Here is the full list of all 18 Z Steel Soldiers achievements.
Use a construction robot to build every type of building
Complete World 6
Kill a Spy
Complete World 5
Plant a virus in an enemy building
Complete World 4
Claim 250 Flags
Complete World 3
Repair 20 Bridges
Complete World 2
Take over 50 enemy structures with Technician
Complete World 1
Visit the Credits Screen
Kill 100 Ground Units
Claim 25 Flags
Complete Level 1
Kill 10 Psychos
Complete the Tutorial