JP2019183181A - HIGH CORROSION RESISTANT Fe OR Ni-BASED ALLOY AND MANUFACTURING METHOD THEREFOR - Google Patents

Abstract

To provide a manufacturing method of a high corrosion resistant Fe or Ni-based alloy suppressing SCC and especially securing impact resistance of boring under low temperature environment.SOLUTION: A manufacturing method includes a two-step aging treatment with an aging treatment at a first temperature and an aging treatment at a second temperature to which the first temperature is lowered, after a solid solution treatment applied on an alloy having a component composition containing, by mass%, C:<0.020, Nb:0.1 to 0.4, Mo:3.0 to 3.5, Cr:19.5 to 22.5, Ni:42.5 to 46.0, Al:0.10 to 0.40, Ti:2.0 to 2.3, Mn:0.6 to 1.0, and Cu:1.5 to 2.0, and the balance impurities and Fe, with a Mn/Cu ratio of 0.3 or more, cooling rate from the first temperature to the second temperature in the two-step aging treatment is 5 to 60°C/h and contraction at a room temperature in a test method according to ASTM A370 is 45% or less.SELECTED DRAWING: None

Description

  The present invention relates to a Fe or Ni-based alloy having a composition mainly comprising Ni and Cr added to Fe and exhibiting high corrosion resistance, and a method for producing the same, and in particular, high corrosion resistance that is excellent in low-temperature impact resistance used in oil drilling applications. The present invention relates to an Fe or Ni-based alloy and a method for producing the same.

  An alloy having a component composition in which a large amount of Ni or Cr is added to Fe, which is an alloying element that can improve corrosion resistance, is used for piping and machine parts used in a corrosive environment. Here, the alloy shown as N09925 in the UNS standard is put on the market as a trade name: INCLOY 925 or a trade name: Alloy 925 equivalent material. The typical component composition range is mass%, C: <0.03, Si: <0.50, Mn: <1.00, S: <0.03, P: <0.03, Cr. : 19.5 to 22.5, Ni: 42.0 to 46.0, Mo: 2.5 to 3.50, Nb: <0.50, Cu: 1.50 to 3.00, Ti: 1. 90-2.40, Al: 0.10-0.50, Fe: bal. It is.

  For example, in Patent Document 1, good stress corrosion cracking resistance and hydrogen cracking resistance are obtained even in an environment where S (sulfur), which is more severe than the sour gas environment, is mixed as a single substance rather than sulfides such as FeS and NiS. A nickel-base alloy for oil country tubular goods is disclosed. Such a Ni-based alloy has a component composition in which Mo and / or W are added in a predetermined range together with Cr, and Cu is added, so that a protective film having higher hardness and excellent repairability can be formed. Specific component composition ranges are mass%, C: <0.10, Si: 0.05 to 0.30, Mn: <2.0, S: <0.0050, P: <0.030. Cr: 15-30, Ni: 45-60, Mo: <16, W <5.0, Nb: 0.30-3.0, Cu: 0.30-3.0, Ti: <2.0 , Al: <1.0, N: <0.050, Fe: bal. In this case, Mo and W are defined within a predetermined range.

  By the way, the American Petroleum Institute API standard stipulates detailed standards such as the component composition of alloy members used in oil drilling applications such as oil drilling drills, shafts, and oil well pipes, and heat treatment in the manufacturing process. It has been. In addition, the NACE standard of the National Association of Corrosion Engineers has a standard for evaluating corrosion resistance. For example, a test method and evaluation criteria of SSRT (Slow Strain Rate Test) which is one of evaluation methods of stress corrosion cracking (SCC) are defined.

Japanese Patent Laid-Open No. 62-158844

  From the viewpoint of corrosion resistance, the use of Fe or Ni-based alloys having a component composition in which a large amount of Ni or Cr is added to Fe is considered as an alloy used for oil drilling applications. On the other hand, it has been found that the manufacturing method according to the API standard of such an alloy does not satisfy the SSRT standard in the NACE standard, and in particular, the impact resistance in the low temperature environment of excavation cannot be obtained sufficiently.

  The present invention has been made in view of the situation as described above, and the object thereof is to suppress SCC, and in particular, highly corrosion-resistant Fe or Ni that secures impact resistance in a low temperature environment for excavation. It is to provide a base alloy and a method for manufacturing the same.

  The present invention intends to improve the corrosion resistance of an alloy indicated as N09925 in the UNS standard to suppress SCC and to secure impact resistance in a low temperature environment for excavation. In addition, the present invention aims to achieve SCC suppression, which was insufficient only by controlling the amount of Mo, by controlling the amount of Cu and Mn and by controlling the precipitation of the γ 'phase in the aging heat treatment. It is.

  That is, the highly corrosion-resistant Fe or Ni-based alloy according to the present invention is, in mass%, C: <0.020, Nb: 0.1 to 0.4, Mo: 3.0 to 3.5, Cr: 19.5. To 22.5, Ni: 42.5 to 46.0, Al: 0.10 to 0.40, Ti: 2.0 to 2.3, Mn: 0.6 to 1.0, and Cu: 1 .5 to 2.0, with the remaining impurities and Fe, and having a Mn / Cu ratio of 0.3 or more, and having a drawing at room temperature of 45% or less according to ASTM A370 compliant test method. Features.

  According to this invention, generation of secondary cracks in SSRT can be suppressed, and impact resistance in a low temperature environment for excavation can be ensured.

  In the above-described invention, the elongation may be 18 to 35% together with the aperture. According to this invention, generation of secondary cracks in SSRT can be suppressed, and impact resistance in a low temperature environment for excavation can be ensured.

  Moreover, the manufacturing method of highly corrosion-resistant Fe or Ni base alloy by this invention is the mass%, C: <0.020, Nb: 0.1-0.4, Mo: 3.0-3.5, Cr: 19.5 to 22.5, Ni: 42.5 to 46.0, Al: 0.10 to 0.40, Ti: 2.0 to 2.3, Mn: 0.6 to 1.0, and An alloy having a component composition including Cu: 1.5 to 2.0, the remaining impurities and Fe, and a Mn / Cu ratio of 0.3 or more is subjected to aging treatment at a first temperature after solution treatment, Including a two-stage aging treatment in which the temperature is lowered to a temperature of 2 and an aging treatment is performed, and the cooling rate from the first temperature to the second temperature in the two-stage aging treatment is 5 to 60 ° C./h, It is characterized in that the aperture at room temperature is 45% or less by the ASTM A370 compliant test method.

  According to this invention, in order to suppress the occurrence of secondary cracks in SSRT, the precipitation of the γ 'phase is controlled by two-stage aging, and as a result, an alloy that ensures impact resistance in the low temperature environment of excavation is obtained. It is done.

  In the above-described invention, the elongation may be 18 to 35% together with the aperture. According to this invention, it is possible to suppress the occurrence of secondary cracks in SSRT, and as a result, it is possible to obtain an alloy that ensures impact resistance in a low temperature environment for excavation.

It is a table | surface of the component composition of the alloy of an Example and a comparative example. It is a table | surface which shows the heat processing conditions of an Example and a comparative example. It is a table | surface which shows the result of the tension test and impact test of an Example and a comparative example. It is a table | surface which shows the stress corrosion cracking test result by the low strain rate method of an Example and a comparative example. 4 is a photograph of secondary cracks that occurred in the test piece of Comparative Example 1.

  A method for producing a highly corrosion-resistant Fe or Ni-based alloy as one embodiment according to the present invention will be described with reference to FIGS.

  Referring to FIG. 1, Examples 1 and 2 and Comparative Examples 1 and 2 are alloys having a component composition within the standard value of an alloy indicated as N09925 in the UNS standard. Here, with respect to the present example including Examples 1 and 2, in order to improve the corrosion resistance of the obtained alloy and suppress the stress corrosion cracking (SCC), the range of the component composition is newly defined within the standard value. The heat treatment conditions are changed.

  Specifically, the newly determined component composition ranges in mass% are C: <0.020, Nb: 0.1 to 0.4, Mo: 3.0 to 3.5, Cr: 19. .5 to 22.5, Ni: 42.5 to 46.0, Al: 0.10 to 0.40, Ti: 2.0 to 2.3, Mn: 0.6 to 1.0, and Cu : 1.5-2.0, the remaining impurities and Fe, and the Mn / Cu ratio is 0.3 or more. In particular, in the UNS standard, Mn: ≦ 1.0 mass% and Cu: 1.50 to 3.00 mass%, whereas in this example, the lower limit value for Mn is set high, and Cu The upper limit value for is set small.

  And as a manufacturing method of high corrosion resistance Fe or Ni base alloy, first, an alloy lump having a component composition within this range is obtained, and the alloy lump is adapted to the shape of the member to be obtained by hot working such as forging. Is molded.

  As shown in FIG. 2, in the heat treatment of the alloy ingot after forging, a two-stage aging treatment is performed after the solution treatment. The solution treatment can be, for example, a process of holding at 1025 ° C. for 2 hours and cooling with water. In the two-stage aging treatment, the aging treatment is performed at the first temperature, and the temperature is lowered to the second temperature and the aging treatment is performed. For example, after the first temperature is maintained at 740 ° C. for 8 hours, the temperature is decreased at a predetermined cooling rate, the second temperature is maintained at 620 ° C. for 8 hours, and air cooling is performed. In particular, the cooling rate from the first temperature to the second temperature is 5 to 60 ° C./h. With this cooling rate, the resulting alloy is made to have a drawing of 45% or less in a tensile test at room temperature in accordance with ASTM A370.

  By the way, the N09925 alloy in the UNS standard described above may not satisfy the standard for SSRT (Slow Strain Rate Test) in the NACE standard, particularly the impact resistance in the low temperature environment of excavation. On the other hand, when ductility is increased in consideration of impact resistance, the occurrence of secondary cracks in SSRT is promoted, and as a result, impact resistance in a low temperature environment may not be satisfied. In this regard, when the aperture is enlarged in the same alloy, necking is likely to occur on the surface due to strain, and a new surface is formed by the slip of the generated necking part and a passive film is divided. It is thought that the corrosion cracking phenomenon is advanced.

  Therefore, the present inventors have focused particularly on the contents of Mn and Cu in the above component composition. In other words, Mn increases stacking fault energy, so by setting its content high, work hardening is promoted, ductility is moderately reduced, necking is reduced, and generation of new surfaces due to destruction of the passive film is suppressed. obtain. On the other hand, since Cu reduces the stacking fault energy, the content can be set to a low level to suppress a decrease in work hardening and not prevent a moderate decrease in ductility. Therefore, the ratio of Mn content to Cu content (Mn / Cu) is set to 0.3 or more.

  In addition, the cooling rate from the first temperature to the second temperature of the two-stage aging treatment is determined as described above, and the occurrence of secondary cracks in the SSRT is suppressed while maintaining the toughness at a low temperature. Thus, the precipitation at the γ 'phase is controlled to reduce the drawing at room temperature to 45% or less. And the alloy which ensured the impact resistance in the low temperature environment of excavation is obtained.

  Thus, in this example, by controlling the cooling rate between the Mn and Cu contents and the two-stage aging treatment in particular, the occurrence of secondary cracks in SSRT is suppressed, and as a result, excavation High impact resistance can be obtained in a low temperature environment.

[Mechanical test]
The alloys of Examples 1 and 2 manufactured by the above-described manufacturing method were subjected to a tensile test at room temperature, a Charpy impact test at low temperature, and an SSRT, and the results will be described with reference to FIGS. .

  Alloys having the component compositions shown in Examples 1 and 2 of FIG. 1 were prepared, heat-treated as shown in FIG. 2 after forging, and test pieces used for each of the above tests were cut out. In Comparative Examples 1 and 2, test pieces were also obtained in the same manner as in the alloys in which the Mn content was reduced and the Cu content was increased as compared with Examples 1 and 2. In the heat treatment, the cooling rate between the first and second temperatures of the two-stage aging described above was 34 ° C./h in Example 1 and Comparative Example 1, and 10 ° C./h in Example 2 and Comparative Example 2. Other conditions were the same.

The tensile test was performed at room temperature, and the Charpy impact test was performed at −60 ° C. using a 2 mmV notch test piece. SSRT was performed at test level 7 as defined in NACE Standard TMD 198-2004. That is, the test temperature was 205 ° C., the Co ₂ partial pressure and the H ₂ S partial pressure were both 508 psia, and the NaCl concentration was 25%. Further, the strain rate was 4 × 10 ⁻⁶ (s ⁻¹ ), and strain was continuously applied until rupture. After rupture, the presence or absence of secondary cracks was confirmed by visual observation, and the class was evaluated.

  As shown in FIG. 3, in the tensile test at room temperature, Examples 1 and 2 and Comparative Examples 1 and 2 were equivalent in 0.2% proof stress and tensile strength, but in Comparative Example 1 in elongation and drawing. Examples 1 and 2 were smaller than No. 2 and No. 2. Moreover, in the Charpy impact test at −60 ° C., Examples 1 and 2 had lower impact values than Comparative Examples 1 and 2. That is, Examples 1 and 2 have lower ductility than Comparative Examples 1 and 2 while ensuring the tensile strength and toughness required as members used in a low temperature environment for drilling such as oil drilling drills. It can be said that it has.

  As shown in FIG. 4, in SSRT, secondary cracks were not observed in each of the three test pieces of Examples 1 and 2, and it was evaluated as class 3. That is, the occurrence of SCC was not confirmed. On the other hand, in Comparative Examples 1 and 2, secondary cracks as evidence of SCC were observed in many test pieces, and it was evaluated as Class 4 judged to be SCC.

  As shown in FIG. 5, for example, in Comparative Example 1, it can be seen that a secondary crack (portion indicated as “crack”) is generated in the vicinity of the fracture surface 1.

  That is, Comparative Examples 1 and 2 have higher ductility than Examples 1 and 2 and have high toughness at low temperatures, but easily generate SCC in a corrosive environment. The impact resistance has been lowered. In other words, Examples 1 and 2 have high impact resistance as a member in a low temperature environment of excavation, while slightly lowering the ductility and toughness as a material compared to Comparative Examples 1 and 2. is there.

  By the way, the composition range of an alloy capable of giving impact resistance in a low temperature environment of excavation almost equivalent to the high corrosion resistance Fe or Ni-based alloy including the above-described embodiments is determined as follows.

  C combines with Nb to produce MC type carbides. This MC type carbide exists stably in a high temperature region and suppresses excessive growth of crystal grains. Therefore, C can be added at less than 0.020% by mass as necessary.

  Nb combines with C to produce MC type carbides. Since C is fixed, Cr-based carbides generated by the heat treatment can be reduced to improve the corrosion resistance of the grain boundary part. Therefore, Nb is in mass% and is in the range of 0.1 to 0.4%.

  Mo forms a solid solution in the austenite of the parent phase to enhance the solid solution and improve the corrosion resistance. On the other hand, when it contains excessively, the production | generation of (alpha) phase will be accelerated | stimulated. Considering these, Mo is mass% and is in the range of 3.0 to 3.5%.

  Cr improves corrosion resistance by combining with oxygen to produce a passive film. On the other hand, when it contains excessively, the production | generation of (alpha) phase will be accelerated | stimulated. Considering these, Cr is in the range of 19.5 to 22.5% by mass.

Ni is essential as a stabilizing element for the austenite of the parent phase, and ensures corrosion resistance and combines with Al and Ti to generate precipitates (γ ′ phase) typified by Ni ₃ (Al, Ti). Improve mechanical strength. Therefore, Ni is in the range of 42.5 to 46.0% by mass.

Al combines with Ni to generate precipitates (γ ′ phase) typified by Ni ₃ (Al, Ti) to improve mechanical strength. Therefore, Al is in mass% and is in the range of 0.10 to 0.40%.

Ti combines with Ni to generate precipitates (γ ′ phase) typified by Ni ₃ (Al, Ti) to improve mechanical strength. Therefore, Ti is in mass% and is in the range of 2.0 to 2.3%.

  Mn promotes work hardening by increasing the stacking fault energy and affects toughness and ductility. Therefore, Mn is in the range of 0.6 to 1.0% by mass.

  Cu is an element having an effect of improving the corrosion resistance. On the other hand, if excessively contained, work hardening is suppressed by reducing stacking fault energy, which affects toughness and ductility. Considering these, Cu is in the range of 1.5 to 2.0% by mass.

As mentioned above, although the typical Example of this invention was described, this invention is not necessarily limited to these, Those skilled in the art will not deviate from the main point of this invention, or the attached claim. Various alternative embodiments and modifications may be found.

Claims (4)

% By mass
C: <0.020,
Nb: 0.1 to 0.4
Mo: 3.0-3.5,
Cr: 19.5 to 22.5,
Ni: 42.5-46.0,
Al: 0.10 to 0.40,
Ti: 2.0-2.3,
Mn: 0.6 to 1.0, and
Cu: 1.5 to 2.0, the remaining impurities and Fe, having a component composition with a Mn / Cu ratio of 0.3 or more,
A highly corrosion-resistant Fe or Ni-based alloy characterized in that the drawing at room temperature is 45% or less according to the ASTM A370 compliant test method.   2. The highly corrosion-resistant Fe or Ni-based alloy according to claim 1, wherein the elongation is 18 to 35% together with the drawing. % By mass
C: <0.020,
Nb: 0.1 to 0.4
Mo: 3.0-3.5,
Cr: 19.5 to 22.5,
Ni: 42.5-46.0,
Al: 0.10 to 0.40,
Ti: 2.0-2.3,
Mn: 0.6 to 1.0, and
An alloy having a component composition including Cu: 1.5 to 2.0, the remaining impurities and Fe, and a Mn / Cu ratio of 0.3 or more is subjected to aging treatment at a first temperature after solution treatment, Including a two-stage aging treatment in which the temperature is lowered to a temperature of 2 and an aging treatment is performed, and the cooling rate from the first temperature to the second temperature in the two-stage aging treatment is 5 to 60 ° C./h, A method for producing a highly corrosion-resistant Fe or Ni-based alloy characterized in that the drawing at room temperature is 45% or less by a test method conforming to ASTM A370. 4. The method for producing a highly corrosion-resistant Fe or Ni-based alloy according to claim 3, wherein the elongation is 18 to 35% together with the drawing.