Effects of alloying and treatment on void swelling of 316 stainless steels
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S. L. Lai Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
J. G. Sun HVEM Laboratory of the General Research Institute of Nonferrous Metals, Beijing 100088, China (Received 26 November 1990; accepted 9 April 1991)
Several samples of type 316 stainless steels, which were treated differently and modified with minor elements (such as Ti, Nb, etc.), were irradiated by 1 MeV electrons in HVEM at temperatures ranging from 823 K to 883 K. Void swelling behavior of the steels was investigated, and three parameters, i.e., swelling, void density, and void size, were measured. The results show that prior cold work improves the swelling resistance of type 316 stainless steels more effectively than solid-solution treatment. It is also shown that Ti is the best alloying element studied that can suppress void nucleation and its growth drastically by acting as sinks and impeding dislocation climb, resulting in the reduction of void swelling. I. INTRODUCTION Austenitic stainless steels, especially type 316 stainless steels, are prospective structural and fuel cladding materials for fast-neutron reactors, because of their good high-temperature strength, unique corrosion resistance, low price, and availability. However, these kinds of steels are susceptible to void swelling1'2 and to hightemperature embrittlement caused by helium resulting from nuclear reactions of some constituents of the alloys. Since the 1970s, there have been many studies concerning the effects of treatment and alloying modification with minor elements, such as Ti, Si, W, Zr, Nb, etc., on radiation damage of the steels.3"5 However, for those countries planning to develop fast-neutron reactors as a long-term energy resource program, it is still necessary to test their own 316 stainless steels. Also, further study of this issue would promote a better understanding of the mechanism for suppressing swelling. It is well known that electron beams from the high voltage electron microscope (HVEM) can be used to simulate neutron radiation effects in metals within a few days instead of years by neutrons alone, with an advantage of in situ observation of the microstructural change. We present, in this paper, the experimental results of the swelling behavior of several types of 316 stainless steels with different treatments and alloy modifications produced in China. Some possible explanations of the results are also proposed. II. EXPERIMENTAL PROCEDURE The compositions of type 316 stainless steels and the prior cold work are presented in Table I. All the steels 1650
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J. Mater. Res., Vol. 6, No. 8, Aug 1991
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listed here were tested in our irradiation experiments, and sample 1163 is the standard 316 stainless steel for comparison. Prior to cold work treatment, the steels were solution-annealed at 1283 K for 30 min in a vacuum chamber. In the table, when steels of group A contained the same extent of cold work, they were modified with different elements, or conversely, when they
