Thanks for your answer, Tim.

Also, there are some subtle differences in the way these terms are used. In the US, people generally consider “welfare” to be more about bodily safety and security. Often, well-being has a connotation of health and happiness. For instance, one might say “spiritual well-being” but no one ever says “spiritual welfare”. As well, a person can have a “sense of well-being” — that is, well-being can refer more to one’s emotional state. Whereas, “welfare” usually refers more to personal safety and security, but usually not happiness or fulfillment. Also, in the US, the term “welfare” can often refer to the government program that provides certain people with some money, if they need it (for instance, single mothers who can’t work enough hours to make ‘ends meet’). So you will often hear people refer to “welfare programs” and such. But there are no such things as “well-being programs” (although perhaps there *should* be!). Tim

They are interchangeable but it is "about his well-being" and "for his welfare". "Because he had no money, I was concerned about his well-being." "Because he had no money, I was concerned for his welfare."