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一、金属的蠕变和珠光体球状化金属长期受温度和应力的作用,会随着时间发生缓慢的塑性变形,这就是蠕变。锅炉部件往往由于蠕变的结果而损坏。蠕变的本质是应力和温度作用下,金属范性变形引起的强化和再结晶的软化不断交替的过程。温度、应力和时间则是影响蠕变的三个主要因素。一般性蠕变发生在450℃～Ac_1的温度区间内,蠕变进行的速度缓慢,导致金属破坏的时间也就冗长,破断属脆性晶间型。加速度蠕变发生在高应力状态下,或是较高的温度区间,一般往往超过Ac_1以上;由于温度的急剧提高,大大加速了金属蠕变的过程,以致跨越二期蠕变,紧接着蠕变的第一阶段就出现三期蠕变,致使金属在极短时间内迅速损坏,破断则属韧性晶内型。因一般性蠕变而损坏的部件,裂缝往往是晶间性的,通常称为蠕胀裂缝。由于酝酿破坏的时间很长,使得固溶体中弥散性化合物因扩散作用得以沉淀于晶界上,从而削弱了晶粒之间的强度,形成晶间裂缝,损坏过程中金属不发生明显的塑性变形。但是,如果蠕变速度加
First, the metal creep and pearlite spherical metal long-term temperature and stress effects, will be a time of plastic deformation, which is creep. Boiler components are often damaged as a result of creep. The nature of creep is the process of stress and temperature, metal-based deformation caused by the strengthening and recrystallization soften alternating process. Temperature, stress and time are the three major factors that affect creep. General creep occurs in the temperature range of 450 ° C to Ac_1, and the creep progresses slowly, resulting in the lengthy time of metal damage, breaking the brittle intergranular type. Acceleration creep occurs at high stress, or at higher temperatures, and often exceeds Ac_1 by a factor of more than 1. Since the temperature rises sharply, the metal creep process is greatly accelerated, causing creep across creep, followed by creep The first phase appears three creep, resulting in rapid destruction of the metal in a very short period of time, the rupture is a tough intragranular. Components damaged by general creep are often intergranular and commonly referred to as creeping cracks. Due to the long time of brewing destruction, the diffusible compounds in the solid solution precipitate on the grain boundary due to the diffusion, thereby weakening the strength between the grains and forming intergranular cracks, and the metal does not undergo obvious plastic deformation during the damage. However, if creep speed is added