CN111687380B

CN111687380B - Production method of pearlite matrix ultrahigh-strength ductile nodular cast iron crankshaft

Info

Publication number: CN111687380B
Application number: CN202010625700.5A
Authority: CN
Inventors: 崔炜; 李胜柱; 李伟柱; 吴宝成; 郭孝江; 陶前昭
Original assignee: Guangxi Yuchai Machine Parts Manufacturing Co Ltd
Current assignee: Guangxi Yuchai Foundry Co ltd
Priority date: 2020-07-01
Filing date: 2020-07-01
Publication date: 2021-09-10
Anticipated expiration: 2040-07-01
Also published as: CN111687380A

Abstract

The invention provides a production method of a pearlite matrix nodular cast iron crankshaft with ultrahigh strength and toughness, which selects low-sulfur low-titanium pig iron, common carbon steel and self-produced recycled iron as main furnace charges, and adds 75 ferrosilicon, 65 high-carbon ferromanganese, electrolytic copper and a graphite carburant in a specific proportion; smelting at a specific frequency of an intermediate frequency furnace, adding a nodulizer, an inoculant and a silicon-calcium-manganese deoxidizer, tapping and nodulizing, wherein the nodulizing process requires specific tapping position, speed and tapping steps, the pouring process selects a specific flow rate and total amount of the inoculant, and a specific normalizing process is adopted for a crankshaft casting to prepare the ultrahigh-strength ductile nodular cast iron material with the strength of more than 1000MPa, the elongation of more than or equal to 5 percent and the base material of pearlite. The comprehensive performance of the alloy far exceeds that of common ductile iron and ADI materials with the same tensile strength. The preparation method is applied to the J4200 crankshaft, the JX400 crankshaft and other parts, realizes the preparation of the pearlite matrix ultrahigh-strength toughness material, reduces the cost and obtains remarkable benefits.

Description

Production method of pearlite matrix ultrahigh-strength ductile nodular cast iron crankshaft

Technical Field

The invention belongs to the field of nodular cast iron casting technology, and particularly relates to a production method of a pearlite matrix ultrahigh-strength ductile nodular cast iron crankshaft with tensile strength of more than 1000MPa and elongation of more than 5%.

Background

When designing engine crankshaft parts, designers usually select materials meeting yield strength according to indexes such as strength, elongation and the like from national standard materials. At present, for tough metal materials with the strength exceeding 1000MPa and the elongation rate not lower than 5%, only 40Cr, 42CrMo, engineering high-strength cast steel or ADI materials are usually used for meeting the structural design requirements of the crankshaft.

1. According to the standard of GB/T1348-2009: the common nodular cast iron has the highest strength of 900MPa and the elongation of 2 percent, and a small number of domestic manufacturers can make QT800-6 and QT900-4 material marks, but the materials can not be used as the material of the crankshaft of the six-country engine, and the high mechanical property requirements of high detonation pressure and high light weight crankshaft parts of the six-country engine can not be met due to the low elongation. The material of the national six crankshafts of the current engine factories still adopts 40Cr and 42CrMo forged materials due to the limitation of cast iron materials.

2. The strength of ordinary cast steel can not reach more than 1000MPa, and the design requirements can be met only by low-alloy cast steel materials. The castingsteel part has the casting manufacturability far inferior to that of cast iron, the molten alloy cast steel has poorer liquidity, and the defects of cold shut and air holes are easily generated, particularly the forming defects are easily generated on the national six-crankshaft parts with complex structures and uneven sections, so the reliability is influenced;

3. the shrinkage of the steel castings is very large, large risers are required to be added in a gating system for feeding, the influence on the yield is great, the yield of the steel castings is usually only about 50%, the shrinkage of alloy cast steel is larger, and cast iron can reach 70-80%. The low-alloy cast steel is not suitable for the molding of the casting with uneven wall thickness of the crankshaft;

the price of 4.40Cr and 42CrMo materials is generally 15-17 yuan/kg, which is much higher than the material cost of 8-10 yuan of common nodular cast iron, and the material forging process cannot meet the design requirement of hollow weight reduction in the national six-crankshaft journal, wastes materials and has limited contribution to light weight.

ADI material is a cast iron material with high strength and high elongation, which can meet the working condition requirement of high-strength crankshaft parts, but has the following limitations:

5.1 the heat treatment cost is very high, the process range is very narrow (ADI material has high isothermal quenching requirement, is transformed into martensite structure after being cooled too fast, and is transformed into pearlite structure after being cooled too slowly), and the heat treatment equipment is usually over ten million. The casting with the wall thickness difference more than 20mm cannot be quenched completely, and the parts cannot be uniform in structure and performance;

5.2ADI material preparation cost reaches 17-20 yuan per kilogram, and even reaches 2 times of value of common nodular cast iron; the material cost is not affordable by the general enterprises.

5.3ADI material is very difficult to process, the austenite structure at normal temperature can generate work hardening phenomenon, and the cost of the cutter is very high.

5.4, the main reason why the ADI material still cannot be widely popularized is that the ADI material is limited by the preparation technology, the preparation cost, the processing cost and the structure.

6. The density of the alloy cast steel is usually 7.8-7.9g/cm³ADI density of 7.3g/cm³While the density of the common pearlite nodular cast iron is 7.1g/cm³. The material density is 10% lighter than that of alloy cast steel, and the alloy cast steel has the advantage of inherent light weight, and under the condition of the same structure, the weight is only 90% of that of the cast steel, so that the alloy cast steel contributes to light weight greatly.

In summary, for crankshaft parts requiring high-strength materials, the selection of 40Cr, 42CrMo or ADI materials is not an ideal solution.

7. The production method of high-strength high-elongation nodular cast iron which refers to Chinese patent document with the patent number of 2017108487584 comprises the following steps: (1) selecting Q10 low-sulfur low-titanium pig iron, common carbon steel and self-produced recycled iron as main furnace charges, and adding 75 ferrosilicon accounting for 0.65-0.8% of the total mass of the main furnace charges, 65 high-carbon ferromanganese accounting for 0.15-0.19%, electrolytic copper accounting for 0.15-0.20% and graphite type carburant accounting for 2.3-2.5%; smelting and melting by an intermediate frequency furnace to obtain molten iron; (2) preparing 2-6 and 3-7 of low rare earth nodulizer according to a mass ratio of 4: 1, adding a special nodulizer prepared by mixing the components in the proportion into a nodulizing ladle to realize that the residual RE of the final molten iron is 0.02-0.025 percent and the residual Mg0.03-0.04 percent, and controlling the residual RE/Mg ratio to 2/3; (3) adding a BS-1A inoculant and 75 ferrosilicon as a primary inoculant before spheroidizing the molten iron; (4) tapping liquid iron from the intermediate frequency furnace to a spheroidizing bag, and tapping for 2 times by adopting a flushing method; (5) during pouring, 75 silicon is added with the flow as a secondary inoculant. In the production method, stable residual Mg and residual RE are obtained through reasonable components and nodulizer proportion and a stable nodulizing process, and a reasonable inoculation process is adopted, so that the spheroidization grade of graphite reaches more than grade 2, the diameter grade of graphite is 5-8, round graphite spheres are obtained, but the spheroidization rate is only 90-92%, the diameter of graphite is 0.015-0.06mm, and the spheroidization rate and the diameter of graphite of crankshaft parts required by high-strength materials do not reach the optimal effect.

Disclosure of Invention

In order to overcome the technical problems, the invention prepares the pearlite type ductile cast iron crankshaft part with the material strength of more than or equal to 1000MPa and the elongation of more than or equal to 5 percent by improving the graphite roundness and ensuring the process innovation of various aspects such as matrix structure strength and the like by a reasonable cooling process, can replace 40Cr, 42CrMo or ADI materials with complex process and high cost, fills the blank of common ductile cast iron materials, and prepares the high-strength crankshaft part of a national six-engine by using the ultrahigh-strength ductile cast iron ductile material, and the specific scheme is as follows:

the production method of the pearlite matrix ultrahigh-strength ductile cast iron crankshaft comprises the following steps:

(1) after the molten iron is poured, opening the box after the crankshaft casting is solidified;

(2) directly feeding the crankshaft casting into a normalizing furnace, wherein the normalizing temperature is 860 ℃ and 900 ℃, the normalizing time is 100 ℃ and 120 minutes, the crankshaft casting needs to be sprayed and cooled within 30 seconds after being discharged from the furnace, and the rotating speed of a hanger during spraying and cooling is 5.5 circles/minute;

(3) and (5) cooling the casting to 250-300 ℃, then entering a tempering furnace, tempering at 500 ℃, and air-cooling to reach the use state after 60 minutes.

Further, the molten iron is prepared from pearlite matrix molten iron through spheroidization and secondary inoculation.

Further, the pearlite matrix iron liquid takes 20% of low-sulfur low-titanium pig iron, 55% of carbon steel and 25% of pearlite type recycled iron in a mass ratio of Q10 as main furnace materials, and then 75 ferrosilicon, 0.35% of 65 high-carbon ferromanganese, 0.5% of electrolytic copper and 2.4% of graphite type carburant in the total mass of the main furnace materials are added, and the pearlite matrix iron liquid is smelted by an intermediate frequency furnace to obtain the following components: c: 3.8-3.9%, Si: 0.7-0.9%, Mn: 0.4-0.5%, Cu: 0.4-0.5 percent of basic iron liquid, less than or equal to 0.03 percent of S and less than or equal to 0.035 percent of Ti, the heat preservation time of the iron liquid is controlled to be less than or equal to 40 minutes, and the medium-frequency stirring frequency is 350-420 Hz.

Further, in the spheroidization step of the pearlite matrix iron liquid, a low rare earth 1-6 nodulizer and a primary inoculant which account for 0.95-1% of the mass of the molten iron are added into a spheroidization ladle, wherein the primary inoculant comprises 0.28-0.32% of BS-1A inoculant, 0.08-0.1% of SiCaMn deoxidizer with the granularity of 3-6mm, 0.2-0.25% of BS-1Sb and 0.4% of 75 ferrosilicon.

Further, in the pearlite matrix iron liquid spheroidizing step, the packaging sequence is as follows: firstly, 1/3 parts of 75 ferrosilicon are placed on one side of a spheroidizing dam, then a spheroidizing agent is poured, the spheroidizing agent is paved, then a BS-1A, BS-1Sb and SiCaMn mixing agent is placed on the spheroidizing agent, the rest 75 ferrosilicon of 2/3 is added after paving, finally 1 kg of pearl sand is scattered in the middle of a bagging material, two corners are exposed, electrolytic copper is placed on the pearl sand, and bagging is completed.

Furthermore, in the pouring step, a sulfur-oxygen inoculant which accounts for 0.15-0.2 percent of the mass of the poured molten iron is added into a funnel with a flow rate of 21g/s as a secondary inoculant along with the flow, and the adding point is the height position of 10cm at the outlet of the pouring ladle.

Further, in the tapping step, 85-90% of the tapping liquid is tapped for the first time, the tapping speed is 500 kg/s, the tapping liquid is flushed to the ladle wall with the height of below 50%, and the tapping time is less than or equal to 10 s; and 2, after 8-10s of the start of the spheroidization reaction, adding the rest 10-15% of iron liquid.

Furthermore, the spraying mode adopts a peripheral matrix distribution spray nozzle and an intermediate cooling shaft spraying mode, and the cooling flow is 2.5-3.0L/s.

Further, the specific steps are as follows:

(1) smelting to obtain a product with the components of C: 3.8-3.9%, Si: 0.7-0.9%, Mn: 0.4-0.5%, Cu: pearlite matrix solution with the weight percentage of 0.4-0.5%, S less than or equal to 0.03% and Ti less than or equal to 0.05%;

(2) adding 1-6 nodulizer of low rare earth and primary inoculant into a nodulizing ladle before nodulizing, and placing the primary inoculant above the nodulizer during packaging;

(3) tapping molten iron from the intermediate frequency furnace to a spheroidizing bag by adopting a flushing method, wherein the tapping spheroidizing temperature is 1530 and 1550 ℃, and tapping the molten iron in two steps;

(4) during pouring, a sulfur-oxygen inoculant with the granularity of 0.3-1mm is used as a secondary inoculant and added along with the flow, the addition point is the height position of 10cm at the outlet of a pouring ladle, the secondary inoculant amount is 0.15-0.2 percent of the mass of the poured molten iron, and the secondary inoculant is added by a funnel with the flow rate of 21 g/s;

(5) injecting the molten iron in the step (4) into a crankshaft casting through a pouring system containing a cross gate with the length of not less than 20-25 cm;

(6) after the molten iron is poured, opening the box after the crankshaft casting is solidified;

(7) opening the box, directly entering a normalizing furnace, normalizing at 860 ℃ and 900 ℃ for 120 minutes, and discharging from the furnace to perform spray cooling within 30 seconds; the spraying mode is that a spraying nozzle matrix with the distance of 20 cm is arranged around the casting within the range of 20-25cm, and the cooling flow is 2.5-3.0L/s; rotating the casting at a rotation speed of 5.5 circles/minute during spraying;

(8) the casting is cooled to the temperature of 250 plus materials and 300 ℃ and enters a tempering furnace, the tempering temperature is 500 ℃, the casting is cooled by blowing after 60 minutes, and the air volume is 3700 plus materials and 6000m³Cooling to less than 100 ℃ to reach a use state;

(9) and (3) inspecting the mechanical property by adopting one mechanical test block for each ladle of molten iron corresponding to the casting.

THE ADVANTAGES OF THE PRESENT INVENTION

Compared with the prior art, the production method of the pearlite matrix nodular cast iron six-engine crankshaft provided by the invention has the following advantages:

1. the traditional national standard pearlite nodular cast iron crankshaft has the maximum tensile strength of 900MPa and the elongation of only 2 percent, and the structure is a troostite and sorbite structure. The pearlite nodular cast iron crankshaft with the strength of more than or equal to 1000MPa and the elongation of more than or equal to 5 percent is prepared by improving the graphite roundness, refining the graphite diameter and carrying out heat treatment and cooling processes; (1) the SiCaMn deoxidizer added in the spheroidizing process can reduce the amount of free oxygen in molten iron in the nodular cast iron smelting process, not only can reduce the addition of a spheroidizing agent, but also can compensate the deoxidation effect on the basis of spheroidizing agent desulfurization, ensure that the molten iron is deoxidized fully in the spheroidizing process, ensure that the residual free oxygen does not cause excessive interference effect on the graphite growth, add the SiCaMn deoxidizer into a spheroidizing bag along with the spheroidizing agent, realize cast iron deoxidation by using the rolling of the spheroidizing agent during reaction, and effectively improve the growth roundness of the graphite; (2) when molten iron is poured, 0.15-0.2% of sulfur-oxygen inoculant is added, the sulfur-oxygen inoculant is in a combined state, free oxygen and sulfur in the molten iron cannot be increased, the sulfur-oxygen inoculant is sulfide and oxide, is a core of a graphite efficient moving core, can greatly promote carbon radicals to attach to the carbon-oxygen inoculant, promotes graphite moving core, increases graphite quantity, promotes graphite quantity, and can obviously reduce graphite diameter. (3) And adjusting the heat treatment process, strictly limiting the temperature, time and cooling mode of the normalizing, if the cooling must be started within 30 seconds, the cooling mode is to spray water on a peripheral matrix and spray water on a pipeline in the middle of a hanging basket, the water quantity is limited, the rotating speed of the hanging basket is limited, and the constant cooling speed of the upper part, the lower part, the inner part and the outer part of the crankshaft part is ensured to meet the process requirements.

2. The common spheroidizing process by the pouring method only can ensure that the spheroidization grade of the spherical graphite can only reach 2-3 grades, the spheroidization rate reaches 80-90 percent, the diameter of the graphite is 5-6 grades, and the quantity of the graphite is 100 plus one 250 pieces/mm²The core of the casting reaches the spheroidization grade of 3-4, and the spheroidization rate is 70-85%. The treatment process for improving the graphite roundness of the nodular cast iron is simple and convenient, has high reliability, can stably improve the spheroidization grade of the nodular graphite to reach 1-2 grade and above, has the spheroidization rate of 93-99 percent, and can spheroidize the center of a casting and the likeThe grade reaches 2 grade, the spheroidization rate reaches 90-95 percent, the graphite diameter reaches 7 grade, and the graphite quantity can reach 300 plus 400 pieces/mm²。

3. Expensive components such as nickel, molybdenum and the like are not added in chemical components (the content of nickel and molybdenum is trace), and 0.5-0.6 nickel and 0.3-0.8 molybdenum are required to be added in an ADI casting or 42CrMo material, so that the cost of the pearlite type nodular cast iron crankshaft prepared by the method is lower.

4. The invention only needs normalizing and tempering in the heat treatment link, has large process interval, and has low control difficulty compared with the ADI material heat treatment process. The invention can cast the crankshaft with the shaft diameter and the central hole structure, and the crankshaft made of 42CRMo forging material can not realize a hollow structure, thereby having obvious advantage of light weight.

5. Compared with steel casting, the invention has casting performance equivalent to that of traditional nodular cast iron, and the technological yield is about 75-85%, while the technological yield of steel casting is only 50-60%, and the invention has higher yield than steel casting.

The market prices of alloy cast steel materials such as 6.40 Cr, 42CrMo and the like are generally 15-17 yuan per kg, the market prices of ADI materials reach 17-20 yuan per kg, and the market prices of raw materials used in the process are only 9-11 yuan per kg and are far lower than the market prices of the materials.

7. The requirement on production equipment is low, and common ductile cast iron casting workshops have equipment conditions.

8. The application field of nodular cast iron is widened, the material grade of the invention fills the domestic blank, the crankshaft made of the QT1000-5 material of the invention can completely replace a crankshaft made of 42CrMo material, iron replaces steel in the field of national six crankshafts, and more choices are provided for the design and manufacture of mechanical parts in the application field of ultrahigh-strength and high-elongation materials.

Drawings

FIG. 1: schematic diagram of the sequence of the spheroidized packaging bag.

FIG. 2: the amount of the first tapping iron is shown schematically.

FIG. 3: schematic drawing of tapping and punching positions of the intermediate frequency furnace.

FIG. 4: the iron liquid amount from the second tapping to the end is shown schematically.

FIG. 5: the pouring process is schematically illustrated as secondary inoculation.

FIG. 6: the structure of the crankshaft gating system is schematic.

FIG. 7: schematic diagram of rotating fog cooling after crankshaft heat treatment and furnace discharge.

In the figure: 1. covering with pearl sand; 2. 75 silicon iron layer; 3. a mixed agent layer of BS-1A, BS-1Sb and SiCaMn; 4. 1-6 low rare earth nodulizer layer; 5. 75 silicon iron layer; 6. a tapping furnace mouth of the intermediate frequency furnace; 7. pouring the tapping iron liquid into the position; 8. packaging materials in the reaction; 9. the height of the liquid level of the first tapping; 10. the height of the secondary tapping; 11. a secondary inoculant funnel; 12. a secondary inoculant; 13. the distance between a hopper feed opening and molten iron; 14. liquid iron; 15. casting a crankshaft; 16. pouring a ladle; 17. a crankshaft gating system; 18. a cross gate; 19. casting; 20: rotating the hanging shaft in a fog cooling mode; 21: cooling the spray pipe in the middle of the crankshaft; 22: a crankshaft casting; 23: a fog cooling nozzle.

Detailed Description

The following further explanation is provided in conjunction with the accompanying drawings and the embodiments, but it should be noted that the embodiments are not intended to limit the scope of the present invention.

The production method for preparing QT100-5 brand pearlite matrix ultrahigh-strength ductile cast iron crankshaft by adopting the following technical scheme comprises the following steps:

(1) q10 low-sulfur low-titanium pig iron, carbon steel and pearlite type return iron are selected as main furnace charges, and the mass ratio of the main furnace charges is as follows: q10 low-sulfur low-titanium pig iron 20%, carbon steel scrap 55%, pearlite type ductile iron returning iron 25%; then adding 75 ferrosilicon accounting for 0.18 percent of the total mass of the main furnace charge, 0.35 percent of 65 high-carbon ferromanganese, 0.5 percent of electrolytic copper (low lead, purity 99.99 percent) and 2.4 percent of graphite type carburant, smelting by an intermediate frequency furnace, controlling the intermediate frequency stirring frequency to be 350-420Hz, and obtaining the component C: 3.8-3.9%, Si: 0.7-0.9%, Mn: 0.4-0.5%, Cu: 0.4-0.5 percent of basic iron liquid, less than or equal to 0.03 percent of S and less than or equal to 0.05 percent of Ti, wherein the heat preservation time of the iron liquid is controlled to be less than or equal to 40 minutes;

(2) spheroidizing the molten iron: adding a low rare earth 1-6 nodulizer accounting for 0.95-1% of the molten iron mass into a nodulizing ladle before nodulizing the molten iron to realize that the residual RE of the final molten iron is 0.005-0.008% and the residual Mg is 0.03-0.04%, and controlling the ratio of the residual RE to the Mg to be 1/5.3-1/5.5;

adding a BS-1A inoculant accounting for 0.28-0.32 percent of the mass of the molten iron, 0.2-0.25 percent of BS-1Sb, 0.08-0.1 percent of SiCaMn deoxidizer and 0.4 percent of 75 ferrosilicon into a spheroidizing ladle as primary inoculants, wherein the granularity of the SiCaMn deoxidizer is 3-6mm, and the SiCaMn deoxidizer and the BS-1A are mixed uniformly in advance, aiming at realizing cast iron deoxidation by using the rolling of the spheroidizing agent, reducing the quantity of free oxygen in pearlite matrix molten iron during reaction, reducing the interference of the free oxygen on the graphite crystallization process, reducing the addition amount of the spheroidizing agent, simultaneously making up the deoxidation effect on the basis of the desulfurization of the spheroidizing agent, ensuring that the molten iron is deoxidized fully in the spheroidizing process, ensuring that the residual free oxygen does not cause excessive interference on the graphite growth, improving the graphite roundness of graphite and enabling the graphite grade of the nodular cast iron to reach 1-2 level, the spheroidization rate reaches 93-99%.

During packaging, the primary inoculant is placed above the low rare earth nodulizer 1-6, the packaging sequence is shown in figure 1, 1/3 of 75 ferrosilicon is placed on one side of a spheroidizing dam, then the nodulizer is poured in, the nodulizer is paved, then a mixture of BS-1A, BS-1Sb and SiCaMn is placed on the nodulizer, the rest 75 ferrosilicon of 2/3 is added after paving, finally 1 kg of pearl sand is scattered in the middle of the packaging material, two corners are leaked, electrolytic copper is placed on the pearl sand, and packaging is completed.

(3) Tapping liquid iron from the intermediate frequency furnace to a spheroidizing bag by adopting an flushing method, wherein the tapping spheroidizing temperature is 1530-1550 ℃, the tapping step is divided into 2 steps, as shown in figure 2, the tapping speed of the liquid iron which accounts for 85-90% of the inner volume of the spheroidizing bag in the step 1 needs to reach 500 kg/10 s, the tapping liquid iron is flushed into the bag wall below 50% (the low rare earth 1-6 spheroidizing agent cannot be flushed directly), and the tapping position of the intermediate frequency furnace is shown in figure 3; the 1 st tapping time is less than or equal to 10 seconds, and after 8-10 seconds of the start of the spheroidization reaction, the 2 nd tapping is carried out, and the rest 10-15% of iron liquid is poured into the reactor as shown in figure 4;

(4) as shown in figure 5, during pouring, a sulfur-oxygen inoculant with the grain size of 0.3-1mm is used as a secondary inoculant and is added along with the flow, the addition point is the height position of 10cm at the outlet of a ladle, the inoculant amount is 0.15-0.2 percent of the mass of the poured molten iron, and the inoculant is added by a funnel with the flow rate of 21 g/s; when the molten iron is poured, the sulfur-oxygen inoculant is added and is in a combined state, free oxygen and sulfur in the molten iron cannot be increased, the sulfur-oxygen inoculant is sulfide and oxide, and is a core of a graphite efficient traveling nucleus, a large number of carbon atomic groups can be promoted to attach to the sulfide and oxide, the graphite traveling nucleus is promoted, and the number of graphite is increased. The increase in the amount of graphite will significantly reduce the diameter of the graphite.

(5) As shown in FIG. 6, the molten iron is poured into the crankshaft casting through a runner gating system with a length of 20-25cm, so that the inoculant and the molten iron are fully melted;

(6) after the molten iron is poured, the casting is solidified and unpacked, the unpacking time is not limited, and only the production line takt is needed to be suitable;

through the steps (1) - (5), the method can prepare the very round graphite spheres with the spheroidization rate of 98 percent and the graphite diameter of 6-7 grades, and the graphite quantity reaches 300-350/mm²The casting structure is graphite, bullseye ferrite and 95 percent pearlite, the casting performance reaches 900-940MPa, and the elongation reaches 5.8-7.5 percent. The good graphite form reduces the cutting action of graphite on a matrix, the strength of a pearlite structure can be fully developed, and the material keeps good as-cast elongation due to the bullseye-shaped ferrite around the graphite, the small graphite diameter and the large amount of graphite.

(7) The crankshaft casting is directly fed into a normalizing furnace, the energy is saved by utilizing the waste heat, the normalizing temperature is 860 ℃ and 900 ℃, the normalizing time is 100 ℃ and 120 minutes, the crankshaft casting is taken out of the furnace and is subjected to spray cooling within 30 seconds, as shown in figure 7, the spray mode is a spray nozzle with peripheral matrix distribution and a spray mode of an intermediate cooling shaft, and the cooling flow is 2.5-3.0L/s; the hanger rotation speed was 5.5 revolutions/min during spray cooling.

(8) Cooling the casting to 250-300 ℃, then entering a tempering furnace, tempering at 500 ℃, and air-cooling to reach a use state after 60 minutes;

and (4) completely austenitizing the matrix structure in the furnace through the heat treatment process in the steps (7) and (8), controlling the cooling speed of the casting within a certain range through water flow after discharging, and completely converting the matrix structure into a fine lamellar pearlite structure, wherein the heat-treated structure is graphite + 98% fine lamellar pearlite. The strength of the material is further improved by the structure refinement, but a part of the elongation index is sacrificed, so the cooling speed is an important control factor for balancing the strength and the elongation. Through heat treatment, the strength of the as-cast property is improved to 1000-1080MPa, and the elongation is reduced to 5-6%, so that the QT1000-5 material mark is obtained.

(9) And (3) detecting mechanical properties by adopting a mechanical test block corresponding to each molten iron package for casting, wherein the mechanical test block is a Y-shaped test block, the size of the Y-shaped test block is determined according to the wall thickness of the crankshaft balance block, and the wall thickness of the test block is 21-25% greater than the main wall thickness of the crankshaft balance block and is equivalent to the main wall thickness of the casting.

Various crankshaft products manufactured by the nodular cast iron QT1000-5 are produced by adopting the technology of the invention, including J4200 crankshaft, JX400 crankshaft, D0800 crankshaft and the like. The following are examples of some of the products therein:

example 1: production of J4200 crankshaft

The part weight was 70Kg, the basic wall thickness 25mm, and the external dimensions 800 x 250 mm.

(1) The ratio of the base iron main furnace burden is as follows: 20% of low-sulfur low-titanium pig iron Q10, 55% of carbon steel scrap, 25% of pearlite type ductile iron recycled iron, and the components of the adjusted iron liquid C: 3.83%, Si: 0.74%, Mn: 0.44%, Cu: 0.48%, Ti: 0.036%, S: 0.012 percent.

(2) The tapping weight is 550 kg, 5.23 kg of 1-6 nodulizer (accounting for 0.95 percent of the weight of the molten iron), 0.29 percent of BS-1A inoculant and 0.23 percent of BS-1Sb inoculant, 0.08 percent of SiCaMn deoxidizer and 0.4 percent of 75 silicon iron are added into a nodulizing ladle, the nodulizing ladle is filled according to the sequence shown in the figure 1, and the mixture is poured into the nodulizing ladle according to the tapping speed of 500 kg/10 seconds, so that the residual magnesium of the final molten iron is 0.037 percent, and the rare earth: 0.007% (rare earth/magnesium 1/5.3).

(3) The spheroidized iron liquid is cast into a J4200 crankshaft mold, and 0.15 percent of sulfur-oxygen inoculant with the diameter of 0.3-1mm is added into the liquid flow (21g/s flow rate funnel) along with the flow.

(4) And opening the box 30 minutes after the pouring is finished.

(5) And hanging the crankshaft casting on a heat treatment hanger, normalizing at 880 ℃ for 120 minutes, and then carrying out spray cooling at the flow rate of 2.8L/S.

(6) Then adding 550 ℃ for tempering and using 4800m³Flow/h air cooling.

The part is detected, the tensile strength of the body is 1065MPa, and the elongation is 5.8%. The metallographic phase is graphite spheroidization grade 1, the spheroidization rate is 98 percent, the graphite diameter is grade 7, and the number of graphite is 330/mm²The matrix structure is graphite + 98% fine lamellar pearlite, and reaches the technical standard of materials.

Example 2: production of JX400 crankshaft

The part weight was 45Kg, the basic wall thickness 25mm, and the external dimension 680 x 250 mm.

(1) The ratio of the base iron main furnace burden is as follows: 20% of low-sulfur low-titanium pig iron Q10, 55% of carbon steel scrap and 25% of pearlite type ductile iron recycled iron. Adjusting the components of molten iron to be C: 3.86%, Si: 0.70%, Mn: 0.42%, Cu: 0.5%, Ti: 0.035%, S: 0.012 percent.

(2) The tapping weight is 500 kg, 4.75 kg of 1-6 nodulizer (accounting for 0.95 percent of the weight of the molten iron), 0.28 percent of BS-1A inoculant, 0.22 percent of BS-1Sb inoculant, 0.08 percent of SiCaMn deoxidizer and 0.4 percent of 75 ferrosilicon are added into a nodulizing ladle, and the mixture is poured into the nodulizing ladle according to the tapping speed of 500 kg/10 seconds to obtain the magnesium residue of the final molten iron of 0.038 percent and rare earth: 0.007% (rare earth/magnesium 1/5.4).

(3) The spheroidized iron liquid is poured into a JX400 crankshaft mould, and 0.15 percent of sulfur-oxygen inoculant with the diameter of 0.3-1mm is added into the liquid flow (21g/s flow rate funnel) along with the flow.

(4) And opening the box 35 minutes after the pouring is finished.

(5) And hanging the crankshaft casting on a heat treatment hanger, normalizing at 880 ℃ for 120 minutes, and then carrying out spray cooling at the flow rate of 2.65L/S.

(6) Tempering at 550 ℃ and then using 4500m³Flow/h air cooling.

The part is detected, the tensile strength of the body is 1065MPa, and the elongation is 5.8%. The metallographic phase is graphite spheroidization grade 1, the spheroidization rate is 99 percent, the graphite diameter is grade 7, and the graphite quantity is 350/mm²The matrix structure is graphite + 98% fine lamellar pearlite, and reaches the technical standard of materials.

Claims

1. The production method of the pearlite matrix ultrahigh-strength ductile cast iron crankshaft is characterized by comprising the following steps of:

(1) after the molten iron is poured, opening the box after the crankshaft casting is solidified; the molten iron is prepared by spheroidizing and secondary inoculation of pearlite matrix molten iron, in the spheroidizing step of the pearlite matrix molten iron, a primary inoculant and a low rare earth 1-6 nodulizer accounting for 0.95-1% of the mass of the molten iron are added into a spheroidizing bag, wherein the primary inoculant comprises a BS-1A inoculant accounting for 0.28-0.32% of the mass of the molten iron, a SiCaMn deoxidizer accounting for 0.08-0.1% of the mass of the molten iron and having the particle size of 3-6mm, a BS-1Sb deoxidizing agent accounting for 0.2-0.25% of the mass of the molten iron and 75 ferrosilicon accounting for 0.4%;

2. The method for producing the pearlite matrix ultrahigh-strength ductile cast iron crankshaft according to claim 1, wherein pearlite matrix iron liquid is prepared by taking 20% of low-sulfur low-titanium pig iron, 55% of carbon steel and 25% of pearlite type recycled iron in a mass ratio of Q10 as main charging materials, adding 75 ferrosilicon accounting for 0.18% of the total mass of the main charging materials, 0.35% of 65 high-carbon ferromanganese, 0.5% of electrolytic copper and 2.4% of graphite type carburant, and smelting by using an intermediate frequency furnace to obtain the following components: c: 3.8-3.9%, Si: 0.7-0.9%, Mn: 0.4-0.5%, Cu: 0.4-0.5 percent of basic iron liquid, less than or equal to 0.03 percent of S and less than or equal to 0.035 percent of Ti, the heat preservation time of the iron liquid is controlled to be less than or equal to 40 minutes, and the medium-frequency stirring frequency is 350-420 Hz.

3. The method for producing a crankshaft made of pearlite base ultra-high strength ductile cast iron according to claim 1, wherein in the pearlite base iron liquid spheroidization step, the packing order is as follows: firstly, 1/3 parts of 75 ferrosilicon are placed on one side of a spheroidizing dam, then a spheroidizing agent is poured, the spheroidizing agent is paved, then a BS-1A, BS-1Sb and SiCaMn mixing agent is placed on the spheroidizing agent, the rest 75 ferrosilicon of 2/3 is added after paving, finally 1 kg of pearl sand is scattered in the middle of a bagging material, two corners are exposed, electrolytic copper is placed on the pearl sand, and bagging is completed.

4. The method for producing a crankshaft made of pearlite based ultra-high strength ductile cast iron according to claim 1, wherein in the step of pouring the molten iron, 0.15-0.2% of a sulfur-oxygen inoculant in terms of the mass of the poured molten iron is added as a secondary inoculant to a funnel with a flow rate of 21g/s at a height of 10cm at an outlet of the ladle.

5. The production method of the pearlite matrix ultrahigh-strength ductile cast iron crankshaft according to claim 1, characterized in that in the tapping step, 85-90% of the tapping liquid is tapped for the 1 st time, the tapping speed is 500 kg/s, the tapping liquid is flushed into the ladle wall for less than 50% of the height, and the tapping time is less than or equal to 10 s; and 2, after 8-10s of the start of the spheroidization reaction, adding the rest 10-15% of iron liquid.

6. The method for producing the crankshaft made of the pearlite matrix and the ultra-high strength ductile cast iron according to claim 1, wherein the spraying mode adopts a peripheral matrix distribution spraying nozzle and an intermediate cooling shaft spraying mode, and the cooling flow rate is 2.5-3.0L/s.

7. The production method of the pearlite matrix ultrahigh-strength ductile cast iron crankshaft according to any one of claims 1 to 6, characterized by comprising the following concrete steps:

(1) smelting to obtain a material with the components of C: 3.8-3.9%, Si: 0.7-0.9%, Mn: 0.4-0.5%, Cu: pearlite matrix iron liquid with the weight percentage of 0.4-0.5%, S less than or equal to 0.03% and Ti less than or equal to 0.05%;