I majored in material chemistry. Why did I refuse to study in the United States twice?

The specific reasons for refusing a visa must be based on a comprehensive analysis of a set of materials. The major "Material Chemistry" you listed may be the most important reason, but it is not necessarily the only reason. Visa materials involve many aspects, which can be summarized as: personal identity information, family information, academic information and financial information. If you are sure that the other three pieces are all right and there are no low-level filling errors in all forms and materials, then the "material chemistry" in the academic field can be taken seriously as long as the reasons are truly explained. Although this is a sensitive major, it is not a major that prohibits foreign students from studying. The first refusal may be inexperienced and not ready for the second direct visa, which is very unfavorable for subsequent re-entry visas. The mind of the visa officer will naturally concentrate a lot. Among the cases I contacted were "in immigration application", "refused visa for three times", "illegally repatriated in the United States" and "sensitive majors such as physical chemistry and biopharmaceuticals". In fact, whether you can get a visa in the end depends on expressing and presenting your background materials honestly and logically, which is very important in visa preparation. Don't waste an opportunity to face VS.