CN114086056A

CN114086056A - Rare earth-containing seamless steel tube special for bearing axle under low-temperature working condition and manufacturing method thereof

Info

Publication number: CN114086056A
Application number: CN202111228345.9A
Authority: CN
Inventors: 姚晓乐; 孙文秀; 董珍; 姜海龙; 米永峰; 郭志文; 刘玉荣; 张文亮
Original assignee: Baotou Iron and Steel Group Co Ltd
Current assignee: Baotou Iron and Steel Group Co Ltd
Priority date: 2021-10-21
Filing date: 2021-10-21
Publication date: 2022-02-25

Abstract

The invention discloses a seamless steel tube special for a bearing axle under rare earth-containing low-temperature working conditions, which is characterized in that: the chemical elements and the mass percentage content are as follows: c: 0.23-0.28%; si: 0.15-0.30%; mn: 1.30-1.45%; p is less than or equal to 0.018 percent; s is less than or equal to 0.008 percent; cr: less than or equal to 0.30 percent; ti: less than or equal to 0.04 percent; cu: less than or equal to 0.2 percent; ni: less than or equal to 0.2 percent; mo is less than or equal to 0.1 percent; al: less than or equal to 0.06 percent; RE is more than or equal to 0.001 percent; the balance of Fe and inevitable impurities, and the mass fraction is 100 percent. Its preparing process is also disclosed. The invention takes the medium C and Mn as the basis, adds a proper amount of rare earth elements, and produces the axle tube with high strength, good low-temperature toughness and high dimensional precision by the processes of steel making, tube rolling, finishing and the like, thereby meeting the production requirements of northern axle manufacturing enterprises in winter.

Description

Rare earth-containing seamless steel tube special for bearing axle under low-temperature working condition and manufacturing method thereof

Technical Field

The invention relates to the technical field of hot-rolled seamless steel pipe production, in particular to a rare earth-containing seamless steel pipe special for a bearing axle under a low-temperature working condition and a manufacturing method thereof.

Background

With the continuous improvement of road traffic conditions in China and the rapid development of the international and domestic logistics industries and other transportation industries, the demands of vehicles such as trucks, freight vehicles, passenger cars and the like are increasing. In recent years, the market of commercial vehicles is continuously warmed up and kept rising under the promotion of favorable factors such as capital investment rising, national III vehicle elimination, rapid development of new energy logistics vehicles, super-tightening treatment and the like. Therefore, the automobile axle industry in China is rapidly developed, and a certain market scale is formed after decades of years. The axle is an important component of the chassis running system of the automobile, is connected with a frame (or a bearing type automobile body) through a suspension, and is provided with a bridge structure of automobile wheels at two ends. In terms of importance and price, an axle is one of the three core assemblies of a commercial vehicle, which is second only to the engine and the vehicle body (cab).

The traditional axle is formed by welding steel plates after the processes of shearing, stamping, bending and the like, the process is complex, the environmental pollution is large, and the quality of a welding seam is difficult to guarantee. Through process improvement, the process for producing the integral axle by using the seamless steel tube is developed, the product has the advantages of excellent fatigue resistance, low self weight, low production cost and the like, accords with the development trend of energy conservation and light weight of vehicles, and has great market potential. The process for producing the integral axle by using the seamless steel tube is approved by various large vehicle manufacturing enterprises, and the process gradually replaces the traditional process to become the mainstream, and mainly comprises two main types of a bearing axle and a driving axle.

Axle manufacturing enterprises have different requirements on the performance of seamless steel tubes for axles due to different production processes and working conditions. When bearing axles are produced in winter by northern axle manufacturing enterprises, the plasticity of axle tubes is reduced due to low plant temperature, and cracks are generated in the square pushing process, so that the development of the special seamless steel tube for the bearing axles suitable for northern low-temperature working conditions is urgent and necessary.

The seamless steel tube special for the bearing axle under the rare earth-containing low-temperature working condition has the characteristics of high strength and good low-temperature toughness, meets the production requirements of axle manufacturing enterprises in the north in winter, and solves the industrial pain of the axle manufacturing industry. The invention enlarges the influence of the steel-clad rare earth axle tube in the industry, improves the product grade, forms the brand effect and creates huge social and economic benefits for steel cladding.

Disclosure of Invention

The invention aims to provide a rare earth-containing seamless steel tube special for a bearing axle under a low-temperature working condition and a manufacturing method thereof.

In order to solve the technical problems, the invention adopts the following technical scheme:

a rare earth-containing seamless steel tube special for a bearing axle under low-temperature working conditions comprises the following chemical elements in percentage by mass: c: 0.23-0.28%; si: 0.15-0.30%; mn: 1.30-1.45%; p is less than or equal to 0.018; s is less than or equal to 0.008; cr: less than or equal to 0.30 percent; ti: less than or equal to 0.04 percent; cu: less than or equal to 0.2 percent; ni: less than or equal to 0.2 percent; mo is less than or equal to 0.1 percent; al: less than or equal to 0.06 percent; RE is more than or equal to 0.001 percent; the balance of Fe and inevitable impurities, and the mass fraction is 100 percent.

The chemical elements and the mass percentage content are as follows: c: 0.25 percent; si: 0.24 percent; mn: 1.40 percent; 0.013 percent of P; s: 0.004%; cr: 0.22 percent; ti: 0.014%; mo: 0.009%; ni: 0.006%; 0.012 percent of Cu; al: 0.018%; 0.001 percent of RE; the balance of Fe and inevitable impurities, and the mass fraction is 100 percent.

Further, the chemical elements and the mass percentage content thereof are as follows: c: 0.24 percent; si: 0.26 percent; mn: 1.39 percent; 0.010 percent of P; s: 0.006%; cr: 0.25 percent; ti: 0.013%; mo: 0.007%; ni: 0.008 percent; 0.011 percent of Cu; al: 0.024%; 0.002% of RE; the balance of Fe and inevitable impurities, and the mass fraction is 100 percent.

Further, the chemical elements and the mass percentage content thereof are as follows: c: 0.26 percent; si: 0.25 percent; mn: 1.41 percent; 0.011 percent of P; s: 0.003%; cr: 0.24 percent; ti: 0.014%; mo: 0.008 percent; ni: 0.009%; 0.010 percent of Cu; al: 0.023%; 0.002% of RE; the balance of Fe and inevitable impurities, and the mass fraction is 100 percent.

Further, the chemical elements and the mass percentage content thereof are as follows: c: 0.25 percent; si: 0.26 percent; mn: 1.41 percent; 0.013 percent of P; s: 0.004%; cr: 0.25 percent; ti: 0.015 percent; mo: 0.011 percent; ni: 0.005 percent; 0.013 percent of Cu; al: 0.022%; RE is 0.003 percent; the balance of Fe and inevitable impurities, and the mass fraction is 100 percent

A manufacturing method of a seamless steel tube special for a bearing axle under a rare earth-containing low-temperature working condition comprises the following steps:

1. the steel-making production process comprises the following steps: molten iron pretreatment → converter smelting → LF refining → VD vacuum treatment → round billet continuous casting. The method can obtain high-quality round billets with low P, low S, uniform components and pure steel quality.

(1) Pretreatment of molten iron

Incoming molten iron must be pretreated with molten iron, thereby ensuring the quality of molten iron supplied to a converter, and the goal of pretreatment of molten iron is as follows: [ S ] the end point is less than or equal to 0.010%.

(2) Smelting in a converter

The alkalinity of final slag smelted by the converter is more than or equal to 3.0; end point control target: c is more than or equal to 0.06%, P is less than or equal to 0.013%, and the tapping temperature is 1610-1630 ℃; ferrosilicon and ferromanganese are adopted for deoxidation alloying, and an aluminum deoxidation process is adopted for final deoxidation; the lower slag amount in the tapping process is strictly controlled, slag must be blocked in the tapping process, and slag must be removed when the slag is blocked; proper amount of lime is added in the tapping process.

(3) LF external refining

Carrying out slagging desulfurization, component adjustment and heating operation according to the components and the temperature of the molten steel of the converter; normally blowing argon according to LF refining requirements in the whole process, controlling the argon blowing strength, keeping molten steel wriggling and not exposing the molten steel; raising the temperature by gradually increasing the temperature raising speed from a low level to a high level; white slag is manufactured during refining, the white slag holding time is more than or equal to 20min, and the slag condition is adjusted according to the condition to ensure the white slag to be tapped; adding ferrochrome at the later stage of refining; and feeding a proper amount of high-calcium wires before the refining is finished.

(4) VD vacuum treatment

After VD is in place, adding a proper amount of cerium-iron alloy; the vacuum degree is less than or equal to 0.10KPa, the target value is less than or equal to 0.06KPa, the deep vacuum time is more than or equal to 15 minutes, the boiling condition of the molten steel should be noticed at any time in the vacuum pumping process, and the Ar gas pressure is adjusted in time; the soft blowing time after the vacuum treatment is more than or equal to 13 minutes, and meanwhile, the weak stirring effect is required, so that the molten steel cannot be exposed, and the removal of non-metallic inclusions in the molten steel is ensured.

(5) Continuous casting of round billets

The baking of the large ladle and the tundish is enhanced, a pouring system must be ensured to be clean and dry, and a tundish covering agent and crystallizer covering slag must be kept dry; in the continuous casting process, the whole-process protective casting and the drawing speed are strictly controlled, so that the constant drawing speed casting is ensured; the covering conditions of the liquid levels of the tundish and the crystallizer are observed at any time in the continuous casting process, so that the phenomena of poor covering of the liquid levels of the tundish and the crystallizer or exposure of the liquid steel are prevented; the height of the liquid level of the tundish is noticed at any moment in the continuous casting process, the casting liquid level is not less than 500mm, and full ladle casting is adopted in the process of casting; controlling the superheat degree of the continuous casting molten steel within the range of 15-35 ℃; adopting crystallizer electromagnetic stirring and tail end electromagnetic stirring processes; the nozzles of the second cold water ensure even spraying, and no cutoff and water column spraying are allowed; and stacking the round billets for slow cooling, and avoiding the air ports.

2. The tube rolling process comprises the following steps: round billet → saw cutting → heating in circular furnace → perforation → MPM continuous rolling → sizing (stretching) diameter → cooling. The high-quality pipe body with high dimensional accuracy and good inner and outer surface quality is obtained by the process.

(1) Tube blank preparation and heating

Before circular tube blank sawing, the central line of a clamping blank and the fixed rigidity of a circular saw are confirmed, and the cutting inclination of the steel blank is ensured to be within 5 mm; before the tube blank is loaded into a furnace, the tube blank is checked, and severe slag pits and scabs are polished; inspecting the quality of the sawed end face, and timely removing tube blanks with defects exceeding standards, such as central cracks, central shrinkage cavities and the like; heating is carried out according to a specified heating system strictly, the temperature and time of each section of the heating furnace are monitored in the heating process, the extension of the thermal stress to the defect of the center or the outer surface of the billet is reduced, the billet is uniformly heated in the heating furnace, and the phenomena of shadow surface, heat impermeability, overheating or overburning are avoided; strictly cooling to the rolling degree so as to ensure the heating quality of the tube blank. The temperature of the heat preservation section of the annular furnace is controlled to be about 1280 ℃.

(2) Perforation

Monitoring the shaking condition of the head end of the hollow billet in front of a holding roller and the shaking condition of an ejector rod, and judging whether the consistency of rolling central lines of the puncher body and the front and rear platforms is in a good stable state; the front extension of the ejector pin is strictly controlled according to the requirements of a rolling table, the state of the roller holding of the ejector pin is good, and the ejector pin does not shake in the punching process; strictly adjusting and monitoring cooling water, and preventing cooling water of a roller, a roller way, a holding roller and a mandril top from entering a capillary as much as possible, so as to prevent an inner hole from having macroscopic water drops when the capillary enters a nitrogen-blowing borax-spraying station; at a nitrogen-blowing borax-spraying station, nozzles are strictly aligned and are consistent with the central line of the capillary, borax is dry and has no caking phenomenon, and proper borax spraying amount and spraying pressure are selected to ensure that borax is uniformly adhered to the inner surface of the capillary and no more residual caking is generated; the temperature of the capillary tube after perforation is about 1220 ℃.

(3) MPM continuous rolling

Confirming the on-line frame, and assembling the frame strictly according to the rolling table and pass design requirements; checking each frame of continuous rolling rolls and the rolls for the pipe removing machine, wherein the surfaces of the rolls are smooth and clean without aging; preparing a new core rod or a non-damaged core rod which is checked and confirmed, wherein the diameter tolerance of the core rod reaches-0.30 mm-0 required by the specification; opening the high-pressure water for descaling, controlling the water pressure and opening time of the high-pressure water for descaling, and avoiding the head end of the capillary for about 200mm to prevent the capillary from entering water; and strictly controlling cooling water of a background roller way of the rolling mill, and strictly forbidding pouring of the black pipe body.

(4) Constant (decreasing) diameter

When the machine frame is on line, the roller surface of the machine frame is checked, whether a roller gap is staggered is touched by hands, a water nozzle, an up-down sliding plate and the like are checked, and the quality of the machine frame is ensured to meet the requirement; checking each roller way before and after the detection to ensure that the roller ways run normally, checking and adjusting the spraying direction of the roller way cooling water to ensure that the cooling water is not sprayed to the inner surface of the pipe body; the temperature of the tube body after diameter setting (expansion) is about 900 ℃.

(5) Cooling down

The rolling rhythm is well controlled, continuous stepping and rotation can be ensured after the light pipe is arranged on a cooling bed, and the bending caused by waiting is avoided; the quality of the pipe body is checked strictly according to a cold bed quality checking system.

Compared with the prior art, the invention has the beneficial technical effects that:

according to the invention, based on medium C and Mn, a proper amount of rare earth elements are added, and through a reasonable smelting continuous casting process and a reasonable rolling process, the steel pipe has higher strength, excellent low-temperature impact toughness and high dimensional precision, and the production requirements of northern axle manufacturing enterprises in winter are met. The invention enlarges the influence of the steel-clad rare earth axle tube in the industry, improves the product grade, forms the brand effect and creates huge social and economic benefits for steel cladding.

Detailed Description

The steel pipe obtained according to the invention takes the production specification phi 178X 9mm as an example:

the steel-making process comprises the following steps: the high-quality round billet with low P, low S, uniform components and pure steel quality is obtained by the production process of molten iron pretreatment → converter smelting → LF refining → VD vacuum treatment → round billet continuous casting. The chemical components of the steel tube are shown in table 1, the steel tube completely meets the requirements of the steel tube on steel grades, the contents of P and S are low, the component design requirements are met, and the table 1 shows that the furnace has small component content deviation and uniform and stable components, and preconditions are provided for the good structure and performance of the tube.

TABLE 1 statistical results wt% of the chemical composition of the inventive steel pipes

The tube rolling process comprises the following steps: round billet → saw cutting → heating in circular furnace → perforation → MPM continuous rolling → sizing (stretching) diameter → cooling. Heating the round billet in an annular furnace at 1280 ℃, wherein the heating temperature deviation of the round billet is +/-10 ℃, the furnace time is not longer, the piercing adopts the process of low-speed biting and high-speed rolling, the temperature after piercing is 1220 ℃, the temperature after entering a continuous rolling mill is 1100 ℃, the temperature after sizing is 920 ℃, cooling and sawing.

The axle tube geometry of the invention is:

outer diameter range: 177.13-178.86 mm

Wall thickness range: 8.31-9.69 mm

Out-of-roundness: OD less than or equal to 1% as a whole

Straightness accuracy: the integral is less than or equal to 0.10 percent, the distance from the end of the pipe is within 1000mm, and the bending of the end is less than or equal to 2.0 mm.

The axle tube has high dimensional precision, the outer diameter is controlled within the range of-0.5% D to + 0.5% D, namely 177.11 to 178.89mm, the wall thickness is controlled within the range of-8% t to + 8% t, namely 8.28 to 9.72mm, the axle tube is beneficial to the production of axle manufacturing enterprises, and the material utilization rate is improved.

The non-metallic inclusions and the structure grain size of the axle tube of the present invention are shown in table 3. It can be seen that the non-metallic inclusion is in a lower level, the structure is uniform, the crystal grains are fine, and the grain size is above grade 7. The steel pipe has the characteristics of high strength and good low-temperature toughness due to high purity and good structure, and is suitable for being produced in winter by northern axle manufacturing enterprises.

TABLE 3 non-metallic impurities and texture grain size of axle tube according to the present invention

The axle tube with the specification of 178 multiplied by 9mm produced by the invention has the characteristics of high steel purity, high dimensional precision, uniform structure, fine crystal grains and the like, and is suitable for being produced in winter by axle manufacturing enterprises in the north.

The steel tube has no cracks in the production process, and the axle manufactured by the axle tube has excellent fatigue resistance, and has no cracks after 160 ten thousand axle body fatigue tests, which are far higher than 80 ten thousand times of standard requirements.

The rare earth-containing seamless steel tube special for the bearing axle under the low-temperature working condition is accepted by the market with excellent quality, meets the production requirements of axle manufacturing enterprises in the north in winter, solves the industrial pain point of the axle manufacturing industry, and is applied in batch at present. The invention enlarges the influence of the steel-clad rare earth axle tube in the industry, improves the product grade, forms the brand effect and creates huge social and economic benefits for steel cladding.

The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.

Claims

1. The utility model provides a contain special seamless steel pipe of rare earth for low temperature operating mode bearing axle which characterized in that: c: 0.23-0.28%; si: 0.15-0.30%; mn: 1.30-1.45%; p is less than or equal to 0.018; s is less than or equal to 0.008; cr: less than or equal to 0.30 percent; ti: less than or equal to 0.04 percent; cu: less than or equal to 0.2 percent; ni: less than or equal to 0.2 percent; mo is less than or equal to 0.1 percent; al: less than or equal to 0.06 percent; RE is more than or equal to 0.001 percent; the balance of Fe and inevitable impurities, and the mass fraction is 100 percent.

2. The rare earth-containing low-temperature working condition seamless steel tube special for the bearing axle according to claim 1, characterized in that: the chemical elements and the mass percentage content are as follows: c: 0.25 percent; si: 0.24 percent; mn: 1.40 percent; 0.013 percent of P; s: 0.004%; cr: 0.22 percent; ti: 0.014%; mo: 0.009%; ni: 0.006%; 0.012 percent of Cu; al: 0.018%; 0.001 percent of RE; the balance of Fe and inevitable impurities, and the mass fraction is 100 percent.

3. The rare earth-containing low-temperature working condition seamless steel tube special for the bearing axle according to claim 1, characterized in that: the chemical elements and the mass percentage content are as follows: c: 0.24 percent; si: 0.26 percent; mn: 1.39 percent; 0.010 percent of P; s: 0.006%; cr: 0.25 percent; ti: 0.013%; mo: 0.007%; ni: 0.008 percent; 0.011 percent of Cu; al: 0.024%; 0.002% of RE; the balance of Fe and inevitable impurities, and the mass fraction is 100 percent.

4. The rare earth-containing low-temperature working condition seamless steel tube special for the bearing axle according to claim 1, characterized in that: the chemical elements and the mass percentage content are as follows: c: 0.26 percent; si: 0.25 percent; mn: 1.41 percent; 0.011 percent of P; s: 0.003%; cr: 0.24 percent; ti: 0.014%; mo: 0.008 percent; ni: 0.009%; 0.010 percent of Cu; al: 0.023%; 0.002% of RE; the balance of Fe and inevitable impurities, and the mass fraction is 100 percent.

5. The rare earth-containing low-temperature working condition seamless steel tube special for the bearing axle according to claim 1, characterized in that: the chemical elements and the mass percentage content are as follows: c: 0.25 percent; si: 0.26 percent; mn: 1.41 percent; 0.013 percent of P; s: 0.004%; cr: 0.25 percent; ti: 0.015 percent; mo: 0.011 percent; ni: 0.005 percent; 0.013 percent of Cu; al: 0.022%; RE is 0.003 percent; the balance of Fe and inevitable impurities, and the mass fraction is 100 percent.

6. The method for manufacturing the seamless steel tube special for the bearing axle under the rare-earth-containing low-temperature working condition according to claim 1, wherein the method comprises the following steps: the method comprises the following steps:

s1, a steel-making production process comprises the following steps: molten iron pretreatment → converter smelting → LF refining → VD vacuum treatment → round billet continuous casting; the method can obtain high-quality round billets with low P, low S, uniform components and pure steel quality;

s1.1 pretreatment of molten iron

Incoming molten iron must be pretreated with molten iron, thereby ensuring the quality of molten iron supplied to a converter, and the goal of pretreatment of molten iron is as follows: [ S ] the end point is less than or equal to 0.010%;

s1.2 converter smelting

The alkalinity of final slag smelted by the converter is more than or equal to 3.0; end point control target: c is more than or equal to 0.06%, P is less than or equal to 0.013%, and the tapping temperature is 1610-1630 ℃; ferrosilicon and ferromanganese are adopted for deoxidation alloying, and an aluminum deoxidation process is adopted for final deoxidation; the lower slag amount in the tapping process is strictly controlled, slag must be blocked in the tapping process, and slag must be removed when the slag is blocked; adding a proper amount of lime in the tapping process;

S1.3LF refining outside furnace

Carrying out slagging desulfurization, component adjustment and heating operation according to the components and the temperature of the molten steel of the converter; normally blowing argon according to LF refining requirements in the whole process, controlling the argon blowing strength, keeping molten steel wriggling and not exposing the molten steel; raising the temperature by gradually increasing the temperature raising speed from a low level to a high level; white slag is manufactured during refining, the white slag holding time is more than or equal to 20min, and the slag condition is adjusted according to the condition to ensure the white slag to be tapped; adding ferrochrome at the later stage of refining; feeding a proper amount of high-calcium wires before refining;

S1.4VD vacuum processing

After VD is in place, adding a proper amount of cerium-iron alloy; the vacuum degree is less than or equal to 0.10KPa, the target value is less than or equal to 0.06KPa, the deep vacuum time is more than or equal to 15 minutes, the boiling condition of the molten steel should be noticed at any time in the vacuum pumping process, and the Ar gas pressure is adjusted in time; the soft blowing time after the vacuum treatment is more than or equal to 13 minutes, and meanwhile, the weak stirring effect is required to be noticed, so that the molten steel cannot be exposed, and the removal of non-metallic inclusions in the molten steel is ensured;

s1.5 round billet continuous casting

The baking of the large ladle and the tundish is enhanced, a pouring system must be ensured to be clean and dry, and a tundish covering agent and crystallizer covering slag must be kept dry; in the continuous casting process, the whole-process protective casting and the drawing speed are strictly controlled, so that the constant drawing speed casting is ensured; the covering conditions of the liquid levels of the tundish and the crystallizer are observed at any time in the continuous casting process, so that the phenomena of poor covering of the liquid levels of the tundish and the crystallizer or exposure of the liquid steel are prevented; the height of the liquid level of the tundish is noticed at any moment in the continuous casting process, the casting liquid level is not less than 500mm, and full ladle casting is adopted in the process of casting; controlling the superheat degree of the continuous casting molten steel within the range of 15-35 ℃; adopting crystallizer electromagnetic stirring and tail end electromagnetic stirring processes; the nozzles of the second cold water ensure even spraying, and no cutoff and water column spraying are allowed; stacking the round billets for slow cooling, and avoiding a tuyere;

s2, the pipe rolling process comprises the following steps: round billet → saw cutting → circular furnace heating → perforation → MPM continuous rolling → diameter setting (tension reducing → cooling); the high-quality pipe body with high dimensional accuracy and good inner and outer surface quality is obtained by the process;

s2.1 preparing and heating tube blank

Before circular tube blank sawing, the central line of a clamping blank and the fixed rigidity of a circular saw are confirmed, and the cutting inclination of the steel blank is ensured to be within 5 mm; before the tube blank is loaded into a furnace, the tube blank is checked, and severe slag pits and scabs are polished; inspecting the quality of the sawed end face, and timely removing tube blanks with defects exceeding standards, such as central cracks, central shrinkage cavities and the like; heating is carried out according to a specified heating system strictly, the temperature and time of each section of the heating furnace are monitored in the heating process, the extension of the thermal stress to the defect of the center or the outer surface of the billet is reduced, the billet is uniformly heated in the heating furnace, and the phenomena of shadow surface, heat impermeability, overheating or overburning are avoided; strictly cooling to-be-rolled degree to ensure the heating quality of the tube blank; the temperature of the heat preservation section of the annular furnace is controlled at 1260-;

s2.2 perforation

Monitoring the shaking condition of the head end of the hollow billet in front of a holding roller and the shaking condition of an ejector rod, and judging whether the consistency of rolling central lines of the puncher body and the front and rear platforms is in a good stable state; the front extension of the ejector pin is strictly controlled according to the requirements of a rolling table, the state of the roller holding of the ejector pin is good, and the ejector pin does not shake in the punching process; strictly adjusting and monitoring cooling water, and preventing cooling water of a roller, a roller way, a holding roller and a mandril top from entering a capillary as much as possible, so as to prevent an inner hole from having macroscopic water drops when the capillary enters a nitrogen-blowing borax-spraying station; at a nitrogen-blowing borax-spraying station, nozzles are strictly aligned and are consistent with the central line of the capillary, borax is dry and has no caking phenomenon, and proper borax spraying amount and spraying pressure are selected to ensure that borax is uniformly adhered to the inner surface of the capillary and no more residual caking is generated; the temperature of the capillary after perforation is 1200 ℃ and 1240 ℃;

S2.3MPM continuous rolling

Confirming the on-line frame, and assembling the frame strictly according to the rolling table and pass design requirements; checking each frame of continuous rolling rolls and the rolls for the pipe removing machine, wherein the surfaces of the rolls are smooth and clean without aging; preparing a new core rod or a non-damaged core rod which is checked and confirmed, wherein the diameter tolerance of the core rod reaches-0.30 mm-0 required by the specification; opening the high-pressure water for descaling, controlling the water pressure and opening time of the high-pressure water for descaling, and avoiding the head end of the capillary for about 200mm to prevent the capillary from entering water; strictly controlling cooling water of a background roller way of the rolling mill, and strictly forbidding pouring of the black pipe body;

s2.4 sizing

When the machine frame is on line, the roller surface of the machine frame is checked, whether a roller gap is staggered is touched by hands, a water nozzle, an up-down sliding plate and the like are checked, and the quality of the machine frame is ensured to meet the requirement; checking each roller way before and after the detection to ensure that the roller ways run normally, checking and adjusting the spraying direction of the roller way cooling water to ensure that the cooling water is not sprayed to the inner surface of the pipe body; the temperature of the tube body after diameter setting (expansion) is 880 plus 920 ℃;

s2.5 Cooling