No, you don't need a torque wrench on cassette lock rings provided you are not ham fisted. I'll share a story. I once ruined a Shimano Dura-Ace hub by stripping the lock ring while replacing the cassette. Luckily, Shimano warrantied it, to my surprise. So, now, I use a torque wrench. I'll be the first to admit that I am a bit ham fisted though.