JPS6026815B2 - Manufacturing method of duplex stainless steel strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a duplex stainless steel strip, and more specifically, it improves the toughness of a hot-rolled steel strip to prevent cracking during winding after hot rolling or during cold rolling. The present invention relates to a manufacturing method that allows duplex stainless steel strip to be manufactured without any process.

Generally, 0.04% or less C, 1.0% or less Si, 4
．． 0% or less Mo, 0.50% or less Cu, 10.0~
15.0% Ni, 20.0-25.0% Cr, 0.
Mo less than 50%, more than 1.0% and less than 2.0% (N
b+Ta), including 0.05% or less N, {the amount of ferrite in austenite determined from equation 11 is 8 to 25%
A duplex stainless steel strip is used as a band arc overlay welding material.

Amount of ferrite = 3.2 {%Cr + %Mo + 1.5 x %S
i+0.5×(%Nb+%Ta)} −2.5{%Ni
+0.5x%Mn+30x%C+30x%N+0.30
x%Cu}-24.7
・・・・・・・・・【1' This steel strip is particularly suitable as a welding material for overlaying of nuclear reactor pressure vessels, oil refining equipment such as desulfurization towers, various chemical plant equipment, etc., and is suitable for use with other materials. It is said that one layer is sufficient even in places where two layers are normally required, and it is superior in workability.

That is, the above steel strip is SUS347 (JISG4307
), Cr, Nb+Ta are high, and therefore,
For example, if the chemical composition of the weld metal part is YB347 (JIS
Z3322), when overlaying with SUS347 steel strip, normally two layers are required, but with the above steel strip, one layer is enough to achieve the purpose. .

Therefore, the above-mentioned steel strip not only significantly improves workability during welding, but also eliminates slag entrainment defects caused by undercuts and overlaps that occur during two-layer welding, and is expected to be used in many fields. ing. However, for example, in order to cold-roll a band arc overlay welding material to a plate thickness of about 0.4, it is necessary to maintain good plowability of the hot-rolled steel strip, but the above-mentioned steel strip has poor toughness. There are many problems in the manufacturing process.

That is, the rutting property of a duplex stainless steel strip, especially the rutting property during the manufacturing process, deteriorates as ferrite-forming elements such as Cr and (Nb+Ta) contents increase.

Therefore, since the steel strip contains more than 1.0% (Nb+Ta) of 20.0 to 25.0% and less than 2.0%, the ballability during the manufacturing process is significantly impaired. To explain in more detail,
If the toughness of the hot-rolled steel strip is poor when it is cold-rolled to a level that can be used as a band arc overlay welding material, such as about 0.4 side, after hot-rolling, the hot-rolled steel strip may be burned with acid. Cracks occur when the hot-rolled steel strip is re-rolled prior to washing, and marginal cracks also occur when it is cold rolled after bran anchoring and pickling.

This not only causes a decrease in yield, but also damages the equipment used therein, making the work extremely dangerous for the operator. For this reason, although the above-mentioned steel strip has excellent properties as a material for band arc overlay welding, its grade quality deteriorates, and the current situation is that problems remain in the manufacturing process. The purpose of the present invention is to solve the above-mentioned drawbacks, and in particular, for a duplex stainless steel strip having the above-mentioned composition, the present invention provides a manufacturing method for producing a hot-rolled steel strip with excellent ballability at a high yield and without danger. Our goal is to provide the following.

That is, the present invention has C of 0.04% or less, Sj of 1.0% or less, Mn of 4.0% or less, Cu of 0.5% or less, 1
0.0-15.0% Nj, 20.0-25.0% C
r, 0.50% or less Mo, more than 1.0% and 2.0% (Nb+Ta), 0.05% or less N, and the following! 1) A hot-rolled steel strip of duplex stainless steel in which the amount of ferrite in austenite is 8 to 25% as determined by the formula,
After finish rolling during hot rolling, it is coiled at 600 qC or less, and then phosphorus annealed at a temperature of 100,000 to 1,250 °C, and from this dulling temperature, Vc = 20.2 × (the amount of ferrite determined by the following formula {1)) It is characterized by cooling down to 600 qo at a cooling rate higher than the rate determined from the formula -120 (00/min). Ferrite amount = 3.2 {%Cr+%Mo+
1.5×%Si+0.5×(%Nb+%Ta)} −2
．． 5{%Ni+0.5x%Mn130x%C+30x%
N10.30×%Cu)-24.7
・・・・・・・・・'11 Below, the method of the present invention will be explained in detail. First, C of 0.04% or less, Si of 1.0% or less, Mn of 4.0% or less, 0.5
0% or less Cu, 10.0-15.0% Ni, 20.
0-25.0% Cr, 0.50% or less Mo, 1.0
(Nb+Ta) exceeding 2.0% and 0.0
A duplex stainless steel ingot containing 5% or less N and 8 to 25% ferrite in austenite is bloomed and hot-rolled in a conventional manner, usually to a thickness of about 5.0 skin. After that, the hot rolled steel strip is rolled up at a temperature of 600 qC or less before being pickled.

Thereafter, the hot-rolled steel strip is competitively dulled at a temperature of 1000q○ to 1250°C, and cooled from this competitive dulling temperature to 600oo at a cooling rate higher than the rate Vc shown in equation (2), and then air-cooled, etc. by the usual method. Vc = 20.2 x (amount of ferrite) - 120 (°C/min)... [2] Next, after cooling as described above, when cold rolling is performed, for example, the plate thickness is 0. A steel strip of about 4 ribs is obtained, and this steel strip can be used as a band arc overlay welding material, etc.

In this case, when a duplex stainless steel strip is manufactured in this way, as mentioned above, despite the increased content of ferrite-forming elements such as Cr and (Nb+Ta),
The grade properties of the hot-rolled steel strip can be maintained in good condition, and it can be rolled without cracking during rewinding prior to dawn anchoring and pickling, as well as during annealing and cold rolling performed after pickling. Stopping is improved, equipment is not damaged, and work safety is improved. That is, when a duplex stainless steel with a large amount of ferrite is hot rolled and the hot rolled steel strip is annealed and then cold rolled as in the method of the present invention, cracks mainly occur after hot rolling. , re-rolling step '2' carried out prior to gradation and pickling. This is the time of cold rolling after gradation and pickling.

Therefore, if cracks occur in these two processes,
In addition to reducing the yield rate, equipment may be damaged, and it is dangerous for workers.

For this reason, the present inventors conducted research to solve these problems and found that ``600
After coiling at a temperature of 0.000000 or less, annealing at 1000 to 1250000, and cooling from this sintered anchor temperature to 60000 at a rate higher than the rate shown by equation 2, good toughness is imparted to the hot-rolled steel strip. It was found that cracking could be prevented during rewinding and cold rolling.

Table 1 To explain in more detail, steel A with the chemical composition shown in Table 1 is melted in a 50-ton furnace, cast into a steel ingot, then divided into portions, and then hot rolled. A hot-rolled steel strip having a thickness of 5.0 was prepared, and the hot-rolled steel strip was wound up to determine the relationship between the winding temperature and the impact value, as shown in FIG.

This impact test was conducted with a thickness of 5. About the side test piece 2
Carry out the V-notch Charpy test, and the test temperature is 0℃.
I did this three times.

In duplex stainless steel with a ferrite content of 8 to 25%, as in the present invention, there is no transition temperature like in general ferritic stainless steel, so the minimum impact value is 5k.
If it is 9 m/ or more, there will be no breakage of the steel strip even in extremely cold weather.

Therefore, as shown in Figure 1, if the coiling temperature is 60,000 or less, the hot rolled steel strip will not crack during the next rewinding and will have sufficient ballability. I understand. Next, the annealing temperature of the hot-rolled steel strip wound as described above was varied in the range of 70,000 to 1,350 qC, while the cooling rate was kept constant (700 °C/min).
The relationship between the dawning temperature and the shock value (at 0°C) was determined and was as shown in Figure 2.

As a result, when annealed in the range of 1000qo to 1250oo, the minimum impact value is 5k9m/ or more, and even if cold rolling is performed afterwards, no cracks will occur at that time and sufficient toughness will be maintained. It turned out that I have. Seven types of hot-rolled steel strips of 5-thickness and ferrite content ranging from 8 to 25% were produced, and these hot-rolled steel strips were heat-treated at 10500C for 1 minute. ~
It was cooled at a cooling rate of 100,000/min and the relationship between the cooling rate and the impact value (at 0°C) was determined, as shown in FIG. In this case, for duplex stainless steel, 6
In castles with a temperature higher than 00℃, the cooling rate has a significant effect on rutting behavior, whereas in castles with a low temperature of 600 qC or less, the effect of cooling rate on rutting behavior is extremely small. After cooling as per 60
Below 0oo, everything was cooled. The compositions of the steel strips B, C, and D shown in FIG. 3 are shown in Table 2. Table 2 From what is shown in this Figure 3, the impact value (0
℃) is found to depend on the cooling rate, and also varies depending on the amount of ferrite.

Therefore, in order to obtain the impact value of 5k9 skin/ground, we investigated the relationship between the minimum cooling rate Vc (℃/min) and the amount of ferrite, and as shown in Figure 4, we found that the amount of ferrite and the cooling rate (
It was found that there was a positive correlation with Vc), and this relationship was found to be organized as the above equation [2}.
Therefore, if a hot rolled steel strip is annealed at 1000°C to 125000°C and then cooled from this temperature to 60000°C at a cooling rate higher than the rate shown in the formula '2}, the impact value will be 5 kgm.
It is more than 9/average, and there is no breakage of the steel strip during cold rolling even in extremely cold weather. In other words, in order to impart toughness to a hot-rolled steel strip made of duplex stainless steel and completely eliminate breakage during cold rolling, the cooling rate from the bowl dull temperature to 600 qo is the rate shown by the formula {2- As described above, cooling is necessary. As explained above, the method of the present invention is to impart toughness to a hot-rolled duplex stainless steel strip, but the reason for limiting the composition of the target duplex stainless steel is as follows. That's right.

Regarding C, when used as a band arc overlay welding material, the intergranular corrosion resistance of the weld will deteriorate if the amount of C increases.

Therefore, the upper limit was set at 0.04%. Regarding Si, when used as a band arc overlay welding material, S
As i increases, the welding properties of the welded portion deteriorate.

Therefore, the upper limit was set at 1.0%. Regarding Mn, when used as a band arc overlay welding material, Mn
If n increases, the oxidation resistance of the welded part deteriorates, making it unsuitable for the purpose of the present invention, so it was set at 4.0% or less.

Regarding Ni, when Ni is used as a band arc overlay welding material, it maintains the corrosion resistance and toughness of the weld.
Add i.

However, if the Ni content increases too much, the amount of ferrite in the welded part decreases, making it easy to cause weld cracks and being expensive, so the upper limit was set at 15.0%. Also, Ni is 1
If it is less than 0.0%, the corrosion resistance and balling properties of the welded part will not be sufficient, and the object of the present invention will not be achieved. Regarding Cr,
Cr is added to improve corrosion resistance when used as a band arc overlay welding material, but as the amount increases, the hot rolled steel strip becomes more warped, and even if manufactured as described above, the grade 20.0-25.0% due to deterioration of
And so.

Regarding Mo and Cu, Mo and Cu are mixed into the raw materials as impurities, but when used as a band arc overlay welding material, the upper limit is 0.0. It was set at 50%.

Regarding Nb+Ta, when used as a band arc overlay welding material, it is preferable to add Nb and Ta to fix C and N and ensure intergranular corrosion resistance of the welded part.

However, if it is less than 1.0%, the fixation of C and N will be insufficient, and if it exceeds 2.0%, the rutting property will be reduced and bloom cracks will occur, making it difficult to manufacture hot-rolled steel strips. It becomes possible. For this reason,
(Nb+Ta) was reduced from 1.0% to 2.0% or less. Regarding N, when N is used as a band arc welding material, the intergranular corrosion resistance of the weld will deteriorate if it increases, so the upper limit is 0.
．． 05%.

Regarding the amount of ferrite, the amount of ferrite is adjusted to prevent stress corrosion cracking and weld cracking when used as a band arc overlay material, but if it is less than 8%, the effect is hard to be seen, and if it is less than 25%. If it exceeds this amount, cracks will occur during hot rolling even if produced as described above, making it impossible to produce a hot rolled steel strip, so the amount of ferrite is set at 8% to 25%.

Next, examples will be described.

Example 1 First, two types of steel E and F having the chemical composition shown in Table 3 were prepared.
was melted in a 50-ton furnace to create a 7-ton steel ingot.

Each steel ingot was bloomed and then hot rolled to produce a hot rolled steel strip having a thickness of 4.5 legs. Next, these hot-rolled steel strips were coiled under the temperature conditions shown in Table 4, then re-rolled prior to moth dulling, further cooled after moth dulling at the temperatures shown in Table 4, and then,
A steel strip was produced by cold rolling from the 4.5 thickness side to the 1.0 thickness side.

At this time, we investigated the impact value (at 0°C) before rewinding and before cold rolling during the manufacturing process of the hot rolled steel strip, and the presence or absence of cracks during rewinding and cold rolling. It was as shown in the table. As is clear from Table 3 and Table 4, when manufactured by the method of the present invention, the impact values (at 0°C) were all 5k9 skin/
or above, of sufficient quality, and when rewinding,
No cracking occurred during cold rolling, whereas in the comparative example, the impact value was less than 5k9m/, and cracking occurred during rewinding or cold rolling.

In addition, as mentioned above, for those with a board thickness of about 1.0 feet,
After performing intermediate phosphorous dulling, it is necessary to roll the material to a plate thickness of about 0.4 so that it can be used as a band arc build-up welding material.

However, if there are no cracks when the plate is rolled to a thickness of about 1.0, there will be no cracks even if it is cold rolled after that, so it is not necessary to roll the plate to a thickness of 1.0. ．． Misaki was stopped. Example 2 First, class 6 steel G, J, 1, J, with chemical composition shown in Table 5 was used.
K and L were melted in a 5-ton furnace to create a 5-ton steel ingot.

These steel ingots are separated and hot rolled to a thickness of 4. Manufactured hot-rolled steel strips from Cape Qiu. Next, these hot-rolled steel strips were wound at the temperature shown in Table 5, the coil was re-wound, and then cooled after rolling under the conditions shown in Table 5, and then rolled to a thickness of 4.0 mm.
The thickness of the ribs is 1. It was cold rolled to Cape Qiu. Next, for each of these steel strips, the impact values (at 0°C) before rewinding after hot rolling and before cold rolling after moth dulling were determined, and the impact values of cracks during rewinding and cold rolling were determined. When the presence or absence was investigated, the results were as shown in Table 5.

As a result, the hot-rolled steel strip produced by the method of the present invention has an impact value (at 000) of 5k9m/ground or more, and has sufficient rutting resistance, so that it can be easily rutted during re-rolling during manufacturing and during cold rolling. No cracking occurred at all. As explained in detail above in Table 5, the method of the present invention has C of 0.04% or less, Si of 1.0% or less, Mh of 4.0% or less, 0.5
0% or less Cu, 10.0-15.0% Ni, 20.
0-25.0% Cr, 0.50% or less Mo, 1.0
(Nb+Ta) exceeding 2.0% and 0.0
A hot-rolled duplex stainless steel strip containing 5% or less of N and having a ferrite amount of 8 to 25% as shown in formula {11 above is rolled at a temperature of 600 qo or less after finish rolling during hot rolling. After that, it is annealed at a temperature of 1000 to 1250 qo, and from this phosphorus obtuse temperature to 600 oo, the above
A hot-rolled steel strip is produced by cooling at a cooling rate higher than the rate shown by the formula.

Therefore, even if the hot-rolled steel strip made of duplex stainless steel contains a large amount of ferrite-forming elements such as Cr and (Nb+Ta), the rutting property can be maintained well during the manufacturing process, and in particular, the rutting property can be maintained well during the manufacturing process. Cracks do not occur during rewinding prior to pickling or during cold rolling performed after dawn anchoring and pickling, improving yields.
Equipment will not be damaged and work safety can be maintained.

As mentioned above, the hot-rolled steel strip produced by the method of the present invention is a duplex stainless steel with a large amount of ferrite, so it is suitable as a band arc overlay molten acid material, and in particular,
It is suitable as an overlay welding material for nuclear reactor pressure vessels, oil refining equipment such as desulfurization towers, and various other chemical plant equipment. In addition, since this hot rolled steel strip contains a large amount of Cr and (Nb+Ta), even when two layers are required,
It goes without saying that one layer is sufficient and workability during welding is significantly improved.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the winding temperature and Charpy impact value (at 0°C) of steel strip of steel type A, and Figure 2 is a graph showing the relationship between the sintering temperature and Charpy impact value (at 0°C) of steel strip of steel type A. Figure 3 is a graph showing the relationship between the cooling rate and the Charpy impact value (at 0°C) when steel strips of steel types B, C, and D are cooled from the dull temperature to 60 mm. The graph shown in Figure 4 shows the ferrite content and Charpy impact value 5.
It is a graph showing the relationship with the minimum cooling rate to obtain k9m/ or more. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1 0.04% or less C, 1.0% or less Si, 4.0
% or less Mn, 0.50% or less Cu, 10.0-15
．． 0% Ni, 20.0-25.0% Cr, 0.50
% or less Mo, more than 1.0% and less than 2.0% (Nb+
Ta), 0.05% or less of N, and the amount of ferrite in austenite determined from the following formula (1) is 8 to 25
A hot-rolled steel strip of duplex stainless steel with a temperature of
Annealed at a temperature of ℃ to 1250℃, and from this annealing temperature Vc
=20.2×(amount of ferrite determined by formula (1) below)
A method for producing a duplex stainless steel strip, characterized by cooling to 600°C at a cooling rate higher than the cooling rate determined from the equation (-120°C c/min). Amount of ferrite = 3.2 {%Cr + %Mo + 1.5 x %S
i+0.5×(%Nb+%Ta)}-2.5{%Ni+
0.5×%Mn+30×%C+30×%N+0.30×
%Cu}-24.7...(1)