Kirin analytical instrument for conventional heat treatment of ductile iron

Kirin analytical instrument for conventional heat treatment of ductile iron

    The heat treatment of ductile iron is a method to improve the quality of metal materials. The heat treatment can change or affect the structure and properties of cast iron, and at the same time obtain higher strength, hardness and wear resistance. Nanjing Kirin Analytical Instruments Co., Ltd. will discuss with you a wide range of heat treatments for cast iron, but basically can be divided into two categories: the first is that the structure will not change or should not be changed by heat treatment, second Classes are those whose basic organizational structure changes. The first heat treatment is mainly used to eliminate internal stress, and the microstructure, strength and other mechanical properties after heat treatment are not significantly changed by heat treatment. The second heat treatment can make a significant change in the matrix structure. This heat treatment is roughly divided into five categories:

1 annealing: its purpose is mainly to decompose carbides, reduce the hardness of cast iron, improve processing performance;

2 normalizing: its purpose is mainly to improve the cast iron structure and obtain uniform distribution of mechanical properties;

3 quenching: its purpose is mainly to obtain relatively high hardness and surface wear resistance;

4 surface hardening treatment: its purpose is mainly to obtain a surface hardened layer, while obtaining a higher surface wear resistance;

5 precipitation hardening treatment: its purpose is mainly to obtain higher strength.

 

1 , annealing treatment

     Annealing can be used to improve the toughness of ductile iron. In the casting process, ductile iron tends to have a larger white mouth than ordinary gray cast iron, and the internal stress is also large. It is difficult to obtain a pure ferrite or pearlite matrix for ductile iron castings. In order to improve the ductility or toughness of ductile iron castings, the ductile iron castings can be reheated to 900 ~ 950 ° C And keep enough time for high temperature annealing, then cool the furnace to 600 ° C It is getting cold. During this process, the cementite in the matrix decomposes graphite, and graphite is precipitated in the austenite. These graphites are concentrated around the original spherical graphite, and the matrix is ​​completely converted into ferrite, thereby improving the toughness of the ductile iron . If the as-cast structure consists of (ferrite + pearlite) matrix + spheroidal graphite, then only the ductile iron castings need to be reheated to 700 ~ 760 ° C The eutectoid temperature is kept warm and then the furnace is cooled to 600 ° C When it is cooled, the cementite in the pearlite can be decomposed into ferrite and spheroidal graphite to improve its toughness.

 

2 , normalizing treatment

    To improve the strength of ductile iron, normalized treatment can be used. The purpose of normalizing ductile iron is to convert the matrix structure into a fine pearlite structure. The process is to reheat the spheroidal graphite castings with ferrite and pearlite to 850 ～ 900 ° C At the temperature, the original ferrite and pearlite are transformed into austenite, and some of the spherical graphite is dissolved in the austenite. After the heat preservation, the air-cooled austenite is transformed into a fine pearlite, thereby improving the strength of the ductile iron casting.

 

3 , quenching plus low temperature tempering treatment

To improve the hardness of ductile iron, a method of quenching and low temperature tempering can be used. When spheroidal graphite cast iron is used as a bearing and other parts, it is often required to have a relatively high hardness . At this time, the ductile iron piece can be quenched and tempered at low temperature. The specific process is: heating the ductile iron parts to a temperature of 860 ~ 900 ° C ......

 

       Nanjing Qilin Scientific Instrument Group Co., Ltd.

       Testing Center

 

  

Garlic & Peeled Garlic

Fresh Garlic,Garlic Price,Red Garlic

Ginger,Garlic &Peeled Garlic, Co., Ltd. , http://www.nsvegetables.com