JPS6047890B2 - Ni-based alloy with excellent intermediate temperature brittleness resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Ni-based alloy that is resistant to so-called annealing cracks and has excellent resistance to intermediate temperature embrittlement during annealing after cold working or welding.

In general, Ni-Mo alloys are corrosion-resistant alloys that are ideal for reducing corrosion atmospheres, and are known to have excellent corrosion resistance against non-oxidizing acids, especially hydrochloric acid, and are used in petrochemical-related applications. It is one of the alloys widely used as materials for towers, tanks, heat exchangers, and piping.

These device parts are made by a combination of cold working such as bending and pipe drawing, and welding, but the residual strain and residual stress generated by such processing are removed after the processing or during intermediate processing steps. It was typically removed by annealing and then processed further or used as a final product. However, although this annealing is normally carried out at a temperature of 1000 to 11500C for several tens of minutes, when the alloy part passes through a temperature range of 700 to 800C while being heated to this temperature, , resulting in significant embrittlement (intermediate temperature embrittlement);
It was known that cracking occurs under the action of high tensile residual stresses. This annealing cracking is due to the 700
Due to the decrease in the bonding strength of grain boundaries at ~800°C and the precipitation of intermetallic compounds Ni and Mo with No and se in this temperature range, the intragrain strength increases, hardness increases, and elongation increases. Since this occurs due to the interaction between the effect of a significant decrease in the stress and the high tensile residual stress during cold working or J-welding, conventional means have been taken to prevent the occurrence of annealing embrittlement cracking in such alloys. As such, the following methods were considered. (a) By reducing the Mo content of the Ni-Mo alloy, precipitation of intermetallic compounds Ni and Mo is suppressed, and by suppressing the hardness in the temperature range of 700 to 800°C, crystal grains are reduced. A method to alleviate stress concentration in the field.

(b) Since a certain amount of time is required for the precipitation of the intermetallic compound Ni4MO, Ni4
A method that removes residual stress before MO precipitation occurs. (
C) A method in which no residual stress remains during cold working or welding, or only compressive residual stress remains.

However, with the method shown in (a) above for reducing the MO content, it is impossible to prevent the occurrence of annealing embrittlement cracking without impairing the excellent hydrochloric acid resistance of the Ni-MO alloy. The method shown in (b) becomes very difficult to implement industrially when the target product becomes large, and the method shown in (c) above cannot predict all the residual stresses in all parts of the actual processed product. Because it is difficult to measure this and the means to measure it are limited, it is extremely difficult to develop a processing method that does not leave tensile residual stress during cold working or welding. There was a problem that it could not be applied to products.

From the above-mentioned viewpoint, the present inventors have developed a method of annealing cold-worked parts or welded parts having high tensile residual stress at a slow heating rate; In order to obtain an alloy with excellent intermediate temperature brittleness resistance and corrosion resistance that does not cause annealing cracking even when
Based on O-based alloys, as a result of repeated research to improve intermediate temperature brittleness without losing its properties, Ni-
We have come to the knowledge that when MO-based alloys contain a small amount of B and limit the content of unavoidable impurities, the bonding strength of grain boundaries at 700 to 800°C is strengthened and the occurrence of cracks is suppressed. It is.

Therefore, the present invention was made based on the above findings, and the present invention is based on a Ni-based alloy having excellent corrosion resistance against non-oxidizing acids. ), Fe: 0.01 to 2.0%,
4B: 0.001-0.01%, N
i and unavoidable impurities: the remainder, and Cr. ．． M
n. ．． C.O. ．． SisC,. The contents of pl and S are as follows: Cr: 1.0% or less, Mn: 1.0% or less, CO: 1.0% or less, Si: 0.1% or less, C: 0.02% or less, P : 0.04% or less, S: 0.03% or less, and is characterized by providing excellent intermediate temperature brittleness resistance.

Next, in the Ni-based alloy of the present invention, MOlFe.
．． The composition range of component B is limited as described above, and Cr.
．． Mn. ．． CO,. Silc. ．． The reason why the amounts of unavoidable impurities of pl and S are limited as described above will be explained.

(a) MO The MO component dissolves in Ni, which is the base metal, and has the effect of improving the corrosion resistance of the alloy, especially hydrochloric acid resistance, and constitutes a Ni-based alloy that has excellent corrosion resistance against non-oxidizing acids. However, if its content is less than 26%, the desired effect cannot be obtained for the above action, while if it is contained in more than 30%, the hot workability of the alloy and the mechanical properties at room temperature are affected. The content was limited to 26 to 30% since it deteriorates the properties.

(b) Fe The Fe component has the effect of improving the hot workability of the alloy and the mechanical properties at room temperature, but when its content is 0.01
If the content is less than 2.0%, the desired effect cannot be obtained, and in particular, an alloy with extremely poor hot workability can be obtained. On the other hand, if the content exceeds 2.0%, the corrosion resistance of the alloy may be reduced. Therefore, the content should be 0.01 to 2.
．． It was limited to 0%.

(c) B The B component segregates at the grain boundaries of the alloy, strengthens the grain boundaries of the alloy, prevents the occurrence and propagation of intergranular cracks, and has the effect of increasing annealing cracking resistance. However, if the content is less than 0.001%, the desired effect cannot be obtained, while if the content exceeds 0.01%, the corrosion resistance of grain boundaries will deteriorate, and the welding Since it also has a negative effect on sex, its content has been reduced to 0.001.
~0.01% was limited.

(d) C The C component is a harmful element that forms carbides of MO at the grain boundaries in the welding heat affected zone, deteriorating the corrosion resistance of the grain boundaries in this area and causing intergranular corrosion. is 0.0
Since this tendency becomes noticeable when it exceeds 2%, the content was limited to 0.02% or less.

However, in order to ensure sufficient corrosion resistance, it is desirable that the C content be 0.01% or less. (e
)Cr. ．． Mn,. CO,. Si,. Pl and S In addition to C, Cr. ．． Mn. ．． C.O. ．． Si,. These impurities cause a decrease in corrosion resistance, a decrease in ductility, and a deterioration in weldability and workability of the alloy. ．． M
1% or less for nl and CO, 0 for Si
．． If it is 1% or less, 0.04% or less for P, and 0.03% or less for 8, it will not pose a practical problem, so the allowable range of the content was limited as described above.

Next, the Nj-based alloy of the present invention will be explained using examples and comparing with comparative examples.

Example 1 First, an alloy having the chemical composition shown in Table 1 was melted, hot-forged and hot-rolled using the methods normally used for Ni alloys, etc., and an annealed flat plate sample was prepared. Created.

In addition, sample numbers 1 to 3 are the invention alloys containing a predetermined amount of the B component, sample number 4 is a 5° comparative alloy in which the B component is not actively added, and sample number 5 is a 5° comparative alloy. This shows a comparative alloy containing more than 0.01% of the B component. Regarding these five types of samples, first,
A high temperature tensile test was conducted. In the high-temperature tensile test, the test piece was heated to a predetermined temperature within 5 minutes, held at this temperature, and then subjected to a tensile test at a tensile rate of 1wLImin.The elongation (%) of the sample at that time was measured. It is used to measure. The test results are also shown in Table 1. From the high-temperature tensile test results shown in Table 1, alloys 1 to 3 of the present invention and comparative alloy 5, in which the B component was actively added, were higher at 700°C and 75°C than the comparative alloy 4, in which the B component was not added.
The elongation at 0° C. was significantly improved, and it is clear that the inclusion of the B component strengthens the grain boundaries. Next, weldability due to the inclusion of B component and 20% HC
The effect on corrosion resistance in boiling solution was investigated.

The weldability test was carried out using a transbale strain test. This test method will be explained below. First of all,
One side of a plate-shaped test piece was fixed on a bending block, and bead-on-plate welding was performed on the surface of the test piece using DC positive polarity TIG. When the TIG torch moved to the center of the test piece, the bending occurred. The test piece is momentarily bent along the bending block, and at this time, the welding direction and the direction of bending strain are perpendicular to each other, and a predetermined bending strain is applied to the bead portion of the surface of the test piece. I'll do what I do. At this time, weldability is evaluated based on the length of the crack that occurs at the center of the bead. A diagram showing the relationship between the amount of strain and the maximum crack length obtained by such a transvalle strain test is shown in FIG.

From the results shown in FIG. 1, the alloy 1 of the present invention containing component B
There is no difference in the maximum crack length (the longer this is, the worse the weldability is) between Comparative Alloy 4 and Comparative Alloy 4 in which the B component is not actively added, but the B component content is less than 0.01%. Comparative Alloy 5, which exceeded the above, had a longer maximum crack length, and this also confirmed that addition of excessive B component deteriorated weldability.

Furthermore, we also conducted corrosion resistance tests against normal corrosion.
This was done by keeping the specimens in a boiling solution of 20% HCl for 3 weeks. The results were as shown in Table 1. The results shown in Table 1 are the average values of the corrosion test results conducted on three samples. There was no difference in corrosion depth between No. 3 and Comparative Alloy No. 4 to which the B component was not actively added, and
None of the alloys caused intergranular corrosion, but in Comparative Alloy 5, where the B content exceeded 0.01%, the corrosion depth was slightly larger and it was confirmed that intergranular corrosion occurred. Ta. Example 2 Invention alloys 1 to 3 used in Example 1 and comparative alloy 4,
A vibrator was made using the flat plate No. 5 using an upward non-filler automatic TIG welding machine.

Outer diameter thus obtained: 27.2wnφ x wall thickness:
2.2T 1m dimension vibrator is 27.0T
A vibrator with dimensions of 1 rfnφ x 2.2 gourd is heated in an electric furnace from 560°C to 1066°C in 2 hours and 30 minutes, then taken out from the furnace at 1066°C and cooled in the air. Annealing was carried out accordingly.

At this time, the temperature increase rate from 700°C to 750°C was 3.3°C for 1 min. After annealing, a color check was performed on the vibrator 5 to check for cracks. As a result, no cracking was observed in the welding vibrators made of Inventive Alloys 1 to 3 and Comparative Alloy 5, in which the B component was actively added. Cracks were observed in the welding vibrator made from Comparative Alloy 4, which does not contain any of the following. The results obtained in Examples 1 and 2 also show that the Ni-MO alloy containing the B component within the scope of the present invention has good weldability and corrosion resistance, and has excellent corrosion resistance. It was confirmed that the material also has intermediate temperature brittleness.

As mentioned above, the Ni-based alloy of the present invention is different from the conventional Ni-based alloy.
It has excellent corrosion resistance and weldability similar to MO alloys, and has high resistance to intermediate temperature embrittlement that conventional Ni-MO alloys do not have, so it can be used after cold working or welding. During the subsequent annealing, residual stress is not considered at all; in other words, even if high tensile residual stress exists, it is not reduced or converted to compressive residual stress, and is heated as it is. There is no need to particularly increase the temperature rate, and it has industrially useful properties such as being able to produce healthy, highly corrosion-resistant parts free of cracks etc. by simply annealing in a normal annealing furnace.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the relationship between the amount of strain and the maximum crack length of alloys with various chemical compositions.

Claims (1)

[Claims] 1 Mo: 26 to 30%, Fe: 0.01 to 2.0%, B: 0.001 to 0.01%, Ni and unavoidable impurities: the remainder; Cr, Mn,
The content of Co, Si, C, P, and S is
r: 1.0% or less, Mn: 1.0% or less, Co: 1.0% or less, Si: 0.1% or less, C: 0.02% or less, P: 0.04% or less, S: A Ni-based alloy with excellent resistance to intermediate temperature embrittlement, characterized in that the content is 0.03% or less (weight% or more).