稀土元素对含铬白口铸铁中共晶碳化物生长的影响

文中研制了一套高温度梯度的区域熔化定向凝固装置,能在工业用共晶成份的含铬白口铸铁试样中,得到平整的液—固界面;并由于在液态保持的时间较短,故可保留稀土变质处理的效果.使用这种装置研究了低铬(4%Cr)白口铸铁和高铬(20%Cr)白口铸铁中共晶碳化物的生长,以及稀土元素的存在对其造成的影响.在低铬白口铸铁中,随着稀土元素的加入,使共晶凝固时的领先相由基本上是碳化物变为基本上是奥氏体,并由于生长过程中,奥氏体在碳化物前端相互搭桥,使许多板状碳化物转变成板条状和杆状,稀土元素含量愈高,转变的份额愈多;高铬铸铁的共晶凝固与低铬铸铁不同,即使在不含稀土元素的情况下,亦主要是奥氏体为领先相,加入稀土元素对共晶生长时的领先相及碳化物的形貌没有明显的影响.

EFFECT OF RE ELEMENTS ON THE GROWTH OF EUTECTIC CARBIDES IN WHITE CAST IRONS CONTAINING CHROMIUM

An apparatus of zone melting unidirectional solidification with high temperature gra- dient was designed and assembled.By using this apparatus,the plane front solidification could be obtained in the specimens of commercial white irons containing chromium with near eutectic composition,and the modifying effect of RE elements could be maintained without pronounced fading because the time for holding the alloys in liquid state was rela- tively short due to zone melting.This apparatus was used to investigate the growth of eutectic carbides in low chromium white iron(4%Cr)and high chromium white iron(20%Cr),and to investigate the effect of RE elements on the growth.With the increase of RE elements content in the low chromium iron,the leading phase of eutectic growth was changed from carbide to austenite,and a lot of plate-like carbides were transformed into lath-like and rod-like because the austenite bridged over carbide edge in growth process. The higher the RE elements content was,the more the fraction of the lath-like and rod-like carbides was.But in high chromium white iron without RE elements,the austenite grew ahead of carbide.The leading phase and the morphology of carbide were not changed by adding RE elements.