Sadly, Windows 8 Sound recorder app is rather crazy, doesn’t allow user recorded sound to store in hard disk. This app stores recorded sound inside the app itself. Windows 8.1 help page says this:
Where are my recordings saved?
Your recordings are stored within the Sound Recorder app. If you uninstall the app, your recordings will be deleted. To send the recording file to someone through another app, use the Share charm.
Source: Sound Recorder app for Windows: FAQ http://windows.microsoft.com/en-us/windows-8/sound-recorder-app-faq