The formation process and characteristics of tempered troostite in steel pipes

Troustite can be divided into quenched troostite and tempered troostite. For example, in the normal martensite quenching process, quenched troostite is formed in the troostite transformation zone due to the slow cooling rate. Another case is to first quench to obtain quenched martensite, and then temper at medium temperature to obtain tempered troostite.

Tempered troostite (tempered troostite) has a tempering temperature of 350~500 degrees Celsius. The mixed structure of the ferrite matrix and a large amount of dispersed fine-grained cementite obtained by the decomposition of martensite at a temperature lower than the pearlite formation temperature is called tempered troostite also called ultrafine pearlite. It is a mixture of carbide and a-phase.

Formation process and characteristics of tempered troostite
After the quenched martensite is tempered at medium temperature (300℃~500℃), most or all of the supersaturated carbon in the martensite is desolvated, and the precipitated carbides begin to aggregate, grow, and spheroidize. The matrix martensite has begun to recover. This structure is called troostite, also known as secondary troostite.

Structural characteristics of tempered troostite
Very fine granular carbides are distributed in the ferrite matrix. The needle-like shape has gradually disappeared, but it is still faintly visible. The carbides cannot be distinguished under an optical microscope. Only dark structures are observed. The two phases can be clearly distinguished under an electron microscope. It can be seen that the carbide particles have grown significantly and have a higher elastic limit and toughness.

Tempered troostite has a tempering temperature of 350-500 degrees Celsius. It is a mixture of ferrite matrix and a large amount of dispersed fine-grained cementite obtained by decomposing martensite at a temperature lower than the pearlite formation temperature. It is called tempered troostite, also called ultrafine pearlite. It is a mixture of carbide and a-phase.

The structural characteristics of tempered troostite are that extremely fine granular carbides are distributed in the ferrite matrix. The needle-like shape has gradually disappeared, but it is still faintly visible. The carbides cannot be distinguished under an optical microscope. Only dark structures are observed. The two phases can be clearly distinguished under an electron microscope. It can be seen that the carbide particles have grown significantly and have a higher elastic limit and toughness.