Why has my beef stew come out hard?

i have cooked a beef stew in a cooking pot not slow cooker dont have one yet., i have cooked it for 1 1/2 hours and the beef has come out really hard and chewy, i cooked it in slow heat and browned the meat before puttin it in the pot with the veggies and water, i used lean beef chunks for stew, so wats the problem please help