JP7708067B2 - Method for manufacturing material simulation test material for clad steel plate base material, material simulation test method, and method for designing manufacturing conditions for clad steel plate - Google Patents

Description

The present invention relates to a manufacturing method and a material simulation test method for a material simulation test material of a clad steel plate base material that requires DWTT (Drop Weight Tear Test) performance and HIC (Hydrogen Induced Cracking) resistance, and a manufacturing condition design method for a clad steel plate using the method.

Clad steel sheet is a steel sheet made by bonding a clad material made of stainless steel or Ni alloy to a base material made of low alloy steel or the like. Clad steel sheet is made by metallurgically bonding dissimilar metals, and unlike plating, there is no risk of peeling. In addition, clad steel sheet can be given new properties that cannot be achieved with a single metal or alloy.

Clad steel plates can provide the same functionality as solid materials (where the entire thickness is the metal structure of the clad material) by selecting clad materials that have the functionality suited to the purpose of each usage environment. Furthermore, by using carbon steel or low alloy steel that is suitable for harsh environments, such as high toughness and high strength, as the base material of the clad steel plate, the clad steel plate can be given high toughness and high strength.

In this way, clad steel plates use less alloying elements than solid wood, while still providing the same corrosion resistance as solid wood, and also providing the same strength and toughness as carbon steel and low-alloy steel, giving them the advantage of being both economical and functional.

For these reasons, clad steel, which uses a composite material composed of stainless steel and Ni alloys, is considered to be a very useful functional steel material, and in recent years the demand for it has been increasing in various industrial fields.

Representative materials for Ni-alloy clad steel plates, which are a type of clad steel plate, include Alloy 825 and Alloy 625. Representative materials for stainless clad steel plates include SUS 316L. Ni-alloy clad steel plates and stainless clad steel plates are preferably used for pipeline applications due to their excellent corrosion resistance.

In addition, HIC resistance is sometimes required for the base material of clad steel plates. In order to develop clad steel plates that require strict performance from the base material, it is essential to adjust the composition, TMCP (Thermo Mechanical Control Process) or heat treatment conditions to satisfy the base material performance. (See Non-Patent Document 1)

Materia Vol. 35, No. 9 (1996) pp. 976-982

However, the conventional technology has the following problems.
The following methods have been conventionally applied to evaluate the performance of clad steel plate base material.
(1) Manufacture clad steel plates and evaluate the base material performance.
(2) Manufacture solid wood with the same components as the base material and evaluate the performance of the base material.

Method (1) can accurately evaluate the base material performance, but because it involves producing clad steel plates, expensive clad materials are used, which increases costs. In other words, clad steel plates are actually advantageous in that they are cheaper than solid clad materials and can ensure the corrosion resistance of the clad materials. Nevertheless, if expensive clad materials are used to evaluate the base material properties, the benefit of low cost is reduced.

For example, when simulating a clad steel plate manufactured by sand clad, method (2) cannot position the central segregation of the base material at the same position as sand clad. In other words, in sand clad, the central segregation is generally at the 1/4 thickness position of the slab, but when solid wood is used, it is at the 1/2 thickness position. Since the thermal history at the 1/4 thickness position of a clad slab is different from the thermal history at the 1/2 thickness position of solid wood, strictly speaking it cannot be said to simulate the manufacturing conditions. As a result, HIC performance and DWTT performance cannot be evaluated correctly.

When manufacturing clad steel plates, as shown in FIG. 1, a base material slab 1 having the components of a base material such as ordinary steel is heated 3 and hot rolled 4 to manufacture a base material material 6. A clad material slab 2 having the components of a clad material such as corrosion-resistant steel is heated 3 and hot rolled 4 to manufacture a clad material material 7. The base material material 6 and the clad material material 7 are then assembled into a clad slab 9. The clad slab 9 is heated 3 and hot rolled 4 to manufacture a clad steel plate 14. Therefore, when manufacturing clad steel plates, two hot rolling processes, base material rolling and clad rolling, are performed. However, simply heating and hot rolling a solid material results in only one heating and hot rolling process, so strictly speaking, it cannot be said that the manufacturing conditions are simulated. Therefore, it is mainly impossible to correctly evaluate the DWTT performance.

In addition, when evaluating the mechanical properties and other characteristics of materials, the effect of the plate thickness of the test material cannot be ignored. It is common knowledge for those skilled in the art that the effect of plate thickness is particularly significant in evaluating toughness. Therefore, even if a thin and small test material is produced in a laboratory by proportionally allocating the same plate thickness configuration as used to produce clad steel plates, the material quality of the resulting base material cannot necessarily be reproduced as would be the case when produced at the actual equipment level, because the plate thickness of the resulting base material is small. From this perspective, too, a method for simulating the base material performance of clad steel plates was needed.

The present invention was made in consideration of the above circumstances, and its purpose is to provide a technology that inexpensively and accurately simulates the base material performance of clad steel plates, which require DWTT performance and HIC performance.

The inventors have conducted extensive research into a method for inexpensively and accurately simulating the performance of clad base material, and have found the following method. First, as a method for inexpensively simulating the performance, they have decided to avoid using expensive cladding materials. Second, in order to accurately simulate the performance of the base material,
(1) Rolling is performed using an assembled slab in which the central segregation of the base material is located in the same position as that of the clad steel plate base material;
(2) Applying two heating and hot rolling steps, followed by accelerated cooling or heat treatment, or both, as in the production of clad steel plates;
As a result, it was found that the simulated conditions (1) and (2) can be realized by stacking a base material (a) having the same product thickness as the clad steel plate base material and an opposing material (b) having a remaining thickness that is the same as the clad slab thickness during clad rolling to form a clad slab.

The present invention has been completed through further development based on these findings, and the gist of the present invention is as follows.
[1] A method for manufacturing a material simulation test material for a clad steel plate base material, the method comprising: a clad base material material manufacturing simulation process, in which a cast or steel slab having a chemical composition of a clad base material is heated and then hot rolled to manufacture a clad base material material; a clad slab assembly simulation process, in which an opposing material material is overlapped with the clad base material material to assemble a simulated clad slab; and a clad steel plate manufacturing simulation process, in which the simulated clad slab is heated and then hot rolled, and the obtained clad hot rolled material is subjected to one or more treatments selected from natural cooling, accelerated cooling and heat treatment to manufacture a simulated clad steel plate.
[2] A manufacturing method for a material simulation test material of a clad steel plate base material described in [1], wherein the thickness of the opposing material is the sum of twice the thickness of the clad matching material material when manufacturing the clad steel plate to be subjected to the material simulation test and the thickness of other clad base material materials.
[3] A manufacturing method for a material simulation test material of a clad steel plate base material described in [1], wherein the thickness of the opposing material is the sum of the thickness of the clad matching material material and the thickness of the sacrificial material material when manufacturing a clad steel plate to be subjected to material simulation test.
[4] The method for manufacturing a material simulation test material for a clad steel plate base material described in [1], wherein the thickness of the opposing material is the thickness of a clad matching material when manufacturing a clad steel plate to be subjected to a material simulation test.
[5] A method for simulating the material properties of a clad steel plate base material, comprising conducting a material simulation test on a material simulation test material of a clad steel plate base material manufactured from one of the clad base material materials by the manufacturing method described in any one of [1] to [4].
[6] A method for designing manufacturing conditions for clad steel plates, comprising the steps of: designing manufacturing conditions for clad steel plates based on test results obtained by carrying out the material simulation test described in [5].
[7] A method for designing manufacturing conditions for clad steel plates described in [6], in which, when designing manufacturing conditions for clad steel plates, the test results are compared with the results of investigating the material properties of the clad steel plates obtained by actually manufacturing the clad steel plates, and machine learning is performed to correct the differences.

The manufacturing method and material simulation test method for the clad steel plate base material of the present invention make it possible to inexpensively and accurately simulate the base material performance of clad steel plates that require DWTT performance and HIC performance. Furthermore, by applying the method to the manufacturing condition design method for clad steel plates, clad steel plates with excellent base material performance can be manufactured.

FIG. 2 is a schematic diagram showing an example of a manufacturing process of a clad steel plate.

The following is a detailed description of the embodiments of the present invention. The following embodiments are intended to illustrate a method for realizing the technical concept of the present invention, and are not intended to limit the configuration to that described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope described in the claims.

As shown in Figure 1, the manufacturing process of clad steel plate 14 is basically as follows: first, clad base material 6 and clad cladding material 7 are appropriately laminated to assemble clad slab 9 (10). Then, the clad slab 9 is heated (3), and the heated clad slab 9 is hot rolled (4). The obtained rolled body 13 is cut or peeled off as necessary (8) to obtain clad steel plate 14.

When assembling (10) the clad slab 9, there are three main ways of overlapping the clad base material 6 and the clad joining material 7, as follows: (1) to (3).
(1) Sandwich method In the sandwich method, a clad base material 6/clad clad material material 7/clad clad material material 7/clad base material material 6 are stacked in this order. A release agent such as oxide powder is applied between the two clad clad material materials 7. A total of two clad steel plates 14 are produced from the clad slab 9 assembled by the sandwich method by rolling the clad slab 9 to produce a rolled body 13, which is then separated into an upper part and a lower part.
(2) Sacrificial material method (semi-sandwich method)
In the sacrificial material method (semi-sandwich method), a sacrificial material, a clad cladding material material 7, and a clad base material material 6 are stacked in this order. A release agent such as oxide powder is applied between the sacrificial material and the clad cladding material material 7. From the clad slab 9 assembled by the sacrificial material method, a rolled body 13 is produced by rolling the clad slab 9, and the sacrificial material is peeled off to produce a clad steel plate 14.
(3) Open sandwich method In the open sandwich method, a pair of clad cladding material materials 7 and a clad base material material 6 are stacked in this order. From the clad slab 9 assembled by the open sandwich method, the clad slab 9 is rolled to produce a rolled body 13, which itself becomes a single clad steel plate 14.

In this specification, the value obtained by dividing the total thickness of the clad slab 9 by the total thickness of the rolled body 13 obtained by hot rolling is referred to as the clad reduction ratio.

In this embodiment, the base material of the clad steel plate 14 whose material is to be simulated and tested/evaluated is referred to as a clad base material 14a.

In the manufacturing method of the clad steel plate base material material simulation test material according to this embodiment, first, a cast piece 1 or a steel piece having the component composition of a clad base material 14a is heated (3), and then hot rolling 4 is performed to manufacture a clad base material material 6. The conditions of this heating 3 and hot rolling 4 are set to the same conditions as when manufacturing a clad steel plate 14 whose base material material is to be simulated. The clad base material material 6 obtained in this way is used in a subsequent process to manufacture a (simulated) clad slab 9.

The thickness of one clad base material 6 is the thickness of the clad base material 14a of the clad steel plate 14 whose base material material is to be simulated, multiplied by the clad reduction ratio.

Next, the opposing material is stacked on top of one clad base material 6 to assemble the simulated clad slab 9.

In the case of the sandwich type, the opposing materials are one clad base material and two clad cladding materials. Therefore, in the case of the sandwich type, the thickness of the opposing material is the sum of the plate thickness of the other clad base material and twice the plate thickness of the clad cladding material multiplied by the clad reduction ratio.
In the case of the sacrificial material method, the opposing materials are one clad cladding material and one sacrificial material. Therefore, in the case of the sacrificial material method, the thickness of the opposing material is the sum of the plate thickness of the clad cladding material and the plate thickness of the sacrificial material multiplied by the clad reduction ratio.
In the case of the open sandwich type, the opposing material is one clad laminate. Therefore, in the case of the open sandwich type, the thickness of the opposing material is the plate thickness of the clad laminate multiplied by the clad reduction ratio.

In either case, just as in the case of the actual production of clad steel plate 14, the surface of the clad base material 6 that comes into contact with the clad cladding material 7 and the surface of the clad cladding material 7 that comes into contact with the clad base material 6 can each be surface ground (surface preparation) (5).

In either case, when manufacturing by inserting an intermediate material between the clad bonding material 7 and the clad base material 6, the thickness of the opposing material may be appropriately adjusted taking into account the thickness of the intermediate material.

The simulated clad slab 9 is preferably prepared by simply stacking the clad base material 6 and the clad cladding material 7 together, and then processing the outer periphery by electron beam welding 12 or the like under a high vacuum (11) atmosphere. The welding method may be laser welding.

In the manufacturing method of the clad steel plate base material material simulation test material according to this embodiment, the obtained simulated clad slab 9 is heated (3) and then hot rolled (4) to manufacture the clad hot rolled material 13. Here, the heating conditions and hot rolling conditions of the simulated clad slab are set to the same conditions as those for manufacturing the clad steel plate 14 whose base material material is to be simulated.

The obtained clad hot-rolled material 13 is subjected to one or more treatments selected from natural cooling, accelerated cooling, and heat treatment to produce a simulated clad steel plate 14. The conditions for natural cooling, accelerated cooling, and heat treatment are also set to the same as those for producing a clad steel plate 14 whose material properties are to be simulated.

The obtained simulated clad steel plate 14 is cut, and a test piece for conducting a material simulation test is taken from the part corresponding to one of the clad base materials 14a, and the test piece is then used for the material test.

As long as a test piece can be taken from the portion corresponding to one clad base material 14a, various material tests can be performed. For example, it is preferable to apply this to material tests in which the thickness of the test piece has a large effect on the test results, such as DWTT (drop weight test) and Charpy impact test. This is because, according to this embodiment, material tests can be performed using test pieces of the same size as the actual ones, and the effectiveness of this embodiment is clearly demonstrated.

By comparing the test results simulating the base material properties using the methods described above with the properties of the base material of actual clad steel plates and providing feedback, it is possible to design the manufacturing conditions for clad steel plates.

Here, factors that affect the material quality of the clad base material include (1) the steel composition of the base material, (2) various manufacturing conditions such as the heating temperature and rolling conditions when manufacturing the base material, and (3) clad steel plate manufacturing conditions. (3) Clad steel plate manufacturing conditions include the clad slab heating temperature, hot rolling conditions such as rolling temperature and reduction rate, cooling conditions such as natural cooling and accelerated cooling after rolling, and heat treatment conditions after cooling. As described above, there are many factors that affect the material quality of the clad base material, so machine learning may be applied to design the clad steel plate manufacturing conditions. For example, the clad steel plate manufacturing conditions can be designed by considering a neural network in which the various factors that affect the material quality of the clad base material as described above are used as the input layer and the material quality of the base material of the manufactured clad steel plate is used as the output layer, and machine learning is performed.

A simulated production of clad steel plate was carried out using Alloy 825 as the mating material. One clad base material slab was produced with the chemical composition shown in Table 1. The remainder of the components other than those listed in Table 1 is Fe and unavoidable impurities. The opposing slab was also produced with the chemical composition shown in Table 1.

Table 2 shows the manufacturing conditions of the simulated clad steel plate. Table 3 shows the manufacturing conditions of the simulated test material of the clad steel plate base material. In Table 2, the notation "27+3" in the product thickness column indicates that the thickness of the clad steel plate base material is 27 mm, and the thickness of the clad steel plate mating material is 3 mm. In Table 3, the notation "27+33" in the product thickness column indicates that the thickness of one simulated test material of the clad steel plate base material is 27 mm, and the thickness of the opposing material is 33 mm. In Table 2, the assembly method column lists the assembly method of the clad slab. "Sand" stands for the sandwich method, "sacrificial material" stands for the sacrificial material method, and "open" stands for the open sandwich method.

Material tests of the manufactured simulated clad steel plate and the base material of the clad steel plate were carried out as follows. Mechanical properties were evaluated by taking tensile test pieces, DWTT test pieces and HIC test pieces according to API-5L standard (API: American Petroleum Institute), and carrying out tensile test, DWTT test and HIC test, respectively.
The tensile test was evaluated as being satisfactorily simulated when the difference in yield strength and tensile strength between the simulated clad steel plate and the target clad steel plate was within 15 MPa.
The DWTT test was evaluated by measuring the ductile fracture area (SA) at a test temperature of -40°C. A satisfactory simulation was achieved when the difference in SA compared to the simulated clad steel plate was within 20%.
The HIC test was evaluated by measuring the crack length ratio (CLR) using NACE TM0284 Solution A. It was considered that the simulation was satisfactory when the difference in CLR compared to the simulated clad steel plate was within 5%.
The material test results are shown in Table 4.

It can be seen that the steel plates Nos. A to E, which are examples of the invention, are able to satisfactorily simulate the base material properties of the corresponding clad steel plates to be simulated.
The comparative examples were unable to simulate well any of the material test results as compared with the corresponding simulated clad steel plates.
For steel plate No. F, the corresponding clad slab was made into a solid slab cast piece, and the first heating and hot rolling were not performed, so the evaluations of the DWTT test and the HIC test were not good.
Steel plate No. F was made by casting a solid slab instead of a clad slab, and therefore the evaluation of the HIC test was not good.
Steel plate No. H was not evaluated as being good in the DWTT test because the first heating temperature was different.
Steel plate No. I was simulated using an open sandwich method using solid wood instead of the sandwich method, so the yield strength and tensile strength were higher than expected.
Steel plate No. J was simulated using a sandwich method instead of an open sandwich method, so the yield strength and tensile strength were low.

1 Base material slab (common steel)
2. Composite cast pieces (corrosion-resistant steel)
3 (Slab) heating 4 (Hot) rolling 5 Surface grinding (surface preparation)
6 Base material 7 Cladding material 8 Cutting/peeling 9 Clad slab 10 Assembly of clad slab 11 High vacuum 12 Electron beam welding 13 Rolled body 14 Clad steel plate 14a One clad base material

Claims (7)

A clad base material manufacturing simulation process, in which a slab or a steel billet having a composition of one clad base material is heated and then hot-rolled to manufacture one clad base material;
A clad slab assembly simulation process includes assembling a simulated clad slab by overlapping a facing material having a component composition of the one clad base material with the one clad base material material;
The simulated clad slab is heated, then hot rolled, and the obtained clad hot rolled material is subjected to one or more treatments selected from natural cooling, accelerated cooling, and heat treatment,
A simulated clad steel plate manufacturing process for manufacturing a simulated clad steel plate;
A method for manufacturing a material simulation test material for a clad steel plate base material having the above structure. The thickness of the opposing material is
Twice the thickness of the clad material used to manufacture the clad steel plate subject to the material simulation test,
The sum of the thickness of the clad base material and the plate thickness of the other clad base material.
A method for producing a material simulation test material for the clad steel plate base material according to claim 1. The thickness of the opposing material is
The sum of the thickness of the clad composite material and the thickness of the sacrificial material when manufacturing the clad steel plate to be subjected to the material simulation test,
A method for producing a material simulation test material for the clad steel plate base material according to claim 1. The thickness of the opposing material is
The plate thickness of the clad composite material when manufacturing the clad steel plate subject to the material simulation test.
A method for producing a material simulation test material for the clad steel plate base material according to claim 1. A method for simulating the material properties of a clad steel plate base material, which performs a material simulation test on a material simulation test material of a clad steel plate base material manufactured from the one clad base material material by the manufacturing method described in any one of claims 1 to 4. A method for designing manufacturing conditions for clad steel plates, which designs manufacturing conditions for clad steel plates based on the test results of a material simulation test described in claim 5. A method for designing manufacturing conditions for clad steel plates according to claim 6, in which, when designing manufacturing conditions for clad steel plates, the test results are compared with the results of investigating the material properties of clad steel plates obtained by actually manufacturing clad steel plates, and machine learning is carried out to correct the differences.