(as) strong as steel

1. Extremely durable and difficult to bend or break. This species of shark is covered in scale-like structures that are strong as steel. This special fabric is remarkably lightweight and flexible but strong as steel. Don't worry about dropping that end table—like all things built by your grandfather, it's as strong as steel.

2. Extremely stable, robust, and enduring. Our relationship has lasted because our love is strong as steel. The unification of the six kingdoms created an empire as strong as steel. This contract is strong as steel, I'm afraid. There's no way you can get out of it without penalty.