JPH07155804A - Cold rolling method of stainless steel strip excellent in surface property - Google Patents

Abstract

PURPOSE:To obtain a thin sheet product high smoothness by preventing lubricating oil from sealing in the recessed parts on the surface of a plate metal before rolling by specifying rolling conditions of the coefficient of viscosity of lubricating oil, rolling speed, draft, roll diameter or the like. CONSTITUTION:At the time of cold-rolling a stainless steel strip by plural passes, when the surface roughness and thickness of a material before the rolling of an n-th pass are respectively expressed by sigmaSn and hn, roughness and diameter of the rolling rolls for the n-th pass by sigmaRn and Rn, coefficient of viscosity of the lubricating oil by r7, pressure index of viscosity by gamma, further draft and rolling speed at the n-th pass respectively by rn and Vn, a composite roughness Sn of the roll and material is taken as the condition of an equation I and a gap between the roll and the material where is nacessary to discharge the lubricating oil is taken as the condition of an equation II, cold rolling is executed under the condition satisfying an equation III. In this way, a cold rolled stainless steel sheet having a high surface property of glossness of >= about 650 is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a stainless steel strip having high smoothness and excellent surface properties.

[0002]

2. Description of the Prior Art As a stainless steel thin plate product, JIS
There are BA products, 2B products, abrasive products, etc. which are specified in the standard. There is a strong demand for excellent surface properties having high smoothness in the stainless cold-rolled steel strip for these thin plate products. Conventionally, it has been attempted to control the surface gloss of a cold rolled stainless steel plate by using the oil film thickness equivalent. That is, when the viscosity coefficient of the lubricating oil at atmospheric pressure is η ₀ , the entrance speeds of the roll and the material are U ₁ and U ₂ , the biting angle is θ, and the yield stress of the material is Y, the oil film thickness equivalent t _d was expressed by the following formula and the relationship with the surface gloss was arranged.

[0003]

[Equation 2]

However, the oil film thickness equivalent t _d is derived as a result of analytically solving the Reynolds equation in the lubricating oil outside the roll bite inlet in the ideal state where the surfaces of the roll and the material are extremely smooth. Therefore, it is essentially applicable only when the surface roughness of the roll and the material is extremely small. Furthermore, the equation of the oil film thickness equivalent t _d includes terms such as the penetration angle and the material strength which are difficult to be grasped directly under the rolling operation conditions, and cannot be practically used as the operation parameters.

On the other hand, as a method for improving the surface gloss, for example, as disclosed in Japanese Patent Application Laid-Open No. 2-175005, pre-rolling is performed by applying a lubricant to the extent that seizure can be prevented before cold rolling. In the subsequent finish cold rolling, there is a method of defining the upper limit of the surface roughness of the work roll of the final 1 to 3 passes to reduce the surface unevenness. However, although this method can reduce the surface roughness of the cold-rolled sheet to some extent, it is not sufficient to secure the surface texture having high smoothness, and further improvement is required.

[0006]

A factor that hinders the high smoothness of stainless steel strips is the residual surface irregularities due to the lubricating oil enclosed on the plate surface during cold rolling. The causes of surface irregularities include surface irregularities of hot-rolled steel strips, grinding marks by flaw grinding, roll marks formed by intermediate rolling such as tandem rolling, and oil pitch. Therefore, the present inventors have conducted a study on a manufacturing process capable of obtaining a stainless steel strip having high smoothness and excellent surface properties for effectively and efficiently reducing and eliminating the surface irregularities. .

The present invention clarifies the interfacial condition between the roll and the material for ensuring the condition that the lubricating oil for cold rolling is discharged into the surface recess of the sheet material before rolling without being enclosed during rolling. In addition, the object is to provide a cold rolling method for achieving the same conditions.

[0008]

The present invention was completed as a result of various studies on the behavior of lubricating oil between a roll and a material to be rolled (hereinafter referred to as a roll bite) in cold rolling. In the method of cold rolling a stainless steel strip in m passes (m ≧ 1), the surface roughness and plate thickness of the material before rolling in the n th pass are σ _Sn and h, respectively.
n, the roughness and radius of the rolling roll of the nth pass are σ _Rn and Rn, respectively, the viscosity coefficient of the lubricating oil is η, the pressure index of the viscosity is γ, and the rolling reduction in the nth pass rolling is rn, When the rolling speed is Vn and the synthetic roughness Sn of the roll and the material in the rolling of the n-th pass and the gap Dn between the roll and the material required to discharge the lubricating oil are represented by the equations (1) and (2), respectively, ) The cold rolling method for a stainless steel strip having excellent surface properties is characterized in that cold rolling is carried out under conditions satisfying the formula.

[0009]

[Equation 3]

[0010]

The reason for limiting the present invention will be described in detail below. The inventors of the present invention have determined that as an interface condition between a roll and a material in a cold rolling plate for obtaining a stainless steel strip having a high smoothness surface having a glossiness Gs (45 °) C direction of 650 or more defined by JIS Z8741. It was found that the formula (3) holds. The contents will be described below.

When a SUS430 intermediate rolled steel strip is cold-rolled in 3 passes from a plate thickness of 2.5 mm before cold rolling to a finished thickness of 1.5 mm, the gloss of the cold-rolled plate and the formula (1) are obtained. The relationship between the roll / material composite roughnesses S ₁ , S ₂ , S ₃ shown in (4) and the roll / material gaps D ₁ , D ₂ , D ₃ required to discharge the lubricating oil shown in equation (2) The results of the investigation are shown in FIG. Here, the intermediate-rolled steel strip is a hot-rolled steel strip rolled to an intermediate plate thickness by, for example, a Sendzimir rolling machine or a tandem rolling machine, or a sheet further subjected to intermediate annealing.

As is apparent from FIG. 1, in the cold rolling, the abscissa, that is, the value on the left side of the equation (3) (when m = 3) increases, the gloss decreases, and as the value decreases, the gloss increases. Become. The larger the value on the left side is Sn
The difference between the value and the Dn value becomes large. When Sn> Dn, the lubricating oil discharge gap is sufficiently secured, so that the oil film becomes thin and seizure occurs due to the oil film rupture.
In the case of Dn, the lubricating oil discharge gap is insufficient and the lubricating oil is not discharged and remains in the oil pit.

On the other hand,

[0014]

[Equation 4]

Roll roughness, roll diameter,
To obtain a stainless steel strip having a high smoothness surface with a glossiness on the surface of a cold rolled sheet of 650 or more in the Gs (45 °) C direction by cold rolling at a viscosity of a lubricating oil, a rolling reduction and a rolling speed. You can Desirably, by setting the value on the left side of the expression (3) to be 0.05 or less, the glossiness on the surface of the cold-rolled sheet is improved to 760 or more in the Gs (45 °) C direction, and further surface high smoothing Is possible.

In the above cold rolling, if the viscosity coefficient η of the lubricating oil exceeds 1.0 × 10 ⁻² Pa · sec, the discharging speed of the lubricating oil from the roll bite becomes extremely slow, so the oil after the cold rolling is It remains as a pit and deteriorates the gloss of the cold-rolled sheet. Therefore, the viscosity coefficient η of the lubricating oil is 1.0 ×
It is preferably 10 ⁻² Pa · sec or less. On the other hand, when the pressure index γ of the viscosity is less than 1.0 × 10 ^-9 Pa ^-1 , the lubricating oil spreads too much in the roll bite, and the oil film becomes extremely thin, so that seizure between the roll and the material frequently occurs due to the breakage of the oil film. . When the pressure index γ exceeds 5.0 × 10 ^-8 Pa ^-1 , the discharging rate of the lubricating oil from the roll bite becomes extremely slow, so that oil pits remain after cold rolling.
Therefore, the pressure index γ of viscosity is 1.0 × 10 ^{−9 to} 5.0.
It is preferably in the range of × 10 ^-8 Pa ^-1 .

The action and mechanism relating to the disappearance of surface dents due to the discharge of lubricating oil in cold rolling are not clear, but are presumed as follows. The lubricating oil is introduced into the roll bite due to the depression of the material before cold rolling, but tends to be discharged from the roll bite due to the hydrostatic pressure acting between the roll and the material. Here, the gap between the roll and the material required to be discharged from the roll bite is defined by the viscosity coefficient indicating the fluid characteristics of the lubricating oil and the rolling conditions such as rolling speed, rolling reduction, roll diameter, etc. The lubricating oil is efficiently discharged from the roll bite as long as it is equal to or smaller than the actual size of the discharge passage determined by the roughness of the roll and the roughness of the roll. As a result, the smoothing of the surface remarkably progresses.

[0018]

EXAMPLES Table 1 shows the types of lubricating oils used in the examples of the present invention and comparative examples, the viscosity coefficient from 40 ° C. to 100 ° C., and the pressure index of viscosity. Steel types are SUS430, SUS
304, the roughness σ of the material of each pass in cold rolling
_Sn and plate thickness h _n , roll roughness σ _Rn and radius R _n ,
The reduction ratio r _n , rolling speed V _n , and lubricating oil temperature are shown in Tables 2 and 3.
(Continued from Table 2-1) and Table 4 (continued from Table 2-2). Further, Table 2 to Table 4 show the combined roughness S _n of the roll and the material in each pass in the cold rolling, the gap D _n between the roll and the material, and the interface condition in the cold rolling (3) formula. Table 5 shows the value on the left side and the glossiness Gs (45 °) C direction after cold rolling. The glossiness is measured based on JIS Z8741.

The example of the present invention satisfies the formula (3) indicating the interface condition in cold rolling, and the gloss after cold rolling is 6 as compared with the comparative example.
It is 50 or more, and it can be seen that it has high surface properties.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

[0023]

[Table 4]

[0024]

[Table 5]

[0025]

As is apparent from the above, according to the present invention, a stainless steel strip having a high surface texture having a gloss of 650 or more of a cold rolled sheet can be obtained.

[Brief description of drawings]

FIG. 1 shows the glossiness of a cold-rolled sheet when cold-rolled from a sheet thickness of 2.5 mm before cold rolling to a finished thickness of 1.5 mm using a SUS430 intermediate-rolled steel strip in 3 passes. Relationship between roll / material synthetic roughness S ₁ , S ₂ , S ₃ expressed by the formula and roll-material gaps D ₁ , D ₂ , D ₃ required to discharge the lubricating oil expressed by formula (2) It is a figure which shows the result of having investigated.

Claims (1)

[Claims] 1. A method of cold rolling a stainless steel strip in m passes (m ≧ 1), wherein the surface roughness and the sheet thickness of the material before rolling in the nth pass are σ _Sn and hn, respectively. The roughness and radius of the rolling rolls are σ _Rn and Rn, the viscosity coefficient of the lubricating oil is η, the pressure index of viscosity is γ, the rolling reduction in the n-th rolling is rn, and the rolling speed is Vn. When the synthetic roughness Sn of the roll and the material in the rolling of n passes and the gap Dn between the roll and the material required to discharge the lubricating oil are represented by the equations (1) and (2), respectively,
A method for cold rolling a stainless steel strip having excellent surface properties, which is characterized in that cold rolling is performed under a condition that satisfies expression (3). [Equation 1]