JPS6245004B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention has put into practical use a new method of directly cold rolling hot rolled steel sheets with scales attached, by omitting the pickling process of the conventional method of manufacturing cold rolled steel sheets, in which hot rolled steel sheets are pickled and then cold rolled. The present invention relates to a rolling method for cold-rolled steel sheets. In the production of conventional cold-rolled steel sheets, most of the hot-rolled steel sheets are pickled with sulfuric acid or hydrochloric acid to almost completely remove scale generated during hot finishing and coiling, and then cold rolling is performed. However, this pickling process requires a large amount of equipment, and not only does the equipment cost and running cost become enormous, but it also has inherent problems such as having to dispose of a large amount of waste acid that is discharged. . If this pickling step can be omitted, the manufacturing cost of cold-rolled steel sheets will be greatly reduced. As one solution to this problem, the present inventors have researched a method of omitting the pickling process and directly cold rolling hot rolled steel sheets with scales attached (hereinafter referred to as the black scale cold rolling method). 134810 first.
It is proposed in the bulletin. If a hot-rolled steel sheet is subjected to black scale cold rolling with scale still attached, a black steel sheet covered with fine powder scale will be obtained. However, if part of this fine powder scale peels off and gets mixed into the rolling oil, and if lubrication is not performed properly, the rolling condition will become unstable, and the steel plate coating scale will become uneven, resulting in uneven rolling lubrication. There is a technical problem. For lubrication in conventional cold rolling, a method is often used in which an oil agent containing an emulsifier is mixed with hot water to form an emulsion oil for circulation. When this emulsion oil circulation system is applied to rolling lubrication in the black crust cold rolling process, the hot rolling scale is crushed by compressive tensile stress during cold rolling, and furthermore, it becomes fine powder and most of it is deposited on the surface of the steel sheet. However, part of the fine powder scale peels off from the surface of the steel sheet and mixes into the circulating emulsion oil, which is not preferable because it significantly contaminates the rolling oil, rolling rolls, and inside of the rolling mill. When this scale peeling progresses, not only does the scale coating the surface of the steel sheet become non-uniform in the rolling direction and the width direction, but also normal rolling becomes impossible. How to suppress the peeling of the fine powder scale during rolling determines whether or not the black crust cold rolling method is possible. In order to solve this problem, the present inventors conducted detailed research on the cold rolling method with black crusting, and as a result, they discovered a method to solve this problem all at once. The gist of the present invention is to perform cold rolling with black skin using an aqueous suspension containing alkaline soap as an active ingredient as a lubricant. When alkaline soap is dissolved in hot water at 50-70°C, a translucent soluble suspension is obtained. This liquid evenly wets and spreads over the black scale surface of the hot-rolled scale, and has good water repelling and spreading properties, so that a uniform lubrication state is maintained between the rolling roll and the black scale surface, and the fine powder scale after rolling is maintained. It has good adhesion and does not peel off. In more detail, the black scale on the surface of hot-rolled steel sheets is called Wustite.
It is composed of three compositions: FeO, magnetite Fe ₃ O ₄ and hematite Fe ₃ O ₃ . The rolling reduction ratio of these hot rolled steel sheets with black scale
When cold rolled to about 70%, the initially layered scale becomes approximately 0.25 to 1.0 as the rolling reduction increases.
It is crushed down to micro-particles of μm size. For example, as described above, in the case of oil emulsion rolling oil, some of the fine scales may peel off and contaminate the rolling oil, or make the scale deposited on the steel sheet non-uniform after rolling. However, in the aqueous suspension of alkaline soap of the present invention, there is no scale peeling, and the scale adhering to the steel plate after rolling is uniform and does not become uneven. The basic composition of the lubricant of the present invention is an aliphatic alkaline soap,
In addition, it is permissible to add lubricity improvers, rust preventives, antioxidants, antifoaming agents, etc. to the extent that they do not impair the performance of the alkaline soap. The rolling agent concentration is
Although it can be selected arbitrarily depending on the type of rolling material, rolling reduction rate, and rolling mill model, hot-rolled plain steel sheets with a carbon content of 0.05 to 0.1% are rolled at a rolling reduction rate of 50 to 70 using a normal tandem rolling mill. A low concentration water suspension of 0.5-5% is sufficient for cold rolling. Although the rolling agent remains on the surface of the rolled sheet after cold rolling with black crusting, it is a feature of the present invention that since it is soap, it can be easily removed by simple washing such as washing with water. As described above, the present invention has the great advantage of solving the problem of scale peeling and omitting the pickling step in the conventional cold rolled steel sheet manufacturing method in order to make the cold rolling method with black crust possible. The present invention will be described with reference to examples. 1 Test steel sheet Hot-rolled steel sheet coils for manufacturing SPCC cold-rolled steel sheets specified in JIS were collected at a production factory and tested at 3.0 for rolling tests.
A piece sheared with dimensions of mm (plate thickness) x 250 mm (plate width) x 100 m (coil length) was used. 2. Rolling conditions (1) Rolling mill; 1 stand, 4Hi levering mill (2) Roll dimensions: 165 mm (diameter) x 400 mm (body length) using bright surface rolls (3) Rolling speed: 100 m/min (4) ) Rolling schedule Rolling was performed under each lubrication condition according to the rolling schedule shown in Table 1.

[Table] (5) Lubrication method Soap-based rolling lubricant A lubricant with an acid value of 230 whose active ingredient is an aliphatic soap with a content of about 20% in terms of Na soap was immersed in hot water at 60°C. The scale was suspended at a concentration of 3%, and scale oil was supplied to the rolling roll and/or the material intake port while circulating. Emulsion rolling oil A commercially available emulsion type rolling oil containing 60% mineral oil and an emulsifier is used at a concentration of 5% at 50-60°C.
It was used in While circulating the emulsion, spray oil was supplied to the material inlet of the rolling roll. 3. Evaluation The scale peeling behavior during rolling and the degreasing ability of the residual lubricant after rolling were investigated. (1) Situation of scale peeling during rolling (visual observation) It was visually determined whether the scale peeled off during rolling spread on the rolling roll or mixed into the rolling oil and contaminated the rolling oil. As a result, in emulsion hydraulic rolling, the spread of fine powder scale is observed in the rolling rolls and rolling mill during rolling using the rolling scale wheel shown in Table 1, and as the number of coils to be passed increases, the rolling oil becomes contaminated. On the other hand, soap-based lubricants
It was found that there was no staining of the rolling rolls or rolling oil during all passes, and that there was no peeling of scale. (2) Measurement of the amount of scale remaining on the steel plate Table 2 shows the results of measuring the amount of scale adhering to the rolled plate for each pass. In cold rolling with black scale, the scale is pulverized as the steel sheet is stretched and smoothed out by rolling rolls, reducing the amount of scale adhesion. The theoretical scale amount in Table 2 was calculated from the reduction/stretching ratio on the assumption that there was no peeling, and was determined from the following formula. Theoretical scale amount = initial scale amount (hot rolled steel sheet scale amount) x 100 - rolling reduction (%) / 100 It was found that in the emulsion rolling oil, the actually measured scale amount was smaller than the theoretical scale amount and the scale peeled off. With the soap-based rolling lubricant, the measured scale amount and the theoretical scale amount matched, and it was found that there was no scale separation.

[Table] (3) Uniformity of the amount of scale attached In order to investigate the uniformity of the amount of scale remaining on the rolled coil, after rolling for 4 passes (reduction ratio 69%), a sample was measured 10 to 60 mm (edge) from the edge of a 250 mm width plate. and 100～
The amount of scale was actually measured at two locations at 150 mm (center) and three locations at 50 m, 150 m, and 300 m from the top of the rolled coil, and is shown in Table 3. It was found that, compared to emulsion hydraulic rolling, the scale adhesion of soap-based rolling lubricants was more uniform in both the width direction and the rolling direction.

[Table] (4) Degreasing properties When a 50 mm x 150 mm test piece was taken from a rolled coil, immersed in hot water at 60 to 80°C for 30 seconds, and then dried with cold air, a 1% sodium orthosilicate solution was obtained. As a result of measuring the residual oil content (carbon analysis) after immersing it at 90℃ for 10 seconds, washing it with running tap water, and drying it with cold air, it was found that almost no oil was removed by emulsion hydraulic rolling.
It was found that only about 30% of the fat was removed.
On the other hand, in soap rolling lubricants, 80-90%,
It was found that almost 100% of the fat had been removed. It was found that the residual lubricant could be sufficiently removed by simple cleaning. As mentioned above, it was found that cold rolling with black crusting according to the method of the present invention did not cause scale peeling and that residual lubricant after rolling could be easily removed. Note that the steel plate rolled by the method of the present invention is then subjected to continuous annealing or batch annealing. In either case, a clean final product steel sheet can be obtained by simple chemical or mechanical descaling before or after annealing.

Claims (1)

[Claims] 1. When cold-rolling a hot-rolled steel sheet with black scale still attached, a black scale characterized by supplying an aqueous suspension of a rolling lubricant containing an alkali soap as an active ingredient and performing cold rolling. Cold rolling method of steel plate.