阅读说明：本技术 一种具有梯度组织的321奥氏体不锈钢管及制备方法 (321 austenitic stainless steel pipe with gradient structure and preparation method thereof ) 是由 涂益友 王畅 刘双 蒋建清 于 2020-05-26 设计创作，主要内容包括：本发明公开了一种具有梯度组织的321奥氏体不锈钢管具有从外至内的梯度组织结构,外层为细晶区,晶粒度为9～10级；内层为粗晶区,晶粒度为5～6级；通过旋压变形和热处理得到。本发明可使得321奥氏体不锈钢产品既有良好的高温强度和抗蠕变性能,在高温烟气腐蚀环境中具有良好的耐蚀性。(The invention discloses a 321 austenitic stainless steel tube with a gradient structure, which has a gradient structure from outside to inside, wherein the outer layer is a fine crystal region, and the grain size is 9-10 grade; the inner layer is a coarse crystal area, and the grain size is 5-6 grade; obtained by spinning deformation and heat treatment. The invention can lead the 321 austenitic stainless steel product to have good high-temperature strength and creep resistance, and good corrosion resistance in a high-temperature smoke corrosion environment.)

1. A321 austenitic stainless steel pipe with a gradient structure is characterized in that: the tube wall of the stainless steel tube has a gradient structure from outside to inside, the outer layer is a fine-grained region, and the grain size is 9-10 grades; the inner layer is a coarse crystal area, and the grain size is 5-6 grade.

2. The 321 austenitic stainless steel pipe of claim 1, wherein: the wall thickness of the stainless steel tube is 10-15 mm.

3. The 321 austenitic stainless steel pipe of claim 1, wherein: the proportion of special grain boundary of the outer fine-grained region is more than 60 percent.

4. A preparation method of 321 austenitic stainless steel pipe with gradient structure is characterized by comprising the following steps:

(1) spinning deformation: carrying out surface spinning deformation on a coarsely crystallized 321 austenitic stainless steel pipe, wherein the grain size of the austenitic stainless steel pipe is 5-6 grade;

(2) and (3) recrystallization annealing: and (4) carrying out recrystallization heat treatment on the stainless steel pipe subjected to the spinning deformation treatment.

5. The method of making a 321 austenitic stainless steel pipe of claim 4, wherein: the spinning deformation indentation depth in the step (1) is 0.1-0.5 mm, the rotating speed is 1-10 r/min, and the pipe feeding speed is 1.0-50 mm/min.

6. The method of making a 321 austenitic stainless steel pipe of claim 4, wherein: the temperature of the recrystallization annealing treatment in the step (2) is 800-900 ℃, the heat preservation time is 1-3 h, and the cooling mode is water quenching.

7. The method of making a 321 austenitic stainless steel pipe of claim 4, wherein: the pressure head in the step (1) is hemispherical.

Technical Field

The invention relates to an austenitic stainless steel pipe and a preparation method thereof, in particular to a 321 austenitic stainless steel pipe with a gradient structure and a preparation method thereof.

Background

The stainless steel pipe for the supercritical ultra-supercritical thermal power generating unit works in complex working environments such as high temperature, corrosion, fatigue and the like for a long time, has long replacement period, and has extremely high requirements on high-temperature mechanical properties and corrosion resistance in high-temperature flue gas and ultra-supercritical water vapor. The austenitic stainless steel has excellent corrosion resistance and high-temperature mechanical property, and is widely applied to high-temperature pipelines of supercritical ultra-supercritical thermal power generating units.

Research shows that the weakening of grain boundaries at high temperature is the main reason for the creep of austenitic stainless steel and the insufficient high-temperature strength. Therefore, coarse crystallization is a technical means for improving the high-temperature strength and the high-temperature creep resistance of austenitic stainless steel. However, the coarse grain austenite structure has insufficient corrosion resistance in the working environment of the supercritical thermal power generating unit, and the corrosion resistance in high-temperature corrosion flue gas is obviously inferior to that of the fine grain structure.

Disclosure of Invention

The purpose of the invention is as follows: one of the purposes of the invention is to provide a 321 austenitic stainless steel tube with a gradient structure, which can simultaneously ensure the corrosion resistance and high-temperature mechanical property of a stainless steel tube product; the second purpose of the invention is to provide a preparation method of the 321 austenitic stainless steel pipe with the gradient structure, and the preparation method is simple and easy to implement.

The technical scheme is as follows: according to the 321 austenitic stainless steel pipe with the gradient structure, the pipe wall of the stainless steel pipe has the gradient structure from outside to inside, the outer layer is a fine grain region, and the grain size is 9-10 grades; the inner layer is a coarse crystal area, and the grain size is 5-6 grade. The grain size was rated according to ASTM E112.

Preferably, the wall thickness of the stainless steel tube is 10-15 mm.

Preferably, the proportion of the special grain boundary of the outer fine-grained region is more than 60 percent; wherein, the special crystal boundary refers to a heavy site lattice crystal boundary CSL < 29.

The 321 austenitic stainless steel pipe is subjected to a high-temperature tensile test at 600 ℃, and the yield strength is more than 110MPa, and the tensile strength is more than 350 MPa; excellent corrosion resistance, no intergranular corrosion cracking (ASTMA262 method), and less than or equal to 6mdd of pitting corrosion (ASTM A923C method).

The invention also provides a preparation method of the 321 austenitic stainless steel pipe with the gradient structure, which comprises the following steps:

(1) spinning deformation: carrying out surface spinning deformation on a coarse grain 321 austenitic stainless steel pipe with the thickness of the pipe wall being 10-15 mm and the grain size being 5-6 grade;

(2) and (3) recrystallization annealing: and (4) carrying out recrystallization annealing treatment on the stainless steel pipe subjected to the spinning deformation treatment.

Preferably, the pressure head in the step (1) is hemispherical, the pressing depth is 0.1-0.5 mm, the rotating speed is 1-10 r/min, and the pipe feeding speed is 1.0-50 mm/min.

Preferably, the temperature of the recrystallization annealing treatment in the step (2) is 800-900 ℃, the heat preservation time is 1-3 h, and the cooling mode is water quenching.

The invention principle is as follows: the 321 austenitic stainless steel pipe has a gradient structure, is composed of a surface fine-grain region and an inner coarse-grain substrate, and can simultaneously ensure the corrosion resistance and the high-temperature mechanical property of a stainless steel pipe product. Carrying out surface spinning deformation on a coarse-grained 321 austenitic stainless steel pipe, and introducing a surface deformation layer; carrying out recrystallization treatment after spinning deformation, and obtaining a surface fine crystal layer through the coupling control of surface deformation and recrystallization treatment processes, wherein the fine crystal layer has a high-proportion special crystal boundary, particularly a heavy-site lattice crystal boundary CSL < 29; the fine grain layer on the surface and the coarse grain matrix form a gradient structure, and simultaneously, the corrosion resistance and the high-temperature mechanical property of the austenitic stainless steel pipe are ensured.

The existence of special grain boundaries in the austenitic stainless steel can effectively block the expansion of the intergranular corrosion. The 321 austenitic stainless steel pipe with the gradient structure has the material structure containing a high proportion of special grain boundaries, and can obviously improve the corrosion resistance of the austenitic stainless steel.

Has the advantages that: the austenitic stainless steel pipe with the gradient structure has the characteristics of self-generated gradient structure, fine-grained structure on the outer surface and coarse-grained structure on the inner surface, and can ensure that the product has good high-temperature strength and creep resistance; stretching at 600 ℃ and high temperature, wherein the yield strength is more than 110MPa, and the tensile strength is more than 350 MPa; in addition, the coating has good corrosion resistance in a high-temperature flue gas corrosion environment, no intergranular corrosion cracks (ASTM A262 method), and pitting corrosion amount less than or equal to 6mdd (ASTM A923C method); the preparation method is simple and easy to implement, and the prepared austenitic stainless steel tube has an obvious effect and a wide application range.

Drawings

FIG. 1 is an EBSD grain boundary characteristic distribution diagram of an outer surface fine grain region;

FIG. 2 is an EBSD grain boundary characteristic distribution diagram of an inner coarse grain region;

fig. 3 is a distribution diagram of grain boundary characteristics in comparative example 1.

Detailed Description

The present invention will be described in detail with reference to examples.