Use utl_raw.substr : utl_raw « System Packages « Oracle PL/SQL Tutorial

1. Oracle PL/SQL Tutorial
2. System Packages
3. utl_raw

SQL>
SQL> create table t ( r raw(10) );

Table created.

SQL>
SQL> insert into t values ( utl_raw.cast_to_raw('helloWorld' ) );

1 row created.

SQL>
SQL> select utl_raw.substr(r,2,3) r1, hextoraw(substr(r,3,6)) r2 from t
  2
SQL> drop table t;

Table dropped.

SQL>