In order to investigate the influence of the cooling rate on the microstructure and thermal stress of 304LN welded joints during cryogenic treatment, 304LN welded steel plates were subjected to cryogenic treatment with 2 K/min, 5 K/min, respectively. And the microstructure and thermal stress of the welded joint before and after cryogenic treatment were investigated by strain gauge, temperature sensor and optical microscope. Results showed that with the increase of the cooling rate, the thermal stress of the welded joints during the deep cryogenic treatment increased in value, but still less than the yield strength of the material. Martensite and carbides could be clearly seen after deep cryogenic treatment, and with the increase of the cooling rate, carbides were increased in number and the distribution was more uniform. At the same time, the content of carbides in welded joints was measured with the aid of energy dispersive spectrometer (EDS), which confirmed the view that the precipitation of carbides was promoted with the increase of the cooling rate. Therefore, it is suggested to adopt cryogenic treatment with a cooling rate of 5 K/min for the workpiece to obtain a more stable microstructure.
