JPS62136524A - Production of martensitic stainless steel sheet having excellent workability and oxidation resistance - Google Patents

Abstract

PURPOSE:To produce the titled stainless steel sheet having excellent workability and oxidation resistance by subjecting a specifically composed martensitic stainless steel stock to hot rolling at the specified coiling temp. and allowing the rolled sheet to cool then immediately subjecting the steel sheet successively to descaling, cold rolling and finish annealing. CONSTITUTION:The martensitic stainless steel stock contg., per weight %, <=0.40% C, <=1.0% Si, <=1.0% Mn, <=0.6% Ni, 10-15% Cr, 0.025-0.3% Al, and 0.025-0.060% N and consisting of the balance substantially Fe and inevitable impurities is hot rolled and the coiling of the hot rolled steel strip in said rolling stage is executed in a 650-800 deg.C range. The steel strip is then subjected successively to descaling, cold rolling and finish annealing without annealing of the hot rolled sheet after allowing the same to tool. The cold rolled sheet of the martensitic stainless steel having the excellent workability and oxidation resistance is thus obtd.

Description

[Detailed Description of the Invention] [Industrial Field of Application] In connection with the production of martensitic stainless steel sheets used in Western tableware, etc., the invention provides excellent workability and oxidation resistance without the need for hot-rolled sheet annealing. The results of the developmental research on acquiring gender are proposed below.

In general, martensitic stainless steel is widely used in applications that require relatively mild corrosion resistance, such as Western tableware and utensils, and its components include CO, 40wt% or less (expressed simply in % for simplicity), Si 1. 0wt% or less! Jn
l, 0% or less, Mn 1.0% or less, Cr'11.5-1
It generally contains 3.5%, and its manufacturing method is to soften it by hot rolling and batch annealing, followed by descaling, cold rolling, and final annealing. Usually, it is considered a product.

[Conventional technology]

Special Publication No. 58-41327 regarding omission of hot-rolled plate annealing process
According to the publication, an example of Al-containing ferritic stainless steel is disclosed, but in this case, high-temperature winding and subsequent heat retention are used as a substitute, and the composition is low in N, and in particular, it is difficult to soften and process. However, there is no consideration given to martensitic stainless steel, and no prior technical literature discloses martensitic stainless steel.

[Problem that the invention seeks to solve]

Batch annealing after hot rolling in the conventional manufacturing method for martensitic stainless steel generally takes several tens of hours, which is an extremely inefficient process. If a hot rolled sheet is annealed for a long period of time, a Cr-free layer will be formed on the surface of the hot rolled sheet, which is particularly problematic for martensitic stainless steel sheets having a relatively low Cr content.

In other words, the Cr-free layer on the surface layer caused by hot-rolled sheet annealing causes deterioration of the oxidation resistance of the surface, so thick scales are formed on the steel sheet surface during finish annealing in the cold-rolled steel strip manufacturing process after hot-rolled sheet annealing. On the other hand, when the surface is processed into a beautiful surface by buffing etc. after finishing annealing, the residual scale generated by finishing annealing makes polishing work difficult. It can also be a cause.

For the problems caused by the formation of a Cr-free layer as described above,
In the descaling step after hot-rolled sheet annealing, for example, the pickling time is sufficiently long, the surface layer is removed sufficiently thickly, and the Cr-free layer is removed, thereby preventing deterioration of oxidation resistance during final annealing. The disadvantages are that the pickling time becomes longer, the amount of chemical solution used increases, leading to an increase in cost, and furthermore, it is difficult to dispose of the pickling waste liquid from which a large amount of metal has been eluted.

Therefore, the inventors investigated and conducted an experiment on a method of preventing the formation of a Cr-free layer by omitting hot-rolled sheet annealing, but they simply annealed a hot-rolled sheet of martensitic stainless steel using a conventional manufacturing method. If you simply omit
Although the effect of reducing the Cr-free layer was remarkable, it was found that the mechanical properties of the cold-rolled product, particularly the workability, were significantly inferior due to insufficient softening.

Therefore, the present invention can sufficiently soften and homogenize a hot rolled sheet even when hot rolled sheet annealing is omitted in order to prevent the formation of a Cr free layer due to hot rolled sheet annealing, and therefore the Cr free layer can be sufficiently softened and homogenized. Problems caused by formation, typically the oxidation resistance of cold-rolled steel sheets, and problems caused by simply omitting hot-rolled sheet annealing, typically deterioration of the mechanical properties of cold-rolled steel sheets, especially workability. It is an object of the present invention to provide a method for manufacturing a martensitic stainless steel sheet having excellent workability and oxidation resistance, which advantageously solves the problem of a decrease in oxidation resistance.

[Means to solve the problem]

The above objectives can be effectively met by the following procedure.

C: 0.4 Qwt% or less Si: 1. Q wt% or less Mn: 1, Q wt% or less Ni: 0.6 wt% or less Cr: 10 to 15 wt% 810.025 to 0.3 wt% N: 0.025 to 0.060 wt%, the remainder being substantially A martensitic stainless steel material consisting of Fe and unavoidable impurities is hot-rolled, and the hot-rolled steel strip is wound up at 650 mm in this hot rolling process.
Excellent workability and oxidation resistance, characterized by performing descaling cold rolling and finish annealing in sequence at a temperature range of ℃ to 800℃, followed by cooling without performing hot-rolled plate annealing. A method for producing martensitic stainless steel sheets.

As a result of repeated experiments, the inventors investigated the composition of martensitic stainless steel and the winding conditions during hot rolling, and found that Al: 0,025-0.30
%, N: 0.025 to 0.060%, and by performing winding during hot rolling in a temperature range of 650 ° C to 800 ° C, cold rolling was performed after descaling without hot-rolled plate annealing. It has been found that a cold-rolled steel sheet having far superior workability can be obtained when a long-time batch annealing is performed according to the conventional method.

1.- When conventional batch annealing is performed on a hot-rolled martensitic stainless steel sheet, the surface layer has a thickness of approximately 20 μm.
In contrast to the formation of a Cr-free layer, the thickness remains at about 3 to 6 μm at the end of hot rolling before annealing, so the method of the present invention, which does not involve hot-rolled sheet annealing, also provides excellent oxidation resistance of cold-rolled sheets. Results will come.

[For production]

In this invention, as mentioned above, Aβ and N are actively contained in the steel, and the hot rolled steel strip is wound at a temperature of 650 to 8
By performing the hot rolling in a temperature range of 00°C, it is possible to sufficiently homogenize and soften the hot rolled sheet.

That is, if L and N are simultaneously contained in the steel, a large amount of fine IN will precipitate in the steel sheet during hot rolling, and recrystallization of the steel sheet will be activated around this precipitate during cooling after winding. Recrystallization and softening are promoted.

Furthermore, since the A1 transformation point increases due to the inclusion of Al1, the T→α transformation during the cooling process after winding is promoted, which is advantageous in contributing to softening.

Here, the content of 8β and N is 0.025% each.
If it is less than 0, the amount of IN precipitated during hot rolling is small, and the effect of promoting recrystallization and softening after winding of the hot rolled sheet due to AβN precipitation is not recognized. Therefore, the lower limits of l and N are each 0.
．． 025%.

On the other hand, even if the Aβ content exceeds 0.30%, the effect does not increase any further, and if the N content exceeds 0.06%,
An increase in the amount of N actually makes the steel sheet harder, leading to problems such as occurrence of edge cracks during hot rolling and deterioration of mechanical properties.

Therefore, the upper limit of Al1 is 0.30%, the upper limit of N is 0,
It is necessary to set it to 0.060%.

Next, the steel components other than Aβ and N may be substantially the same as those of conventional normal martensitic stainless steel.

C is an element necessary to ensure strength, but 0.4
If it exceeds 0%, the steel plate will become hard, so set the upper limit to 0.40.
%.

Although Si is effective as a deoxidizer, if it exceeds 1.0%, toughness deteriorates, so the upper limit was set at 1.0%.

Mn is effective in improving strength and toughness, but 1.0%
If it exceeds 1, the mechanical properties of the steel plate will deteriorate, so the upper limit is set at 1.
．． It was set to 0%.

Ni is an element that improves corrosion resistance, but since it is an expensive element, the upper limit has been set at 0.6% due to cost and balance considerations.
And so.

Cr is a basic element in martensitic stainless steel, and 10% or more is required to obtain the necessary corrosion resistance.Although increasing the amount of Cr added improves corrosion resistance, the corrosion resistance for martensitic stainless steel applications is 1
Since 5% or less is sufficient, it was set within the range of 10 to 15%.

By controlling the winding conditions during hot rolling of martensitic stainless steel having the above-mentioned components, a cold rolled steel sheet with excellent workability and oxidation resistance can be obtained.

Regarding the upper limit of the coiling temperature of hot rolled steel strip in the hot rolling process, when coiling is performed at a temperature exceeding 800°C, the γ→α transformation is further promoted due to the annealing effect in the cooling process after coiling. Although it is advantageous for softening the steel sheet, it is limited because the oxidation resistance during final annealing of the cold-rolled sheet is poor due to the increase in the amount of Cr-free layer generated during the cooling process after coiling. If the temperature is lower than 650°C, the r→α transformation and recrystallization of the steel sheet will not occur sufficiently, making it impossible to obtain good workability of the cold-rolled sheet.

For the above reasons, the coiling temperature of the hot rolled steel strip is set at 650°C to 800°C.
℃ range.

The cooling rate of the coil after winding may be as long as it is allowed to cool in the general atmosphere, and specifically, the cooling rate may be lower than 300°C/hr between the winding temperature and 500°C. .

(Example) (A) steel, (B) steel, (C) steel with chemical components shown in Table 1,
(D) Steel and (F) I were used as test materials, and continuous casting slabs of each steel were hot-rolled to form hot-rolled plates with a plate thickness of 3.5 mm,
At that time, these hot-rolled steel strips are wound at a temperature of 600°C to 850°C.
The experiments were carried out at various temperatures at 50° C. intervals within the temperature range of .

Furthermore, the conventional steel listed as steel (A) for comparison was also annealed for a long time at 800° C. for 3 hours using the conventional method.

Furthermore, those samples were pickled under the conditions shown in Table 2, and then cold-rolled once. 12%CD□-3%0□-15% which is the general combustion atmosphere when using heavy oil, natural gas, etc. as fuel after making a cold-rolled sheet with a thickness of Qrnm.
Finish annealing was performed at 800° C. x 1 m1 in an atmosphere of H2O-residual N2.

Figure 1 shows the influence of the coiling temperature of the hot-rolled steel strip on the hardness of the hot-rolled sheet.
On the contrary, (A) steel hardly softens when coiled at a temperature of 0°C or higher, and (E) with low N content,
(D) Steel is also not sufficiently softened.

Table 3 summarizes the effects of manufacturing conditions on excellent mechanical properties, ridging resistance, and oxidation resistance during final annealing. It can be seen that it is excellent in processability, formability as indicated by 1, ridging resistance, and oxidation resistance.

<Effects of the Invention> As is clear from the above examples, by incorporating appropriate amounts of Aβ and N into martensitic stainless steel and winding the hot-rolled sheet at an appropriate temperature, The plate can be sufficiently recrystallized and softened without annealing, resulting in significantly superior workability. At the same time, the oxidation resistance of the cold-rolled plate can be improved by not annealing the hot-rolled plate. It is possible to significantly improve the

As described above, it is possible to actually produce a cold rolled sheet of martensitic stainless steel that is excellent in both workability and oxidation resistance.

[Brief explanation of drawings]

FIG. 1 is a comparative chart showing the influence of coiling temperature on the hardness of hot rolled sheets.

Claims (1)

[Claims] 1. C: 0.40 wt% or less Si: 1.0 wt% or less Mn: 1.0 wt% or less Ni: 0.6 wt% or less Cr: 10-15 wt% Al: 0.025-0. A martensitic stainless steel material containing 3 wt% N: 0.025 to 0.060 wt% with the remainder substantially consisting of Fe and unavoidable impurities is hot rolled, and hot rolled steel strip is wound up in this hot rolling process. workability and oxidation resistance, characterized by performing descaling, cold rolling, and finish annealing in sequence without performing hot-rolled plate annealing after being carried out at a temperature range of 650 ° C to 800 ° C and subsequently allowed to cool. A method for producing martensitic stainless steel sheets with excellent properties.