钢的热处理种类分为整体热处理和表面热处理两大类。常用的整体热处理有退火，正火、淬火和回火；表面热处理可分为表面淬火与化学热处理两类。

The heat treatment of steel can be divided into two categories: heat treatment and surface heat treatment. The overall heat treatment annealing, normalizing, quenching and tempering; surface heat treatment and surface hardening can be divided into two types of chemical heat treatment.

正火是将钢件加热到临界温度以上30-50℃,保温适当时间后，在静止的空气中冷却的热处理工艺称为正火。正火的主要目的是细化组织，改善钢的性能，获得接近平衡状态的组织。

The fire is to heat the steel above the critical temperature of 30-50 DEG C, holding an appropriate time after the heat treatment process of cooling in still air is called normalizing. The main purpose of normalizing is to refine, improve the performance of the steel, close to the equilibrium state of organization.

正火与退火工艺相比，其主要区别是正火的冷却速度稍快，所以正火热处理的生产周期短。故退火与正火同样能达到零件性能要求时，尽可能选用正火。大部分中、低碳钢的坯料一般都采用正火热处理。一般合金钢坯料常采用退火，若用正火，由于冷却速度较快，使其正火后硬度较高，不利于切削加工。

Compared with the process of normalizing and annealing, the main difference is the fire of the cooling speed is fast, so are hot processing production cycle is short. The annealing and normalizing to achieve the same parts performance requirements, choose as far as possible is fire. Most of the medium and low carbon steel billets are generally treated with positive heat treatment. General alloy steel material used with annealing, normalizing, due to fast cooling rate, the normalized high hardness, is not conducive to cutting.

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