JPH0366402A - Manufacture of cold rolled steel sheet - Google Patents

Abstract

PURPOSE:To subject a steel sheet to cold rolling at high speed without any heat scratch and slippage, by executing a chrome or chrome alloy plating on the surface of one or all rolls after working the work roll surface of the stand having a specified draft in a limited roughness, in a tandem rolling mill. CONSTITUTION:In the cold tandem rolling of a steel sheet 1, the work roll executed with a chrome or chrome alloy plating on the roll surface of one or all parts of the work roll group 2... of the cold tandem rolling mill is used, after working the surface roughness in 0.3-2.0 muRa as the work roll 2 of the stand whose draft is >=10%. The reason why the stand of >=10% draft only is regulated is because of no heat scratch nor slippage being caused in the case of <=10% draft. Also the reason why the surface roughness is limited is because of no slippage being prevented in the case of <=0.3 muRa and in the case of exceeding 2.0 muRa, an adverse effect being exerted on the product surface and the roll wear being quickened. The plating may be limited to the stand which becomes a bottle-neck most.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a cold rolled steel sheet, and more particularly to a method for manufacturing a cold rolled steel sheet by high speed cold rolling that does not generate slips or heat scratches.

(Prior art) Generally, cold-rolled steel sheets are manufactured in a cold tandem rolling mill having 3 to 6 stands, and the material of the rolling work rolls used at that time is 0.8% C forged steel (Its 90). is used, and lubricated rolling is performed using rolling oil.

In recent years, high-reduction, high-speed rolling has been required to improve production efficiency.

However, when high-speed rolling or high-pressure rolling is performed in the conventional method, the temperatures of the tA plate, rolls, and rolling oil rise excessively due to processing heat, making it impossible to perform normal lubricated rolling and causing oil film failure. , the steel plate (-rolled material) and the work roll may come into metal contact. When such metal-to-metal contact occurs, heat scratches that cause seizing of the steel plate and work roll occur. Therefore, the actual situation is that the maximum rolling speed is regulated to prevent heat scratches from occurring.

Fig. 1 shows a schematic diagram of an example of a 5-stand tandem mill. The work roll 2 of NQI to 4 stands is a bride roll (surface roughness 0.1 to 0.2 μRa), and the Na5 stand is used for the next annealing process. A dull roll (surface roughness of 2.0 to 3.5 μRa) is used to prevent seizure.

Figure 2 shows an example of the rolling reduction ratio distribution and rolling speed of each stand under normal conditions.The rolling reduction ratio is lower in the magnetic 5 stand due to rolling with dulling, and the rolling speed is higher in the later stages. . Heat scratches occur under high pressure and high speed.
There are many 114 stands and the rolling speed is limited due to the occurrence of heat scratches on the 4th floor stand. The last stand, Hiro 5 stand, is under low pressure so there is no problem.

Even in the past, as this heat scratch prevention technology, Japanese Patent Application Laid-Open No. 57-156824 and Japanese Patent Application Laid-Open No. 60-2616
No. 09 etc. have been proposed.

JP-A No. 57-156824 discloses that the amount of strip coolant is determined and injected according to the material of the rolled material, the temperature of the strip coolant, the rolling reduction rate, and the rolling speed, and the strip temperature is detected and the set temperature is determined. If it becomes more than that,
This method attempts to increase the amount of strip coolant.

JP-A No. 60-261609 discloses that the surface of the work roll is
This is a technology that prevents heat scratches and obtains a steel sheet with excellent surface cleanliness by coating it with a high-hardness, high-melting-point substance, etc., and lubricating it with mineral oil, etc., which has excellent cleanliness.

By the way, after the cold rolling process, the steel plate is annealed to recover its workability, but during annealing, the rolling oil remaining on the surface of the steel plate becomes graphitized, and carbon in the steel diffuses onto the surface of the steel plate during annealing. There is a problem called "black stain" in which the surface of the TI4 plate is stained black due to the precipitation.

As a technique to prevent this problem of steel plate staining, there is a method of reducing the amount of residual oil in the rolling oil, that is, using a mineral oil type oil in order to improve the cleanliness, but this method has poor lubricity and heat scratches. The disadvantage is that it is more likely to occur. Also,
If the oil type is made from beef tallow, the lubricity will improve, but there is a problem in that the cleanliness will deteriorate and the steel plate will become more likely to get dirty.

Another technique, as shown in Japanese Patent Publication No. 51-6604, is a technique in which an organic sulfur compound such as a mercaptan compound is applied to the surface of a steel sheet before annealing the steel sheet.

(Problem to be solved by the invention) As described above, what is required today is high-speed rolling that ensures the cleanliness of the steel sheet surface and is free from heat scratches, but at present heat scratches occur locally. For,
Even if the temperature of the steel plate is measured, it is not possible to deal with heat scratches, and even if the amount of strip coolant is increased, there is a limit, so it is difficult to dramatically increase the rolling speed.

In addition, as already mentioned, when the type of rolling oil is made from tallow, the lubricity improves, but the main cleanliness is poor (staining of the steel sheet occurs during annealing.) When the type of rolling oil is made from mineral oil, However, the lubricity is poor and high-speed rolling is difficult.Also, when applying an organic sulfur compound to the surface of the steel sheet before annealing, the cleanliness of the steel sheet is ensured even if it is applied to areas where there is a lot of residual rolling oil. Also, if the amount of rolling oil is reduced to ensure the cleanliness of the steel plate, heat scratches will occur.
High speed rolling is difficult.

Furthermore, JP-A No. 60-261609 proposes a technology in which the work roll surface is coated with a high-hardness, high-melting-point material and rolled using mineral oil as the rolling oil, but the work roll surface is coated with Cr plating. When subjected to cold tandem rolling,
Although the coefficient of friction is lowered and heat scratches are significantly improved, there is a problem that slip occurs during rolling, making it impossible to continue rolling.

Thus, the first object of the present invention is to provide a method for manufacturing a cold rolled steel sheet with good steel sheet cleanliness during high speed rolling.

A more specific object of the present invention is to enable high-speed rolling that prevents the occurrence of heat scratches and slips, and also to reduce the concentration of rolling oil, improve product yield, improve rolling efficiency, and roll raw material. It is an object of the present invention to provide a method for manufacturing a cold rolled steel sheet that can improve unit production.

(Means for Solving the Problems) The gist of the present invention is that in cold tandem rolling of steel strips, the work roll surface roughness of a stand with a rolling reduction of 10% or more is 0.3 to 0.3. After processing to 2.0 μRa, the surface of some or all of the work rolls of the cold tandem rolling mill is plated with chromium or chromium alloy and rolled at high speed without slips or heat scratches. This is a method for manufacturing a cold rolled steel sheet.

In cold rolling tandem mills, it has been common practice to use dull rolls only in the final stand and to use blind rolls in the other stands, but according to the present invention, rolls other than the final stand are also plated with chrome to provide a surface with a certain roughness. This is what we do. The idea is completely different from the conventional method. 1) In addition to applying chrome plating to the work roll surfaces of all stands, it is also possible to apply chrome plating to only some work roll surfaces, that is, the work roll surfaces above or below specific stands where heat scratches are likely to occur. It should be noted that the limitation to the rolling reduction rate of 10% or more refers to the rolls of the remaining stands excluding the final stand.

Preferably, the chromium or chromium alloy plating of the roughened rolls includes at least the rolls of the stand immediately before the final stand.

Still another aspect of the present invention is a method for producing a cold-rolled steel sheet as described above, in which the surface of the steel sheet is coated with
If high-speed rolling is carried out with a low concentration rolling oil that will cause the rolling oil to adhere, and then annealing is performed prior to annealing, i.e., the next step is annealing without electrolytic cleaning or other surface cleaning steps, Organic sulfur compounds are applied to the surface of the steel sheet at the entry or exit side of the final stand of a cold tandem rolling mill, or if electrolytic cleaning or other surface cleaning processes are to be performed in the next process, at the exit side of that process. This is a method for producing cold-rolled m@, which is characterized in that it is then annealed.

Because the work rolls are rough-surfaced rolls, slips are prevented, and heat scratches do not occur even with low-concentration rolling oil, and the amount of residual oil is small, so it can be used not only with mineral oils but also with beef tallow. Staining of steel plates can be prevented by applying sulfur compounds.

As described above, according to the present invention, when performing high-speed rolling in a cold tandem mill, the surfaces of the work rolls other than the final stand are also coated with chrome plating to suppress the occurrence of heat scratches, and the work rolls are surface roughness of 0.
By chrome plating at 3-2.0 μRa,
The high-speed rolling targeted in the present invention is about 1,100 m/sin or higher, although it is not particularly limited thereto, to prevent slips during rolling and feature high-speed cold tandem mill rolling.

In addition, although it is unthinkable based on conventional common sense, by using roughened chrome plated rolls on stands other than the final stand, the surface of the steel plate can be increased by 0.05 to 0.2
It was found that even in low-concentration hydraulic rolling where the rolling oil of "gem" remains, the occurrence of heat scratches is suppressed and high-speed rolling is possible.

According to another aspect of the present invention, when the next step after cold rolling is an electrolysis cleaning line, an organic sulfur compound is applied on the outlet side of the electrolysis cleaning line, and annealing is performed as it is after the cold rolling. In such cases, black staining after annealing can be prevented by applying an organic sulfur compound at the entrance or exit side of the final stand of the tandem spring. In particular, when annealing is performed as is, there is less residual rolling oil than in the past, so the degree of improvement in surface cleanliness of the steel plate is remarkable.

(Operation) Next, the present invention will be described in more detail with reference to the accompanying drawings.

First, according to the present invention, in FIG.
The surface roughness of any one of the stands is 0.3 to 2.0.
Chromium plating is performed after setting μRa, preferably 0.5 to 1.5 μRa, and as is clear from the graph in FIG. 2 showing the results of Examples described later, according to the present invention, the rolling speed is The improvement is remarkable, almost 1.5 at rolling speed.
An improvement of twice as much can be seen.

Here, in the present invention, only stands with a rolling reduction ratio of 10% or more are regulated because the problems of heat scratches and slips do not occur when the rolling reduction ratio is less than 10%, and also the roll This is to make it clear that is a roll upstream from the final stand.

In addition, the work roll surface roughness was set to 0.3 to 2.0 μRa, because if it is less than 0.3 μRa, slipping cannot be prevented, whereas if it exceeds 2.0 μRa, it is effective in preventing slipping. This is because it adversely affects the product surface and accelerates roll wear.

The processing method to obtain a surface roughness of 0.3 to 2.0 μRa may be any one of the grindstone grinding method, the Sigitplast method, the electric discharge machining method, the laser machining method, the electron beam machining method, etc.
A whetstone grinding method is preferred from the viewpoint of ease of handling.

Cr plating or Cr alloy plating on the roll surface should be applied to all work rolls, or the normal quantity would be a bottleneck, for example, the 4-stand work roll shown in Figure 1 (it is also possible to limit it to just the upper and lower rolls). Plating may be performed in a limited manner.For the plating process itself, a conventional method may be used.

Figure 3 shows an example of lubricated rolling in the present invention.
．． In stand No. 5, rolling oil is sprayed onto the back surface of the stand through nozzle 3 on the entry side, and after cold rolling is completed, an organic sulfur compound is applied through nozzle 4 prior to the annealing step.

The amount of residual oil on the surface of conventional steel sheets after cold rolling is usually 0.1 to 0.
．． 5 g/m". In this respect, the present invention reduces the
The amount of residual oil regulated as -0.2 g/- is 0.05 g.
This is because if it is less than 0.2 g, lubricity may not be ensured in some cases, and heat scratch prevention and high-speed rolling, which are the objectives of the present invention, may not be sufficiently ensured.
/m”, when annealing is performed directly after tandem rolling, it is difficult to clean the surface of the steel plate because of the large amount of residual rolling oil, even if an organic sulfur compound is applied to prevent brushstrokes on the tandem inlet or outlet side. This is because the oil content may not be good.The amount of residual oil is adjusted by regulating the amount of oil supplied.

Examples of the organic sulfur compound in this case include mercaptan compounds.

In addition, by applying an organic sulfur compound such as a mercaptan-based compound to the surface of the steel sheet prior to the annealing step and annealing it, the cleanliness of the surface of the steel sheet can be ensured and the effect of preventing black stain can be exhibited.

That is, if an electrolytic cleaning line is provided, the organic sulfur compound is applied after the completion of the line, or at the entrance or exit side of the final cold rolling stand if annealing is performed directly after cold rolling.

The amount applied at this time is not particularly limited, but is 0.1 to 0.3 g.
It can be determined according to the amount of remaining oil within the range of /-.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 The entrance side plate thickness is 2.6 with the 5-stand tandem ξru shown in Fig. 1.
~4.5 open, 900~150hm wide steel plate with plate thickness 0.6
Cold rolled to ~3.011 m.

An example of the prior art is shown in case l of Table 1, where the work roll surface roughness is kl, 0.2μRa for 2 stands, Na
3.4 stand is 0.1 gRaSft5 stand is 3
．． It was 0μRa. As for the processing method, the ht~4 stand roll was ground with a whetstone, and the 5 stand was shot dulled after grinding with a whetstone. The roll was not chromium plated and rolled as it was as a forged roll (Hs 90.0.8C-3Cr).

An example of the rolling results of such a conventional method is shown in FIG. 2 as a conventional method, but since heat scratches occur on the 4-stand roll, the rolling speed is 1000 on the exit side of No. 5 stand.
mpH was the limit. Note that the rolling reduction ratio of each stand is also as shown in FIG. 2, and is the same throughout this example.

In Case 2, the roll of Case I was directly plated with Cr and rolled, but slippage occurred in the 3rd and 4th stands at an early stage, making rolling impossible.

Case 3.4 is an example of the present invention, and the roughness of each roll surface of No. 3 and d stands is 0.8 μR by Sittdal processing method.
Case 3 is an example in which only the roll of the Hiro 3.4 stand, which is the neck of the heat scratch, is Cr-plated, and Case 4 is an example in which all stands are C-plated.

An example of the results is shown in Fig. 2 as an example of the present invention. Cases 3 and 4 are almost the same; heat scratches are controlled, No. 5 stand exit speed can be increased to 1500 mpm, and even during rolling. Rolling was possible without slipping.

Example 2 Using the roll of Case 4 in Table 1, the influence of rolling oil concentration was investigated. Case 5, whose results are shown in Table 2, is a comparative example (conventional example), and when rolled with a conventional cold rolling oil at a concentration of 3% (see Figure 3), the The amount of residual oil on the surface of the steel plate was 0.3 a+g/s, and the steel plate was sprayed with a mercaptan compound from the nozzle 3 on the outlet side of the NQ57 tan as shown in FIG. 3, and then annealed as it was.

Case 6 is an example of the present invention, and when rolling is performed with the 5 cold rolling oil concentration at 1%, the amount of residual oil on the surface of the steel plate on the exit side of the Ko 5 stand is 0.1.
mg/-, and on the outlet side of the Na5 stand, the mercaptan compound was streaked 1/- as in Case 5, and then annealed as it was.

As shown in Table 2, when looking at the cleanliness of the product, in case 5 black stains were seen, but in case 6 of the present invention it was good. /w'' according to the method of the present invention, no heat scratches occurred and high-speed rolling was also possible.

Table 1 (Unit: μRa) (Note) O: No Cr plating, .; With Cr plating Table 2 (Effects of the invention) The present invention prevents heat scratches and slips, and enables high-speed rolling of 1500 mpm or more. As a result, rolling efficiency is improved. Furthermore, the industrial usefulness of the present invention is remarkable, as product quality can be improved and material costs for rolling oil and rolls can be reduced.

[Brief explanation of drawings]

Figure 1 is a schematic illustration of a cold tandem mill; Figure 2 is a
A graph showing a comparison of rolling conditions of a cold tandem mill according to an example of the present invention and a conventional example: and FIG. 3 are schematic explanatory diagrams showing an example of another modification of the present invention. 1: Steel plate 2: Work roll 3: Nozzle for rolling oil 4: Nozzle for organic sulfur compound Fig. 1 No, / iJo, 2' do, 3JQ4 Fig. 2 Fig. 3 yJo, S

Claims (2)

[Claims] (1) In cold tandem rolling of steel plates, the rolling reduction is 10
% or more, after processing the surface roughness to 0.3 to 2.0 μRa, chromium or chromium alloy plating is applied to the surface of some or all of the work rolls of the cold tandem rolling mill. 1. A method for producing a cold-rolled steel sheet, the method comprising using a work roll obtained by applying the same method. (2) When rolling using the work rolls, cold rolling is performed with 0.05 to 0.2 g/m^2 of rolling oil remaining on the surface of the steel plate, and prior to the subsequent annealing process, 2. The method for producing a cold-rolled steel sheet according to claim 1, wherein the surface of the steel sheet is coated with an organic sulfur compound and annealed.