High-strength corrosion-resistant GH3625 alloy bar and preparation method thereof

Abstract

The invention belongs to the technical field of high-temperature alloys, and particularly relates to a high-strength corrosion-resistant GH3625 alloy bar and a preparation method thereof.The preparation method comprises the following steps that S1, weighed raw materials are added into a vacuum induction furnace according to the composition of a GH3625 alloy, an electroslag consumable electrode bar is obtained through a melting period, a refining period and a pouring period, and after arcing, steady state and hot top sealing of electroslag remelting are conducted, the high-strength corrosion-resistant GH3625 alloy bar is obtained; electroslag ingots are obtained; s2, the electroslag ingot is placed in a heating furnace to be subjected to high-temperature diffusion; s3, machining the electroslag ingot, and directly drawing the electroslag ingot into a black skin state bar; and S4, the black skin state bar is turned to the required specification, and the bar is put in storage after being qualified through performance detection and flaw detection. According to the GH3625 alloy bar, the grain size is larger than or equal to grade 5, the corrosion performance index is smaller than or equal to 0.68 mm / year, the impact energy at the temperature of-60 DEG C is larger than or equal to 115 J, the hardness is smaller than or equal to 260 HBW, the tensile strength is larger than or equal to 891 MPa, and the yield strength is larger than or equal to 535 MPa.

Description

Technical Field

[0001] The present invention belongs to the technical field of superalloy manufacturing, and particularly relates to a high-strength and corrosion-resistant GH3625 alloy bar and a preparation method thereof. Background Art

[0002] The GH3625 alloy is a solid-solution strengthened nickel-based superalloy, which contains relatively high Mo and Nb elements and has excellent creep properties, corrosion resistance and mechanical properties. Since the corrosion resistance and mechanical properties of the GH3625 alloy have different requirements for the grain structure, it is easy to fail to simultaneously meet the requirements of intergranular corrosion and high-strength mechanical properties during the preparation of alloy bars. Especially when preparing large-sized bars, it is necessary to meet high mechanical properties and intergranular corrosion requirements, and the production challenge is difficult. Summary of the Invention

[0003] The purpose of the present invention is to overcome and supplement the deficiencies existing in the prior art. The present invention provides a high-strength and corrosion-resistant GH3625 alloy bar and a preparation method thereof. Through double melting + homogenization diffusion + forging process, the present invention prepares a high-strength and corrosion-resistant GH3625 alloy bar. The obtained bar has a grain size of ≥5 levels, excellent room-temperature tensile properties, and a corrosion performance index of ≤0.91 mm / year.

[0004] To achieve the above technical purposes, the technical solutions adopted in the embodiments of the present invention are as follows:

[0005] In the first aspect, the embodiments of the present invention provide a preparation method of a high-strength and corrosion-resistant GH3625 alloy bar, including the following steps:

[0006] Step S1: Weigh all raw materials including Cr, Ni, Mo, Al, Ti, Nb and C according to the composition of the GH3625 alloy, add the above raw materials into a melting furnace for melting and evacuating, and after three stages of melting period, refining period and casting period, an electroslag consumable electrode bar is obtained after casting. Weld the bottom of the electroslag consumable electrode bar to a dummy electrode and put it into an electroslag remelting furnace to obtain an electroslag ingot after arc starting, steady state and hot capping;

[0007] Step S2: Place the ingot obtained by vacuum induction melting and electroslag remelting in Step S1 in a gas heating furnace for high-temperature homogenization diffusion;

[0008] Step S3: Polish the surface of the electroslag ingot after high-temperature homogenization diffusion in Step S2, and heat the polished electroslag ingot through a heating furnace before forging. The pre-forging heating process uses two-stage heating. First, heat up to 750±14°C for preheating, and then heat up to the forging temperature. After holding for at least 4 hours, perform forging. The forging blanking is carried out by direct drawing to forge to the bar blank size;

[0009] Step S4: Turn the black-skin state bar stock to the finished GH3625 alloy bar of the required specifications, and store it in the warehouse after passing the performance test and immersion flaw detection.

[0010] Further, by weight fraction, the GH3625 alloy comprises the following components: C ≤ 0.10%, Cr 20.0% - 23.0%, Ti ≤ 0.40%, Al ≤ 0.40%, Mo 8.0% - 10.0%, Nb 3.15% - 4.15%, S ≤ 0.015%, P ≤ 0.015%, Mn ≤ 0.5%, Fe ≤ 5.0%, Si ≤ 0.5%, and the balance is Ni.

[0011] Further, in step S1, the temperatures in the melting stage, refining stage, and pouring stage of the vacuum induction melting are respectively: the full melting temperature in the melting stage is 1490 - 1540 °C, the refining temperature in the refining stage is 1490 - 1550 °C, and the pouring temperature in the pouring stage is 1500 - 1530 °C.

[0012] Further, in step S1, the induction electrode bar is subjected to electroslag remelting to obtain an electroslag ingot. The selected slag system includes CaF2, Al2O3, and CaO, and the weight ratio of CaF2:Al2O3:CaO in the slag system is 60 - 70:10 - 20:10 - 20.

[0013] Further, in step S2, the alloy ingot after duplex smelting is subjected to high-temperature homogenization diffusion. The diffusion temperature is 1190 - 1210 °C, and the holding time is 48 - 72 h.

[0014] Further, in step S3, in the first heat, the ingot is rolled round, and the downward pressure is 5 - 20 mm; in the 2nd - 3rd heats, the blooming of the electroslag ingot is completed, and the average deformation amount of drawing is controlled to be 10% - 30%. The heating temperature for each heat is controlled to be 1100 - 1150 °C, and the holding time is 60 - 180 min; in the 4th - 5th heats during the drawing process, the heating temperature is reduced, the heating temperature is controlled to be 1060 - 1100 °C, the deformation temperature is gradually reduced, the deformation amount for each heat is controlled to be 25% - 30%, and the holding time is 30 - 120 min; in the last heat of deformation, the heating temperature is controlled to be 1020 - 1080 °C, the deformation amount is controlled to be 20% - 35%, and the holding time is 30 - 120 min. After the deformation is completed, a rolling-round operation is performed.

[0015] Further, in step S4, the surface roughness of the finished GH3625 alloy bar is ≤ 1.6 μm.

[0016] In a second aspect, an embodiment of the present invention provides a high-strength corrosion-resistant GH3625 alloy bar, which is prepared by using the preparation method described in the first aspect. The grain size of the GH3625 alloy bar is ≥ grade 5, the corrosion performance index is ≤ 0.68 mm / year, the impact energy at -60°C is ≥ 115 J, the hardness is ≤ 260 HBW, the tensile strength is ≥ 891 MPa, and the yield strength is ≥ 535 MPa.

[0017] The beneficial effects brought by the technical solution provided by the embodiment of the present invention are as follows:

[0018] (1) For the preparation method of the high-strength corrosion-resistant GH3625 alloy bar of the present invention, the alloy composition range and the homogenization and diffusion process are optimized, and the size of primary massive carbides is significantly reduced, with the size ≤ 10 μm.

[0019] (2) The present invention adopts a direct drawing forging process. No metallurgical defects such as shrinkage cavities, cracks, and delamination are found in the macrostructure of the obtained bar, there is no abnormal aggregation of inclusions, and no obvious precipitation of (Cr, Mo)-rich phases is found in the microstructure analysis of the obtained bar. The structure is uniform, the carbides are evenly distributed and fine, and the grain size is greater than grade 5.

[0020] (3) By controlling the deformation process, deformation temperature, holding time, and deformation amount, the present invention prepares a high-strength corrosion-resistant GH3625 alloy bar with excellent performance. The grain size of the GH3625 alloy bar is ≥ grade 5, the corrosion performance index is ≤ 0.68 mm / year, the impact energy at -60°C is ≥ 115 J, the hardness is ≤ 260 HBW, the tensile strength is ≥ 891 MPa, and the yield strength is ≥ 535 MPa.

[0021] (4) The present invention solves for the first time the problem that the GH3625 bar cannot simultaneously meet the requirements of intergranular corrosion and high-strength mechanical properties. The uniformity of its microstructure, mechanical properties reach the level of high-standard bars, and excellent corrosion resistance meet the application requirements of high-strength corrosion-resistant GH3625 alloy bars in the fields of civil gas turbines and thermal power generation. Description of the Drawings

[0022] Figure 1 It is a grain size test chart of the GH3625 alloy bar in Embodiment 1 of the present invention.

[0023] Figure 2 It is a grain size test chart of the GH3625 alloy bar in Embodiment 2 of the present invention. Detailed Embodiments

[0024] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] Example 1

[0026] A preparation method of high-strength and corrosion-resistant GH3625 alloy bars includes the following steps:

[0027] Step S1: Weigh metals Cr, Ni, Mo, Al, Nb, Ti, Mn, B and graphite C according to the composition of GH3625 alloy, and add the above raw materials into a melting furnace for melting and evacuating. After three stages of melting period, refining period and pouring period, the full melting temperature in the melting period is 1500 °C, the refining temperature in the refining period is 1530 °C, and the pouring temperature in the pouring period is 1510 °C. After pouring, an electroslag remelting electrode bar is obtained. The bottom of the electrode bar is welded to a dummy electrode and placed in an electroslag remelting furnace. After arcing, steady state and hot capping, an electroslag ingot is obtained. The slag system selected for electroslag remelting includes CaF2, Al2O3 and CaO, and the weight ratio of CaF2:Al2O3:CaO in the slag system is 70:15:15;

[0028] Step S2: Place the ingot after vacuum induction melting + electroslag remelting in step S1 in a gas heating furnace for high-temperature homogenization diffusion. The diffusion temperature is 1200 °C and the holding time is 56 h;

[0029] Step S3: Perform circumferential surface grinding on the electroslag ingot after high-temperature homogenization diffusion in step S2, and heat the ground electroslag ingot through a heating furnace before forging. The pre-forging heating process uses two-stage heating. First, heat up to 750 ± 14 °C for preheating, and then heat up to 11 (the value here seems incorrect, assuming it should be a specific temperature) and hold for at least 6 h before forging. The forging process uses the drawing method for blooming and forges to the size of the bar billet. In the first heat, the ingot is rolled round to make the surface structure denser and improve the plasticity of the alloy. The rolling-round heating temperature is 1120 °C, and the single-side reduction is 10 - 15 mm; In the second and third heats, the blooming of the electroslag ingot is completed. Control the heating temperature of each heat to be 1120 °C, control the average deformation amount of each heat to be 25%, and the holding time is 180 min; In the fourth and fifth heats during the drawing process, control the heating temperature to be 1080 °C, control the average deformation amount of each heat to be 28%, and the holding time is 120 min; In the sixth heat, control the heating temperature to be 1050 °C, control the deformation amount to be 30%, and the holding time is 30 min. After deformation, perform a rolling-round operation;

[0030] Step S4: Turn the black-skin state bars to a Φ200 mm specification. The surface roughness of the finished GH3625 alloy bars is ≤1.6 μm. After passing the water immersion flaw detection, they are warehoused.

[0031] Example 2

[0032] A preparation method of high-strength and corrosion-resistant GH3625 alloy bars includes the following steps:

[0033] Step S1: According to the composition of GH3625 alloy, metals Cr, Ni, Mo, Al, Nb, Ti, Mn, B and graphite C are taken, and the above raw materials are added to a melting furnace for melting and evacuation. Through three stages: the melting stage, the refining stage and the casting stage, the full melting temperature in the melting stage is 1500 °C, the refining temperature in the refining stage is 1530 °C, and the casting temperature in the casting stage is 1510 °C. After casting, an electroslag remelting electrode bar is obtained. The bottom of the electrode bar is welded to a dummy electrode and placed in an electroslag remelting furnace. After arcing, steady state and hot topping, an electroslag ingot is obtained. The slag system selected for electroslag remelting includes CaF2, Al2O3 and CaO, and the weight ratio of CaF2:Al2O3:CaO in the slag system is 70:15:15;

[0034] Step S2: The ingot after vacuum induction melting + electroslag remelting in Step S1 is placed in a gas heating furnace for high-temperature homogenization diffusion. The diffusion temperature is 1200 °C and the holding time is 56 h;

[0035] Step S3: The electroslag ingot after high-temperature homogenization diffusion in Step S2 is subjected to circumferential surface grinding, and the ground electroslag ingot is preheated before forging through a heating furnace. The preheating process before forging adopts two-stage heating. First, it is heated to 750 ± 14 °C for preheating, and then it is heated to 1150 °C and held for at least 6 h before forging. The forging process adopts the drawing method for blooming and is forged to the size of the bar blank. In the first heat, the ingot is rolled round to make the surface structure denser and improve the plasticity of the alloy. The rolling round heating temperature is 1150 °C, and the unilateral reduction is 10 - 15 mm; In the second and third heats, the blooming of the electroslag ingot is completed. The heating temperature for each heat is controlled at 1130 °C, the average deformation per heat is controlled at 27%, and the holding time is 180 min; In the fourth and fifth heats, the heating temperature is controlled at 1090 °C during the drawing process, the average deformation per heat is controlled at 30%, and the holding time is 120 min; In the sixth heat, the heating temperature is controlled at 1070 °C, the deformation is controlled at 25%, and the holding time is 30 min. After deformation, a rolling round operation is carried out.

[0036] Step S4: The black skin state bar is turned to a Φ200 mm specification. The surface roughness of the finished GH3625 alloy bar is ≤1.6 μm. After passing the water immersion flaw detection, it is warehoused.

[0037] The chemical composition of the GH3625 alloy bar in Examples 1 - 2 is shown in Table 1.

[0038] Table 1 Chemical composition of the GH3625 alloy bar in Examples 1 - 2

[0039] element standard control range Example 1 Example 2 C ≤0.10 0.04～0.07 0.045 0.048 Cr 20.0～23.0 21.0～22.0 21.30 21.32 Ti ≤0.40 0.10～0.40 0.25 0.29 Al ≤0.40 0.10～0.40 0.23 0.19 Nb 3.15～4.15 3.50～4.10 3.60 3.59 Mo 8.0～10.0 8.5～9.5 9.17 9.12 S ≤0.015 ≤0.010 ＜0.0005 ＜0.0005 P ≤0.015 ≤0.010 ＜0.001 ＜0.001 Mn ≤0.5 ≤0.2 0.019 0.017 Fe ≤5.0 ≤3.5 1.09 1.08 Si ≤0.5 ≤0.1 0.038 0.062 Ni balance balance balance balance

[0040] The grain size of the alloy bar obtained in Examples 1 - 2 was tested at R / 2, and the test results are shown inFigure 1 and Figure 2 as shown in Figure 2 , mechanical property tests were carried out on the bars. The grain size and mechanical properties of the GH3625 alloy bars in Examples 1-2 are shown in Table 2.

[0041] Table 2 Grain Size and Mechanical Properties of GH3625 Alloy Bars in Examples 1-2

[0042]

[0043] As can be seen from Table 1 and Table 2, the high-strength and corrosion-resistant GH3625 alloy bars prepared by the present invention meet the common industry standards, with good indicators for each item and good market competitiveness.

[0044] Finally, it should be noted that the above specific embodiments are only explanations of the present application and do not limit the present application. Although the present invention has been described in detail with reference to the examples, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A preparation method of a high-strength and corrosion-resistant GH3625 alloy bar, characterized in that, It includes the following steps: Step S1: Weigh all raw materials including Cr, Ni, Mo, Al, Ti, Nb and C according to the composition of GH3625 alloy, add the above raw materials into a melting furnace for melting and evacuating, go through three stages of melting period, refining period and casting period, and obtain an electroslag consumable electrode rod after casting. Weld the bottom of the electroslag consumable electrode rod to a dummy electrode and put it into an electroslag remelting furnace to obtain an electroslag ingot after arc starting, steady state and hot topping; Step S2: Place the ingot obtained by vacuum induction melting and electroslag remelting in Step S1 in a gas heating furnace for high-temperature homogenization diffusion; Step S3: Polish the surface of the electroslag ingot after high-temperature homogenization diffusion in Step S2, and heat the polished electroslag ingot in a heating furnace before forging. The pre-forging heating process adopts two-stage heating. First, heat up to 750±14°C for preheating, then heat up to the forging temperature, keep warm for at least 4h and then forge. The forging blanking is carried out by direct drawing to forge to the size of the bar blank; Step S4: Turn the black-skin state bar into a finished GH3625 alloy bar of the required specification, and store it in the warehouse after passing performance testing and immersion flaw detection.

2. The preparation method of the high-strength and corrosion-resistant GH3625 alloy bar according to claim 1, characterized in that, In Step S1, by weight fraction, the GH3625 alloy includes the following components: C≤0.10%, Cr 20.0%~23.0%, Ti≤0.40%, Al≤0.40%, Mo 8.0%~10.0%, Nb 3.15%~4.15%, S≤0.015%, P≤0.015%, Mn≤0.5%, Fe≤5.0%, Si≤0.5%, and the balance is Ni.

3. The preparation method of the high-strength and corrosion-resistant GH3625 alloy bar according to claim 1, characterized in that, In Step S1, the temperatures of the three stages of melting period, refining period and casting period in vacuum induction melting are respectively: the full melting temperature in the melting period is 1490~1540°C, the refining temperature in the refining period is 1490~1550°C, and the casting temperature in the casting period is 1500~1530°C.

4. The preparation method of the high-strength and corrosion-resistant GH3625 alloy bar according to claim 1, characterized in that, In Step S1, the electroslag consumable electrode rod is subjected to electroslag remelting to obtain an electroslag ingot. The selected slag system includes CaF2, Al2O3 and CaO, and the weight ratio of CaF2:Al2O3:CaO in the slag system is 60~70:10~20:10~20.

5. The preparation method of the high-strength and corrosion-resistant GH3625 alloy bar according to claim 1, characterized in that, In Step S2, the alloy ingot after duplex smelting is subjected to high-temperature homogenization diffusion, the diffusion temperature is 1190~1210°C, and the holding time is 48~72h.

6. The preparation method of the high-strength and corrosion-resistant GH3625 alloy bar according to claim 1, characterized in that, In Step S3, in the first heat, the ingot is rolled round and pressed down by 5~20mm; in the 2nd to 3rd heats, the blanking of the electroslag ingot is completed, and the average deformation amount of drawing is controlled at 10%~30%, and the heating temperature of each heat is controlled at 1100~1150°C, and the holding time is 60~180min; in the 4th to 5th heats, the heating temperature is reduced during the drawing process, the heating temperature is controlled at 1060~1100°C, the deformation temperature is gradually reduced, the deformation amount of each heat is controlled at 25%~30%, and the holding time is 30~120min; in the last heat of deformation, the heating temperature is controlled at 1020~1080°C, the deformation amount is controlled at 20%~35%, and the holding time is 30~120min. After the deformation is completed, a rolling-round operation is carried out.

7. The preparation method of the high-strength and corrosion-resistant GH3625 alloy bar according to claim 1, characterized in that, In step S4, the surface roughness of the finished GH3625 alloy bar is ≤ 1.6 μm.

8. A high-strength and corrosion-resistant GH3625 alloy bar, characterized in that, Prepared by the preparation method according to any one of claims 1-7, the grain size of the GH3625 alloy bar is ≥ grade 5, the corrosion performance index is ≤ 0.68 mm / year, the impact energy at -60 °C is ≥ 115 J, the hardness is ≤ 260 HBW, the tensile strength is ≥ 891 MPa, and the yield strength is ≥ 535 MPa.

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