Really, there has been a fairly radical change in how Google measures relevance of a page against a given keyword. A year or more ago, you'd have been better off making separate landing pages for each of those terms, putting the target term in the page title, H1 heading, body text, ALT text on an image, etc. etc.
Whether it's the new RankBrain piece of the algo or something else--it seems that Google is no longer as laser-focused on the page title having the EXACT words in it that were in the search term. Google appears to be able to identify the topic that a page is about by looking at the words on the page and how those words co-occur on other pages on the web.
As an example, my travel site has a page on it that I very carefully tuned for the term "best time of year to visit tahiti". So that's the page title, H1 heading, etc. etc....all the usual stuff. That page now ranks #3 for "tahiti weather", which is SUPER competitive, despite not having "weather" in the page title. I think it's only on the page maybe once, in fact. But, the page content talks about storms, precipitation, temperature, seasons, etc. etc. So, even though I'm telling Google that the page is about "the best time of year to visit Tahiti", Google is able to look at all that content and understand that really, it's about weather in Tahiti.
Long-winded story, I know. But I am indeed going somewhere with this...
I'd recommend having a single page targeted at "metal doors", then work all of the other terms into the page content, using subsections and H2's as Attain Design has suggested above.
I'd go a step further, though. Do a search for "metal doors", and look at the top 20 or 30 pages in the results. Look at the subtopics those pages discuss. Are they talking about locking mechanisms? Corrosion resistance? Insulation R-values? You're looking for other aspects of the core topic that you can add to your page to make it a more thorough discussion of the topic.
The theory I've seen as to how Google is doing this relevance is this: they're looking at a set of pages (maybe the top 100?) that they currently rank well for a given topic, and looking at the fairly rare OTHER terms that are showing up on at least some of those 100 pages. As an example, let's say a given term occurs on 90 of those 100 pages--that's a clue that if a page is supposed to be about topic X, and it does NOT have that term on it, it's probably a pretty poor page for that topic. Now, let's say we're looking at a term that occurs on 15 out of those 100 pages--that's probably a subtopic term that only the best pages...the most thorough pages on that topic...will have. If the term occurs on just 1 or 2 of those pages--well, that's probably an anomaly.