CN112048660B - Preparation method of nodular cast iron QT700-7 - Google Patents
Preparation method of nodular cast iron QT700-7 Download PDFInfo
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- 229910001141 Ductile iron Inorganic materials 0.000 title claims abstract description 22
- 238000002360 preparation method Methods 0.000 title claims abstract description 12
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical group [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 198
- 229910052742 iron Inorganic materials 0.000 claims abstract description 95
- 239000000463 material Substances 0.000 claims abstract description 62
- 238000011081 inoculation Methods 0.000 claims abstract description 50
- 229910000805 Pig iron Inorganic materials 0.000 claims abstract description 44
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 32
- 239000010959 steel Substances 0.000 claims abstract description 32
- 238000000034 method Methods 0.000 claims abstract description 31
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 15
- 229910052718 tin Inorganic materials 0.000 claims abstract description 15
- 239000003795 chemical substances by application Substances 0.000 claims abstract description 14
- 239000000126 substance Substances 0.000 claims abstract description 14
- 239000002994 raw material Substances 0.000 claims abstract description 10
- 238000002844 melting Methods 0.000 claims abstract description 9
- 230000008018 melting Effects 0.000 claims abstract description 9
- 238000005070 sampling Methods 0.000 claims abstract description 7
- 239000007787 solid Substances 0.000 claims abstract description 3
- 239000002054 inoculum Substances 0.000 claims description 51
- MIDOFQRPAXDZET-UHFFFAOYSA-N [Si].[Sr] Chemical compound [Si].[Sr] MIDOFQRPAXDZET-UHFFFAOYSA-N 0.000 claims description 24
- 230000008569 process Effects 0.000 claims description 24
- 229910052710 silicon Inorganic materials 0.000 claims description 24
- 239000011573 trace mineral Substances 0.000 claims description 21
- 235000013619 trace mineral Nutrition 0.000 claims description 21
- 239000010703 silicon Substances 0.000 claims description 14
- 239000002245 particle Substances 0.000 claims description 11
- 229910052799 carbon Inorganic materials 0.000 claims description 10
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims description 9
- 229910052782 aluminium Inorganic materials 0.000 claims description 9
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 9
- 229910052791 calcium Inorganic materials 0.000 claims description 9
- 239000011575 calcium Substances 0.000 claims description 9
- 229910001018 Cast iron Inorganic materials 0.000 claims description 8
- OOJQNBIDYDPHHE-UHFFFAOYSA-N barium silicon Chemical compound [Si].[Ba] OOJQNBIDYDPHHE-UHFFFAOYSA-N 0.000 claims description 7
- 239000011777 magnesium Substances 0.000 claims description 7
- 229910052788 barium Inorganic materials 0.000 claims description 6
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 claims description 6
- 229910052717 sulfur Inorganic materials 0.000 claims description 6
- 229910052749 magnesium Inorganic materials 0.000 claims description 5
- 239000000203 mixture Substances 0.000 claims description 4
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims description 3
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 claims description 3
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 3
- 150000002910 rare earth metals Chemical class 0.000 claims description 3
- 229910052712 strontium Inorganic materials 0.000 claims description 3
- CIOAGBVUUVVLOB-UHFFFAOYSA-N strontium atom Chemical compound [Sr] CIOAGBVUUVVLOB-UHFFFAOYSA-N 0.000 claims description 3
- 229910052726 zirconium Inorganic materials 0.000 claims description 3
- 229910052802 copper Inorganic materials 0.000 claims description 2
- 229910052759 nickel Inorganic materials 0.000 claims description 2
- 229910052698 phosphorus Inorganic materials 0.000 claims description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 13
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 10
- 229910002804 graphite Inorganic materials 0.000 description 9
- 239000010439 graphite Substances 0.000 description 9
- 230000000694 effects Effects 0.000 description 8
- 238000004519 manufacturing process Methods 0.000 description 6
- 239000011159 matrix material Substances 0.000 description 6
- 238000003723 Smelting Methods 0.000 description 5
- 229910052745 lead Inorganic materials 0.000 description 5
- 229910052721 tungsten Inorganic materials 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- 238000010438 heat treatment Methods 0.000 description 4
- 238000010309 melting process Methods 0.000 description 4
- -1 P is 0.03% Inorganic materials 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 229910052720 vanadium Inorganic materials 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 238000011031 large-scale manufacturing process Methods 0.000 description 2
- 229910001562 pearlite Inorganic materials 0.000 description 2
- 238000005204 segregation Methods 0.000 description 2
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 238000000498 ball milling Methods 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
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- 230000002349 favourable effect Effects 0.000 description 1
- 230000002452 interceptive effect Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 238000005058 metal casting Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 239000010421 standard material Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
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- 238000006467 substitution reaction Methods 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C37/00—Cast-iron alloys
- C22C37/04—Cast-iron alloys containing spheroidal graphite
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C1/00—Refining of pig-iron; Cast iron
- C21C1/10—Making spheroidal graphite cast-iron
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C1/00—Refining of pig-iron; Cast iron
- C21C1/10—Making spheroidal graphite cast-iron
- C21C1/105—Nodularising additive agents
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/08—Making cast-iron alloys
- C22C33/10—Making cast-iron alloys including procedures for adding magnesium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C37/00—Cast-iron alloys
- C22C37/10—Cast-iron alloys containing aluminium or silicon
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Mechanical Engineering (AREA)
- Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
Abstract
A preparation method of nodular cast iron QT700-7 comprises the following steps: 1) preparing materials: preparing raw materials including 10-30% of pig iron, 20-50% of scrap steel and 30-60% of furnace burden made of the same material according to the following weight percentage; 2) melting: comprises the following steps: sequentially adding pig iron and scrap steel into the furnace, wherein the adding amount of the pig iron is 30-50% of the total weight of the pig iron; adding a carburant and a pretreating agent when pig iron forms a solution state at the bottom of the furnace; adding furnace materials of the same material and residual pig iron, and adding electrolytic Cu, pure Sn, Mn iron and Si iron when the solid furnace materials of the whole furnace are melted; when the temperature in the furnace is higher than 1400 ℃, sampling and analyzing chemical components, and entering spheroidizing and inoculation procedures after the chemical components are qualified. The tensile strength of the cast 700-7 nodular cast iron material with high strength and high toughness is improved to over 700MPa, and the elongation index is ensured to reach over 7 percent.
Description
Technical Field
The invention belongs to the technical field of cast iron materials, and particularly relates to a preparation method of nodular cast iron QT 700-7.
Background
The nodular cast iron has the characteristics of high strength, high toughness, low price, good mechanical property and the like, so the nodular cast iron plays an important role in the material market and is widely applied to the fields of automobiles, agricultural machinery and the like. However, as the horsepower of commercial vehicles increases, higher demands are placed on the quality of the metal fittings of the engine. If the strength of the metal fittings is not enough, the metal fittings are unstable, the toughness index is low, the power of the engine is lost due to the failure of parts in the heavy bearing process, and accidents can happen in severe cases. This requires high strength and high toughness castings to ensure.
According to the nodular cast iron grade 700 of the national standard material, the general elongation index requirement is more than 2 percent. In general, the tensile strength requirement of more than 700MPa is satisfied, and the pearlite in the matrix structure of the material is more than 80%, but the elongation index is lowered. It is very difficult to satisfy the tensile strength of more than 700MPa and the elongation index of more than 7%. It is necessary to properly reduce the amount of pearlite in the matrix structure and to control a certain amount of ferrite in the matrix. This is the basis, and in the actual production, only these are achieved, and the performance index of the material still can not meet the requirement of 700-7.
The existing ball milling cast iron process needs heat treatment, improves the strength and elongation index, and invisibly increases the heat treatment equipment and energy cost; and in some special occasions, the index requirement of 700-7 cannot be stably met. The stability is poor.
Secondly, the conditions of pig iron resources in China are poor, trace interfering elements are high, and the mass production of high-strength and high-toughness castings is difficult.
Therefore, how to ensure that the metal casting meets the requirement of high toughness while improving the strength has the advantage of low cost, and the realization of large-scale production becomes a technical problem to be solved urgently.
Disclosure of Invention
The invention aims to provide a preparation method of ball-milled cast iron QT 700-7.
In order to realize the purpose, the invention adopts the following technical scheme:
a preparation method of nodular cast iron QT700-7 comprises the following steps:
1) preparing materials: preparing raw materials including 10-30% of pig iron, 20-50% of scrap steel and 30-60% of furnace burden made of the same material according to the following weight percentage; wherein,
in the cast iron, the weight percentage of P is less than 0.04 percent, S is less than 0.02 percent, Ti is less than 0.035 percent, V is less than 0.015 percent, and Si is less than 1.00 percent;
in the scrap steel, the weight percentage of C is less than 0.6 percent, Si is less than 0.5 percent, Mn is less than 0.5 percent, Ti is less than 0.015 percent, the rest trace elements V are less than 0.02 percent, Pb is less than 0.01 percent, Sn is less than 0.008 percent, and W is less than 0.01 percent;
2) melting: comprises the following steps: firstly, sequentially adding pig iron and scrap steel into a furnace, wherein the adding amount of the pig iron is 30-50% of the total weight of the pig iron; secondly, adding a carburant and a pretreating agent when pig iron forms a solution state at the bottom of the furnace; thirdly, adding furnace materials of the same material and residual pig iron, and fourthly, adding electrolytic Cu, pure Sn, Mn iron and Si iron when the solid furnace materials of the whole furnace are melted; fifthly, when the temperature in the furnace is higher than 1400 ℃, sampling and analyzing chemical components, determining that the chemical components are qualified when the conditions are met, and entering the spheroidizing and inoculation procedures:
control range of main elements: 3.5 to 3.8 percent of C, 2.3 to 2.7 percent of Si, 0.3 to 0.5 percent of Mn, 0.009 to 0.02 percent of S, less than 0.08 percent of Ni, less than 0.04 percent of P, 0.04 to 0.05 percent of Mg, 0.2 to 0.5 percent of Cu and 0.02 to 0.04 percent of Sn;
control range of trace elements: cr is less than 0.05 percent, Mo is less than 0.05 percent, V is less than 0.015 percent, Ti is less than 0.025 percent, Al is less than 0.02 percent, Zn is less than 0.05 percent, Sb is less than 0.01 percent, Pb is less than 0.005 percent, and Nb is less than 0.05 percent;
3) spheroidizing and inoculating: placing a nodulizer accounting for 1.35-1.45% of the weight of the treated molten iron into a pit type nodulizing chamber, covering a silicon-strontium inoculant accounting for 0.2-0.3 wt% of the molten iron to be added, covering scrap iron with the same material on the nodulizing chamber, finally covering a cover plate with holes, pouring the molten iron, and performing first inoculation on the molten iron in the nodulizing process; the granularity of the silicon-strontium inoculant is 3-10 mm; the scrap iron made of the same material is added in the step, so that the scrap iron is tightly covered with a nodulizer and an inoculant, the contact time with molten iron is controlled, and the nodulizing and inoculation quality is ensured;
and (3) second inoculation: after the first inoculation, the mixture enters a ladle pouring, and a long-acting inoculant (silicon-barium inoculant) with the weight percent of 0.2-0.3 wt% of molten iron is added into the ladle pouring for the second inoculation, wherein the granularity of the long-acting inoculant is 1-3 mm;
in the third inoculation, in the pouring process, a silicon-strontium inoculant in an amount of 0.08-0.12 wt% of molten iron is added for third inoculation to obtain a nodular cast iron QT700-7 product; the grain size of the silicon-strontium inoculant is 0.1-0.5 mm.
In the silicon-strontium inoculant, 70-75 wt% of silicon, 0.1wt% of calcium, 1-2 wt% of strontium and 0.5wt% of aluminum are used; in the long-acting inoculant, 60-68 wt% of silicon, 1-2 wt% of calcium, 10-14 wt% of barium and 1.5wt% of aluminum are used; in the nodulizer, 42-47% of silicon, 5.5-6.5% of magnesium, 0.5-1.5% of rare earth RE and 1-3% of barium.
The pretreatment agent comprises 60-66 wt% of silicon, 3.5-4.5 wt% of aluminum, 1-2 wt% of calcium, 3-5 wt% of zirconium and the balance of iron, and the particle size is 3-10 mm.
The invention effectively monitors the production process: using a high-quality material; the use proportion of the scrap steel is increased and is in a certain control range; the order of the charging of the melt is defined and standardized; the main elements and the trace elements are controlled, so that the influence of large fluctuation on the matrix structure is reduced; and then the simple and feasible spheroidization process and multiple inoculation means are matched to ensure the quantity and the roundness of the spherical graphite. A stable production state is achieved. The tensile strength of the produced cast 700-7 nodular cast iron material with high strength and high toughness is improved to more than 700MPa, and the elongation index is ensured to reach more than 7 percent (compared with the national standard of materials, the elongation index is improved by more than 3 times), so that the cast nodular cast iron material can be applied to products such as engine tile covers, supports, crankshafts and the like. The requirements of the use performance of parts are met, and the method is simple to operate, simple in process, low in cost and convenient for large-scale stable production.
The grain size of the inoculant in the invention is selected according to the following steps: for the first inoculation, 0.2 to 0.3 percent of silicon-strontium inoculant is covered on the nodulizer, and the granularity is 3 to 10 mm. Plays the roles of covering and inoculation. The molten iron is stirred in the spheroidizing process, so that the molten iron can be smoothly melted, and the effect of inoculation on the end of pouring is kept. If the granularity is too large, the covering effect cannot be achieved, gaps among the inoculants can quickly enter molten iron, the inoculants are not easy to absorb by the molten iron, and the segregation of silicon elements is caused. The particle size is too small, the inoculation effect is attenuated, and in the final stage of pouring, the inoculation is declined, the nodularity is reduced, and the elongation is reduced. And (3) inoculating for the second time, wherein 0.2-0.3% of long-acting inoculant with the granularity of 1-3mm is added during ladle pouring. The process has no stirring effect and the particle size needs to be reduced. When the size is too large, the alloy is not easy to melt and causes silicon element segregation, and when the size is too small, the defect of inoculation recession occurs and the elongation rate is reduced. And (3) inoculating for the third time, adding 0.08-0.12% of a silicon-strontium inoculant with the granularity of 0.1-0.5mm, and taking the mixture as powder when viewed by a screen. Inoculation and pouring are synchronous at the moment, the action of nodulizing, primary inoculation and ladle pouring on the molten iron temperature and secondary inoculation is sharply reduced, and the molten iron cannot be melted and absorbed when the granularity is large. The particle size is too small, and the particles can directly become impurities and lose the inoculation effect.
The key points of the technology of the invention are as follows: 1. making requirements on components of pig iron and scrap steel in raw materials; 2. increasing and controlling the use ratio of the scrap steel to be 20-50%; 3. during melting, the feeding sequence needs to be controlled. The adding sequence of various furnace charges needs to be standardized; 4. control ranges of major elements and trace elements; 5. spheroidizing process and auxiliary devices, such as spheroidizing bags and special cover plates; 6. and (3) carrying out inoculation for multiple times.
Compared with the prior art, the invention achieves the technical effects that:
1) the proportion of the used scrap steel is increased and controlled within a certain range, and meanwhile, a certain amount of carburant is added to increase external crystal nuclei in the molten iron, so that the activity of carbon in the molten iron is increased, and the quantity of spherical graphite is increased;
2) the invention makes requirements on the control of the upper limit of the content of the trace elements in the material. This is because, as the content of trace elements increases, the elongation in the performance index decreases. The trace elements are reduced, and the elongation in the performance index is gradually improved. Considering that the trace elements are mainly brought in as raw materials, the requirement is made on the upper limit of the control range according to data obtained in the implementation process, and when the upper limit of the content of the trace elements in the material is controlled within the range of the invention, the obtained nodular cast iron has excellent performance;
3) the method limits the charging sequence of the furnace burden during melting, can stabilize the melting state and the element content, is favorable for accurately controlling element fluctuation, and avoids the difference influence caused by larger fluctuation; firstly, a certain amount of pig iron and scrap steel are added, so that solution is formed at the bottom of the furnace, the temperature is uniform, the melting time of the whole furnace can be shortened, and the electric energy is saved; and then adding a carburant and a pretreating agent, which is beneficial to the absorption of the carburant and the formation of effective cores in molten iron. And finally, adding furnace materials made of the same material, and remaining pig iron, so that good activity of C in molten iron can be ensured, excellent raw iron liquid is provided for later spheroidization and inoculation of products, the matrix structure of the products is stabilized, and the hardness is stabilized, which is very critical to the material quality.
4) The pit type spheroidizing chamber is adopted to realize stable spheroidizing process, and the pit type spheroidizing chamber can be designed into a spheroidizing chamber with proper size according to the treatment capacity of molten iron, the weight of a spheroidizing agent to be added and the corresponding inoculant amount, so that the quality of spheroidizing reaction is favorably controlled during molten iron treatment, the spheroidizing reaction process is stabilized, the absorption rate fluctuation of spheroidizing element Mg is small, the residual Mg value is stable, the spheroidizing rate of a product is favorably stabilized, and the elongation index of the material is favorably improved;
5) the three-time inoculation process ensures that enough and effective graphite cores exist in molten iron, and refines the spherical graphite, thereby being beneficial to controlling the graphite roundness, ensuring that the nodularity of the material can stably reach more than 90 percent, and being beneficial to obtaining more spherical graphite on the product by the compound use of two inoculants, which is the guarantee of improving the toughness index. The graphite in unit area is small in quantity and not round, and the elongation index is low; the amount of graphite in unit area is increased, and when the graphite is rounded, the elongation index is improved;
6) the product prepared by the invention can be directly supplied according to the cast state, the heat treatment link is cancelled, the investment cost and the energy cost of heat treatment equipment are reduced, the production cost of the product is reduced, and the product has price competitiveness.
Drawings
FIGS. 1 to 5 are metallographic structure photographs of examples 1 to 5, respectively.
Detailed Description
In order that the invention may be better understood, the invention will now be further described with reference to the following specific examples.
The same material in the same material furnace burden and the same material scrap iron in the embodiment of the invention refers to the same component as the nodular cast iron QT700-7 product, for example, the same material furnace burden is the furnace burden produced in the processing process, and the same material scrap iron is the scrap iron produced after processing and is used after drying.
In the invention and the embodiment, the silicon-strontium inoculant, the long-acting inoculant and the nodulizer are all commercial products, and the specific specifications are as follows: in the silicon-strontium inoculant, 70-75 wt% of silicon, 0.1wt% of calcium, 1-2 wt% of strontium and 0.5wt% of aluminum are used; in the long-acting inoculant, 60-68 wt% of silicon, 1-2 wt% of calcium, 10-14 wt% of barium and 1.5wt% of aluminum; in the nodulizer, 42-47% of silicon, 5.5-6.5% of magnesium, 0.5-1.5% of rare earth RE and 1-3% of barium; the recarburizer is a graphitized recarburizer, wherein the volatile content is less than 0.05 percent, the ash content is less than 0.5 percent, the sulfur content is less than 0.05 percent, the nitrogen content is less than 0.03 percent, and the fixed carbon content is more than or equal to 99.5 percent. The pretreatment agent comprises 60-66 wt% of silicon, 3.5-4.5 wt% of aluminum, 1-2 wt% of calcium, 3-5 wt% of zirconium and the balance of iron, and the particle size is 3-10mm, and the pretreatment agent is commercially available.
Example 1
A preparation method of nodular cast iron QT700-7 comprises the following steps:
1) preparing the following raw materials in percentage by weight: 20 percent of pig iron, 20 percent of scrap steel and 60 percent of furnace burden made of the same material; wherein,
in the pig iron (by weight percent): 0.8% of Si, 0.035% of P, 0.015% of S, 0.03% of Ti and 0.01% of V;
in the scrap steel (by weight percent): 0.5 percent of C, 0.45 percent of Si, 0.35 percent of Mn, 0.015 percent of Ti, 0.01 percent of the rest trace elements of V, 0.0008 percent of Pb, 0.005 percent of Sn and 0.008 percent of W;
2) melting: smelting 5 tons of molten iron, firstly adding 500Kg of pig iron and 1000Kg of scrap steel into the furnace in sequence, adding 35Kg of carburant and 10Kg of pretreating agent when the pig iron forms a solution state at the furnace bottom, then adding 3000Kg of furnace charge made of the same material and the rest 500Kg of pig iron, finally adding electrolytic Cu, pure Sn, Mn iron and Si iron, raising the temperature, sampling and analyzing chemical components when the temperature in the furnace is more than 1400 ℃, meeting the requirements, namely being qualified, and entering the spheroidizing and inoculating process.
Control range of main elements:
other trace elements:
3) spheroidizing and inoculating: treating each package of 800Kg molten iron, firstly adding 1.45 wt% of nodulizer of the molten iron into a pit type nodulizing chamber, covering 0.2 wt% of silicon-strontium inoculant with the granularity of 3-10mm, covering 5Kg of scrap iron made of the same material, finally covering a cover plate with holes on the nodulizing chamber, adding the molten iron, and performing first inoculation on the molten iron in the nodulizing process; adding a long-acting inoculant (silicon-barium inoculant) with the iron water amount of 0.2 wt% and the granularity of 1-3mm for secondary inoculation during pouring; and during pouring, adding 0.08 wt% of silicon-strontium inoculant with the granularity of 0.1-0.5mm into the iron flow for third inoculation.
Example 2
A preparation method of nodular cast iron QT700-7 comprises the following steps:
1) preparing the following raw materials in percentage by weight: 20 percent of pig iron, 30 percent of scrap steel and 50 percent of furnace burden made of the same material;
wherein, according to the weight percentage, the pig iron: 0.033% of P, 0.017% of S, 0.033% of Ti, 0.01% of V and 0.75% of Si;
scrap steel: 0.35 percent of C, 0.35 percent of Si, 0.23 percent of Mn, 0.010 percent of Ti, 0.009 percent of the rest trace elements of V, 0.0009 percent of Pb, 0.004 percent of Sn and 0.008 percent of W;
2) and (3) melting process: smelting according to 5 tons of molten iron: firstly, 500Kg of pig iron and 1500Kg of scrap steel are added into a furnace in sequence, when the pig iron forms a solution state at the furnace bottom, 55Kg of carburant and 10Kg of pretreating agent are added, then 2500Kg of furnace charge made of the same material and the rest 500Kg of pig iron are added, finally electrolytic Cu, pure Sn, Mn iron and Si iron are added, the temperature is raised, when the temperature in the furnace is higher than 1400 ℃, the chemical components are sampled and analyzed, the condition is met, the product is qualified, and the product enters the procedures of spheroidization inoculation and inoculation.
Element control:
other trace elements:
4) spheroidizing and inoculating: treating each package of 800Kg molten iron, firstly adding 1.4 wt% of nodulizer of the molten iron into a pit type nodulizing chamber, covering 0.25 wt% of silicon-strontium inoculant with the granularity of 3-10mm on the nodulizing chamber, simultaneously adding 5Kg of scrap iron made of the same material, covering a cover plate with holes on the nodulizing chamber, adding the molten iron, and performing first inoculation on the molten iron in the nodulizing process; adding a long-acting inoculant (silicon-barium inoculant) with the iron water amount of 0.2 wt% and the granularity of 1-3mm for secondary inoculation during pouring; when pouring, 0.10 wt% of silicon-strontium inoculant with the particle size of 0.1-0.5mm is added along with the iron flow for the third inoculation.
Example 3
A preparation method of nodular cast iron QT700-7 comprises the following steps:
1) preparing the following raw materials in percentage by weight: 20 percent of pig iron, 40 percent of scrap steel and 40 percent of furnace burden made of the same material;
wherein, according to the weight percentage,
in the cast iron, P is 0.03%, S is 0.012%, Ti is 0.028%, V is 0.012%, and Si is 0.70%;
scrap steel, 0.2 percent of C, 0.2 percent of Si, 0.19 percent of Mn, 0.011 percent of Ti, 0.007 percent of the rest trace elements of V, 0.0011 percent of Pb, 0.003 percent of Sn and 0.005 percent of W;
2) and (3) melting process: smelting according to 5 tons of molten iron: firstly, adding 500Kg of pig iron and 2000Kg of scrap steel into a furnace in sequence, adding 75Kg of carburant and 10Kg of pretreating agent when the raw iron forms a solution state at the furnace bottom, then adding 2000Kg of furnace charge made of the same material and the rest 500Kg of pig iron, finally adding electrolytic Cu, pure Sn, Mn iron and Si iron, raising the temperature, sampling and analyzing chemical components when the temperature in the furnace is more than 1400 ℃, determining that the product is qualified when the conditions are met, and entering the processes of spheroidization and inoculation.
Element control:
other trace elements:
3) spheroidizing and inoculating: treating each package of 800Kg molten iron, firstly adding 1.35 wt% of nodulizer of the molten iron into a pit type nodulizing chamber, covering 0.3wt% of silicon-strontium inoculant with the granularity of 3-10mm on the nodulizing chamber, simultaneously adding 5Kg of scrap iron made of the same material, covering a cover plate with holes on the nodulizing chamber, adding the molten iron, and performing first inoculation on the molten iron in the nodulizing process; adding a long-acting inoculant (silicon-barium inoculant) with the iron water amount of 0.2 wt% and the granularity of 1-3mm for secondary inoculation during pouring; when pouring, 0.12wt% of silicon-strontium inoculant with the particle size of 0.1-0.5mm is added along with the iron flow for the third inoculation.
Example 4
A preparation method of nodular cast iron QT700-7 comprises the following steps:
1) preparing the following raw materials in percentage by weight: 10 percent of pig iron, 50 percent of scrap steel and 40 percent of furnace burden made of the same material;
wherein, according to the weight percentage,
in the pig iron, P is 0.029%, S is 0.015%, Ti is 0.025%, V is 0.009%, and Si is 0.92%;
in the scrap steel, 0.15 percent of C, 0.15 percent of Si, 0.15 percent of Mn, 0.008 percent of Ti, 0.005 percent of the rest trace elements of V, 0.009 percent of Pb, 0.0025 percent of Sn and 0.004 percent of W;
2) and (3) melting process: smelting according to 5 tons of molten iron: firstly, adding 250Kg of pig iron and 2500Kg of scrap steel into a furnace in sequence, adding 95Kg of carburant and 10Kg of pretreating agent when the pig iron forms a solution state at the furnace bottom, then adding 2000Kg of furnace charge made of the same materials and the rest 250Kg of pig iron, finally adding electrolytic Cu, pure Sn, Mn iron and Si iron, raising the temperature, sampling and analyzing chemical components when the temperature in the furnace is more than 1400 ℃, meeting the following conditions, namely being qualified, and entering the processes of spheroidization and inoculation.
Element control:
other trace elements:
4) spheroidizing and inoculating: treating each package of 800Kg molten iron, firstly adding 1.4 wt% of nodulizer of the molten iron, covering 0.3wt% of silicon-strontium inoculant with the granularity of 3-10mm, simultaneously adding 5Kg of scrap iron made of the same material, covering a cover plate with holes on the nodulizer, adding the molten iron, and performing first inoculation on the molten iron in the nodulizing process; adding a long-acting inoculant (silicon-barium inoculant) with the iron water amount of 0.2 wt% and the granularity of 1-3mm for secondary inoculation during pouring; when pouring, 0.10 wt% of silicon-strontium inoculant with the particle size of 0.1-0.5mm is added along with the iron flow for the third inoculation.
Example 5
A preparation method of nodular cast iron QT700-7 comprises the following steps:
1) preparing the following raw materials in percentage by weight: 30 percent of pig iron, 40 percent of scrap steel and 30 percent of furnace burden made of the same material;
wherein, according to the weight percentage,
in the cast iron, P is 0.025%, S is 0.016%, Ti is 0.021%, V is 0.001%, and Si is 0.65%;
0.13 percent of scrap steel, 0.20 percent of C, 0.15 percent of Si, 0.011 percent of Mn, 0.006 percent of Ti, and the balance of trace elements of V, 0.008 percent of Pb, 0.003 percent of Sn and 0.006 percent of W;
2) and (3) melting process: smelting according to 5 tons of molten iron: firstly, 750Kg of pig iron and 2000Kg of scrap steel are added into a furnace in sequence, when the raw iron forms a solution state at the furnace bottom, 70Kg of carburant (graphitizing carburant) and 10Kg of pretreating agent are added, then 1500Kg of furnace charge made of the same material and the rest 750Kg of pig iron are added, finally electrolytic Cu, pure Sn, Mn iron and Si iron are added, the temperature is raised, when the temperature in the furnace is higher than 1400 ℃, sampling is carried out to analyze chemical components, the chemical components are qualified when the conditions are met, and the procedures of spheroidization and inoculation are carried out.
Element control:
other trace elements:
5) spheroidizing and inoculating: treating each package of 800Kg molten iron, firstly adding 1.45 wt% of nodulizer of the molten iron, covering 0.25 wt% of silicon-strontium inoculant with the granularity of 3-10mm, simultaneously adding 5Kg of scrap iron made of the same material, covering a cover plate on the nodulizing process, adding the molten iron, and performing first inoculation on the molten iron in the nodulizing process; adding a long-acting inoculant (silicon-barium inoculant) with the iron water amount of 0.25 wt% and the granularity of 1-3mm for secondary inoculation during pouring; when pouring, 0.12wt% of silicon-strontium inoculant with the particle size of 0.1-0.5mm is added along with the iron flow for the third inoculation.
Performance testing
The tensile strength, elongation and matrix structure of the spheroidal graphite cast iron QT700-7 prepared in examples 1-5 were measured, and the results are shown in the following tables and FIGS. 1-5.
In examples 3 to 5, compared with examples 1 to 2, the strength was improved and the elongation index reached 8.5 to 9.78%. From the proportion difference analysis, the use proportion of the scrap steel is mainly improved, and the use proportion of the furnace burden made of the same material is reduced. In consideration of materials, the melting temperature of steel making is higher than that of cast iron, the impurity amount in the materials is reduced, and molten iron is purer. In addition, after the amount of scrap steel is increased and the amount of furnace burden made of the same material is reduced, a large amount of carbon needs to be increased by a carburant, substances which become cores of graphite in molten iron are increased, and strength and elongation indexes are improved under the condition that chemical composition differences are small. During large-scale production, the angles of easy popularization and cost reduction need to be considered, the dosage of furnace materials of the same material needs to be increased, the source stability of scrap steel needs to be considered, and experiments prove that the examples 1 and 2 also meet the requirements of strength and elongation of 700-7, so that the proportion of pig iron, scrap steel and furnace materials of the same material in the proportion is adjusted.
The above-mentioned embodiments only express the embodiments of the present invention, and the description is more specific and detailed, but not understood as the limitation of the patent scope of the present invention, but all the technical solutions obtained by using the equivalent substitution or the equivalent transformation should fall within the protection scope of the present invention.
Claims (1)
1. A preparation method of nodular cast iron QT700-7 is characterized by comprising the following steps:
1) preparing materials: preparing raw materials including 10-30% of pig iron, 20-50% of scrap steel and 30-60% of furnace burden made of the same material according to the following weight percentage; wherein,
in the cast iron, the weight percentage of P is less than 0.04 percent, S is less than 0.02 percent, Ti is less than 0.035 percent, V is less than 0.015 percent, and Si is less than 1.00 percent;
in the scrap steel, the weight percentage of C is less than 0.6 percent, Si is less than 0.5 percent, Mn is less than 0.5 percent, Ti is less than 0.015 percent, the rest trace elements V are less than 0.02 percent, Pb is less than 0.01 percent, Sn is less than 0.008 percent, and W is less than 0.01 percent;
melting: comprises the following steps: firstly, sequentially adding pig iron and scrap steel into a furnace, wherein the adding amount of the pig iron is 30-50% of the total weight of the pig iron; secondly, adding a carburant and a pretreating agent when pig iron forms a solution state at the bottom of the furnace; thirdly, adding furnace materials of the same material and residual pig iron, and fourthly, adding electrolytic Cu, pure Sn, Mn iron and Si iron when the solid furnace materials of the whole furnace are melted; fifthly, when the temperature in the furnace is higher than 1400 ℃, sampling and analyzing chemical components, determining that the chemical components are qualified when the conditions are met, and entering the spheroidizing and inoculation procedures:
control range of main elements: 3.5 to 3.8 percent of C, 2.3 to 2.7 percent of Si, 0.3 to 0.5 percent of Mn, 0.009 to 0.02 percent of S, less than 0.08 percent of Ni, less than 0.04 percent of P, 0.04 to 0.05 percent of Mg, 0.2 to 0.5 percent of Cu and 0.02 to 0.04 percent of Sn;
control range of trace elements: cr is less than 0.05 percent, Mo is less than 0.05 percent, V is less than 0.015 percent, Ti is less than 0.025 percent, Al is less than 0.02 percent, Zn is less than 0.05 percent, Sb is less than 0.01 percent, Pb is less than 0.005 percent, and Nb is less than 0.05 percent;
3) spheroidizing and inoculating: placing a nodulizer accounting for 1.35-1.45% of the weight of the treated molten iron into a pit type nodulizing chamber, covering a silicon-strontium inoculant accounting for 0.2-0.3 wt% of the molten iron to be added, covering scrap iron with the same material on the nodulizing chamber, finally covering a cover plate with holes, pouring the molten iron, and performing first inoculation on the molten iron in the nodulizing process; the granularity of the silicon-strontium inoculant is 3-10 mm;
and (3) second inoculation: after the first inoculation, the mixture enters a ladle pouring, and a long-acting inoculant (silicon-barium inoculant) with the weight percent of 0.2-0.3 wt% of molten iron is added into the ladle pouring for the second inoculation, wherein the granularity of the long-acting inoculant is 1-3 mm;
in the third inoculation, in the pouring process, a silicon-strontium inoculant in an amount of 0.08-0.12 wt% of molten iron is added for third inoculation to obtain a nodular cast iron QT700-7 product; the grain size of the silicon-strontium inoculant is 0.1-0.5 mm;
the pretreatment agent comprises 60-66 wt% of silicon, 3.5-4.5 wt% of aluminum, 1-2 wt% of calcium, 3-5 wt% of zirconium and the balance of iron, and the particle size is 3-10 mm;
in the silicon-strontium inoculant, 70-75 wt% of silicon, 0.1wt% of calcium, 1-2 wt% of strontium and 0.5wt% of aluminum are used; in the long-acting inoculant, 60-68 wt% of silicon, 1-2 wt% of calcium, 10-14 wt% of barium and 1.5wt% of aluminum are used; in the nodulizer, 42-47% of silicon, 5.5-6.5% of magnesium, 0.5-1.5% of rare earth RE and 1-3% of barium.
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