It is difficult to say exactly which industries use DD12 and DX52 grades of steel without further information. However, steel grades like DD12 and DX52 are commonly used in various industrial sectors such as automotive, construction, manufacturing, and engineering. These grades of steel are known for their strength, durability, and versatility, making them suitable for a wide range of applications. The specific usage areas may vary depending on the unique properties and characteristics of each steel grade.