NC-case hardening

例句：

1. 1.The steel undergoes NC-case hardening to improve its strength and toughness.
   钢铁经过淬火处理以增强其强度和韧性。
2. 2.During the NC-case hardening process, the metal is heated and then quickly quenched in water.
   在淬火过程中，金属被加热然后迅速在水中冷却。
3. 3.The engineer explained how the NC-case hardening process affects the material's properties.
   工程师解释了淬火处理过程如何影响材料的性质。