Pbの混入による片状黒鉛鋳鉄の強度低下と音速による強度評価について

About the intensity evaluation by the strength reduction of flake graphite cast iron by mixing of Pb, and acoustic velocity

羽鳥 雅一; 小林 孝典; 坂本 勉; 中江 秀雄*

Hatori, Masakazu; Kobayashi, Takanori; Sakamoto, Tsutomu; Nakae, Hideo*

片状黒鉛鋳鉄の一種である高P鋳鉄において引張強さの低下が認められたため、化学成分分析を実施したところ、微量のPb及びCaの含有が確認された。当該品の金属組織には、片状黒鉛の形状に異常が生じたウィドマンステッテン黒鉛が観察された。このため、他の既納品についての健全性の評価が求められた。ウィドマンステッテン黒鉛の有無については、スンプ法による評価も可能であるが、既納品に対して行うことは作業性に大きな問題があることから、非破壊検査による評価方法が求められた。片状黒鉛鋳鉄において引張強さと試料中を伝播する音速には相関が見られることが報告されていることから、黒鉛形状の異常であるウィドマンステッテン黒鉛の発生した片状黒鉛鋳鉄に同様の関係が成立つか否かについて、超音波厚さ計による音速測定を実施し確認を行った。この結果、Pbの混入による黒鉛形状の異常(ウィドマンステッテン黒鉛)が発生した場合にも、試料中を伝播する音速と引張強さに相関があることが確認された。これにより、Pb混入の可能性を有した片状黒鉛鋳鉄の非破壊での識別が可能になったものと考えられる。

Since the fall of tensile strength was accepted in high P cast iron which is a kind of flake graphite cast iron, when chemical component analysis was carried out, content of a little Pb(s) and Ca was checked. The Widmannstatten black lead which abnormalities produced in the form of flake graphite was observed by the metal organization of the elegance concerned. For this reason, evaluation of the soundness about other having existing delivered is called for. Although evaluation by the SUMP method was also possible about the existence of Widmannstatten black lead, since carrying out to having existing delivered had a big problem in workability, the valuation method by a non-destructive test was searched for. From it having been reported to the acoustic velocity which spreads the inside of tensile strength and a sample in flake graphite cast iron that correlation is seen, About whether the same relation is realized also in the flake graphite cast iron which widow Widmannstatten black lead which is black lead-shaped abnormalities generated, it checked by carrying out sonic measurement by an ultrasonic thickness gage. Generating of the abnormalities (Widmannstatten black lead) of the black lead form by mixing of Pb and the fall of the tensile strength accompanying this were accepted, and the result checked that correlation was between the acoustic velocity which spreads the inside of a sample, and tensile strength. Thereby, it is thought that discernment by un-destroying of flake graphite cast iron with the possibility of Pb mixing was attained.