Process method for improving durability of valve body casting and valve body casting

Abstract

The invention relates to the technical field of nodular cast iron production, in particular to a technological method for improving durability of a valve body casting and the valve body casting, and the technological method comprises the following steps: (1) smelting 20% by weight of high-purity pig iron, 46% by weight of high-purity scrap steel and 34% by weight of foundry returns to obtain molten iron; (2) molten iron obtained after smelting is poured into a spheroidizing bag to be subjected to primary inoculation treatment, a pretreating agent and an alloy are added in the primary inoculation treatment process, and the alloy is an alloy containing Sb; (3) carrying out spheroidizing treatment and inoculation treatment on the molten iron in the spheroidizing ladle; (4) carrying out ladle-to-ladle inoculation on the molten iron; (5) carrying out stream inoculation on the molten iron to form a valve body casting; and (6) the cooling time of the valve body casting in the sand box is not less than 15 hours. The valve body casting manufactured through the technological method is low in internal stress, good in durability, high in graphite spheroidizing rate, uniform in graphite spheroidizing distribution, capable of effectively preventing graphite distortion and high in ductility.

Description

Technical Field

[0001] The invention relates to the technical field of ductile iron production, and in particular to a process method for improving the durability of a valve body casting and the valve body casting. Background Art

[0002] In the automobile braking system, a variety of cast iron metal parts are needed, such as differentials, pneumatic valves, brake valves, etc. The above-mentioned high-pressure valve body is the core component of the high-pressure valve, which is directly subjected to the high-pressure fluid. Therefore, it needs to have high mechanical properties. Its design, manufacturing and material selection are crucial. The shape and structure of the high-pressure valve body are relatively complex. At present, the casting process is often used for mass production of high-pressure valve bodies. In the preparation process, steel is usually melted and then directly die-casted. Not only is the production cost high, but the mechanical properties of the workpiece are not high, and it is difficult to guarantee the performance indicators and service life of the high-pressure valve body. When this valve body is used, it will cause the car to be unable to brake completely, posing a great safety hazard.

[0003] Ductile iron is a spherical graphite obtained by spheroidizing and inoculating, which effectively improves the mechanical properties of cast iron and is currently widely used in the casting production of high-pressure valve bodies. High-pressure valve bodies usually have thick and large sections. When using the horizontal continuous casting process to produce large-section (diameter greater than 250mm) ductile iron profiles, due to the long liquid cooling and solidification time, thick and large-section ductile iron castings are prone to spheroidization and inoculation decline, and the core is often accompanied by abnormal graphite such as blooming, fragments, and coarse shapes, which affects the matrix structure, seriously affects the roundness of the profile and the density of the section and other comprehensive properties, and deteriorates the mechanical properties of the casting; at the same time, the existing manufacturing process of thick and large high-pressure valve body ductile castings is difficult to ensure durability requirements, which greatly affects the service life of the valve body.

[0004] The Chinese invention patent with publication number CN103805731A discloses a method for inoculating ductile iron, which includes ladle inoculation, inverted ladle inoculation, and flow inoculation. The invention patent adds an inverted ladle inoculation process between the original spheroidizing ladle inoculation and flow inoculation steps to achieve a special process of instantaneous multiple inoculation; however, the inoculation method disclosed is more suitable for the production of small ductile iron parts, and has no obvious effect on the production of large and large-tonnage ductile iron parts, and is still prone to graphite deformity in local sections, which cannot meet customer requirements. Summary of the invention

[0005] In order to solve the above technical problems existing in the prior art, the present invention provides a process method for improving the durability of a valve body casting and a valve body casting.

[0006] The technical solution of the present invention to solve the above technical problems is as follows:

[0007] The first aspect of the present invention is to provide a process method for improving the durability of valve body castings, comprising the following steps:

[0008] (1) Melting high-purity pig iron, high-purity scrap steel and return materials to obtain molten iron, wherein the weight percentages of the high-purity pig iron, high-purity scrap steel and return materials are 20%, 46% and 34% respectively;

[0009] (2) Pouring the molten iron after melting into a nodulizing ladle for primary inoculation treatment, and adding a pretreatment agent and an alloy during the primary inoculation treatment, wherein the alloy is an alloy containing Sb;

[0010] (3) Conducting nodulizing treatment and inoculation treatment on the molten iron in the nodulizing ladle;

[0011] (4) Pouring the molten iron in the nodulizing ladle into a pouring ladle for in-pouring inoculation, and adding an in-pouring inoculant during the process of pouring the molten iron into the pouring ladle;

[0012] (5) Pouring the molten iron in the pouring ladle into a sand box and conducting in-stream inoculation, and adding an in-stream inoculant during the process of pouring the molten iron into the sand box to form a valve body casting;

[0013] (6) The cooling time of the valve body casting in the sand box is not less than 15 hours.

[0014] By adopting the process method for improving the durability of valve body castings of the present invention, through melting molten iron, adding an Sb (antimony) alloy during the primary inoculation treatment and synergistically enhancing the effect with the pretreatment agent, the graphite nodules are refined, so that the graphite nodulization rate is high and the graphite distribution is uniform, the mechanical properties of the valve body ductile iron casting are improved, and at the same time, the graphite distortion is prevented, the distortion of graphite nodules during solidification is inhibited, and their spherical shape is maintained, avoiding the appearance of flaky or vermicular graphite; at the same time, through the appropriate ratio of raw materials and the combination of the process method provided by the present invention, the toughness and elongation rate of the valve body casting are greatly improved; by improving the graphite distortion, the toughness and elongation rate of the valve body casting are improved, so that the durability of the obtained thick and large valve body casting is greatly improved, meeting the use requirements.

[0015] The molten iron comes from the mixed melting of high-purity pig iron, high-purity scrap steel and return materials. Among them, by weight percentage, the components of high-purity pig iron are: C 3.81%, Si 0.313%, Mn 0.007%, P 0.009%, S 0.005%, Ti 0.005%, Cu 0.011%, Cr 0.005%, V 0.002%, Alt 0.0030%, Pb 0.0001%, B 0.0003%, Bi 0.00001%, and the balance is Fe; by weight percentage, the components of high-purity scrap steel are: Mn ≤ 0.3%, C ≤ 0.5%, Si ≤ 0.45%, P ≤ 0.035%, S ≤ 0.02%, Cr ≤ 0.03%, Sn ≤ 0.003%, Sb ≤ 0.005%, Pb ≤ 0.002%, Bi ≤ 0.003%, Te ≤ 0.002%, As ≤ 0.003%, B ≤ 0.0006%, Al ≤ 0.035%, Ti ≤ 0.03%, V ≤ 0.015%, Zn ≤ 0.004%, and the balance is Fe.

[0016] On the basis of the above technical solutions, the present invention can also be improved as follows:

[0017] Further, in step (2), by volume fraction, the pretreatment agent and the alloy are added when 1 / 3 of the molten iron is poured into the nodulizing ladle.

[0018] The beneficial effect of adopting the above further technical solution is that: adding the alloy containing Sb and the pretreatment agent into the nodulizing ladle at a specific time can improve the nodulizing rate of the valve body castings, and the stability of the nodulizing rate of the valve body castings in batch production is improved.

[0019] Further, by mass percentage, the alloy composition is: Sb 38 - 43%, Si 40 - 45%, and the balance is Fe.

[0020] Further, in step (2), by mass percentage, the addition amount of the alloy is 0.015 - 0.025% of the mass of the molten iron.

[0021] Further, in step (2), by mass percentage, the addition amount of the alloy is 0.024% of the mass of the molten iron.

[0022] The beneficial effect of adopting the above further technical solution is that: adding an appropriate amount of antimony alloy can play a role in refining graphite balls and promoting the formation of pearlite, thereby improving strength, hardness and wear resistance; adding excessive antimony will lead to the formation of brittle phases in the nodular cast iron parts and reduce the toughness of the valve body castings, so the addition amount needs to be strictly controlled.

[0023] Further, by mass percentage, the composition of the pretreatment agent is as follows: 10-15% of the long-acting core material, 10-15% of crystalline graphite carbon, 50-55% of unbalanced silicon, and the balance is iron; the addition amount of the pretreatment agent is 0.2% of the mass of the molten iron.

[0024] The long-acting core material includes carbon, and the pretreatment agent of the present invention is selected from the W-1 model of the "HM" brand pretreatment agent of Henan Weiye New Materials Co., Ltd.

[0025] The beneficial effect of adopting the above further technical solution is as follows: a long-acting graphite core is formed, which cooperates with the Sb-containing alloy, increases the number of graphite cores, improves graphite nucleation, and avoids graphite deformation, thereby improving the graphite spheroidization rate.

[0026] Further, in step (1), by weight percentage, the composition of the molten iron is as follows: 3.5-3.8% of carbon, 2.2-2.6% of silicon, 0.3-0.4% of manganese, sulfur ≤ 0.02%, phosphorus ≤ 0.035%, magnesium ≥ 0.040%, copper 0.4-0.45%, and the balance is iron and other inevitable impurities.

[0027] The beneficial effect of adopting the above further technical solution is as follows: using molten iron with the above-mentioned ratio composition, while ensuring a high graphite spheroidization rate, the toughness and elongation of the valve body casting are improved. When preparing thick and large valve body castings, the durability of the thick and large valve body castings can be ensured to be improved, and the stability of the thick and large valve body castings prepared in batches is good.

[0028] Further, in step (3), the ladle containing the molten iron is placed in the spheroidizing station for spheroidizing treatment and inoculation treatment. The spheroidizing treatment is carried out using a spheroidizing wire. By weight percentage, the spheroidizing wire includes the following components: 19-21% of magnesium, 42-47% of silicon, 2-2.5% of rare earth elements, 1.5-2.5% of calcium, magnesium oxide < 1.5%, and the balance is iron; the inoculation treatment is carried out using an inoculation wire. By weight percentage, the inoculation wire includes the following components: 3-4% of magnesium, 54-56% of silicon, 1-1.5% of rare earth elements, 2-2.5% of calcium, and 4-6% of barium.

[0029] The beneficial effect of adopting the above further technical solution is as follows: by placing the ladle containing the molten iron in the spheroidizing station for spheroidizing treatment and inoculation treatment, automatic control and automatic addition of the spheroidizing agent and inoculant are realized, ensuring the spheroidization and inoculation of the molten iron; the rare earth elements are added in the form of Mg 20 Re(2-8), the rare earth elements are a mixed rare earth element containing La and Ce, and the mass ratio of La to Ce is 2:8. By adding specific rare earth elements, the graphite spheroidization rate is further improved, and graphite distortion is prevented.

[0030] Further, by weight percentage, the tipping ladle inoculant comprises the following components: silicon ≥ 70%, barium 2.3 - 3.0%, calcium 1.0 - 2.0%, aluminum < 1.6%; the particle size of the tipping ladle inoculant is 1 - 3 mm; by weight percentage, the in-stream inoculant comprises the following components: silicon ≥ 70%, barium 3.5 - 4.5%, calcium 1.0 - 2.0%, aluminum < 1.6%; the particle size of the in-stream inoculant is 0.2 - 0.7 mm.

[0031] Further, the addition amount of the tipping ladle inoculant is 0.3% of the mass of the molten iron, and the addition amount of the in-stream inoculant is 0.1% of the mass of the molten iron.

[0032] Further, in step (4), by volume fraction, the tipping ladle inoculant is added when 1 / 3 of the molten iron is poured into the pouring ladle.

[0033] Another aspect of the present invention lies in providing a valve body casting prepared by using the above process method for improving the durability of the valve body casting.

[0034] Compared with the prior art, the present invention has the following technical effects:

[0035] The process method for improving the durability of the valve body casting provided by the present invention is applicable to the batch production of high-pressure valve body castings, especially the stable and quantitative production of thick and large valve body castings. It improves the spheroidization rate of thick and large high-pressure valve body castings, effectively avoids the graphite distortion in thick sections, and at the same time improves the toughness and elongation of thick and large high-pressure valve body castings. By combining the improvement of the spheroidization rate and the elongation rate, the durability of the high-pressure valve body casting is greatly improved, the product quality is stable, and the product life is extended.

[0036] The process method provided by the present invention adds Sb (antimony) alloy during the primary inoculation treatment of the molten iron and cooperates with the pretreatment agent. The two work synergistically to improve graphite nucleation, jointly inhibit the distortion of graphite balls during solidification, avoid graphite distortion, thereby improving the graphite spheroidization rate, maintaining their spherical shape, avoiding the appearance of flaky or vermicular graphite, ensuring the spheroidization rate of thick and large high-pressure valve body ductile iron castings, and improving the strength of the valve body casting.

[0037] The pretreatment agent and Sb (antimony) alloy are selected to be added when 1 / 3 of the molten iron is poured into the spheroidizing ladle, which improves the stability of the spheroidization rate result of the valve body casting, meets the requirements of customers, and avoids the performance fluctuation of products during the batch casting production of valve body castings.

[0038] By controlling the addition amount of Sb (antimony) alloy, it plays a role in refining graphite balls and promoting the formation of pearlite, thereby improving strength, hardness and wear resistance.

[0039] By appropriately proportioning raw materials, increasing the proportion of high-purity scrap steel, and utilizing the heredity of raw materials, the elongation of the casting is increased to obtain a valve body casting with high toughness;

[0040] The in-mold cooling time of the casting is increased to not less than 15 hours, so that the unpacking temperature is less than 300 °C, ensuring the release of internal stress in the casting to obtain a casting with less internal stress; the hardness of the internal casting is uniform, and the hardness gradient is less than HB30;

[0041] The process method provided by the present invention selects molten iron with a specific component ratio for valve body casting, and performs multiple spheroidizing and inoculation treatments in combination, improving the elongation of thick and large high-pressure valve body castings;

[0042] The valve body casting prepared by using the process method provided by the present invention has performance parameters: the spheroidization rate is ≥80%, the graphite size is 5-8 grades, and the number of graphite balls is not less than 70 per mm 2 , the solid tensile strength is ≥440 MPa, and the hardness HB is 163-229 N / mm 2 , under an oil pressure of 60 MPa, it can withstand more than 500,000 impacts, meeting the use requirements. Brief Description of the Drawings

[0043] Figure 1 Shows the metallographic structure diagram of the valve body casting prepared in Example 1 of the present invention;

[0044] Figure 2 Shows the metallographic structure diagram of the valve body casting prepared in Comparative Example 1 of the present invention;

[0045] Figure 3 Shows the metallographic structure diagram of the valve body casting prepared in Comparative Example 2 of the present invention;

[0046] Figure 4 Shows the metallographic structure diagram of the valve body casting prepared in Comparative Example 3 of the present invention;

[0047] Figure 5 Shows the metallographic structure diagram of the valve body casting prepared in Comparative Example 4 of the present invention. Detailed Description of the Invention

[0048] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention will be introduced in conjunction with preferred embodiments, this does not mean that the features of this invention are limited to this implementation manner. On the contrary, the purpose of introducing the invention in conjunction with the implementation manner is to cover other alternatives or modifications that may extend based on the claims of the present invention. In order to provide a deep understanding of the present invention, many specific details will be included in the following description. The present invention can also be implemented without these details. In addition, in order to avoid confusing or obscuring the key points of the present invention, some specific details will be omitted in the description. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0049] Embodiment 1

[0050] The process method for improving the durability of the valve body casting in this embodiment includes the following steps:

[0051] (1) Melting the molten iron. By weight percentage, the molten iron includes the following components: carbon 3.66%, silicon 2.57%, manganese 0.37%, sulfur 0.014%, phosphorus 0.021%, magnesium 0.049%, copper 0.42%, and the balance is iron and other inevitable impurities; the weight ratio of the furnace charges for melting the molten iron is high-purity pig iron: high-purity scrap steel: return material = 1200:2760:2040 (the weight percentages of high-purity pig iron, high-purity scrap steel, and return material are 20%, 46%, and 34% respectively);

[0052] (2) Pouring the melted molten iron into a nodulizing ladle for primary inoculation treatment. During the primary inoculation treatment, a pretreatment agent and an alloy are added. The alloy is an alloy containing Sb. The pretreatment agent and the alloy are added when 1 / 3 of the molten iron is poured into the nodulizing ladle. The addition amount of the alloy is 0.024% of the mass of the molten iron, and the addition amount of the pretreatment agent is 0.2% of the mass of the molten iron. The alloy composition is: Sb 40%, Si 43%, and the balance is Fe;

[0053] (3) Placing the molten iron nodulizing ladle at the nodulizing station for nodulizing treatment and inoculation treatment. The nodulizing treatment is carried out using a nodulizing wire. By weight percentage, the nodulizing wire includes the following components: magnesium 20%, silicon 45%, rare earth elements 2.3%, calcium 2.0%, magnesium oxide 1.3%, and the balance is iron. The rare earth elements are a mixed rare earth element containing La and Ce, and the mass ratio of La to Ce is 2:8; the inoculation treatment is carried out using an inoculation wire. By weight percentage, the inoculation wire includes the following components: magnesium 3.5%, silicon 55%, rare earth elements 1.3%, calcium 2.5%, barium 5%;

[0054] (4) Pour the molten iron in the spheroidizing ladle into the pouring ladle for in-pouring inoculation. During the process of pouring the molten iron into the pouring ladle, add the in-pouring inoculant. The addition amount of the in-pouring inoculant is 0.3% of the mass of the molten iron. Calculated by volume fraction, the in-pouring inoculant is added when 1 / 3 of the molten iron is poured into the pouring ladle. Calculated by weight percentage, the in-pouring inoculant includes the following components: silicon ≥ 70%, barium 2.3 - 3.0%, calcium 1.0 - 2.0%, aluminum < 1.6%; the particle size of the in-pouring inoculant is 3 mm.

[0055] (5) Pour the molten iron in the pouring ladle into the sand box for in-stream inoculation. During the process of pouring the molten iron into the sand box, add the in-stream inoculant. The addition amount of the in-stream inoculant is 0.1% of the mass of the molten iron. Calculated by weight percentage, the in-stream inoculant includes the following components: silicon ≥ 70%, barium 3.5 - 4.5%, calcium 1.0 - 2.0%, aluminum < 1.6%; the particle size of the in-stream inoculant is 0.5 mm.

[0056] Comparative Example 1

[0057] The process method of this comparative example includes the following steps:

[0058] (1) Melt the molten iron. Calculated by weight percentage, the molten iron includes the following components: carbon 3.66%, silicon 2.47%, manganese 0.39%, sulfur 0.012%, phosphorus 0.024%, magnesium 0.045%, copper 0.43%, and the balance is iron and other inevitable impurities; the weight ratio of the furnace charge for melting the molten iron is high-purity pig iron: pressed scrap steel: return scrap is 900:2300:2800.

[0059] (2) Pour the melted molten iron into the spheroidizing ladle for primary inoculation treatment. During the primary inoculation treatment process, add the pretreatment agent and the alloy. The alloy is an alloy containing Sb. The pretreatment agent and the alloy are added when 1 / 3 of the molten iron is poured into the spheroidizing ladle. The addition amount of the alloy is 0.028% of the mass of the molten iron. The addition amount of the pretreatment agent is 0.2% of the mass of the molten iron. The alloy composition is: Sb 40%, Si 43%, and the balance is Fe.

[0060] (3) Place the molten iron spheroidizing ladle at the spheroidizing station for spheroidizing treatment and inoculation treatment. Use the spheroidizing wire for spheroidizing treatment. Calculated by weight percentage, the spheroidizing wire includes the following components: magnesium 20%, silicon 45%, rare earth elements 2.3%, calcium 2.0%, magnesium oxide 1.3%, and the balance is iron. The rare earth elements are a mixed rare earth element containing La and Ce, and the mass ratio of La to Ce is 2:8; use the inoculation wire for inoculation treatment. Calculated by weight percentage, the inoculation wire includes the following components: magnesium 3.5%, silicon 55%, rare earth elements 1.3%, calcium 2.5%, barium 5%.

[0061] (4) Pour the molten iron in the spheroidizing ladle into the pouring ladle for in-pouring inoculation. During the process of pouring the molten iron into the pouring ladle, add the in-pouring inoculant. The addition amount of the in-pouring inoculant is 0.3% of the mass of the molten iron. By volume fraction, the in-pouring inoculant is added when 1 / 3 of the molten iron is poured into the pouring ladle. By weight percentage, the in-pouring inoculant comprises the following components: silicon ≥70%, barium 2.3 - 3.0%, calcium 1.0 - 2.0%, aluminum <1.6%; the particle size of the in-pouring inoculant is 3 mm.

[0062] (5) Pour the molten iron in the pouring ladle into the sand box for in-stream inoculation. During the process of pouring the molten iron into the sand box, add the in-stream inoculant. The addition amount of the in-stream inoculant is 0.1% of the mass of the molten iron. By weight percentage, the in-stream inoculant comprises the following components: silicon ≥70%, barium 3.5 - 4.5%, calcium 1.0 - 2.0%, aluminum <1.6%; the particle size of the in-stream inoculant is 0.5 mm.

[0063] Comparative Example 2

[0064] The process method of this comparative example includes the following steps:

[0065] (1) Melt the molten iron. By weight percentage, the molten iron comprises the following components: carbon 3.66%, silicon 2.47%, manganese 0.39%, sulfur 0.012%, phosphorus 0.024%, magnesium 0.045%, copper 0.43%, and the balance is iron and other inevitable impurities; the weight ratio of the furnace charge for melting the molten iron is high-purity pig iron: pressed scrap steel: return scrap is 900:2300:2800.

[0066] (2) Pour the molten iron after melting into the spheroidizing ladle for primary inoculation treatment. During the primary inoculation treatment process, add the pretreatment agent. The pretreatment agent is added when 1 / 3 of the molten iron is poured into the spheroidizing ladle. The addition amount of the pretreatment agent is 0.2% of the mass of the molten iron.

[0067] (3) Place the molten iron spheroidizing ladle at the spheroidizing station for spheroidizing treatment and inoculation treatment. Use the spheroidizing wire for spheroidizing treatment. By weight percentage, the spheroidizing wire comprises the following components: magnesium 20%, silicon 45%, rare earth elements 2.3%, calcium 2.0%, magnesium oxide 1.3%, and the balance is iron. The rare earth elements are a mixed rare earth element containing La and Ce, and the mass ratio of La to Ce is 2:8; use the inoculation wire for inoculation treatment. By weight percentage, the inoculation wire comprises the following components: magnesium 3.5%, silicon 55%, rare earth elements 1.3%, calcium 2.5%, barium 5%.

[0068] (4) Pour the molten iron in the nodulizing ladle into the pouring ladle for in-ladle inoculation. During the process of pouring the molten iron into the pouring ladle, add the in-ladle inoculant. The addition amount of the in-ladle inoculant is 0.3% of the mass of the molten iron. By volume fraction, the in-ladle inoculant is added when 1 / 3 of the molten iron is poured into the pouring ladle. By weight percentage, the in-ladle inoculant comprises the following components: silicon ≥70%, barium 2.3 - 3.0%, calcium 1.0 - 2.0%, aluminum <1.6; the particle size of the in-ladle inoculant is 3 mm.

[0069] (5) Pour the molten iron in the pouring ladle into the sand mold for in-stream inoculation. During the process of pouring the molten iron into the sand mold, add the in-stream inoculant. The in-stream inoculant is an alloy containing Sb. The composition of the in-stream inoculant is: Sb 40%, Si 43%, and the balance is Fe; the addition amount of the in-stream inoculant is 0.15% of the mass of the molten iron, and the particle size of the in-stream inoculant is 0.5 mm.

[0070] Comparative Example 3

[0071] The process method of this comparative example includes the following steps:

[0072] (1) Melt the molten iron. By weight percentage, the molten iron comprises the following components: carbon 3.66%, silicon 2.47%, manganese 0.39%, sulfur 0.012%, phosphorus 0.024%, magnesium 0.045%, copper 0.43%, and the balance is iron and other inevitable impurities; the weight ratio of the furnace charges for melting the molten iron is high-purity pig iron: pressed scrap steel: return scrap = 900:2300:2800.

[0073] (2) Pour the melted molten iron into the nodulizing ladle for primary inoculation treatment. During the primary inoculation treatment process, add an alloy. The alloy is an alloy containing Sb. The alloy is added when 1 / 3 of the molten iron is poured into the nodulizing ladle. The addition amount of the alloy is 0.028% of the mass of the molten iron. The composition of the alloy is: Sb 40%, Si 43%, and the balance is Fe.

[0074] (3) Place the nodulizing ladle of the molten iron at the nodulizing station for nodulizing treatment and inoculation treatment. Use the nodulizing wire for nodulizing treatment. By weight percentage, the nodulizing wire comprises the following components: magnesium 20%, silicon 45%, rare earth elements 2.3%, calcium 2.0%, magnesium oxide 1.3%, and the balance is iron. The rare earth elements are a mixed rare earth element containing La and Ce, and the mass ratio of La to Ce is 2:8; use the inoculating wire for inoculation treatment. By weight percentage, the inoculating wire comprises the following components: magnesium 3.5%, silicon 55%, rare earth elements 1.3%, calcium 2.5%, barium 5%.

[0075] (4) Pour the molten iron in the nodulizing ladle into the pouring ladle for in-pouring inoculation. During the process of pouring the molten iron into the pouring ladle, add the in-pouring inoculant. The addition amount of the in-pouring inoculant is 0.3% of the mass of the molten iron. By volume fraction, the in-pouring inoculant is added when 1 / 3 of the molten iron is poured into the pouring ladle. By weight percentage, the in-pouring inoculant comprises the following components: silicon ≥ 70%, barium 2.3 - 3.0%, calcium 1.0 - 2.0%, aluminum < 1.6%; the particle size of the in-pouring inoculant is 3 mm.

[0076] (5) Pour the molten iron in the pouring ladle into the sand mold for in-stream inoculation. During the process of pouring the molten iron into the sand mold, add the in-stream inoculant. The addition amount of the in-stream inoculant is 0.1% of the mass of the molten iron. By weight percentage, the in-stream inoculant comprises the following components: silicon ≥ 70%, barium 3.5 - 4.5%, calcium 1.0 - 2.0%, aluminum < 1.6%; the particle size of the in-stream inoculant is 0.5 mm.

[0077] Comparative Example 4

[0078] The process method of this comparative example comprises the following steps:

[0079] (1) Smelt the molten iron. By weight percentage, the molten iron comprises the following components: carbon 3.66%, silicon 2.47%, manganese 0.39%, sulfur 0.012%, phosphorus 0.024%, magnesium 0.045%, copper 0.43%, and the balance is iron and other inevitable impurities; the weight ratio of the furnace charge for smelting the molten iron is high-purity pig iron: briquetted scrap steel: return scrap = 900:2300:2800.

[0080] (2) Pour the smelted molten iron into the nodulizing ladle for primary inoculation treatment. During the primary inoculation treatment process, add the pretreatment agent. The pretreatment agent is added when 1 / 3 of the molten iron is poured into the nodulizing ladle. The addition amount of the pretreatment agent is 0.2% of the mass of the molten iron.

[0081] (3) Place the molten iron nodulizing ladle at the nodulizing station for nodulizing treatment and inoculation treatment. Use the nodulizing wire for nodulizing treatment. By weight percentage, the nodulizing wire comprises the following components: magnesium 20%, silicon 45%, rare earth element 2.3%, calcium 2.0%, magnesium oxide 1.3%, and the balance is iron. The rare earth element is La; use the inoculating wire for inoculation treatment. By weight percentage, the inoculating wire comprises the following components: magnesium 3.5%, silicon 55%, rare earth element 1.3%, calcium 2.5%, barium 5%.

[0082] (4) Pour the molten iron in the nodulizing ladle into the pouring ladle for in-ladle inoculation. During the process of pouring the molten iron into the pouring ladle, add the in-ladle inoculant. The addition amount of the in-ladle inoculant is 0.3% of the mass of the molten iron. By volume fraction, the in-ladle inoculant is added when 1 / 3 of the molten iron is poured into the pouring ladle. By weight percentage, the in-ladle inoculant comprises the following components: silicon ≥70%, barium 2.3 - 3.0%, calcium 1.0 - 2.0%, aluminum <1.6%; the particle size of the in-ladle inoculant is 3 mm.

[0083] (5) Pour the molten iron in the pouring ladle into the sand mold for in-stream inoculation. During the process of pouring the molten iron into the sand mold, add the in-stream inoculant. The addition amount of the in-stream inoculant is 0.1% of the mass of the molten iron. By weight percentage, the in-stream inoculant comprises the following components: silicon ≥70%, barium 3.5 - 4.5%, calcium 1.0 - 2.0%, aluminum <1.6%; the particle size of the in-stream inoculant is 0.5 mm.

[0084] Perform the following performance tests on the valve body castings of Example 1 and Comparative Examples 1 - 4: tensile strength, elongation, hardness, metallographic structure photos, spheroidization rate. The obtained performance test results are shown in Table 1.

[0085] Table 1 Performance test results of the valve body castings of Example 1 and Comparative Examples 1 - 4

[0086]

[0087] Figure 1 This is the metallographic structure diagram of the cross-section center of the valve body casting obtained in Example 1 of the present invention. Its spheroidization rate is 87%, the spheroidization rate grade is 3, the metallographic structure is qualified, and it has high strength, high elongation, improved toughness, and passes the durability test. Figure 2 This is the metallographic structure diagram of the cross-section center of the valve body casting obtained in Comparative Example 1 of the present invention. Its spheroidization rate is 81%, the metallographic structure is qualified, but the elongation is low and the toughness is poor. Cracks appear in the high-pressure oil passage inside the valve body during the durability test. Figure 3 This is the metallographic structure diagram of the cross-section center of the valve body casting obtained in Comparative Example 2 of the present invention. Its spheroidization rate is 76%, and the elongation is low. Although the deformed graphite disappears, the hardness is unstable, the spheroidization rate is unqualified, and cracks appear in the oil passage inside the valve body during the durability test. Figure 4 This is the metallographic structure diagram of the cross-section center of the valve body casting obtained in Comparative Example 3 of the present invention. Its spheroidization rate is 40%, and the number of graphite balls is 28 per mm 2 , deformed graphite appears, and the spheroidization rate is unqualified. Cracks appear in the oil passage inside the valve body during the durability test. Figure 5It is the metallographic structure diagram of the cross-section center of the valve body casting obtained in Comparative Example 4 of the present invention. Its spheroidization rate is 10.97%, a large number of deformed massive graphite appears, and cracks occur in the oil passage inside the valve body during the durability test.

[0088] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A process method for improving the durability of valve body castings, characterized in that, It includes the following steps: (1) Smelt high-purity pig iron, high-purity scrap steel and return scrap to obtain molten iron, and the weight percentages of the high-purity pig iron, high-purity scrap steel and return scrap are 20%, 46% and 34% respectively; (2) Pour the molten iron after smelting into a nodulizing ladle for primary inoculation treatment. During the primary inoculation treatment, a pretreatment agent and an alloy are added, and the alloy is an alloy containing Sb; (3) Carry out nodulizing treatment and inoculation treatment on the molten iron in the nodulizing ladle; (4) Pour the molten iron in the nodulizing ladle into a pouring ladle for in-pouring inoculation, and add an in-pouring inoculant during the process of pouring the molten iron into the pouring ladle; (5) Pour the molten iron in the pouring ladle into a sand box for in-stream inoculation, and add an in-stream inoculant during the process of pouring the molten iron into the sand box to form a valve body casting; (6) The cooling time of the valve body casting in the sand box is not less than 15 hours.

2. The process method for improving the durability of valve body castings according to claim 1, characterized in that, In step (2), calculated by volume fraction, the pretreatment agent and the alloy are added when 1 / 3 of the molten iron is poured into the nodulizing ladle.

3. The process method for improving the durability of valve body castings according to claim 1, characterized in that Calculated by mass percentage, the alloy composition is: Sb 38 - 43%, Si 40 - 45%, and the balance is Fe.

4. The process method for improving the durability of valve body castings according to claim 1, characterized in that, In step (2), calculated by mass percentage, the addition amount of the alloy is 0.015 - 0.025% of the mass of the molten iron.

5. The process method for improving the durability of valve body castings according to claim 4, characterized in that, In step (2), calculated by mass percentage, the addition amount of the alloy is 0.024% of the mass of the molten iron.

6. The process method for improving the durability of valve body castings according to claim 1, characterized in that, In step (1), calculated by weight percentage, the components of the molten iron are: carbon 3.5 - 3.8%, silicon 2.2 - 2.6%, manganese 0.3 - 0.4%, sulfur ≤ 0.02%, phosphorus ≤ 0.035%, magnesium ≥ 0.040%, copper 0.4 - 0.45%, and the balance is iron and other inevitable impurities.

7. The process method for improving the durability of valve body castings according to claim 1, characterized in that, In step (3), place the nodulizing ladle containing molten iron at a nodulizing station for nodulizing treatment and inoculation treatment. Use a nodulizing wire for nodulizing treatment. Calculated by weight percentage, the nodulizing wire includes the following components: magnesium 19 - 21%, silicon 42 - 47%, rare earth elements 2 - 2.5%, calcium 1.5 - 2.5%, magnesium oxide < 1.5%, and the balance is iron; use an inoculating wire for inoculation treatment. Calculated by weight percentage, the inoculating wire includes the following components: magnesium 3 - 4%, silicon 54 - 56%, rare earth elements 1 - 1.5%, calcium 2 - 2.5%, barium 4 - 6%.

8. The process method for improving the durability of valve body castings according to claim 1, characterized in that, Calculated by weight percentage, the in-pouring inoculant includes the following components: silicon ≥ 70%, barium 2.3 - 3.0%, calcium 1.0 - 2.0%, aluminum < 1.6%; the particle size of the in-pouring inoculant is 1 - 3 mm; calculated by weight percentage, the in-stream inoculant includes the following components: silicon ≥ 70%, barium 3.5 - 4.5%, calcium 1.0 - 2.0%, aluminum < 1.6%; the particle size of the in-stream inoculant is 0.2 - 0.7 mm.

9. The process method for improving the durability of a valve body casting according to claim 1, characterized in that, The addition amount of the in-pouring inoculant is 0.3% of the mass of the molten iron, and the addition amount of the in-stream inoculant is 0.1% of the mass of the molten iron.

10. A valve body casting, characterized in that, Prepared by using the process method for improving the durability of valve body castings according to any one of claims 1 to 9.

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