Preparation method of ultrahigh-strength C250 super-large-specification steel bar

Abstract

The invention relates to the technical field of metal material manufacturing, and particularly discloses a preparation method of an ultrahigh-strength C250 super-large-specification steel bar. The preparation method specifically comprises the following steps that high-temperature homogenization heat treatment is conducted on a steel ingot, wherein the heating temperature T of the steel ingot is 1200-1220 DEG C, and the heat preservation time t is larger than or equal to 40 h; the steel ingot is a steel ingot with the diameter of 810 mm; forging the steel ingot: pressing a clamp handle on the head of the steel ingot, and upsetting and drawing the steel ingot for four times to obtain a steel bar; the steel ingot deformation is larger than 50%, the last heating number forging starting temperature T is larger than or equal to 950 DEG C, and the final forging temperature T is larger than or equal to 800 DEG C; and performing heat treatment control on the oversized steel bar: performing air cooling on the forged steel bar until T is less than or equal to 200 DEG C, and performing solution treatment. According to the method, the problems of ultra-fine grain forging, structure homogenization control and the like of the C250 ultra-large-specification steel bar with the diameter being 375 mm are solved, and the metallurgical quality of the ultra-large-specification steel bar completely reaches the physical level of a small-specification steel bar.

Description

Technical Field

[0001] The present application relates to the technical field of metal material manufacturing, and more specifically, to a method for preparing ultra-high strength C250 ultra-large specification steel bars. Background Art

[0002] An aircraft engine is a highly complex and sophisticated thermal machine that provides aircraft with the power they need to fly. As the heart of an aircraft, it directly affects the performance, reliability and economy of the aircraft and is an important manifestation of a country's scientific, industrial and national defense strength.

[0003] With the rapid development of my country's national defense construction, the updating and iteration of weapons and equipment has accelerated, and aircraft are developing towards large-scale and long-range, and the raw materials for engine shafts are developing towards large specifications and large sizes. At present, the C250 steel used for the shafts of my country's civil aviation engines adopts vacuum induction and vacuum consumable production processes. The production specifications of steel bars are mainly Φ≤304mm, and the size of the vacuum consumable steel ingots used is Φ660mm. In order to meet the needs of large-scale development, the specifications of the raw materials are required to be greatly increased, from the original Φ≤304mm to Φ≤375mm, and the vacuum consumable steel ingots are increased from the original Φ660mm to Φ810mm.

[0004] There is no mature process for forging and producing super-large vacuum consumable steel bars of C250 steel. It is necessary to conduct process exploration and trial production on the forging production process of Φ810mm steel ingots so that the overall metallurgical quality of super-large C250 steel bars can fully meet the technical specifications of small-sized round bars of Φ300mm. The production difficulty is enormous. Summary of the invention

[0005] In view of the above relevant analysis, this application aims to provide a method for preparing ultra-high strength C250 ultra-large-size steel bars. This application ensures uniform chemical composition and organization of the steel ingots through vacuum consumable steel ingot homogenization heat treatment control. This application ensures that the comprehensive metallurgical quality (macrostructure, non-metallic inclusions, grain size, mechanical properties, fracture toughness) of ultra-large-size steel bars meets the technical requirements of small-size steel bars through fine organization forging production control of ultra-large-size steel bars. This application ensures that the steel bars fully meet the technical requirements of small-size steel bars through post-forging heat treatment control of ultra-large-size steel bars.

[0006] The present application provides a method for preparing ultra-high strength C250 ultra-large specification steel bars, which adopts Φ810mm steel ingots + high temperature homogenization heat treatment + 7000T fast forging equipment forging production + post-forging heat treatment.

[0007] The preparation method specifically comprises the following steps: (1) High temperature homogenization heat treatment of steel ingot: the heating temperature T of the steel ingot is 1200-1220°C, and the holding time t≥40h; the steel ingot is Φ810mm steel ingot; (2) Ingot forging process: The head of the ingot is pressed with a clamp, and the ingot is subjected to four upsetting and four drawing to obtain a steel bar; the deformation of the ingot is greater than 50%, the final forging temperature T≥950℃, and the final forging temperature T≥800℃; (3) Heat treatment control of super-large size steel bars: After forging, the steel bars are air-cooled to T≤200℃ for solution treatment.

[0008] Optionally, in the high-temperature homogenization heat treatment of the steel ingot, a step-by-step insulation heating method is adopted, specifically: 630℃±10℃, insulation for 3h; heating to 800-900℃ at a rate of ≤100℃ / h, insulation for 3h; heating to 1200-1220℃ at a rate of ≤100℃ / h, insulation for ≥40h.

[0009] Compared with the prior art, this application can at least achieve the following beneficial effects: (1) Before forging the steel ingot, the present application needs to carry out high-temperature homogenization diffusion heat treatment to reduce the chemical composition segregation of the steel ingot and further improve the chemical composition uniformity of the steel ingot, thereby improving the microstructure uniformity of the super-large specification steel bar.

[0010] The steel ingot of the present application uses a forging machine with a tonnage of 7000 T. Since the Φ810 mm steel ingot needs to be forged, upsetting and elongated using a large tonnage forging machine, a large amount of reduction is achieved during the processing, thereby making the internal quality of the prepared steel bar more uniform.

[0011] (2) In the process of forging steel ingots, the present application adopts step cooling and four-fire production, and the deformation of the steel ingot in each fire is ≥50%, thereby improving the mechanical properties and grain size of the finished steel bars.

[0012] (3) After the steel ingot is forged, the steel bar needs to be cooled in air to below 200°C and then subjected to solution heat treatment to achieve the purpose of refining the steel bar structure without cracking. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is the heating curve of the steel ingot. DETAILED DESCRIPTION

[0014] Before describing the embodiments of the present application in detail, it should be understood that the terms used herein are only used for the purpose of describing specific embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by ordinary technicians in the field to which the terms belong.

[0015] At present, the C250 steel for civil aviation engine shafts in my country is manufactured by vacuum induction + vacuum consumable smelting method. In order to meet the needs of large-scale and long-distance development, the Φ≤304mm steel bars produced by the current mature Φ660mm steel ingots can no longer meet the requirements. It is necessary to increase the size and weight of the steel ingots, increase the size of the finished steel bars, increase the delivery weight of the steel bars, and improve the utilization rate of each batch of forgings to further meet the needs of large-scale tasks.

[0016] As the size of steel ingots continues to expand, the inclusions and chemical composition of steel ingots are seriously segregated, which greatly affects the performance indicators of super-large steel bars. In order to meet the performance specifications of small specifications, the production of ultra-high strength C250 super-large steel bars is an urgent problem that needs to be solved in my country.

[0017] The present application achieves low segregation control of large-size Φ375mm steel bars by precisely controlling the steps of the steel ingot forging production process, and the comprehensive mechanical properties of the ultra-large-size steel bars can meet the requirements of technical specifications and are stable.

[0018] The present application provides a method for preparing an ultra-high strength C250 ultra-large specification steel bar, the preparation method comprising: (1) High temperature homogenization heat treatment of steel ingot: The heating temperature T of the steel ingot is 1200-1220℃, and the holding time t≥40h. The steel ingot is Φ810mm. The specific heating curve of the steel ingot is as follows: Figure 1 As shown, a step-by-step insulation heating method is adopted, specifically: 630℃±10℃, insulation for 3h; heating to 800-900℃ at a rate of ≤100℃ / h, insulation for 3h; heating to 1200-1220℃ at a rate of ≤100℃ / h, insulation for ≥40h.

[0019] (2) Ingot forging process: The head of the ingot (riser end) is pressed with a clamp, and the ingot is subjected to four upsetting and four drawing to obtain a steel bar. The deformation of the ingot is greater than 50%, the final forging temperature T≥950℃, and the final forging temperature T≥800℃.

[0020] (3) Heat treatment control of super-large size steel bars: After forging, the steel bars are air-cooled to T≤200℃ for solution treatment.

[0021] Compared with the current C250 Φ660mm steel ingot forging processing technology, this application provides the fine structure forging technology of ultra-large specification Φ810mm steel ingot for the first time, which is an unprecedented metallurgical technology breakthrough.

[0022] The homogenization heat treatment control of the steel ingot in the present application solves the problem of low-multiple organization and chemical composition uniformity of large-sized steel bars. The preparation method of the present application can obtain ultra-high strength C250 ultra-high uniformity ultra-large-sized steel bars that are qualified for magnetic particle inspection.

[0023] By adopting the preparation method of the present application, the performance of the super-large-sized steel bars after heat treatment is excellent, and the technical index requirements of small-sized bars can be fully achieved, while the delivery and utilization rate of the steel ingots is improved.

[0024] By adopting the preparation method of the present application, through the methods of step heating, cooling and high-temperature homogenization heat treatment, the ultra-large specification steel rod can obtain a fine structure, and the grain size of the steel rod is far better than grade 5.0.

[0025] To make the purpose, technical solutions and advantages of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely below. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of this application.

[0026] The present application is further described in detail below in conjunction with the embodiments and performance test results. Example Example 1

[0027] This embodiment provides a method for preparing ultra-high strength C250 ultra-large specification steel bars.

[0028] The preparation method specifically comprises the following steps: (1) High temperature homogenization heat treatment of steel ingot: The heating temperature T of the steel ingot is 1220℃ and the holding time t is 41h.

[0029] (2) Ingot forging process: The head of the ingot (riser end) is pressed with a clamp, and the ingot is subjected to four upsetting and four pulling. The specific parameters of the ingot forging process are shown in Table 1.

[0030] Table 1 Ingot forging process parameters

[0031] (3) Heat treatment control of super-large size steel bars: After forging, the steel bars are air-cooled to 150℃ for solution treatment; the solution temperature T is 820℃ and the holding time is 31h. Example 2

[0032] This embodiment provides a method for preparing ultra-high strength C250 ultra-large specification steel bars.

[0033] The differences between this embodiment and embodiment 1 are as follows: the steel ingot forging process parameters are specifically shown in Table 2.

[0034] The remaining steps are consistent with those in Example 1.

[0035] Table 2 Ingot forging process parameters Example 3

[0036] This embodiment provides a method for preparing ultra-high strength C250 ultra-large specification steel bars.

[0037] The differences between this embodiment and embodiment 2 are as follows: High temperature homogenization heat treatment of steel ingot: holding time t is 45h.

[0038] Heat treatment control of super-large size steel bars: After forging, the steel bars are air-cooled to 130℃ for solution treatment; the solution temperature T is 820℃ and the holding time is 30h.

[0039] The remaining steps are consistent with those in Example 2. Performance testing

[0040] The following performance tests were performed on the ultra-high strength C250 ultra-large specification steel bars prepared in the above embodiments.

[0041] 1. Chemical composition analysis and testing.

[0042] The detection method refers to "3 Sampling and sample preparation methods for finished product analysis" and "5 Allowable deviations of chemical composition of finished products" in GB / T222-2006 "Allowable tolerances for chemical composition of finished steel products" and GB / T223 "Chemical analysis methods for steel and alloys".

[0043] The test results are shown in Table 3.

[0044] Table 3 Chemical composition of steel bars (wt%)

[0045] 2. Low-magnification tissue detection The test method refers to ASTM A604-2007 "Standard Practice for Macroetching of Consumable Electrode Remelted Steel Bars and Billets".

[0046] The test results are shown in Table 4.

[0047] Table 4 Low-magnification tissue detection results

[0048] (III) Mechanical properties testing The test methods refer to GB / T 228 "Room Temperature Tensile Test Method for Metallic Materials", GB / T 229 "Charpy Notch Impact Test Method for Metallic Materials", GB / T 230 "Rockwell Hardness Test Method for Metallic Materials", and GB / T4161 "Plane Strain Fracture Toughness KIC Test Method for Metallic Materials".

[0049] The test results are shown in Table 5.

[0050] Table 5 Mechanical properties test results

[0051] (IV) Non-metallic impurities and grain size detection, The detection method refers to GB / T 10561 "Standard rating chart microscopic examination method for determination of non-metallic inclusion content in steel".

[0052] The test results are shown in Table 6.

[0053] Table 6 Non-metallic impurities and grain size

[0054] According to the test results of Tables 3 to 6, the chemical composition, macrostructure, mechanical properties, non-metallic impurities and grain size of the ultra-high strength C250 ultra-large specification steel bars prepared by the preparation method of the present application can meet the requirements of the technical standards. Comparative Example Comparative Example 1

[0055] This comparative example provides a method for preparing ultra-high strength C250 ultra-large specification steel bars.

[0056] The differences between this comparative example and Example 3 are as follows: Ingot forging process: The ingot forging process parameters are shown in Table 7.

[0057] The remaining steps are consistent with those in Example 3.

[0058] Table 7 Ingot forging process parameters of comparative example Comparative Example 2

[0059] This comparative example provides a method for preparing ultra-high strength C250 ultra-large specification steel bars.

[0060] The differences between this comparative example and Example 3 are as follows: Ingot forging process: The ingot forging process parameters are shown in Table 8.

[0061] The remaining steps are consistent with those in Example 3.

[0062] Table 8 Ingot forging process parameters of comparative example

[0063] The following macrostructure tests and mechanical property tests were performed on the ultra-high strength C250 ultra-large specification steel bars prepared in the above comparative example.

[0064] The detection method of macrostructure detection refers to ASTM A604-2007 "Standard Practice for Macroetching of Consumable Electrode Remelted Steel Bars and Billets". The test results are shown in Table 9.

[0065] The test methods for mechanical properties testing refer to GB / T 228 "Room Temperature Tensile Test Method for Metallic Materials", GB / T 229 "Charpy Notch Impact Test Method for Metallic Materials", GB / T 230 "Rockwell Hardness Test Method for Metallic Materials", and GB / T4161 "Plane Strain Fracture Toughness KIC Test Method for Metallic Materials". The test results are shown in Table 10.

[0066] Table 9 Low-magnification tissue test results of comparative examples

[0067] Table 10 Mechanical properties test results of comparative examples

[0068] It can be seen from Tables 9 and 10 that by comparing the test results of Example 3 and Comparative Examples 1-2, the secondary deformation amount in the ingot forging process and the start forging temperature and final forging temperature of the last fire will affect the radial segregation and annular pattern of the ingot, and even affect the elongation, impact energy and fracture toughness of the prepared steel bar.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing ultra-high strength C250 ultra-large specification steel bars, characterized in that: The preparation method specifically comprises the following steps: (1) High temperature homogenization heat treatment of steel ingot: the heating temperature T of the steel ingot is 1200-1220°C, and the holding time t≥40h; the steel ingot is Φ810mm steel ingot; (2) Ingot forging process: The head of the ingot is pressed with a clamp, and the ingot is subjected to four upsetting and four drawing to obtain a steel bar; the deformation of the ingot is greater than 50%, the final forging temperature T≥950℃, and the final forging temperature T≥800℃; (3) Heat treatment control of super-large size steel bars: After forging, the steel bars are air-cooled to T≤200℃ for solution treatment.

2. The method for preparing the ultra-high strength C250 ultra-large specification steel bar according to claim 1, characterized in that: In the high-temperature homogenization heat treatment of the steel ingot, a step-by-step insulation heating method is adopted, specifically: 630℃±10℃, insulation for 3h; heating to 800-900℃ at a speed of ≤100℃ / h, insulation for 3h; heating to 1200-1220℃ at a speed of ≤100℃ / h, insulation for ≥40h.

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