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

Abstract

This invention discloses a hot rolling process for seamless steel pipes containing rare earth elements and rated for 890MPa for crane booms. The process utilizes a natural gas-fired annular furnace for heating. The furnace heating temperatures and furnace dwell times are set as follows: first stage furnace temperature 800-1150℃, second stage 1000-1200℃, third stage 1000-1300℃, fourth stage 1200-1300℃, fifth stage 1240-1290℃, and sixth stage 1240-1290℃. The heating rate is controlled from the start of furnace loading, with a heating speed of 6-12 cm / min for Φ270mm billets. The billet dwell time in the furnace is ≥4 hours. High-pressure water descaling is mandatory during rolling, with a water pressure not lower than 10MPa. This invention, through precise rolling parameters and temperature control, creates favorable conditions for subsequent heat treatment processes.

Description

Technical Field

[0001] This invention belongs to the field of seamless steel pipe production technology, and in particular relates to a hot rolling process for seamless steel pipes containing rare earth elements and rated at 890MPa for crane booms. Background Technology

[0002] In recent years, with the continuous investment and development of national infrastructure construction, the demand for engineering machinery and equipment has been increasing. Tracked cranes are high-tech, complex-manufacturing construction machinery used in high-rise building construction, and are widely used in the construction of bridges, power generation equipment, oil refining equipment, wind turbine generators, and offshore work platforms. The crane boom is a key component of tracked cranes, and its operation requires seamless steel pipes to possess not only high strength and toughness but also good weldability. Summary of the Invention

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

[0004] To achieve the above-mentioned process effects, the present invention adopts the following technical solution:

[0005] This invention discloses a hot rolling process for seamless steel pipes containing rare earth elements and rated for 890MPa for crane booms. The rolling production process is as follows: billet sawing → heating → piercing → continuous rolling → pipe removal → tension reduction → cooling bed → sawing → straightening. When rolling this rare earth steel, the rolling temperature must be strictly controlled. This requires controlling the heating temperature of the annular heating furnace and ensuring the furnace exit temperature. Excessive temperature may lead to overheating of the steel pipe and coarse grains, while excessively low temperature may increase rolling force and affect the rolling rhythm. The invention is characterized by using a natural gas annular heating furnace for heating.

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

[0007] Setting the piercing speed during piercing and precisely controlling it ensures the stability and efficiency of the piercing process, laying a solid foundation for subsequent processing;

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

[0009] Furthermore, the straightness of the tube ends is controlled during sizing to ensure that the ends of the tubes exiting the sizing process are not bent. During the rolling process, the speed of the inlet roller table and the speed of the tension reduction exit are adjusted to match the speed of the rolling mill.

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

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

[0012] The Φ180*16mm boom tube is produced using a Φ270mm blank. The wall thickness S tolerance is controlled at ±10%S, the unevenness is controlled at ≤1.5mm / L for the entire length of the steel pipe, the outer diameter D is controlled at ±1%D, the roller speed is set to 8000rpm, and the tension reduction exit speed is set to 6500rpm.

[0013] Further rolling is carried out on the Φ460mm unit. The ring furnace temperatures are set as follows: Section 1: 850-900℃; Section 2: 1020-1060℃; Section 3: 1060-1220℃; Section 4: 1230-1250℃; Section 5: 1250-1290℃; Section 6: 1250-1285℃, with the heating rate controlled from the start of furnace loading. The heating rate for Φ350mm billets is set to 7-10cm / min, and the billet time in the furnace is ≥5 hours.

[0014] The Φ273*20mm boom tube is produced using a Φ350mm blank. The wall thickness S tolerance is controlled at ±10%S, the non-uniformity is controlled at ≤1.5mm / L for the entire length of the steel pipe, and the outer diameter D is controlled at ±1%D.

[0015] Furthermore, the rolled microstructure consists of bainite, ferrite, and pearlite.

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

[0017] This invention provides a seamless steel pipe for crane booms containing rare earth elements with excellent material properties, superior performance, and reasonable rolling production technology, in order to meet the demand for high-strength and high-toughness boom steel. Attached Figure Description

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

[0019] Figure 1 The morphology is that of a rolled microstructure. Detailed Implementation

[0020] Example: Steel production process and technical solution design:

[0021] Example 1: This example provides a hot-rolling preparation method for a Φ270mm billet. Rolling is performed on a Φ180mm mill. The ring furnace temperatures are set as follows: Section 1: 800-1100℃; Section 2: 1100-1200℃; Section 3: 1200-1275℃; Section 4: 1250-1295℃; Section 5: 1250-1290℃; Section 6: 1240-1290℃. The heating rate is controlled from the start of furnace loading. The heating rate for the Φ270mm billet is set to 8-9 cm / min, and the billet time in the furnace is ≥4 hours.

[0022] The Φ180*16mm boom tube is produced using a Φ270mm blank. The wall thickness S tolerance is controlled at ±10%S, the unevenness is controlled at ≤1.5mm / L for the entire length of the steel pipe, the outer diameter D is controlled at ±1%D, the roller speed is set to 8000rpm, and the tension reduction exit speed is set to 6500rpm.

[0023] Example 2: This example provides a hot-rolling preparation method for a Φ350mm billet. Rolling is performed on a Φ460mm mill. The ring furnace temperatures are set as follows: Section 1: 850-900℃; Section 2: 1020-1060℃; Section 3: 1060-1220℃; Section 4: 1230-1250℃; Section 5: 1250-1290℃; Section 6: 1250-1285℃. The heating rate is controlled from the start of furnace loading. The heating rate for the Φ350mm billet is set to 7-10 cm / min, and the billet time in the furnace is ≥5 hours.

[0024] The Φ273*20mm boom tube is produced using a Φ350mm blank. The wall thickness S tolerance is controlled at ±10%S, the non-uniformity is controlled at ≤1.5mm / L for the entire length of the steel pipe, and the outer diameter D is controlled at ±1%D.

[0025] The rolled tubes were subjected to mechanical property and microstructure testing. The mechanical properties are shown in Table 1. The microstructure is shown in... Figure 1 .

[0026] Table 1 Rolled Properties of BT890 Seamless Steel Pipes

[0027]

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

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

[0030] ① When setting the heating temperature for Φ350mm billets compared to Φ270mm billets, the heating temperature should be appropriately reduced. Larger billets, due to their significant advantages in volume and mass, can retain heat energy more effectively during heating, reducing heat loss. In contrast, smaller billets, with their relatively larger surface area to volume ratio, may experience a rapid increase in surface temperature under the same heating conditions, but a slower increase in internal temperature, and are more susceptible to greater temperature fluctuations due to external environmental influences. Furthermore, smaller billets experience greater temperature loss during the longer period of exposure to air after exiting the furnace and before rolling.

[0031] ② To ensure that the large tube billet reaches a uniform and stable rolling temperature before rolling, and to avoid problems such as grain coarsening and increased internal stress caused by excessively high temperatures, the heating temperature setting of the annular furnace is correspondingly lowered. This ensures both the heating efficiency of the large tube billet and the uniformity of its internal microstructure and the stability of its mechanical properties. Furthermore, by precisely controlling the heating temperature and time, the heating process of the large tube billet can be further optimized, improving production efficiency and product quality.

[0032] ③ Rare earth elements can influence the nucleation and growth process of austenite grains. On the one hand, rare earth elements can act as nucleation sites, promoting the nucleation of austenite grains and thus 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 for grain boundary migration. They can also interact with other elements in steel to form temperature-sensitive compounds or complexes, which can act as grain boundary pinning points, further hindering grain boundary migration and thus further slowing down the grain growth rate. Therefore, when rolling rare earth-containing boom tubes, the heating temperature should be appropriately increased compared to ordinary carbon-manganese steel to ensure the homogenization of austenite grains.

[0033] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A hot rolling process for seamless steel pipes containing rare earth elements and rated for 890MPa grade for crane booms, comprising the following rolling production process: billet sawing → heating → piercing → continuous rolling → pipe removal → tension reduction → cooling bed → sawing → straightening; characterized in that... When rolling this rare earth steel, the rolling temperature must be strictly controlled. The heating temperature of the annular heating furnace and the exit temperature must be controlled. If the temperature is too high, the steel pipe may overheat and the grains may become coarse, while if the temperature is too low, the rolling force may increase and affect the rolling rhythm. A natural gas annular heating furnace is used for heating. Rolling is performed on a Φ460mm unit; the ring furnace is set with the following temperatures: Section 1: 850-900℃, Section 2: 1020-1060℃, Section 3: 1060-1220℃, Section 4: 1230-1250℃, Section 5: 1250-1290℃, and Section 6: 1250-1285℃. The heating rate is controlled from the start of loading into the furnace. The heating rate for Φ350mm billets is set to 7-10cm / min, and the billet time in the furnace is ≥5 hours. The Φ273*20mm boom tube is produced using a Φ350mm blank. The wall thickness S tolerance is controlled at ±10%S, the non-uniformity is controlled at ≤1.5mm / L for the entire length of the steel pipe, and the outer diameter D is controlled at ±1%D. Setting the piercing speed during piercing and precisely controlling it ensures the stability and efficiency of the piercing process, laying a solid foundation for subsequent processing; High-pressure water descaling must be used during rolling, with a water pressure of not less than 10 MPa. The rolled microstructure consists of bainite, ferrite, and pearlite.

2. The hot rolling process for seamless steel pipes containing rare earth elements and rated for 890MPa grade for crane booms according to claim 1, characterized in that, The sizing control ensures the straightness of the tube ends, guaranteeing that the tube ends exiting the sizing control are not bent. During the rolling mill operation, the speed of the inlet roller table and the speed of the tension reduction exit are adjusted to match the mill speed.

3. The hot rolling process for seamless steel pipes containing rare earth elements and rated for 890MPa grade for crane booms 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 there must be no scratches, blue lines, scars and pitting defects; the inner surface must not have ridges, inward folds, internal scars and scratches.

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