Prep for Investment Grade Credit Trading

I will be starting a full time gig as an investment grade credit trader at a BB this summer. I have never really learned anything specifically about the investment grade credit market, as opposed to government bonds and high yield bonds; it seems like an in-between market.

if anyone has any insight on some good books or papers on investment grade credit, that would be very helpful. anything that you think would be good for me to learn in preparation for the job would also be great.

thanks