Not all versions of the BCM4312 chipset work with the b43 driver. IMO, you will have a better chance of success with the Broadcom 802.11 STA Linux driver (aka broadcom-wl). A binary yum-installable version of it is available from RPM Fusion.
But if you want to press on with b43 just to find out, then confirm that the firmware is there. This should list a few dozen .fw files...
What files did you use when you extracted the firmware? Make sure you installed version 4 firmware. I'm still extracting the firmware from wl_apsta_mimo.o that I get from broadcom-wl-220.127.116.11.tar.bz2 at OpenWrt. It's not the latest tarball, but I intend to keep using it until it stops working.
Next, look at the loaded kernel modules to confirm b43 and ssb are there and there are no conflicting modules (unlikely, but look anyway)...
Then restart NetworkManager and look in the panel applet for available networks...
service NetworkManager restart
If there are no networks available when some are known to be in range, then I think I would move on to broadcom-wl.