to my knowledge China sent troops to Korea, not after Mao Zedong met with Stalin.
When the Korean War started, Mao Zedong immediately dispatched several Army troops to the China - North Korea border, known as border guards, once they are in China's civil war, the fighting in the region over the forces, but also elite troops.
With the North Korea military was defeated, Pyongyang was occupied, Kim Il-sung, fled into the mountains north of the border, Mao Zedong's request to send troops, after a night of consideration, Mao ordered border forces quietly went into North Korea border mountains area, and hiding there. While the UN troops in the northern mountain area combat with the residual North Korea troops , the Chinese army is also involved in a small-scale fighting, but the U.S. military not know.
the fighting subsided for a period of time that Mark arthur thought the North Korean army already have all escaped, but 300,000 chinese troops hiding in the north mountain area of North Korea, waiting for the opportunity, there is also commander Peng Dehuai plan military operations in this mountain area.
When the UN forces large-scale entered to the north mountain area of North Korea, the Chinese army launched a military offensive to the UN troops, while Chinese army from China entered to North Korea, from northwest to southeast direction attack UN troops,with the hiding northern mountains of Chinese army operation, UN troops were surrounded and separated,
All of these occurre and Mao Zedong visited Soviet Union almost the same time, it is difficult to distinguish the right time,after Mao Zedong return to China the war officially announced.