JPS62214132A - Manufacture of martensitic stainless steel sheet having superior formability, oxidation and ridging resistances - Google Patents

Abstract

PURPOSE:To improve the formability, oxidation and ridging resistances of a martensitic stainless steel sheet by annealing a hot rolled sheet of a steel obtd. by adding proper amounts of Al and N to a martensitic stainless steel under prescribed conditions satisfactory for recrystallization and softening. CONSTITUTION:A steel contg., by weight, <=0.4% C, <=1% Si, <=1% Mn, <=0.6% Ni, 10-15% Cr, 0.025-0.3% Al and 0.025-0.06% N is refined. This martensitic stainless steel stock is hot rolled and the resulting hot rolled sheet is annealed at 650-800 deg.C for <=300sec. It is then descaled, cold rolled and finish-annealed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing martensitic stainless steel sheets used for Western tableware, etc., and particularly relates to a method for manufacturing martensitic stainless steel sheets used for Western tableware, etc. This paper presents the results of research and development to obtain oxidation resistance and ridging resistance.

[Conventional technology]

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 GO, 40 wt% or less (hereinafter simply expressed as %), and Si 1.0. % or less, Mn 1.0
% or less, Ni 1.0% or less, Cr 11.5-13.
It generally contains 5%, and its manufacturing method involves batch-type hot-rolled sheet annealing after hot rolling, followed by descaling, cold rolling, and final annealing. This is usually done.

Special Publication No. 57-557 regarding short-time annealing of hot rolled sheet annealing
According to Publication No. 87, an example of AI-containing ferritic stainless steel is disclosed, but it is mainly a composite additive network of Al and B that is annealed for a short time in a temperature range of 800 to 1050°C. The content of N is low in terms of composition, and no drastic measures have been taken especially for the ridging resistance, and furthermore, there is no disclosure in conventional technical literature regarding martensitic stainless steel.

(Problems to be Solved by the Invention) In the conventional manufacturing method of martensitic stainless steel, batch annealing after hot rolling generally takes several tens of hours and is an extremely inefficient process. If Cr-based stainless steel is subjected to hot-rolled sheet annealing for such a long period of time, a Cr-free layer will be formed on the surface of the hot-rolled sheet, which is a particular problem for martensitic stainless steel sheets with 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 puff polishing etc. after finish annealing, the residual scale generated by finish annealing becomes difficult to remove from the polishing process. It can also make it difficult.

For the problems caused by the formation of a Cr-free layer as described above,
In the descaling process after hot-rolled sheet annealing, for example, the pickling time is made sufficiently long and the surface layer is removed sufficiently thickly to remove the Cr-free layer, thereby preventing deterioration of oxidation resistance during secondary annealing. However, there are serious disadvantages such as the pickling time becomes longer, the amount of chemicals used increases, leading to increased costs, and it is difficult to dispose of the pickling waste liquid in which a large amount of metal is 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 the method was simply annealing a hot-rolled sheet of martensitic stainless steel using the conventional manufacturing method. It has been found that, if only omitted, the mechanical properties of the cold-rolled sheet product, particularly the formability and ridging resistance, were significantly inferior due to insufficient annealing, although the effect of reducing the Cr-free layer was significantly recognized.

Therefore, it is an object of the present invention to obtain excellent formability and ridging resistance of a cold-rolled sheet even when hot-rolled sheet annealing is performed for a short time to prevent the formation of a Cr-free layer due to hot-rolled sheet annealing. Therefore, there are problems caused by the formation of a Cr-free layer, typically problems with the oxidation resistance of cold-rolled steel sheets, and problems caused by simply shortening hot-rolled sheet annealing, typically problems with the mechanical properties of cold-rolled steel sheets. To provide a method for manufacturing a martensitic stainless steel sheet having excellent formability, oxidation resistance, and ridging resistance, which advantageously solves the problem of deterioration of properties, particularly deterioration of formability and ridging resistance. With the goal.

[Means for solving problems]

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

C: 0.40wt% or less Si: 1.0wt%t% Mn: 1. OHt%t% Ni: 0.6 ivL% or less Cr: 10-15wt% A 1 F 0.025-0.3 butt% and N +
After hot rolling a martensitic stainless steel material containing 0.025 to 0.060-t% and the remainder substantially consisting of Fe and unavoidable impurities to form a hot-rolled sheet, 6
Short-time hot rolled sheet annealing within 300 seconds at a temperature range of 50°C to less than 800°C, followed by descaling, cold rolling,
A method for manufacturing a martensitic stainless steel sheet with excellent formability, oxidation resistance, and ridging resistance, which is characterized by sequentially applying final annealing.

Now, the inventors used martensitic stainless steel.

As a result of repeated experiments and consideration of the steel components and hot-rolled sheet annealing conditions, we found that A 1 F 0.025~ as the steel component.
0.30%, N: 0.025 to 0.060%, and hot-rolled plate annealing is performed within 300 seconds at a temperature range of 650°C to less than 800°C, so that cold rolling after descaling is performed. It has been found that when rolled, a cold-rolled steel sheet can be obtained that has much better formability and ridging resistance than when long-term Basochid annealing is performed according to the conventional method.

When conventional batch annealing is performed on a hot-rolled martensitic stainless steel sheet, about 20 μm of Cr-free material is removed on the surface layer.
30°C at 650°C to less than 800°C.
In short-time annealing within 0 seconds, the Cr-free layer is formed with a thickness of 3 to 6 μm.
Therefore, the method of the present invention provides excellent results in the oxidation resistance of the cold-rolled sheet.

[For production]

In this invention, as mentioned above, Al and N are actively included in the steel, and the hot rolled sheet is annealed at 650°C to 800°C.
By carrying out the heating in a temperature range below .degree. C. for a short time of 300 seconds or less, the hot rolled sheet can be sufficiently recrystallized and softened.

In other words, if Al and N are simultaneously contained in the steel, a large amount of fine ll1N will precipitate in the steel sheet during hot rolling, and recrystallization of the steel sheet during annealing of the hot rolled sheet will be activated around these precipitates. Crystallization and softening are promoted.

Furthermore, since the inclusion of 8p increases the transformation point strength, the γ-α transformation during hot rolling is promoted and it is advantageous that it contributes to softening.

Here, the content of AN and N is 0.025% each.
Less than ^7 during hot rolling! The lower limits of AN and N were each set at 0.025% because the amount of N precipitated was small and the effect of accelerating recrystallization during hot rolled sheet annealing was not observed, resulting in deterioration of ridging resistance and formability.

On the other hand, even if the N content exceeds 0.30%, no further increase in the effect can be expected, and on the contrary, the ridging resistance deteriorates, 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 AA is 0.30%, and the upper limit of N is 0.0%.
It is necessary to set it to 60%.

Next, the steel components other than An 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 becomes hard, so the upper limit is set at 0.4.
It was set to 0%.

Although Si is effective as a deoxidizing agent, 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 1.0%, the mechanical properties of the steel sheet will deteriorate, so the upper limit was set at 1.0%.

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 at least 10% 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 Since 15% or less is sufficient, it was set within the range of 10 to 15%.

By subjecting a martensitic stainless steel having a composition such as ``2-Run'' to a hot-rolled sheet annealing for a short time, a cold-rolled steel sheet with excellent formability, oxidation resistance, and ridging resistance can be obtained.

Next, the reasons for limiting the hot-rolled sheet annealing conditions will be explained.

First, regarding the annealing temperature, if the processing temperature is less than 150℃, recrystallization will not be sufficient in short-time annealing within 300 seconds, and satisfactory formability will not be obtained; Although the crystals and moldability were good, the crystal grains became somewhat coarse and the ridging resistance deteriorated, so the treatment temperature was limited to a range of 650°C to less than 800°C.

Next, the reason why the treatment time in the above temperature range was limited to 300 seconds or less is that in the temperature range mentioned above, the steel plate is sufficiently recrystallized and softened by short annealing within 300 seconds, so that it cannot be held for longer. This is because not only is it not necessary, but holding for more than 300 seconds is accompanied by an increase in the amount of Cr-free layer produced, and rather leads to deterioration of the oxidation resistance of the cold rolled sheet.

(Example) (Δ) steel, (B) steel, (C) steel with chemical components shown in Table 1,
(D) Steel and steel were used as test materials, and after hot-rolling excellent continuous casting slabs, they were rolled at 60"C
, 100s at each temperature of 750℃ and tooo℃
The hot rolled sheet was annealed.

Further, the conventional steel listed as steel (A) for comparison was also annealed for a long time at 800° C. for 8 hours using the conventional method.

Furthermore, those samples were pickled under the conditions shown in Table 2, and then cold-rolled once to form cold-rolled sheets with a thickness of 1.0 mm. The combustion atmosphere is 12%CO□-3%0□-15%H
Finish annealing was performed at 800°C x 60°C in an atmosphere of J-N2.

The oxidation resistance and moldability (Y
Table 3 shows the results of the investigation regarding S, TS, r value, EJ) and ridging resistance.

” As is clear from the results shown in Table 3, an appropriate amount of Aj! and N,
By annealing the hot-rolled sheet at an appropriate treatment temperature and treatment time, a cold-rolled sheet rich in various mechanical properties and ridging resistance, and also having good oxidation resistance was obtained.

<Effects of the Invention> Thus, according to the present invention, it is possible to easily obtain a martensitic stainless steel sheet that not only has excellent oxidation resistance but also excellent formability and ridging resistance.

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. 3 wt% and N: 0.025 to 0.060 wt%, with the remainder substantially consisting of Fe and unavoidable impurities. After hot rolling into a hot rolled sheet, the material was heated at 650°C to Formability, oxidation resistance, and ridging resistance characterized by short-time hot-rolled sheet annealing within 300 seconds at a temperature range of less than 800°C, followed by descaling, cold rolling, and final annealing in sequence. A method for manufacturing martensitic stainless steel sheets with excellent properties.