应力松弛方法研究2种HR3C耐热钢的高温蠕变行为

CREEP BEHAVIOR OF TWO KINDS OF HR3C HEAT RESISTANT STEELS BASED ON STRESS RELAXATION TESTS

采用应力松弛方法研究了2种不同晶粒大小HR3C耐热钢的初始态试样和时效态试样的高温蠕变变形行为,并分析了其微观组织特点.结果表明,尽管2种HR3C耐热钢的化学成分相近,但其蠕变行为有明显差异.相同条件下,晶粒较粗的HR3C耐热钢初始态与时效态的蠕变速率均低于晶粒较细的HR3C耐热钢,具有较高的蠕变抗力.2种HR3C耐热钢经过高温时效处理后,蠕变抗力均明显降低.晶粒较细小的HR3C钢在高温时效后其应力指数(n)与蠕变表观激活能(Q)的降低幅度更加显著,表明晶粒较细的HR3C耐热钢的蠕变抗力的稳定性低于晶粒较粗的HR3C耐热钢.

Rupture life is a main property for a material using at high-temperature condition. Usually, the rupture life is gained from creep rupture test. As creep and stress relaxation are two main behaviors for a material served in high-temperature environment, it is important to work out the interrelationship through which one of the two behaviors can be deduced from the other one. Recently, a number of researchs have taken stress relaxation test to replace creep rupture test on studying the creep behavior, and furthermore predicting the rupture life and the stress relaxation test is proved to be superior to the traditional creep rupture test for its short time, small at damage,abundant of information and so on. In this work, the stress relaxation test was used to analyze the creep behavior of two HR3 C heat resistant steels with different grain sizes. Additionally, considering the change of microstructure during serve period, the aged HR3 C steel was used to compare with as-received HR3 C steel for studying the aging effects on the creep behavior. Furthermore, the creep behavior was correlated to their microstructure characteristics. The result was shown that the creep behaviors of two HR3 C heat resistant steels varied significantly in spite of their similarity in chemical composition. The coarse grained HR3 C steel had lower creep rate, larger stress exponent, greater activation energy and higher creep resistance than that of fine grained HR3 C steel for both as-received one and aged one. The long-term aging process damaged the microstructures of two HR3 C steels, increased aged HR3 C steel’s creep rate, lowered stress exponent and activation energy and reduced creep resistance. And the dam-aging effects on the coarse grained HR3 C steel were larger than that on fine grained HR3 C steel, which meant the coarse grained HR3 C steel had much more stable creep resistance than that of fine grained HR3 C steel.