Hot rolling process of rare-earth-containing 890MPa-grade seamless steel tube for crane boom

Abstract

The invention discloses a hot rolling process for a rare-earth-containing 890MPa-grade seamless steel pipe for a crane boom. A natural gas annular heating furnace is adopted for heating; the furnace temperature of the first section is 800-1150 DEG C, the furnace temperature of the second section is 1000-1200 DEG C, the furnace temperature of the third section is 1000-1300 DEG C, the furnace temperature of the fourth section is 1200-1300 DEG C, the furnace temperature of the fifth section is 1240-1290 DEG C, the furnace temperature of the sixth section is 1240-1290 DEG C, the rhythm is controlled from furnace charging, the heating speed of a blank with the diameter being 270 mm is set to be 6-12 cm / min, and the furnace time of the blank is longer than or equal to 4 hours; during rolling, high-pressure water is required to remove phosphorus, and the water pressure is not lower than 10MPa. Through precise rolling parameter and temperature control, favorable conditions are created for the subsequent heat treatment process.

Description

Technical Field

[0001] The invention belongs to the technical field of seamless steel pipe production, and in particular relates to a hot rolling process for a rare earth-containing 890MPa-grade seamless steel pipe for a crane boom. Background Art

[0002] In recent years, with the continuous investment and development of national infrastructure, the demand for construction machinery and equipment has been increasing. Crawler cranes are high-tech and complex manufacturing process mechanical products for high-rise building construction. They are widely used in the construction of bridges, power generation equipment, oil refining equipment, wind turbines, offshore work platforms and other projects. The crane boom is a key component of the crawler crane. Its use conditions require that the seamless steel pipe not only has high strength and high toughness, but also has good welding performance. Summary of the invention

[0003] The purpose of the present invention is to provide a hot rolling process for a seamless steel pipe containing rare earth 890MPa for crane booms. The present invention creates favorable conditions for subsequent heat treatment processes through precise rolling parameters and temperature control. This is because a reasonable rolling process can refine the grain structure of the steel pipe and eliminate internal defects of the steel pipe, thereby improving the mechanical properties and service life of the steel pipe.

[0004] In order to achieve the above process effects, the present invention adopts the following technical solutions:

[0005] The invention discloses a hot rolling process for a seamless steel pipe containing rare earth and used for a crane boom of 890MPa grade. The rolling production process includes: tube billet sawing→heating→perforation→continuous rolling→tube stripping→diameter reduction→cooling bed→sawing→straightening. When rolling the rare earth steel, the rolling temperature must be strictly controlled, which requires controlling the heating temperature of the annular heating furnace and ensuring the furnace discharge temperature. Too high a temperature may cause the steel pipe to overheat and the crystal grains to be coarse, while too low a temperature may cause the rolling force to increase and affect the rolling rhythm. The invention is characterized in that a natural gas annular heating furnace is used for heating.

[0006] Set the heating temperature and furnace time of the annular furnace: the first stage furnace temperature is 800-1150℃, the second stage furnace temperature is 1000-1200℃, the third stage furnace temperature is 1000-1300℃, the fourth stage furnace temperature is 1200-1300℃, the fifth stage furnace temperature is 1240-1290℃, and the sixth stage furnace temperature is 1240-1290℃. The rhythm is controlled from the start of furnace loading. The heating speed of the Φ270mm billet is set to 6-12cm / min, and the billet time in the furnace is ≥4 hours.

[0007] Set the perforation speed during perforation, and ensure the stability and efficiency of the perforation process through precise control, laying a solid foundation for subsequent processing;

[0008] High-pressure water must be used to remove phosphorus during rolling, and the water pressure must be no less than 10MPa.

[0009] Furthermore, the sizing controls the straightness of the pipe end to ensure that the end of the sizing pipe cannot be bent. When rolling starts, the entrance roller table and the tension and reduction outlet speed are adjusted to be consistent with the rolling mill speed.

[0010] Furthermore, the straightening process must strictly control the straightening force to ensure the curvature of the steel pipe, and no scratches, blue lines, scars or pitting defects should be present; the inner surface should not have convexities, inward folds, internal scars or scratches.

[0011] Furthermore, in the Φ180mm unit, the temperature of the annular furnace is set as follows: the first stage furnace temperature is 800-1100℃, the second stage furnace temperature is 1100-1200℃, the third stage furnace temperature is 1200-1275℃, the fourth stage furnace temperature is 1250-1295℃, the fifth stage furnace temperature is 1250-1290℃, and the sixth stage furnace temperature is 1240-1290℃. The rhythm is controlled from the start of furnace loading. The heating speed of the Φ270mm billet is set to 8-9cm / min, and the billet is in the furnace for ≥4 hours.

[0012] Φ270mm billet is used to produce Φ180*16mm boom tube. The wall thickness S tolerance is controlled according to ±10%S, the unevenness is controlled according to the full length of the steel pipe ≤1.5mm / L, the outer diameter D is controlled according to ±1%D, the roller speed is set to 8000rpm, and the tension reduction outlet speed is set to 6500rpm.

[0013] Further, rolling is carried out in the Φ460mm unit. The temperature setting of the ring furnace is as follows: the first stage furnace temperature is 850-900℃, the second stage furnace temperature is 1020-1060℃, the third stage furnace temperature is 1060-1220℃, the fourth stage furnace temperature is 1230-1250℃, the fifth stage furnace temperature is 1250-1290℃, and the sixth stage temperature is 1250-1285℃. The rhythm is controlled from the start of furnace loading. The heating speed of the Φ350mm billet is set to 7-10cm / min, and the billet is in the furnace for ≥5 hours;

[0014] The Φ273*20mm boom tube is produced using the Φ350mm billet. The wall thickness S tolerance is controlled as ±10%S, the unevenness is controlled as ≤1.5mm / L over the entire length of the steel tube, and the outer diameter D is controlled as ±1%D.

[0015] Furthermore, the rolled microstructure is bainite+ferrite+pearlite.

[0016] Compared with the prior art, the beneficial technical effects of the present invention are:

[0017] The present invention provides a rare earth-containing 890MPa grade seamless steel pipe for crane booms with excellent material quality, superior performance and reasonable rolling production technology and process, so as to meet the demand for high-strength and high-toughness steel for booms. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described below in conjunction with the accompanying drawings.

[0019] Figure 1 This is the rolled microstructure morphology. DETAILED DESCRIPTION

[0020] Example steel production process such as technical solution design:

[0021] Embodiment 1: This embodiment provides a hot rolling preparation method for a billet of Φ270 mm. Rolling is performed in a Φ180 mm unit, and the temperature of the annular furnace is set as follows: the first stage furnace temperature is 800-1100°C, the second stage furnace temperature is 1100-1200°C, the third stage furnace temperature is 1200-1275°C, the fourth stage furnace temperature is 1250-1295°C, the fifth stage furnace temperature is 1250-1290°C, and the sixth stage furnace temperature is 1240-1290°C. The rhythm is controlled from the time of charging the furnace. The heating speed of the Φ270 mm billet is set to 8-9 cm / min, and the billet is in the furnace for ≥4 hours.

[0022] Φ270mm billet is used to produce Φ180*16mm boom tube. The wall thickness S tolerance is controlled according to ±10%S, the unevenness is controlled according to the full length of the steel pipe ≤1.5mm / L, the outer diameter D is controlled according to ±1%D, the roller speed is set to 8000rpm, and the tension reduction outlet speed is set to 6500rpm.

[0023] Embodiment 2: This embodiment provides a hot rolling preparation method for a billet of Φ350mm. Rolling is performed in a Φ460mm unit. The temperature of the annular furnace is set as follows: the first stage furnace temperature is 850-900°C, the second stage furnace temperature is 1020-1060°C, the third stage furnace temperature is 1060-1220°C, the fourth stage furnace temperature is 1230-1250°C, the fifth stage furnace temperature is 1250-1290°C, and the sixth stage temperature is 1250-1285°C. The rhythm is controlled from the time of charging the furnace. The heating speed of the Φ350mm billet is set to 7-10cm / min, and the billet is in the furnace for ≥5 hours.

[0024] The Φ273*20mm boom tube is produced using the Φ350mm billet. The wall thickness S tolerance is controlled as ±10%S, the unevenness is controlled as ≤1.5mm / L over the entire length of the steel tube, and the outer diameter D is controlled as ±1%D.

[0025] The rolled tube was tested for mechanical properties and microstructure. The mechanical properties are shown in Table 1. The microstructure is shown in Figure 1 .

[0026] Table 1 Rolling properties of BT890 seamless steel pipe

[0027]

[0028] The rolled structure of BT890 is bainite + ferrite + pearlite, the non-metallic inclusions A, B, C, and D are all less than or equal to level 0.5, and the grain size is 8.5.

[0029] During the heating process of rare earth steel in the ring furnace, the heating temperature setting needs to be carefully differentiated and adjusted for different sizes of tube billets. In particular, the heating temperature setting of large tube billets is often slightly lower than that of small tube billets. This setting strategy is mainly based on the fact that large tube billets have a smaller temperature drop during heating and subsequent processing.

[0030] ① When setting the heating temperature of the Φ350mm billet, the heating temperature should be appropriately lower than that of the Φ270mm billet. Due to its significant advantages in volume and mass, the large billet can more effectively retain heat energy and reduce heat loss during heating. In contrast, due to the relatively large surface area to volume ratio of the small billet, its surface temperature may rise rapidly under the same heating environment, but the internal temperature rises slowly, and the overall temperature is more susceptible to the influence of the external environment and has a large temperature fluctuation. In addition, during the transmission process from the furnace to the rolling, the small billet is exposed to the air for a long time, and its temperature loss will also be relatively large.

[0031] ② In order to ensure that the large tube billet can reach a uniform and stable rolling temperature before rolling, and to avoid problems such as grain coarsening and increased internal stress caused by excessive temperature, the heating temperature setting of the ring furnace will be lowered accordingly. This can not only ensure the heating efficiency of the large tube billet, but also ensure the uniformity of its internal organizational structure and the stability of its mechanical properties. At the same time, by accurately controlling the heating temperature and time, the heating process of the large tube billet can be further optimized to improve production efficiency and product quality.

[0032] ③ Because rare earth elements can affect the nucleation and growth process of austenite grains. On the one hand, rare earth elements can act as nucleation particles to promote the nucleation of austenite grains, thereby increasing the number of austenite grains. On the other hand, rare earth elements can inhibit the growth of austenite grains by reducing the driving force of grain boundary migration. It can also interact with other elements in steel to form temperature compounds or complexes, which can serve as grain boundary pinning points to further hinder the migration of grain boundaries, thereby further slowing down the grain growth rate. Therefore, when rolling rare earth-containing boom tubes, compared with general carbon-manganese steel, when setting the heating temperature, the heating temperature should be appropriately increased to ensure the homogenization of austenite grains.

[0033] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A hot rolling process for a rare earth-containing 890MPa grade seamless steel pipe for crane boom, the rolling production process flow: tube billet sawing → heating → perforation → continuous rolling → tube removal → stretching and reducing → cooling bed → sawing → straightening; characterized in that, When rolling the rare earth steel, the rolling temperature must be strictly controlled. The heating temperature of the annular heating furnace must be controlled and the furnace exit temperature must be guaranteed. Too high a temperature may cause the steel pipe to overheat and the grains to be coarse, while too low a temperature may increase the rolling force and affect the rolling rhythm. A natural gas annular heating furnace is used for heating. Set the heating temperature and furnace time of the annular furnace: the first stage furnace temperature is 800-1150℃, the second stage furnace temperature is 1000-1200℃, the third stage furnace temperature is 1000-1300℃, the fourth stage furnace temperature is 1200-1300℃, the fifth stage furnace temperature is 1240-1290℃, and the sixth stage furnace temperature is 1240-1290℃. The rhythm is controlled from the start of furnace loading. The heating speed of the Φ270mm billet is set to 6-12cm / min, and the billet time in the furnace is ≥4 hours. Set the perforation speed during perforation, and ensure the stability and efficiency of the perforation process through precise control, laying a solid foundation for subsequent processing; High-pressure water must be used to remove phosphorus during rolling, and the water pressure must be no less than 10MPa.

2. The hot rolling process of the rare earth-containing 890MPa grade seamless steel pipe for crane boom according to claim 1, characterized in that: Sizing controls the straightness of the pipe end to ensure that there is no bending at the end of the sizing pipe. When rolling starts, the entrance roller table and the tension and reduction outlet speed are adjusted to be consistent with the rolling mill speed.

3. The hot rolling process of the rare earth-containing 890MPa grade seamless steel pipe for crane boom according to claim 1, characterized in that: The straightening process must strictly control the straightening force to ensure the curvature of the steel pipe, and no abrasions, blue lines, scars or pitting defects should be present; the inner surface must not have convexities, inward folds, internal scars or scratches.

4. The hot rolling process of the rare earth-containing 890MPa grade seamless steel pipe for crane boom according to claim 1, characterized in that: Rolling is carried out in the Φ180mm unit, and the temperature of the annular furnace is set as follows: the first stage furnace temperature is 800-1100℃, the second stage furnace temperature is 1100-1200℃, the third stage furnace temperature is 1200-1275℃, the fourth stage furnace temperature is 1250-1295℃, the fifth stage furnace temperature is 1250-1290℃, and the sixth stage furnace temperature is 1240-1290℃. The rhythm is controlled from the start of furnace loading. The heating speed of the Φ270mm billet is set to 8-9cm / min, and the billet is in the furnace for ≥4 hours; Φ270mm billet is used to produce Φ180*16mm boom tube. The wall thickness S tolerance is controlled according to ±10%S, the unevenness is controlled according to the full length of the steel pipe ≤1.5mm / L, the outer diameter D is controlled according to ±1%D, the roller speed is set to 8000rpm, and the tension reduction outlet speed is set to 6500rpm.

5. The hot rolling process of the rare earth-containing 890MPa grade seamless steel pipe for crane boom according to claim 1, characterized in that: Rolling is carried out in the Φ460mm unit. The temperature setting of the ring furnace is as follows: the first stage furnace temperature is 850-900℃, the second stage furnace temperature is 1020-1060℃, the third stage furnace temperature is 1060-1220℃, the fourth stage furnace temperature is 1230-1250℃, the fifth stage furnace temperature is 1250-1290℃, and the sixth stage temperature is 1250-1285℃. The rhythm is controlled from the start of furnace loading. The heating speed of the Φ350mm billet is set to 7-10cm / min, and the billet is in the furnace for ≥5 hours. The Φ273*20mm boom tube is produced using the Φ350mm billet. The wall thickness S tolerance is controlled as ±10%S, the unevenness is controlled as ≤1.5mm / L over the entire length of the steel tube, and the outer diameter D is controlled as ±1%D.

6. The hot rolling process of the rare earth-containing 890MPa grade seamless steel pipe for crane boom according to claim 1, 4 or 5, characterized in that: The rolled structure is bainite + ferrite + pearlite.

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