hardening of steel

例句：

1. 1.Steel is a material that undergoes hardening during the process of heat treatment.
   钢材是一种在热处理过程中发生硬化的材料。
2. 2. The hardening of steel is crucial for its strength and durability.
   钢材的硬化对其强度和耐用性至关重要。
3. 3. The hardening of steel can be achieved through various methods such as quenching and tempering.
   通过淬火和回火等方法可以实现钢材的硬化。