材料期刊网

Cr-Mn-N奥氏体耐热钢在时效过程中有变脆的倾向,可能成为高溫长期使用的障碍.本文研究了下列三方面变脆的影响因素:(1)碳和氮含量的增加,促进时效变脆,硼防止时效变脆的作用随C+N含量的增加而減弱.在时间-溫度-等冲击值曲线上出现双C形式,它们与碳氮化物的析出和χ相生成有关.(2)碳、硼及钼等元素在晶界有偏聚现象.碳、钼等元素的偏聚促进沿晶界碳化物析出,加速钢的变脆.硼则有延缓晶界碳化物析出的作用,抑制时效脆性.(3)在长期时效过程中,碳氮化物及中间相的析出引起基体合金元素的贫化,从而降低γ相的稳定性,在形变过程中发生ε及马氏体相变,也会引起钢的变脆.

The influence of various factors on the aging embrittlement of Cr-Mn-N austenitic heat-resisting steels strengthened with Mo, V and B have been studied. It is shown that there are three factors controlling the aging embrittlement. (1) Loss of ductility is accompanied by fine precipitation of carbide and nitride along the grain boundaries. With increasing C and N content, the ductility of the aged steel is dropped sharply. The time-temperature-iso-impact values curves are in form of double C shape. The noses of the curves may possibly be related to the precipitation of carbide and X phase. (2) Strengthening elements such as Mo and B tend to segregate at grain boundaries. The effect of B in steel is to prevent the formation of the continuous fine precipitation film along grain boundaries, thus the aging embrittlement is minimized. Segregation of Mo along grain boundaries promotes brittlement. (3) After aging at temperature interval between 600—850℃ for a long time, austenite will become less stable due to the precipitation of carbide and nitride as M_(23)C_6 and (Cr, Fe)_2N of the solid solution. Thus the diffusionless transformation such as γ→s→α' or γ→α' can easily occur when shock load is applied, and therefore the aged specimens will show low ductility at temperature of testing.