"Investment grade" and "High yield" (aka "junk") are two completely different animals. Even though Vanguard is a lot more conservative than most other fund families, their high yield bond funds are vastly more risky than their investment grade bond funds. That's especially true when you consider the different maturities of the two funds. The big difference in the yields tells the story. You don't get anything for nothing. High yield = high risk. The higher the grade and the shorter the maturity the lower the risk.