You can scrape HN as long as you respect the robots.txt[1] and don't retreive more than a couple of pages per minute.

Have you considered just pulling the data from HNSearch's API[2] or the one by iHackerNews[3]?

[1] https://news.ycombinator.com/robots.txt

[2] https://www.hnsearch.com/api

[3] http://api.ihackernews.com/