JP2000061655A - Base material for clad steel superior in toughness in solution and manufacture of clad steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a clad steel sheet superior in corrosion resistance to be used in solution. SOLUTION: Cladding is performed between a base material and a cladding material, the base material containing >=0.15% C, >=0.5% Si, >=1.5% Mn, >=3.0% Ni, 0.008-0.025% Ti, 0.0004-0.0020% B, and 0.006-0.015% N; after a solution heat treatment, it is slow cooled to the BN precipitation temperature or below, precipitating BN and then rapidly quenched. Consequently, a superior toughness is secured in solution, permitting the use of the clad steel in solution with a tempering process omitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a base material for clad steel having excellent toughness in the as-solution-treated state, that is, after the solution-treatment and before tempering, and a method for producing the clad steel.

[0002]

2. Description of the Related Art In fields requiring high corrosion resistance such as smoke exhaust systems for chimneys, desulfurizers, and chemical equipment, clad steel plates are used that are clad with a stainless steel-like laminated material with excellent corrosion resistance. ing. In this clad steel sheet, the corrosion resistance of the laminated material decreases due to the thermal history of clad rolling during manufacturing. Therefore, after clad, solution treatment is performed at a high temperature (for example, 1000 ° C or higher) and quenching is performed to secure the corrosion resistance of the laminated material. is doing. Further, when the solution treatment is performed at such a high temperature, the crystal grains become coarse in the base material, and bainite or a part of the structure becomes a structure in which martensite is mixed, and the toughness deteriorates. , Tempering is performed to secure the toughness of the base material.

[0003]

However, if the tempering is carried out after the solution treatment as in the conventional case, there is a problem that the corrosion resistance of the laminated material is lowered, and the number of steps for tempering is increased to manufacture the laminated material. There is a problem that the cost increases. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a base material for clad steel that exhibits excellent toughness in the as-solution-treated state, and a method for producing the clad steel.

[0004]

In order to solve the above-mentioned problems, the first invention of the base material for clad steel of the present invention, which is excellent in toughness in the as-solution state, is the weight% C: 0.15% or less. , Si: 0.5% or less, Mn: 1.5% or less, Ni:
3.0% or less, Ti: 0.008 to 0.025%, B:
0.0004 to 0.0020%, N: 0.006 to 0.
It is characterized by containing 015% and the balance consisting of Fe and unavoidable impurities. A base material for clad steel which is excellent in toughness as a solution of the second invention is characterized in that in the base material for a clad steel of the above invention, the content of N, Ti and B (% by weight) satisfies the following formula. To do. N (wt%) ≧ Ti (wt%) / 3.4 + 3 × B (wt%)

Further, a method for producing a clad steel which is excellent in toughness as a solution is as follows. The clad steel base material of the first or second aspect of the invention is clad with the laminated material, and then the clad steel is subjected to solution treatment. The method is characterized by heating to a solutionizing temperature, gradually cooling to a temperature not higher than the BN precipitation temperature to precipitate BN, and then rapidly cooling. The method for producing a clad steel excellent in toughness in the as-solution state of the second invention is
In the invention of the method for producing a clad steel, after heating to the solution temperature, 1050 at a cooling rate of 100 ° C./min or less.
It is characterized by slow cooling to below ℃.

The clad steel of the present invention, as described above,
It is suitable for use in fields requiring high corrosion resistance, strength, and toughness, such as smoke exhaust devices for chimneys, desulfurization devices, and chemical equipment, but the fields of use are not particularly limited.
Further, the clad steel of the present invention is manufactured as a plate material,
The shape is not limited to this, and may be manufactured in a tubular shape, for example. From the above, in the clad steel of the present invention, an appropriate laminating material, for example, stainless steel, Ni-based alloy steel, iron-based Ni alloy steel, etc. is selected.

On the other hand, the above-mentioned composition is essential in the base material for clad steel of the present invention. The reason will be described below. C: 0.15% or less C is an element effective in improving strength and improving hardenability, but if it is contained in excess of 0.15%, the amount of bainite increases and the toughness deteriorates. To 0.1
5%. From the above viewpoint, the lower limit of C is preferably 0.02%, and more preferably the upper limit is 0.10%.

Si: 0.5% or less Since Si is added as a deoxidizer, it is inevitably contained in the base material. However, if it is contained excessively, the toughness is lowered, so the upper limit is set to 0. 0.5%. Mn: 1.5% or less Mn is effective in improving the strength and is contained if desired, but if it is contained in an amount exceeding 1.5%, the hardenability is increased and the toughness is adversely affected, so the upper limit is 1.5%. And In addition,
For the same reason, it is more desirable to set the upper limit to 1.0%. Ni: 3.0% or less Ni is effective in improving strength and toughness and is contained if desired, but an effect of improving toughness is not observed even if it is contained excessively, and conversely is added in combination with C, Si and Mn. Then, since the bainite structure is increased, the upper limit is made 3.0%. For the same reason, it is desirable to set the upper limit to 1.0%.

Ti: 0.008 to 0.025% Ti forms stable TiN at high temperature and suppresses coarsening of crystal grains during high temperature solution heating. In order to generate sufficient TiN and obtain this effect, the content of 0.008% or more is required. On the other hand, an excessive content causes excessive precipitation of TiN and impairs toughness, so the upper limit is made 0.025%.
For the same reason, it is desirable to set the upper limit to 0.02%. B: 0.0004 to 0.0020% B forms BN at the time of cooling after solution heating and its BN
Promotes precipitation of fine-grained pro-eutectoid ferrite and prevents deterioration of toughness due to quenching. To this end, 0.000
It is necessary to contain at least 4%. On the other hand, if contained excessively, excess B that does not form BN during the cooling increases the hardenability and reduces the toughness, so the upper limit is 0.0020.
%. For the same reason, the lower limit is 0.0008%,
The upper limit is preferably 0.0015%.

N: 0.006 to 0.015% N combines with Ti and B to form TiN and BN,
The above-mentioned function is achieved. Therefore, it is necessary to contain 0.006% or more. On the other hand, if it is contained excessively, it will cause generation of prohole during welding, so the upper limit is made 0.15%. For the same reason, the upper limit is 0.012%.
Is desirable. N is within the above range,
It is desirable that the amount is relatively sufficient with respect to Ti and B so that BN is surely formed without the presence of B alone during quenching. When this is shown by a relational expression in weight% of each component, it is desirable that the amount of N satisfies N ≧ Ti / 3.4 + 3 × B 2. When the content of N is less than the right formula in the above formula, it is more likely that B does not combine with N and exists alone, and the toughness of the base material is likely to decrease. For the same reason, it is more desirable that the amount of N be (Ti / 3.4 + 5 × B) or more.

Impurities Furthermore, in the base material of the present invention, it is desirable to control the following impurities in addition to the above components. The reason will be described below. Cr: 0.50% or less, Mo: 0.15% or less These components are positioned as impurities, but if they are contained excessively, the hardenability is increased and the toughness is adversely affected. Therefore, it is desirable to set an upper limit for each. . For the same reason, it is more desirable to set Mo: 0.10% or less. Al: 0.06% or less Al is inevitably contained in the base material because it is added as a deoxidizer, but when it is contained in excess, it forms a compound with N to form TiN and BN. Since it inhibits and reduces toughness, it is desirable to set the upper limit to 0.06%. For the same reason, it is more desirable to set the content to 0.040% or less. P: 0.020% or less Since P is an element that promotes segregation and impairs toughness,
It is desirable to regulate it to 0.020% or less. S: 0.010% or less S is an element that binds to Mn and becomes a non-metallic inclusion MnS and adversely affects toughness, so it is desirable to regulate to 0.010% or less.

Further, in the production of the clad steel using the above base metal, it is desirable to control the cooling operation after the solution heat treatment so that the BN can be surely formed. That is, at the time of high temperature such as solution heating, BN is decomposed into B and N, and BN is produced with cooling. However, if this cooling is performed at a high cooling rate, BN is not sufficiently generated. On the other hand, if cooling is completed at a slow cooling rate, problems such as carbonitride precipitation will occur. Therefore, the BN is gradually cooled to a temperature not higher than the BN precipitation temperature to sufficiently precipitate BN, and then rapidly cooled.
As for the temperature range of gradual cooling at this time, it is desirable to set the lower limit temperature to a temperature lower by 50 to 100 ° C. than the BN precipitation temperature.
This is because when the temperature is close to the BN precipitation temperature,
The reason for this is that when rapid cooling to a temperature much lower than BN does not occur, the quenching start temperature is too low and the action of rapid cooling cannot be sufficiently obtained. Considering the above, the lower limit temperature of slow cooling, that is, the rapid cooling start temperature is preferably 1050 ° C. or lower, and more preferably 1000 ° C. or lower. Further, as described above, it is not desirable that the slow cooling lower limit temperature, that is, the rapid cooling start temperature is too low. Therefore, this temperature is desirably set to 900 ° C. or higher. Further, at the time of slow cooling, it is desirable to cool at a sufficiently slow cooling rate so that BN is surely generated. Although this rate depends on the contents of B and N, it is desirable that the cooling rate is 100 ° C./min or less. The cooling rate can be shown as an average cooling rate during slow cooling, but it is more preferable that the cooling rate is substantially the same during slow cooling.

That is, according to the present invention, the growth of crystal grains is suppressed by TiN which is stable at a high temperature during the solution heat treatment, and BN is precipitated during cooling to promote the precipitation of proeutectoid ferrite during quenching. Achieves grain refinement, suppresses hardening, and improves toughness. According to the above, the clad steel of the present invention has good toughness without being tempered after the solution treatment, and the tempering step after the solution treatment can be omitted. The manufacturing cost can be reduced. Further, since deterioration of the corrosion resistance of the laminated material due to tempering can be avoided, the quality of the laminated material can be surely maintained.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The clad steel of the present invention is manufactured by clad with the above-mentioned base material and a laminated material of an appropriate material. At this time, the thicknesses of the base material and the laminated material can be appropriately determined. The clad itself can be formed by a conventional method, for example, the base material and the laminated material are pressure-bonded by hot rolling. The rolling temperature at this time is 120
The temperature can be exemplified from 0 to 750 ° C., and rolling is performed at an appropriate rolling ratio. However, the clad method is not limited to this method.

After that, solution treatment is performed as described above. The heating in solution heat treatment is usually 1000 to 1180 ° C. in a heating furnace, though it depends on the material of the laminated material.
The temperature is maintained for 10 to 30 minutes / 25 mm. After solution heating, as described above, it is preferably 10
Gradually cool at a cooling rate of 0 ° C./minute or less. Examples of this slow cooling method include air cooling, standing cooling, and furnace cooling. Further, in the rapid cooling after the gradual cooling, airflow cooling, oil cooling, water cooling and the like can be mentioned, and for example, the cooling rate can be 100 ° C./min or more. After that, as described above, since it has a good toughness as a solution, it can be used without a tempering step. Further, the clad steel obtained by the present invention can be tempered after the solution treatment, but in this case, the clad steel (base metal) has good toughness as it is as a solution as described above. Therefore, the load in the tempering process can be reduced (the processing time can be shortened and the processing temperature can be lowered).

[0016]

EXAMPLE An example of the present invention will be described below. Table 1
In order to investigate the effect of the solution treatment, the steel material for base metal shown in (1) was heated at 1150 ° C. for 15 minutes, air-cooled to 950 ° C. (cooling rate of about 60 ° C./minute), and then water-cooled. A tensile test and a 2 mmV Charpy impact test were performed on the obtained test material, and the results are shown in Table 2.

[0017]

[Table 1]

[0018]

[Table 2]

As is clear from Table 2, the test material of the present invention has a low transition temperature in the Charpy test and shows good toughness in the as-solution state, but the comparative material has a high transition temperature. However, the toughness was insufficient as it was solution-treated, and it could not be used as it was. That is, it has been found that the present invention can only provide a clad steel having good toughness in the as-solution state.

[0020]

As described above, according to the base material for clad steel of the present invention, C: 0.15% or less by weight% and S
i: 0.5% or less, Mn: 1.5% or less, Ni: 3.0
% Or less, Ti: 0.008 to 0.025%, B: 0.0
004 to 0.0020%, N: 0.006 to 0.015
%, And the balance consisting of Fe and unavoidable impurities, it is possible to exhibit good toughness even as a solution. Further, in the above base material, in the content (% by weight) of N, Ti and B, the formula N (% by weight) ≧ Ti (% by weight)
If the content is determined so as to satisfy /3.4+3×B (% by weight), the toughness can be secured more reliably.

A method of manufacturing a clad steel sheet in which the base material and the laminated material are clad and then subjected to a solution treatment, which is heated to a solution temperature and then gradually cooled to a temperature lower than a BN precipitation temperature. By precipitating BN and then quenching it, it becomes possible to prevent excessive quenching that impairs toughness and ensure good toughness. In addition, in the above method, after heating to the solution temperature, 105 at a cooling rate of 100 ° C./min or less.
By gradually cooling to 0 ° C. or less, it is possible to more reliably secure the toughness while avoiding the appearance of components that impair the toughness. As mentioned above, the clad steel with excellent toughness as solution treated can omit or simplify tempering, which can reduce the manufacturing cost and avoid the deterioration of the corrosion resistance of the laminated material due to tempering. be able to.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshihiko Yamamura             4 Chatsu-cho, Muroran-shi, Hokkaido Japan Co., Ltd.             Inside the steel mill F term (reference) 4E067 AA02 BD02 BD03 DC05 DD01                       EB11

Claims (4)

[Claims] 1. By weight%, C: 0.15% or less, Si:
0.5% or less, Mn: 1.5% or less, Ni: 3.0% or less, Ti: 0.008 to 0.025%, B: 0.000
4 to 0.0020%, N: 0.006 to 0.015%, the balance being Fe and unavoidable impurities, the base material for clad steel having excellent toughness as solution 2. A base material for clad steel having excellent toughness as solution as set forth in claim 1, characterized in that the content (% by weight) of N, Ti and B satisfies the following formula: N (% by weight) ≧ Ti (wt%) / 3.4 + 3 × B (wt%) 3. A method for producing a clad steel sheet, which comprises subjecting a base material according to claim 1 or 2 to a clad material and then subjecting it to solution treatment, which comprises heating to a solution treatment temperature and then applying B
A method for producing a clad steel excellent in toughness as a solution, characterized in that BN is precipitated by gradually cooling to a temperature not higher than N precipitation temperature, and then rapidly cooled. 4. The clad steel excellent in toughness as solution as set forth in claim 3, which is gradually cooled to 1050 ° C. or less at a cooling rate of 100 ° C./min or less after heating to the solution temperature. Production method