A high strength seamless pipe and a method of manufacturing the same

Abstract

The present application provides a kind of high-strength seamless tube, it contains Fe and inevitable impurities, also contains the following each chemical element with mass percentage content as follows: C:0.19-0.23%, Si:0.1-0.6%, Mn:0.6-1.5%, Cr:0.1-0.4%, Mo:0.1-0.18%, Nb:0.02-0.04%, Ti:0.01-0.03%, B:0.0015-0.005%, Al:0.01-0.05%, Ca:0.0005-0.005%.The present application also provides the manufacturing method of the seamless tube, it includes the following steps: smelting and continuous casting, to obtain pipe blank;Heating, piercing, rolling, sizing;Heat treatment: austenitizing temperature is 900-930 DEG C, after heat preservation 30-60min quenching, then in 550-650 DEG C tempering, heat preservation time 50-80min;Hot sizing straightening.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of steel and its manufacturing method, especially a kind of seamless tube and its manufacturing method. BACKGROUND

[0002] High-strength structural tube products are widely used in the field of construction machinery, used as core components of truck cranes and caterpillar cranes, and are required to have good strength, low-temperature toughness, good surface quality and weldability.

[0003] In current conventional high-strength seamless tubes, high W and Ni alloy elements are contained. By adding such low-carbon equivalent contributing elements, the low-temperature toughness can be improved, and a certain strength and low carbon equivalent level can be ensured.

[0004] For example, the composition system of the oil casing disclosed in the Chinese patent document with publication number CN101586450A and publication date November 25, 2009, entitled "A kind of oil casing with high strength and high toughness and its manufacturing method" is as follows: C: 0.16-0.28%, Si: ≤0.50%, Mn: 0.30-1.10%, Cr: 0.50-1.10%, Mo: 0.60-0.95%, Al: 0.015-0.060%, among which acid-soluble Als / Al ≥0.80%, Ni <0.60%, Cu: 0.05%-0.25%, V: 0.060-0.20%, Ca >0.0015%, Nb: ≤0.05%, Ti: ≤0.05%, P <0.010%, S <0.002%, O: <0.0024%, H <0.0002%, N <0.008%, B: 0.0000%-0.005%, and the rest is iron. It can be seen that the patent document adds Ni element, and in addition, the Cr content is also relatively high.

[0005] However, such elements are high in cost, and under the situation of homogenization competition in domestic construction machinery, it is expected to provide a high-strength seamless tube with innovative component combination design, which can reduce or remove high-cost alloy elements while maintaining high-strength performance, thereby greatly reducing the cost of construction machinery components. SUMMARY

[0006] One of the purposes of the present application is to provide a high-strength seamless tube which, by means of reasonable chemical element composition design supplemented by process design, achieves higher strength on the basis of reducing or removing high-cost alloy elements, while also having excellent low-temperature impact toughness and good weldability.

[0007] In order to achieve the above-mentioned purposes, the present application provides a high-strength seamless tube containing Fe and unavoidable impurities, and in addition, the following chemical elements in mass percentage:

[0008] C: 0.19-0.23%, Si: 0.1-0.6%, Mn: 0.6-1.5%, Cr: 0.1-0.4%, Mo: 0.1-0.18%, Nb: 0.02-0.04%, Ti: 0.01-0.03%, B: 0.0015-0.005%, Al: 0.01-0.05%, Ca: 0.0005-0.005%, the balance being Fe and other inevitable impurities.

[0009] The high-strength seamless pipe does not contain Ni and W elements.

[0010] Correspondingly, the application also provides a high-strength seamless pipe, each element mass percentage of which is:

[0011] C: 0.19-0.23%, Si: 0.1-0.6%, Mn: 0.6-1.5%, Cr: 0.1-0.4%, Mo: 0.1-0.18%, Nb: 0.02-0.04%, Ti: 0.01-0.03%, B: 0.0015-0.005%, Al: 0.01-0.05%, Ca: 0.0005-0.005%, the balance being Fe and other inevitable impurities.

[0012] In the high-strength seamless pipe provided by the application, the design principles of each chemical element are as follows:

[0013] C: In the high-strength seamless pipe provided by the application, C element is a carbide forming element, which can improve the strength of the steel. When the content of C element is lower than 0.19%, the hardenability will be reduced, thereby reducing the toughness, and when the content of C element is higher than 0.23%, the heat-affected zone position will be embrittled during welding, thereby reducing the welding performance. Therefore, the mass percentage of C element is controlled to be between 0.19% and 0.23% in the application.

[0014] Si: In the high-strength seamless pipe provided by the application, Si element can be dissolved in ferrite to improve the yield strength of the steel. However, the content of Si element should not be too high, otherwise the processing and toughness will be deteriorated. When the content of Si element is lower than 0.1%, the steel will be easily oxidized. Therefore, the mass percentage of Si element is controlled to be between 0.1% and 0.6% in the application.

[0015] Mn: In the high-strength seamless pipe provided by the application, Mn is an austenite forming element, which can improve the hardenability of the steel. In the steel system, when the content of Mn is less than 0.6%, the hardenability of the steel will be significantly reduced, thereby reducing the proportion of martensite and the toughness; when the content of Mn is greater than 1.5%, the carbon equivalent will be too high, thereby deteriorating the welding performance. Therefore, the mass percentage of Mn element is controlled to be between 0.6% and 1.5% in the application.

[0016] Cr: In the high-strength seamless pipe described in the present application, Cr is a strong hardenability element and a strong carbide-forming element, which can precipitate carbides to improve the strength of the steel during tempering. However, when the Cr content is higher than 0.4%, it will cause the carbon equivalent to increase, and the welding performance to deteriorate. When the Cr content is lower than 0.1%, it is difficult to improve the hardenability, resulting in a significant decrease in the strength and low-temperature toughness matching of the product. Therefore, the mass percentage of Cr element in the present application is controlled between 0.1-0.4%.

[0017] Mo: In the high-strength seamless pipe described in the present application, Mo element can improve the strength and tempering stability of the steel through carbide and solid solution strengthening, and improve the low-temperature impact toughness at the same time. In the steel system, when the Mo element content is higher than 0.18%, it will cause the carbon equivalent to increase, and the welding performance to deteriorate. When the Mo element content is lower than 0.1%, it will cause the hardenability to decrease significantly, resulting in a significant decrease in the strength and low-temperature toughness. Therefore, the mass percentage of Mo element in the present application is controlled between 0.1-0.18%.

[0018] Nb: In the high-strength seamless pipe described in the present application, Nb is a fine-grain and precipitated strengthening element, which can compensate for the decrease in strength caused by the reduction of carbon. At the same time, Nb element can inhibit the grain growth in the heat-affected zone during welding, and has a certain inhibitory effect on the deterioration of the performance of this area. When the Nb element content is less than 0.02%, the effect is not obvious, and when the Nb element content is higher than 0.04%, coarse Nb(CN) is easily formed, thereby reducing the toughness. Therefore, the mass percentage of Nb element in the present application is controlled between 0.02-0.04%.

[0019] Ti: In the high-strength seamless pipe described in the present application, Ti is a strong carbonitride-forming element, which can significantly refine the austenite grains and compensate for the decrease in strength caused by the reduction of carbon. At the same time, the carbonitride formed by Ti has high thermal stability, which has a good effect on inhibiting the organization coarsening in the heat-affected zone during welding, thereby improving the welding performance. When the Ti element content is higher than 0.03%, coarse TiN is easily formed, thereby reducing the low-temperature impact toughness; if the Ti element content is too low, Ti cannot fully form TiN with N, and B and N in the steel will form BN brittle phase, thereby reducing the toughness of the material. Therefore, the mass percentage of Ti element in the present application is controlled between 0.01-0.03%.

[0020] B: In the high-strength seamless pipe described in the present application, B element can significantly improve the hardenability. When the B element content is lower than 0.0015%, the effect of improving the hardenability is not significant, and when the B element content is higher than 0.005%, the cold crack sensitivity of the material will increase. Therefore, the mass percentage of B element in the present application is controlled between 0.0015-0.005%.

[0021] Al: Al is mainly used for deoxidation treatment, which can effectively control the oxygen content in the material. Based on this, the content of Al is controlled to be 0.01-0.05% in the present application.

[0022] Ca: In the high-strength seamless pipe described in the present application, Ca element can purify the molten steel and promote MnS spheroidization to improve impact toughness. However, when the content of Ca element is too high, coarse non-metallic inclusions are easily formed. Therefore, the mass percentage of Ca element is controlled to be 0.0005-0.005% in the present application.

[0023] Further, in the high-strength seamless pipe described in the present application, unavoidable impurities include P≤0.015%, S≤0.003%, and N≤0.007%.

[0024] It should be noted that in the high-strength seamless pipe described in the present application, the unavoidable impurity elements mainly include S, P and N. Under the condition that the technical conditions permit, in order to obtain a seamless steel pipe with better performance and higher quality, the content of impurity elements in the seamless steel pipe should be as low as possible, and the lower the better. Among them:

[0025] When the content of N element is higher than 0.007%, a large amount of Ti nitride will be precipitated in the structure, which is a large and sharp angle phase, and will significantly reduce the low temperature impact toughness. Therefore, in some embodiments, the mass percentage of Ti element is controlled to be N≤0.007% in the present application.

[0026] High content of P and S will affect the toughness of the steel. Therefore, in some embodiments, the mass percentage of P and S elements is controlled to be P≤0.015% and S≤0.003%, respectively, in the present application.

[0027] Further, in the high-strength seamless pipe described in the present application, the carbon equivalent is ≤0.55.

[0028] Further, in the high-strength seamless pipe described in the present application, the microstructure is tempered sorbite.

[0029] Further, in the high-strength seamless pipe described in the present application, the grain size is 10-18 μm.

[0030] Further, in the high-strength seamless pipe described in the present application, the performance satisfies: yield strength ≥770 MPa, tensile strength 820-1000 MPa, elongation ≥23%, and impact toughness KV8 at-40℃ ≥45 J.

[0031] Correspondingly, another object of the present application is to provide a manufacturing method of high-strength seamless pipes, which can achieve higher strength and excellent low-temperature impact toughness and good weldability on the basis of reducing or removing high-cost alloying elements by using a unique heat treatment process in combination with the component design of the present application.

[0032] To achieve the above object, the present application proposes a manufacturing method of high-strength seamless pipes, which comprises the steps of:

[0033] smelting and continuous casting to obtain a pipe blank;

[0034] heating, piercing, rolling, sizing;

[0035] heat treatment: austenitizing temperature is 900-930℃, holding for 30-60min, then quenching, and then tempering at 550-650℃, holding time is 50-80min;

[0036] hot sizing and straightening.

[0037] In the manufacturing method described in the present application, the heat treatment adopts austenitizing temperature of 900-930℃, holding for 30-60min, then quenching, and then tempering at 550-650℃, holding time is 50-80min, because: the present application re-austenitizes and water quenches the as-rolled pipe, which can refine the original austenite grains and make the element distribution more uniform, and the precipitation strengthening phase is more uniformly distributed by tempering, thereby improving the strength and toughness matching performance.

[0038] Further, in the continuous casting step of the manufacturing method described in the present application, the superheat of the molten steel is controlled to be lower than 30℃, and the continuous casting speed is 1.8-2.2m / min.

[0039] In some embodiments of the present application, the superheat of the molten steel can be controlled to be lower than 30℃ during casting, and the continuous casting speed is ensured to be 1.8-2.2m / min, which can effectively reduce the composition segregation.

[0040] Further, in the heating step of the manufacturing method described in the present application, the heating is to the soaking temperature of 1200-1240℃.

[0041] Further, in the piercing step of the manufacturing method described in the present application, the piercing temperature is 1180-1240℃.

[0042] Further, in the rolling step of the manufacturing method described in the present application, the finish rolling temperature is 900-950℃.

[0043] Further, in the sizing step of the manufacturing method, the sizing temperature is 850-900℃. Further, in the manufacturing method, the temperature for the sizing and straightening is 450-550℃.

[0044] The high-strength seamless pipe and the manufacturing method thereof have the following advantages and beneficial effects:

[0045] The high-strength seamless pipe has the following advantages and beneficial effects:

[0046] The high-strength seamless pipe has the following advantages and beneficial effects:

[0047] The high-strength seamless pipe has the following advantages and beneficial effects: BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 The microstructure of the high-strength seamless pipe of Example 1 of the present application is shown.

[0049] Figure 2 The grain size of the high-strength seamless pipe of Example 1 of the present application is shown. DETAILED DESCRIPTION

[0050] The high-strength seamless pipe and the manufacturing method thereof will be further explained and described below in conjunction with specific examples, however, the explanation and description do not constitute undue limitations on the technical solutions of the present application.

[0051] Examples 1-6 and Comparative Examples 1-5

[0052] The high-strength seamless pipe of Examples 1-6 is prepared by the following steps:

[0053] (1) Smelting and continuous casting to obtain a pipe blank:

[0054] In some embodiments, a scrap steel + blast furnace molten iron batching scheme can be used: for example, the molten iron ratio is 50-60%, the molten steel is smelted by an electric furnace, after external refining, vacuum degassing and argon stirring, the inclusions are modified by Ca treatment to reduce the O and H content.

[0055] In some preferred embodiments, the superheat of the molten steel can be controlled to be less than 30℃, and the continuous casting speed is 1.8-2.2 m / min.

[0056] (2) heating, piercing, rolling and sizing the pipe blank to obtain a pipe body;

[0057] In the heating step of some embodiments, the heating temperature is 1200-1240℃, the piercing temperature is controlled to be 1180-1240℃, the finish rolling temperature is controlled to be 900-950℃, and the sizing temperature is controlled to be 850-900℃.

[0058] (3) heat treatment: the austenitizing temperature is controlled to be 900-930℃, and after holding for 30-60 min, quenching is performed, and then tempering is performed at 550-650℃, and the holding time is 50-80 min;

[0059] (4) hot sizing and straightening: in some embodiments, the temperature for hot sizing and straightening can be controlled to be 450-550℃.

[0060] It should be noted that the chemical element compositions and related process designs of the high-strength seamless pipes of Examples 1-6 described in the present application all meet the design specification requirements of the present application. Although the step processes of Comparative Examples 1-5 are also roughly the same as those of the present application, the chemical element contents or specific process parameters thereof do not meet the requirements of the present application.

[0061] Table 1 lists the mass percentage of each chemical element of the high-strength seamless pipes of Examples 1-6 and the comparative pipes of Comparative Examples 1-5.

[0062] Table 1. (wt%, the balance is Fe and other unavoidable impurities except P, S and N)

[0063] Number C Si Mn Cr Mo Nb Ti B Al Ca P S N Carbon equivalent Example 1 0.19 0.2 1.5 0.1 0.12 0.03 0.02 0.0015 0.01 0.0005 0.009 0.002 0.004 0.48 Example 2 0.19 0.1 1 0.2 0.18 0.02 0.025 0.002 0.04 0.001 0.010 0.001 0.005 0.43 Example 3 0.23 0.4 1.3 0.3 0.15 0.03 0.03 0.003 0.05 0.005 0.010 0.003 0.006 0.54 Example 4 0.2 0.6 0.8 0.4 0.1 0.03 0.03 0.004 0.03 0.003 0.012 0.002 0.007 0.43 Example 5 0.22 0.25 0.6 0.2 0.16 0.04 0.03 0.005 0.02 0.002 0.013 0.002 0.005 0.39 Example 6 0.19 0.51 1.1 0.25 0.15 0.02 0.01 0.0025 0.03 0.003 0.010 0.0015 0.006 0.45 Comparative Example 1 0.25 0.26 0.8 0.2 0.17 0.04 0.02 0.005 0.023 0.002 0.007 0.003 0.007 0.46 Comparative Example 2 0.21 0.33 1.8 0.15 0.1 0.03 0.01 0.003 0.04 0.002 0.008 0.003 0.005 0.55 Comparative Example 3 0.23 0.2 1.5 0.4 0.18 0.02 0.02 0.004 0.04 0.001 0.010 0.001 0.006 0.60 Comparative Example 4 0.19 0.3 1.2 0.3 0.4 0.04 0.02 - 0.05 0.003 0.010 0.003 0.006 0.53 Comparative Example 5 0.2 0.35 1 0.28 0.15 0.03 0.025 0.0035 0.003 0.004 0.01 0.002 0.009 0.45

[0064] Note: Carbon equivalent = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu)15, in which the mass percentage of each chemical element is brought into the value before the percentage sign.

[0065] Tables 2-1 and 2-2 list the process parameters of the high-strength seamless pipes of Examples 1-6 and the comparative pipes of Comparative Examples 1-5.

[0066] Table 2-1.

[0067]

[0068] Table 2-2.

[0069]

[0070] Samples were taken from the high-strength seamless tubes of Examples 1-6 and the comparative tubes of Comparative Examples 1-5, and tested. The test results are listed in Table 3. The relevant test procedures are as follows:

[0071] (1) Tensile test: The tensile properties at room temperature are tested according to GB / T 228.1-2000 standard.

[0072] (2) Microstructure observation: The cross-section of the tube was taken for microstructure observation. The sample was polished and etched with 4% nitric acid + alcohol. The microstructure was observed using a metallographic microscope.

[0073] (3) Impact test: The impact energy test at -40℃ was conducted in accordance with GB / T 229-2007 "Metallic Materials Charpy Pendulum Impact Test Method".

[0074] (4) Welding performance testing: Welding evaluation shall be carried out in accordance with NB / T-47014-2011 Welding process qualification for pressure equipment.

[0075] Table 3 lists the test results of the high-strength seamless tubes of Examples 1-6 and Comparative Examples 1-5.

[0076] Table 3.

[0077]

[0078] As can be seen from Table 3, the high-strength seamless tubes of Examples 1-6 of the present invention have a yield strength ≥780MPa, a tensile strength between 860-930MPa, an impact toughness KV8 ≥80J at -40℃, an elongation ≥23%, a grain size between 10-18μm, and good weldability.

[0079] also, Figure 1 The metallographic structure of the high-strength seamless tube of Embodiment 1 of the present invention is shown. For example... Figure 1 As shown, the microstructure of this high-strength seamless tube is a uniform and fine tempered sorbite structure.

[0080] Figure 2 The microstructure of the high-strength seamless tube of Embodiment 1 of the present invention is shown. Figure 2 It can be seen that its grains are fine and uniform.

[0081] Comparative Examples 1-5, however, could not achieve excellent low-temperature impact toughness and good weldability because their chemical element composition did not meet the design requirements of this invention.

[0082] It should be noted that the combination of the technical features in the case is not limited to the combination of the claims in the case or the combination of the embodiments in the case. All the technical features disclosed in the case can be freely combined or combined in any way, unless contradictory.

[0083] It should also be noted that the above-mentioned embodiments are only specific embodiments of the present application. Obviously, the present application is not limited to the above-mentioned embodiments, and similar changes or modifications made by those skilled in the art from the disclosure of the present application are directly derived or easily conceived, and should belong to the protection scope of the present application.

Claims

1. A high strength seamless pipe characterized by, The mass percentage of each element is: C: 0.19-0.23%, Si: 0.1-0.6%, Mn: 0.6-1.5%, Cr: 0.1-0.4%, Mo: 0.1-0.18%, Nb: 0.02-0.04%, Ti: 0.01-0.03%, B: 0.0015-0.005%, Al: 0.01-0.05%, Ca: 0.0005-0.005%; the balance is Fe and other inevitable impurities; The microstructure of the high-strength seamless pipe is tempered sorbite, the grain size is 10-18 μm, and the performance meets: yield strength ≥770 MPa, tensile strength is 820-1000 MPa, elongation ≥23%, impact toughness KV8 at -40℃ ≥45J.

2. The high strength seamless pipe of claim 1, wherein, Among the inevitable impurities: P ≤0.015%, S ≤0.003%, N ≤0.007%.

3. The high strength seamless pipe of claim 1 wherein, The carbon equivalent is ≤0.

55.

4. The method of producing a high-strength seamless pipe according to any one of claims 1 to 3, characterized by, It includes the steps of: Smelting and continuous casting to obtain a pipe blank; Heating, piercing, rolling, sizing; Heat treatment: austenitizing temperature is 900-930℃, holding for 30-60min, then quenching, and then tempering at 550-650℃, holding time is 50-80min; Hot sizing and straightening.

5. The production method according to claim 4, wherein In the continuous casting step, the superheat of the molten steel is controlled to be lower than 30℃, and the continuous casting speed is 1.8-2.2m / min.

6. The production method according to claim 4, wherein In the heating step, heating to the soaking temperature of 1200-1240℃.

7. The production method according to claim 4, wherein In the piercing step, the piercing temperature is 1180-1240℃.

8. The production method according to claim 4, wherein In the rolling step, the finish rolling temperature is 900-950℃.

9. The production method according to claim 4, wherein In the sizing step, the sizing temperature is 850-900℃.

10. The production method according to claim 4, wherein The temperature of hot sizing and straightening is 450-550℃.

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