This study examines associations between writing behaviors manifested by keystroke analytics and the formulation of argument elements in L2 undergraduate writers' writing processes. Ninety-nine persuasive essays written by L2 undergraduate writers were human annotated for Toulmin argument elements. The corresponding keystroke logs were segmented and analyzed to characterize the dynamics of writing processes for different categories of the elements. A multinomial mixed-effects logistic regression model was built to predict argument categories using the keystroke analytics. The study reported that L2 undergraduate writers' text production for final claims and primary claims featured P-bursts (execution processes delimited by pauses exceeding 2 seconds) of longer spans but lower production fluency compared to that for data. In addition, fewer revisions were observed when L2 writers were constructing final claims than when they were formulating data. These findings shed light on the varying cognitive loads and activities L2 undergraduate writers may experience when building different argument elements in written argumentation.