JPH0636993B2 - Method for producing stainless clad steel sheet with excellent corrosion resistance and toughness - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Object of the Invention" (Field of Industrial Application) The present invention relates to a method for producing a stainless clad steel sheet by rolling.

(Prior art) The main uses of low temperature toughness stainless clad steel are for line pipes used in oil fields in low temperature areas containing a large amount of hydrogen sulfide and carbon dioxide, for offshore structures in ice waters, and for icebreakers. Etc. In these applications, naturally, the corrosion resistance of the laminated material, the excellent strength of the base material, and the low temperature toughness are required.

The main methods of manufacturing clad steel are the joining method by rolling and other methods such as explosion welding, overlaying, casting, etc., but the joining method by rolling is the most excellent in terms of productivity and cost, and is widely adopted. Has been done.

Generally, as a method for assembling a rolled clad, there are methods called a sandwich type (a), an open type (b) and a double-sided clad type (c) as shown in FIG. When there is a concern of deterioration of corrosion resistance, a method of inserting an intermediate material such as Ni foil between a stainless laminated material and a base material and rolling it is also adopted. In the figure, 1 is a laminated material,
Reference numeral 2 represents a base material, and 3 represents a release agent.

The material of the rolled clad that has been subjected to the above-mentioned predetermined assembly is charged into a heating furnace, usually heated to 1150 ° C. or higher, joined by hot rolling, and finished to a predetermined thickness. In addition, in order to obtain high bondability, a reduction ratio of 1050 ° C. or higher and 2-3 or higher is usually adopted.

In addition, the combination material is SUS316 (L), SUS304 (L)
Etc., the finishing temperature of rolling is 750 ° C or higher, Cr
SUS329J2L containing 25% or more, Mo 3% or more
When using, the finishing temperature of rolling is 950 ° C or higher,
Similarly, for SUS444 and the like, the finishing temperature for rolling is required to be 950 ° C or higher.

(Problems to be Solved by the Invention) As described above, maintaining the finishing temperature of rolling at a high temperature is performed by, for example, using SUS316 (L) or SUS304 for the composite material.
In the case of (L), there is a risk that the laminated material may be broken or peeled off at the clad interface due to work hardening in the case of low temperature rolling. Therefore, the rolling finishing temperature is 750 ° C.
In addition, when using SUS329J2L or the like containing Mo: 3% or more and Cr: 25% or more as a composite material, there is a risk of precipitating a σ phase and causing cracking in the rolling process. This is because it is necessary to finish rolling at 950 ° C. or higher. Even when SUS444 and SUS310S are used as a composite material, there is a possibility that Cr carbides may precipitate during the rolling process to cause sensitization. Therefore, the rolling finishing temperature needs to be 950 ° C. or higher as described above. In reality, it is difficult to completely suppress sensitization unless rapid cooling from 950 ° C to 10 ° C / s or more is performed.

As described above, in the conventional rolling of stainless clad steel, the rolling temperature is largely regulated by the characteristics of the laminated material, and from the viewpoint of maximizing the strength and toughness of the base metal, finish rolling is the optimum condition. Is not done in. For example, if the rolling of carbon steel is completed at 950 ° C or higher,
Its toughness is low and the fracture surface transition temperature vT of the Charpy impact test
s rises to near room temperature. Therefore SUS329J2
It is extremely difficult to manufacture a low temperature stainless clad steel sheet using L, SUS444, SUS310S, etc. as a composite material by rolling.

The present invention was devised in view of such a current situation, suppresses the sensitization of the laminated material during clad rolling,
It is an object of the present invention to provide a method for producing a stainless clad steel having excellent corrosion resistance under rolling conditions that prevents cracking, breakage of the laminated material, peeling at the clad interface, and maximizes the low temperature toughness of the base metal side. .

“Structure of the Invention” (Means for Solving the Problems) In order to achieve the above-mentioned object, the present inventors have used (1) a ferrite or austenitic stainless steel or a duplex stainless steel as a composite material, and a base material % By weight, C: 0.01 to 0.2%, Si: 0.05 to 0.8%, Mn: 0.3
~ 2.2%, Al: 0.001 to 0.07%, using a steel material consisting of the balance iron and unavoidable impurities, in the middle of clad rolling, the composite material side is rapidly heated by rapidly heating the composite material side. A method for producing a stainless clad steel sheet excellent in corrosion resistance and toughness, characterized in that the finishing temperature of rolling is controlled to be 650 to 850 ° C. on the base metal side.

(2) Ferrite or austenitic stainless steel or duplex stainless steel is used as a composite material, and C: 0.01 to 0.2%, Si: 0.05 to 0.8%, Mn: 0.
3 to 2.2%, Al: 0.001 to 0.07%, and Nb: 0.08
% Or less, Cu: 2.0% or less, Ni: 3.0% or less, Ti: 0.1% or less, Cr: 1.0% or less, Mo: 1.0% or less, V: 0.1% or less,
B: 0.004% or less, Ca: 0.008% or less, using a steel material containing the balance iron and unavoidable impurities containing one or two or more kinds, and by performing rapid heating on the side of the material to be bonded during clad rolling, The material side is not higher than the base material side, and the finishing temperature of rolling is 650 to 850 on the base material side.
A method for producing a stainless clad steel sheet having excellent corrosion resistance and toughness, which is characterized by controlling the temperature to ℃.

(3) Ferrite-based or austenitic stainless steel or duplex stainless steel is used as a composite material, and by weight% as a base material, C: 0.01 to 0.2%, Si: 0.05 to 0.8%, Mn: 0.
Using a steel material containing 3 to 2.2% and Al: 0.001 to 0.07% and the balance iron and unavoidable impurities, the cladding material side is rapidly heated in the middle of the clad rolling, so that the cladding material side is heated to the mother material side. The temperature is set higher than the material side, and the finishing temperature of rolling is controlled to 650 to 850 on the base material side, and then 3 to
A method for producing a stainless clad steel excellent in corrosion resistance and toughness, which comprises rapid cooling at 60 ° C / s.

(4) Ferrite-based or austenitic stainless steel or duplex stainless steel is used as a composite material, and C: 0.01 to 0.2%, Si: 0.05 to 0.8%, Mn: 0.
3 to 2.2%, Al: 0.001 to 0.07%, and Nb: 0.08
% Or less, Cu: 2.0% or less, Ni: 3.0% or less, Ti: 0.1% or less, Cr: 1.0% or less, Mo: 1.0% or less, V: 0.1% or less,
B: 0.004% or less, Ca: 0.008% or less, using a steel material containing the balance iron and unavoidable impurities containing one or two or more kinds, and by performing rapid heating on the side of the material to be bonded during clad rolling, The material side is not higher than the base material side, and the finishing temperature of rolling is 650 to 850 on the base material side.
The method for producing a stainless clad steel sheet having excellent corrosion resistance and toughness, characterized by rapidly controlling the temperature at 3 ° C and then rapidly cooling at 3 to 60 ° C / s, is proposed. According to the method of the present invention, in the process of clad rolling, the laminated material was not cracked, fractured, peeled at the clad interface, etc., and excellent toughness, particularly excellent low temperature toughness was imparted to the base metal side. A stainless clad steel having excellent corrosion resistance can be manufactured.

(Function) As is clear from the description of the claims, the feature of the present invention is that a ferrite or austenitic stainless steel or a duplex stainless steel is used as a composite material, and a specific composition is used as a base material. Use the steel material that we have (details will be described later), and regarding the rolling conditions, in order to adopt the temperature conditions that allow the laminated material and the base material to exhibit their characteristics sufficiently, there is a temperature difference between the two during the rolling process. Is to be provided.

First, from the condition of the base material side, in order to improve the strength and toughness, it is necessary to finish rolling in the low temperature region of austenite or the two-phase region. Rolling in the low temperature region of austenite is to elongate the austenite grains and introduce a deformation zone into the austenite grains. This is because the elongation of austenite grains and the introduction of a deformation zone increase the nucleation side of ferrite, which ultimately makes the structure finer and improves the strength and toughness of steel.
Rolling in the two-phase region achieves the same purpose as in the case described above. In addition, the strain in the ferrite grains is introduced to improve the strength, and at the same time, the deformation texture is introduced to improve the toughness. The goal is to achieve In the present invention, the finishing temperature of rolling is 650 to 850 ° C.
If the temperature exceeds 850 ° C., it is difficult to extend the austenite grains and to introduce a deformation zone due to recrystallization of the austenite grains. On the other hand, if the temperature is lower than 650 ° C., excessive strain is introduced into the ferrite grains. This is because the work hardening is remarkable.

Further, by performing accelerated cooling after the above-mentioned rolling, austenite → ferrite transformation occurs at a low temperature in carbon steel, and bainite transformation also occurs in part, and as a result, higher strength and higher toughness are achieved. Become. In the present invention, the acceleration cooling rate is limited to 3 to 60 ° C./s by 3 ° C.
If it is less than 60 ° C./s, the effect is not remarkable, and if it exceeds 60 ° C./s, the effect is saturated.

The lower limit of the rolling temperature of the composite material is as described in the above-mentioned "Problems to be solved by the invention". Therefore, in order to maintain the temperature, high frequency or flame treatment may be applied in the rolling process. Rapid heating is performed, and for example, in the case of SUS329J2L clad steel, the laminated material side may be heated so that finish rolling is completed at 950 ° C or higher. As the heating method, high frequency or flame heating was used in the examples, but the heating method is not limited to these.

Since the method of the present invention cannot be carried out by the conventional sandwich type assembly, it is necessary to use the new sandwich type shown in FIG. 1 of the present invention, or the conventional open type and double-sided clad type.

In the case of the new sandwich type and the double-sided clad type, heating is performed from the top and bottom, and in the case of the open type, only the mating material on one side is heated, so that semi-warpage occurs. As a heating method for preventing the warp, for example, as shown in FIG. 2, a mechanism capable of following the warp by a high frequency coil or a flame treatment header enables uniform heating in the longitudinal direction and the width direction. In any case, heat treatment by high frequency, flame, etc. can be freely performed in the rolling process, and it is sufficiently possible to keep the vicinity of the contact interface between the laminated material and the base material at 1050 ° C. or higher, so there is no problem in bondability. .

FIG. 1 shows a sandwich type assembly of the present invention in a cross section thereof, in which a mating material 1 is arranged outside the upper and lower surfaces, and a base material 2 is set with a peeling agent 3 in the central portion sandwiched therebetween. Is shown. The second is an explanatory view showing a heating device on the side of the laminated material in a perspective view. The high frequency coil 4 is provided on the upper side (the laminated material side) of the curved surface following the warp of the laminated material 1 and the base material 2, and the carriage 5 is attached. It is shown that they are connected by a spring 6 so that the mating material side is heated.

Next, in order to achieve the object of the present invention, the chemical composition that the base material should have and the reason for limiting the numerical values will be described.

C: 0.01 to 0.2% C is an important strengthening element. If it is less than 0.01%, sufficient strength cannot be obtained as steel for line pipes, steel for shipbuilding and steel for offshore structures, and if it exceeds 0.2%. Therefore, the weldability and the toughness of the welded portion are impaired, so the range was made 0.01 to 0.2%.

Si: 0.05-0.8% Si is an element necessary for deoxidation in the steelmaking process,
It is also a solid solution strengthening element. If it is less than 0.05%, the deoxidizing effect is not sufficient, while if it exceeds 0.8%, the toughness of the steel,
Since it deteriorates the workability, it was limited to the range of 0.05 to 0.8%.

Mn: 0.3-2.2% Mn is an extremely important element in performing controlled rolling. Mn
Since it lowers the Ar ₃ point, it facilitates rolling in the low temperature range of austenite, and is an element that works effectively for improving strength and toughness.

However, if it is less than 0.3%, the effect of lowering the Ar ₃ point is small, and it is impossible to obtain a sufficient reduction ratio in the low temperature range of austenite. Cannot be secured. On the other hand, 2.2%
If it exceeds, the deterioration for welding will be significant, so it was limited to 0.3-2.2%.

Al: 0.001 to 0.07% Al is an important element as a deoxidizing element for steelmaking, and is an element that also has an effect on improving the toughness of the weld heat affected zone.

However, if less than 0.001%, the deoxidizing effect is not sufficient, while
Even if added in excess of 0.07%, the effect on the weld heat affected zone saturates, so the range was limited to 0.001 to 0.07%.

The above are the essential additive elements that belong to the first group.

Next, the selective addition element will be described.

Nb: 0.08% or less Nb has the effect of suppressing recrystallization of austenite and expanding the recrystallization temperature range. Therefore, elongation of austenite grains and introduction of deformation zones are facilitated, remarkable grain refinement is achieved, and toughness is improved. Nb is also effective as a precipitation strengthening element. However, if it exceeds 0.08%, the toughness of the welded part deteriorates significantly, so it was limited to 0.08% or less.

Cu: 2.0 or less Cu is an element that improves strength and is effective in improving corrosion resistance and weather resistance. By aging treatment, ε-Cu
Precipitation occurs in the phase and a remarkable improvement in strength is achieved. But 2.0%
If it is added in excess of 10%, surface cracking due to Cu tends to occur during heating, so the content was limited to 2.0% or less.

Ni: 3.0% or less Ni is an element effective for improving toughness, but it is expensive, and 3.
Even if added in excess of 0%, the effect of improving toughness does not improve so much, so it was limited to 3.0% or less.

Ti: 0.1% or less Ti, like Nb, is an element effective in suppressing recrystallization of austenite and strengthening precipitation.

It is also effective in improving the toughness of the weld heat affected zone.

However, if it exceeds 0.1%, the toughness deteriorates due to the precipitation of TiC, so the content is limited to 0.1% or less.

Cr: 1.0% or less, Mo: 1.0% or less, V: 0.1% or less Cr, Mo, and V are both effective elements for improving hardenability and precipitation strengthening. However, when added in excess of the above specified amounts, respectively, Cr: 1.0% or less, Mo:
It is limited to 1.0% or less and V: 0.1% or less.

B: 0.004% or less B adds significantly to the hardenability by adding a small amount. But 0.
If added in excess of 004%, the toughness of the welded part will be significantly impaired, so the content was limited to 0.004% or less.

Ca: 0.008% or less Ca is an element effective in controlling the morphology of inclusions in steel.

HIC is suppressed by adding Ca. But 0.008
If it is added in excess of%, clusters of Ca inclusions are likely to be formed, and HIC will be deteriorated. Therefore, the amount of Ca added is limited to 0.008% or less.

The elements of the second group described above, Nb, Cu, Ni, Ti, Cr, Mo,
V, B, and Ca will be added in an amount of one kind or two or more kinds within the respective stipulated ranges, depending on the use of the produced stainless clad steel.

(Example) Table 1 shows the chemical compositions of the base material and the composite material used in the examples of the present invention.

The clad assembly of these materials is a new sandwich type,
There are three types, open type and double-sided clad type. Table 2 shows the details of the assembled thickness and the finished thickness.

The furnace heating prior to rolling was 1200 ° C. (The example in Table 4 is 1050 ° C.) Rapid heating in the rolling process was performed by high frequency and flame on the exit side of the rolling mill. The high frequency used is 30 KHZ. In the case of sandwich type and double-sided clad, a spiral coil is used to heat from the upper and lower surfaces during rolling, and in the case of open type, a device that follows the warp of the rolled plate as shown in Fig. 2 is used. Only the side of the laminated material was heated. Flame heating used pressurized coke oven gas as fuel. The number of times of heating in the rolling process is 1 to 6 times.

The rolling temperature was measured and controlled by thermocouples inserted in the base material and the laminated material.

At the time of rapid cooling after the completion of rolling, water was used as a refrigerant and the cooling rate was controlled by the amount of water.

Survey items include peeling of the interface, cracking of the composite material, shear test (JIS G 0601), and corrosion resistance test (JIS G 0601).
0573, 65% nitric acid corrosion test), tensile test of base material,
The V notch Charpy impact test and the like of the base material were performed. Third
The results are shown in the table in comparison with the conventional stainless clad steel manufacturing method.

In Table 3, the conventional method (high) shows the finish rolling process at high temperature from the viewpoint of cracking and corrosion resistance of the laminated material, and the conventional method (low) emphasizes the toughness of the base material in the low temperature finishing process. It means that you have done it. Further, as a matter of course, in the conventional method, rapid heating in the rolling process is not performed in any case. As the cooling method after rolling, both standing cooling and rapid cooling were performed.

From the results shown in Table 3, in the case of the conventional method, the toughness of the base material is extremely high in the process of the conventional method (high) in any combination of the laminated material and the base material, for example, SUS 310S / B steel. Very low. Further, in the conventional method (low) process, a crack occurs in the laminated material (SUS329JL2) or a remarkable sensitization occurs (SUS310S, SUS44).
4), interfacial peeling occurs (SUS304, SUS31
6L).

On the other hand, examples of the present invention (in the table, the present invention (1), the present invention
(3), etc. indicate the number of the invention in the claims) in all of the present inventions (1) to (4). It can be seen that the toughness of the base material is remarkably improved as compared with the conventional method. Moreover, when rapidly cooled after rolling, it is clarified that not only the physical properties of the base material are improved, but also the corrosion resistance is significantly improved (SUS329JL2 /
D steel Invention (4), SUS310S / E steel Invention
(Four)).

Table 4 shows an example of performing clad rolling with furnace heating at 1050 ° C., and rapid heating of the laminated material side is performed in the rolling process. However, in this example, heating was performed for every two passes for a slightly long time so that the temperature near the interface was maintained at 1050 ° C. or higher until the plate thickness reached 80 mm. It can be seen that by adopting the method of the present invention, high shear strength can be obtained even at about 1050 ° C. heating before rolling.

"Effects of the Invention" As described in detail above, according to the method of the present invention, the occurrence of cracks in the laminated material is prevented, its sensitization is suppressed, and the occurrence of peeling at the interface is completely prevented. It has become possible to manufacture stainless clad steel with excellent corrosion resistance that has significantly improved toughness. Further, as a secondary effect of the present invention, the cladding is heated at a low temperature and the solution is directly solutionized (direct ST
Processing is also possible, so that the effect of the present invention on the industry is extremely large.

[Brief description of drawings]

FIG. 1 is a drawing showing a sandwich type clad assembly drawing of an embodiment of the present invention in its cross section, and FIG. 2 is an explanatory view showing an example of a heating device for a laminated material for carrying out the method of the present invention in a perspective view. FIG. 3 is a sectional view showing a conventional clad assembly diagram. 1: Laminated material, 2: Base material 3: Release material, 4: High frequency coil, 5: Carriage, 6: Spring.

Claims (4)

[Claims] 1. A ferrite or austenitic stainless steel or a duplex stainless steel as a composite material, and C: 0.01 to 0.2%, Si: 0.05 to 0.8% by weight as a base material.
Mn: 0.3 to 2.2%, Al: 0.001 to 0.07%, using a steel material consisting of the balance iron and unavoidable impurities, in the middle of clad rolling, by rapidly heating the composite material side A method for producing a stainless clad steel sheet excellent in corrosion resistance and toughness, which is characterized in that the finishing temperature of rolling is controlled to 650 to 850 ° C. on the base material side without being higher than the base material side. 2. A ferrite or austenitic stainless steel or a duplex stainless steel as a composite material, and C: 0.01 to 0.2%, Si: 0.05 to 0.8% by weight as a base material.
Mn: 0.3-2.2%, Al: 0.001-0.07%, and N
b: 0.08% or less, Cu: 2.0% or less, Ni: 3.0% or less, Ti:
0.1% or less, Cr: 1.0% or less, Mo: 1.0% or less, V: 0.1%
Hereinafter, by using a steel material composed of the balance iron and unavoidable impurities containing one or more of B: 0.004% or less and Ca: 0.008% or less, the mating material side is rapidly heated during clad rolling. The temperature of the laminated material side is set to be higher than that of the base material side, and the finishing temperature of rolling is 650 to 50 on the base material side.
A method for producing a stainless clad steel sheet excellent in corrosion resistance and toughness, characterized by controlling at 850 ° C. 3. A ferrite or austenitic stainless steel or a duplex stainless steel as a composite material, and C: 0.01 to 0.2%, Si: 0.05 to 0.8% by weight as a base material.
Mn: 0.3 to 2.2%, Al: 0.001 to 0.07% is used, a steel material composed of the balance iron and unavoidable impurities is used, and during the clad rolling, the material side is rapidly heated by heating the material side. Excellent in corrosion resistance and toughness, characterized in that the temperature is higher than that of the base metal side, the finishing temperature of rolling is controlled to 650 to 850 ° C. on the base material side, and then rapidly cooled at 3 to 60 ° C./s. Method for producing stainless clad steel. 4. A ferrite or austenitic stainless steel or a duplex stainless steel as a composite material, and C: 0.01 to 0.2%, Si: 0.05 to 0.8% by weight as a base material.
Mn: 0.3-2.2%, Al: 0.001-0.07%, and N
b: 0.08% or less, Cu: 2.0% or less, Ni: 3.0% or less, Ti:
0.1% or less, Cr: 1.0% or less, Mo: 1.0% or less, V: 0.1%
Hereinafter, by using a steel material containing the balance iron and unavoidable impurities containing one or more of B: 0.004% or less and Ca: 0.008% or less, and rapidly heating the side of the laminated material during clad rolling. The temperature of the laminated material side is set to be higher than that of the base material side, and the finishing temperature of rolling is 650 to 50 on the base material side.
A method for producing a stainless clad steel sheet having excellent corrosion resistance and toughness, which comprises controlling at 850 ° C. and then rapidly cooling at 3 to 60 ° C./s.