In the long-term production practice and scientific experiment, the people to understand the metal internal organization change laws, especially since the '60 s, transmission electron microscopy (sem) and electron diffraction technology application, all kinds of testing technology constantly improve, in the study of martensite morphology, structure and its relationship with mechanical properties, and get different forms and the condition of the structure of the martensite, the second phase of the shape, size, quantity and distribution influence on mechanical properties, etc. , have made great progress, based on the new technology of hardening is also emerge in endlessly.
Seller cycle of rapid heating quenching hardening and tempering steel strength is associated with the austenitic grain size, the fine grain size, the higher the strength, thus how to obtain higher than 10 grain size of the ultrafine grain is one of the important ways to improve the strength of steel.
Steel after alpha - gamma - alpha phase change many times recrystallization can make the grain refining;
Improve the heating speed, increase the crystallization center also can make the grain refinement.
Cycle of rapid heating quenching is based on the principle to obtain ultrafine grain so as to achieve the new technology of reinforcement.
45 # steel, for example, in 815 ℃ lead bath quenching 4 - over and over again
5 times, can make the austenitic grain refinement level from 6 to 12 ~ 15 level;
And 20 crni9mo steel, such as the use of 3000 Hertz, 200 kw intermediate frequency induction heating equipment at the speed of 11 ℃ / s heated to 760 ℃, and water quenching, the sigma s increased from 960 mn/m2 to 1215 mn/m2, gas by 1107 mn/m2, increased to 1274 mn/m2, while the elongation remains the same, all is 18%.
Denominated in high temperature quenching temperature here is relatively normal quenching heating temperature, low carbon steel and medium carbon steel with high quenching temperature, the plate strip martensite can be obtained, or increase the number of lath martensite, thereby gaining a good comprehensive performance.
From the morphological characteristics of the carbon content of austenite and martensite experiment proves that the carbon content less than 0.
3% of the steel quenching all board strips martensite.
Ordinary low carbon steel hardenability is poor, however, if you want to obtain martensitic, in addition to the alloying to enhance the stability of supercooled austenite, only improve the austenitizing temperature, and must strengthen the quenching cooling.
For example made five plough with 16 mn steel plow arm, with 940 ℃ in 10% NaOH aqueous solution at quenching and low falling in tempering, can obtain good effect.
Medium carbon steel with high temperature quenching can make uniform austenitic composition: get more analysis strip martensite, in order to improve the comprehensive performance.
AISl4340 steel, for example, after 870 ℃ quenching oil, 200 ℃ tempering, the sigma s of 1621 mn/m2, fracture toughness Kc for 67.
Six mn/m, and in the 1200 ℃ heating, cooling, and 870 ℃ 200 ℃ tempering after quenching oil, sigma s of 1586 mn/m2, fracture toughness Kc for 81.
8MN/m。
If the hardening state, fracture toughness of high temperature quenching than ordinary quenching almost doubled.
Metallographic analysis shows that high temperature quenching to avoid the lamellar martensite (
Twin martensite)
The emergence of all plate strip martensite are obtained.
In addition, the martensite lath are coated with a layer of thick - 100
To high carbon steel at low temperature, fast, short-time heating quenching high carbon steel in generally low
