CN115786655A

CN115786655A - Method for avoiding thick-wall precipitation strengthening high-temperature alloy post-welding hot cracking

Info

Publication number: CN115786655A
Application number: CN202210885697.XA
Authority: CN
Inventors: 尹宏飞; 袁勇; 党莹樱; 谷月峰; 严靖博; 黄锦阳
Original assignee: Xian Thermal Power Research Institute Co Ltd; Huaneng Power International Inc
Current assignee: Xian Thermal Power Research Institute Co Ltd; Huaneng Power International Inc
Priority date: 2022-07-26
Filing date: 2022-07-26
Publication date: 2023-03-14

Abstract

The invention belongs to the technical field of material heat treatment, and particularly relates to a method for avoiding hot cracks after thick-wall precipitation strengthening high-temperature alloy welding, which comprises the following steps: firstly, heating the welded alloy from room temperature to 20 ℃ below an isothermal transformation curve of gamma' phase precipitation at a heating rate of less than or equal to 100 ℃/hour, and preserving heat for 1 to 2 hours; secondly, heating to 20-70 ℃ above the recrystallization temperature of the parent metal at the heating rate of 160-220 ℃/hour, and keeping the temperature for 1.5-3 hours; and finally, cooling to 250 ℃ along with the furnace, discharging from the furnace, and cooling to room temperature. By the postweld heat treatment method, the strain aging cracks are avoided, the welding residual stress can be completely eliminated, and the welding heat affected zone is strengthened, so that the comprehensive performance of a welding joint is guaranteed to be equal to that of a base metal.

Description

Method for avoiding thick-wall precipitation strengthening high-temperature alloy post-welding hot cracking

Technical Field

The invention belongs to the technical field of material heat treatment, and particularly relates to a method for avoiding hot cracking of thick-wall precipitation-strengthened high-temperature alloy after welding.

Background

With the development of 700 ℃ ultra-supercritical coal-fired power generation technology, the service temperature of key high-temperature components in a boiler reaches 700-750 ℃, and a solid solution strengthening type high-temperature alloy is difficult to reach the service temperature, so that a precipitation strengthening type high-temperature alloy material (such as Haynes 282 and Inconel 740H) needs to be selected. Aiming at a precipitation strengthening type high-temperature alloy welding joint, the traditional postweld heat treatment is mostly carried out in a gamma' phase aging treatment, so that a welding Heat Affected Zone (HAZ) is aged again to precipitate a strengthening phase. The method is easy to cause HAZ cracks of thick-wall and large-size component materials. However, thick-walled and large-sized components cannot eliminate welding residual stress without post-welding heat treatment, and thus cause deterioration of mechanical properties and deterioration of service life. Therefore, a post-weld heat treatment system for thick-wall, large-size precipitation-strengthened superalloy welded components is needed to ensure the performance of the welded components.

The weld reheat cracking of the precipitation strengthened superalloy is Strain Age Cracking (SAC), which is a solid phase edgewise crystal cracking that occurs in a weld heat affected zone next to a weld line after the precipitation strengthened superalloy is in service (in use) at high temperature after welding or during postweld heat treatment. The sensitivity of SAC is an essential property of an alloy (base material), and once the composition and structure of the alloy (even the design intention of the alloy) are determined, the SAC tendency has been determined. 3 inducers of reheat cracking:

1. residual stress of welding

The level of welding residual stress can reach the sigma of the solid solution state of the parent metal _s The level of (c). Controlling residual stress during welding of large size, thick walled materials is an effective way to avoid SAC in precipitation strengthened superalloys with moderate SAC sensitivity.

2. Thermal stress

Thermal stress caused by expansion and contraction of weld metal and base metal in heating process

3. Structural stress caused by aging precipitation

The gamma' phase is heated and separated out after welding to cause phase change shrinkage, and further a heat affected zone generates tensile stress.

Disclosure of Invention

The invention aims to solve the problem of reheat cracking in the heat treatment after welding of the conventional precipitation-strengthened high-temperature alloy, and provides a method for avoiding the reheat cracking of the thick-wall precipitation-strengthened high-temperature alloy after welding.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a method for avoiding hot cracking of thick-wall precipitation-strengthened superalloy after welding comprises the following steps:

in the first stage, heating to 20 ℃ below an isothermal transformation curve of gamma 'phase precipitation at a slower heating rate, and keeping the temperature for 1-2 hours to avoid the gamma' phase precipitation while ensuring thorough heat transfer;

and in the second stage, the temperature is raised to 20-70 ℃ above the recrystallization temperature of the parent metal at a relatively high temperature raising rate, the temperature is maintained for 1.5-3 hours, and the gamma' phase precipitated in the temperature raising process is completely dissolved back while the complete release of the residual stress is ensured.

The further improvement of the invention is that the temperature reduction process after the second stage heat preservation adopts slow cooling and furnace cooling to 200-250 ℃, and then air cooling is carried out, and forced convection heat dissipation can not be adopted.

The invention is further improved in that the applicable base material is gamma 'phase reinforced high-temperature alloy, and the gamma' phase forms high-temperature alloy with the element Ti + Al more than or equal to 1.6% according to mass fraction.

The invention is further improved in that the high-temperature alloy material with Ni more than or equal to 35 percent in the parent metal is applicable according to the mass fraction.

The invention is further improved in that the thickness of the welding joint is 200-900 mm.

The further improvement of the invention is that the temperature rise rate of the first stage of the postweld heat treatment is less than or equal to 100 ℃/hour.

The invention is further improved in that the temperature rise rate of the second stage of the postweld heat treatment is 160-220 ℃/hour.

The invention further improves the method that the supply state of the applicable precipitation strengthening superalloy base metal before welding is in a solid solution state.

The invention has the further improvement that no welding reheating crack is generated after the postweld heat treatment by the method, and the welding strength factor reaches more than 0.8.

Compared with the prior art, the invention has the advantages that:

1. compared with the traditional method for performing aging heat treatment after welding to cause the close base metal of a welding joint to perform aging treatment once, the method avoids the overaging of the base metal;

2. in the second stage of the method, the rapid heating rate passes through a precipitation hardening interval of HAZ in a short time, and the residual stress is eliminated at the recrystallization temperature, so that the occurrence of recracking cracks in a welding heat affected zone is effectively avoided;

3. the method heats (raises) stage by stage, reduces the temperature difference inside and outside the welding joint to the maximum extent, and reduces the thermal stress of the welding joint to the maximum extent.

Drawings

FIG. 1 is a schematic view of a post-precipitation strengthening type superalloy shaft weld stress relief heat treatment process.

Detailed Description

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. It should be noted that the embodiments and features of the embodiments of the present invention may be combined with each other without conflict. The present invention will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.

The invention provides a method for avoiding hot cracking of a thick-wall precipitation-strengthened high-temperature alloy after welding, which comprises the first stage of heating to 20 ℃ below an isothermal transformation curve of gamma 'phase precipitation at a slow heating rate and keeping the temperature for 1-2 hours, so that the gamma' phase precipitation is avoided while heat penetration is ensured;

Wherein, the temperature reduction process after the second stage of heat preservation adopts slow cooling and furnace cooling to 200-250 ℃, and then air cooling is carried out, and forced convection heat dissipation can not be adopted. The temperature rise rate of the first stage of postweld heat treatment is less than or equal to 100 ℃/h. The temperature rise rate of the second stage of postweld heat treatment is 160-220 ℃/hour.

Example 1:

referring to table 1 and fig. 1, the butt joint of the solid solution state ferronickel precipitation strengthening alloy shaft with the outer diameter of 500mm is welded by adopting GTAW + SMAW, and the post-welding heat treatment is carried out according to the method of the invention, wherein the temperature of the equal temperature transition curve of the ferronickel precipitation strengthening alloy gamma' is 610 ℃, and the recrystallization temperature is 960 ℃. In the first stage, heating to 20 ℃ below the gamma' phase precipitation temperature, and keeping the temperature for 1.5 hours, wherein the temperature rise rate in the first stage is 70 ℃/hour; heating to 20 ℃ above the recrystallization temperature in the second stage, and keeping the temperature for 2 hours, wherein the temperature rise rate in the second stage is 220 ℃/hour; and finally, cooling the steel plate to 200 ℃ along with the furnace, discharging the steel plate out of the furnace, air-cooling the steel plate to Room Temperature (RT), and performing nondestructive testing to avoid reheating crack and other defects. And (5) carrying out a lasting experiment on the welding joint sample, wherein the welding strength factor is 0.81.

TABLE 1

Although the invention has been described in detail hereinabove with respect to a general description and specific embodiments thereof, it will be apparent to those skilled in the art that modifications or improvements may be made thereto based on the invention. Accordingly, it is intended that all such modifications and alterations be included within the scope of this invention as defined in the appended claims.

Claims

1. A method for avoiding hot cracking of thick-wall precipitation strengthened high-temperature alloy after welding is characterized by comprising the following steps:

in the first stage, heating to 20 ℃ below an isothermal transformation curve of the separated gamma 'phase at a slow heating rate, and preserving heat for 1-2 hours to avoid the separation of the gamma' phase while ensuring heat penetration;

2. The method for avoiding the hot cracks after welding of the thick-wall precipitation strengthening superalloy as claimed in claim 1, wherein the temperature reduction process after the second stage heat preservation is slow cooling, furnace cooling to 200-250 ℃, and then air cooling, and forced convection heat dissipation is not available.

3. The method for avoiding the hot cracking of the thick-walled precipitation strengthened superalloy after welding as claimed in claim 1, wherein the base material is a gamma '-phase strengthened superalloy, and the gamma' -phase forming superalloy with Ti + Al content of 1.6% or more by mass fraction.

4. The method for avoiding hot cracking of thick-walled precipitation-strengthened superalloy after welding as claimed in claim 1, wherein the superalloy material with Ni ≥ 35% in the base material is used according to mass fraction.

5. The method for avoiding the hot cracking of the thick-wall precipitation strengthening superalloy after welding as claimed in claim 1, wherein the thickness of the applied welding joint is 200-900 mm.

6. The method for avoiding hot cracking of thick-walled precipitation-strengthened superalloy after welding as claimed in claim 1, wherein the first stage heating rate of the post-weld heat treatment is 100 ℃/hr or less.

7. The method for avoiding hot cracking of thick-walled precipitation-strengthened superalloy after welding as claimed in claim 1, wherein the second stage heating rate of the post-weld heat treatment is 160-220 ℃/hr.

8. The method of claim 1, wherein the pre-weld precipitation strengthened superalloy base material is in a solid solution state.

9. The method for avoiding the hot cracking of the thick-walled precipitation-strengthened superalloy after welding as set forth in claim 1, wherein no weld reheating crack is generated after the heat treatment of the thick-walled precipitation-strengthened superalloy after welding, and the welding strength factor is more than 0.8.