Seamless steel pipe for crane boom and preparation method thereof

Abstract

The present invention relates to the technical field of steel pipe production processes, and specifically discloses a seamless steel pipe for a crane boom and a preparation method thereof. The present invention designs the composition of the seamless steel pipe for the crane boom. When the mass percentages of Ni, Cr, Mo, Mn, and B satisfy the relationship 730≤([Ni]+[Cr]+[Mo]+[Mn]) / [B]≤2140, the tensile properties and impact toughness of the seamless steel pipe can be significantly improved. At the same time, the addition amounts of Ni, Cr, Mo, and Mn can be reduced, avoiding the addition of metals such as Nb and Ti, thereby reducing production costs. Through specific quenching and tempering treatments, the hardenability, grain refinement, and overall uniformity of the crystal structure of the seamless steel pipe are further improved, resulting in the prepared seamless steel pipe for the crane boom having higher tensile properties and impact toughness.

Description

Technical Field

[0001] The present invention relates to the technical field of steel pipe production technology, in particular to a seamless steel pipe for a crane boom and a preparation method thereof. Background Art

[0002] Cranes are widely used in the construction of high-rise buildings, bridges, oil refineries, and other projects. They are lifting equipment products with complex manufacturing processes and high technical content among engineering machinery. Seamless steel pipes for crane booms are key components for load bearing and transportation, and therefore require higher strength and toughness. GB 30584-2014, "Seamless Steel Pipes for Crane Booms," requires seamless steel pipes for crane booms with an outer diameter of less than 219mm, a wall thickness of ≤20mm, and a grade of BJ770 to have a lower yield strength or specified plastic elongation strength of not less than 770MPa, a tensile strength of 820-1000MPa, a longitudinal elongation of not less than 15%, a transverse elongation of not less than 13%, and a longitudinal impact energy absorption of not less than 55kV² / J at -20°C, and a transverse impact energy absorption of not less than 35kV² / J at -20°C.

[0003] As crane lifting capacity increases, higher performance requirements are placed on seamless steel pipes used in crane booms, requiring them to have higher strength and toughness. Existing technologies typically add metals such as Nb and Ti to further enhance the mechanical properties of seamless steel pipes used in crane booms. Furthermore, the addition of Ni, Cr, Mo, and Mn is often quite high, increasing production costs. Summary of the Invention

[0004] In response to the above problems, the present invention provides a seamless steel pipe for crane booms. Through composition design, the tensile properties and impact toughness of the seamless steel pipe can be significantly improved. At the same time, the addition amount of Ni, Cr, Mo and Mn can be reduced, and the addition of metals such as Nb and Ti can be avoided, thereby reducing production costs. Through the heat treatment process, the hardenability, grain refinement and overall uniformity of the crystal phase structure of the steel pipe are further improved, and the prepared seamless steel pipe for crane booms has higher tensile properties and impact toughness.

[0005] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0006] A seamless steel pipe for a crane boom, having the following chemical composition and mass percentage: C 0.13% to 0.17%, Si 0.35% to 0.45%, Mn 1.45% to 1.55%, Cr 0.32% to 0.40%, Mo 0.24% to 0.26%, Alt 0.020% to 0.040%, V 0.07% to 0.09%, W 0.18% to 0.22%, B 0.001% to 0.003%, Ni ≤ 0.10%, Cu ≤ 0.20%, 0.50 ≤ CE ⅡW ≤0.56, the balance is Fe and unavoidable trace impurity elements;

[0007] 730≤([Ni]+[Cr]+[Mo]+[Mn]) / [B]≤2140;

[0008] Among them, [Ni], [Cr], [Mo], [Mn] and [B] are the mass percentages of the corresponding elements.

[0009] Compared with existing technologies, the present invention significantly improves the tensile properties and impact toughness of seamless steel pipes through composition design. It also reduces the addition of Ni, Cr, Mo, and Mn, avoiding the addition of metals such as Nb and Ti, thereby reducing production costs. The synergistic effect of Ni, Cr, Mo, Mn, and B improves the hardenability and mechanical properties of seamless steel pipes for crane booms, reduces the amount of Ni, Cr, Mo, and Mn used, and reduces the manufacturing cost of seamless steel pipes for crane booms. When the mass percentages of Ni, Cr, Mo, Mn, and B satisfy the relationship 730 ≤ ([Ni] + [Cr] + [Mo] + [Mn]) / [B] ≤ 2140, the resulting seamless steel pipes for crane booms exhibit even higher tensile properties and impact toughness.

[0010] Preferably, the chemical composition and mass percentage of the seamless steel pipe for crane boom are: C 0.16%, Si 0.40%, Mn 1.46%, Cr 0.34%, Mo 0.25%, Alt 0.033%, V 0.078%, W 0.18%, B 0.002%, Ni 0.044%, Cu 0.034%, CE ⅡW 0.54, the balance is Fe and inevitable trace impurity elements;

[0011] ([Ni]+[Cr]+[Mo]+[Mn]) / [B]=1047;

[0012] Among them, [Ni], [Cr], [Mo], [Mn] and [B] are the mass percentages of the corresponding elements.

[0013] Preferably, the grain size of the seamless steel pipe for crane jib is 9.5 to 10.0. The grain size of 9.5 to 10.0 enables the seamless steel pipe for crane jib to have high strength and hardness as well as good plasticity and toughness.

[0014] Preferably, the volume percentage of tempered bainite in the metallographic structure of the seamless steel pipe for crane boom is 90% to 100%. 90% to 100% volume percentage of tempered bainite can further ensure the toughness and plasticity of the seamless steel pipe for crane boom while also having good strength.

[0015] Another aspect of the present invention provides a method for preparing the seamless steel pipe for crane boom, comprising the steps of smelting, pre-deoxidation and alloying, refining, degassing, continuous steel casting, rolling and heat treatment;

[0016] The heat treatment process is to keep the rolled steel pipe at 900°C to 920°C, then perform quenching treatment, and then perform tempering treatment at 645°C to 665°C.

[0017] Compared to existing technologies, the present invention first performs a quenching treatment at 900°C to 920°C, heating the seamless steel pipe to above the Ac3 phase transformation point to austenitize it, followed by rapid cooling to obtain a martensitic structure. Tempering treatment is then performed at 645°C to 665°C, achieving a tempered bainite structure through high-temperature tempering and further grain refinement. This synergistic treatment of limited quenching and tempering further improves the steel pipe's hardenability, grain refinement, and overall uniformity of the crystal structure. The resulting seamless steel pipe for crane booms exhibits higher strength, ductility, and toughness.

[0018] Preferably, the rolled steel pipe is quenched at 910°C and then tempered at 655°C.

[0019] Preferably, the rolled steel pipe is kept at 900° C. to 920° C. for 20 min to 40 min and then quenched.

[0020] Preferably, the quenching treatment is to cool the steel pipe to 90°C to 110°C by internal spraying and external showering;

[0021] Among them, the water spray volume of the external shower is 1600m 3 / h~2100m 3 / h, pressure is 0.10MPa~0.15MPa, time is 8s~12s;

[0022] The water volume of the internal spray is 1600m 3 / h~2100m 3 / h, pressure is 0.5MPa~1.0MPa, time is 6s~10s.

[0023] By limiting the process parameters of water quenching, external spraying and internal spraying, the martensite structure can be further refined and its toughness can be improved.

[0024] Preferably, the water temperature of the quenching treatment is 20°C to 28°C.

[0025] Preferably, the heating and holding time of the tempering treatment is 70 to 80 minutes in total. By limiting the tempering time, the tempered bainite structure is further refined and the overall uniformity of the crystal structure is improved.

[0026] Preferably, the heating rate of the tempering is 20°C / min to 50°C / min.

[0027] Preferably, during the pre-deoxidation and alloying process, aluminum ingots are added for precipitation deoxidation when the furnace tapping volume reaches 17% to 18% of the total steel volume, ferrotungsten is added when the tapping volume reaches 19% to 20% of the total steel volume, and alloying is added when the tapping volume reaches 20% to 31% of the total steel volume. Adding ferrotungsten after the aluminum ingots are added to the furnace and before the alloy is added increases the utilization rate of the ferrotungsten, further reduces manufacturing costs, and improves the performance of the seamless steel pipe. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] In order to better illustrate the present invention, further examples are given below.

[0030] Example 1

[0031] This embodiment provides a seamless steel pipe for crane boom, the chemical composition and mass percentage of which are: C 0.16%, Si 0.40%, Mn 1.46%, Cr 0.34%, Mo 0.25%, Alt 0.033%, V 0.078%, W 0.18%, B 0.002%, Ni 0.044%, Cu 0.034%, CE ⅡW 0.54, the balance being Fe and inevitable trace impurity elements.

[0032] After calculation, ([Ni]+[Cr]+[Mo]+[Mn]) / [B]=1047, where [Ni], [Cr], [Mo], [Mn] and [B] are the mass percentages of the corresponding elements.

[0033] After testing, the grain size of the seamless steel pipe for crane boom is 10.0 grade, and the volume percentage of tempered bainite in the metallographic structure is 96%.

[0034] This embodiment also provides a method for preparing the seamless steel pipe for the crane boom, comprising the following steps:

[0035] (1) Melt the raw materials and adjust the composition and content of molten steel.

[0036] (2) Pre-deoxidation and alloying

[0037] When the amount of molten steel tapped from the electric furnace reaches 5.5%, 0.35 kg / t of silicon carbide is added for pre-deoxidation, and the ladle is opened to blow argon to stir the molten steel.

[0038] When the molten steel volume reaches 17.5%, 1.6kg / t aluminum ingots are added for precipitation deoxidation.

[0039] When the molten steel volume reaches 19.5%, 3kg / t of ferrotungsten and 4.5kg / t of ferromolybdenum are added.

[0040] When the molten steel volume reaches 30.5%, 17.5kg / t of silicon manganese, 3.5kg / t of high carbon ferromanganese, 4.5kg / t of high carbon ferrochrome, and 1.5kg / t of ferrovanadium are added for alloying. The added amounts are precisely calculated to ensure that when fine-tuning the alloy in the LF process, the total alloy addition amount is ≤1kg / t, so as to reduce the free oxygen content introduced during the LF alloying process.

[0041] When the molten steel volume reaches 36.5%, 6.0 kg / t of lime and 3.5 kg / t of synthetic slag are added for primary slagging; the chemical components of the synthetic slag include by weight: Al2O3: 49%, CaO: 39%, SiO2: 10%, and MgO: 2%.

[0042] When the steel is tapped to 50.5%, 0.46 kg / t of calcium carbide is added to achieve further diffusion deoxidation.

[0043] (3) Refining: Continue smelting during the refining process, adjust the composition and temperature of the molten steel, and ensure that all components except B are within the control composition requirements.

[0044] (4) Degassing: Under vacuum degree ≤ 67Pa, the treatment was carried out for 12 minutes. After the treatment, 0.07kg / t of ferroboron was added. Under argon flow rate of 12NL / min, soft blowing was carried out for 18 minutes, and the product was hoisted to the continuous casting process.

[0045] (5) Continuous steel casting: Carry out molten steel pouring according to the casting parameter requirements of the steel grade.

[0046] (6) Rolling: The annular heating furnace is divided into a preheating section, a heating section, and a soaking section according to the conveying direction of the continuously cast round billets. Each section is temperature-controlled. The preheating section is controlled at 920°C, the heating section at 1250°C, and the soaking section at 1240°C. The discharge temperature of the continuously cast round billets is 1120°C, and the distribution angle of the annular furnace is 1.725°.

[0047] In the piercing process, a new tapered two-roll piercing machine with a rolling angle of 15° and a feed angle of 15° was used. The temperature of the continuous casting round billet before piercing was 1055°C and the temperature after piercing was 1140°C. A rough tube was obtained after piercing.

[0048] During the rolling process of the five-stand PQF mill, the shell tube temperature before hot rolling is 1045°C, and the raw tube is obtained after rolling. The high-pressure water descaling pressure of the continuous rolling mill is guaranteed to be 4MPa.

[0049] In the micro-tension reducing process, the temperature of the rough pipe entering the micro-tension reducing process is 870℃, the reducing rate is 20%, and the high-pressure water dephosphorization pressure before tension reducing is ≥10.0MPa.

[0050] (7) Heat treatment process

[0051] (a) The continuous cast crane boom is heated at 910°C for 30 minutes using seamless steel pipes and then cooled to 100°C by water quenching. The water temperature for the water quenching is 25°C and the water spraying volume for the external shower is 1900m3. 3 / h, pressure is 0.13MPa, time is 10s; the water volume of the internal spray is 1900m 3 / h, pressure is 0.8MPa, time is 8s, high-pressure water dephosphorization pressure ≥10.0MPa.

[0052] (b) The quenched crane boom seamless steel pipe is heated to 655°C at a rate of 40°C / min and then kept at this temperature for a total of 75 min.

[0053] Example 2

[0054] This embodiment provides a seamless steel pipe for crane boom, the chemical composition and mass percentage of which are: C 0.17%, Si 0.45%, Mn 1.55%, Cr 0.32%, Mo 0.26%, Alt 0.040%, V 0.07%, W 0.22%, B 0.001%, Ni 0.01%, Cu 0.02%, CE ⅡW 0.56, the balance being Fe and inevitable trace impurity elements.

[0055] After calculation, ([Ni]+[Cr]+[Mo]+[Mn]) / [B]=2140, where [Ni], [Cr], [Mo], [Mn] and [B] are the mass percentages of the corresponding elements.

[0056] After testing, the grain size of the seamless steel pipe for crane boom is 9.5, and the volume percentage of tempered bainite in the metallographic structure is 94%.

[0057] This embodiment also provides a method for preparing the seamless steel pipe for the crane boom, comprising the following steps:

[0058] (1) Melt the raw materials and adjust the composition and content of molten steel.

[0059] (2) Pre-deoxidation and alloying

[0060] When the amount of molten steel in the electric furnace reaches 5%, 0.36 kg / t of silicon carbide is added for pre-deoxidation, and the ladle is opened to blow argon to stir the molten steel.

[0061] When the molten steel volume reaches 17%, 1.7kg / t aluminum ingots are added for precipitation deoxidation.

[0062] When the molten steel volume reaches 19%, add 4kg of ferrotungsten and 5kg / t of ferromolybdenum.

[0063] When the molten steel volume reaches 30%, 18kg / t of silicon manganese, 4kg / t of high carbon ferromanganese, 4kg / t of high carbon ferrochrome, and 1kg / t of ferrovanadium are added for alloying. The added amounts are precisely calculated to ensure that when the alloy is fine-tuned in the LF process, the total alloy addition amount is ≤1kg / t, so as to reduce the free oxygen content introduced during the LF alloying process.

[0064] When the amount of molten steel tapped reaches 35%, 6.2 kg / t of lime and 3.6 kg / t of synthetic slag are added for primary slagging; the chemical components of the synthetic slag include by weight percentages: Al2O3: 50%, CaO: 40%, SiO2: 8%, and MgO: 2%.

[0065] When the steel is tapped to 49%, 0.47kg / t of calcium carbide is added to achieve further diffusion deoxidation.

[0066] (3) Refining: Continue smelting during the refining process, adjust the composition and temperature of the molten steel, and ensure that all components except B are within the control composition requirements.

[0067] (4) Degassing: Under vacuum degree ≤ 67Pa, process for 10-15min. After the process is completed, add 0.05-0.09kg / t of ferroboron, and soft blow for 15-20min under the condition of argon flow rate of 10-15NL / min, and then hoist to the continuous casting process.

[0068] (5) Continuous steel casting: Carry out molten steel pouring according to the casting parameter requirements of the steel grade.

[0069] (6) Rolling: The annular heating furnace is divided into a preheating section, a heating section, and a soaking section according to the conveying direction of the continuously cast round billets. Each section is temperature-controlled. The preheating section is controlled at 920°C, the heating section at 1250°C, and the soaking section at 1240°C. The discharge temperature of the continuously cast round billets is 1120°C, and the distribution angle of the annular furnace is 1.725°.

[0070] In the piercing process, a new tapered two-roll piercing machine with a rolling angle of 15° and a feed angle of 15° was used. The temperature of the continuous casting round billet before piercing was 1055°C and the temperature after piercing was 1140°C. A rough tube was obtained after piercing.

[0071] During the rolling process of the five-stand PQF mill, the shell tube temperature before hot rolling is 1045°C, and the raw tube is obtained after rolling. The high-pressure water descaling pressure of the continuous rolling mill is guaranteed to be 4MPa.

[0072] In the micro-tension reducing process, the temperature of the rough pipe entering the micro-tension reducing process is 870℃, the reducing rate is 20%, and the high-pressure water dephosphorization pressure before tension reducing is ≥10.0MPa.

[0073] (7) Heat treatment process

[0074] (a) The continuous cast crane boom is heated to 920°C for 20 minutes using seamless steel pipes and then cooled to 110°C by water quenching. The water temperature for the water quenching is 28°C and the water spray volume for the external shower is 2100m3. 3 / h, pressure is 0.15MPa, time is 8s; the water volume of internal spray is 2100m 3 / h, pressure is 1.0MPa, time is 10s. High-pressure water dephosphorization pressure ≥10.0MPa.

[0075] (b) The quenched crane boom seamless steel pipe is heated to 665°C at a rate of 50°C / min and then kept at this temperature for a total of 80 min.

[0076] Example 3

[0077] This embodiment provides a seamless steel pipe for crane boom, the chemical composition and mass percentage of which are: C 0.13%, Si 0.35%, Mn 1.45%, Cr 0.4%, Mo 0.24%, Alt 0.02%, V 0.09%, W 0.20%, B 0.003%, Ni 0.1%, Cu 0.2%, CE ⅡW 0.54, the balance being Fe and inevitable trace impurity elements.

[0078] Calculation shows that ([Ni]+[Cr]+[Mo]+[Mn]) / [B]=730, where [Ni], [Cr], [Mo], [Mn], and [B] are the mass percentages of the corresponding elements.

[0079] After testing, the grain size of the seamless steel pipe for crane boom is 9.5, and the volume percentage of tempered bainite in the metallographic structure is 93%.

[0080] This embodiment also provides a method for preparing the seamless steel pipe for the crane boom, comprising the following steps:

[0081] (1) Melt the raw materials and adjust the composition and content of molten steel.

[0082] (2) Pre-deoxidation and alloying

[0083] When the amount of molten steel in the electric furnace reaches 6%, 0.34 kg / t of silicon carbide is added for pre-deoxidation, and the ladle is opened to blow argon to stir the molten steel.

[0084] When the molten steel volume reaches 18%, 1.5kg / t aluminum ingots are added for precipitation deoxidation.

[0085] When the molten steel volume reaches 20%, add 2kg of ferrotungsten and 4kg / t of ferromolybdenum.

[0086] When the molten steel volume reaches 31%, 17kg / t of silicon manganese, 3kg / t of high carbon ferromanganese, 5kg / t of high carbon ferrochrome, and 2kg / t of ferrovanadium are added for alloying. The added amounts are precisely calculated to ensure that when the alloy is fine-tuned in the LF process, the total alloy addition amount is ≤1kg / t, so as to reduce the free oxygen content introduced during the LF alloying process.

[0087] When the molten steel volume reaches 37%, 5.8 kg / t of lime and 3.4 kg / t of synthetic slag are added for primary slagging; the chemical components of the synthetic slag include by weight percentages: Al2O3: 49%, CaO: 39%, SiO2: 10%, and MgO: 2%.

[0088] When the steel is tapped to 51%, 0.45kg / t calcium carbide is added to achieve further diffusion deoxidation.

[0089] (3) Refining: Continue smelting during the refining process, adjust the composition and temperature of the molten steel, and ensure that all components except B are within the control composition requirements.

[0090] (4) Degassing: Under vacuum degree ≤ 67Pa, process for 10-15min. After the process is completed, add 0.05-0.09kg / t of ferroboron, and soft blow for 15-20min under the condition of argon flow rate of 10-15NL / min, and then hoist to the continuous casting process.

[0091] (5) Continuous steel casting: Carry out molten steel pouring according to the casting parameter requirements of the steel grade.

[0092] (6) Rolling: The annular heating furnace is divided into a preheating section, a heating section, and a soaking section according to the conveying direction of the continuously cast round billets. Each section is temperature-controlled. The preheating section is controlled at 920°C, the heating section at 1250°C, and the soaking section at 1240°C. The discharge temperature of the continuously cast round billets is 1120°C, and the distribution angle of the annular furnace is 1.725°.

[0093] In the piercing process, a new tapered two-roll piercing machine with a rolling angle of 15° and a feed angle of 15° was used. The temperature of the continuous casting round billet before piercing was 1055°C and the temperature after piercing was 1140°C. A rough tube was obtained after piercing.

[0094] During the rolling process of the five-stand PQF mill, the shell tube temperature before hot rolling is 1045°C, and the raw tube is obtained after rolling. The high-pressure water descaling pressure of the continuous rolling mill is guaranteed to be 4MPa.

[0095] In the micro-tension reducing process, the temperature of the rough pipe entering the micro-tension reducing process is 870℃, the reducing rate is 20%, and the high-pressure water dephosphorization pressure before tension reducing is ≥10.0MPa.

[0096] (7) Heat treatment process

[0097] (a) The continuous cast crane boom is heated at 900℃ for 40 minutes using seamless steel pipes and then cooled to 90℃ by water quenching. The water temperature for the water quenching is 20℃ and the water spraying volume for the external shower is 1600m3. 3 / h, pressure is 0.10MPa, time is 12s; the water volume of internal spray is 1600m 3 / h, pressure 0.5MPa, time 6s. High-pressure water dephosphorization pressure ≥10.0MPa.

[0098] (b) The quenched crane boom seamless steel pipe is heated to 645°C at a rate of 20°C / min and then kept at this temperature for a total of 70 min.

[0099] Comparative Example 1

[0100] The present comparative example provides a seamless steel pipe for crane boom, the chemical composition and mass percentage of which are: C 0.16%, Si 0.40%, Mn 1.46%, Cr 0.34%, Mo 0.25%, Alt 0.033%, V 0.078%, W 0.18%, B 0.003%, Ni 0.044%, Cu 0.034%, CE ⅡW 0.54, the balance being Fe and inevitable trace impurity elements.

[0101] Calculation shows that ([Ni]+[Cr]+[Mo]+[Mn]) / [B]=698, where [Ni], [Cr], [Mo], [Mn], and [B] are the mass percentages of the corresponding elements.

[0102] After testing, the grain size of the seamless steel pipe for crane boom is 9.0 grade, and the volume percentage of tempered bainite in the metallographic structure is 91%.

[0103] The preparation method of the seamless steel pipe for the crane boom provided in this comparative example refers to Example 1 and will not be described in detail.

[0104] Comparative Example 2

[0105] The present comparative example provides a seamless steel pipe for crane boom, the chemical composition and mass percentage of which are: C 0.17%, Si 0.45%, Mn 1.55%, Cr 0.4%, Mo 0.26%, Alt 0.04%, V 0.07%, W 0.22%, B 0.001%, Ni 0.03%, Cu 0.034%, CE ⅡW 0.56, the balance being Fe and inevitable trace impurity elements.

[0106] Calculation shows that ([Ni]+[Cr]+[Mo]+[Mn]) / [B]=2240, where [Ni], [Cr], [Mo], [Mn] and [B] are the mass percentages of the corresponding elements.

[0107] After testing, the grain size of the seamless steel pipe for crane boom is 9.0 grade, and the volume percentage of tempered bainite in the metallographic structure is 90%.

[0108] The preparation method of the seamless steel pipe for the crane boom provided in this comparative example refers to Example 1 and will not be described in detail.

[0109] Comparative Example 3

[0110] This comparative example provides a seamless steel pipe for a crane boom, the chemical composition and mass percentage of which are the same as those in Example 1 and will not be repeated here.

[0111] The preparation method of the seamless steel pipe for crane boom provided in this comparative example is similar to that in Example 1, except that, in the heat treatment process of step (7), (a) the continuous cast seamless steel pipe for crane boom is kept at 930°C for 30 minutes and then cooled to 100°C by water quenching. The water temperature of the water quenching is 25°C, and the water spraying volume of the external shower is 1900m 3 / h, pressure is 0.13MPa, time is 10s; the water volume of the internal spray is 1900m 3 / h, pressure is 0.8MPa, time is 8s, high-pressure water dephosphorization pressure ≥10.0MPa.

[0112] After testing, the grain size of the seamless steel pipe for crane boom is 8.5, and the volume percentage of tempered bainite in the metallographic structure is 85%.

[0113] Comparative Example 4

[0114] This comparative example provides a seamless steel pipe for a crane boom, the chemical composition and mass percentage of which are the same as those in Example 1 and will not be repeated here.

[0115] The preparation method of the seamless steel pipe for crane boom provided in this comparative example refers to Example 1, except that, in the heat treatment process of step (7), (b) the quenched seamless steel pipe for crane boom is heated to 630°C at a rate of 40°C / min and then kept warm, and the heating and holding time is 75 minutes in total.

[0116] After testing, the grain size of the seamless steel pipe for crane boom is 8.5, and the volume percentage of tempered bainite in the metallographic structure is 82%.

[0117] Mechanical property testing was performed on the seamless steel pipes for crane booms prepared in Examples 1-3 and Comparative Examples 1-4. The testing methods were based on the standards GB 30584-2014, "Seamless Steel Pipes for Crane Booms," and GB / T 229-2020, "Charpy Pendulum Impact Test Method for Metallic Materials." The test results are detailed in Table 1. Table 1 shows that the seamless steel pipes for crane booms provided by the present invention have improved tensile properties and impact toughness.

[0118] Table 1

[0119]

[0120] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A seamless steel pipe for crane boom, characterized in that: Its chemical composition and mass percentage are: C 0.13%~0.17%, Si 0.35%~0.45%, Mn 1.45%~1.55%, Cr 0.32%~0.40%, Mo 0.24%~0.26%, Alt 0.020%~0.040%, V 0.07%~0.09%, W 0.18%~0.22%, B 0.001%~0.003%, Ni≤0.10%, Cu≤0.20%, 0.50≤CE ⅡW ≤0.56, the balance is Fe and unavoidable trace impurity elements; 730≤([Ni]+[Cr]+[Mo]+[Mn]) / [B]≤2140; Wherein, [Ni], [Cr], [Mo], [Mn] and [B] are the mass percentages of the corresponding elements; The grain size of the seamless steel pipe for the crane boom is 9.5 to 10.0; The volume percentage of tempered bainite in the metallographic structure of the seamless steel pipe for the crane boom is 90% to 100%.

2. The method for preparing a seamless steel pipe for a crane boom according to claim 1, wherein: It includes smelting, pre-deoxidation and alloying, refining, degassing, continuous casting, rolling and heat treatment processes; The heat treatment process is to keep the rolled steel pipe at 900°C to 920°C, then perform quenching treatment, and then perform tempering treatment at 645°C to 665°C.

3. The method for preparing a seamless steel pipe for a crane boom according to claim 2, wherein: The rolled steel pipe is kept at 900℃~920℃ for 20min~40min and then quenched.

4. The method for preparing a seamless steel pipe for a crane boom according to claim 2 or 3, wherein: The quenching treatment is to cool the steel pipe to 90℃~110℃ by internal spraying and external showering; Among them, the water spray volume of the external shower is 1600m 3 / h~2100m 3 / h, pressure is 0.10MPa~0.15MPa, time is 8s~12s; The water volume of the internal spray is 1600m 3 / h~2100m 3 / h, pressure is 0.5MPa~1.0MPa, time is 6s~10s.

5. The method for preparing a seamless steel pipe for a crane boom according to claim 4, wherein: The water temperature of the quenching treatment is 20°C~28°C.

6. The method for preparing a seamless steel pipe for a crane boom according to claim 2 or 3, wherein: The heating and holding time of the tempering treatment is 70 to 80 minutes in total.

7. The method for preparing a seamless steel pipe for a crane boom according to claim 2 or 3, wherein: The heating rate of the tempering is 20°C / min to 50°C / min.

8. The method for preparing a seamless steel pipe for a crane boom according to claim 2, wherein: In the pre-deoxidation and alloying process, aluminum ingots are added for precipitation deoxidation when the steel tapping amount of the electric furnace is 17% to 18% of the total steel tapping amount, ferrotungsten is added when the steel tapping amount is 19% to 20% of the total steel tapping amount, and alloy is added for alloying when the steel tapping amount is 20% to 31% of the total steel tapping amount.

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