JPS6277423A - Manufacture of ferritic stainless steel sheet superior in workability - Google Patents

Abstract

PURPOSE:To economically manufacture the titled steel sheet, by holding roughly not rolled piece of ferritic stainless steel precipitating a suitable quantity of gammaphase at a specified temp., then finish annealing and coiling it at high temp. CONSTITUTION:Ferritic stainless steel slab contg. by weight about <=1% C, about 10-20% Cr and precipitating >=10% gamma phase is hot rolled. Thereat, after rough rolling completion, the obtd. piece is held at 1,050-1,150 deg.C range for >=30sec, favorably <= about 30min to thoroughly precipitate gamma phase, next finish rolled. The obtd. steel sheet is coiled at >=80 deg.C to accelerate gamma alpha transformation, gamma mother phase is recrystallized and carbonitride is precipitated. By adding 0.08-0.30% Al to the ferritic stainless steel, the coiling temp. can be lowered to 700 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing a ferritic stainless steel sheet with excellent workability. In addition, in the present invention,
Unless otherwise specified, what is shipherite stainless steel?
．． Steel containing 0% to 10 to 20% by weight of Cr is 1% by weight or less.

(Prior art) Conventionally, the manufacturing method for ferritic stainless steel sheets was to hot roll the material to form a hot rolled steel strip, and then heat the material in a Gutchi annealing furnace for 80°C.
After performing hot-rolled plate annealing treatment over several days, such as raising the temperature to 0 to 850°C, holding and cooling, one cold rolling or two or more cold rolling with intermediate annealing in between, final annealing. The product is made with

In the conventional manufacturing method as described above, the annealing treatment performed before cold rolling requires a long time, resulting in poor productivity and high manufacturing costs. In order to eliminate the above-mentioned drawbacks, conventionally, for example, in Japanese Patent Publication No. 49-17932, after hot rolling, it is rapidly cooled and rolled at 600°C or less.
This shows that it is possible to produce a ferritic stainless steel with ridging properties by cold rolling and final annealing without hot-rolled plate annealing. However, when the hot rolling winding temperature is set to 600° C. or less, the ridging properties are improved, but problems arise such as poor deep drawing C% property and high yield stress. Furthermore, Japanese Patent Publication No. 58-32217 discloses that by increasing the hot-rolling temperature to a high temperature of 850 to 950°C, the yield stress, total elongation, and deep drawability become comparable to those of conventional patch annealed materials. However, such high-temperature winding has the disadvantage that the ridging properties deteriorate, as disclosed in the above-mentioned low-temperature winding patent documents.

In addition, in developing a manufacturing technology that can omit the hot-rolled sheet annealing process, the present inventors focused on retaining heat between rough rolling and finish rolling, which was already disclosed in Japanese Patent Application Laid-Open No. 59-25933. An application has been filed for an invention that has been developed. This invention is mainly aimed at promoting the r→α transformation by retaining heat after rough rolling and improving the deep drawing properties.For this purpose, Atf is added to ferritic stainless steel to transform the γ→α transformation. It causes metamorphosis to occur quickly. However, such heat retention has no effect on improving the ridging properties, and therefore, in order to prevent ridging, it is necessary to use other methods such as rough hot rolling with large reduction in the "α+γ" two-phase region. However, large reduction rolling in this two-phase region causes problems such as the formation of hot rolling defects and impairing the interfacial properties of the finished sheet.

(Problems to be Solved by the Invention) The present invention aims to improve the deep drawability and mechanical properties of ferritic stainless steel sheets without considering the rolling conditions, especially when manufacturing ferritic stainless steel sheets by omitting the hot-rolled sheet annealing process. However, it is difficult to simultaneously improve the ridging characteristics, and the aim is to solve six or nine points.

(Means for Solving the Problems) In order to solve the above problems, the present invention specifically limits the hot rolling conditions of ferritic stainless steel, the gist of which is that 10% or more of γ phase precipitates. When hot rolling a ferritic stainless steel slab, after rough rolling, the obtained rough rolled piece is heated to a temperature range of 1050 to 1150°C for 3
After heat retention for 0 seconds or more, finish rolling is performed, and the obtained finish rolled steel plate is rolled at a temperature of 1 degree above 5-800 degrees Celsius, and contains At'io, 08 to 0.30% by weight. When hot rolling a ferritic stainless steel slab in which 10% or more of the γ phase is precipitated, the rough rolled piece is kept in a temperature range of 11050 to 1150°C for 30 seconds or more after rough rolling, and then finish rolled. Obtained finished rolled steel plate 1
! The purpose is to roll it up at a temperature of 1-700°C or higher.

The present invention will be explained in detail below.

The present inventors continued research and investigation in order to resolve the contradiction in material properties disclosed in the above-mentioned known examples, and
→The improvement in the rolling properties caused by γ transformation is not due to the randomization of the cold-rolling texture due to the martensitic phase (M phase) formed after hot rolling and the low-temperature transformed phase, as previously thought. We found that the γ phase generated during heat retention before finish hot rolling has a significant effect of improving ridging properties due to the metallurgical phenomenon caused during finish hot rolling, and furthermore, we found that the high temperature rolling after finish hot rolling described above It was discovered that even if the steel sheet is subjected to cold rolling after the γ→α transformation occurs, the above-mentioned effect of improving the rolling properties is not lost, and the deep drawing properties are also improved, and the present invention has been fully completed. be.

That is, the effect of improving material properties according to the present invention is currently considered as follows.

(1) After completion of rough rolling, the obtained rough hot-rolled piece is heated near the temperature at which the γ phase is most precipitated (hereinafter referred to as TN), so that the γ phase is sufficiently extracted before finishing hot rolling, Then, the α matrix is recrystallized by finish rolling and heat retention.

(2) After the above finish hot rolling, the transformation of the γ phase to the α phase in the hot rolled coil is promoted and α Recrystallization of parent phase and precipitation of carbonitrides.

Normally, ferritic stainless steel does not undergo complete transformation, so a texture is formed during the final hot rolling process, and its preferential orientation is ND/<100> at the center of the plate thickness.

RD/<110> (hereinafter referred to as 45° cube).

This 45° cube ultimately becomes a major factor in the formation of ridging. However, as described in (1) above, if the γ phase is sufficiently precipitated before finish rolling, the γ phase is harder than the α parent phase and becomes an obstacle to deformation, so the texture is randomized. . In other words, it inhibits the formation of a 45° cube, and
D/<110>? develop. This orientation is advantageous in improving the bulging characteristics, and when compared with the 45° cube, it is also advantageous in improving the deep drawing characteristics.

It is also believed that a large strain near the γ phase (high dislocation density) has an advantageous effect on promoting the T→α transformation during winding and recrystallizing the α matrix as described in (2) above.

Generally, when the residual γ phase at the end of finish rolling cannot undergo γ→α transformation during winding and is air-cooled, it transforms into a martensitic phase (hereinafter referred to as M phase) or a low-temperature transformed phase. When a hot-rolled sheet containing all of the M phase as described above is cold-rolled, a texture is formed (especially ND/<100>
, ND/<111>, etc.), and ultimately the ridging properties are improved, but the deep drawing properties are significantly deteriorated. Regarding mechanical properties (particularly yield point), the M phase decomposes during final annealing to increase solid solution C and N9 degrees, resulting in a higher yield stress. On the other hand, if high-temperature rolling that allows γ→α transformation is carried out completely, the M phase in the hot-rolled sheet will be small and the texture during cold rolling will develop, and the deep drawing properties will improve (development of ND/(111) However, the ridging properties deteriorate. (ND/(
111) and ND/(100)C)) Furthermore, the amount of solid solution C and N during final annealing is small, and the yield stress decreases.

However, as in the present invention, when the tube is processed in (1) and subjected to high-temperature rolling (2), the texture during cold rolling develops (ND/<111>, ND/<100>). ), the ridging characteristics do not deteriorate. This inhibits the formation of a 45° cube during finish hot rolling, and if the size of the ND/(100) colony is kept small, ND during cold rolling.
This is thought to be because even if the /(100) orientation develops, the ridging characteristics do not deteriorate because the colony size is small. In addition, the deep drawing properties are more advantageous because the 45° cube is less developed before cold rolling, and the yield stress is better due to less M phase.

As mentioned above, one of the features of the present invention is the contradiction in the dependence of winding temperature on material properties of the prior art. , @Note (1).

The problem can be solved by combining the processes in (2).

Incidentally, in (1) and (2) above, "recrystallization of the α matrix" is also included in the effect, but according to the research of the present inventors, when the γ;α transformation occurs after processing, In the case of recrystallization of the α matrix phase, metamorphosis takes precedence, and recrystallization of the α matrix phase is not a minor problem in the case of the present invention. However, this does not occur at all, and especially when the heat retention temperature is higher than the rough rolling completion temperature in the above (1), or when the winding temperature is high in the above (2), recrystallization of the α matrix occurs. It has also been found that recrystallization of this alpha matrix has an extremely large effect on improving material properties (particularly on ridging properties), so it has been included in the effects of (1) and (2) above.

Next, the effect of At will be described. In general, the transformation of ferritic stainless copper is extremely slow compared to ordinary copper, and a winding temperature of 800° C. or higher is required to satisfy the condition (2) above. However, in normal hot rolling, it is generally difficult to achieve a winding temperature of 800° C. or higher, and variations in the thermal history within the hot rolled coil tend to occur, resulting in a deterioration of the yield b't. To avoid the above problems, for example, "installation of close filler".

"Charging the hot-rolled coil into a heat retention furnace or slow cooling box, etc."
There are countermeasures such as these, but they are not desirable in terms of productivity and cost.

Regarding the above points, the present inventors found that when Att- is added to ferritic stainless steel, the rate of γ→α transformation increases and the lower limit of the winding temperature that satisfies the condition (2) above can be lowered to 700°C. I found out.

Furthermore, At is precipitated during hot rolling and winding, and as a result, the deep drawing properties and mechanical properties of the finished sheet are significantly improved. This is essential when manufacturing steel sheets for drawing without the hot-rolled sheet annealing step.

As described above, the present invention provides the above (1) t (2)
With this effect, the contradictions of the prior art can be resolved, and furthermore, the addition of At can significantly improve the p-material properties and workability.

Next, the reasons for limiting the constituent elements of the present invention will be described.

The reason why the steel types targeted by the present invention are limited to ferritic stainless steel slabs in which 10% or more of the γ phase is precipitated is that, as described above, the present invention utilizes the γ phase during finish hot rolling. In order to achieve this effect, at least 10% or more of the γ phase is required in terms of volume fraction, so it is limited to 109b or more. Needless to say, the upper limit is limited to ferritic stainless steel, with a bulk of 50 inches or less.

The reason why such a slab is heat-retained for 30 seconds or more in a temperature range of 1050 to 1]50'C after rough hot rolling is to fully extract the γ phase before finishing hot rolling. Therefore, as mentioned above, it is desirable that the heat retention temperature is the temperature TN at which the γ phase of iron-copper precipitates the most, and since TN of ferritic stainless steel is generally in the temperature range of 1050 to 1150°C, it is limited to that temperature range. did.

In addition, the heat retention time is not particularly limited as long as it is sufficient time to finish precipitation of the γ phase, but since it takes at least about 30 seconds after normal rough rolling, 30 seconds was set as the lower limit. . The upper limit of the heat retention time is not particularly limited, but it is preferably within 30 minutes from the viewpoint of productivity, surface decarburization, Cr removal, and prevention of abnormal grain growth in the surface layer.

In addition, when winding a finished hot-rolled steel plate of 1800u or more, γ
This is to decompose the phase into an α phase and carbonitride, and to recrystallize it. In the case of general Atf-free ferritic stainless steel, a winding temperature of soo'c or higher is required to sufficiently advance the γ→α transformation, so the temperature was limited as described above. At this time, if the rolled hot-rolled coil ti is charged into the heat furnace and a slow cooling cover is used for slow cooling, γ→
Needless to say, it is useful in promoting α metamorphosis. Furthermore, when using a heat retention furnace, it goes without saying that the heat retention temperature can be lowered by increasing the heat retention time.

The upper limit of the winding temperature is metallurgically the A3 point, and in actual operation it is about 1000°C at most.

Next, the reason for the limitation in the case of ferritic stainless steel containing K ht + will be described. The reason for adding At is that the lower limit of the winding temperature required in the present invention can be lowered to 700°C in order to increase the T→α transformation rate instead of improving the material properties as described above. be. In order to produce the above effect, it is necessary to contain O,OS at a weight of 0.30% or more, and since the effect is saturated at 0.30% by weight or more, the AA content should be reduced to 0.08 to 0.30% by weight. %.

There are no particular restrictions on the slab heating and rough hot rolling conditions, which have a great effect on the quality of the finished product, but the slab heating temperature is from the viewpoint of generating hot rolling defects. The temperature is desirably 1300° C. or lower in order to suppress this and abnormal grain growth.

Also, regarding the rough rolling conditions, it is preferable not to perform large reduction rolling (reduction ratio of 50% or more) from the viewpoint of generating hot rolling defects.

In other words, "low-temperature slab hot rolling (~110°C)" and "rough reduction hot rolling," which conventionally improve material properties (especially ridging properties) but have the contradiction of easily generating hot rolling defects, According to the method of the present invention, all of the deep drawing properties, ridging properties, and mechanical properties can be fully satisfied without using the "method".

This point is also a feature of the present invention.

(Example) The present invention will be explained in detail below based on all the embodiments.

SUS 430 steel with the chemical composition shown in Table 1, ■
.

■ is melted according to the normal stainless steel melting method, and 25
A continuously cast slab with a thickness of 0xta was used. This slab 1200+
Cut into +m thickness x 210m @ x 250” length,
After heating to 1200 tons, rough hot rolling was carried out for 6 times, and 2
As a rough-rolled piece with a thickness of 0 m, it is further subjected to 6 passes of finishing hot rolling.
A hot-rolled sheet with a thickness of 3.0 mm was used. The hot rolling conditions at this time are shown in Table 2.

Heat retention for rough rolling and finish rolling is 4! The rough rolled piece obtained after rough rolling was immediately charged and held in an electric furnace maintained at a temperature at which the γ phase of the r steel type is considered to precipitate the most. In addition, when this heat retention step was not carried out completely, finish rolling was performed after a delay of about 1 minute after the completion of rough rolling. Further, in the winding process, the obtained hot rolled sheet was immediately charged into an electric furnace maintained at each winding temperature after finish rolling, held for 60 minutes, then removed, and air cooled to room temperature. The above-mentioned winding process corresponds to winding in a continuous hot rolling mill on an actual production scale.

After pickling the hot-rolled sheet produced as described above, it was cold-rolled in a cold rolling mill with a work roll diameter of 150 wφ to obtain a cold-rolled sheet with a thickness of 04, and then annealed at 875°C for 40 seconds to produce a finished product. It was made into a board. The r-value and yield stress of this finished plate are determined by the second
They are shown in Table 3 in correspondence with the manufacturing codes in the table. 7 value is a guideline for deep drawing characteristics), and for normal flat plate applications 068~
It is desirable that it be 0.9 or more, and 1.1 to 1.2 or more for deep drawing applications. The ridging height was determined by measuring the ridges of the plate produced when the finished sheet metal was pulled in the rolling direction using a roughness meter. As evaluated by the present inventors, it is usually desirable that the ribbing height is about 20 μm or less, and in applications where there is a strict requirement for ridging of 1%, it is desirably about 18 μm or less. Also, the yield stress is.

A finished board with a thickness of 0.4 mm costs 37 kl? /mz2 or less is desirable, and even lower values are desirable for deep drawing applications.

Table 3 Material Properties As is clear from Table 3, the steel types manufactured according to the method of the present invention (steel type ■■, steel type ■Q10-@
) Fi, it is introduced that the material properties are superior compared to others. For the steel type ■, manufactured based on the method shown in Japanese Patent Publication No. 58-32217, which is a known technology, Although the value and yield stress are sufficient for flat plate applications, the ridging properties cannot be said to be good. Also the winding temperature? Patent 111E to lower
49-17932, which were manufactured according to the method described in Publication No. 49-17932, have excellent gluing properties, but the value of 7 is by no means good, and furthermore, the yield stress is extremely low (which causes problems in normal use). The results are almost the same in (2) where the winding temperature was set at 700°C. On the other hand, in the case (2) manufactured by the method of the present invention, the i value and yield stress are comparable to those of the case (2) manufactured by the method described in Japanese Patent Publication No. 58-32217, which satisfies all flat plate applications, and also has ridging properties. Also based on Japanese Patent Publication No. 49-17932 (■.

■) Shows a good value comparable to that of (2). That is, by the method of the present invention, it is possible to completely eliminate all contradictions in material properties of conventional known techniques. In addition, in cases (1), (2), and (3) in which the winding temperature was lowered by performing heat retention between rough and finish rolling of the present invention, the ridging properties are extremely excellent, but the 7-value and yield stress are not sufficient.

In the case of @species ■ which is 5US430 steel with Atf addition.

Although the Schiff value and yield stress are improved due to the effect of At addition, the creasing properties are deteriorated (■ to 0). In particular, the effect of reducing yield stress is remarkable, and this is due to the N of AtN precipitated during manufacturing.
It depends on fixed effects. @Aside from the absolute value of the characteristic, steel type ■ exhibits almost the same behavior as steel type ■. That is, when the winding temperature is high, the deep drawing characteristics improve, but the ridging characteristics deteriorate. In particular, in the case of steel type (■), the deterioration of ridging properties is remarkable (■ to 0). On the other hand, in the case of the present invention (0
゜ [phase], O), 7 value is about 1.2 and the yield stress is also 3
012 or less, which fully satisfies deep drawing applications, and the ridging properties are also good at 20 μm or less.

In addition, O and U of the comparative methods have low 7 values, so they are not satisfactory for deep drawing applications, but can be used for flat plate applications.

In the above embodiments, a manufacturing method that omitted the hot-rolled sheet annealing process was described, but as mentioned above, the method of the present invention is to reduce the colony size that causes ridging in the hot-rolling process. It goes without saying that the same effect is obtained even if the plate annealing process is performed.In addition, hot-rolled plate annealing? :80
When hot rolling is carried out at 0 to 1000°C for a short time of 10 minutes or less, there is a dependence of the hot rolling winding temperature on the material properties in the present invention, and in this case, the material properties are improved even at a lower winding temperature. This is clear from the idea of the present invention.

For the above reasons, the present invention is not limited to the case where the hot rolled sheet annealing process is omitted.

(Effects of the Invention) As detailed above, according to the present invention, a ferritic stainless steel copper plate having excellent ridging properties and other properties (deep drawing properties, mechanical properties) that are usually satisfied or higher can be produced. ε
Since it can be manufactured economically, it is of great industrial benefit.

Procedural amendment (voluntary) December 6, 1985 Mr. Michibu Uga, Commissioner of the Patent Office ■, Case description 1985 Patent Application No. 214772 2, Name of invention Manufacture of ferritic stainless steel sheet with excellent workability Method 3, Relationship with the case of the person making the amendment Takeshi, representative of the patent applicant 1) Amount 5, Date of the amendment order Showa year, month, day 6 Column 7, Detailed explanation of the invention in the specification subject to the amendment, Contents of the amendment ( 1) In the specification, page 6, lines 11-12, "precipitation, then finish rolling, and heat retention" is amended to "precipitate, then finish rolling, and heat retention."

(2) On page 8, line 11, “Makitori (2nd process)” was changed to “Makitori (processing in step 2)”.
(2) Process)”.

(3) On page 10, line 12, "A/N is precipitated during winding up" is corrected to "A/N is precipitated during winding up."

(4) Page 14, lines 4-5 “SUS 430 ill,■
, , ■ , ko , SUS 430! 11 Correct (■, ■) to ``.

Claims (2)

[Claims] (1) When hot rolling a ferritic stainless steel slab in which 10% or more of the γ phase precipitates, after the rough rolling is completed, the obtained rough rolled piece is heated to a temperature range of 1050 to 1150°C for 30 minutes.
A method for producing a fluorite-based stainless steel sheet with excellent workability, which comprises performing finish rolling after heat retention for at least a second, and winding the thus obtained finish-rolled copper sheet at a temperature of 800° C. or more. (2) Contains 0.08 to 0.30% by weight of Al, and
When hot rolling a ferritic stainless steel slab in which 10% or more of the γ phase is precipitated, after finishing the rough rolling, the obtained rough rolled piece is kept in a temperature range of 1050 to 1150°C for 30 seconds or more, and then finish rolling is carried out. A method for producing a ferritic stainless steel sheet with excellent workability, which comprises rolling up the finished rolled steel sheet obtained in this way at a temperature of 700° C. or higher.