JP2009066644A - Piercer boring method of hard-to-work material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piercer boring method of a hard-to-work material capable of preventing generation of inner flaw when performing the piercer boring of the hard-to-work material. <P>SOLUTION: In the piercer boring method for manufacturing a seamless steel tube by rolling and boring a hard-to-work material by a piercer mill, the relationship between the material temperature and the hot deformation resistance (σ[MPa]) is expressed by formula (1), and relational formula (2) between the material temperature immediately before the boring (T[k]) and the material advancing speed during the boring (V[mm/sec]) when performing the piercer boring of the hard-to-work material is satisfied, preventing generation of inner flaw due to the overheat during the boring. σ[MPa]=A×exp(D/T[K])×(dε/dt)<SP>m</SP>...(1), T[K]+(1+0.002V[mm/sec])×K(T)<T<SB>0</SB>[K]...(2). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a piercer drilling method for difficult-to-work materials that prevents the occurrence of internal flaws at the time of piercing difficult-to-work material.

  Conventionally, when a difficult-to-work material is rolled by a Piercer mill, a pleated delamination defect and internal flaws often occur in an element tube obtained by drilling a round steel piece. Therefore, in order to prevent the occurrence of these fold-like delamination defects and inner surface flaws, the stainless steel pipe has a drillable range in which the drilling speed and the drilling temperature are regulated, such as reducing the drilling speed and further reducing the drilling temperature. It is shown.

  Further, in difficult-to-work materials other than the stainless steel, the deformation resistance is lower than that of the stainless steel, but since the overheat temperature is lower than that of the stainless steel, a pleated defect and an inner surface flaw are generated under the conventional drilling conditions. Furthermore, in order to avoid overheating, if the billet heating temperature is lowered too much, it will not bite into the piercer mill, and so drilling will not be possible. Therefore, it is necessary to determine an appropriate billet heating temperature and perforation speed to prevent overheating.

  As described above, it is a problem that difficult-to-process materials are likely to overheat due to processing heat generation during piercer mill drilling. Overheating causes a defect in the intermediate portion of the tube, and the defect is stretched by an elongator mill, and becomes a flaking-like peeling defect by a sizing mill. Therefore, in order to eliminate the occurrence of fold-like peeling defects and internal flaws, it is necessary to perforate with a piercer mill so as to prevent overheating. In addition, in order to prevent overheating and perform drilling, it is necessary to determine the optimum drilling conditions in consideration of billet heating temperature, billet temperature decrease during conveyance, drilling time, and drilling speed.

Therefore, as a method for producing a seamless pipe that does not cause a pipe inner surface flaking-like peeling defect due to overheating when drilling into a seamless pipe material with a Piercer mill, for example, Japanese Patent Laid-Open No. 2000-301212 (Patent Document 1) As disclosed, the billet temperature that satisfies the relational expression between the drilling speed and the billet heating temperature, and the seamless pipe of the difficult-to-process material that prevents the pleated flaking defect on the inner surface of the pipe that drills the difficult-to-work material at the rolling speed. Piercer drilling methods have been proposed.
JP 2000-301212 A

  However, there are problems in that there are difficult-to-work materials that are out of the scope of patents in Patent Document 1, and these difficult-to-work materials cannot prevent the occurrence of internal flaws.

  In order to solve the above-mentioned problems, the inventors have made extensive developments. As a result, the material temperature at the time of drilling reaches the overheat temperature by controlling the material temperature before drilling, the material temperature immediately after drilling, or the drilling speed. By providing this method, there is provided a method for piercing a piercer of a difficult-to-work material capable of preventing internal flaws due to overheating.

The gist of the invention is that
(1) In a method of producing a seamless steel pipe by rolling and drilling a difficult-to-work material with a Piercer mill, the difficult-to-work material represented by the relational expression (1) with the hot deformation resistance (σ [MPa]) with respect to the material temperature Is set so as to satisfy the relational expression (2) between the material temperature immediately before drilling (T [K]) and the material advanced speed during drilling (V [mm / s]). A method for piercing a piercer of a difficult-to-work material, characterized by preventing generation of internal flaws due to overheating. σ [MPa] = A × exp (D / T [K]) × (dε / dt) ^m (1)
T [K] + (1 + 0.002V [mm / sec]) × K (T) <T ₀ [K] (2)
However, A: 0 to 1
D: A value determined by the steel type obtained in the experiment m: Strain rate sensitivity index, a value determined by the steel type V: Piercer drilling speed (m / sec)
K (T): Value determined by steel type and temperature T ₀ : Overheat temperature [K], the temperature at which the aperture value decreases by 5% of the maximum value when the test temperature is raised in the greeble test ( 2) The relationship between the material temperature immediately before drilling (T [K]) described in (1) and the material temperature immediately after drilling (T ′ [K]) is expressed by Equation (3). T ′ [K]) is lower than the overheat temperature (T ₀ ). T ′ [K] ≈T [K] + (1 + 0.002 V [mm / sec]) × K (T) (3)

  As described above, by controlling the material temperature immediately before drilling or the material temperature immediately after drilling according to the present invention, and the drilling speed, the material temperature at the time of drilling can be prevented from reaching the overheat temperature, and the defect of the inner surface flaw can be reduced. It has an extremely excellent effect.

Hereinafter, the present invention will be described in detail.
The piercer mill drilling conditions are analyzed by considering the billet heating temperature, drilling speed, and processing heat generation, and the temperature inside the billet is below the overheating temperature and above the temperature at which the piercer mill can be bitten and drilled. To be decided. The overheat temperature is obtained by a greeble test. The calculation of billet internal temperature distribution after piercer mill drilling was analyzed using a known finite element method.

  Difficult-to-work materials generally have higher deformation resistance than ordinary alloys when drilled with a piercer mill, and the temperature range where high hot ductility can be obtained is narrow, so billet heating temperature, drilling speed, etc. can be drilled Conditions are narrow. Therefore, when adding conditions to difficult-to-work materials and performing piercer drilling on difficult-to-work materials expressed by the relational expression (1) with hot deformation resistance (σ [MPa]) relative to material temperature, immediately before drilling It is set so as to satisfy the relational expression (2) between the material temperature (T [K]) and the material advanced speed (V [mm / sec]) during drilling. This prevents the occurrence of internal flaws due to overheating during drilling.

For example, the overheat temperature (T ₀ ) is 1225 ° C., and the hot deformation resistance (σ [MPa]) is σ [MPa] = 0.3 × exp (7600 / T [K]) × (dε / dt) ^0.15 . When drilling a material to be drilled, if the material temperature immediately before drilling (T [K]) is set to 1070 ° C. and the drilling and rolling speed is set to 400 mm / s, it is possible to prevent generation of internal flaws due to overheating.

Further, there is a relationship of the formula (3) between the material temperature immediately before drilling (T [K]) and the material temperature immediately after drilling (T ′ [K]), and the material temperature immediately after drilling (T ′ [K]) is By making the temperature lower than the overheat temperature (T ₀ ), the generation of internal flaws due to overheating during drilling is prevented. T ′ [K] ≈T [K] + (1 + 0.002V [mm / s]) × K (T) (3)
Thereby, by controlling the material temperature immediately after drilling, the occurrence of flaws on the inner surface of the pipe can be reduced by setting the billet heating temperature and drilling speed appropriately.

Hereinafter, the present invention will be specifically described with reference to examples.
Difficult workability represented by an overheat temperature (T ₀ ) of 1523 (K) and hot deformation resistance (σ [MPa]) of 0.3 × exp (7600 / T [K]) × (dε / dt) ^0.15 Piercer drilling was performed on the material. As shown in Table 1, piercer drilling was performed by changing the material temperature immediately before drilling (T [K]) and the material temperature immediately after drilling (T ′ [K]), and the material temperature immediately after piercing drilling (T ′ [K]). Was measured with a thermo-laser, and the inner surface of the material after drilling was visually observed to investigate the presence of inner surface flaws. The results are shown in Table 1.

表１は、穿孔直前材料温度（Ｔ［Ｋ］）とＫ（Ｔ）〔鋼種、温度によって決まる値〕と材料先進速度（Ｖ［ｍｍ／ｓｅｃ］）が１００、２００、３００、４００、５００、および６００［ｍｍ／ｓｅｃ］での各穿孔直後材料温度（Ｔ´［Ｋ］）を変化させた時の内面疵の発生状態の有無を目視で調査した結果である。

Table 1 shows that the material temperature immediately before drilling (T [K]) and K (T) [steel type, a value determined by temperature] and the material advanced speed (V [mm / sec]) are 100, 200, 300, 400, 500, And the result of visual inspection of the presence or absence of internal flaws when the material temperature (T '[K]) immediately after each drilling was changed at 600 [mm / sec].

As a result, when the material advanced speed is 100 [mm / sec] to 600 [mm / sec], no wrinkle is generated when the material temperature is 1526K or less immediately after drilling. Therefore, it is found that there is a relationship of Equation 3 between the material temperature immediately before drilling (T [K]) and the material temperature immediately after drilling (T ′ [K]), and the material temperature immediately after drilling (T ′ [K]). ) Lower than the overheat temperature (T ₀ ), it can be seen that generation of internal flaws due to overheat can be prevented.

As described above, the fact that there is a relationship of Equation 3 between the material temperature immediately before drilling and the material temperature immediately after drilling has been found by many experiments, and by managing the temperature of the material temperature immediately after drilling on the operation, By setting the billet heating temperature and the perforation speed appropriately, it is possible to prevent the generation of soot on the inner surface of the pipe, and it is possible to reduce the generation of soot and achieve an extremely excellent effect that enables stable operation.


Patent Applicant Sanyo Special Steel Co., Ltd.
Attorney: Attorney Shiina

Claims (2)

In a method of manufacturing seamless steel pipes by rolling and drilling difficult-to-process materials with a Piercer mill, the relationship between the hot deformation resistance (σ [MPa]) with respect to the material temperature is expressed by the formula (1), and the difficult-to-work materials are Pierce drilled. In doing so, the inner surface due to overheating during drilling is set by satisfying the relational expression (2) between the material temperature immediately before drilling (T [K]) and the material advanced speed (V [mm / sec]) during drilling. A piercer drilling method for difficult-to-process materials, characterized by preventing wrinkles.
σ [MPa] = A × exp (D / T [K]) × (dε / dt) ^m (1)
T [K] + (1 + 0.002V [mm / sec]) × K (T) <T ₀ [K] (2)
However, A: 0 to 1
D: A value determined by the steel type obtained in the experiment m: Strain rate sensitivity index, a value determined by the steel type V: Piercer drilling speed (m / sec)
K (T): Value determined by steel type and temperature T ₀ : Overheat temperature [K], the temperature at which the aperture value decreases by 5% of the maximum value when the test temperature is raised in the greeble test The relationship between the material temperature immediately before drilling (T [K]) and the material temperature immediately after drilling (T ′ [K]) according to claim 1 is represented by the equation (3), and the material temperature immediately after drilling (T ′ [ K]) is made lower than the overheat temperature (T ₀ ).
T ′ [K] ≈T [K] + (1 + 0.002 V [mm / sec]) × K (T) (3)