CN115679137B - Method for refining equiaxed crystal grains of K4750 nickel-based superalloy casting test bar - Google Patents

Abstract

The invention discloses a method for refining equiaxed crystal grains of a K4750 nickel-based superalloy casting test bar, and belongs to the technical field of superalloy preparation. The method adopts quartz sand to fill between the mould shell and the wall of the sand box, the width between the mould shell and the wall of the sand box is required to be 60 mm-80 mm, the sand box is preheated at 800-950 ℃ for heat preservation treatment, then the sand box is moved into a vacuum induction melting furnace to melt K4750 master alloy, and the alloy melt is poured into the mould shell at the temperature of 1390-1480 ℃, so that a casting test bar with fine equiaxed crystal grains can be prepared. The quartz sand is used as a cooling material in the solidification process of the alloy melt, the width between the mould shell and the wall of the sand box is 60-80 mm, the cooling rate of the alloy in the solidification process can be controlled, and the good filling of the cast test bar, the grain shape being equiaxed and the average grain size being less than or equal to 300 mu m can be ensured by controlling the preheating temperature of the mould shell and the casting temperature of the alloy melt.

Description

A method for refining equiaxed crystal grains of K4750 nickel-based superalloy casting test bar

technical field

The invention relates to the technical field of high-temperature alloy material preparation, in particular to a method for refining equiaxed crystal grains of a K4750 nickel-based high-temperature alloy casting test rod.

Background technique

K4750 alloy is a new type of equiaxed crystal cast superalloy independently developed by the Institute of Metal Research, Chinese Academy of Sciences. The alloy’s temperature bearing capacity reaches 750°C, especially in the temperature range of 650°C to 750°C. The high-temperature mechanical properties are significantly better than the widely used K4169 alloy. At the same time, it has good comprehensive properties such as castability and weldability, and can be widely used in complex thin-walled precision castings that work for a long time below 750°C. For high-temperature alloy castings of investment casting, the alloy grains after pouring are usually relatively coarse, which will reduce the fatigue resistance of the alloy. Fine equiaxed grains have stronger fatigue resistance than coarse equiaxed grains, columnar grains, and mixed grains, and can withstand more fatigue cycles. Therefore, the preparation of ideal fine equiaxed grains is of great significance for improving the fatigue resistance of alloys. Under this background, the implementation of the present invention can obtain fine equiaxed crystal grains on the K4750 alloy casting test rod, and provide technical guarantee for the application of the material in complex thin-walled precision castings.

Contents of the invention

The object of the present invention is to provide a method for refining the equiaxed crystal grains of K4750 nickel-based superalloy casting test rods. In this method, ordinary quartz sand is used as the cooling material in the solidification process of the casting test rods, and is filled between the mold shell and the wall of the sand box. The width between the mold shell and the sand box wall is required to be 60 mm to 80 mm, which is used to control the cooling rate of the alloy solidification process. At the same time, the preheating temperature of the mold shell is controlled to be 800 ° C to 950 ° C, and the pouring temperature of the alloy melt is 1390 ° C to 1480 ° C. The cast test bars with good mold filling and fine equiaxed grains were prepared, with an average grain size ≤ 300 μm.

The technical scheme adopted in the present invention is as follows:

A method for refining K4750 nickel-based superalloy casting test bar equiaxed crystal grains, the method comprises the steps of:

(1) Preparation of solidification cooling material: using ordinary quartz sand as raw material, after screening, uniformly mixing according to different particle size ratios, to obtain solidification cooling material;

(2) Filling of solidified cooling material: filling the solidified cooling material between the mold shell and the wall of the sand box;

(3) Furnace loading and vacuuming treatment of the mold shell: the mold shell is put into a vacuum induction melting furnace after preheating, and vacuumed to a vacuum degree ≤ 1.0Pa;

(4) Master alloy melting and casting test rod pouring: When the vacuum degree is ≤ 1.0Pa, the K4750 master alloy is melted, and then the temperature of the alloy melt is increased to 1390 ° C ~ 1480 ° C and poured into the mold shell, that is, the casting test rod with fine equiaxed grains is prepared.

By weight percentage, the chemical composition of the K4750 casting master alloy is as follows:

C 0.08～0.13%, Cr 18.00～21.00%, W 2.70～5.00%, Mo 1.00～2.50%, Al 0.80～1.50%, Fe 4.00～5.00%, B 0.005～0.012%, Nb 1.00～2.00%, Ti 2.40～3.20%, Ni for the margin.

In step (1), when quartz sands of different particle sizes are mixed, the quartz sand with a particle size of Φ3 mm to Φ4 mm accounts for 10% to 20%, the quartz sand with a particle size of Φ2mm to Φ3mm accounts for 20% to 30%, and the quartz sand with a particle size of Φ1mm to Φ2mm accounts for 50% to 60%.

Step (2) During the quartz sand filling process, the width between the mold shell and the sand box wall is required to be 60mm-80mm, and it needs to be squeezed once every 50mm-80mm filled in the direction of gravity to ensure that the quartz sand is densely filled.

In step (3), the preheating process of the mold shell is as follows: put the sand box with the mold shell and quartz sand into the heat treatment furnace, slowly raise the temperature from room temperature to 800°C-950°C with the furnace, and keep the temperature at 800°C-950°C for 3h-5h.

The crystal grains of the K4750 casting test rod prepared by the method of the invention are equiaxed crystals, and the average grain size is less than or equal to 300 μm.

Design principle of the present invention and beneficial effect are as follows:

The present invention uses ordinary quartz sand as the cooling material in the solidification process of the alloy melt. After the quartz sand is evenly mixed according to the fixed ratio according to the particle size of the quartz sand, it is filled between the mold shell with a width of 60 mm to 80 mm and the wall of the sand box, and is preheated at 800°C to 950°C. After heat preservation treatment, it is loaded into a vacuum induction melting furnace, and the master alloy is melted after vacuuming to make the vacuum degree ≤ 1.0Pa. When injected into the mold shell, the quartz sand around the mold shell can control the cooling rate of the alloy during the solidification process, coupled with the control of the preheating temperature of the mold shell and the pouring temperature of the alloy melt, it can ensure good mold filling of the casting test rod, the grain shape is equiaxed, and the average grain size is ≤300μm.

Description of drawings

Fig. 1 is the sand box that mold shell and quartz sand have been packed into in embodiment 1.

Fig. 2 is the photograph that adopts thermal insulation cotton to wrap formwork in comparative example 3.

Fig. 3 is the macroscopic grain structure morphology of the cast test bars in Example 1 and Comparative Examples 1-3.

Fig. 4 is the metallographic photograph of the cast test bar grain structure in embodiment 1 and comparative example 1-3.

Detailed ways

In order to further understand the present invention, the present invention is described below in conjunction with examples, but the examples are only to further illustrate the features and advantages of the present invention, rather than limiting the claims of the present invention.

The invention provides a method for refining equiaxed crystal grains of K4750 nickel-based superalloy casting test rods. The process flow of the method is: solidification cooling material screening and mixing→solidification cooling material filling→mold shell preheating treatment→mold shell furnace charging and vacuuming treatment→master alloy melting→casting test rod pouring→grain inspection; wherein: the solidification cooling material of the method is ordinary quartz sand, which is uniformly mixed according to a fixed ratio after screening, and filled between the mold shell and the sand box wall, and the width between the mold shell and the sand box wall is required to be 6 0mm to 80mm, then preheated at a temperature of 800°C to 950°C, then moved into a vacuum induction melting furnace, vacuumed to make the vacuum degree ≤ 1.0Pa, melted the master alloy and increased the temperature of the alloy melt to 1390°C to 1480°C, poured the alloy melt into the mold shell to prepare a casting test rod, and inspected the shape and size of the grain of the test rod by metallographic analysis.

The inventive method specifically comprises the steps:

(1) Screening and mixing of solidification cooling material: the solidification cooling material of this method is ordinary quartz sand, and its main component is SiO ₂ , which is uniformly mixed according to the following ratio according to the particle size of the quartz sand: 10% to 20% of the quartz sand with a particle size of Φ3mm to Φ4mm, 20% to 30% of the quartz sand with a particle size of Φ2mm to Φ3mm, and 50% to 60% of the quartz sand with a particle size of Φ1mm to Φ2mm.

(2) Filling of solidified cooling material: Ordinary quartz sand is filled between the mold shell and the wall of the sand box, and the width between the mold shell and the wall of the sand box is 60 mm to 80 mm. During the filling process of the quartz sand, it needs to be squeezed once every 50 mm to 80 mm in the direction of gravity to ensure that the quartz sand is filled densely.

(3) Form shell preheating treatment: Put the sand box with the form shell and quartz sand into the heat treatment furnace, slowly raise the temperature from room temperature to 800°C-950°C with the furnace, and heat-preserve at 800°C-950°C for 3h-5h.

(4) Furnace loading and vacuuming of the mold shell: move the preheated sand box with the mold shell and quartz sand into the vacuum induction melting furnace, close the furnace door and carry out vacuuming treatment, so that the vacuum degree of the vacuum induction melting furnace is ≤ 1.0Pa.

(5) Master alloy melting treatment: when the vacuum degree of the vacuum induction melting furnace is ≤1.0Pa, power is supplied to the induction coil to completely melt the master alloy to obtain an alloy melt.

(6) Casting test bar pouring: After the master alloy is completely melted, increase the power of the vacuum induction melting furnace to make the alloy melt temperature reach 1390 ° C ~ 1480 ° C, and then pour the alloy melt into the mold shell. After the pouring is completed, the induction coil is powered off, and the vacuum is broken after staying for ≥ 10 minutes, and the sand box is removed from the vacuum induction furnace.

(7) Grain inspection: Cut the alloy casting test bar longitudinally, polish the surface of the sample to 2000# sandpaper in a semi-automatic polishing machine, and use 2.5 μm diamond polishing paste to polish to remove scratches. After ultrasonic cleaning with alcohol, configure 20gCuSO ₄ +100mLHCl+5mLH ₂ SO ₄ +100mLH ₂ O etchant to wipe and corrode for 7 to 12 seconds, then ultrasonically clean with alcohol, dry, and use metallographic electron microscope to analyze the crystal of the test bar grains, the grains of the K4750 casting test rod prepared by this method are equiaxed grains, and the average grain size is ≤300 μm.

Example 1:

(1) Select 10kg of K4750 master alloy for use.

(2) Weigh 50kg of ordinary quartz sand, remove the quartz sand with a particle size exceeding Φ4mm, weigh 6kg of the quartz sand with a particle size of Φ3mm-Φ4mm, weigh 10kg of the quartz sand with a particle size of Φ2mm-Φ3mm, weigh 24kg of the quartz sand with a particle size of Φ1mm-Φ2mm, remove the quartz sand with a particle size below Φ1mm, and mix the above-mentioned quartz sand with different particle sizes evenly to obtain a solidification cooling material.

(3) Prepare a cylindrical sand box, then place the mold shell in the middle of the sand box, and then fill the mixed ordinary quartz sand between the mold shell and the sand box wall. The thickness between the mold shell and the sand box wall is 75mm, and squeeze once every 50mm to 80mm in the direction of gravity to ensure that the quartz sand is filled tightly (Figure 1).

(4) Put the sand box with the mold shell and quartz sand into the heat treatment furnace, slowly raise the temperature from room temperature to 900°C with the furnace, and keep it at 900°C for 3.5h.

(5) Move the heat-treated sandbox into a 25kg vacuum induction furnace, close the furnace door and then vacuumize it. When the vacuum degree is 0.9Pa, power is applied to the induction coil to completely melt 10kg of master alloy to obtain an alloy melt.

(6) Increase the power of the vacuum induction furnace so that the temperature of the alloy melt reaches 1410°C, and pour the alloy melt into the mold shell. After the pouring is completed, the induction coil is powered off, and the vacuum is broken after 10 minutes, and the sand box or the mold shell wrapped in insulation cotton is removed from the vacuum induction furnace.

Comparative example 1:

(1) Select 10kg of K4750 master alloy for use.

(2) Weigh 50kg of ordinary quartz sand, remove the quartz sand with a particle size exceeding Φ4mm, weigh 6kg of the quartz sand with a particle size of Φ3mm-Φ4mm, weigh 10kg of the quartz sand with a particle size of Φ2mm-Φ3mm, weigh 24kg of the quartz sand with a particle size of Φ1mm-Φ2mm, remove the quartz sand with a particle size below Φ1mm, and mix the above-mentioned quartz sand with different particle sizes evenly to obtain a solidification cooling material.

(3) Prepare a cylindrical sand box, then place the mold shell in the middle of the sand box, and then fill the mixed ordinary quartz sand between the mold shell and the wall of the sand box. The thickness between the mold shell and the wall of the sand box is 75mm. Squeeze once every 50mm to 80mm in the direction of gravity to ensure that the quartz sand is filled tightly.

(4) Put the sand box with the mold shell and quartz sand into the heat treatment furnace, slowly raise the temperature from room temperature to 900°C with the furnace, and keep it at 900°C for 3.5h.

(5) Move the heat-treated sandbox into a 25kg vacuum induction furnace, close the furnace door and then vacuumize it. When the vacuum degree is 0.9Pa, power is applied to the induction coil to completely melt 10kg of master alloy to obtain an alloy melt.

(6) Increase the power of the vacuum induction furnace so that the temperature of the alloy melt reaches 1510°C, and pour the alloy melt into the mold shell. After the pouring is completed, the induction coil is powered off, and the vacuum is broken after 10 minutes, and the sand box or the mold shell wrapped in insulation cotton is removed from the vacuum induction furnace.

Comparative example 2:

(1) Select 10kg of K4750 master alloy for use.

(2) Weigh 40kg of ordinary quartz sand, remove the quartz sand with a particle size of more than Φ4mm, weigh 5kg of the quartz sand with a particle size of Φ3mm to Φ4mm, weigh 8kg with a particle size of Φ2mm to Φ3mm, weigh 19kg with a particle size of Φ1mm to Φ2mm, remove the quartz sand with a particle size below Φ1mm, and mix the above-mentioned quartz sand with different particle sizes evenly.

(3) Prepare a cylindrical sand box, then place the mold shell in the middle of the sand box, and then fill the mixed ordinary quartz sand between the mold shell and the wall of the sand box. The thickness between the mold shell and the wall of the sand box is 40mm. Squeeze once every 50mm to 80mm in the direction of gravity to ensure that the quartz sand is filled tightly.

(4) Put the sand box with the mold shell and quartz sand into the heat treatment furnace, slowly raise the temperature from room temperature to 900°C with the furnace, and keep it at 900°C for 3.5h.

(5) Move the heat-treated sandbox into a 25kg vacuum induction furnace, close the furnace door and then vacuumize it. When the vacuum degree is 0.9Pa, power is applied to the induction coil to completely melt 10kg of master alloy to obtain an alloy melt.

(6) Increase the power of the vacuum induction furnace so that the temperature of the alloy melt reaches 1410°C, and pour the alloy melt into the mold shell. After the pouring is completed, the induction coil is powered off, and the vacuum is broken after 10 minutes, and the sand box or the mold shell wrapped in insulation cotton is removed from the vacuum induction furnace.

Comparative example 3:

(1) Select 10kg of K4750 master alloy for use.

(2) Choose insulation cotton.

(3) Wrap the formwork with thermal insulation cotton (Figure 2).

(4) Put the mold shell wrapped with thermal insulation cotton into a heat treatment furnace, slowly raise the temperature from room temperature to 900°C with the furnace, and heat-preserve at 900°C for 3.5h.

(5) Move the heat-treated sandbox into a 25kg vacuum induction furnace, close the furnace door and then vacuumize it. When the vacuum degree is 0.9Pa, power is applied to the induction coil to completely melt 10kg of master alloy to obtain an alloy melt.

(6) Increase the power of the vacuum induction furnace so that the temperature of the alloy melt reaches 1410°C, and pour the alloy melt into the mold shell. After the pouring is completed, the induction coil is powered off, and the vacuum is broken after 10 minutes, and the sand box or the mold shell wrapped in insulation cotton is removed from the vacuum induction furnace.

The casting test bars prepared in Example 1 and Comparative Examples 1-3 were inspected by metallographic analysis for the shape and size of the grains of the test bars. Specifically, the alloy casting test bars were cut longitudinally, and the surface of the samples was polished to 2000 _# sandpaper with a semi _- automatic grinding and polishing machine, and then polished with 2.5 _μm diamond polishing paste to remove scratches. Wipe and corrode for 7-12 seconds, then ultrasonically clean with alcohol _and dry.

Observation with a metallographic electron microscope shows that the casting test bars of Example 1 and Comparative Examples 1-3 are well filled, and no obvious microporosity is seen, but the grains of the casting test bars are different. The casting test rod of Example 1 is equiaxed crystal, and the average grain size is 250 μm. The casting test rod of Comparative Example 1 has equiaxed grains, but the grain size is relatively large, and the average grain size is 1.5mm. The casting test rod of Comparative Example 2 is columnar crystals, the average lateral length of columnar crystals is 800 μm, and the average width of columnar crystals is 120 μm. The casting test bar in Comparative Example 3 has equiaxed grains, but the grain size difference between the upper end and the lower end of the test bar is large, and the average grain size in the middle part of the test bar is 600 μm (Figure 3-4).

The above-mentioned examples and comparative examples are only to illustrate the technical conception and characteristics of the present invention, and its purpose is to allow those familiar with this technology to understand the content of the present invention and implement it accordingly, and cannot limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention shall fall within the protection scope of the present invention.

Claims (6)

1. A method for refining equiaxed crystal grains of a K4750 nickel-based superalloy casting test bar is characterized by comprising the following steps: the method comprises the following steps:

(1) Preparing a solidification cooling material: taking common quartz sand as a raw material, and uniformly mixing the common quartz sand according to different particle size ratios through screening to obtain a solidification cooling material;

(2) And (3) filling a solidification cooling material: filling a solidification cooling material between the mould shell and the sand box wall;

(3) And (5) die shell charging and vacuumizing treatment: placing the mould shell into a vacuum induction smelting furnace after preheating treatment, and vacuumizing until the vacuum degree is less than or equal to 1.0Pa;

(4) Melting master alloy and pouring casting test bars: when the vacuum degree is less than or equal to 1.0Pa, the K4750 master alloy starts to be melted, then the temperature of the alloy melt is increased to 1390 ℃ to 1480 ℃ and the alloy melt is poured into a mould shell, thus preparing the casting test bar with fine equiaxed crystal grains.

2. A method of refining equiaxed grain grains of a K4750 nickel-based superalloy cast test bar in accordance with claim 1, wherein: the K4750 casting master alloy comprises the following chemical components in percentage by weight:

0.08 to 0.13 percent of C, 18.00 to 21.00 percent of Cr, 2.70 to 5.00 percent of W, 1.00 to 2.50 percent of Mo, 0.80 to 1.50 percent of Al, 4.00 to 5.00 percent of Fe, 0.005 to 0.012 percent of B, 1.00 to 2.00 percent of Nb, 2.40 to 3.20 percent of Ti and the balance of Ni.

3. A method of refining equiaxed grain grains of a K4750 nickel-based superalloy cast test bar in accordance with claim 1, wherein: in the step (1), when quartz sand with different granularities is mixed, the quartz sand with granularity phi 3 mm-phi 4mm accounts for 10% -20% by weight, the quartz sand with granularity phi 2 mm-phi 3mm accounts for 20% -30% by weight, and the quartz sand with granularity phi 1 mm-phi 2mm accounts for 50% -60% by weight.

4. A method of refining equiaxed grain grains of a K4750 nickel-based superalloy cast test bar in accordance with claim 1, wherein: in the filling process of the quartz sand in the step (2), the width between the mould shell and the sand box wall is required to be 60-80 mm, and the quartz sand is required to be extruded once every 50-80 mm in the gravity direction, so that the packing compactness of the quartz sand is ensured.

5. A method of refining equiaxed grain grains of a K4750 nickel-based superalloy cast test bar in accordance with claim 1, wherein: in the step (3), the preheating treatment process of the mould shell is as follows: the sand box with the mould shell and the quartz sand is put into a heat treatment furnace, the temperature is slowly raised to 800 ℃ to 950 ℃ along with the furnace from the room temperature, and the heat is preserved for 3h to 5h at 800 ℃ to 950 ℃.

6. A method of refining equiaxed grain grains of a K4750 nickel-based superalloy cast test bar in accordance with claim 1, wherein: the crystal grains of the prepared K4750 cast test bar are equiaxed crystals, and the average crystal grain size is less than or equal to 300 mu m.