low-grade metal

例句：

1. 1. The construction of the bridge required the use of low-grade steel.
   建造这座桥需要使用低等级的钢材。
2. 2.This machine is made from low-grade iron.
   这台机器是用低等级的铁制成的。
3. 3.Low-grade metal is often used in the production of electrical wiring.
   低等级金属常用于电线的生产。