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| INFLUENCE OF RE ADDITION ON CREEP-RUPTURE BEHAVIOUR OF A CrNi AUSTENITIC STEEL |
| by QIU Jufeng (Baotou Institute of Metallurgy; Ministry of Metallurgical Industry) (Manuscript received 15 November; 1982: revised manuscript 26 August; 1983) |
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Cite this article:
by QIU Jufeng (Baotou Institute of Metallurgy; Ministry of Metallurgical Industry) (Manuscript received 15 November; 1982: revised manuscript 26 August; 1983). INFLUENCE OF RE ADDITION ON CREEP-RUPTURE BEHAVIOUR OF A CrNi AUSTENITIC STEEL. Acta Metall Sin, 1984, 20(2): 92-212.
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Abstract An investigation was made of the effects of 0.15％ RE mischmetal addition on the creep-rupture strength and ductility of Cr18Ni18Si2 austenitic stainless steel. The examinations of creep damage and fracture morphology by means of optical and scanning electron microscopy were also carried out to clarify a general aspect for the effects of RE addition on creep-rupture mechanism. The results show that the creep-rupture lives of containing 0.064％RE Cr18Ni18Si2 steel at 650 to 750℃ under 5—10 kgf/mm~2 are greater than those of the steel without RE by factors of about 1 to 4. The creep-rupture strength at 700℃ for 1000 h increases 2 kgf/mm~2 over. The creep-rupture ductility enhances by 0.2 to 2. The fractures of creep-ruptured specimens transit from typical ductile intergranular to mixed mode consisting of major ductile intergranular fracture and minor transgranular tearing. The typical wedge-type cracks form at the triple grain boundary junctions. The average density and length of wedge-type cracks in specimens with RE addition are smaller than that without RE. It is apparent that the creep-rupture process of Cr18Ni18Si2 steel is controlled by grain boundary sliding-stress concentration mechanism. The observations on fracture and creep damage may suggest that the RE addition can strengthen the grain boundary, inhibit their sliding, hence decrease the level of stress concentration at the grain corners. On the other hand, because the deformation resistance within the grains is decreased by RE addition, therefore, the stress concentration may be relaxed by the adjustment due to deformation of adjacent grains. Consequently, it is not easy for cracks to nucleate and propagate in steel Cr18Ni18Si2 with RE addition, resulting in the improvement in creep-rupture properties.
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Received: 18 February 1984
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