JP6554243B1 - Ni-based alloy and method for producing slab for hot rolling using Ni-based alloy - Google Patents

Abstract

The present invention relates to a Ni-based alloy capable of preventing the occurrence of cracks in the initial stage of the hot forging process even in a large square Ni-based alloy ingot, and a method for producing a slab for hot rolling using the Ni-based alloy The purpose is to provide. SOLUTION: In mass%, carbon (C): 0.001 to 0.045%, silicon (Si): 0.05 to 1.00%, manganese (Mn): 0.05 to 1.00%, Phosphorus (P): 0.015% or less, sulfur (S): 0.0030% or less, chromium (Cr): 14-24%, niobium (Nb): 1.5-4.0%, iron (Fe) : 3-25%, Aluminum (Al): 0.01-0.20%, Nitrogen (N): 0.003-0.020%, Boron (B): 0.0010-0.0100%, Oxygen ( O): A Ni-based alloy comprising 0.0002 to 0.0020%, the balance nickel (Ni) and unavoidable impurities, and an Nb / B value of 500 or more. [Selection figure] None

Description

  The present invention relates to a Ni-based alloy having excellent stress corrosion cracking resistance and intergranular corrosion resistance. In particular, the present invention relates to a Ni-based alloy excellent in manufacturability capable of suppressing cracking and chipping in a forging process, and a method for manufacturing a hot rolling slab using the Ni-based alloy.

  Ni-based alloys have excellent corrosion resistance and heat resistance, and are therefore applied in harsh usage environments. Among the Ni-based alloys, for example, JIS NCF 600 equivalent materials are used as core materials of nuclear reactors because they have excellent resistance to stress corrosion cracking and intergranular corrosion resistance. In a more severe environment, an alloy is generally used in which Nb or the like is added and solid solution carbon is fixed as a carbide.

  However, the Ni-based alloy to which Nb is added has a problem in hot workability. Therefore, Patent Document 1 proposes a solution heat treatment of NbC. Patent Document 2 proposes improvement of grain boundary strengthening by adding B and reducing the O content. However, although both have certain effects, there is room for improvement in stress corrosion cracking resistance and intergranular corrosion resistance.

  Therefore, in Patent Document 3, a Ni-based alloy excellent in hot workability and excellent in stress corrosion cracking, and in Patent Document 4, hot rolled so as not to generate surface defects in a slab containing B and A method of manufacturing a Ni-based alloy hot-rolled sheet is proposed.

  On the other hand, even in Patent Documents 3 and 4, when the large-angle alloy ingot is used, cracks sometimes occur in the hot forging process, although the manufacturing cannot be continued. Therefore, especially when it is a large square type alloy lump, it is required to further improve cracking. The cracks in the hot forging process occurred after upset forging which is the initial process of the hot forging process, and it was found that the cracks were expanded in the press working of the next process. Further, it was found that this crack does not progress, that is, does not expand in the processes after press working. Therefore, particularly in the case of a large-angle alloy ingot, in order to further improve the crack resistance, it is required to prevent the occurrence of cracking in upset forging, which is an initial step of the hot forging step. .

Japanese Patent Application Laid-Open No. 63-53235 Japanese Patent Application Laid-Open No. 61-84348 Patent No. 4,993,327 Patent No. 4414588 gazette

  In view of the above circumstances, the present invention provides a Ni-based alloy and a slab for hot rolling using the Ni-based alloy, which can prevent the occurrence of cracking in the initial step of the hot forging process even in a large angle Ni-based alloy ingot. The purpose is to provide a manufacturing method.

  The inventors repeatedly studied earnestly in order to solve the above-mentioned problem, and considered that the crack could be prevented if the rolling reduction in the first pass of upset forging was reduced in order to solve the above-mentioned problem. As a result, no cracks were visible after 5% reduction. However, when forging was added and the process proceeded, cracks were confirmed. As a result, cracking could not be prevented even when the rolling reduction was reduced to 5%. Therefore, when the Ni-based alloy ingot after 5% reduction was ground and subjected to a penetration flaw detection test, fine cracks were partially confirmed. Further, when a penetration flaw detection test was performed on a Ni-based alloy ingot which had just been heated and heated, that is, a fine crack was partially observed. In contrast, no cracks were observed in the as-cast Ni-based alloy ingot. That is, it was considered that cracking occurred in the process of heating the Ni-based alloy ingot before the hot forging process.

  Then, when the cross-sectional microstructure of the crack part was observed about the Ni base alloy lump, there was a crack in the grain boundary of the coarse columnar crystal of the Ni base alloy lump, and a precipitate was confirmed there. When this precipitate was analyzed, it was a compound (carbide) containing Nb and C as main components, but the presence of B was also confirmed. Thus, as a result of examining the influence of Nb content, B content, and heating conditions on cracking, it was found that the Nb / B content must be controlled as a component for suppressing cracking. Moreover, as a heating condition of the Ni-based alloy before the hot forging step, it was found that it is necessary to hold at 1000 to 1049 ° C. for at least one hour or more to further promote the solid solution of NbC containing B.

The summary of the configuration of the present invention is as follows.
[1] By mass%, carbon (C): 0.001 to 0.045%, silicon (Si): 0.05 to 1.00%, manganese (Mn): 0.05 to 1.00%, phosphorus (P): 0.015% or less, sulfur (S): 0.0030% or less, chromium (Cr): 14-24%, niobium (Nb): 1.5-4.0%, iron (Fe): 3 to 25%, aluminum (Al): 0.01 to 0.20%, nitrogen (N): 0.003 to 0.020%, boron (B): 0.0010 to 0.0100%, oxygen (O 2.) A Ni-based alloy comprising 0.0002 to 0.0020%, the balance Ni and unavoidable impurities, and having an Nb / B value of 500 or more.
[2] The Ni-based alloy according to [1], wherein the Nb / B value is 650 or more.
[3] By mass%, carbon (C): 0.005-0.035%, niobium (Nb): 2.1-3.2%, boron (B): 0.0010-0.0070% Ni base alloy as described in [1] or [2] characterized by the above.
[4] The Ni-based alloy according to any one of [1] to [3], wherein the mass is greater than 5000 kg and at least one surface is a quadrangle.
[5] By mass%, carbon (C): 0.001 to 0.045%, silicon (Si): 0.05 to 1.00%, manganese (Mn): 0.05 to 1.00%, phosphorus (P): 0.015% or less, sulfur (S): 0.0030% or less, chromium (Cr): 14-24%, niobium (Nb): 1.5-4.0%, iron (Fe): 3 to 25%, aluminum (Al): 0.01 to 0.20%, nitrogen (N): 0.003 to 0.020%, boron (B): 0.0010 to 0.0100%, acid (O ): 0.0002 to 0.0020%, a balance of nickel (Ni) and inevitable impurities, an Nb / B value of 500 or more, a mass of more than 5000 kg, and at least one surface of a quadrilateral Ni-based alloy is 1000 After holding at -1049 ° C for 1 hour or more, the temperature is raised again to 1100-1250 ° C A first press step for performing upsetting forging of 5 to 20%, further heating to a range of 1150 to 1250 ° C., and forging with a rolling reduction per press of 5 to 15%;
Until the ingot subjected to the first pressing step is heated to a range of 1200 to 1300 ° C. and kept in a temperature range of 800 to 1300 ° C., forging with a reduction ratio of each press of 5 to 85%. A second pressing step of performing one step one or more times;
A third pressing step in which the ingot subjected to the second pressing step is heated to 1050 to 1230 ° C. and the total rolling reduction is set to 10% or more, and the pressing is performed;
A method of producing a slab for hot rolling comprising:

  According to the Ni-based alloy of the present invention, it is possible to prevent the occurrence of cracking and chipping even in a large-angle Ni-based alloy lump that tends to cause a temperature difference when the temperature is raised. Further, by applying the Ni-based alloy of the present invention, it is possible to manufacture a slab for hot rolling that prevents generation of cracks and chips even in a large-angle Ni-based alloy lump. For this reason, the Ni-based alloy of the present invention can be applied to a nuclear reactor material having strict required quality.

  Next, the Ni-based alloy of the present invention will be described in detail. The Ni-based alloy of the present invention is in mass% (hereinafter, mass%, which is the content of each component of the Ni-based alloy, is simply referred to as “%”), and carbon (C): 0.001 to 0.045%. , Silicon (Si): 0.05 to 1.00%, manganese (Mn): 0.05 to 1.00%, phosphorus (P): 0.015% or less, sulfur (S): 0.0030% or less , Chromium (Cr): 14 to 24%, niobium (Nb): 1.5 to 4.0%, iron (Fe): 3 to 25%, aluminum (Al): 0.01 to 0.20%, nitrogen (N): 0.003 to 0.020%, Boron (B): 0.0010 to 0.0100%, Oxygen (O): 0.0002 to 0.0020%, balance nickel (Ni) and inevitable impurities And has an Nb / B value of 500 or more.

C: 0.001 to 0.045%
C in the Ni-based alloy is an essential element to stabilize the austenite phase and to ensure mechanical strength at room temperature. For this purpose, a content of 0.001% or more is required. On the other hand, addition of an excessive amount generates a compound (carbide) containing Nb and C as main components, forms a Cr-deficient portion in the vicinity thereof, and remarkably reduces corrosion resistance. Moreover, the compound which has Nb and C as a main component increases, and a crack is generated. Therefore, the upper limit of the content is 0.045%. The preferable lower limit of the content is 0.003%, and the particularly preferable lower limit is 0.005%. The upper limit of the content is preferably 0.040%, and particularly preferably 0.035%.

Si: 0.05-1.00%
Si in the Ni-based alloy is an essential element for deoxidation, and is further required to improve stress corrosion cracking resistance. This effect is obtained by addition of 0.05% or more. However, the addition of an excessive amount leads to the increase of inclusions and the associated generation of surface defects. Therefore, the upper limit of the content is 1.00%. A preferable lower limit of the content is 0.08%, and a particularly preferable lower limit is 0.10%. Moreover, the upper limit with preferable content is 0.80%, and an especially preferable upper limit is 0.60%.

Mn: 0.05-1.00%
Mn in the Ni-based alloy is, like Si, an element essential for deoxidation, and also contributes to the stability of the austenite phase. In particular, it is an element capable of securing the stability of the austenite phase while the increase in hardness due to the addition is small and the mechanical strength is optimized. For this reason, addition of at least 0.05% or more is necessary. However, the addition of an excessive amount reduces the corrosion resistance, so the upper limit of the content is 1.00%. A preferable lower limit of the content is 0.08%, and a particularly preferable lower limit is 0.10%. Moreover, the upper limit with preferable content is 0.80%, and an especially preferable upper limit is 0.60%.

P: 0.015% or less P in the Ni-based alloy is an element which segregates at grain boundaries and lowers corrosion resistance and hot workability. For this reason, the upper limit needs to be strictly limited. In the present invention, the content is limited to 0.015% or less. A preferable upper limit of the content is 0.012%, and a particularly preferable upper limit is 0.010%. Moreover, although the minimum of content is so preferable that it is near 0%, 0.001% is mentioned, for example.

S: 0.0030% or less S in the Ni-based alloy is an element that segregates at the grain boundary to form a low-melting-point compound and causes a decrease in hot workability, and should be reduced as much as possible. For this reason, the upper limit needs to be strictly limited. In the present invention, the content is limited to 0.0030% or less. Preferably it is 0.0025% or less, especially preferably 0.0020% or less. Moreover, although the minimum of content is so preferable that it is near 0%, 0.0001% is mentioned, for example.

Cr: 14-24%
Cr in the Ni-based alloy is an important element contributing to the improvement of the corrosion resistance, and an element essential for use in severe environments. For this reason, an addition of at least 14% is necessary. However, if it is contained in excess of 24%, the mechanical strength at high temperatures becomes high and processing becomes difficult. Furthermore, the austenite phase is destabilized and the precipitation of carbides is promoted. Therefore, the upper limit of the content is 24%. A preferable lower limit of the content is 15.0%, and a particularly preferable lower limit is 15.5%. The preferable upper limit of the content is 23.0%, and the particularly preferable upper limit is 22.0%.

Nb: 1.5-4.0%
Nb in the Ni-based alloy has the effect of precipitating C and N as carbides, nitrides or carbonitrides to improve the corrosion resistance. In order to obtain this effect, addition of at least 1.5% or more is necessary. However, if the content is too large, excessive precipitates may cause grain boundary brittleness, so the upper limit of the content is 4.0%. The preferable lower limit of the content is 2.0%, and the particularly preferable lower limit is 2.1%. The preferable upper limit of the content is 3.7%, and the particularly preferable upper limit is 3.2%.

Fe: 3 to 25%
Fe in the Ni-based alloy is a component that contributes to improvement in toughness. At least 3% addition is required to achieve this effect. However, if the content exceeds 25%, the corrosion resistance is lowered. Therefore, the upper limit of the content is 25%. The preferable lower limit of the content is 5%, and the particularly preferable lower limit is 6%. The preferable upper limit of the content is 23%, and the particularly preferable upper limit is 21%.

Al: 0.01-0.20%
Al in the Ni-based alloy is an element essential for deoxidation, and addition of at least 0.01% or more is necessary. However, when it is added in excess of 0.20%, the hot workability is deteriorated, many inclusions are formed in the base material, and the corrosion resistance tends to be lowered. Therefore, the upper limit of the content is 0.20%. A preferable lower limit of the content is 0.02%, and a particularly preferable lower limit is 0.03%. The preferable upper limit of the content is 0.18%, and the particularly preferable upper limit is 0.16%.

N: 0.003-0.020%
N in the Ni-based alloy improves the mechanical strength at room temperature, increases the stability of the austenite phase, and further improves the corrosion resistance. For this reason, addition of 0.003% or more is required. However, the formation of a compound with Nb reduces the amount of Nb that is effective, and blow holes are likely to occur. Therefore, the upper limit of the content is 0.020%. A preferable lower limit of the content is 0.005%, and a particularly preferable lower limit is 0.008%. The preferable upper limit of the content is 0.014%, and the particularly preferable upper limit is 0.012%.

B: 0.0010 to 0.0100%
B in the Ni-based alloy is an important element that improves hot workability. In hot forging and hot rolling, at least 0.0010% of addition is required to stably prevent cracking. On the other hand, when it contains exceeding 0.0100%, hot workability will fall rather. Therefore, the upper limit of the content is 0.0100%. A preferable lower limit of the content is 0.0015%, and a particularly preferable lower limit is 0.0020%. Moreover, the upper limit with preferable content is 0.0080%, and an especially preferable upper limit is 0.0070%.

O: 0.0002 to 0.0020%
O in the Ni-based alloy facilitates reduction of the N amount in the melting and refining processes. For this reason, it is necessary to contain at least 0.0002% or more. However, O combines with Al, Ti, Si, and Mn to produce a deoxidation product. When it is contained in excess of 0.0020%, the corrosion resistance is reduced due to the deoxidation product, which causes surface defects. For this reason, the upper limit of the content is made 0.0020%. A preferable lower limit of the content is 0.0003%, and a particularly preferable lower limit is 0.0004%. The preferable upper limit of the content is 0.0019%, and the particularly preferable upper limit is 0.0018%.

  In the Ni-based alloy of the present invention, the balance other than the above components is Ni and inevitable impurities. The Ni-based alloy of the present invention contains Ni as a main component.

Nb / B value of 500 or more The value of Nb / B in the Ni-based alloy of the present invention is an index for preventing cracks that occur when the large-angle Ni-based alloy ingot is heated and upset. When the value of Nb / B is less than 500, the amount of B becomes excessive with respect to the amount of Nb, precipitates of Nb, C, and B are formed, and cracks occur in the large-angle Ni-based alloy ingot. Therefore, the value of Nb / B is set to 500 or more. A preferable lower limit of the value of Nb / B is 600, and a particularly preferable lower limit is 650. The upper limit of the value of Nb / B is not particularly limited, but is 2000, for example. In the present specification, "large-angle type" means that a mass is more than 5000 kg and at least one surface is a square.

  According to the Ni-based alloy of the present invention, it is possible to prevent the occurrence of cracking and chipping even in a large-angle Ni-based alloy lump that tends to cause a temperature difference when the temperature is raised. Therefore, the Ni-based alloy of the present invention can be applied, for example, as a nuclear reactor material with strict required quality.

  Next, a method for producing a slab for hot rolling using the Ni-based alloy of the present invention, particularly from the state of a large-angle Ni-based alloy lump will be described below. The method of producing a slab for hot rolling using the Ni-based alloy of the present invention comprises a first pressing step, a second pressing step, and a third pressing step for the Ni-based alloy mass of the present invention. It includes the steps to be carried out in order.

First Pressing Process In the first pressing process, the Ni-based alloy of the present invention is heated again after heating treatment to 1100 to 1250 ° C. before upsetting forging, which is the initial process of the hot forging process. Heat to 5 to 20% upset forging, and then include upset forging at 1150-1250 ° C.

  In the Ni-based alloy of the present invention, as described above, particularly, when hot forging is performed in the form of a large rectangular Ni-based alloy mass, the heating process before upset forging, which is the initial process of the hot forging process, In the step of heating the Ni-based alloy before the hot forging step, fine cracks may occur depending on the heating conditions. Therefore, it is necessary to control the heating conditions before upset forging the Ni based alloy of the present invention in order to prevent fine cracks during upset forging to further improve the characteristics of the Ni based alloy. .

  The heating conditions for the large-angle Ni-based alloy ingot before upset forging are a heating temperature of 1000 to 1049 ° C. and a holding time at a heating temperature of 1000 to 1049 ° C. of 1 hour or more. By setting the above heating conditions, solid solution of NbC containing B precipitated when solidifying the Ni-based alloy can be promoted, and precipitates of NbC containing B can be efficiently dissolved again and made harmless.

  When the heating temperature is less than 1000 ° C., the re-solution of the NbC precipitate containing B is insufficient, and a sufficient detoxifying effect cannot be obtained. On the other hand, when maintained at a heating temperature exceeding 1049 ° C., partial dissolution occurs in the Ni-based alloy before the NbC-containing precipitate containing B re-dissolves, and rather, the Ni-based alloy cracks. Make it happen. Therefore, the heating temperature is set to 1000 to 1049 ° C. The lower limit of the heating temperature is preferably 1010 ° C., particularly preferably 1020 ° C. Moreover, 1047 degreeC is preferable and the upper limit of heating temperature has especially preferable 1045 degreeC.

  It is necessary to control the holding time at the heating temperature of 1000 to 1049 ° C in order to stably obtain the effect of the solid solution of the precipitate of NbC containing B on the heating of the large square Ni base alloy mass before upset forging. There is. The holding time needs to be 1.0 hour or more. If it is less than 1.0 hour, the effect of re-dissolution of the NbC precipitate containing B cannot be sufficiently obtained. The holding time is preferably 1.5 hours or more, and particularly preferably 2.0 hours or more. Although the upper limit of the said holding time is not specifically limited, For example, 10 hours or less are preferable from the point of production efficiency.

  After heating before the above-mentioned upset forging, the Ni-based alloy of the present invention is heated again and heated to 1100 to 1250 ° C. to perform upset forging of 5 to 20%.

  Next, the large angle Ni-based alloy mass is further forged. In the case of this further forging, the heating temperature is preferably high. This is because a large-angle type alloy ingot requires a large rolling force during forging, but can be reduced by heating at a high temperature, and a necessary rolling reduction rate can be easily secured. From the above, when further forging the large square Ni-based alloy ingot, heating at 1150 ° C. or higher is necessary. However, in the large angle Ni base alloy ingot, the heating temperature exceeding 1250 ° C. makes the heating and soaking time too long to lower the productivity, and causes local melting in the solidification segregation portion. Therefore, the heating temperature when further forging the large-angle Ni-based alloy ingot is 1150 to 1250 ° C. The lower limit of the heating temperature is preferably 1160 ° C, particularly preferably 1170 ° C. Moreover, 1240 degreeC is preferable and the upper limit of the said heating temperature has especially preferable 1230 degreeC.

  Moreover, in the case of the further forging which further forges a large square type Ni base alloy ingot, the rolling reduction rate for every press shall be 5 to 15% of range.

Second press step In the second press step, the ingot (Ni-based alloy ingot) subjected to the first press step is heated in the range of 1200 to 1300 ° C and kept in the temperature range of 800 to 1300 ° C while pressing. One step or more is performed one or more times until forging with a rolling reduction in each range of 5 to 85%.

Third Pressing Process In the third pressing process, the ingot (Ni-based alloy ingot) subjected to the second pressing process is heated to a range of 1050 to 1230 ° C., and the total rolling reduction is performed at 10% or more. .

  By applying the Ni-based alloy of the present invention and carrying out the first to third pressing steps, a slab for hot rolling in which the occurrence of cracking or chipping is prevented even for a large-square Ni-based alloy mass is produced. can do.

  Next, examples of the present invention will be described, but the present invention is not limited to these examples as long as the gist thereof is not exceeded.

Manufacture of Ni-based alloys of Examples 1 to 10 and Comparative Examples 1 to 6 In a 60 t electric furnace, a predetermined amount of raw materials such as scrap, nickel, chromium, niobium, etc. are charged and melted, and then AOD (Argon Oxygen Decarburization) Or, at VOD (Vacuum Oxygen Decarburization), a mixed gas of oxygen and Ar was blown to decarburize. Thereafter, ferrosilicon alloy and / or aluminum were added to reduce Cr, and then limestone and fluorite were added to perform deoxidation and desulfurization. Thereafter, the so-called ordinary ingot casting method was performed by injecting a molten metal from the lower side of the mold and casting it into a large rectangular Ni-based alloy mass. The mass of the large angle Ni-based alloy block was 8 tons, and the cross-sectional dimensions were 280 mm × 850 mm on the injection side and 550 mm × 1100 mm on the feeder side. The component compositions of the Ni-based alloys of Examples 1 to 10 and Comparative Examples 1 to 6 are shown in Table 1 below.

Heat treatment and upset forging of Ni-based alloys of Examples 1 to 10 and Comparative Examples 1 to 6 before casting and casting Forging After casting, the large-angle Ni-base alloy ingot cooled and solidified is heated to 2 at 1030 ° C. After holding for a time, it was reheated to 1200 ° C. to perform upset forging of 20%.

Cracks of Ni-base alloys of Examples 1 to 10 and Comparative Examples 1 to 6 For each large square Ni-base alloy ingot subjected to the above heat treatment and upset forging, the plane in the vicinity of the corner portion is an area of 1 m × 1 m. Oxidation scale is ground and removed, and a penetrant flaw test (Taseto Co., Ltd., 3-liquid type, cleaning liquid FR-Q, permeating liquid FP-S, developer FD-S) is performed on the portion where the oxidized scale is ground and removed. The number was detected and the crack was evaluated in the following four steps.
:: no cracks ○: 1 to 3 cracks: Δ: 4 to 6 cracks ×: 7 or more cracks

  The evaluation results of the cracks are shown in Table 1 below.

From Table 1 above, carbon (C): 0.001 to 0.045%, silicon (Si): 0.05 to 1.00%, manganese (Mn): 0.05 to 1.00%, phosphorus (P ): 0.015% or less, sulfur (S): 0.0030% or less, chromium (Cr): 14-24%, niobium (Nb): 1.5-4.0%, iron (Fe): 3- 25%, aluminum (Al): 0.01-0.20%, nitrogen (N): 0.003-0.020%, boron (B): 0.0010-0.0100%, oxygen (O): In Examples 1 to 10 consisting of 0.0002 to 0.0020%, the balance Ni and unavoidable impurities and having an Nb / B value of 500 or more, the evaluation of cracking was Δ or more. Therefore, in Examples 1 to 10, even when cracking occurred, the degree was minor, and it was found that there was no influence on the next process, and that there was no occurrence of the remaining process. In particular, in Examples 3 to 5 and 8 to 10 in which the Nb / B value is 600 or more, the evaluation of cracking is ○ or more, and the occurrence of cracking could be prevented more reliably. Moreover, in Examples 8 to 10 in which the Nb / B value is 750 or more, the evaluation of cracking was ◎, and no cracking occurred.

  On the other hand, Comparative Example 1 in which the Nb / B value is 500 or more but the B content is outside the range of 0.0010 to 0.0100%, and Comparative Examples 2 to 6 in which the Nb / B value is less than 500. Then, it was found that the evaluation of cracking was “x”, and there were many cracks, and the occurrence of the extra process was essential.

Heating conditions before upset forging Next, the heating conditions for the large-angle Ni-base alloy ingot after cooling and solidification were changed to the heating conditions shown in Table 2 below instead of holding at 1030 ° C. for 2 hours. In the same manner as above, evaluation of cracking was performed. Example 7 was used as the Ni-based alloy. The heating conditions before upset forging and the evaluation results of cracks are shown in Table 2 below.

As shown in Table 2, in Example 7-1～7- 4 and held 1 hour or more at a range of heating temperature from 1000 to 1,049 ° C. prior upset it was cracked △ or more. Thus, in Example 7-1～7- 4, even when a crack occurs, the degree is slight, no influence on the next process, it was found that no generation of excess process. Moreover , in Examples 7-1 to 7-4 where the heating temperature before upset forging was 1000 to 1045 ° C., the evaluation of cracking was not less than ○, and the occurrence of cracking could be prevented more reliably.

  On the other hand, Comparative Example 7-1 in which the heat treatment is not performed before upset forging, and Comparative Examples 7-2, 7-3, 7- in which the heating temperature before upset forging is 1080 ° C., 1100 ° C., 1050 ° C. 5. The heating temperature before upset forging is in the range of 1000 to 1049 ° C., but in Comparative Example 7-4 in which the holding time is less than 1 hour, in all cases, the evaluation of cracking is x, and the occurrence of cracking is large It turned out that the occurrence of extra steps is essential.

Further Forging Further forging was performed under the heating conditions shown in Table 3 below for the Ni-based alloys of Examples 7-3 and 7-4 that were subjected to the heat treatment and upset forging before upset forging. As a result of the evaluation of heating temperature and cracking of the further forging, the presence or absence of securing of the rolling reduction of 15% is shown in Table 3 below. In Table 3, a case where a reduction rate of 15% could be secured was indicated as “◯”, a case where the reduction rate of 15% could not be ensured as “x”, and a case where further forging could not be carried out as “−”. .

  From Table 3 above, in Examples 7-3C, 7-4A, and 7-4B heated to a range of 1150 to 1250 ° C. for further forging, the evaluation of cracking after further forging is ○, which is certain Could prevent the occurrence of cracking. It was also possible to secure a rolling reduction of 15%.

  On the other hand, in the further forging, in Comparative Example 7-3A heated to 1130 ° C., the evaluation of cracking was ○ even in the further forging, but the reduction rate of 15% could not be ensured. Moreover, in the further forging, in Comparative Example 7-3B heated to 1270 ° C., cracking occurred in further forging, and further forging could not be performed.

  The Ni-based alloy of the present invention can be used in a wide range of fields because it is possible to prevent the occurrence of cracks in the initial process of the hot forging process even if it is a large square Ni-based alloy ingot that tends to cause a temperature difference during heating. For example, it can be applied as a material for nuclear reactors having strict required quality.

Claims (3)

In mass%, carbon (C): 0.005 to 0.035 %, silicon (Si): 0.05 to 1.00%, manganese (Mn): 0.05 to 1.00%, phosphorus (P) : 0.015% or less, sulfur (S): 0.0030% or less, chromium (Cr): 14 to 24%, niobium (Nb): 2.1 to 3.2 %, iron (Fe): 3 to 25 %, aluminum (Al): 0.01 to 0.20%, nitrogen (N): 0.003-0.020%, boron (B): 0.0022 ~ 0.0070% , oxygen (O): 0 A Ni-based alloy comprising 0002 to 0.0020%, the balance nickel (Ni) and unavoidable impurities, and having an Nb / B value of 650 or more. The Ni-based alloy according to claim 1, which has a mass of more than 5000 kg and at least one face is a square. In mass%, carbon (C): 0.001 to 0.045%, silicon (Si): 0.05 to 1.00%, manganese (Mn): 0.05 to 1.00%, phosphorus (P) : 0.015% or less, sulfur (S): 0.0030% or less, chromium (Cr): 14 to 24%, niobium (Nb): 1.5 to 4.0%, iron (Fe): 3 to 25 %, Aluminum (Al): 0.01-0.20%, nitrogen (N): 0.003-0.020%, boron (B): 0.0010-0.0100%, oxygen (O): 0 A Ni-based alloy consisting of .0002 to 0.0020%, the balance nickel (Ni) and inevitable impurities, having an Nb / B value of 500 or more, a mass of more than 5000 kg, and at least one surface being a square is 1000 to 1049 ° C. Hold for 1 hour or more, and then warm again to 1100-1250 ° C. Heating, performing upset forging of 5 to 20%, further heating to a range of 1150 to 1250 ° C., and forging with a rolling reduction per press in a range of 5 to 15%;
Until the ingot subjected to the first pressing step is heated to a range of 1200 to 1300 ° C. and kept in a temperature range of 800 to 1300 ° C., forging with a reduction ratio of each press of 5 to 85%. A second pressing step of performing one step one or more times;
A third pressing step in which the ingot subjected to the second pressing step is heated to 1050 to 1230 ° C. and the total rolling reduction is set to 10% or more, and the pressing is performed;
A method of producing a slab for hot rolling comprising: