晶粒细化剂对K403合金返回料微观组织及持久性能的影响

Effect of Grain Refiner on Microstructure and Stress Rupture Properties of K403 Revert Alloy

目的探索不同浇注温度下晶粒细化剂添加的有无对K403合金返回料微观组织及持久性能的影响,并建立合金的浇注工艺与微观组织和持久性能的关系。方法通过调整浇注温度及晶粒细化剂的有无制备了8组合金,并进行了微观组织表征与高温持久性能测试。结果晶粒细化剂的加入对K403合金的晶粒组织有细化作用,在较高浇注温度下的细化作用更为显著;晶粒细化剂的加入对碳化物的形貌、分布及尺寸没有明显影响;晶粒细化剂的加入使合金在1420℃和1460℃浇注温度下的持久寿命降低,1490℃和1520℃浇注温度下的持久寿命提高;不加晶粒细化剂、1420℃下浇注获得的合金具有最优持久性能。结论建立了合金的浇注工艺与微观组织和持久性能的对应关系,并探寻了细化剂对合金持久寿命的影响机制:晶粒细化剂的加入配合较低的浇注温度获得了细晶组织,使晶界上的碳化物密度过高,晶界成为裂纹源,合金的持久寿命相比不添加晶粒细化剂较短;晶粒细化剂的加入配合较高的浇注温度获得了具有适中尺寸的晶粒,在一定的晶界强化作用下,合金的持久寿命相比不添加晶粒细化剂较长。

The work aims to explore the effect of the addition of grain refiners on the microstructure and stress rupture properties of the K403 revert alloy at different pouring temperatures,and establish the relationship between the pouring process of the alloy and the microstructure and stress rupture properties.8 alloys were prepared by adjusting the pouring temperature and the addition of grain refiners.Microstructure was characterized and stress rupture properties were tested.It was found that the addition of grain refiner refined the grain of K403 alloy,and the effect was more significant at higher pouring temperature.The addition of grain refiner had no obvious effect on the morphology,distribution and size of carbides.The addition of grain refiner reduced the alloy’s stress rupture life poured at 1420℃and 1460℃,and increased the alloy’s stress rupture life poured at 1490℃and 1520℃.The alloy poured at 1420℃without grain refiner presented the best stress rupture life.Finally,the relationship between the casting process of the alloy and the microstructure and stress rupture properties is established.The influence mechanism of the grain refiner on the stress rupture life of the alloys is acquired and described to be:The addition of grain refiner combined with lower pouring temperature can obtain fine grain,which leads to the high density of carbides on the grain boundary.The grain boundary hence becomes the source of cracks.The stress rupture life is reduced compared with the alloy without grain refiner.The addition of grain refiner combined with higher pouring temperature can obtain grains with moderate size.And the stress rupture life is improved compared with the alloy without grain refiner due to grain boundary strengthening.