High-canning rate high-strength cylinder head smelting production method

Abstract

The application provides a high-strength cylinder head smelting production method with high vermiculation rate, which optimizes the composition of cylinder head raw materials and the unpacking mode, increases the air cooling step under the premise that normal unpacking is not followed by sand cleaning, solves the problems of low strength and low vermiculation rate of the current cylinder head, improves the strength of the cylinder head, and has high vermiculation rate; under the condition that the molding condition is not changed and the unpacking is not advanced, perfect cylinder head castings are obtained, the qualified mechanical properties and metallographic structure meet the use requirements of the cylinder head, the mechanical properties and the casting quality of the cylinder head are improved, and the application has high use value.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of diesel engine cylinder head, and particularly relates to a high-cordierite-rate high-strength cylinder head smelting production method. BACKGROUND

[0002] The cylinder head of a marine diesel engine is a key component, and its material is required to have good heat conductivity, shock absorption, high strength and heat fatigue resistance. The material grade of the cylinder head is RT500, and the mechanical properties of the attached casting sample are required to be that the tensile strength is not less than 500 MPa, the yield strength is not less than 350 MPa, the elongation after fracture is not less than 0.5%, and the cordierite rate is not less than 70%. The main wall thickness of the casting is about 15 mm to 25 mm, and the pouring liquid weight of the casting is about 500 kg. At present, the resin sand production of the as-cast RT500 (RT500 refers to the tensile strength of 500 MPa) has the problems that the cordierite rate is less than 70% or the tensile strength is less than 500 MPa, and it is difficult to simultaneously satisfy the two requirements. On the other hand, increasing the alloy amount or opening the box in advance to improve the strength will cause the casting to crack and other problems. Therefore, it is necessary to improve the cylinder head smelting production method. SUMMARY

[0003] The application solves the technical problem of providing a high-cordierite-rate high-strength cylinder head smelting production method. By optimizing the composition of the cylinder head raw material and the opening box mode, the problems of low strength and low cordierite rate of the cylinder head are solved. The perfect cylinder head casting, the qualified mechanical properties and the metallographic structure meet the use requirements of the cylinder head, the mechanical properties and the casting quality of the cylinder head are improved, and the cylinder head has high use value.

[0004] The application adopts the technical scheme of a high-cordierite-rate high-strength cylinder head smelting production method, which comprises the following steps:

[0005] 1) The composition and proportion of the cylinder head raw material are as follows: 20% to 30% of pig iron, 40% to 50% of scrap steel, 1.0% to 1.2% of silicon iron, 0.8% to 1% of manganese iron, 0.7% to 0.8% of molybdenum iron, 0.7% to 0.8% of copper, and the rest is cordierite back furnace material;

[0006] 2) The 20% to 30% of pig iron, the 40% of scrap steel, and the silicon iron, the 0.8% to 1% of manganese iron, the 0.7% to 0.8% of molybdenum iron, and the 0.7% to 0.8% of copper are added into a smelting furnace, the remaining scrap steel and the cordierite back furnace material are added after the pig iron and the scrap steel in the furnace are completely melted, the surface dross is removed after complete melting, and the cylinder head is obtained by opening the box.

[0007] 3) After the temperature rises to above 1420℃, take a spectral sample and a chemical sample at a position about 100mm below the liquid surface of the molten iron to perform chemical composition analysis, if the chemical composition of the molten iron reaches the pre-furnace chemical composition, then raise the temperature to 1480℃-1520℃ to reach the tapping temperature, otherwise, add alloy or carbon additive to reach the corresponding composition content according to the difference between the pre-furnace chemical composition;

[0008] 4) Put 0.50%-0.55% of the graphitizing agent into the graphitization pit on the side of the graphitization pit, mix 0.05% of tin, 0.01% of antimony and 0.5% of ferrous sulfide with the graphitizing agent, lay them flat on the bottom of the graphitization pit and compact them properly, then cover 0.2% of the calcium-barium inoculant on the graphitization pit, lay it flat and compact it properly, then cover multiple silicon steel sheets on the calcium-barium inoculant, and finally cover the iron plate and press several pieces of pig iron around it;

[0009] 5) When tapping, use 0.3%-0.4% of the silicon-manganese-zirconium inoculant to perform the flushing inoculation, and use 0.2% of the antimony-containing inoculant to perform the transient inoculation when pouring;

[0010] 6) After pouring, open the sand box about 2.5h later, do not clean the sand, and keep the castings in the broken sand mold, use a powerful fan to cool for several minutes, then stop, and in winter, keep still for about 1h, and in other seasons, keep still for about 3h, then perform the sand cleaning treatment, and when the castings cool to room temperature, perform the cleaning and polishing of the castings, and then perform the normal stress relief treatment.

[0011] In the above step 3), the pre-furnace chemical composition is: carbon (C): 3.7%-3.9%; silicon (Si): 1.1%-1.2%; manganese (Mn): 0.75%-0.85%; sulfur (S): 0.015-0.19%; phosphorus (P): <0.07%; copper (Cu): 0.75%-0.85%; titanium (Ti): 0.03%-0.05%, molybdenum (Mo): 0.4%-0.5%, nickel (Ni): <0.05%, and chromium (Cr): <0.05%.

[0012] In the above step 5), the particle size of the silicon-manganese-zirconium inoculant is 3mm-7mm.

[0013] In the above step 6), the powerful fan cooling time is 8min-12min.

[0014] Compared with the prior art, the present application has the following advantages:

[0015] 1. The technical solution optimizes the material composition of the cylinder head, and increases the air cooling step under the condition of normal opening of the box without sand cleaning, thereby greatly improving the strength of the cylinder head, and the tensile strength and yield strength meet the use requirements.

[0016] 2、The technical scheme improves the vermicularity of the cylinder head by adding tin, antimony and ferrous sulfide in the inoculation process, and improves the vermicular cast iron quality and production process level.

[0017] 3、The technical scheme has simple structure, novel design, simple process steps, solves the problems of low strength and low vermicularity of the cylinder head, obtains perfect cylinder head castings, qualified mechanical properties and metallographic structure under the condition of not changing the molding condition and not opening the box in advance, meets the use requirements of the cylinder head, improves the mechanical properties and casting quality of the cylinder head, and has high use value. DETAILED DESCRIPTION

[0018] The technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0019] It should be noted that in this paper, the term "include", "contain" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or includes elements inherent to such process, method, article or device. Without more limitations. The element defined by the sentence "includes a..." does not exclude the presence of another identical element in the process, method, article or device including the element.

[0020] The high vermicularity high-strength cylinder head smelting production method comprises the following steps:

[0021] 1) The composition and proportion of the raw materials of the cylinder head are as follows: 20%-30% of pig iron, 40%-50% of scrap steel, 1.0%-1.2% of silicon iron, 0.8%-1% of manganese iron, 0.7%-0.8% of molybdenum iron, 0.7%-0.8% of copper, and the rest is vermicular cast iron return material;

[0022] 2) 20%~30% pig iron, 40% or so scrap steel and ferrosilicon, 0.8%~1% ferromanganese, 0.7%~0.8% ferromolybdenum, 0.7%~0.8% copper are added into a smelting furnace, after the pig iron and scrap steel in the furnace are completely melted, the remaining scrap steel and vermicular iron are added, after complete melting, surface dross is removed; silicon is a graphitizing element, and an appropriate amount of silicon content can form vermicular graphite; manganese, molybdenum and copper are pearlite-forming elements, manganese and molybdenum are undercooling positive segregation elements that can form pearlite between the crystals, strengthen the intercrystalline, copper is a graphitizing element that can balance the adverse effects of undercooling elements such as manganese and molybdenum and form pearlite in the crystal and refine the pearlite, the comprehensive use of manganese, molybdenum and copper can make the pearlite more uniform and refined, and can improve the strength of the matrix, in addition, molybdenum can improve the thermal fatigue strength of the matrix, etc.

[0023] 3) after the temperature rises to above 1420℃, a spectral sample and a chemical sample are taken at a position about 100mm below the surface of the molten iron to perform chemical composition analysis, if the chemical composition of the molten iron reaches the pre-furnace chemical composition, the temperature is raised to 1480℃~1520℃ to reach the tapping temperature, otherwise, according to the difference between the pre-furnace chemical composition, an alloy or a carbon additive is added to reach the corresponding composition content; specifically, the pre-furnace chemical composition is: carbon (C): 3.7%~3.9%; silicon (Si): 1.1%~1.2%; manganese (Mn): 0.75%~0.85%; sulfur (S): 0.015%~0.19%; phosphorus (P): <0.07%; copper (Cu): 0.75%~0.85%; titanium (Ti): 0.03%~0.05%, molybdenum (Mo): 0.4%~0.5%, nickel (Ni): <0.05%, chromium (Cr): <0.05%; the carbon equivalent of the casting is about 4.3, the final silicon content is about 2.3, and manganese, molybdenum, copper, tin and antimony are alloyed; carbon and silicon are graphitizing elements, and an appropriate amount of carbon and silicon content can form vermicular graphite, when the carbon equivalent of the casting is about 4.3%, it will be close to eutectic solidification, which can greatly reduce the shrinkage tendency of the casting; manganese, molybdenum and copper are pearlite-forming elements, manganese and molybdenum are undercooling positive segregation elements that can form pearlite between the crystals, strengthen the intercrystalline, copper is a graphitizing element that can balance the adverse effects of undercooling elements such as manganese and molybdenum and form pearlite in the crystal and refine the pearlite, the comprehensive use of manganese, molybdenum and copper can make the pearlite more uniform and refined, and can improve the strength of the matrix, in addition, molybdenum can improve the thermal fatigue strength of the matrix, etc.; tin and antimony are strong pearlite-forming elements, which can greatly increase the pearlite content, the higher the pearlite content, the higher the strength of the matrix, in addition, tin and antimony can also improve the vermiculation rate;

[0024] 4) Put 0.52% of the vermiculite agent into the vermiculite pocket of the spheroidization pit, mix 0.05% of tin, 0.01% of antimony and 0.5% of ferrous sulfide with the vermiculite agent, lay flat to the bottom of the spheroidization pit and compact properly, then cover 0.2% of calcium bar inoculant on the vermiculite agent, lay flat and compact properly, then cover a plurality of silicon steel sheets on the calcium bar inoculant, and finally cover an iron plate and press a plurality of pig irons around; the silicon steel sheets can delay the vermiculite reaction, improve the absorption rate of the vermiculite agent, tin and antimony, tin and antimony are strong pearlite elements, which can greatly improve the pearlite content, the higher the pearlite content, the higher the matrix strength, in addition, tin and antimony can also improve the vermiculite rate, and the ferrous sulfide can react with the rare earth magnesium in the vermiculite agent to generate the nucleation points of vermiculite graphite, and the appropriate sulfur content can improve the vermiculite rate;

[0025] 5) 0.35% of the silicon manganese zirconium inoculant is used for flushing inoculation when the casting is discharged, and 0.2% of the antimony-containing inoculant is used for instantaneous inoculation when pouring; specifically, the particle size of the silicon manganese zirconium inoculant is 5 mm;

[0026] 6) The sand box is opened about 2.5 hours after pouring, and the sand is not cleaned so that the casting is still retained in the broken sand mold, and after 10 minutes of air cooling by using a powerful fan, the air cooling is stopped, and after about 1 hour of standing in winter and about 3 hours of standing in the rest seasons, the sand cleaning treatment is performed, and after the casting is cooled to room temperature, the cleaning and polishing of the casting are performed, and then the normal stress relief treatment is performed;

[0027] After about 2.5 hours of pouring, the casting is about to enter the phase change stage, the sand box is opened for air cooling, which can accelerate the cooling and the phase change reaction, is beneficial to the formation and refinement of pearlite and improves the matrix strength, and the incomplete cleaning of the sand is to prevent the casting from cracking due to the rapid cooling, the air cooling is performed for 10 hours, the phase change is basically completed, the slow cooling stage is entered, the casting is gradually released from the stress to prevent deformation and cracking, and after the slow cooling stage is completed, the sand can be completely cleaned.

[0028] Table 1 is the mechanical property value of the attached casting sample

[0029] Test item Tensile strength Yield strength Elongation Hardness National standard requirement ≥500 ≥350 ≥0.5 / Actual 563 425 1.5 236

[0030] After the casting is subjected to the body dissection, the body mechanical property value is detected and is shown in Table 2

[0031] Table 2

[0032] Test item Tensile strength Yield strength Elongation Hardness National standard requirement ≥450 ≥300 ≥0.5 / Actual 513 330 2 218

[0033] The piston skirt casting produced by the present application has a qualified rate of 95% in the mechanical property detection, magnetic powder detection and ultrasonic detection, the vermiculite rate of the attached casting sample reaches 80%-85%, and the body vermiculite rate is as high as 85%-90%.

[0034] The technical scheme improves the strength of the cylinder cover by optimizing the material composition of the cylinder cover and adding the air cooling step under the condition of normal unpacking without sand cleaning, and the tensile strength and yield strength meet the use requirements; the vermicularity of the cylinder cover is improved by adding tin, antimony and ferrous sulfide in the inoculation process, and the vermicular graphite cast iron quality and production process level are improved; the structure is simple, the design is novel, the process steps are simple and easy to master, the problems of low strength and low vermicularity of the cylinder cover are solved, the perfect cylinder cover casting is obtained under the condition of not changing the molding condition and not unpacking in advance, the qualified mechanical properties and metallographic structure meet the use requirements of the cylinder cover, the mechanical properties and casting quality of the cylinder cover are improved, and the cylinder cover has high use value.

[0035] It is apparent to those skilled in the art that the application is not limited to the details of the foregoing exemplary embodiments, and that the present application can be implemented in other particular forms without departing from the spirit or essential characteristics of the application. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive, the scope of the application being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

[0036] Furthermore, it should be understood that although the present specification is described in terms of embodiments, not every implementation embodies an independent technical solution, and the description of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be combined appropriately to form other embodiments that those skilled in the art can understand.

Claims

1. A method of melting production of high-creep-rate high-strength cylinder heads, characterized in that The method comprises the following steps: 1) the composition and proportion of the cylinder head raw material are as follows: 20-30% of pig iron, 40-50% of scrap steel, 1.0-1.2% of silicon iron, 0.8-1% of manganese iron, 0.7-0.8% of molybdenum iron, 0.7-0.8% of copper, and the rest is vermiculite back furnace material; 2) 20-30% of pig iron, about 40% of scrap steel, 1.0-1.2% of silicon iron, 0.8-1% of manganese iron, 0.7-0.8% of molybdenum iron and 0.7-0.8% of copper are added into a smelting furnace, after the pig iron and scrap steel in the furnace are completely melted, the remaining scrap steel and vermiculite back furnace material are added, and after complete melting, the surface dross is removed; 3) after the temperature rises to above 1420℃, the chemical composition is analyzed by taking a spectrum sample and a chemical sample at a position about 100mm below the liquid surface of the molten iron, if the chemical composition of the molten iron reaches the pre-furnace chemical composition, the temperature is raised to the tapping temperature, otherwise, according to the difference between the pre-furnace chemical composition, the corresponding component content is supplemented by adding alloy or carbon additive; 4) 0.50-0.55% of spheroidizing agent is placed in the spheroidizing pit on the side of the vermiculite bag pit, 0.05% of tin, 0.01% of antimony and 0.5% of ferrous sulfide are mixed with the spheroidizing agent, and are laid flat on the bottom of the spheroidizing pit and are properly compacted, then 0.2% of calcium bar inoculant is covered on the spheroidizing agent, is laid flat and is properly compacted, then a plurality of silicon steel sheets are laid flat on the calcium bar inoculant, and finally an iron plate is covered and pressed, and several pieces of pig iron are pressed around; 5) 0.3-0.4% of silicon manganese zirconium inoculant is used for flushing inoculation when tapping, and 0.2% of antimony-containing inoculant is used for instantaneous inoculation when pouring; 6) the flask is opened about 2.5h after pouring, and the sand is not cleaned so that the castings remain in the broken sand mold, after using a powerful fan for air cooling for several minutes, the sand is cleaned after stopping for about 1h in winter and about 3h in other seasons, after the castings are cooled to room temperature, the castings are cleaned and polished, and then normal stress relief treatment is performed.

2. The high-creep-rate high-strength cylinder head melting production method according to claim 1, characterized by: In the step 3), the pre-furnace chemical composition is as follows: carbon (C): 3.7-3.9%; silicon (Si): 1.1-1.2%; manganese (Mn): 0.75-0.85%; sulfur (S): 0.015-0.19%; phosphorus (P): <0.07%; copper (Cu): 0.75-0.85%; titanium (Ti): 0.03-0.05%; molybdenum (Mo): 0.4-0.5%; nickel (Ni): <0.05%; and chromium (Cr): <0.05%.

3. The high-creep-rate high-strength cylinder head melting production method according to claim 1, characterized by: In the step 3), the tapping temperature is 1480-1520℃.

4. The high-creep-rate high-strength cylinder head melting production method according to claim 1, characterized by: In the step 5), the particle size of the silicon manganese zirconium inoculant is 3-7mm.

5. The high-creep-rate high-strength cylinder head melting production method according to claim 1, characterized by: In the step 6), the air cooling time of the powerful fan is 8-12min.