阅读说明：本技术 一种超大型不锈钢结构件的深冷处理方法 (Cryogenic treatment method for ultra-large stainless steel structural member ) 是由 周鹏 周荣田 桂林 谢晶 陈文韬 郑小舟 吕政� 吕志杰 于 2019-12-25 设计创作，主要内容包括：本发明公开了一种超大型不锈钢结构件的深冷处理方法,包括以下步骤：清洁工件、根据超大型不锈钢结构件底部支撑筋的位置布置好用于支撑的工字钢和垫块,保证承重均匀,并将工件吊入深冷箱中；在工件表面及内部各个温区安装热电偶,并将各热电偶连接到外部控制设备。解决了超大型不锈钢结构件深冷处理过程中降温速度过快、各区域降温速度不均匀造成热应力过大的技术难题。(The invention discloses a cryogenic treatment method of an ultra-large stainless steel structural member, which comprises the following steps: cleaning a workpiece, arranging I-shaped steel and cushion blocks for supporting according to the position of a bottom support rib of an ultra-large stainless steel structural member, ensuring uniform bearing, and hoisting the workpiece into a deep cooling tank; thermocouples are installed at each temperature zone on the surface and inside of the workpiece, and each thermocouple is connected to an external control device. The technical problems of overlarge thermal stress caused by overhigh cooling speed and uneven cooling speed of each area in the subzero treatment process of the ultra-large stainless steel structural member are solved.)

1. A subzero treatment method of an ultra-large stainless steel structural member is characterized by comprising the following steps: the method comprises the following steps:

1) cleaning the workpiece, and removing scrap iron, slag, water and oil stains attached to the surface and the interior of the workpiece;

2) i-shaped steel and cushion blocks for supporting are arranged according to the position of a supporting rib at the bottom of the ultra-large stainless steel structural member, so that uniform bearing is ensured, and a workpiece is lifted into a deep cooling tank;

3) installing thermocouples on the surface of the workpiece and in each temperature zone inside the workpiece, and connecting each thermocouple to external control equipment;

4) installing a strain gauge in the stress concentration area to monitor stress change, and connecting the strain gauge to external control equipment;

5) after the preparation work is done, the box cover is covered, and after the fixation is finished, nitrogen or dry air starts to be blown into the cryogenic box to replace the air in the inner cavity of the cryogenic box;

6) injecting liquid nitrogen into a heat exchange bin of the cryogenic box, cooling gas in the heat exchange bin after the liquid nitrogen is gasified, and then blowing cold air into the cryogenic box through a fan to cool the workpiece;

7) after the temperature of the workpiece is reduced to-180 ℃, injecting liquid nitrogen into the deep cooling box, completely soaking the workpiece, and after the temperature of the workpiece is completely reduced, continuing to soak for not less than 30 min;

8) pressing the liquid nitrogen in the cryogenic box back to a liquid nitrogen tank, and blowing dry air or nitrogen slightly higher than normal temperature into the box body through a heater in the heat exchange bin to carry out temperature return;

9) after the workpiece is completely warmed up, introducing liquid nitrogen into the heat exchange bin again after 3 hours of time interval, cooling the workpiece by gasified cold air, directly injecting liquid nitrogen into the box body after the workpiece is cooled to-180 ℃, soaking and cooling to the temperature of the liquid nitrogen, and circulating for three times;

10) and after the third cryogenic cycle is completed, the workpiece is lifted out of the cryogenic box, the strain gauge and the thermocouple are disassembled, and the cryogenic treatment of the ultra-large stainless steel structural member is completed.

2. The cryogenic treatment method for the ultra-large stainless steel structural member according to claim 1, characterized in that: in step 1, the workpiece is cleaned and then dried.

3. The cryogenic treatment method for the ultra-large stainless steel structural member according to claim 1, characterized in that: in step 2, the effective size of the interior of the cryogenic box is 11m multiplied by 5.8m multiplied by 4.5m, heat exchange bins are arranged on two sides of the inner cavity of the cryogenic box, 12 air outlets are arranged, the air speed and the air outlet temperature of each air outlet can be independently controlled, and the temperature of each area of the whole inner cavity is adjusted by controlling the air speed and the air temperature of the 12 air outlets.

4. The cryogenic treatment method for the ultra-large stainless steel structural member according to claim 1, characterized in that: in step 3, at least 6 thermocouples are respectively arranged on the upper side and the lower side of the two side surfaces of the workpiece, at least 3 thermocouples are arranged in the workpiece, and the total number of the thermocouples is not less than 27.

5. The cryogenic treatment method for the ultra-large stainless steel structural member according to claim 1, characterized in that: and 4, simulating the deep cooling treatment process of the workpiece by digital simulation software in the stress concentration area of the workpiece.

6. The cryogenic treatment method for the ultra-large stainless steel structural member according to claim 1, characterized in that: and 6, monitoring the temperature of each region of the workpiece in the cryogenic box at any time through external monitoring equipment, and ensuring the cooling speed and the temperature uniformity in the cooling process by controlling the flow of liquid nitrogen or a heat preservation method.

Technical Field

The invention belongs to the field of stainless steel deep heat treatment processes, and particularly relates to a cryogenic treatment method for an ultra-large stainless steel structural member.

Background

With the development of society and science and technology, stainless steel equipment and parts working at low temperature are required more and more, and the sizes of the required parts are also larger and larger, particularly in the fields of aerospace, nuclear power and the like. Most of Cr — Ni austenitic stainless steels are in a metastable state at normal temperature, and undergo martensitic transformation due to lattice distortion in an ultra-low temperature range. When the operating temperature of austenitic stainless steel is equal to or lower than its martensite transformation point (Tmd), martensite transformation occurs. Because martensite has a larger specific volume than austenite, the resulting volume expansion and structural stresses cause part dimensional changes. It is necessary to perform cryogenic treatment on stainless steel parts in the manufacturing process to improve the dimensional stability and related properties of the stainless steel structural member in an ultralow temperature working environment. The stainless steel structural member with a complex structure and large internal welding residual stress and uneven distribution has the defects that the internal stress and the thermal stress generated by the change of the internal dimension are too large when the cooling speed is too fast in the cryogenic treatment process, and the welding seam generates cracks and defects due to the superposition of the internal stress and the welding residual stress. The deep cooling treatment process needs to control the cooling speed.

At present, the size of the existing cryogenic treatment parts is smaller and is within 2 m. The lowest temperature of the cryogenic treatment process of parts with slightly larger size, such as rollers produced by steel mills, reaches-140 ℃ to-150 ℃. The problem of overlarge thermal stress caused by the fact that the cooling speed is too high and the cooling speed of each area is not uniform exists in the deep cooling treatment process of the overlarge stainless steel structural member.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides the cryogenic treatment method of the ultra-large stainless steel structural member, which has the advantages of low cooling speed, uniform temperature of each area and effective reduction of overlarge thermal stress.

In order to achieve the purpose, the invention adopts the following technical scheme: a cryogenic treatment method for an ultra-large stainless steel structural member comprises the following steps:

1) cleaning the workpiece, and removing scrap iron, slag, water and oil stains attached to the surface and the interior of the workpiece;

2) i-shaped steel and cushion blocks for supporting are arranged according to the position of a supporting rib at the bottom of the ultra-large stainless steel structural member, so that uniform bearing is ensured, and a workpiece is lifted into a deep cooling tank;

3) installing thermocouples on the surface of the workpiece and in each temperature zone inside the workpiece, and connecting each thermocouple to external control equipment;

4) installing a strain gauge in the stress concentration area to monitor stress change, and connecting the strain gauge to external control equipment;

5) after the preparation work is done, the box cover is covered, and after the fixation is finished, nitrogen or dry air starts to be blown into the cryogenic box to replace the air in the inner cavity of the cryogenic box;

6) injecting liquid nitrogen into a heat exchange bin of the cryogenic box, cooling gas in the heat exchange bin after the liquid nitrogen is gasified, and blowing cold air into the cryogenic box through a fan to cool the workpiece;

7) after the temperature of the workpiece is reduced to-180 ℃, injecting liquid nitrogen into the deep cooling box, completely soaking the workpiece, and after the temperature of the workpiece is completely reduced, continuing to soak for not less than 30 min;

8) pressing the liquid nitrogen in the cryogenic box back to a liquid nitrogen tank, and blowing dry air or nitrogen slightly higher than normal temperature into the box body through a heater in the heat exchange bin to carry out temperature return;

9) after the workpiece is completely heated for 3 hours, introducing liquid nitrogen into the heat exchange bin again, cooling the workpiece by gasified cold air, directly injecting the liquid nitrogen into the box body after the temperature is reduced to-180 ℃, soaking and cooling to the liquid nitrogen temperature, and circulating for three times;

10) and after the third cryogenic cycle is completed, the workpiece is lifted out of the cryogenic box, the strain gauge and the thermocouple are disassembled, and the cryogenic treatment of the ultra-large stainless steel structural member is completed.

In the above technical solution, in step 1, the workpiece is cleaned and then dried.

In the above technical scheme, in step 2, the inside effective size of the cryogenic box is 11m × 5.8m × 4.5m, heat exchange chambers are arranged on two sides of the inner cavity of the cryogenic box, and 12 air outlets are provided, the air speed and the air outlet temperature of each air outlet can be independently controlled, and the temperature of each area of the whole inner cavity is adjusted by controlling the air speed and the air temperature of the 12 air outlets.

In the technical scheme, in the step 3, not less than 6 thermocouples are respectively arranged on the upper side and the lower side of the two side surfaces of the workpiece, not less than 3 thermocouples are arranged in the workpiece, and the total number of the thermocouples is not less than 27.

In the technical scheme, in the step 4, the stress concentration area of the workpiece is obtained by simulating the deep cooling treatment process of the workpiece through digital simulation software.

In the above technical scheme, in step 6, the temperature of each region of the workpiece in the cryogenic box is monitored at any time through external monitoring equipment, and the temperature reduction speed and the temperature uniformity in the temperature reduction process are ensured by controlling the flow of liquid nitrogen or a heat preservation method.

The invention has the beneficial effects that: the technical problems of overlarge thermal stress caused by overhigh cooling speed and uneven cooling speed of each region in the cryogenic treatment process of the ultra-large stainless steel structural member are solved, and the problems of cracks and defects of a welding line caused by the superposition of the overlarge thermal stress and welding residual stress are solved.

Detailed Description

The present invention will be further described with reference to the following specific examples.

In this embodiment, the cryogenic treatment process method for the ultra-large 304LN welded piece with the size of 10100mm × 4191mm × 3800mm includes the following steps:

1) cleaning the workpiece, removing scrap iron, slag, water and oil stains attached to the surface and the interior of the workpiece, and then drying;

2) i-shaped steel and cushion blocks for supporting are arranged according to the position of a bottom support rib of the ultra-large stainless steel structural member, so that the uniform weighing is ensured, and the workpiece is lifted into a deep cooling tank;

3) at least 6 thermocouples are respectively arranged on the upper part and the lower part of the two side surfaces of the workpiece, at least 3 thermocouples are arranged in the workpiece, the total number of the thermocouples is not less than 27, and each thermocouple is connected to external control equipment;

4) simulating a stress concentration area of the deep cooling treatment process of the workpiece through digital simulation software, installing a strain gauge in the stress concentration area to monitor stress change, and connecting the strain gauge to external control equipment;

5) after the preparation work is done, the box cover is covered, and after the fixation is finished, nitrogen or dry air starts to be blown into the cryogenic box to replace the air in the inner cavity of the cryogenic box;

6) injecting liquid nitrogen into a heat exchange bin of the cryogenic box, cooling gas in the heat exchange bin after the liquid nitrogen is gasified, and blowing cold air into the cryogenic box through a fan to cool the workpiece;

7) after the temperature of the workpiece is reduced to-180 ℃, injecting liquid nitrogen into the deep cooling box, completely soaking the workpiece, and after the temperature of the workpiece is completely reduced, continuing to soak for not less than 30 min;

8) pressing the liquid nitrogen in the cryogenic box back to a liquid nitrogen tank, and blowing dry air or nitrogen slightly higher than normal temperature into the box body through a heater in the heat exchange bin to carry out temperature return;

9) after the workpiece is completely heated for 3 hours, introducing liquid nitrogen into the heat exchange bin again, cooling the workpiece by gasified cold air, directly injecting the liquid nitrogen into the box body after the temperature is reduced to-180 ℃, soaking and cooling to the liquid nitrogen temperature, and circulating for three times;

10) and after the third cryogenic cycle is completed, the workpiece is lifted out of the cryogenic box, the strain gauge and the thermocouple are disassembled, and the cryogenic treatment of the ultra-large stainless steel structural member is completed.

In the above technical scheme, in step 2, the inside effective size of the cryogenic box is 11m × 5.8m × 4.5m, heat exchange chambers are arranged on two sides of the inner cavity of the cryogenic box, and 12 air outlets are provided, the air speed and the air outlet temperature of each air outlet can be independently controlled, and the temperature of each area of the whole inner cavity is adjusted by controlling the air speed and the air temperature of the 12 air outlets.

In the technical scheme, in the step 6, the temperature of each region of the workpiece in the cryogenic box is monitored at any time through external monitoring equipment, and the temperature reduction speed and the temperature uniformity in the temperature reduction process are ensured by controlling the liquid nitrogen retention or the heat preservation method.

The above description is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention should be covered within the scope of the present invention.