JPS60187404A - Hot rolling method of stainless steel - Google Patents

Abstract

PURPOSE:To prevent a stainless steel from producing surface flaws by supplying an aqueous solution containing caroxylic acid to a material to be rolled between the passes of rough rollings and reforming oxidized scales on a metallic surface part exposed by stripping the former oxidized scales. CONSTITUTION:In hot rolling a stainless steel containing >=11% Cr, an aqueous solution containing carboxylic acid or a liquid prepared by adding a rolling lubricating-oil to said solution is supplied to a material to be rolled between the passes of rough rollings or the passes of rough and finish rollings. Further, mono or dicarboxylic acid is preferable for said acid. In this way, oxidized scales are reformed in a short time, and a metallic surface, exposed by stripping the former oxidized scales stuck to the surface of material during rolling, it covered by the reformed scales, and then the material surface is prevented from producing oxidized scales in the next rolling.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for hot rolling stainless steel, which aims to prevent the occurrence of surface defects on a rolled material during the hot rolling process.

Stainless steel products are required to have a beautiful surface appearance and are also susceptible to minute scratches. However, since stainless steel has high deformation resistance, if flaws occur during the hot rolling process, the flaws do not disappear easily even after subsequent cold rolling, and minute flaws persist. For this reason, conventional hot rolling of stainless steel has required strict control to prevent flaws from occurring.

However, in the past, when stainless steel with a Cr content of 11% or more was hot rolled, surface defects such as cracks and cracks due to rolling roll seizure often occurred. Generally, when such surface flaws occur.

If the amount of occurrence is significant, scrap it or
The only way to repair minor defects is to take care of them in addition to the polishing process, so if a single surface defect occurs, the yield and production efficiency will drop significantly. Furthermore, when seizing occurs on a rolling roll, the roll cannot be used and must be replaced after stopping rolling, resulting in an increase in the roll unit consumption and rolling cost.

Conventional countermeasures to prevent such surface defects include raising the total rolling temperature of the rolled plate material and reducing the deformation resistance during rolling to reduce the rolling load. Methods have been adopted such as reducing the number of rolling holes or increasing the number of rolling defects to reduce the rolling rate of the pass, but surface defects cannot be completely prevented, and furthermore, production efficiency decreases and production costs increase. ? The drawback of inviting people is rare.

Has this invention increased production efficiency or reduced production costs in recent years? In view of the fact that it is necessary to increase the slab RL weight and perform rolling under harsh conditions for the purpose of improving the yield rate, etc., it is necessary to increase the slab RL weight and perform rolling under harsh conditions. The present invention provides a rolling method that does not generate surface defects.

The present inventors investigated the causes of surface flaws such as creases and cracks due to rolling roll seizing that occur during the hot rolling process of stainless steel V-stainless steel under rolling conditions as shown below. As a result of investigating various changes, it was found that the oxidation scale on the surface of the rolled material was completely peeled off during the rolling process, exposing the metal surface of the rolled material.

Table 1 shows the rolling conditions for a 200 m long rolled material with a thickness of 3 o IIO 11, a length of 100 mm and a length of 100 m, heated at 1150°C for 1 hour to investigate the cause of surface defects, and then hot rolled. Use the one shown in purple.

(3) (4) In Table 1, rolling conditions A, Bs, and C are all rolled in the width direction, and rolling in the thickness direction is 'fil-?
Although it is set to be performed with &, the rolling amount of widthwise rolling ′j
Cs, J: The arrangement between the rolling nozzles in the width direction and the thickness direction is changed, and the layering situation of the oxidation schools is made to be different. In other words, rolling condition A has a total rolling amount of 2 cm in the width direction, which is small (
Then, only the surface oxide scale generated during heating is removed.

The thin material on the base material side remains. This remaining thin oxide scale does not change after a short time of air cooling, so during rolling in the thickness direction, the sheet is rolled while being surrounded by the thin oxide scale. On the other hand, in both rolling conditions B and C, the rolling amount in the width direction is increased to 104, so that most of the oxidized schools generated during heating are peeled off from the base metal, leaving an exposed part of the wire mesh surface. This is what I did. Then, in the case of rolling condition Ha), the exposed part is maintained even during thickness direction rolling, and in the case of rolling condition C, it is oxidized by heating to 1100°C, and a thin oxide scale is regenerated. be. Therefore, in the case of rolling conditions Ag and C, the material to be rolled is wrapped in a thin oxide school during rolling in the thickness direction, but in the case of rolling condition B, the exposed metal surface is rolled. It will be rolled.

Table 2 shows hot-rolled stainless steels with different chromium contents under the rolling conditions set above.

Surface conditions of the rolled material and rolling rolls after rolling Table 2 (Note) ○ indicates no abnormality 17) As shown in Table 2 (with the metal surface of the rolled material exposed) In the case of rolling condition B in which rolling 7 in the thickness direction is performed, seizing and cracking of the rolling rolls will occur if the Cr content of the rolled plate material is 11% or more.

However, when Table 2 is examined in its entirety, (1) rolling conditions A and C in which rolling is performed in the thickness direction with the rolled plate surrounded by a thin oxide scale; and (2) rolling conditions. Even when rolled at B, when the material to be rolled is low Cr steel, seizing and cracking of the rolling rolls did not occur in any case.

So, why is there no seizure or cracking of the rolling roll in these cases? When considering (11), it is thought that the thin oxide scale plays the role of lubrication, and (2
), low Cr steel has poor high-temperature oxidation resistance and has the property of regenerating oxide scale 2 in a short period of time, so does this oxide scale play a similar role? It is thought that this has been achieved. Is this causing seizing or cracking of the rolling roll? It can be seen that this can be prevented by completely regenerating the thin oxide scale on the exposed metal surface of the rolled material. The rolled material has a Cr content of 11% or more.
Seizure of rolling rolls when made of steel (8) The reason why sheath cracks occur is because it has excellent thermal oxidation resistance, so oxide scale does not regenerate on the exposed metal surface, and frictional resistance is large. Recognize.

Conventionally, with regard to oxidized scale, if it is rolled while it is attached to a rolled plate, it will be pushed into the surface of the J:υ plate and cause indentation scratches. Descale as completely as possible by injection, etc.
Furthermore, it was considered preferable that the particles formed during rolling be completely descaled during the rolling process. However, as is clear from the above investigation, if the base metal surface is completely decooled and the base metal surface is exposed, surface defects will occur during hot rolling.

The oxidized school can be simply removed; however, it is necessary to control its amount appropriately, and if the base metal surface is exposed, it may be necessary to regenerate it.

Therefore, the present invention provides a rolling method in which a thin oxidation school is entirely regenerated on the exposed metal surface of a rolled plate during the hot rolling process in order to prevent surface defects.

As mentioned above, in stainless steel with a Cr content of 11% or more, oxide scale is difficult to regenerate in a short period of time in the atmospheric environment.

Therefore, in the second aspect of the present invention, the organic acid is completely supplied, the oxidation is completely promoted by the organic acid, and the oxidized scale is regenerated in a short time.

However, in order to prevent the corrosion of stainless steel and equipment, it is important to use sulfonic acids (those that leave inorganic acid radicals are not good luck, so we use carbon &'&, which is included in all horizontal rolling lubricants, etc.). We will supply the following items.

That is, the present invention applies an aqueous solution containing carboxylic acid and a rolling lubricating oil to the rolled material between passes of rough rolling or between passes of rough rolling and finish rolling in hot rolling of stainless steel with a Cr content Vt of 11% or more. By supplying either 10,000 yen or both, the oxidized school adhering to the surface of the liquid-rolled material during rolling will be peeled off and the oxidized scale will be completely regenerated on the exposed metal surface. Do rolling? This article provides a complete method for hot rolling stainless steel with special features.

In the present invention, the carboxylic acid contained in the aqueous solution or rolling lubricating oil may be an aliphatic acid, regardless of the species, as long as it promotes the total oxidation of the exposed metal surface of the rolled material.

It can be aromatic. However, in terms of base, polybasic acids of tricarzenic acid or higher are expensive, so mono- and dicargenic acids are preferred. Of course, in the case of the present invention, only one type of carboxylic acid is included in the aqueous solution or rolling lubricating oil (
Something with a different molecular weight and structure? There is no problem even if it contains 2m class or more.

Does the oxidized scale that is regenerated by promoting oxidation with carboxylic acid in the present invention have the Kiriname effect? It is for the purpose of obtaining
Thick oxide scale, which is generated during the heating process before hot rolling, can cause indentation scratches, so it should be thin.

In addition, even in the hot rolling of the present invention, the oxidized scale that forms on the rolled material during the heating process before hot rolling is extremely thick, and if it is rolled with the scale still attached, indentation scratches will occur. Then, descale using high-pressure water injection. However, when descaling, it is necessary to control the metal surface so that it is not exposed and surface defects such as seizure and cracks occur.

The present invention will be fully explained below with reference to Examples.

Table 3 Slab of 5US430 steel with g4cr content 17.1% (thickness 3200111. width 1050mm, weight 315
7 tons) After soaking at 1100℃ in a heating furnace, it is roughly rolled to 2
5111111, width IQ59w, then finish rolling to thickness 3.61111.11! How does the occurrence of seizing and cracking of rolling rolls when making hot-rolled coils of a1060 ym change depending on whether or not a carboxylic acid-containing aqueous solution and rolling lubricating oil are supplied to the rolled material8 and the supply conditions? Ka'Ik
It was inspected by M.

The carboxylic acid-containing aqueous solution and rolling lubricating oil (hereinafter referred to as organic acid solution) were supplied to the material to be rolled through an injection nozzle, and the organic acid solution was completely injected onto the entire width 8 and near the edges of the material to be rolled. The reason why gold was also targeted was that the oxidized scale of the rolled material KfCjN generally peels off during rolling due to strain during vertical rolling (width direction rolling), and the amount of rolling in the vertical direction This is because when the oxidation school is small, peeling of oxidized schools occurs concentrated near the edges.

3. Rough rolling was carried out according to the following A schedule, and the organic acid solution was supplied between the rough rolling and the cess in the case of Example 1.2, and between the rough rolling and finish rolling in the cases of Examples 3 to 5. I did it in the middle of nowhere.

(Heating) → Vertical rolling l-+ Horizontal rolling l → Horizontal rolling 2-+
Vertical rolling 2→Horizontal rolling 3→Horizontal rolling 4→Vertical rolling 3→Horizontal rolling 5→Vertical rolling 4→Horizontal rolling 6→(finish rolling) *From the organic acid solution supply table 3 of Example 1.2, the rolled material In the case of the conventional method in which an organic acid solution is not supplied during rolling, oxidized scale is peeled off during rolling and no oxide scale is formed on the exposed metal surface, resulting in seizure defects and cracks. However, the flaws disappeared when the entire organic acid solution was supplied. In Example 2.4.5, the entire organic acid solution was supplied only near the edges, but surface flaws were prevented from occurring. When the material to be rolled is wide and the amount of rolling in the width direction is small, surface flaws can be prevented by simply supplying all the organic acid WJg near the edges, so it is inexpensive when the amount of rolling in the vertical direction is small. It can be prevented.

In Example 8 above, a case was shown in which the organic acid solution contained a class 13 carboxylic acid, but it is clear that the same effect can be obtained even if an I\IL solution containing two or more types of carboxylic acids is supplied. It is.

Further, in the above embodiments, the case of hot rolling of steel plates is shown, but it is clear that the present invention can also be applied to hot rolling of steel materials such as stainless steel sections, wire rods, etc.

As described above (according to the present invention, surface flaws do not occur even when hot rolling is carried out under conventional rolling conditions that would cause surface flaws, so hot rolling does not occur even under harsh rolling conditions that correspond to the increase in the number of slab motorbikes). Rolling improves yield and productivity and reduces physiological costs.

According to the present invention, since the surface flaws are completely prevented by supplying an organic acid solution to the material to be rolled during rolling, the gE and cost associated with the supply are slightly increased. However, this increase in production cost is small compared to the reduction in production cost due to improvements in yield and productivity, so the overall production cost is reduced.

patent applicant Nisshin Steel Co., Ltd. agent Susumu Fujiran

Claims (1)

[Claims] (1) In the hot rolling of stainless steel with a Cr content of 11% or more, an aqueous solution containing carboxylic acid 8 is applied to the rolled material between the A groove 1 of rough rolling or between the rough rolling and finish rolling. By supplying 10,000 times of either rolling lubricating oil or rolling lubricating oil, the oxidized scale adhering to the surface of the rolled material during P1 rolling is peeled off and oxidized scale is regenerated on the exposed metal surface. A method for hot rolling stainless steel in which the next step of rolling is carried out in t%. (2) If the material to be rolled is a wide material and the amount of rolling in the width direction is small, supply water bath liquid 3 and rolling lubricant to the material to be rolled in the range 2007111 from the edge in the width direction. A method for hot rolling stainless steel according to claim 1, wherein the temperature is expressed as a percentage.