alloy. The material of the steel matrix includes chromium molybdenum steel or chromium steel. There is a molten pool groove and a boss at the upper end of the steel matrix. The boss is located in the middle position, and the molten pool groove surrounds the boss. The copper alloy includes any one or a combination of at least two of tin-lead bronze, tin bronze, bismuth bronze, aluminum bronze or silicon bronze. The pretreatment is to clean with an alkaline cleaning agent. The composition of the alkaline cleaning agent includes amines, organic acids, surfactants and water. The concentration of the alkaline cleaning agent is 1-3 wt%. The cleaning temperature is 50-70 °C, and the time is 20-30 min. Then they are jointly put into a casting device for heating and insulation. The casting device includes a casting furnace. After the copper alloy is put into the molten pool groove of the steel matrix, the two are jointly put into the casting furnace. The heating is divided into two-stage heating. The temperature of the first-stage heating is 790-980 °C, and the insulation time is 60-100 min. The temperature of the second-stage heating is 1020-1040 °C, and the insulation time is 50-80 min;

[0055] (2) After the heating and heat preservation in step (1) are completed, cooling is carried out. The cooling is carried out in a cooling furnace. The heated steel matrix and molten copper liquid are jointly transferred from the melting and casting furnace to the cooling furnace. The cooling is divided into four-stage cooling. The medium used for cooling is liquid nitrogen. Blowing is carried out during the gasification of liquid nitrogen into nitrogen, and the blowing direction of the gas is controlled. The blowing direction is realized by the fans arranged at the top and bottom inside the cooling furnace, and the gas flow rate is controlled by the rotation speed of the fans. The blowing directions in the first stage, the third stage and the fourth stage of cooling are all vertically upward from the bottom of the steel matrix, and the blowing direction in the second stage of cooling is vertically downward from the upper end face of the steel matrix. The nitrogen pressure during the first stage of cooling is 1000 - 4000 mbar, the fan rotation speed is 800 - 1200 rpm, and the cooling time is 2 - 6 s. The nitrogen pressure during the second stage of cooling is 1000 - 4000 mbar, the fan rotation speed is 1500 - 2500 rpm, and the cooling time is 2 - 6 s. The nitrogen pressure during the third stage of cooling is 1000 - 4000 mbar, the fan rotation speed is 2500 - 3500 rpm, and the cooling time is 2 - 6 s. After the third stage of cooling, the molten liquid of the copper alloy has completed solidification. At this time, the temperature of the cylinder block is 880 - 950 °C. The cooling rate in the fourth stage of cooling is 1.2 - 5 °C / s, the nitrogen pressure is 8000 - 14000 mbar, the fan rotation speed is 2500 - 3500 rpm, and the cooling end temperature is below 80 °C. Then the cylinder block is taken out and further air-cooled to room temperature.

[0056] (3) After the cooling in step (2) is completed, tempering treatment is carried out. The temperature of the tempering treatment is 560 - 630 °C, and the heat preservation time is 120 - 180 min. The cooling method after the tempering treatment is to directly take out the furnace and air-cool it to room temperature or cool it in the furnace to below 150 °C and then take out the furnace and air-cool it to room temperature to obtain a copper-steel dual-alloy cylinder block. The metallographic structure of the steel matrix after the tempering treatment is tempered sorbite.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] (1) In the process of cylinder block melting and casting processing of the present invention, multi-stage cooling is carried out on the heated cylinder block, and the gas blowing direction in different cooling stages is controlled, which can not only realize the rapid solidification of the copper liquid, but also avoid the formation of undulations of the copper liquid, effectively control the solidification defects, and obtain a dense copper layer.

[0059] (2) Through the control of the last-stage cooling and the tempering process of the present invention, the matrix structure of the steel matrix is regulated to form tempered sorbite, improving the mechanical properties of the cylinder block and the yield rate of the cylinder block, which can reach more than 98%.

[0060] (3) The method of the present invention has a reasonable operation design, high production efficiency, can effectively shorten the processing time and reduce the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 is a schematic structural view of the steel substrate provided in Embodiment 1 of the present invention;

[0062] Figure 2 is the metallographic structure of the entire copper layer in the copper - steel bimetallic cylinder block provided in Embodiment 1 of the present invention;

[0063] Figure 3 is the metallographic structure of a partial position in the copper layer of the copper - steel bimetallic cylinder block provided in Embodiment 1 of the present invention;

[0064] Figure 4 is the metallographic structure of the steel substrate in the copper - steel bimetallic cylinder block provided in Embodiment 1 of the present invention;

[0065] Figure 5 is the metallographic structure of the entire copper layer in the copper - steel bimetallic cylinder block provided in Embodiment 2 of the present invention;

[0066] Figure 6 is the metallographic structure of a partial position in the copper layer of the copper - steel bimetallic cylinder block provided in Embodiment 2 of the present invention;

[0067] Figure 7 is the metallographic structure of the steel substrate in the copper - steel bimetallic cylinder block provided in Embodiment 2 of the present invention;

[0068] Among them, 1 - molten pool tank, 2 - boss, 3 - upper center hole, 4 - lower center hole. DETAILED DESCRIPTION OF THE INVENTION

[0069] To better illustrate the present invention and facilitate understanding of its technical solutions, the present invention is further described in detail below. However, the following embodiments are only simple examples of the present invention and do not represent or limit the scope of the claimed rights of the present invention. The scope of protection of the present invention is subject to the claims.

[0070] The following are typical but non - restrictive embodiments of the present invention:

[0071] Embodiment 1:

[0072] This embodiment provides a melting and casting method for a copper - steel bimetallic cylinder block. The melting and casting method includes the following steps:

[0073] (1) Pretreat the steel substrate and the copper alloy. The material of the steel substrate is chromium - molybdenum steel 42CrMoS4, and the schematic structural view of the steel substrate is as shown in Figure 1As shown, a molten pool groove 1 and a boss 2 are provided at its upper end. The boss 2 is located at the middle position, and the molten pool groove 1 is arranged around the boss 2. A central hole is provided at the central position of the steel matrix. The central hole is divided into upper and lower sections with different diameters. The diameter of the upper central hole 3 is smaller than that of the lower central hole 4. The upper central hole 3 longitudinally penetrates the boss 2. The copper alloy is tin-lead bronze CuSn10Pb10. The pretreatment is to clean with an alkaline cleaning agent. The composition of the alkaline cleaning agent includes ethanolamine, citric acid, and sodium dodecylbenzenesulfonate with a mass ratio of 3:1:0.5. The total concentration of the alkaline cleaning agent is 2 wt%. The cleaning temperature is 60 °C and the time is 25 min. Then they are jointly put into a melting and casting device for heating and heat preservation. The melting and casting device includes a melting and casting furnace. After the copper alloy is put into the molten pool groove of the steel matrix, the two are jointly put into the melting and casting furnace. The heating is divided into two-stage heating. The temperature of the first-stage heating is 840 °C and the heat preservation time is 70 min. The temperature of the second-stage heating is 1025 °C and the heat preservation time is 75 min.

[0074] (2) After the heating and heat preservation in step (1) are completed, cooling is carried out. The cooling is carried out in a cooling furnace. The heated steel matrix and molten copper liquid are jointly transferred from the melting and casting furnace to the cooling furnace. The cooling is divided into four-stage cooling. The medium used for cooling is liquid nitrogen. Blowing is carried out during the vaporization of liquid nitrogen into nitrogen, and the blowing direction of the gas is controlled. The blowing direction is realized by fans arranged at the top and bottom inside the cooling furnace, and the gas flow rate is controlled by the rotation speed of the fans. The blowing directions in the first stage, the third stage, and the fourth stage of cooling are all vertically upward from the bottom of the steel matrix. The blowing direction in the second stage of cooling is vertically downward from the upper end face of the steel matrix. The nitrogen pressure during the first stage of cooling is 4000 mbar, the fan rotation speed is 1000 rpm, and the cooling time is 4 s. The nitrogen pressure during the second stage of cooling is 4000 mbar, the fan rotation speed is 2000 rpm, and the cooling time is 4 s. The nitrogen pressure during the third stage of cooling is 4000 mbar, the fan rotation speed is 3000 rpm, and the cooling time is 4 s. After the third stage of cooling, the molten liquid of the copper alloy has solidified completely. At this time, the temperature of the cylinder block is 900 °C. The cooling rate in the fourth stage of cooling is 2.5 °C / s, the nitrogen pressure is 12000 mbar, the fan rotation speed is 3000 rpm, and the cooling end temperature is 80 °C. Then the cylinder block is taken out and further air-cooled to room temperature.

[0075] (3) After the cooling in step (2) is completed, tempering treatment is carried out. The temperature of the tempering treatment is 600 °C and the heat preservation time is 120 min. The cooling method after the tempering treatment is to directly take it out of the furnace and air-cool it to room temperature to obtain a copper-steel double-alloy cylinder block.

[0076] In this embodiment, the prepared copper-steel bimetallic cylinder block is observed by an optical microscope. The metallographic structure of the copper layer in the cylinder block is asFigure 2 and 3 As shown, the metallographic structure of the steel substrate is as Figure 4 shown; and the mechanical properties of the copper-steel bimetallic cylinder block are detected. Among them, the hardness is detected by a Brinell hardness tester. The detection position of the copper layer is the surface, and the detection position of the steel substrate is the bottom surface of the cylinder block (the surface decarburized layer is removed before detection). The sampling positions for the tensile strength and impact energy tests of the steel substrate are at the center of the cylinder block, that is, at 1 / 2 of the cylinder block radius.

[0077] In this embodiment, Figure 2 is the metallographic structure of the entire copper layer, Figure 3 is the metallographic structure of a local position in the copper layer. The Pb phase in the copper layer is fine and uniform, and all the shrinkage porosity aggregates at the center boss. The rest of the parts are dense without shrinkage porosity; from Figure 4 it can be seen that the metallographic structure of the steel substrate after tempering treatment is tempered sorbite;

[0078] After the above mechanical property tests, the hardness of the steel substrate in the cylinder block is 260 - 280 HBW2.5 / 187.5, the tensile strength at the center is 890 MPa, the impact energy is 89.5 J, and the hardness of the copper layer is 118 HBW2.5 / 62.5.

[0079] Example 2:

[0080] This embodiment provides a melting and casting method for a copper-steel bimetallic cylinder block. The melting and casting method includes the following steps:

[0081] (1) Pretreat the steel substrate and the copper alloy. The material of the steel substrate is chromium molybdenum steel 42CrMoS4. There are a melting pool groove 1 and a boss 2 at the upper end of the steel substrate. The boss 2 is located in the middle position. The melting pool groove 1 is arranged around the boss 2. A central hole is arranged at the center position of the steel substrate. The central hole is divided into upper and lower sections with different diameters. The diameter of the upper central hole 3 is smaller than that of the lower central hole 4. The upper central hole 3 longitudinally penetrates the boss 2; the copper alloy is tin-lead bronze CuSn10Pb10. The pretreatment is to clean with an alkaline cleaning agent. The composition of the alkaline cleaning agent includes ethanolamine, citric acid, and sodium dodecylbenzenesulfonate with a mass ratio of 4:1:0.8. The total concentration of the alkaline cleaning agent is 1 wt%. The cleaning temperature is 70 °C and the time is 20 min. Then they are put into the melting and casting equipment together for heating and heat preservation. The melting and casting equipment includes a melting furnace. After the copper alloy is put into the melting pool groove of the steel substrate, the two are put into the melting furnace together. The heating is divided into two-stage heating. The temperature of the first-stage heating is 950 °C and the heat preservation time is 100 min. The temperature of the second-stage heating is 1040 °C and the heat preservation time is 80 min;

[0082] (2) After the heating and heat preservation in step (1) are completed, cooling is carried out. The cooling is carried out in a cooling furnace. The heated steel matrix and molten copper liquid are jointly transferred from the melting and casting furnace to the cooling furnace. The cooling is divided into four-stage cooling. The medium used for cooling is liquid nitrogen. Blowing is carried out during the vaporization of liquid nitrogen into nitrogen, and the blowing direction of the gas is controlled. The blowing direction is realized by the fans arranged at the top and bottom inside the cooling furnace, and the gas flow rate is controlled by the rotation speed of the fans. The blowing directions in the first stage, the third stage and the fourth stage of cooling are all vertically upward from the bottom of the steel matrix, and the blowing direction in the second stage of cooling is vertically downward from the upper end face of the steel matrix. The nitrogen pressure during the first stage of cooling is 1000 mbar, the fan rotation speed is 800 rpm, and the cooling time is 6 s. The nitrogen pressure during the second stage of cooling is 1500 mbar, the fan rotation speed is 1600 rpm, and the cooling time is 6 s. The nitrogen pressure during the third stage of cooling is 1000 mbar, the fan rotation speed is 2500 rpm, and the cooling time is 6 s. After the third stage of cooling, the molten liquid of the copper alloy has been completely solidified. At this time, the temperature of the cylinder block is 950 °C. The cooling rate in the fourth stage of cooling is 5 °C / s, the nitrogen pressure is 14000 mbar, the fan rotation speed is 3500 rpm, and the cooling end temperature is 75 °C. Then the cylinder block is taken out and air-cooled to room temperature continuously.

[0083] (3) After the cooling in step (2) is completed, tempering treatment is carried out. The temperature of the tempering treatment is 560 °C, and the heat preservation time is 180 min. The cooling method after the tempering treatment is to directly take out the furnace and air-cool it to room temperature to obtain a copper-steel dual-alloy cylinder block.

[0084] In this embodiment, the prepared copper-steel bimetallic cylinder block is observed by an optical microscope. The metallographic structure of the copper layer in the cylinder block is as shown in Figure 5 and 6 , and the metallographic structure of the steel matrix is as shown in Figure 7 ; and the mechanical properties of the copper-steel bimetallic cylinder block are detected, and the detection conditions are the same as those in Example 1.

[0085] In this embodiment, Figure 5 is the metallographic structure of the entire copper layer, Figure 6 is the metallographic structure of a local position in the copper layer. The Pb phase in the copper layer is fine and uniform, and the shrinkage porosity is all concentrated at the central boss. The rest of the parts are dense and without shrinkage porosity; as can be seen from Figure 7 , the metallographic structure of the steel matrix after tempering treatment is tempered sorbite;

[0086] After the above detection of mechanical properties, the hardness of the steel matrix in the cylinder block is 260 - 300 HBW2.5 / 187.5, the tensile strength of the core is 867 MPa, the impact energy is 99 J, and the hardness of the copper layer is 90 HBW2.5 / 62.5.

[0087] Example 3:

[0088] This embodiment provides a melting and casting method for a copper-steel bimetallic cylinder block. The melting and casting method includes the following steps:

[0089] (1) Pretreat the steel substrate and the copper alloy. The material of the steel substrate is chromium molybdenum steel 42CrMoS4. A melting pool groove 1 and a boss 2 are provided at the upper end of the steel substrate. The boss 2 is located at the middle position. The melting pool groove 1 is arranged around the boss 2. A central hole is provided at the center position of the steel substrate. The central hole is divided into upper and lower sections with different diameters. The diameter of the upper central hole 3 is smaller than that of the lower central hole 4. The upper central hole 3 longitudinally penetrates the boss 2. The copper alloy is tin-lead bronze CuSn10Pb10. The pretreatment is to clean with an alkaline cleaning agent. The composition of the alkaline cleaning agent includes diethanolamine, oxalic acid, and sodium dodecylbenzenesulfonate with a mass ratio of 3:1:1. The total concentration of the alkaline cleaning agent is 3 wt%. The cleaning temperature is 50 °C and the time is 30 min. Then they are jointly put into a melting and casting device for heating and heat preservation. The melting and casting device includes a melting furnace. After the copper alloy is put into the melting pool groove of the steel substrate, the two are jointly put into the melting furnace. The heating is divided into two-stage heating. The temperature of the first-stage heating is 900 °C and the heat preservation time is 80 min. The temperature of the second-stage heating is 1020 °C and the heat preservation time is 60 min.

[0090] (2) After the heating and heat preservation in step (1) are completed, cooling is carried out. The cooling is carried out in a cooling furnace. The heated steel substrate and the molten copper liquid are jointly transferred from the melting furnace to the cooling furnace. The cooling is divided into four-stage cooling. The medium used for cooling is liquid nitrogen. Blowing is carried out during the vaporization of liquid nitrogen into nitrogen, and the blowing direction of the gas is controlled. The blowing direction is realized by fans arranged at the top and bottom inside the cooling furnace, and the gas flow rate is controlled by the rotation speed of the fans. The blowing directions in the first stage, the third stage, and the fourth stage of cooling are all vertically upward from the bottom of the steel substrate. The blowing direction in the second stage of cooling is vertically downward from the upper end face of the steel substrate. The nitrogen pressure during the first stage of cooling is 2500 mbar, the fan rotation speed is 1200 rpm, and the cooling time is 2 s. The nitrogen pressure during the second stage of cooling is 3000 mbar, the fan rotation speed is 2500 rpm, and the cooling time is 2 s. The nitrogen pressure during the third stage of cooling is 2500 mbar, the fan rotation speed is 3500 rpm, and the cooling time is 2 s. After the third stage of cooling, the molten liquid of the copper alloy has been completely solidified. At this time, the temperature of the cylinder block is 920 °C. The cooling rate in the fourth stage of cooling is 1.5 °C / s, the nitrogen pressure is 10000 mbar, the fan rotation speed is 3500 rpm, and the cooling end temperature is 70 °C. Then the cylinder block is taken out and further air-cooled to room temperature.

[0091] (3) After the cooling in step (2) is completed, tempering treatment is carried out. The temperature of the tempering treatment is 630 °C, and the holding time is 135 min. The cooling method after the tempering treatment is to cool in the furnace to 150 °C and then take out and air-cool to room temperature to obtain a copper-steel dual-alloy cylinder block.

[0092] In this embodiment, the prepared copper-steel bimetallic cylinder block is observed for its metallographic structure by an optical microscope. The shrinkage porosity in the copper layer all aggregates at the central boss, and the rest of the parts are dense without shrinkage porosity. The mechanical properties of the cylinder block are detected, and the detection conditions are the same as those in Example 1. Among them, the hardness of the steel matrix in the cylinder block is 273 - 310 HBW2.5 / 187.5, the tensile strength of the core is 880 MPa, the impact energy is 95 J, and the hardness of the copper layer is 95 HBW2.5 / 62.5.

[0093] Example 4:

[0094] This embodiment provides a melting and casting method for a copper-steel bimetallic cylinder block. The melting and casting method includes the following steps:

[0095] (1) The steel matrix and the copper alloy are pretreated. The material of the steel matrix is chromium steel 40Cr. There are a melting pool groove 1 and a boss 2 at the upper end of the steel matrix. The boss 2 is located in the middle position. The melting pool groove 1 is arranged around the boss 2. A central hole is arranged at the center position of the steel matrix. The central hole is divided into upper and lower sections with different diameters. The diameter of the upper central hole 3 is smaller than that of the lower central hole 4. The upper central hole 3 longitudinally penetrates the boss 2. The copper alloy is tin-lead bronze CuSn10Pb10. The pretreatment is to clean with an alkaline cleaning agent. The composition of the alkaline cleaning agent includes diethanolamine, ethylenediaminetetraacetic acid, and sodium lauryl polyether sulfate with a mass ratio of 5:1:1. The total concentration of the alkaline cleaning agent is 2.5 wt%. The cleaning temperature is 65 °C and the time is 27 min. Then they are jointly put into a melting and casting device for heating and holding. The melting and casting device includes a melting furnace. After the copper alloy is put into the melting pool groove of the steel matrix, the two are jointly put into the melting furnace. The heating is divided into two-stage heating. The temperature of the first-stage heating is 800 °C and the holding time is 90 min. The temperature of the second-stage heating is 1030 °C and the holding time is 65 min.

[0096] (2) After the heating and heat preservation in step (1) are completed, cooling is carried out. The cooling is carried out in a cooling furnace. The heated steel matrix and molten copper liquid are jointly transferred from the melting and casting furnace to the cooling furnace. The cooling is divided into four-stage cooling. The medium used for cooling is liquid nitrogen. Blowing is carried out during the vaporization of liquid nitrogen into nitrogen, and the blowing direction of the gas is controlled. The blowing direction is realized by the fans arranged at the top and bottom inside the cooling furnace, and the gas flow rate is controlled by the rotation speed of the fans. The blowing directions in the first stage, the third stage and the fourth stage of cooling are all vertically upward from the bottom of the steel matrix, and the blowing direction in the second stage of cooling is vertically downward from the upper end face of the steel matrix. The nitrogen pressure during the first stage of cooling is 3000 mbar, the fan rotation speed is 1100 rpm, and the cooling time is 3 s. The nitrogen pressure during the second stage of cooling is 3000 mbar, the fan rotation speed is 2200 rpm, and the cooling time is 5 s. The nitrogen pressure during the third stage of cooling is 3000 mbar, the fan rotation speed is 3200 rpm, and the cooling time is 3 s. After the third stage of cooling, the molten liquid of the copper alloy has been completely solidified. At this time, the temperature of the cylinder block is 890 °C. The cooling rate in the fourth stage of cooling is 3.5 °C / s, the nitrogen pressure is 13000 mbar, the fan rotation speed is 3200 rpm, and the cooling end temperature is 72 °C. Then the cylinder block is taken out and further air-cooled to room temperature.

[0097] (3) After the cooling in step (2) is completed, tempering treatment is carried out. The temperature of the tempering treatment is 580 °C, and the heat preservation time is 160 min. The cooling method after the tempering treatment is to directly take out the furnace and air-cool it to room temperature to obtain a copper-steel dual-alloy cylinder block.

[0098] In this embodiment, the prepared copper-steel bimetallic cylinder block is observed for its metallographic structure by an optical microscope. The shrinkage porosity in the copper layer all aggregates at the central boss, and the rest of the parts are dense without shrinkage porosity. And the mechanical properties of the cylinder block are detected, and the detection conditions are the same as those in Example 1. Among them, the hardness of the steel matrix in the cylinder block is 257-298 HBW2.5 / 187.5, the tensile strength at the core is 860 MPa, the impact energy is 88 J, and the hardness of the copper layer is 93 HBW2.5 / 62.5.

[0099] Example 5:

[0100] This embodiment provides a melting and casting method for a copper-steel bimetallic cylinder block. The melting and casting method includes the following steps:

[0101] (1) Pretreat the steel matrix and the copper alloy. The material of the steel matrix is chromium molybdenum steel 30CrMo. There are a melting pool groove 1 and a boss 2 at the upper end of the steel matrix. The boss 2 is located in the middle position. The melting pool groove 1 is arranged around the boss 2. A central hole is arranged at the center position of the steel matrix. The central hole is divided into upper and lower sections with different diameters. The diameter of the upper central hole 3 is smaller than that of the lower central hole 4. The upper central hole 3 longitudinally penetrates the boss 2. The copper alloy is tin-lead bronze CuSn7Pb15. The pretreatment is to clean with an alkaline cleaning agent. The composition of the alkaline cleaning agent includes triethanolamine, citric acid, and sodium lauryl polyether sulfate with a mass ratio of 4:0.5:1. The total concentration of the alkaline cleaning agent is 1.5 wt%. The cleaning temperature is 55 °C and the time is 22 min. Then they are jointly put into a melting and casting device for heating and heat preservation. The melting and casting device includes a melting and casting furnace. After the copper alloy is put into the melting pool groove of the steel matrix, the two are jointly put into the melting and casting furnace. The heating is divided into two-stage heating. The temperature of the first-stage heating is 980 °C and the heat preservation time is 60 min. The temperature of the second-stage heating is 1035 °C and the heat preservation time is 55 min.

[0102] (2) After the heating and heat preservation in step (1) are completed, cooling is carried out. The cooling is carried out in a cooling furnace. The heated steel matrix and the molten copper liquid are jointly transferred from the melting and casting furnace to the cooling furnace. The cooling is divided into four-stage cooling. The medium used for cooling is liquid nitrogen. Blowing is carried out during the gasification of liquid nitrogen into nitrogen, and the blowing direction of the gas is controlled. The blowing direction is realized by the fans arranged at the top and bottom inside the cooling furnace, and the gas flow rate is controlled by the rotation speed of the fans. The blowing directions in the first stage, the third stage, and the fourth stage of cooling are all vertically upward from the bottom of the steel matrix. The blowing direction in the second stage of cooling is vertically downward from the upper end face of the steel matrix. The nitrogen pressure during the first-stage cooling is 1500 mbar, the fan rotation speed is 900 rpm, and the cooling time is 5 s. The nitrogen pressure during the second-stage cooling is 2000 mbar, the fan rotation speed is 1800 rpm, and the cooling time is 3 s. The nitrogen pressure during the third-stage cooling is 2500 mbar, the fan rotation speed is 2700 rpm, and the cooling time is 5 s. After the third-stage cooling, the molten liquid of the copper alloy has been completely solidified. At this time, the temperature of the cylinder block is 910 °C. The cooling rate in the fourth stage of cooling is 4 °C / s, the nitrogen pressure is 9000 mbar, the fan rotation speed is 2800 rpm, and the cooling end temperature is 78 °C. Then the cylinder block is taken out and air-cooled to room temperature.

[0103] (3) After the cooling in step (2) is completed, tempering treatment is carried out. The temperature of the tempering treatment is 620 °C and the heat preservation time is 130 min. The cooling method after the tempering treatment is to cool in the furnace to 140 °C and then take out and air-cool to room temperature to obtain a copper-steel dual-alloy cylinder block.

[0104] In this embodiment, the prepared copper-steel bimetallic cylinder block was observed for its metallographic structure using an optical microscope. The shrinkage porosity in the copper layer was all concentrated at the central boss, and the remaining parts were dense without shrinkage porosity. The mechanical properties of the cylinder block were tested under the same conditions as in Example 1. Among them, the hardness of the steel matrix in the cylinder block was 253 - 293 HBW2.5 / 187.5, the tensile strength at the core was 878 MPa, the impact energy was 90 J, and the hardness of the copper layer was 89 HBW2.5 / 62.5.

[0105] Comparative Example 1:

[0106] This comparative example provides a casting method for a copper-steel bimetallic cylinder block. The casting method refers to the method in Example 1, with the difference that: in step (2), the blowing direction during the second-stage cooling is also vertically upward from the bottom of the steel matrix.

[0107] In this comparative example, since the copper liquid was not directly blown and cooled during the second-stage cooling, within the same time, the copper liquid did not solidify completely, and the cooling rate was inconsistent, which easily caused solidification defects and reduced the density of the copper layer. At this time, the shrinkage porosity in the copper layer did not all gather at the central boss, and the hardness of the copper layer decreased relatively to 73 HBW2.5 / 62.5, while the hardness and tensile strength of the steel matrix did not change.

[0108] Comparative Example 2:

[0109] This comparative example provides a casting method for a copper-steel bimetallic cylinder block. The casting method refers to the method in Example 1, with the difference that: step (2) does not include the third-stage cooling, and the cooling time of the original third stage is added to the second-stage cooling.

[0110] In this comparative example, since the third-stage cooling was not set separately but the cooling time of the second stage was extended, the direct blowing time of the copper layer was prolonged. At this time, the solidification process of the copper liquid would be accelerated, especially the heat sink capacity of the boss decreased, resulting in that the solidification shrinkage and other defects did not fully gather around the boss, and the density and hardness of the copper layer decreased, with the hardness dropping to 75 HBW2.5 / 62.5.

[0111] From the above examples and comparative examples, it can be seen that in the process of casting and processing the cylinder block by the method of the present invention, the heated cylinder block is subjected to multi-stage cooling, and the gas blowing direction in different cooling stages is controlled, which can not only achieve the rapid solidification of the copper liquid, but also avoid the formation of undulations in the copper liquid, effectively control the solidification defects, and obtain a dense copper layer; through the control of the last-stage cooling and the tempering process, the matrix structure of the steel matrix is regulated to form tempered sorbite, improving the mechanical properties of the cylinder block and the yield rate of the cylinder block; the method has a reasonable operation design, high production efficiency, can effectively shorten the processing time, and reduce the production cost.

[0112] The applicant declares that the present invention illustrates the detailed method of the present invention through the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of the method of the present invention, the addition of auxiliary steps, the selection of specific methods, etc. all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for melting and casting a copper-steel bimetallic cylinder, characterized in that: The melting and casting method comprises the following steps: (1) After pretreatment, the steel matrix and the copper alloy are placed together in a melting and casting device for heating and heat preservation; (2) After the heating and heat preservation in step (1) are completed, cooling is performed, and the cooling is divided into four stages of cooling. The purge direction of the first stage, the third stage, and the fourth stage of cooling is from bottom to top, and the purge direction of the second stage of cooling is from top to bottom. After the third stage of cooling, the molten copper alloy has been solidified; (3) After cooling in step (2), a tempering treatment is performed to obtain a copper-steel dual alloy cylinder body.

2. The melting and casting method according to claim 1, characterized in that: The material of the steel substrate in step (1) is alloy steel, including chrome-molybdenum steel or chrome steel; The chromium-molybdenum steel includes 42CrMoS4 or 30CrMo, and the chromium steel includes 40Cr; The metallographic structure of the 42CrMoS4 is pearlite + ferrite; Step (1) The upper end of the steel substrate is provided with a molten pool groove and a boss, the boss is located in the middle, and the molten pool groove is arranged around the boss; A center hole is arranged at the center position of the steel substrate, and the center hole is divided into two sections, an upper section and an lower section, with different diameters. The diameter of the upper center hole is smaller than that of the lower center hole, and the upper center hole passes through the boss longitudinally.

3. The melting and casting method according to claim 1, characterized in that: The copper alloy in step (1) includes any one of tin-lead bronze, tin bronze, bismuth bronze, aluminum bronze or silicon bronze, or a combination of at least two thereof; The tin-lead bronze includes CuSn10Pb10 or CuSn7Pb15, and its metallographic structure is α-Cu+spherical rod-shaped Pb; The copper alloy is placed in a molten pool tank of a steel matrix.

4. The melting and casting method according to claim 1, characterized in that: The pretreatment of the steel substrate and the copper alloy in step (1) is cleaning with an alkaline cleaning agent; The alkaline cleaning agent comprises amines, organic acids, surfactants and water; The concentration of the alkaline cleaning agent is 1-3wt%; The cleaning temperature is 50-70°C and the cleaning time is 20-30 minutes.

5. The melting and casting method according to claim 1, characterized in that: The melting and casting equipment in step (1) includes a melting and casting furnace. After the copper alloy is placed in a molten pool tank of a steel substrate, both are placed in the melting and casting furnace together. The heating in step (1) is divided into two stages, the heating temperature in the first stage is 790-980°C, and the heating temperature in the second stage is 1020-1040°C; The heat preservation time of the first stage heating is 60-100 minutes, and the heat preservation time of the second stage heating is 50-80 minutes.

6. The melting and casting method according to claim 1, characterized in that: The cooling in step (2) is carried out in a cooling furnace, and the heated steel substrate and molten copper are transferred from the melting and casting furnace to the cooling furnace; The cooling medium used in step (2) is liquid nitrogen, and blowing is performed during the process of liquid nitrogen being gasified into nitrogen gas, and the blowing direction of the gas is controlled; The blowing direction is achieved by fans arranged at the top and bottom of the cooling furnace, and the gas flow rate is controlled by the rotation speed of the fans.

7. The melting and casting method according to claim 6, characterized in that: Step (2) During the first stage of cooling, the blowing direction is vertical to the bottom of the steel substrate and upward, the nitrogen pressure is 1000-4000 mbar, the fan speed is 800-1200 rpm, and the cooling time is 2-6 s; Step (2) During the second stage of cooling, the blowing direction is vertical to the upper end of the steel substrate and downward, the nitrogen pressure is 1000-4000 mbar, the fan speed is 1500-2500 rpm, and the cooling time is 2-6 s; In step (2), the blowing direction during the third stage of cooling is vertical to the bottom surface of the steel substrate and upward, the nitrogen pressure is 1000-4000 mbar, the fan speed is 2500-3500 rpm, and the cooling time is 2-6 s; After three stages of cooling, the copper liquid has completely solidified, and the cylinder temperature is now 880~950℃.

8. The melting and casting method according to claim 6, characterized in that: In step (2), the blowing direction during the fourth stage of cooling is vertical to the bottom of the steel substrate and upward, and the liquid nitrogen flow rate is increased for rapid cooling, and the cooling rate is 1.2-5°C / s; The nitrogen pressure of the fourth stage cooling is 8000-14000 mbar, the fan speed is 2500-3500 rpm, and the cooling end temperature is below 80°C; After the fourth stage of cooling is completed, the cylinder is taken out and air-cooled to room temperature.

9. The melting and casting method according to claim 1, characterized in that: The temperature of the tempering treatment in step (3) is 560-630°C; The holding time of the tempering treatment in step (3) is 120 to 180 minutes; The cooling method after the tempering treatment in step (3) is to directly take out of the furnace and air cool to room temperature or to cool in the furnace to below 150° C. and then take out of the furnace and air cool to room temperature; The metallographic structure of the steel matrix after the tempering treatment in step (3) is tempered troostite.

10. The melting and casting method according to any one of claims 1 to 9, characterized in that: The melting and casting method comprises the following steps: (1) Pre-treating a steel substrate and a copper alloy, wherein the material of the steel substrate comprises chromium-molybdenum steel or chromium steel, a molten pool groove and a boss are provided at the upper end of the steel substrate, the boss is located in the middle, and the molten pool groove is arranged around the boss, and the copper alloy comprises any one of tin-lead bronze, tin bronze, bismuth bronze, aluminum bronze or silicon bronze, or a combination of at least two thereof, and the pre-treatment is cleaning with an alkaline cleaning agent, wherein the alkaline cleaning agent comprises amines, organic acids, surfactants and water, and the concentration of the alkaline cleaning agent is 1 to 3wt%, the cleaning temperature is 50-70°C, the time is 20-30min, and then they are put into a melting and casting equipment for heating and heat preservation. The melting and casting equipment includes a melting and casting furnace. After the copper alloy is put into the molten pool tank of the steel matrix, the two are put into the melting and casting furnace together. The heating is divided into two stages. The temperature of the first stage is 790-980°C, the heat preservation time is 60-100min, and the temperature of the second stage is 1020-1040°C, and the heat preservation time is 50-80min. (2) After the heating and heat preservation in step (1) are completed, cooling is performed. The cooling is performed in a cooling furnace. The heated steel substrate and molten copper are transferred from the melting furnace to the cooling furnace. The cooling is divided into four stages. The cooling medium is liquid nitrogen. Blowing is performed during the process of liquid nitrogen being gasified into nitrogen. The blowing direction of the gas is controlled. The blowing direction is achieved by fans arranged at the top and bottom of the cooling furnace. The gas flow rate is controlled by the speed of the fan. The blowing direction of the first stage, the third stage and the fourth stage of cooling is vertical to the bottom of the steel substrate upward. The blowing direction of the second stage of cooling is vertical to the upper end of the steel substrate downward. The nitrogen pressure during the first stage of cooling is 1000-4000 mbar, and the fan speed is 800-1200 r / min. pm, the cooling time is 2~6s, the nitrogen pressure during the second stage cooling is 1000~4000mbar, the fan speed is 1500~2500rpm, the cooling time is 2~6s, the nitrogen pressure during the third stage cooling is 1000~4000mbar, the fan speed is 2500~3500rpm, the cooling time is 2~6s, the molten copper alloy has solidified after the third stage cooling, and the cylinder temperature at this time is 880~950℃; the cooling rate of the fourth stage cooling is 1.2~5℃ / s, the nitrogen pressure is 8000~14000mbar, the fan speed is 2500~3500rpm, the cooling end temperature is below 80℃, and then the cylinder is taken out and air-cooled to room temperature; (3) After the cooling in step (2) is completed, a tempering treatment is performed, wherein the tempering treatment temperature is 560-630° C., and the holding time is 120-180 min. The cooling method after the tempering treatment is to directly take the cylinder out of the furnace and air cool to room temperature or to cool in the furnace to below 150° C. and then take the cylinder out of the furnace and air cool to room temperature, thereby obtaining a copper-steel dual alloy cylinder body. The metallographic structure of the steel matrix after the tempering treatment is tempered troostite.

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