Effect of low temperature toughness of 9NI steel in 1, heat treatment parameters
Have different effects on low temperature toughness of 9NI steel heat treatment parameters are different, the tempering temperature had the greatest impact toughness, low temperature toughness with the increase of tempering temperature and increased gradually, when the peak, but decreases with the increase of the tempering temperature, a non-linear relationship existed between them, the reason and the rotary austenite precipitation of. When the tempering temperature 400 - 450 ℃, reversed austenite precipitation rarely, so the low temperature toughness changes little, tempering temperature reaches 500 ℃, began to have reversed austenite precipitation amount, low temperature toughness increases rapidly, the tempering temperature is 580 ℃, low temperature toughness reached a peak value. Then despite the tempering temperature, but the low temperature toughness but decreased rapidly, this is due to the rotary austenite mechanical instability and thermal instability. Rotary austenite after IHT heat treatment than dispersed, uniform QT after heat treatment, so it can play its toughness matrix, purify grain boundaries, the low temperature toughness of microstructure refinement effect, therefore, in the tempering temperature is same, after low temperature toughness of 9NI steel IHT treatment are higher than for QT processing. The quenching temperature on 9NI steel QT after heat treatment has great influence on Akv, 9NI steel IHT heat treatment has little effect on the Akv, mainly with the reversed austenite precipitation location. In addition, little effect of tempering time on low temperature toughness of 9NI steel, to ensure the full atomic diffusion time basis, to extend the tempering time on low temperature toughness increases a little effect.
The low temperature toughness of 9NI steel is increased by 2, the mechanism of heat treatment
9NI steel by proper heat treatment, mechanism of low temperature toughness is improved greatly, the NI alloy can change the basic nature of ferrite, the stability and lead alloy toughening. The addition of NI improved the ferritic steel hardenability, and suppress look first generation eutectoid, promote the transformation of martensite, transformation products of ultrafine reduced the ductile brittle transition temperature. 9NI steel after (alpha + gamma) dual phase heat treatment, the precipitation of reversed austenite has good mechanical stability and thermal stability, its location, the precipitation on low temperature toughness of 9NI steel distribution and quantity have important effects. The (alpha + gamma) dual phase heat treatment, the new generation of austenite, which reversed austenite or reverse austenite uniformly dispersed in the original grain boundary of austenite, martensite lath boundaries and martensite lath, and after quenching and tempering, reversed austenite precipitation areas, mainly in the original austenite grain boundaries in martensite the world body beam precipitation. Rotary austenite in austenite, which is lower than the Ac1 temperature, the supersaturated solid solution turned, NI and impurity elements containing high, cooled to very low temperatures remain steady. If reversed austenite is evenly distributed in all kinds of grain boundary, will make the grain boundaries and the common toughening, this is (alpha + gamma) causes higher than quenching and tempering heat treatment of 9NI steel after Akv dual phase zone after heat treatment.