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Carburizing and Quenching for investment castings

Carburizing and quenching  is a common heat treatment process,After carburizing,the surface of investment castings could obtain high hardness,Thusimprove its wear-resisting degree.Traditional process mainly include:the low temperature tempering,direct quenching after cooling,first heating quenching,carburizing and high temperature tempering,secondary hardening after cold treatment,carburizing and induction heating,etc.Most important parts,espcially in the application of automobile,airplane,ect are all required to do this process.To meet the technical requirements of various parts,quenching is developed.


Carburizing is a process used for investment casting surface.Most material of metal parts using this process is low carbon steel or low alloy steel.Specific approach is to put investment castings in the carburizing active medium, heated to 900-950 degrees Celsius single-phase austenitic area, after the heat preservation time, make the carburizing medium decomposition of active carbon atoms into the steel surface, to obtain high carbon surface layer, while the core retain the original composition. There are similar to that of low temperature nitriding treatment.

Carburizing process in China can be traced back to 2000 years ago. The first is to use solid carburizing medium carburizing. Liquid and gas carburizing is appeared and widely used in the 20th century.United States started to adopt drum boiler  for gas carburizing in the 20 s. In the 30 s,continuous gas carburizing furnace started in industry application.In the '60 s high temperature (960 ~ 1100 ℃) gas carburizing was developed. To the 70 s,appearing the vacuum carburizing and ion carburizing.


The purpose of quenching is to transform the supercooled austenite to martensite and bainite,then to get martensite.Quenching is a metal heat treatment  process that heating investment castings to a proper temperature and maintain for a period of time,then rapid cooling in th quenching cooling medium.Common quenching cooling medium is salt water,water,mineral oil,air,ect.Quenching can improve the hardness and wear resistance of the investment casting parts.So it is popular for manufacturing investment castings with high hardness.By combine carburizing and different temperature quenching,we can significantly improve the strength,toughness and fatigue strength of investment castings.Besides,carburzing could also make steel parts with special properties to obtain certain and chemical properties.In a word,quenching is mostly used for cast steel parts.