Clay,
As far as the words used in the title, those that are closest together and closest to the beginning of title will be given more weight but there is no clear delineation of what's a keyword and what's not a keyword in the title. Rather, think of your title as a lens through which Google sees the rest of the words on your page.
When the copy on the page contains the same words in the same order as what's found in the title, such combinations will be seen by google as highly relevant to the same combination used in a search query. In your example, if your tile contains only "steel fabrication" and your page copy contains only "steel fabrication" then the page would be far more relevant to the "steel fabrication" search query than it would be to the "structural steel fabrication" search query.
If your title used "steel fabrication" towards the beginning and "structural" towards the end and you sprinkled the terms "structural" and "steel fabrication" throughout your page copy, the page would still be highly relevant to the search query "steel fabrication", while increasing in relevance to the "structural steel fabrication" query.
If your title began with "structural steel fabrication" and you used that combination of words throughout your copy, the page would probably become more relevant to that query than to "steel fabrication" but could possibly still rank for both.
That said, there is a fundamental difference between the concepts of "structural steel fabrication" and "structural steel " (and "steel fabrication" for that matter) and Google is recognizing that the way each is used in context gives big clues to the page concepts. Thus, more and more, Goolge knows that just because the words "steel fabrication" are used next to each other on a page, if structural is used in front of them, then the page may be considered irrelevant to "structural steel fabrication".
So, if your page is about "structural steel", use your copy to clearly this product or service. If the page is about "steel fabrication" use the page copy to clearly describe that service to your visitors. If the page is about "structural steel fabrication", be clear about that. Doing so will pay off more and more, as Google continues to get better at providing search results and as visitor expectations of landing pages get higher.