Effect Of Thermal Cycling On Microstructure And Performance Of2.25Cr1Mo0.25V Steel

At present,2.25Cr1Mo0.25V steel is chosen as manufacturing material for hydrogenation reactor generally in our country, because it still has good performance although in high temperature, high pressure and hydrogen environment. However, due to the increase of alloying element, more difficult will bring to welding, and HAZ is also a weak region of welding joint. So it is significance for us to research the microstructure and properties of HAZ of2.25Cr1Mo0.25V steel.This paper use welding thermal simulation technology simulate actual weld thermal cycle of HAZ of2.25Cr1Mo0.25V steel, and then use Leica metallographic microscope, SEM, Vickers microhardness hardness tester, pendulum impact tester, etc. experimental instrument to study the effect thermal cycle on microstructure and performance of to2.25Cr1Mo0.25V steel. It can figure out from the result of experiment that for the first thermal cycling of different peak temperature, grain coarsening is serious when peak temperature reaches1320℃and1200℃. Coarse upper bainite microstructure and amount of granulous bainite microstructure has formed which is the main reason of worsening toughness and hardness of coarse grain in HAZ. However, when temperature reaches1000℃, metal austenitizing is completely at this point because of being in fine grained region, and grain does not grow in the reason of alloying element, on the contrary, is by the reason of process of spontaneous recrystallization that lead to the microstructure in this region is fine, uniformity and has got better performance. However, other peak temperature comparing to parent material toughness and hardness does not change a lot in the microstructure and performance. From the results of the first thermal cycling experiment with the same temperature and different liner energy show that both the microstructure and performance after thermal cycle with different liner energy are bad, but by contrast, toughness and hardness is better when liner energy is20kJ/cm than is10kJ/cm,40kJ/cm,60kJ/cm. This is because that short, uniform lath bainite has formed when liner energy reaches20kJ/cm which can be better in performance compared with other microstructures such as lath bainite, coarse upper bainite and granulous bainite. From the results of the second thermal cycling experiment show that both the microstructure and performance do not change a lot compared with the first thermal cycling due to the microstructure in coarse grain region when peak temperature reaches1200℃. But when peak temperature reaches1000℃, performance is similar with the first thermal cycling, grain is refined and performance has been improved. When peak temperature of the second thermal cycling reaches850℃, it is in two-phase region, the remaining ferrite is also increasing which lead to softening of metal material compared with the first thermal cycling. Likewise, when peak temperature of the second thermal cycling is under AC1of2.25Cr1Mo0.25V steel, only soften occurred, while the microstructure does not change at all.