JPH0688051B2 - Chrome-plated roll for cold rolling - Google Patents

Description

TECHNICAL FIELD The present invention relates to a chrome-plating roll which is inexpensive and has excellent wear resistance and surface roughening resistance, and is mainly used for cold rolling of steel sheets.

(Prior art) Cold rolling rolls are rolls for skin pass mills for the purpose of improving the flatness and mechanical properties of black steel sheets, tandem mill rolls for cold pressing pickled sheets, and mechanical properties of annealed materials. There are various types of rolls, such as a temper mill roll for improving the above, an embossing roll for patterning a steel plate surface, and a forming mill roll for grooving.

In order to improve the wear resistance of various cold rolling rolls as described above, rolls whose surfaces are plated with chromium have recently been used and have been proven.

Conventionally, light load rolls such as pinch rolls, table rolls and bridle rolls have been plated with chrome. However, since the rolling roll has a large load and the chromium plating is easily peeled off and its practical application has been delayed, the chromium plating roll has also been adopted as the rolling roll due to the recent improvement in plating technology. For example, the invention of Japanese Patent Application No. 63-9405 proposed by the applicant of the present application is one of the improved techniques for plating a roll with chromium.

Generally, a forged steel quenching roll is used as the cold rolling roll. For example, C: 0.8%, Si: 1.0%, Mn: 0.
Forged steel with a composition such as 6%, Cr: 3.0%, Mo: 0.30%, balance Fe (in this specification, all% in the composition of the steel is% by weight) is mainly used, and the surface hardness is about Hs95. There are many.
That is, in order to secure the toughness and wear resistance of the roll, Cr,
Mo, or an alloying element such as W, V, or Co is added, and the surface of the roll body is hardened by hardening.

In addition to the above forged steel rolls, Ni-grain cast iron rolls and Hi-Cr cast iron rolls that have wear resistance with precipitated carbides may be used.

Chromium plating, which has recently become widespread, is often applied to the above-mentioned commonly used rolls, and the material and hardness of the roll itself have not yet been examined for use in the chrome plating roll.

These conventionally used rolls have the following drawbacks, especially when chromium plating is performed.

First, forged steel quenching rolls are very expensive because they often contain alloying elements and require the use of steel with good cleanliness to prevent quenching cracks during quenching. If this is chrome plated, there is a further problem. That is, in order to improve the adhesion of the chromium plating film, electrolytic etching may be performed as a pretreatment for plating. At that time, a forged steel roll having a large amount of alloy components and high hardness easily causes hydrogen embrittlement. To prevent this, an extra step of baking treatment (for example, heating at 200 ° C. × 1 hr) for dehydrogenation is required after the plating treatment.

In the case of cast iron roll, because of the structure of the roll surface,
The adhesion of chrome plating is even worse than forged steel rolls. That is, since the cast iron roll has a structure in which graphite and carbide are dispersed, since the carbide is decomposed into smut (free graphite) by the above etching and covers the surface, the adhesion of the plating film is reduced and the roll life is reduced. Can not be expected to extend.

In the case of forming rolls such as grooved rolls, when the grooves are shallow, the quenching roll is surface-processed to form grooves, while those with deep grooves are roll-processed at the soft base material stage before hardening and then quenched. The former has difficulty in processing a hard surface, and the latter has problems such as quench cracking and scale formation during heating.

(Problems to be Solved by the Invention) An object of the present invention is to solve the problems of the above-described conventional cold rolling rolls, in particular, the problems of rolls to be used with chrome plating on the surface, and the material itself. An object of the present invention is to provide a chrome-plating roll that is inexpensive, has excellent plating processability, and can withstand long-term use.

(Means for Solving the Problem) The present inventor has improved the roll material on the premise that the wear resistance of the cold rolling roll is mainly improved by the chromium plating film on the surface. Achieved the purpose.

The gist of the present invention resides in the following chrome plating roll.

% By weight, 0.1 to 1.2% C, 0.15 to 0.80% Si, 0.30 to
It contains 1.70% Mn, 1.5% or less Cr, the balance Fe and unavoidable impurities, and the surface hardness is Shore hardness (H
s) A chrome-plated roll for cold rolling in which a 60-85 forged steel or cast steel roll is chrome-plated.

In the present invention, cast steel or forged steel is selected as the roll to be plated (hereinafter referred to as roll base material) from the viewpoint of the adhesion of the chromium plating film.

Table 1 shows the test method as shown in FIG. 1 (a chrome-plated roll is rolled in combination with a roll made of S45C and Hs40).
The results are obtained by evaluating the adhesion of the plating film by changing the roll base material. The chrome plating was performed by degreasing the surface of the roll base material with an alkaline solution, followed by electrolytic treatment in the chrome plating solution using the roll as an anode, and then using the roll base material as a cathode under the following conditions. The plating thickness is 10 μm.

Chromium plating solution composition: CrO ₃ 230g /, H ₂ SO ₄ 2.2g / Solution temperature: 50 ℃ Electrolytic treatment condition: 25A / dm ² × 4 minutes Chromium plating condition: 30A / dm ² × 25 minutes As shown in Table 1, the adhesion of the plating film to the rolls of cast steel and forged steel is extremely superior to that of cast iron.

Next, the surface hardness of the roll base material will be described.

Conventionally, it is common knowledge that rolling rolls have a surface hardness of Hs90 or higher in order to improve wear resistance. However, in the chrome plating roll, the plating film has a high hardness such as Hv1000, which contributes to the improvement of wear resistance.
The roll base material itself does not require very high hardness. That is, the present inventor recognizes that the roll base material only needs to have a hardness enough to withstand the rolling surface pressure, and that the adhesion with the chromium plating film is important.

FIG. 2 shows the occurrence of dents (plastic flow) on the roll surface after rolling 5 × 10 ^{4 by} the test method of FIG. 1 by changing the hardness and roll surface pressure of the roll base material.

〔Test condition〕

Roll base material: 0.8% C-0.3% Si-0.4% Mn Forged steel (Hardness Hs40 ~ 80 adjusted by tempering temperature) Chromium plating: Alkali degreasing, electrolytic treatment in chrome plating solution, then plating to a thickness of 10 μm 2 As shown in the figure, when the roll base material hardness is Hs 60 or more, no dent occurs even at a surface pressure of 80 kgf / mm ² or more, and there is no problem in normal cold rolling. On the other hand, the higher the hardness,
Naturally, it can withstand high surface pressure. However, in order to increase the hardness, it is necessary to add an alloying element for improving hardenability, and also severe heat treatment is required, which causes problems such as an increase in roll price and quenching cracks, and a grooved roll. However, there is a problem that processing becomes difficult. When the rolling roll is worn or roughened, the body is ground and reused.However, it is sufficient to secure Hs60 or more in the so-called effective diameter range from the initial diameter to disposal, and the quenching depth can be increased. Considering this, surface hardness up to Hs85 is sufficient.

The steel type of the roll base material should be as inexpensive as possible as long as the above surface hardness is secured. Further, addition of alloying components must be minimized to prevent hydrogen embrittlement due to electrolytic etching performed as a pretreatment for plating. From this point of view, the material of the roll of the present invention is determined by the weight%, 0.1 to 1.2% C, 0.15 to 0.80%
Si, 0.30 to 1.70% Mn, 1.5% or less Cr, balance F
Cast steel or forged steel consisting of e and inevitable impurities.

In the above composition, C is 0.1% or more in order to secure hardenability and obtain a desired hardness, but if it exceeds 1.2%, toughness decreases and hardenability deteriorates, so the upper limit is made 1.2%. There is. Si is a deoxidizing component and also helps improve hardenability. However, if present in a large amount, toughness is reduced, so 0.15 to 0.80% is an appropriate content. Mn is necessary as a deoxidizing and desulfurizing component, and serves as an element for improving hardenability to improve strength and toughness. 0.30% or more is required to obtain this effect. However, if the content exceeds 1.70%, the increase rate of the effect is small and the cost is only increased. Cr has a remarkable effect in improving quenching. However, the addition of a large amount defeats the purpose of the present invention to provide an inexpensive roll, so the content is limited to at most 1.5%. If the content exceeds 1.5%, the toughness may decrease.

The method for manufacturing the roll of the present invention is as follows.

First, the roll base material may be manufactured by a conventional roll manufacturing method. That is, for example, in the case of cast steel, the components are melted and adjusted in an electric furnace, and in the case of cast steel, the hardness is adjusted by casting into a predetermined shape and heat treatment. In the case of forged steel, it is ingot, forged and heat treated.

As described above, the chromium plating is preferably performed by degreasing and electrolytically etching (electrolytically treating with a roll as an anode in a chromium plating solution) before plating.

(Example 1) Five types of rolls shown in Table 2 were prepared as the rolls of the skin pass mill for rolling the black leather plate.

The roll size is 630 mmφ x 1950 mm. This roll was treated under the conditions in Table 3 to obtain a thickness of 10 μm and a surface hardness of Hv10.
I applied 00 chrome plating.

The roll manufactured in this way is installed in a skin pass mill and subjected to rolling of black leather steel plate (JIS SPHC, plate thickness 3.0 mm) until the roll life is exhausted due to abrasion or peeling of the plating layer (replacement or repair is required) The amount of rolling was examined. The results are shown in Table 2.

From this result, it can be seen that the durability of the chrome-plated forged steel roll is extremely excellent.

(Example 2) As a roll for a temper mill of an annealed steel plate, a roll shown in Table 4 (size 700 mmφ x 1730 mm) was manufactured. The plating conditions are the same as those shown in Table 3.

Using the above rolls, temper rolling of JIS SPCC annealed cold rolled steel sheets was performed. Table 4 shows the amount of steel sheets that could be rolled before roll repair.

The high alloy forged steel rolls shown in Table 4 are those conventionally used. By applying chrome plating to this,
The roll life is greatly improved, but for that purpose, a baking treatment (here, heating at 200 ° C. × 2 hr) is required. In contrast, the low alloy forged steel roll of the present invention has an equivalent life without the baking treatment. It is clear that the rolls of the present invention are inexpensive, even when looking at the alloy components contained.

(Example 3) As a groove forming roll for a black leather plate, a roll shown in Table 5 (size 550 mmφ x 1300 mm) was manufactured. The plating conditions are the same as those shown in Table 3.

The above roll has a corrugated groove shape with a depth of 10 mm, the surface of which is processed by a cutting tool after heat treatment of the base material. If the base material is low alloy cast steel, this surface processing is easy. Using the above rolls, JIS SPHC black leather plate was formed and rolled. Table 5 also shows the amount of steel sheets that could be rolled before roll repair.

Similar to the results shown in Table 4, the life of the high alloy forged steel rolls conventionally used is improved by chrome plating. However, because of the roll change due to plating peeling,
The rolling amount is only 1000 tons. On the other hand, the low alloy cast steel roll of the present invention plated with chrome,
Good plating adhesion and significantly improved roll life.

(Effect of the invention) As is clear from the examples, the present invention provides a roll for cold rolling which has a life equivalent to or higher than that of conventional expensive high alloy steel and alloy cast iron. It is a thing.

Since the base material of the roll of the present invention is not too hard, it can be easily processed into a groove forming roll. Since the chrome plating having good adhesiveness is applied, the wear resistance and the surface roughening resistance are superior to those of the conventional chrome plating roll.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a rolling test for examining the life of a chrome plating roll, and FIG. 2 is a diagram showing the results of examining the influence of the surface hardness of the roll base material and the roll surface pressure on the dent of the chrome plating roll,
Is.

Claims (1)

[Claims] 1. By weight%, 0.1-1.2% C, 0.15-0.80%
Si, 0.30 to 1.70% Mn, 1.5% or less Cr, the balance consisting of Fe and unavoidable impurities, and the surface hardness of wrought steel or cast steel rolls with Shore hardness (Hs) of 60 to 85 A chrome-plated chrome-plated roll for cold rolling.