JPH06210325A - Manufacture of work roll for cold rolling - Google Patents

Abstract

PURPOSE:To provide a work roll with an excellent wear resistance for a cold rolling. CONSTITUTION:Nickel plating is performed on the surface of a roll, further, trivalent chrome composite platings obtained by dispersing hard particles on a nickel-plated layer, are performed, and a soaking treatment is performed under a condition of <=1 soaking time tauX19<25>/T<10.3>(hr), where T is a soaking temperature ( deg.C). Since the high hardness of the plating film is obtained in a range in which the hardness of the roll base material does not lower, the roll shows an excellent wear resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold rolling work roll, and more particularly to a method for manufacturing a cold rolling work roll having excellent wear resistance.

[0002]

2. Description of the Related Art One of the properties required of rolling rolls is wear resistance. Conventionally, the hardness of the roll material is increased by adding Cr, heat treatment, etc. to improve wear resistance. Recently, in order to improve wear resistance, chrome plating is also performed on the roll surface. Among chrome plating, "materials and processes" (3 (1990), 1350) and "materials and processes" (5 (1992), 511) and the like are known as those for performing hexavalent chromium plating. Regarding trivalent chromium plating, "Hardness of chromium plating from chromium (III) sulfate-potassium formate bath" (Matsufumi Takatani et al., Metal Surface Technology, 10-37)
(1986), 621) is known. Furthermore, regarding trivalent chromium composite plating, "Preparation and wear characteristics of Cr-SiC composite coating" (Matsufumi Takatani et al., Metal surface technology, 3-
38 (1987), 97) and "Cr-SiC, Cr-Diamond composite coating from trivalent chromium plating bath" (Matsufumi Takatani et al., Metal Surface Technology, 11-37 (1986), 6).
71) and the like are known. The latter document describes that when a steel sheet is subjected to trivalent chromium composite plating, it is subjected to degreasing and pickling and then subjected to Ni strike undercoating.

[0003]

The trivalent chromium composite plating can raise the hardness of the coating film to 1600 Hv or more by heat treatment, but there is a problem that the wear resistance of the roll is not improved. That is, the work roll for cold rolling is subjected to a large rolling force and frictional force, and further rolls and slides on the surface of the rolled material. Therefore, when the above-mentioned technique of forming a nickel plating layer on a steel sheet and forming a trivalent chromium composite plating layer on it is simply applied to a work roll for cold rolling, sufficient wear resistance cannot be obtained. It was For this reason, the work roll for cold rolling has a short life, and the roll unit is reduced, resulting in high product cost.

The present invention is intended to provide a work roll for cold rolling which is excellent in wear resistance.

[0005]

A method for manufacturing a work roll for cold rolling according to the present invention comprises a trivalent chromium composite plating in which hard surfaces are plated with nickel and hard particles are dispersed on a nickel plating layer. Soaking time τ ≦ 1 × 10 ²⁵ / T ^10.3 (hr) T: Soaking is performed at soaking temperature (° C.).

Forged steel, chrome steel or the like is used as the roll base material. As hard particles, SiC, ZrB ₂ , Si
₃ N ₄ , Al ₂ O ₃ , Cr ₃ C ₂ , B ₄ C, CBN, and diamond. Multiple types of hard particles may be dispersed in the chrome plating matrix. There are an electrolytic method and an electroless method as the plating method, but the electrolytic method is preferable in consideration of the efficiency of the plating operation and the efficient co-deposition of the dispersant. Further, in order to uniformly disperse the dispersant in the plating bath, a chemical method using a surfactant or a physical method using air stirring is used.

For the soaking treatment, a heating furnace such as an electric furnace or a gas combustion furnace, which is suitable for preventing the decrease of the strength of the roll base material and increasing the hardness of the plating film, is used. Soaking time τ is the maximum soaking time τ
When max = 1 × 10 ²⁵ / T ^10.3 is exceeded, the hardness of the roll base material decreases and the wear resistance of the roll deteriorates.

[0008]

FUNCTION The hardness of the plating film hardens as the heat treatment temperature and the heat treatment time increase, and the roll base material hardness softens as the heat treatment temperature and the heat treatment time increase. Further, the wear resistance is not only affected by the hardness of the plating film, but also by the average hardness of the plating film and the roll base material (hardness including the plating layer and the roll base material). In soaking, by keeping the soaking time τ below the maximum soaking time τ max,
A high plating film hardness can be obtained as long as the base material hardness of the roll does not decrease. Therefore, the wear resistance of the roll is improved.

[0009]

[Example] In order to clarify the effect of heat treatment conditions on wear resistance, a roll rolling wear experimental device (test piece: φ80 mm
× 10mm, partner piece: φ160mm × 15mm, slip ratio:
4.4%, partner piece heating temperature: 200 ° C, pressing load: 7
The experiment was conducted using 0 kgf, rotation speed: 3000 rpm, cooling: water lubrication).

For the material of the test piece, forged steel (SUJ-2) heat-treated (hardness: about 800 Hv) was used, and for the material of the mating piece, S45C was used.

The plating baths shown in Table 1 were used.

[Table 1]

The nickel pre-plating thickness is 1 μm and 0.
The thickness of the μm trivalent chromium composite plating was set to 20 μm (for wear test) and 30 μm (for plating film hardness measurement).
The average particle size of SiC was 0.7 μm, and the eutectoid amount of SiC was about 4 to 5%.

Polishing, degreasing, pre-plating, and trivalent chromium composite plating were sequentially carried out to prepare a test piece.

An electric furnace was used as the heating furnace. The atmosphere was air, and the temperature was raised, soaked, and cooled (furnace cooling), and the hardness of the plating film and the hardness of the roll base material were measured using a micro Vickers hardness meter. The measurement results are shown in FIGS. The effects of heat treatment temperature and heat treatment time on the plating film hardness and roll base metal hardness are shown in FIGS. 2 to 5, respectively. Figure 2
Indicates that the higher the heat treatment temperature, the higher the hardness of the plating film. FIG. 3 shows that the longer the heat treatment time, the harder the plated coating becomes. FIG. 4 shows that the roll base material hardness decreases as the heat treatment temperature increases. Further, FIG. 5 shows that the roll base material softens as the heat treatment time increases.

Furthermore, as a result of the rolling wear test, the wear resistance is not affected only by the hardness of the plating film, but the average hardness of the plating film and the roll base material (Shore hardness measured from the roll surface). It was also found to be affected. From the above, it became clear that it is preferable to increase the hardness of the plating film as much as possible within the range where the hardness of the base material of the roll is not reduced.

Referring to the data shown in FIGS. 2 to 5, etc.,
Performing additional experiments, the temperature T when increasing the hardness of the plating film without lowering the base metal hardness of the roll below about 800 Hv
Figure 1 shows the relationship between (℃) and maximum time τ max (hr).
Is. In the figure, a circle indicates a condition that the plating hardness increases and the base metal hardness does not decrease, and a cross indicates a condition that the plating hardness increases but the base metal hardness decreases.

The result of deriving this relationship is expressed by equation (1). τ max = 1 × 10 ²⁵ / T ^10.3 (hr) (1) Note that the applicable range of the formula (1) is 200 ° C. ≦ T ≦ 350 ° C.

Regarding the formula (1), the hardness of the base material of the roll does not sharply decrease when the time τ max is exceeded, but it is useful as a guide for the operation.

Here, a specific example of cold rolling of a steel sheet will be described. A normal steel plate (plate thickness: 1.1 mm, plate width: 250 mm, length: 250 m) was multi-pass cold-rolled using the following work rolls. Roll size Diameter: 165 mm Width: 400 mm Roll base material C: 1% Cr: 3% Si:
0.6% S: 0.4% Mo: 0.3% Fe: Residual pre-plating Nickel Plating thickness: 1 μm Composite plating Matrix: Trivalent chromium Plating thickness: 10 μm Dispersed particles: SiC Average particle size: 4 μm Eutectoid amount: 5 wt % Soaking treatment Temperature: 200 ° C Time: 20Hr Surface hardness 1000Hv Surface roughness 0.3μm Ra Reduction rate is 20%, pass number is 5, rolling speed is 10m /
It was min. The front tension and the rear tension were each 10 kgf / mm ² . A beef tallow rolling lubricating oil was used as the lubricating oil.

As a result of rolling under the above conditions, the roll surface roughness was about 0.29 μm Ra.

As a comparative example, a forged steel roll (surface roughness:
Cold rolling was carried out under the same rolling conditions as described above by using 0.3 μm Ra). As a result, the roll surface roughness is 0.15 to 0.
It was 16 μm Ra, and the roll surface roughness was remarkably reduced as compared with that of the present invention.

[0022]

According to the method of manufacturing a work roll for cold rolling of the present invention, a high plating film hardness can be obtained within a range in which the hardness of the base material of the roll does not decrease, so that the roll exhibits excellent wear resistance. Therefore, it is possible to reduce the manufacturing cost by improving the roll unit consumption due to the extension of the roll life, and further by improving the roll unit unit and reducing the number of rolls possessed.

[Brief description of drawings]

FIG. 1 is a diagram showing a range of good wear resistance with a soaking temperature and a soaking time as variables.

FIG. 2 is a diagram showing a relationship between a heat treatment temperature and Vickers hardness of a plating film.

FIG. 3 is a diagram showing a relationship between heat treatment time and Vickers hardness of a plating film.

FIG. 4 is a diagram showing the relationship between the heat treatment temperature and the Vickers hardness of the roll base material.

FIG. 5 is a diagram showing a relationship between heat treatment time and Vickers hardness of a roll base material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyuki Shiraishi 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd. Corporate Technology Development Division (72) Inventor Fuyasu Yamamoto 20-1 Shintomi, Futtsu City, Chiba Prefecture New Japan Steel Engineering Co., Ltd.Technical Development Division (72) Inventor Matsuo Ataka 20-1 Shintomi, Futtsu-shi, Chiba Shin Nippon Steel Co., Ltd. 2-1 Ishikawa Metal Industry Co., Ltd. (72) Inventor Ryoji Sato 495-143 Niijima, Fukushima, Wakamatsu-ku, Kitakyushu City, Fukuoka Prefecture Fujimura Industry Co., Ltd.

Claims (1)

[Claims] 1. A method for producing a work roll for cold rolling in which a roll surface is plated with chromium, wherein the roll surface is plated with nickel, and hard particles are dispersed on a nickel plating layer. A method for manufacturing a work roll for cold rolling, which comprises performing plating, and soaking time τ ≦ 1 × 10 ²⁵ / T ^10.3 (hr) T: soaking heat treatment at a soaking temperature (° C.).