JPS6053108B2 - Manufacturing method of nickel-based high chromium alloy with excellent stress corrosion cracking resistance - Google Patents

Description

Detailed Description of the Invention This invention has excellent stress corrosion cracking resistance, and the excellent stress corrosion cracking resistance can be applied to welding and subsequent SE (Str
ssrelief) relates to a method for producing a nickel-based high chromium alloy that does not deteriorate even after heat treatment.

In recent years, 30%Cr-60%Ni alloy has attracted attention as a material for pipes and heat exchangers for chemical equipment used in high-temperature, high-pressure environments containing pure water or Cl- ions, and its practical application is currently underway. There is. 30%Cr-60%Ni system is
This is because it has superior resistance to stress corrosion cracking compared to other steels and alloy materials.

Although the advantages of this material are certain, even when this material is used, stress corrosion cracking (hereinafter abbreviated as SCC) occurs in the weld heat affected zone and even in the base metal during use under the above environment. ) is unavoidable. This is because Cr carbide precipitates at the grain boundaries during the manufacturing process of the finished product, or during welding during equipment assembly and subsequent SR treatment (heating and holding at 55()C for a period of time), resulting in a Cr-depleted layer near the grain boundaries. It is thought that this is because the original performance of the Cr-60% Ni system is impaired as a result of SCC occurring. The present invention not only has the excellent SCC resistance inherent to the Cr-60% Ni system at the finished product stage immediately after manufacture, but also has the ability to resist subsequent welding and SR.
The object of the present invention is to provide a method for manufacturing Ni-based alloy products that do not become sensitive to SCC even after treatment. That is, the present invention provides 1C of 0.04% or less, Sil. 0% or less, Mnl. O%
Below, P.O. O3% or less, SO. OO5% or less, Ni5
O~80%, Crl5~35%, AlO. 50% or less, MOO. 5-2.0%, WO. An alloy containing 5 to 2.0% of one or both of them, with the remainder consisting essentially of Fe, 2
C0.04% or less, Sil. 0% or less, Mnl. 0% or less, PO. O3% or less, SO. OO5% or less, Ni5O
~80%, Crl5-35%, AlO. 50% or less, T
iO. 2 to 1.0%, and further contains MOO. 5-2.0%
, W.O. An alloy containing 5 to 2.0% of one or both of the elements, with the remainder substantially consisting of Fe, any of the above alloys is hot-worked and then cold-rolled at a working rate of % or more, followed by the attached drawings. A (0.5, 800), B (0.5,
750), C (101675), D (100, 675)
A nickel-based high chromium alloy with excellent SCC resistance, characterized in that the final annealing is carried out within the range surrounded by the straight line connecting the five points of E (1001800) and at a heating temperature and holding time that do not include 800°C. The gist is the manufacturing method.

In the case of 30%Cr-60%Ni alloy, finished products such as plates and tubes are generally subjected to cold rolling of 30% or less after hot working, and as a final heat treatment, the heating temperature is 950 to 1100 °C,
It is manufactured by performing short-time annealing with a holding time of about 2 to 3 times.

For such steel types, in order to avoid sensitization during SR treatment, it is necessary to suppress carbide precipitation after annealing as much as possible. This is a common sense view. That is, when the amount of carbide precipitation is large, Cr carbide precipitation due to SR treatment is accelerated, which tends to cause sensitization due to Cr deficiency. Precipitation of undissolved carbides decreases because the higher the annealing temperature, the more solid solubility of C increases. Also,
Regarding cold working before annealing, the smaller the degree of working, the
Since the slip band, which is the core of carbide precipitation, is small, carbide precipitation tends to be suppressed. For this reason,
The above-mentioned manufacturing method has been applied to the 30% Cr-60% Ni alloy, but since this method requires a high annealing temperature, there is a risk that the annealing may become sensitive during the cooling process. Furthermore, products that have undergone high-temperature annealing have a large amount of carbide precipitated at the grain boundaries due to the SR treatment performed at a temperature where C solid solubility is low. In some cases, there is a risk of becoming more sensitive. However,
If cold working before annealing is performed at a higher degree of working than before based on the method of the present invention, a significantly large number of slip bands will be generated in the alloy.

Here, if annealing is carried out at a temperature below 800°C, which is considerably lower than the conventional temperature, a large amount of carbides will form in the grains of the alloy in a short period of time, completely contrary to the conventional case. It will be dispersed and precipitated. As the solid solubility of C decreases due to the lower annealing temperature, the amount of carbides to be precipitated increases. This is the result of effective preservation of the situation. Furthermore, in this case, in terms of the precipitation of Cr carbide, which causes sensitization, as the precipitation is accelerated by a large amount of slip bands, the recovery of the Cr-depleted layer caused by the precipitation is also effectively accelerated. Therefore, during annealing, the recovery of the Cr-depleted layer is completed within a relatively short period of time, exceeding the line ABC in Figure 1.The product in which the Cr-depleted layer has been recovered is at least sensitive at that stage. The alloy has the inherent high SCC resistance.When the product obtained above is subjected to SR treatment,
Further, carbides are precipitated, but the amount is kept to be extremely small.

In other words, the amount of carbide precipitated by SR treatment is basically proportional to the difference in C solid solubility between the treatment temperature and the previous annealing temperature, and therefore, the lower the annealing temperature, the greater the amount of carbide in the SR treatment. The amount of precipitation decreases. At the same time, if Cr carbide has already precipitated sufficiently at the annealing stage, the amount of precipitation can be further reduced. In this way, if the amount of carbide precipitated by the SR treatment is small, and if the carbide is already finely dispersed in the alloy as described above, even if Cr carbide is precipitated by the SR treatment, the Cr-depleted layer will be in the grains. It only occurs around the carbides that are dispersed in the carbide. As is well known, sensitization is a phenomenon that occurs only when a Cr-depleted layer is continuously generated along grain boundaries, and there is no concern about sensitization in the above-mentioned dispersed state. Further, even when subjected to welding and SR treatment after the annealing, sensitization can be avoided when the C content in the alloy is 0.04% or less as in the present invention.

When heated to a high temperature by welding, the precipitated carbide melts again according to the C solid solubility corresponding to the heating temperature, and follows a trajectory where it precipitates again in the next SR treatment, but this S
During the R treatment, if the C content exceeds 0.04%, a Cr-depleted layer will be formed at the grain boundaries, causing cracking even if appropriate processing and heat treatment are performed. The manufacturing conditions and reasons for limiting the alloy components used in the present invention will be explained below.

Figure 1 shows the heating temperature and holding time in the final annealing.
It is a chart showing the influence on SCC resistance after treatment.

This was obtained through experiments, and the experiments were basically conducted in accordance with the method shown in Examples below. The alloys used in the experiment had the components shown in Table 1 below, and the degree of cold work was expressed in %. 0Δmouth◇ in the figure: Crack depth 0.0
Less than 57vn, ●A? ◆: Same as 0.05Wr! The scope of the present invention is defined by connecting and encircling the points A, B, C, D, and E. When the heating temperature exceeds 800°C, the solid solubility of C is too high and precipitation of carbides during annealing becomes insufficient, and the amount of precipitation increases in the subsequent SR treatment, which improves SCC resistance through sensitization due to continuous precipitation at grain boundaries. deteriorates. On the other hand, if the temperature is lower than 675°C, recrystallization, which is the original purpose of annealing, cannot be sufficiently achieved no matter how long the temperature is maintained. Regarding the holding time, if the holding time is less than 0.5 hours, recrystallization may not progress sufficiently in the case of a heating temperature of less than 800°C.
SR due to insufficient recovery of the Cr-depleted layer due to r-carbide precipitation.
SCC resistance decreases after treatment. If the duration exceeds 100 hours, there will be a significant economic disadvantage.

Furthermore, the heating temperature is 675 to 800°C, and the holding time is 0.5 to 1.
Even if the range 0CJIff is satisfied, point B (a) in the figure. Ichima,
750℃) and point C (10 hours, 675℃)
In the region below, both recrystallization and recovery of the Cr-depleted layer are insufficient. Figure 2 shows the cold working rate before annealing and C in the alloy.
FIG. 4 is a diagram showing the influence of the amount of heat on the fermentation temperature C property after welding + SR treatment.

The experiment that yielded this result was basically conducted in the same manner as in the examples described below, and the final annealing was performed at 800°C x 1
The alloy used in 0h1 is the same as in the case of FIG. In the figure, the area surrounded by a solid line indicates the scope of the present invention. The meanings of the symbols are the same as in FIG. If the cold working rate is less than 38%, a sufficient amount of slip bands cannot be secured, and a precipitation state in which carbides are dispersed within the grains during annealing cannot be obtained, and the effect of promoting recovery of the Cr-depleted layer is insufficient. Since recovery of the Cr-depleted layer cannot be expected by annealing at a low temperature and for a relatively short time as described above, there is a concern that sensitization may occur not only after welding + SR treatment but also at the stage after annealing. Even if the cold working rate is 1% or more, if the amount of C in the alloy is too large, good SCC resistance cannot be expected after welding + SR treatment. Generally, the higher the amount of C, the
Although it is easy to obtain a large amount of carbide by annealing, on the other hand, the carbide precipitated by the cold working + annealing melts again during welding, and the amount of reprecipitated carbide increases by the SR treatment. It becomes difficult to avoid Cr deficiency near grain boundaries due to carbide precipitation. In order to prevent Cr deficiency near the grain boundaries, which causes sensitization, a C content of 0.04% or less is required. Next, limit the ingredients of the alloy subject to the present invention (excluding C)
I will write about. Si, Mn, Al: All are deoxidizing elements, and below their respective lower limits they are ineffective, and when they exceed their upper limits, their effects become saturated and the cleanliness of the alloy deteriorates.

Ni: It is a key element that has a remarkable effect of improving corrosion resistance and improves resistance to SCC in high-temperature water containing C1- and in an alkaline solution (NaOFI) environment, and extremely high corrosion resistance can be expected with a content of 50% or more.

On the other hand, if it exceeds 80%, the effect is saturated and the amount of C that can be added is
Since the r amount is limited, it was set to 80% or less. Cr:N
Like i, it is an essential element for improving corrosion resistance.

If it is less than 15%, the effect is insufficient, and if it exceeds 35%, the hot workability deteriorates significantly.

Ti: A carbide-forming element, and because C is fixed as TiC through sensitization treatment, it is effective in suppressing the precipitation of harmful Cr carbide.

If it is less than 0.2%, the effect cannot be fully expected; 1.
If it exceeds 0%, problems arise in terms of alloy cleanliness.

In the case of an alloy in which C and Cr are relatively low in the alloy components, it is not necessary to add Ti. MO, W: These are components that are effective in strengthening the passive film, and their addition improves corrosion resistance.In particular, they are effective in delaying the occurrence of SCC caused by concentrated carbon. This effect is not observed unless 0.5% or more is added, and 2.0%
Exceeding this will cause deterioration in the cleanliness of the alloy.

P, S: Both are impurity components, P is 0.030%
If S exceeds 0.005%, hot workability will be impaired.

Next, examples of the present invention will be described.

30 alloys having each of the components (4) to (L) shown in Table 1
After vacuum melting, forging and softening, cold working and final annealing were performed under the conditions shown in Table 2.

After that, low-temperature heat treatment (corresponding to SR treatment) at 550℃ and 2C@ is performed, or TIG welding (with a 60A
1 (no error) and then subjected to the same low-temperature heat treatment as above as SR treatment, and from these materials 2 sequential thickness x 10
Two test pieces each measuring m width x 75 wm length were taken. This 2
Stack two test pieces and bend them into a U-shape.
TnIn was restrained to form a so-called double U-shaped bending test piece, which was stored in a 3e autoclave at 300 ppm.
It was immersed for 100 hours in non-degassed high temperature water of 300°C containing C1-. After the test, the crack depth in the cross section of the U-shaped inner test piece was investigated. The results are summarized in Table 2 1~■
Shown below. In Table 2 1 and ■ and ■, those (1) to (54) whose degree of cold rolling and annealing conditions are within the range of the present invention are SC
The maximum depth of C showed an extremely small value of 0.03 Tm or less in both the low temperature heat treated material and the welded + SR treated material.

On the other hand, in the comparative examples (55) to (82), the annealing conditions are outside the range of the present invention, so the SCC of the low-temperature heat-treated material is much larger than that of the present invention examples, and (75) to (82) are Since the degree of stretching is below the range of the present invention, the SCC resistance of the welded + SR treated material is significantly inferior. Furthermore, (55) to (58
), the amount of C in the alloy is too high, so welding + SC of SR treated material
C is getting worse. Incidentally, from conventional examples (83) to (84) manufactured by conventional methods, even if the amount of C in the alloy is lowered, the resistance of the low temperature heat treated material and the welded + SR treated material is lower. It can be seen that the 5CC properties are hardly improved. As is clear from the above explanation, according to the manufacturing method of the present invention, the original characteristics of the 30% Cr-60% Ni alloy, which has excellent stress corrosion cracking resistance, can be achieved not only at the finished product stage. , it is possible to obtain an alloy product which is also good and maintained even when subjected to subsequent welding or further SR treatment, and thus the present invention provides for welding-assembled corrosion-resistant equipment with 60% N1-30
This invention can be said to have extremely high utility value in the sense that it makes it possible to take advantage of the excellent corrosion resistance of the %Cr alloy.

[Brief explanation of the drawing]

Figure 1 shows the influence of final annealing heating temperature and holding time on SCC resistance after δR treatment for a 60%N1-30%Cr alloy, and Figure 2 also shows the cold rolling degree and C content in the alloy. FIG. 3 is a diagram showing the influence on SCC resistance after welding + SR treatment.

Claims (1)

[Claims] 1 C 0.04% or less, Si 1.0% or less, Mn 1.0
% or less, P0.03% or less, S0.005% or less, Ni
50% to 80%, Cr15 to 35%, Al 0.50% or less, and contains one or both of Mo0.5 to 2.0% and W0.5 to 2.0%, and the remainder is substantially made of Fe. After hot working, the alloy is cold rolled at a working rate of 38% or more, and then A(0.5,800) shown in FIG. 1 of the attached drawings,
B (0.5, 750), C (10, 675), D (10
0, 675), E (100, 800), and the final annealing is performed at a heating temperature and holding time that do not include 800°C. A method for producing a nickel-based high chromium alloy with excellent properties. 2 C0.04% or less, Si1.0% or less, Mn1.0
% or less, P0.03% or less, S0.005% or less, Ni
50 to 80%, Cr 15 to 35%, Al 0.50% or less, Ti 0.2 to 1.0%, and further Mo 0.5 to 2.
After hot working, an alloy containing one or both of 0% and 0.5 to 2.0% W, with the remainder substantially consisting of Fe, is cold rolled at a working rate of 38% or more, and then the alloy shown in FIG. A (0.5, 800), B (0.5, 750), C shown in Figure 1
(10, 675), D (100, 675), E (100
A method for producing a nickel-based high chromium alloy having excellent stress corrosion cracking resistance by heating within the range surrounded by the straight line connecting the five points of , 800) and not including 800°C.