low-grade vs second-rate

low-grade

adj

Of inferior quality.

second-rate

adj

Of mediocre quality; not first-rate.
Of a Royal Navy ship of the line in the Napoleonic Era: having 80–98 guns across three gun decks, a complement of 700–750, and weighing approximately 2,200 tons burthen.

noun

A second-rate ship of the line.

How often have the words low-grade and second-rate occurred in a corpus of books? (source: Google Ngram Viewer )