Set & Get session variable value

I am setting session variable in function of a controller like below.

use Illuminate\Support\Facades\Session;

class UserController extends Controller
{
	public function store(Request $request)
	{
		session(['user_name' => $user_name]);
	}
}

I am trying to access that session variable in another function of another controller.

use Illuminate\Support\Facades\Session;

class DashboardController extends Controller
{
    public function __construct()
    {
        dd(session('user_name'));   // I am not getting value here
    } 
}

I am not getting value from Session Variable.