JP2002167619A - Ferritic stainless steel wire rod and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferritic stainless steel wire rod having excellent cold plastic workability and causing neither crack nor breakage during steps of drawing and straightening in manufacturing a cold-finished steel bar from a coil of the ferritic stainless steel wire rod by a process including the steps of drawing and straightening and also to provide an economical method for manufacturing the same. SOLUTION: In hot rolling the ferritic stainless steel wire rod, hot-rolling- finishing temperature is made to 800-930 deg.C by regulating hot-rolling speed and the grain size of the above ferritic stainless steel wire rod after the completion of hot rolling is regulated to fine grains of grain size No.6 or above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferritic stainless steel polished steel bar having excellent cold plastic workability which does not cause cracking or breakage during cold plastic working such as cold drawing and straightening.

[0002]

2. Description of the Related Art In recent years, OA equipment, personal computer peripherals,
Other machined parts of stainless steel are often used as various control equipment parts. Many of these are machined from stainless steel polished bar steel by an automatic cutting machine such as an automatic lathe.

[0003] In general, a hot-rolled steel bar is subjected to heat treatment such as annealing and normalizing as necessary after hot rolling, straightened into a straightened bar, cut into a predetermined length, and then cut. It is manufactured by smoothing the surface of the steel bar by cutting such as turning and peeling and finishing the outer diameter to a predetermined size.

[0004] Further, the outer diameter and the surface skin are adjusted by drawing hot-rolled steel bars, and then straightened by a straightening device such as a multi-roll straightener to produce a polished steel bar. Is being done. Furthermore, after hot rolling, it is wound into a coil to form a long coil-shaped wire, and the wire is continuously drawn to a predetermined outer diameter and substantially linear, and from the tip of the drawn material. 2. Description of the Related Art Bars of a predetermined length are sequentially cut out, and subsequently, the bars are straightened by a straightening device such as a multi-roll straightener to form a polished bar.

[0005] A method of manufacturing a polished bar steel including a drawing process has a better material yield than a method of cutting, and in particular, a method of continuously drawing from a coil material is an extremely economical manufacturing method. On the other hand, since this method involves drawing, the plastic workability of steel poses a problem. When a polished bar is manufactured from a ferritic stainless steel coil material by a drawing process and a straightening process, cracking and breakage often occur during the process, which is a problem in manufacturing.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a polished bar from a coil material of a ferritic stainless steel wire by a process including a drawing process and a straightening process. It is an object of the present invention to provide a ferritic stainless steel wire having excellent cold plastic workability, which does not cause cracking, and an economical production method thereof.

[0007]

As a result of research conducted to solve the above-mentioned problems, it was found that only ferritic stainless steel including drawing and straightening was used to prevent cracking and breakage of the bar in the bar production process. Therefore, the crystal grain size of the ferritic stainless steel wire, which is a material, has a remarkable effect, and the crystal grain size is refined to improve the cold plastic workability of the ferritic stainless steel. And breakage can be prevented. In addition, in hot working of ferritic stainless steel, it has been found that the end temperature of hot working needs to be 930 ° C. or lower in order to reduce the crystal grain size.

[0008] The present invention has been made based on the above findings. That is, the method for producing a ferritic stainless steel wire excellent in cold plastic workability of the present invention is as follows: (1) In hot rolling of a ferritic stainless steel wire, the hot rolling end temperature is set to 800 to 930 ° C. It is characterized by. (2) In the hot rolling of a ferritic stainless steel wire, the hot rolling end temperature is set to 800 to 930 ° C. by adjusting the hot rolling speed. (3) In the hot rolling of the ferritic stainless steel wire, the hot rolling end temperature is adjusted to 800 to 930 ° C. by adjusting the hot rolling speed, and the crystal of the ferritic stainless steel wire after the hot rolling is completed. The feature is that the grain size is 6 or more. Further, the ferritic stainless steel wire excellent in cold plastic workability of the present invention is characterized in that (4) the grain size after completion of hot rolling is a grain size number 6 or more. (5) In hot rolling of a ferritic stainless steel wire, the grain size after hot rolling is adjusted to a grain size of 6 or more by adjusting the hot rolling speed. (6) In the hot rolling of the ferritic stainless steel wire, the hot rolling end temperature is adjusted to 800 to 930 ° C. by adjusting the hot rolling speed, and the crystal of the ferritic stainless steel wire after the hot rolling is completed. The feature is that the grain size is 6 or more.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A ferritic stainless steel wire excellent in cold plastic workability according to the present invention is, for example, JIS SUS.
Stainless steel such as 410 or SUS430 having a high Cr content and a ferrite phase of at least 95% or more in a solid state, and may contain various alloying elements as necessary.

[0010] The ferritic stainless steel wire of the present invention having excellent cold plastic workability is obtained by casting molten steel in the same manner as ordinary ferritic stainless steel to form an ingot, and further performing hot forging or hot rolling. Billet.
In producing a billet, the molten steel may be continuously cast to form a billet.

The billet is heated to a hot-rolling heating temperature, hot-rolled by a hot-rolling machine to obtain a rolled material having a required outer diameter, and then the rolled material is coiled using a winding device. It is wound into a coiled steel wire. When manufacturing a long rolled material, it is preferable to perform rolling using, for example, a tandem-type continuous rolling mill having a large number of roll pairs.

The method for producing a ferritic stainless steel wire excellent in cold plastic workability according to the present invention is characterized in that the temperature of the rolled material immediately after the completion of the hot rolling (referred to as a hot rolling end temperature).
Is set to 800 to 930 ° C. If the hot rolling end temperature is too low, the deformation resistance of the steel is large, and
Since the deformability is small, problems such as difficulty in rolling during rolling and generation of cracks and flaws in the rolled material occur. Therefore, the lower limit of the hot rolling end temperature is 800 ° C.
And On the other hand, if the hot-rolling end temperature is too high, the crystal grains of the rolled material become coarse, which causes problems such as cracking and breakage in the product in the post-rolling steel bar manufacturing process. Therefore, the upper limit of the hot rolling end temperature is 9
30 ° C.

In order to adjust the hot rolling end temperature, any method such as adjusting the heating temperature of the billet or forcibly heating or cooling the workpiece during hot rolling is selected. However, it is preferable to adjust the hot rolling end temperature by adjusting the rolling speed in hot rolling.

During the hot rolling, the workpiece is cooled due to natural heat dissipation and heat loss due to contact with a roll for a rolling mill, and the temperature of the workpiece is raised by the heat generated during the rolling. As the rolling speed increases, the processing time decreases.
Even if the processing amount is the same and the processing heat is the same, the amount of heat loss is reduced,
The rolling end temperature rises. Decreasing the rolling speed increases the processing time and lowers the rolling end temperature. According to the method of adjusting the rolling speed in the hot rolling, the special equipment for forced heating and cooling is not required, and the end-of-rolling temperature can be adjusted extremely economically.

The rolled material thus hot-rolled is wound into a coil shape by a winder, and then subjected to a preliminary treatment including an annealing treatment and a lubricant application, if necessary, to produce a polished bar steel. Provided to the process. The polished bar is manufactured by a polished bar manufacturing method including cold drawing and straightening with a multi-roll straightener.

In a ferritic stainless steel wire having a coarse crystal structure having a crystal grain size of less than a crystal grain size number 6, problems such as cracks and breakage occur in the cold drawing or straightening process in the above-mentioned polished bar manufacturing process. Therefore, the ferritic stainless steel wire excellent in cold plastic workability of the present invention has a fine crystal structure having a crystal grain size of 6 or more after completion of hot rolling. Here, the crystal grain size number is measured according to ASTM E112.

Since the ferritic stainless steel to which the present invention is directed is a solid phase and substantially one phase, the crystal grain size is determined by hot working conditions, and the crystal grain cannot be refined by the subsequent heat treatment. According to the present invention, a rolled material having a fine crystal structure having a crystal grain size of 6 or more after completion of hot rolling is obtained, and in the subsequent process of producing a polished bar including cold drawing-straightening, A ferritic stainless steel wire excellent in cold plastic workability can be obtained without causing problems such as cracks and breakage.

A ferritic stainless steel having the composition shown in Table 1 was melted in an arc furnace to obtain a 4.6-ton ingot. The ingot is hot rolled to 1
The billet was a 53 mm square × 5 to 10 m long.

[Table 1]

The billet is heated to 1200 to 1300 ° C., and a row of rough rolling mills including eight two-roll rolling mills, a row of intermediate rolling mills including six two-roll rolling mills, and four two-roll rolling mills are provided. Hot rolling is performed by a continuous wire rolling machine having a finishing rolling mill line including two 4-roll rolling mills, and has a diameter of 1 mm.
7mm round or 20mm round wire rod, wound using a poling reel type winding device, weight about 950kg,
A wire coil having an outer diameter of about 1.5 m was used. Table 2 shows values of the dimensions, temperature, rolling speed, and the like of the rolled material measured on the entrance side and the exit side of each rolling mill row. ASTM was applied to the center of the longitudinal section including the axis of the wire test piece taken from the wire coil.
The crystal grain size was measured by the comparison method defined in E112. The results are shown in Table 2 as crystal grain size numbers.

[Table 2]

After the wire coil was heated at a temperature of 750 ° C. for an hour and then allowed to cool, the scale was removed by pickling and a lubricating film treatment was performed. Using a continuous drawing and straightening machine (combined machine) including a continuous drawing mechanism, a cutting mechanism, and a roll-type wire straightening mechanism composed of a pair of straightening rolls, the wire coil subjected to the lubricating film treatment is straightened and cut. A polished steel bar having a diameter of 4 to 5 m and a diameter shown in FIG.

[Table 3]

As can be seen from Table 3, in Examples 1 to 7,
After the straightening cut by the combined machine, no harmful defects such as flaws and cracks were found in the obtained polished bar and the bending of the polished bar was sufficiently small at 1 mm / m or less, and normal straightening was performed. Was. As can be seen from Table 2, in Examples 1 to 7, the rolling speed of the intermediate rolling mill and the finishing mill was appropriately adjusted in accordance with the level of the entrance temperature of the intermediate rolling mill row, so that the output of the finishing rolling mill row was obtained. The side temperature (hot rolling end temperature) was within the temperature range of 800 to 930 ° C.

In the sixth embodiment, in which the temperature at the middle of the intermediate rolling mill is lower than that of the fifth embodiment, the rolling speeds of the intermediate rolling and the finish rolling are increased. In Example 7, in which the temperature was higher, the exit temperature (hot rolling end temperature) of the finishing rolling mill row was adjusted by lowering the rolling speeds of the intermediate rolling and the finish rolling. Example 1
In Nos. To 7, the grain size after the completion of the hot rolling is a fine grain having a grain size number of 6 or more.

In Comparative Examples 1 to 5, the exit temperature of the finishing mill row (the end point of hot rolling) was 930 because the adjustment of the entrance temperature of the intermediate rolling mill row and the rolling speed of the intermediate rolling and the finish rolling were not appropriate. C. and a coarse crystal structure with a crystal grain size of less than 6. As can be seen from Table 3, in Comparative Examples 1 to 5, cracks occurred in the cold drawing step or breakage occurred in the straightening step, and normal straightening could not be performed.

As described above, according to the present invention, it is possible to obtain a ferritic stainless steel wire having excellent cold plastic workability, which does not cause cracking or breakage in the drawing process and the straightening process. Further, according to the present invention, the finish rolling mill row exit temperature (the hot rolling end temperature) is adjusted by adjusting the rolling speed in the intermediate rolling and the finish rolling, so that the apparatus for adjusting the hot rolling end temperature is provided. For example, a forced cooling device for a rolled material is not required. The method for producing a ferritic stainless steel wire excellent in cold plastic workability according to the present invention can be said to be an economical method.

[0025]

As described above, according to the present invention, when a polished bar is manufactured from a coil material of a ferritic stainless steel wire by a process including a drawing process and a straightening process, a drawing process and a straightening process are performed. It is possible to provide a ferritic stainless steel wire having excellent cold plastic workability, which does not cause cracking or breakage in the process, and an economical production method thereof.

Claims (6)

[Claims] 1. A method for producing a ferritic stainless steel wire excellent in cold plastic workability, wherein a hot rolling end temperature is 800 to 930 ° C. in hot rolling of a ferritic stainless steel wire. 2. In hot rolling of ferritic stainless steel wire, the hot rolling end temperature is adjusted to 800 to 930 ° C. by adjusting the hot rolling speed, so that it is excellent in cold plastic workability. Manufacturing method of ferritic stainless steel wire. 3. The hot-rolling of a ferritic stainless steel wire by adjusting the hot-rolling speed so that the hot-rolling end temperature is 800 to 930 ° C. The method for producing a ferritic stainless steel wire excellent in cold plastic workability, characterized in that the crystal grain size is 6 or more. 4. A ferritic stainless steel wire excellent in cold plastic workability, characterized in that the crystal grain size after completion of hot rolling is a crystal grain size number of 6 or more. 5. The hot rolling of a ferritic stainless steel wire, wherein the grain size after hot rolling is adjusted to a grain size number of 6 or more by adjusting a hot rolling speed. Ferritic stainless steel wire with excellent plastic workability. 6. The hot-rolling of a ferritic stainless steel wire by adjusting a hot-rolling speed so that the hot-rolling end temperature is 800 to 930 ° C. A ferritic stainless steel wire excellent in cold plastic workability, characterized by having a crystal grain size of 6 or more.