Method for preparing small-size rod of fine-grained high-strength GH4720Li alloy

Abstract

The application discloses a preparation method of fine-grain high-strength GH4720Li alloy small-size rod, and specifically comprises the following steps: preparing a GH4720Li alloy blank; pretreating the GH4720Li alloy blank; hot-rolling the GH4720Li alloy blank to obtain a GH4720Li alloy rod; and using the residual heat after hot rolling to heat straighten the GH4720Li alloy rod to obtain a GH4720Li alloy small-size rod. The GH4720Li alloy small-size rod prepared by the method has a diameter of 15mm-20mm, a grain size of 10-13, a room-temperature tensile strength greater than 1620MPa, and a 650 DEG C tensile strength greater than 1450MPa, and can be used to manufacture high-performance high-temperature alloy blades for aero-engines.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of alloy material processing, and particularly relates to a preparation method of fine-grain high-strength GH4720Li alloy small-size rod. BACKGROUND

[0002] As an important strategic resource, high-temperature alloy has excellent properties such as high-temperature resistance, wear resistance, corrosion resistance and oxidation resistance, and is widely used in the fields of aviation, aerospace, petroleum, ship, chemical industry and power. High-temperature alloy can be divided into iron-based high-temperature alloy, nickel-based high-temperature alloy and cobalt-based high-temperature alloy according to the main elements of the alloy, and can be divided into deformed high-temperature alloy, cast high-temperature alloy, cast high-temperature alloy and new high-temperature alloy according to the product series. With the breakthrough of aerospace industry in the field of advanced engines, gas turbines, nuclear power equipment and other fields, the market demand for high-end and new high-temperature alloy is increasing year by year.

[0003] GH4720Li alloy belongs to Fe-Ni-Cr-based precipitation hardening type deformed high-temperature alloy, and the long-term use temperature range is 500 DEG C ~ 750 DEG C, and the maximum use temperature is 800 DEG C. Chromium and tungsten elements are added in the alloy for solid solution strengthening, aluminum and titanium elements are added to form aging strengthening phase, boron and cerium elements are added to purify and strengthen the grain boundary, and the alloy has high strength and good hot working plasticity. The sum of Al and Ti elements in GH4720Li alloy is about 7.5%, and the content of the strengthening phase gamma prime phase is as high as 40% or more, which leads to large thermal deformation resistance of the alloy, and low hot working plasticity, thereby making it a difficult-to-deform high-temperature alloy. Based on this, according to the characteristics of GH4720Li alloy, a reasonable hot working process is designed to prepare a fine-grain high-strength GH4720Li alloy small-size hot-rolled rod. SUMMARY

[0004] The purpose of the application is to provide a preparation method of fine-grain high-strength GH4720Li alloy small-size rod, which has a grain size between 10-12 levels and a room temperature tensile strength greater than 1620MPa.

[0005] The technical scheme adopted by the application is that the preparation method of fine-grain high-strength GH4720Li alloy small-size rod is implemented according to the following steps:

[0006] Step 1, preparing GH4720Li alloy blank;

[0007] Step 2, pretreating the GH4720Li alloy blank;

[0008] Step 3, hot rolling the GH4720Li alloy blank to obtain GH4720Li alloy rod;

[0009] Step 4, using the heat of hot rolling to heat straighten GH4720Li alloy bar, and GH4720Li alloy small size bar is obtained.

[0010] The application also has the characteristics that,

[0011] In step 1, specifically, a GH4720Li alloy ingot with a specification of Φ508mm is prepared by adopting vacuum induction, electroslag remelting and vacuum consumable melting processes, the head and tail composition risk areas of the ingot are cut off by using a band saw, and a Φ150mm billet is prepared by using a drop hammer to perform open forging; the intermediate billet is cut by using a band saw, and then a Φ55mm extruded intermediate billet is prepared on an extrusion machine, that is, the GH4720Li alloy billet.

[0012] The GH4720Li alloy ingot has the following chemical components in percentage by mass: C: 0.01-0.02%, Si: 0-0.50%, Mn: 0-0.50%, P: 0-0.015%, S: 0-0.008%, Ag: 0-0.0005%, Al: 2.25-2.75%, B: 0.01-0.02%, Bi: 0-0.00005%, Co: 14.0-15.5%, Cr: 15.5-16.5%, Cu: 0-0.10%, Fe: 0-0.50%, Mo: 2.75-3.25%, Pb: 0-0.0010%, Ti: 4.75-5.25%, W: 1.00-1.50%, Zr: 0.025-0.050%, O: 0-0.0020%, N: 0-0.0032%, and the balance is Ni, and the sum of the above components is 100%.

[0013] In step 2, specifically,

[0014] The head of the GH4720Li alloy billet is cut off, the surface oxide skin of the GH4720Li alloy billet is treated by using a sand belt polishing method, and the surface defects are point polished by using an angle grinder, local defects are allowed to be polished, the polished pit is required to be smoothly transitioned, the width-depth ratio of the polished pit is not less than 5:1, the GH4720Li alloy billet after polishing is cut, and a GH4720Li alloy billet with a length of 450-650mm and a diameter of Φ50-54mm is obtained; the GH4720Li alloy billet is polished by using a grinding machine, so that the bite angle after polishing becomes a wedge shape meeting the rolling bite condition, the long axis of the wedge shape is 39-42mm, and the short axis is 30-33mm.

[0015] In step 3, the hot rolling temperature is 1080-1130℃, the holding time is 60-180min, 1 fire rolling is adopted, and the deformation is between 80%-95%; and the rolling of the last pass needs to be stopped for 5-15s.

[0016] In step 4, the straightening frequency is 2-3 times, the diameter is reduced by less than or equal to 0.1 mm, and the bending degree of the rod after straightening is less than or equal to 2 mm / m.

[0017] In step 4, the diameter of the GH4720Li alloy small-size rod is 15-20 mm.

[0018] The GH4720Li alloy small-size rod prepared by the method has a diameter of 15-20 mm, a grain size of 10-13, a room temperature tensile strength of greater than 1620 MPa, and a 650 DEG C tensile strength of greater than 1450 MPa, and is a GH4720Li alloy small-size rod with excellent surface quality and can be used to manufacture high-performance high-temperature alloy blades for aircraft engines. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a morphology diagram of the rod prepared in Example 1 of the present application;

[0020] Figure 2 is a morphology diagram of the rod prepared in Example 2 of the present application;

[0021] Figure 3 is a morphology diagram of the rod prepared in Example 3 of the present application;

[0022] Figure 4 is a shape diagram of the bite angle of the GH4720Li alloy blank after pretreatment. DETAILED DESCRIPTION

[0023] The present application will be described in detail below with reference to the drawings and specific embodiments.

[0024] The preparation method of the fine-grained high-strength GH4720Li alloy small-size rod is specifically implemented according to the following steps:

[0025] Step 1, preparing a GH4720Li alloy blank;

[0026] A GH4720Li alloy ingot with a specification of Φ508 mm is prepared by vacuum induction, electroslag remelting and vacuum consumable melting process, the composition risk area at the head and tail of the ingot is cut off by a band saw, and the ingot is forged and bloomed on a fast forging machine to prepare a Φ150 mm intermediate blank. The intermediate blank is cut by a band saw, and then an extruded intermediate blank with a specification of Φ55 mm is prepared on an extrusion machine, which is the GH4720Li alloy blank.

[0027] The GH4720Li alloy ingot has the following chemical components in percentage by mass: C: 0.01-0.02%, Si: 0-0.50%, Mn: 0-0.50%, P: 0-0.015%, S: 0-0.008%, Ag: 0-0.0005%, Al: 2.25-2.75%, B: 0.01-0.02%, Bi: 0-0.00005%, Co: 14.0-15.5%, Cr: 15.5-16.5%, Cu: 0-0.10%, Fe: 0-0.50%, Mo: 2.75-3.25%, Pb: 0-0.0010%, Ti: 4.75-5.25%, W: 1.00-1.50%, Zr: 0.025-0.050%, O: 0-0.0020%, N: 0-0.0032%, and the balance of Ni, wherein the sum of the above components is 100%.

[0028] Step 2, pretreating the GH4720Li alloy blank;

[0029] The rotten head of the GH4720Li alloy blank is cut off by a grinding wheel saw or a band saw, and the end surface after sawing is required to be free of cracks. The surface oxidation scale of the GH4720Li alloy blank is treated by a sand belt polishing method, and the surface defects are point-ground by an angle grinder. Local defects are allowed to be ground, and the ground pit is required to be smoothly transitioned, and the width-depth ratio of the ground pit is not less than 5:1. The GH4720Li alloy blank after grinding is cut by a grinding wheel saw or a band saw to obtain a GH4720Li alloy blank with a length of 450mm-650mm. The specification of the GH4720Li alloy blank is Φ52±2mm. The above GH4720Li alloy blank is polished by a grinding wheel machine, so that the bite angle after polishing becomes a wedge shape meeting the rolling bite condition, and the end head is approximately an ellipse. The long axis of the wedge shape is 39-42mm, and the short axis is 30-33mm, as shown in Figure 4 .

[0030] Step 3, hot rolling the GH4720Li alloy blank by using a cross-type rolling mill to obtain a GH4720Li alloy rod with a diameter of 15mm-20mm.

[0031] The hot rolling temperature is 1080℃-1130℃, the holding time is 60min-180min, and 1 fire rolling is adopted with a deformation of 80%-95%;

[0032] In order to ensure the stability of the rolling process, the four passes before rolling must adopt the feeding of one end of the polished bite angle, and with the diameter of the rolling bar gradually approaching the size of the bite angle, the significance of improving stability through one-way bite has been lost, and at the same time, the direction operation in front of the rolling mill becomes difficult, and the subsequent passes can be reciprocating feeding rolling. In order to obtain uniform rolling bar organization, the surface temperature of the last pass of the rolling bar needs to be monitored during rolling, and if the temperature is higher than 1050 DEG C, 5s-15s of pass residence needs to be carried out.

[0033] Step 4, the GH4720Li alloy bar is subjected to 2-3 times of hot straightening by utilizing the residual heat of hot rolling, and the GH4720Li alloy small-size bar with a diameter of 15mm-20mm is obtained;

[0034] The diameter reduction of straightening is less than or equal to 0.1mm, and the bending degree of the bar after straightening is less than or equal to 2mm / m; example 1

[0035] The preparation method of the fine-grained high-strength GH4720Li alloy small-size bar is specifically implemented according to the following steps:

[0036] Step 1, preparing GH4720Li alloy blank;

[0037] A casting ingot with a specification of Φ508mm is prepared by adopting vacuum induction+electroslag remelting+vacuum consumable melting process, the composition risk area of the head and tail of the casting ingot is cut off by using a band saw, and the specification of Φ150mm is prepared by performing open-knock forging on a quick forging machine. The band saw is used to cut the intermediate blank in the forging, and then the extruded intermediate blank with a specification of Φ55mm is prepared on an extrusion machine.

[0038] The chemical composition of the GH4720Li alloy casting ingot according to mass percentage is: C: 0.010%, Si: <0.05%, Mn: <0.005%, P: <0.004%, S: <0.0005%, Ag: <0.0005%, Al: 2.51%, B: 0.013%, Bi: <0.00001%, Co: 14.84%, Cr: 16.66%, Cu: <0.01%, Fe: 0.18%, Mo: 3.08%, Pb: <0.0005%, Ti: 4.95%, W: 1.27%, Zr: 0.039%, O: 0.0001%, N: 0.0012%, and the balance is Ni, and the sum of the above component mass percentages is 100%;

[0039] Step 2, blank pretreatment

[0040] The rotten head of the GH4720Li alloy blank is cut off by a grinding wheel saw or a band saw, the end surface after sawing is required to be free of cracks, the surface oxidation of the GH4720Li alloy blank is treated by a sand belt polishing method, a surface defect is point-ground by an angle grinder, local defects are allowed to be ground, the ground pit is required to be smooth transition, and the width-depth ratio of the ground pit is not less than 5:1. The GH4720Li alloy blank after grinding is cut by a grinding wheel saw or a band saw to obtain a GH4720Li alloy blank with a length of 450mm; the sand belt polishing specification of the GH4720Li alloy blank is Φ54mm; the GH4720Li alloy blank is polished by a grinding machine, the bite angle is polished into a wedge-shaped block meeting the rolling bite condition, and the end is approximately elliptical.

[0041] In step 3, the blank is hot rolled by a cross-type rolling mill, the blank is heated by a box-type furnace resistance heating furnace, the holding temperature is 1130℃, the holding time is 120min, 1 heating is adopted, a total of 10 rolling passes are adopted, the first four passes are fed by the end with the polished bite angle, the total deformation is 92%, and the last pass is stopped for 5s according to the material temperature. After hot rolling, the diameter of the rod is 15mm.

[0042] In step 4, hot straightening is performed by using the rolling residual temperature, straightening is performed for 2 times, the diameter is reduced by not more than 0.1mm, the bending degree after straightening is equal to 2mm / m, and the diameter of the rod after straightening is 15mm.

[0043] The rod after hot rolling is sampled at the head and tail positions, the sampled test sample is subjected to a heat treatment system of 1107℃ / 1h, oil cooling+760℃ / 8h, air cooling+650℃ / 24h, after the heat treatment system, the grain size and tensile properties are evaluated.

[0044] As shown in Figure 1 , the grain size at the rod R / 2 is observed, the structure is uniform, the grain is small, and the ASTM 13 level requirement is met.

[0045] The rod sample is prepared into a standard tensile sample, then the room temperature and high temperature tensile strength are tested on an electronic universal tensile testing machine, and the test results are shown in Table 1, wherein the room temperature tensile strength is more than 1600MPa, and the 650℃ tensile strength is more than 1450MPa, which can meet the strength requirement of the rod for a certain type of aircraft engine compressor blade.

[0046] Table 1 Tensile properties and grain size of the GH4720Li rod prepared in Example 1

[0047]

[0048]

[0049] Example 2

[0050] The application discloses a preparation method of a fine-grained high-strength GH4720Li alloy small-size rod, and specifically comprises the following steps:

[0051] Step 1, preparing a GH4720Li alloy blank;

[0052] A Φ508mm ingot is prepared by adopting a vacuum induction + electroslag remelting + vacuum consumable melting process, the composition risk area at the head and tail of the ingot is cut off by using a band saw, and the ingot is subjected to open cogging on a fast forging machine to prepare a Φ150mm intermediate blank; the intermediate blank is cut by using a band saw, and then an extruded intermediate blank with a specification of Φ55mm is prepared on an extruding machine.

[0053] The ingot of the GH4720Li alloy has the following chemical components in percentage by mass: C: 0.012%, Si: <0.05%, Mn: 0.003%, P: <0.004%, S: <0.0005%, Ag: <0.0005%, Al: 2.51%, B: 0.016%, Bi: <0.000005%, Co: 14.66%, Cr: 16.73%, Cu: <0.01%, Fe: 0.050%, Mo: 3.04%, Pb: <0.0001%, Ti: 4.97%, W: 1.25%, Zr: 0.040%, O: <0.002%, N: 0.0016%, and the balance is Ni, and the sum of the above components is 100%.

[0054] Step 2, blank pretreatment

[0055] The rotten head of the GH4720Li alloy blank is cut off by using a grinding wheel saw or a band saw, the end surface after cutting is required to be crack-free, the surface oxide skin of the GH4720Li alloy blank is treated by adopting a sand belt polishing method, a surface defect is point-ground by using an angle grinder, local defects are allowed to be ground, the ground pit is required to be smoothly transitioned, and the width-depth ratio of the ground pit is not less than 5:1. The GH4720Li alloy blank after grinding is cut by using a grinding wheel saw or a band saw to obtain a GH4720Li alloy blank with a length of 550mm; the specification of the GH4720Li alloy blank is Φ50mm; the GH4720Li alloy blank is polished by using a grinding machine, the bite angle is required to be polished into a wedge shape meeting the bite condition of rolling, and the end is approximately elliptical.

[0056] Step 3, the blank is subjected to hot rolling open cogging by adopting a cross-type rolling mill, the blank is heated by adopting a box-type furnace resistance heating furnace, the holding temperature is 1080 DEG C, the holding time is 90min, 1 heating is adopted, a total of 8 rolling passes are adopted, the first four passes must adopt the end feeding of the polished bite angle, the total deformation is 84%, and the last pass is subjected to 10s of pass stop according to the material temperature; and the diameter of the rod after hot rolling is 20mm.

[0057] Step 4: Use the residual heat of rolling to perform hot straightening, straighten twice, reduce the diameter to 0.1 mm or less, the curvature after straightening is less than or equal to 2 mm / m, and the diameter of the straightened bar is 20 mm.

[0058] Samples were taken from the hot-rolled bars at positions equivalent to the head and tail of the ingot. The samples were then subjected to a heat treatment process of 1107℃ / 1h, oil cooling + 760℃ / 8h, air cooling + 650℃ / 24h, and air cooling. The grain size and tensile properties were then evaluated.

[0059] like Figure 2 As shown, the grain size at R / 2 of the bar was observed. The microstructure was uniform and the grains were fine, meeting the requirements of ASTM 10.5 grade.

[0060] The bar specimens were prepared into standard tensile specimens, and then the room temperature and high temperature tensile strengths were tested on an electronic universal tensile testing machine. The test results are shown in Table 2. The room temperature tensile strength exceeded 1600 MPa, and the 650℃ tensile strength exceeded 1450 MPa, which can meet the strength requirements of the bar material for compressor blades of a certain type of aero-engine.

[0061] Table 2. Tensile properties and grain size of the GH4720Li rods prepared in Example 2.

[0062]

[0063]

[0064] Example 3

[0065] The method for preparing fine-grained, high-strength GH4720Li alloy small-diameter bars of the present invention is specifically implemented according to the following steps:

[0066] Step 1: Prepare GH4720Li alloy billet;

[0067] A Φ508mm ingot was prepared using a vacuum induction melting + electroslag remelting + vacuum arc remelting process. The high-risk compositional areas at the beginning and end of the ingot were removed using a band saw. The ingot was then forged on a high-speed forging mill to produce a Φ150mm billet. The forged intermediate billet was then cut using a band saw, and subsequently, a Φ55mm extruded intermediate billet was prepared on an extrusion press.

[0068] The GH4720Li alloy ingot has the following chemical components in percentage by mass: C: 0.012%, Si: <0.05%, Mn: <0.005%, P: <0.004%, S: <0.0005%, Ag: <0.00005%, Al: 2.47%, B: 0.016%, Bi: <0.000005%, Co: 14.71%, Cr: 16.84%, Cu: <0.01%, Fe: <0.050%, Mo: 3.03%, Pb: <0.0001%, Ti: 5.01%, W: 1.26%, Zr: 0.045%, O: 0.0010%, N: 0.0011%, and the balance of Ni, and the sum of the above components is 100%.

[0069] Step 2, blank pre-treatment

[0070] The head of the GH4720Li alloy blank is cut off by a grinding wheel saw or a band saw, and the end surface after cutting is required to be free of cracks. The surface oxide of the GH4720Li alloy blank is treated by a sand belt polishing method, and the surface defects are point-ground by an angle grinder. Local defects are allowed to be ground, and the ground pit is required to be smoothly transitioned, and the width-depth ratio of the ground pit is not less than 5:1. The GH4720Li alloy blank after grinding is cut by a grinding wheel saw or a band saw to obtain a GH4720Li alloy blank with a length of 650 mm. The specification of the GH4720Li alloy blank is Φ52 mm. The GH4720Li alloy blank is polished by a grinding machine, and the bite angle is polished into a wedge shape that meets the rolling bite condition, and the end is approximately elliptical.

[0071] Step 3, the blank is hot-rolled by a cross-column type rolling mill. The blank is heated by a box-type resistance heating furnace, the holding temperature is 1100°C, the holding time is 120 min, and the deformation is 88% by 1 rolling pass. The diameter of the hot-rolled bar is 18 mm. In order to ensure stable bite during rolling, the blank is fed from the end with polished bite angle in the first four passes before rolling, and the subsequent passes can be reciprocally fed. In order to obtain uniform rolling bar structure, the surface temperature of the rolling bar in the last pass is monitored during rolling. If the temperature is higher than 1050°C, the pass is stopped for 15 s.

[0072] Step 4, hot straightening is performed by using the rolling residual temperature, and the straightening is performed for 3 times, the diameter shrinkage is less than or equal to 0.1 mm, the bending degree after straightening is less than or equal to 2 mm / m, and the diameter of the bar after straightening is between 18 mm.

[0073] The hot-rolled bar is sampled at the head and tail positions, and the samples are subjected to the following heat treatment: 1107°C / 1h, oil cooling + 760°C / 8h, air cooling + 650°C / 24h. After the heat treatment, the grain size and tensile properties are evaluated.

[0074] As Figure 3As shown, the grain size at the bar R / 2 is observed, the structure is uniform, the grain is small, and the ASTM 11.5 level requirement is met.

[0075] Table 3 Tensile properties and grain size of GH4720Li bar prepared in Example 3

[0076]

[0077] The bar sample is machined into standard tensile samples, and then the room temperature and high temperature tensile strength is tested on an electronic universal tensile testing machine, and the test results are shown in Table 3, wherein the room temperature tensile strength is more than 1600 MPa, and the 650℃ tensile strength is more than 1450 MPa, which can meet the strength requirement of the bar for the compressor blade of a certain type of aero-engine.

Claims

1. A method for preparing small-diameter bars of fine-grained, high-strength GH4720Li alloy, characterized in that, The specific steps are as follows: Step 1: Prepare GH4720Li alloy billet; Step 2, pre-treat the GH4720Li alloy billet; specifically: Remove any damaged ends from the GH4720Li alloy billet. Use a belt abrasive to polish the surface oxide scale. Use an angle grinder to spot-grind surface defects; localized defects are permissible, but the grinding pits must have a smooth transition and a width-to-depth ratio of at least 5:

1. Cut the ground GH4720Li alloy billet to obtain billets with a length of 450mm-650mm and a diameter of Φ50-54mm. Grind the GH4720Li alloy billet with a grinding wheel to create a wedge-shaped bite angle that meets rolling bite requirements. The major axis of the wedge should be 39-42mm, and the minor axis 30-33mm. Step 3: Hot-roll the GH4720Li alloy billet to obtain GH4720Li alloy bars; the hot rolling temperature is 1080℃~1130℃, the holding time is 60min~180min, and a single-pass rolling is used, with a deformation of 80%~95%; and a 5s~15s pass is required during the last rolling pass. Step 4: Use the residual heat after hot rolling to hot straighten the GH4720Li alloy bar to obtain small-diameter GH4720Li alloy bars; the grain size of the small-diameter GH4720Li alloy bars is between 10 and 13, and the tensile strength at 650℃ is greater than 1450MPa.

2. The method for preparing small-diameter fine-grained high-strength GH4720Li alloy bars according to claim 1, characterized in that, In step 1, specifically: a GH4720Li alloy ingot with a specification of Φ508mm is prepared using vacuum induction, electroslag remelting and vacuum consumable melting processes; the high-risk composition areas at the beginning and end of the ingot are cut off using a band saw; the ingot is forged and opened on a high-speed forging mill to prepare a billet with a specification of Φ150mm; the forging intermediate billet is cut off using a band saw; and then an extrusion intermediate billet with a specification of Φ55mm is prepared on an extrusion press, which is the GH4720Li alloy billet.

3. The method for preparing fine-grained, high-strength GH4720Li alloy small-diameter bars according to claim 2, characterized in that, In step 1, the chemical composition of the GH4720Li alloy ingot, by mass percentage, is as follows: C: 0.01–0.02%, Si: 0–0.50%, Mn: 0–0.50%, P: 0–0.015%, S: 0–0.008%, Ag: 0–0.0005%, Al: 2.25–2.75%, B: 0.01–0.02%, Bi: 0–0.00005%, Co: 14.0–15%. 5%, Cr: 15.5-16.5%, Cu: 0-0.10%, Fe: 0-0.50%, Mo: 2.75-3.25%, Pb: 0-0.0010%, Ti: 4.75-5.25%, W: 1.00-1.50%, Zr: 0.025-0.050%, O: 0-0.0020%, N: 0-0.0032%, with the balance being Ni. The sum of the above components by mass percentage is 100%.

4. The method for preparing small-diameter bars of fine-grained high-strength GH4720Li alloy according to claim 1, characterized in that, In step 4, the straightening is performed 2-3 times, the diameter is reduced to 0.1 mm or less, and the bending degree of the straightened bar is less than or equal to 2 mm / m.

5. The method for preparing small-diameter fine-grained high-strength GH4720Li alloy bars according to claim 1, characterized in that, In step 4, the diameter of the small-sized GH4720Li alloy bar is 15mm to 20mm.

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