铸铁组织

组织：铸铁的组织是由钢的基体和石墨组成的。

铸铁的基体组织：珠光体、铁素体、珠光体加铁素体。

铸铁名称与铸铁显微组织：

1.灰口铸铁F+G片，F+P+G片，P+G片

2.球墨铸铁F+G球，F+P+G球，P+G

3.蠕墨铸铁F+G蠕虫，F+P+G蠕虫

4.可锻铸铁F+G团絮，P+G团絮

由于铸铁中的碳主要是以石墨的形态存在，所以铸铁的组织是由金属基体和石墨所组成的。铸铁的金属基体可以是铁素体、珠光体或铁素体加珠光体，经热处理后还可以是马氏体或贝氏体等组织，它们相当于钢的组织，因此可以把铸铁理解为在钢的组织基体上分布有不同形状、大小、数量的石墨。铸铁中石墨的形态可分为6种：片状、蟹状、开花状、蠕虫状、团絮状和球状，如下图所示。

普通灰铸铁的组织是由片状石墨和钢的基体两部分组成的。根据不同阶段石墨化程度的不同金属基体可分为铁素体，铁素体＋珠光体和珠光体三种，相应地便有三种不同基体组织的灰铸铁，它们的显微组织如下图所示。

8.2.1 灰铸铁的成分、组织与性能特点

1．灰铸铁的化学成分

⏹化学成分范围一般为：w C=2.7%~3.6%，w Si=1.0%~2.5%，w Mn=0.5%~1.3%，

w P≤0.3%，w S≤0.15%。

2．灰铸铁的组织

三种不同基体组织的灰铸铁：

（1）铁素体灰铸铁

（2）珠光体灰铸铁

（3）珠光体+铁素体灰铸铁

3．灰铸铁的性能特点

（1）力学性能

⏹铸铁的强度、塑性与韧性低。

⏹灰铸铁的抗压强度σbc、硬度与耐磨性接近钢（主要取决于基体，石

墨的存在对其影响不大）。

（2）其它性能

⏹铸造性能良好熔点低，流动性好，收缩率小。

⏹减摩性好摩擦系数小。

⏹减振性强

⏹切削加工性良好

⏹缺口敏感性小

8.2.2 灰铸铁的孕育处理

⏹孕育处理：向出炉的铁水中加入孕育剂。

⏹人工形核：细化晶粒工艺。

⏹孕育剂：含硅75%的硅铁。

8.2.3 灰铸铁的牌号和应用

1．灰铸铁的牌号

⏹HT100、HT150、HT200等

2．灰铸铁的应用

⏹形状复杂，静载荷，减摩的床身、箱体、座架类零件。

8.2.4 灰铸铁的热处理

⏹可以进行消除内应力退火、改善切削加工性退火、表面淬火等热处理工艺

改善工艺性能和使用性能。

position of cast iron

As the carbon in cast iron mainly exists in the form of graphite, so the organization of cast iron is made of graphite and matrix of metal. Metal matrix of cast iron may be a ferrite, pearlite, or ferrite and pearlite, or it also be organizations such as martensite or bainite after heat treatment, which correspond to the structure of the steel. So the cast iron can be understood as different shapes, size, number of graphite be distributed in cast tissue of steel. Graphite of cast iron can be divided into six kinds of forms: flake, crab-like, flower-like, worm-like, flocculent and spherical, as shown below.

ponents, organization and performance characteristics of gray cast iron (1)Chemical composition of gray cast iron

Ranges of Chemical composition generally are: wC=2.7%~3.6%，wSi=1.0%~2.5%，wMn=0.5%~1.3%，wP≤0.3%，wS≤0.15%。

(2) Organization of gray cast iron

Normal tissue of gray cast iron is composed of flake graphite and matrix of steel. Depending on the degree of graphite in different stages ,metal matrix can be divided into three kinds ,ferrite, pearlite and ferrite and pearlite,So there are three different matrix structure of gray cast iron, and their microstructure as shown below .

(3)Performance characteristics of gray cast iron

① Mechanical Properties

Low strength, ductility and toughness

Compressive strength , hardness and wear resistance of steel are closed to steel ② Other properties

Good casting performance ,low melting point, good fluidity, low shrinkage 3.Inoculation of gray cast iron

Inoculation: The molten iron is added to baked inoculant