The purpose of this study is to identify the formation and evolution patterns of a trading zone and to explore the difficulties teachers experience in the trading zone and their perceptions of the experience. Seven teachers involved in the ``STEAM Teacher Community`` in a middle school located in the southern part of South Korea participated in this study. Participant observation and in-depth interviews were carried out, and reflective essays were collected for analysis. The results show that teachers successfully fanned a trading zone to share their expertise when they developed teaching materials for the convergence of different subject matters. Moreover, such a trading zone evolved in the order of pre-trading zone, trading zone under elite control, trading zone with boundary object, and trading zone of shared mental model. The difficulties teachers experienced in the trading zone were categorized under the difference of culture and opinion across subject matters, the lack of motivation for convergence, the hegemony of convergence and far-fetched factors for convergence, and difficulty of communication due to jargons. Also teachers in this study experienced perceptual changes in the trading zone. The trading zone model drawn from the results of this study bring forth implications for voluntary teachers` learning community activity for the convergence of different subject matters.