JPS589934A - Production of ferritic stainless steel plate - Google Patents

Abstract

PURPOSE:To produce a titled steel plate of quality more than equal to that of conventional products in simpler stages by heating a low carbon hot rolled steel plate contg. Cr, Ni, Mo, Al, N to temps. higher than its recrystallization temp., and cooling the same at specific average rates then subjecting the strip to controlled cooling and cold rolling to product thickness. CONSTITUTION:The hot rolled steel strip contg., by wt%, <=0.10 C, 15-20 Cr, <=0.6 Ni, <=2.5 Mo, <=0.4 Al, <=0.025 Ni, and if necessary, contg. >=1 kind of <=1.0% Cu, <=0.5% Ti, <=0.5% Nb, <=0.5% V, <=0.006% B and consisting of the balance substantially Fe is subjected to the following heat treatments: After said steel strip is heated to a temp. region of the recrystallization temp. - the recrystallization temp. +100 deg.C, it is cooled at <=10 deg.C/sec average rate down to a 700-900 deg.C temp. region. Thereafter, it is cooled under controlling at the average rate in accordance with the content of Al or the contents of Al+Ti+ Nb+V down to <=200 deg.C. Such steel strip is cold rolled down to product thickness.

Description

[Detailed Description of the Invention] The present invention relates to a method for manufacturing ferritic stainless steel sheets, which simplifies the creation process and produces products with the same or better material quality than products manufactured by conventional methods. The purpose is to be

Conventionally, cold-rolled products of ferritic stainless steel sheets are produced by winding hot-rolled copper strips into coils.
After annealing at 0 to 900°C, the final product is manufactured by cold rolling and recrystallization annealing. Since a hot-rolled copper strip has a non-uniform structure, if it is cold-rolled as it is, the desired workability cannot be obtained, so long-term diffusion annealing using a patch method has been required. However, since the copper strip wound into a coil is uniformly heated to the inside of the coil and subjected to diffusion annealing, K usually requires a furnace time of over 40 hours, which not only increases the production time but also increases the production time. This is extremely disadvantageous in terms of manufacturing costs.

Instead of this long patch method of long-time diffusion annealing of hot-rolled ferritic stainless steel strips, various conventional methods have been used, the so-called continuous annealing method in which a coil is expanded and passed through a furnace continuously to be annealed in a short period of time. Proposed. An example of this is heating in a region that produces a large amount of austenite phase in addition to the ferrite phase, but this actually reduces the thickness of the cold-rolled product and the deep drawing processability. Furthermore, when a film such as mourning vinyl is removed from a KJ1 board, it has the problem of causing so-called gold dust, which causes local peeling of the product surface. Union.

The device @ is made of ferritic stainless steel. The Nesseki black rolled copper strip is annealed using a short-time continuous annealing method instead of the conventional patch method, and the ridging and deep drawing properties are equal to or better than products made by the conventional method. can be obtained,
It is an object of the present invention to provide a method for manufacturing a ferritic stainless steel sheet without problems such as generation of gold dust.In other words, the gist of the first invention of the present invention is to
, Cr 15-20 fb, Nl<0.611
, Mo<2.511, AJI<0.41,
A hot-rolled copper strip consisting of N<0.025%, the balance being F and unavoidable impurities, was heated at a recrystallization temperature to a recrystallization temperature of 1100
After heating to a temperature range of 700°C to 900°C, cooling at an average cooling rate of 10°C/second or less,
Thereafter, the method for producing a ferritic stainless steel sheet is characterized in that the steel sheet is cooled in a controlled manner to 200° C. or lower depending on the U content, and then the product sheet is manufactured using a combination of cold rolling and recrystallization annealing.

Furthermore, the gist of the second invention is that C<0.1'Ik, C
r 15~20'4, Nf <0.6'lr,
No<2J4, A1. <, 0.4 fb, N
(=0.025- included, further K Cu< i, o *
e T1 <o, s '6, Nb <o, s Excellent-
A hot-rolled copper strip containing V (□0.5 excellent, B<0.0061i]-fit or two or more, with the remainder being F- and unavoidable impurities is heated at a temperature of recrystallization temperature to recrystallization temperature + 100 ° C. After heating to a temperature range of 700℃ to 900℃, the temperature is cooled at an average cooling rate of 10℃/second or less, and the temperature is controlled according to the At, Tt, Nb, and V contents until the temperature reaches 200"C or less. A method for manufacturing a ferritic stainless steel sheet is characterized in that after cooling, the sheet is manufactured by a combination of cold rolling and recrystallization annealing until the thickness of the product sheet is reached.

First, the limited passage of ferritic stainless steel OWt in the present invention will be explained.

The first invention is as follows.

C; C deteriorates corrosion resistance and workability, so a lower value is preferable.
T, I, Follow” CJIS O8U8430 and SUB
434 is also set at a slightly lower angle of 0°1096 or less.

Cr', Cri is an essential element for improving corrosion resistance and oxidation resistance of the pipe, but if it is too large, toughness and ductility deteriorate, so the content was set at 15 to 20g6.

Ni: Ni improves the toughness, rust resistance, and low-temperature toughness of the S joint, but if it is too large, the workability deteriorates and the resistance to stress corrosion cracking in a chloride solution deteriorates, so it should be 0.6 or less. And so.

Mo: Mo improves acid resistance, pitting corrosion resistance, and crevice corrosion resistance. MO is expensive, so it has a direct impact on product costs. Also, from the viewpoint of applications such as automobile decoration materials and water heaters, Since it is sufficient to contain .5 regrets, MoF
i2.5'j or less.

M; u combines with N and improves workability and toughness. However, if it is too large, these properties will deteriorate and the number of nonmetallic inclusions in the steel will tend to increase.

Like C, NUN deteriorates corrosion resistance and workability, so it is preferable to have it as low as possible. Considering practical considerations, NUN of about 0.0251 is permissible, so it is set to 0.025% or less.

The reasons for limiting the amounts of Cu, Ti, and B added in the second invention are as follows.

Cu; Cu improves workability and acid resistance, but if too much, hot workability deteriorates. Also, intermetallic compounds precipitate,
T1. Nb and V: Tl, Nb and V are elements that form leg nitrides and improve workability and toughness as well as corrosion resistance. However, if the amount is too high, the workability and creep properties will deteriorate, and this will also increase the cost, so each 0.51
It was set to 6 or less.

B: B improves hot workability and toughness, but too much B tends to produce compounds with low melting points and causes embrittlement, so 0.
00616 or less Toshitomo.

Next, the reasons for limiting the manufacturing method will be explained.

In the present invention, first, a hot-rolled steel strip of ferritic stainless steel having the above composition manufactured by a conventional method is continuously annealed, and the heating temperature at this time is between the recrystallization temperature and the recrystallization temperature + 100°C. range (hereinafter, this temperature will be referred to as H1 temperature). Here, the recrystallization temperature used in the present invention refers to a temperature at which recrystallization reaches 90% or more within 30 seconds.

If the H1 temperature is lower than the recrystallization temperature, no recrystallization occurs or the recrystallization rate is low, and the material properties of the product obtained by performing the following cold rolling and recrystallization annealing in this state are deteriorates. Among these, heating is performed above the recrystallization temperature because it has a particularly bad effect on resin properties. On the other hand, if the heating temperature is too high, austenite is cracked depending on the temperature and becomes martensite during cooling, which deteriorates the toughness of the annealed plate. In addition, since the crystal grains become coarse and roughness is likely to occur when the product is processed, the upper limit of the heating temperature is set to the recrystallization temperature + 100°C.

After heating to H1 temperature, to a temperature range of 700°C or more and 900°C or less (hereinafter, this temperature is referred to as H3 temperature),
Cool at an average cooling rate of 10°C/sec or less. In Figure 1,
Relationship between average cooling rate from H1 temperature to Hs temperature Kt and corrosion loss in nitric acid aqueous solution Pipe #f (Example sample material A1:) Average cooling rate from Is temperature to 200°C 512 ℃, 4sha). This corrosion loss is used to evaluate intergranular corrosion as a measure of gold dust generation. If the average cooling rate exceeds 10° C./sec, the corrosion loss will increase rapidly and the generation of dust will become more likely, so the cooling rate should be lower than this. In addition, the inventors have already discovered that the □r value, which is an index of deep drawing properties, increases as the cooling rate from H1 temperature to H3 temperature decreases, and that when the cooling rate increases to 15°C/sec, it deteriorates rapidly. ing.

H. If the temperature is lower than 700℃, pooled dust is generated because Cr does not diffuse sufficiently around the Cr carbonitrides that precipitate at grain boundaries during cooling, and the Cr-depleted layer does not disappear. However, if the temperature exceeds 900°C, carbonitrides will not be sufficiently precipitated during cooling, and the r value will decrease. Therefore H! Humidity temperature should be in the range of 700°C or higher and 900°C or lower. In addition, if H1 temperature is 900℃ or less, H snow temperature is H
1 temperature.

In the case of the first invention, the subsequent cooling from the aS temperature to 200°C or lower is controlled according to the M content; in the case of the second invention, AI-+Ti, Nb, and V are Controlled cooling is performed depending on the content. Figure 2 shows various types of AA,
Test materials containing Ti, Nb, and V were cooled at various cooling rates until the Hs humidity temperature reached 200°C or less, and the intergranular corrosion in 6511 nitric acid aqueous solution was investigated, and the practical goal was achieved. No bidust generation 1? /-・hr or less and a curved cooling curve. As is clear from the figure, the allowable cooling rate varies depending on the content of kt+Ti+Nb+V9, and in the case of the first invention, the Since only the content is included, the average cooling rate may be controlled to be 30° C./second or more when Ajo is 030%, and 3° C./second or more when At0.1096 or more is −t−. Moreover, in the case of the second invention, the average cooling rate may be controlled according to the content of AA+Tl+Nb+V as shown in the figure. After cooling, a ferritic stainless steel sheet is manufactured by performing a thorough cleaning and combining cold rolling and recrystallization annealing to the product thickness.

The present invention will be explained in detail below.

The test materials shown in Table 13 were melted in a conventional manner and finished into hot rolled steel strips with a thickness of 3.8 M. Thereafter, the heat-treated plate was annealed under the conditions shown in Table 2, cold rolled twice and recrystallized annealed, and a material test was conducted on a 0.4 m thick thin plate product.

For comparison, a heat-resistance plate annealed using conventional box-type annealing was also subjected to the same process. This result is the third
Shown in the table.

The treated material of the present invention has the same yield strength, tensile strength, and elongation as the conventionally treated material, but is superior in in-plane plastic anisotropy, Δr1 resin, and earrings after cylindrical drawing. Δr
A small number of cylinders and a high earring value after the number of cylinders mean that both of these mean that the edges of the edges are small and are advantageous for processing when searching for stamping such as press processing. A small diameter means that it is advantageous in polishing after drawing. In addition, vinyl tape was pasted on the surface of the product, and when it was peeled off, it was confirmed that no dust was generated using the conventional method.

This is because the cooling rate after hot-rolled sheet annealing is extremely slow.
It is considered that no defect layer of r is generated.

In addition, this was not observed in any of the test materials using the method of the present invention, but this is because cooling after heating to the Fl Hs temperature was appropriately controlled.

According to the present invention as described in detail above, the deep drawability is equal to or higher than that of materials manufactured by conventional methods, and the rift 1. A ferritic stainless steel sheet having good corrosion resistance and corrosion resistance can be provided, and the hot-rolled sheet can be annealed by continuous annealing for a short period of time (instead of the conventional process of annealing the hot-rolled sheet over a long period of time). By combining the cold rolling and annealing process, it is possible to achieve the effect of continuous production of ferritic stainless steel sheets used for deep drawing purposes, and therefore, the present invention greatly contributes to the mining industry.

[Brief explanation of drawings]

Figure H1 is a diagram showing the influence of the average cooling rate from HslL degree to H8 temperature on corrosion weight loss, and Figure 2 is A1. ,
FIG. 2 is a controlled cooling curve diagram of H and temperature up to 200° C. according to Ti, Nb and V contents. Patent applicant Nippon Steel Corporation

Claims (2)

[Claims] (1) C<0.101LCr15~20 嗟, N1 0.6 tatami 1Mo 2.51 Beni<0.4 tatami, N<:0.0
After heating a hot-rolled copper strip of 25 yen, the remainder of which is F and unavoidable impurities, to a temperature range of recrystallization temperature to recrystallization temperature f + 100°C, it is heated in a temperature range of 700°C to 900°C.
Cooled at an average cooling rate of 0°C/sec or less, then 200°C
A method for producing a ferritic stainless steel sheet using IFI mold, which is controlled cooling according to the U content and then formed by a combination of cold rolling and recrystallization annealing to the product thickness. (2) C<, 0.1'11. Cr15~20ts,
Ni<0.6'%, Mo<2.5t, Aj<0.49
1, N<0.025%, and Cu<1.
0, TI<:0.5, Nb<0.5, V<,0.
5 saliva, containing 0.006% of one kind or two or more kinds of B,
After heating a hot-rolled copper strip, the remainder of which is F and q unavoidable impurities, to a temperature range from the recrystallization temperature to the recrystallization temperature + 100°C, it is heated to a temperature range of 700°C or higher and 900°C or lower at 10 u/
It is cooled at an average cooling rate of less than 1 second, and then controlled to cool at less than 200C according to the content of Nb, Nb, and V, and then cold rolled and recrystallized annealed to the product thickness. A method for producing a ferritic stainless steel sheet characterized by: