JPS63215308A - Rolling method for sizing tube - Google Patents

Abstract

PURPOSE:To prevent seizing flaws by using an Ni grain roll specifying a graphite crystallizing area ratio and specifying a solid lubricant content of a lubricant and its viscosity. CONSTITUTION:An Ni grain roll is used as a rolling roll for a sizer; a roll for which >=2.5% graphite is crystallized on the working surface is used. On the other hand, a lubricant containing a solid lubricant is used and a solid lubricant content of 5-30 wt.% is preferred; a lubricant having a viscosity of 1000-5000 cps is used so that generation of seizing flaws is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for sizing a pipe in a sipe (sizing mill) in the Mannesmann seamless pipe manufacturing process.

[Conventional technology]

Since sipe rolling is a finishing step of the hot pipe manufacturing process, the rolled material must have a good surface quality free of defects. However, Sipe's roll is the first
As shown in the figure, since it is a grooved roll, the relative speed between the roll and the outer surface of the tube differs between the outer circumference of the roll and the bottom of the groove. Seizure deposit Y is attached, and this seize deposit Y is attached to the pipe P.
It is transferred to the outer surface of the tube, causing the seizing scratches X and further deteriorating the surface quality of the tube.

Therefore, conventionally, as a rolling roll for sipes, a chilled roll (composition: Habo C: 3%, S
i: 0.3%, Mn: 0.6%, Cr: 1.5%,
Ni: 2%) is used, and hot rolling oil, which is a mixture of about 50% oil and fat in mineral oil, is supplied to the interface between the rolls and the rolled tube material to prevent seizure.

[Problem that the invention seeks to solve]

However, with the conventional rolling rolls and hot rolling oil mentioned above,
Particularly when rolling materials with excellent oxidation resistance such as high chromium steel, there is little formation of an oxide film that has the effect of preventing seizure, so the occurrence of seizure defects is unavoidable, and manual maintenance such as polishing is required after rolling. There were times when it was necessary.

SUMMARY OF THE INVENTION Therefore, the main object of the present invention is to provide a method for rolling a tube to a fixed diameter, which can reliably prevent seizure defects and in which occurrence of seizure defects is extremely small even in high Cr steel.

[Means for solving problems]

In order to solve the above conventional problems, the present invention uses a Ni grain roll having a graphite crystallization area ratio of 2.5% or more as a rolling roll of a diameter rolling mill, and also uses a solid lubricant of 5 to 3%.
Contains 0% by weight, viscosity at room temperature is 1500-5000
It is characterized by the combined use of CPS lubricant.

[For production]

In general, seizure is often caused by direct metal-to-metal contact, but the reason why chilled rolls were conventionally used as rolling rolls is that chilled rolls contain a large amount of metal carbide, about 20 to 40%. Therefore, there is little contact between metals on the friction surface, and there is contact between the metal carbide and the metal, so that seizure is less likely to occur. In fact, when working with ordinary steel or low alloy steel, there is almost no seizure with the help of the formation of an oxide film, but with high Cr steel, seizure occurs during hot working. Because it generates less oxide film due to heat than ordinary steel, etc., and has higher deformation resistance, the surface pressure is higher and the degree of direct contact between the metal tool and the metal material during plastic working is increased. Easy to cause seizure.

On the other hand, the reason why hot rolling oils such as those mentioned above are conventionally used is that mineral oils do not have polar groups, so they have weak adsorption power to metal surfaces and do not exhibit good lubricity when used alone. The aim is to prevent the occurrence of seizure by mixing oils and fats with strong adsorption properties.

However, as is clear from the comparison method shown in the Examples below, seizure cannot be prevented when high Cr or the like is targeted. On the other hand, according to the present invention, seizure can be reliably prevented as in the embodiments described later.

Conventionally, Ni grain rolls have not been used for sipes, probably because they cause a large amount of friction. However, it has been found that friction does not actually become a problem even if the Ni grain roll is used for a long time. Therefore, the graphite crystallization rate is 2.
When a Ni grain roll containing 5% or more is used, the graphite itself exhibits self-lubricating properties due to the presence of graphite on the machined surface, increasing the anti-seizure effect.In addition, in sipe rolling, the contact time between the roll and the rolled pipe material increases. Under the circumstances that the solid lubricant according to the present invention is used in conjunction with the use of Ni grain rolls under the circumstances of a relatively long period of time and a temperature of around 800°C, it is possible to reduce seizure, although it is unclear why the combination exhibits a synergistic effect. It can definitely be prevented.

[Specific structure of the invention]

The present invention will be explained in more detail below.

In the present invention, a Ni grain roll is used as the sipe rolling roll. The components may be known ones, but usually about C: 3%, Si: 1%, Mn:
0.6%, Cr: 1.5%, Ni: 4.5%, M.

:0.5% is good. The Ni grain roll containing at least 2.5% graphite on at least the processed surface (hole-shaped surface) is used. The graphite crystallization rate means the area ratio occupied by graphite within a certain region of the roll surface, and can be determined, for example, by observation under a microscope.

If the crystallization rate of graphite is less than 2.5%, the lubricating effect of graphite cannot be expected.

On the other hand, lubricants including solid lubricants are used in combination.

Graphite is preferred as a solid lubricant due to its large lubrication effect, but if the material to be rolled is austenitic stainless steel or duplex stainless steel, where there is a concern about carburization due to graphite, boron nitride (BN) powder may be used. Powders of mica, molybdenum disulfide, tungsten disulfide, calcium fluoride, etc. may also be used. Alternatively, a mixture thereof may be used. The content of the solid lubricant is preferably 5 to 30 wt%; if it is less than 5%, the anti-seizure effect will be small, and if it exceeds 30%,
As shown in FIG. 2, lubricant 1 is transferred from nozzle 2 to roll
When supplying the lubricant to the surface and rolling the pipe material 4 to be rolled, the lubricant, as indicated by the symbol Q, accumulates in the shape of a grain of rice and is drawn into the interface between the roll 3 and the pipe material 4 at irregular intervals, causing the pipe material 4 to be rolled. This is not preferable as it may cause indentation scratches on the surface.

The lubricant in the present invention is obtained by mixing a solid lubricant such as graphite into mineral oil, and the lubricant used has a viscosity of 1000 to 5000 cps at room temperature. If it is less than 1000 cps, the viscosity is low, so
As the oil film becomes thinner, the amount of solid lubricant contained therein is insufficient to penetrate into the interface, resulting in less anti-seizure effect.
If it exceeds 0 cps, it becomes difficult to smoothly supply lubricant by a pump or the like.

C Example] Next, examples will be shown.

In a sizer mill consisting of 7 stands, the rolling speed is set to 1.
m/sec, the occurrence of flaws was investigated by changing the steel type, roll type, and lubricant type, and the results shown in Table 1 were obtained. In addition, the pipe material dimensions are 17? , 8 tm
φX10.36wtXl 2m, and the evaluation of the occurrence of flaws was performed visually, and flaws with a depth of 0.1 or more were marked as x.

Further, based on the above experimental results, the overall flaw occurrence rate was as shown in Table 2.

Table 2 [Effects of the Invention] As described above, according to the present invention, seizure can be reliably prevented.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the occurrence of seizing defects in sizer mills, Figure 2
The figure is a schematic diagram of the retention status of solid lubricant in lubricant. DESCRIPTION OF SYMBOLS 1... Lubricant, 3... Roll, 4... Tube material to be rolled.

Claims (1)

[Claims] (1) As the rolling roll of the sizing rolling mill, use a Ni grain roll with a graphite crystallization area ratio of 2.5% or more, contain 5 to 30% by weight of a solid lubricant, and have a viscosity of 1 at room temperature.
A method for rolling a pipe to a fixed diameter, characterized by using a lubricant of 000 to 5000 cps.