Production method for improving magnetic powder inspection qualification rate of nickel-containing low-alloy steel castings

Abstract

The production method for improving the magnetic powder inspection qualification rate of the nickel-containing low-alloy steel castings comprises the following process steps of shell making, shell roasting and pouring, renovating, heat treatment, primary catenary sanding, acid pickling and secondary catenary sanding, a graphite sand shell is adopted, oxidation of molten steel in the cooling process after pouring is greatly reduced, and the yield of the molten steel is improved. The nickel-containing low-alloy steel casting is subjected to heat treatment by adopting an inert gas shielding method, oxide skin formation can be effectively prevented, the heating efficiency is improved, so that the quality of the casting is improved, a groove type soaking and pickling process is arranged between primary catenary sanding and secondary catenary sanding, and the oxide skin on the surface of the casting can be thoroughly removed. According to the production process adopted by the invention, the defects of slag inclusion, air holes, pits, flow lines and the like of the nickel-containing low-alloy steel casting are greatly reduced, oxide skin on the surface of the casting can be thoroughly removed, the casting quality is greatly improved, the magnetic powder detection qualification rate is greatly improved, delay of delivery time due to multiple times of repair is avoided, the product rejection rate is also reduced, and the production cost is reduced. And obvious economic benefits can be brought to enterprises.

Description

Technical Field

[0001] The invention relates to the technical field of casting nickel-containing low alloy steel, in particular to a production method for improving the qualified rate of magnetic powder flaw detection of nickel-containing low alloy steel castings. Background Art

[0002] Magnetic particle nondestructive testing is a necessary means to detect the quality of ferromagnetic pressure castings. It is often used to detect surface and near-surface cracks, pores, non-metallic inclusions and other defects in castings such as low-alloy steel, carbon steel, and martensitic stainless steel. The principle is: a magnetic field is established in the casting to be tested, and a leakage magnetic field is generated due to the presence of defects, which will adsorb magnetic powder on the surface of the casting and gather to form magnetic marks. The defect information of the casting is obtained through the position and size of the magnetic marks.

[0003] For low-alloys containing nickel, not only will the magnetic particle inspection fail due to casting defects such as slag inclusions, pores, pits, and flow lines on the surface of the castings, but nickel will also be enriched in the inner layer of the iron oxide scale to form a nickel-rich metal mesh. This mesh can connect the iron oxide scale with the metal matrix, and it is difficult to remove the iron oxide scale by catenary sand blasting, resulting in dense "filamentous" magnetic marks displayed during magnetic particle inspection, which are very similar to the shape of cracks and are difficult to distinguish. Based on the principle of "strict quality", during the casting production process, it is necessary to ensure that 100% of the castings are qualified by magnetic particle inspection.

[0004] As described in patents CN202311822129.6 and CN202310056313.8, special heating processes and high-pressure water dephosphorization methods are used to remove iron oxide scale, which is not suitable for casting. The foundry industry usually uses catenary sandblasting, high-powered sandblasting and mechanical grinding to remove iron oxide scale, but the iron oxide scale of nickel-containing low-alloy steel has strong adhesion and needs to be removed by mechanical grinding. The production efficiency is low, the labor intensity is high, and the surface needs to be repeatedly polished to meet the requirements of magnetic particle inspection.

[0005] Therefore, to improve the pass rate of magnetic particle inspection of nickel-containing low-alloy steel castings, it is necessary not only to solve the casting defects such as slag inclusions, pores, pits, flow lines on the casting surface, but more importantly to solve the problem of iron oxide scale on the casting surface, thereby improving the pass rate of magnetic particle inspection, avoiding multiple repairs and delays in delivery, and reducing product scrap rate.

[0006] In view of the above problems, the present invention proposes a new technical solution. Summary of the invention

[0007] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a production method for improving the qualified rate of magnetic particle flaw detection of nickel-containing low-alloy steel castings. The technical solution adopted is:

[0008] A production method for improving the pass rate of magnetic particle flaw detection of nickel-containing low-alloy steel castings comprises the following steps:

[0009] (1) Shell making: After the wax mold is dipped in slurry, graphite sand is applied to the outer surface of the wax mold to make a graphite sand mold shell;

[0010] (2) roasting and pouring the shell to obtain a nickel-containing low-alloy steel casting;

[0011] (3) Renovation;

[0012] (4) Heat treatment; the heat treatment includes quenching treatment process and high temperature tempering treatment process, and the heat treatment stage is carried out using an inert gas protection method, and the oxygen content in the heat preservation stage of the heat treatment is required to be ≤0.5%;

[0013] (5) One-time catenary sand blasting;

[0014] (6) Pickling: Pickling is carried out by tank immersion method;

[0015] (7) Secondary catenary sand blasting.

[0016] A production method for improving the magnetic particle inspection pass rate of nickel-containing low-alloy steel castings, characterized in that in step (1), after gluing two layers of 16-30 mesh backing sand, 16-30 mesh graphite sand is further glued.

[0017] According to a production method for improving the magnetic particle flaw detection pass rate of nickel-containing low-alloy steel castings according to an embodiment of the present invention, for castings weighing ≤30Kg, one layer of graphite sand is bonded, and for castings weighing >30Kg, two layers of graphite sand are bonded.

[0018] According to an embodiment of the present invention, a production method for improving the magnetic particle inspection pass rate of nickel-containing low-alloy steel castings, in step (1), after the slurry sticking action is completed, the slurry at the angle position of the casting structure of the wax mold needs to be blown off with an air gun, and then graphite sand is applied.

[0019] According to an embodiment of the present invention, a production method for improving the pass rate of magnetic particle flaw detection of nickel-containing low-alloy steel castings is provided. In step (4), an atmosphere-protected electric furnace is used in both the quenching process and the high-temperature tempering process. After the nickel-containing low-alloy steel castings are loaded into the furnace, argon gas is introduced. After the oxygen content drops to 15%, the heating function is turned on and argon gas is continuously introduced to reduce the oxygen content. When the insulation temperature is reached, the oxygen content in the furnace is reduced to below 0.5%.

[0020] According to an embodiment of the present invention, a production method for improving the qualified rate of magnetic particle flaw detection of nickel-containing low-alloy steel castings, in step (6), the pickling process includes the following steps in sequence: acid immersion, water washing, alkali solution immersion, clean water immersion, and natural drying; wherein the acid immersion, alkali solution immersion and clean water immersion are all carried out by a tank immersion method; wherein the acid immersion is carried out at room temperature for a immersion time of 20 to 25 minutes, the alkali solution immersion is carried out at room temperature for a immersion time of 30 to 60 seconds, and the clean water immersion is carried out at room temperature for a immersion time of 3 to 5 minutes.

[0021] According to an embodiment of the present invention, a production method for improving the pass rate of magnetic particle flaw detection of nickel-containing low-alloy steel castings is provided. In step (6), the acid solution includes, by mass fraction, 35% citric acid, 11% hydrochloric acid, 19% dispersant and 35% penetrant, and the alkali solution includes, by mass fraction, 15% industrial ammonia water, 15% corrosion inhibitor and 70% water.

[0022] According to a production method for improving the qualified rate of magnetic particle flaw detection of nickel-containing low-alloy steel castings according to an embodiment of the present invention, in step (5), the time of the first catenary sand blasting is 10 to 15 minutes, and in step (7), the time of the second catenary sand blasting is 5 to 10 minutes.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The invention proposes a production process suitable for casting nickel-containing low-alloy steel, which solves the problem of low qualified rate of magnetic particle flaw detection of nickel-containing low-alloy steel castings at present. The invention adopts a graphite sand mold shell. Since graphite sand has good yield, air permeability and disintegration, the graphite sand mold shell made by the mold shell can greatly reduce the oxidation of molten steel in the cooling process after pouring. The nickel-containing low-alloy steel casting adopts an inert gas protection method for heat treatment. The gas protection can effectively prevent the formation of oxide scale, clean the metal surface, improve the heating efficiency, and thus improve the quality of the casting. In addition, a tank immersion pickling process is arranged between the primary catenary sand blasting and the secondary catenary sand blasting. After the primary catenary sand blasting, impurities such as oil, oxide scale, rust and the like on the surface of the casting are greatly removed. For relatively stubborn oxide scale, the oxide scale can be loosened after tank immersion pickling without excessively corroding the casting matrix. Then, the oxide scale can be completely removed in the secondary catenary sand blasting. The production process adopted by the present invention greatly reduces defects such as slag inclusions, pores, pits, flow lines, etc. in nickel-containing low-alloy steel castings, and can also completely remove the oxide scale on the surface of the casting, greatly improving the quality of the casting, greatly improving the pass rate of magnetic particle inspection, avoiding multiple repairs and delays in delivery, and also reducing the product scrap rate, which can bring obvious economic benefits to the enterprise. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0026] Figure 1 This is a magnetic particle inspection photograph of nickel-containing low-alloy steel cast by traditional technology;

[0027] Figure 2 The magnetic particle inspection photograph of the nickel-containing low alloy steel cast by the production process of the present invention is shown. DETAILED DESCRIPTION

[0028] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below in conjunction with specific embodiments.

[0029] A production method for improving the pass rate of magnetic particle flaw detection of nickel-containing low-alloy steel castings comprises the following steps:

[0030] (1) Shell making: After the wax mold is dipped in slurry, graphite sand is applied to the outer surface of the wax mold to make a graphite sand mold shell;

[0031] (2) roasting and pouring the shell, and obtaining a nickel-containing low alloy steel casting after pouring, wherein the nickel content is 1.40% to 2.00%;

[0032] (3) Renovation;

[0033] (4) Heat treatment; the heat treatment includes quenching treatment process and high temperature tempering treatment process, and the heat treatment stage is carried out using an inert gas protection method, and the oxygen content in the heat preservation stage of the heat treatment is required to be ≤0.5%;

[0034] (5) One-time catenary sand blasting;

[0035] (6) Pickling: Pickling is carried out by tank immersion method;

[0036] (7) Secondary catenary sand blasting.

[0037] The invention proposes a production process suitable for casting nickel-containing low-alloy steel, which solves the problem of low qualified rate of magnetic particle flaw detection of nickel-containing low-alloy steel castings at present. The invention adopts a graphite sand mold shell. Since graphite sand has good yield, air permeability and disintegration, the graphite sand mold shell made by the mold shell can greatly reduce the oxidation of molten steel in the cooling process after pouring. The nickel-containing low-alloy steel casting adopts an inert gas protection method for heat treatment. The gas protection can effectively prevent the formation of oxide scale, clean the metal surface, improve the heating efficiency, and thus improve the quality of the casting. In addition, a tank immersion pickling process is arranged between the primary catenary sand blasting and the secondary catenary sand blasting. After the primary catenary sand blasting, impurities such as oil, oxide scale, rust and the like on the surface of the casting are greatly removed. For relatively stubborn oxide scale, the oxide scale can be loosened after tank immersion pickling without excessively corroding the casting matrix. Then, the oxide scale can be completely removed in the secondary catenary sand blasting. The production process adopted by the present invention greatly reduces the defects of slag inclusion, pores, pits, flow lines and the like in nickel-containing low alloy steel castings, and can also completely remove the oxide scale on the surface of the castings, thereby greatly improving the quality of the castings, greatly improving the qualified rate of magnetic particle inspection, avoiding multiple repairs and delays in delivery, and also reducing the product scrap rate, which can bring obvious economic benefits to the enterprise, such as Figure 1 The magnetic particle inspection photos of nickel-containing low-alloy steel cast by traditional technology are shown in the figure. It can be clearly seen from the figure that the magnetic particle inspection shows dense "filamentous" magnetic marks, and the magnetic particle inspection fails. Figure 2 The magnetic particle inspection photos of the nickel-containing low-alloy steel cast by the production process of the present invention are shown in the figure. The surface of the casting is smooth, without obvious defects such as pores, cracks, slag inclusions, etc., and there are no "filamentous" magnetic marks. The magnetic particle inspection is qualified.

[0038] During the roasting process of the graphite sand mold shell before pouring, the graphite sand is easily oxidized and lost, and it is difficult to retain its function of reducing alloy oxidation until the cooling stage after pouring. Therefore, in some embodiments of the invention application, in step (1), after gluing two layers of 16-30 mesh backing sand, 16-30 mesh graphite sand is glued. According to multiple tests and verifications, generally, for castings with a weight of ≤30Kg, one layer of graphite sand is glued, and for castings with a weight of >30Kg, two layers of graphite sand are glued. In addition, when roasting the graphite sand mold shell, a piece of honeycomb coal is placed on each side of the furnace door in the roasting furnace, which can effectively reduce the oxidation loss of graphite sand during roasting. Secondly, due to the exothermic reaction of graphite sand during high-temperature oxidation, the angle position of the casting will shrink. Therefore, in step (1), after completing the slurry gluing action, the slurry at the angle position of the casting structure of the wax mold needs to be blown off with an air gun, and then graphite sand is applied.

[0039] In some embodiments of the invention application, in step (4), an atmosphere-protected electric furnace is used in both the quenching process and the high-temperature tempering process. After the nickel-containing low-alloy steel casting is loaded into the furnace, argon gas is introduced. After the oxygen content drops to 15%, the heating function is turned on and argon gas is continuously introduced to reduce the oxygen content. When the insulation temperature is reached, the oxygen content in the furnace is reduced to below 0.5%, that is, the oxygen content in the furnace during the insulation stage of the heat treatment process is required to be ≤0.5%.

[0040] In some embodiments of the invention application, in step (6), the pickling process includes the following steps in sequence: acid immersion, water washing, alkali immersion, clean water immersion, and natural drying; wherein the acid immersion, alkali immersion, and clean water immersion all adopt a tank immersion method; wherein the acid immersion is carried out at room temperature for 20 to 25 minutes, the alkali immersion is carried out at room temperature for 30 to 60 seconds, and the clean water immersion is carried out at room temperature for 3 to 5 minutes. The immersion method comprehensively and effectively reacts with the overall surface of the casting, loosens, and even removes the oxide scale on the surface of the casting. In step (6), by mass fraction, the acid solution includes 35% citric acid, 11% hydrochloric acid, 19% dispersant, and 35% penetrant, and by mass fraction, the alkali solution includes 15% industrial ammonia water, 15% corrosion inhibitor, and 70% water.

[0041]

[0042] For the dimensional accuracy of the blank casting, a dimensional difference of ≤0.03mm is within the acceptable range, so the acid immersion is preferably 20min to 25min, and the magnetic particle inspection pass rate can reach 100% in one time.

[0043] In some embodiments of the invention, in step (5), the first catenary sand blasting time is 10 to 15 minutes, and in step (7), the second catenary sand blasting time is 5 to 10 minutes.

[0044] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0045] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A production method for improving the pass rate of magnetic particle flaw detection of nickel-containing low-alloy steel castings, characterized in that: The following steps are included: (1) Shell making: After the wax mold is dipped in slurry, graphite sand is applied to the outer surface of the wax mold to make a graphite sand mold shell; (2) roasting and pouring the shell to obtain a nickel-containing low-alloy steel casting; (3) Renovation; (4) Heat treatment; the heat treatment includes quenching treatment process and high temperature tempering treatment process, and the heat treatment stage is carried out using an inert gas protection method, and the oxygen content in the heat preservation stage of the heat treatment is required to be ≤0.5%; (5) One-time catenary sand blasting; (6) Pickling: Pickling is carried out by tank immersion method; (7) Secondary catenary sand blasting.

2. A production method for improving the pass rate of magnetic particle flaw detection of nickel-containing low-alloy steel castings according to claim 1, characterized in that: In step (1), after gluing two layers of 16-30 mesh backing sand, 16-30 mesh graphite sand is then gluing.

3. A production method for improving the pass rate of magnetic particle flaw detection of nickel-containing low-alloy steel castings according to claim 2, characterized in that: For castings with a weight of ≤30Kg, one layer of graphite sand is applied; for castings with a weight of >30Kg, two layers of graphite sand are applied.

4. The production method for improving the pass rate of magnetic particle flaw detection of nickel-containing low-alloy steel castings according to claim 1 is characterized in that: In step (1), after the slurry sticking action is completed, the slurry at the angle position of the casting structure of the wax model needs to be blown off with an air gun, and then graphite sand is applied.

5. The production method for improving the pass rate of magnetic particle flaw detection of nickel-containing low-alloy steel castings according to claim 1 is characterized in that: In step (4), an atmosphere-protected electric furnace is used in both the quenching process and the high-temperature tempering process. After the nickel-containing low-alloy steel casting is loaded into the furnace, argon gas is introduced. After the oxygen content drops to 15%, the heating function can be turned on and argon gas is continuously introduced to reduce the oxygen content. When the insulation temperature is reached, the oxygen content in the furnace is reduced to below 0.5%.

6. The production method for improving the magnetic particle flaw detection pass rate of nickel-containing low-alloy steel castings according to claim 1 is characterized in that: In step (6), the pickling process includes the following steps in sequence: acid immersion, water rinsing, alkali immersion, clean water immersion, and natural drying; wherein the acid immersion, alkali immersion and clean water immersion are all carried out by a tank immersion method; wherein the acid immersion is carried out at room temperature for 20 to 25 minutes, the alkali immersion is carried out at room temperature for 30 to 60 seconds, and the clean water immersion is carried out at room temperature for 3 to 5 minutes.

7. A production method for improving the pass rate of magnetic particle flaw detection of nickel-containing low-alloy steel castings according to claim 6, characterized in that: In step (6), the acid solution includes, by mass fraction, 35% citric acid, 11% hydrochloric acid, 19% dispersant and 35% penetrant, and the alkali solution includes, by mass fraction, 15% industrial ammonia water, 15% corrosion inhibitor and 70% water.

8. The production method for improving the magnetic particle flaw detection pass rate of nickel-containing low-alloy steel castings according to claim 1, characterized in that: In step (5), the first catenary sand blasting time is 10 to 15 minutes, and in step (7), the second catenary sand blasting time is 5 to 10 minutes.

Images