How To Improve The Low-temperature Toughness of 304 Precision Tubes?

Low-temperature toughness refers to the ability of materials to resist brittle fracture in low-temperature environments. For 304 precision tube, low-temperature toughness is manifested as the ability of the pipeline to withstand certain external force impact, stretching, bending and other loads at low temperatures without sudden brittle fracture, and still maintain a certain plastic deformation capacity.

For 304 precision tubes used in low-temperature environments, good low-temperature toughness can ensure its safety and reliability in applications such as liquefied natural gas (LNG) transportation and low-temperature refrigeration systems. For example, in the storage and transportation of LNG, pipelines need to work in ultra-low temperature environments of around -162℃. If the low-temperature toughness is poor, the pipeline may be brittle, resulting in LNG leakage and causing serious safety accidents.

So how to improve the low-temperature toughness of 304 precision tubes?

Chemical composition adjustment

1. Increase nickel content

Nickel is a key element in 304 stainless steel. Properly increasing the nickel content can expand the austenite phase region. At low temperatures, stable austenite structure can effectively prevent crack propagation and improve toughness. For example, appropriately increasing the nickel content from the standard 8% to 9% - 10% can help enhance the toughness of 304 precision tubes at low temperatures.

2. Control of impurity elements

Strictly control the content of impurity elements such as carbon, sulfur, and phosphorus. These impurities are concentrated at the grain boundaries, which will reduce the grain boundary bonding force and make the material more brittle at low temperatures. The use of advanced smelting technologies, such as vacuum induction melting or electroslag remelting, can effectively reduce the impurity content.

Optimize processing technology

1. Optimize hot processing process

During hot rolling or hot forging, reasonably control parameters such as processing temperature, deformation amount, and cooling rate. For example, after hot processing, proper controlled cooling is performed to avoid excessive organizational stress caused by too fast cooling. Appropriate hot processing technology can refine the grains and improve the organizational structure of the material, thereby improving low-temperature toughness.

2. Combination of cold processing and annealing

For cold processing of 304 precision tubes, such as cold drawing or cold rolling, attention should be paid to controlling the degree of deformation. Excessive cold working will cause work hardening of the material and reduce toughness. Annealing should be carried out in time after cold working to eliminate work hardening and internal stress and restore the toughness of the material. The annealing temperature is generally between 1010-1150℃, and the time depends on the size and processing of the pipe, usually about 30-60 minutes.

Surface treatment measures

1. Shot peening

Shot peening is performed on the surface of 304 precision tube. The surface compressive stress generated by shot peening can offset part of the tensile stress generated by thermal shrinkage at low temperature, inhibit the generation and expansion of cracks, and improve the low-temperature toughness of the pipe.

2. Surface coating

Apply a suitable coating, such as ceramic coating or polymer coating. The coating can play an isolating and protective role, reduce the erosion of the external environment on the pipe, and at the same time, it can also alleviate the stress concentration of the pipe at low temperature to a certain extent, thereby improving the low-temperature toughness.