Effects Copper Phosphus on Temper Embrittlement Mn-Mo-Ni Low Alloy Steel (ASTM )* ByMasayoshiHasegawa**, NobuyaNakajima***, NobuharuKusunoki*** KazuhiroSuzuki*** effect copper on temper steel. After beg quenched tempered, various lengths time up to 1000hr. was vestiged usg four hes ASTM each specimen was 300, 400, 500 impact test was carried out several observed by means scanng electron microscopy Auger electron spectroscopic techniques. results obtaed are summarized as follows: (1) contag 0.37%. copper showed temper, phenomenon was similar to th caused by phosphus under same he trement conditions. (2) contag copper phosphus, degree was affected by temperure, time pri austenite gra size. F same time, this showed a maximum value about, was still progressg after 1000hr. (3) At fracture surface Charpy impact test pieces, tergranular fracture was observed copper phosphus added specimen after trement. (4) After prolonged, concentrion copper phosphus on fracture surface was observed by Auger electron spectroscopy. (ReceivedFebruary18, 1975) electron Ⅰ. Introduction In recent years, many papers regardg temper steel have been repted(1). In consequence se vestigions, it was found th temper low alloy steels occurred as a result heg temperures range 300 slow coolg through this range spectroscopic technique(7) (9). On h, durg irradiion high temperure nuclear reacts, an pressure vessel steel weldment is known to be reled to presence residual elements, especially such as copper phosphus(10) (12), this phenomenon has present auths temper but mechanism not been explaed yet. have assumed th caused by copper from temperg temperure(2). It is also well known th impurities such as phosphus, phosphus irradiion antimony, perure react. Although no effect copper steel on temper was repted, this vestigion showed th copper ptant arsenic role this t steel play type an im- (3) (6). In last few years, it has been observed th segregion se impurities gra sub-gra boundaries is reled to usg a newly developed might be cluded lently service tem- had same fluence on temper steel as case phosphus. Auger Ⅱ. Experimental Procedure * This paper was igally published Japanese Tetsu-to-Hagane, 60 (1974), 2185. ** Department Metallurgy, Faculty Science Engeerg, Waseda University, Tokyo 160, Japan. *** Gradue School, Waseda University, Tokyo 160, Japan. Trans. JIM 1. Merials In this study, four hes ASTM steel (Mn-Mo-Ni steel) contag copper phosphus melted an duction 1975 Vol. 16
Masayoshi Hasegawa, Nobuya Nakajima, Nobuharu Kusunoki Kazuhiro Suzuki 642 Table l Chemical composition ASTM steels (wt%). furnace as 50kg gots n ged rolled to 17mm-thick ples. chemical composition se is shown Table 1. Specimen 1 with less impurities was high purity merial; specimen 2 was stard this vestigion; specimen 3 contag 0.37% copper was copperbearg merial, specimen 4 contag 0.06% phosphus was phosphusbearg merial. 2. He trement hr, steel wer austenitized quenched 850 tempered 1 670 30m followed by coolg wer. austenite gra size steels was range from ASTM gra size numbers 6.0 to 6.5 after this he trement. After beg quenched 300, tempered, 400, 500 up to 1000 hr n cooled wer. In der to vestige effect austenite gra size, itized wer. 670 number 1200 se schemically 1 3 austen- 1hr 30m. se 3.5 to 4.0. steels shown to tempered austenite se he 2 size from only trements Fig. 1. Table gra was range 100hr. quenched Tensile properties are Fig. 1 Schemicrepresention variousconditions he trement. 3. Mechanical properties To defe mechanical properties, tensile Charpy impact tests carried out after each he trement. Tensile tests room temperure with a stra re 0.5 mm/m permed on fl with a gage length 30mm, a width 10 mm a thickness 2.5mm. In quenched tempered ste, chemical composition had no effect, general, on tensile properties four. Charpy impact test on subsize, 5mm square by 55mm long with 1mm V-notch, done various temperures to cover transition curve each specimen. area brittle fracture was determed on fracture surface percentage brittle fracture was calculed. transition temperures appeared 50 percent brittle fracture determed from se curves. To evalue sensitivity to temper, value transition tem- as quenched tempered.
Effects Cu P on Temper shift (ΔTrS) ASTM (a) (b) (c) (d) Fig. 2 perure Embrittlement 643 Steel Transition curves quenched tempered specimen. (a) specimen 1 (b) specimen 2 (c) specimen 3 (d) specimen 4 was estimed from se transition curves. On condition quenched tempered, impact test results four (from 1 to 4) are shown Fig. 2. It was recognized th ductile-brittle transition temperures -72 th range presence phosphus steels had no effects quenched tempered shift transition 1000hr, is shown temperures 300 to Figs. -86 copper significant ste. (ΔTrS) 100 3 4. After Fig. 4 Effects copper phosphus steels on temper 300-1000hr. 100hr, effect impurities steel was observed specimen 3 after 1000hr, marked rise transition temperure occurred 3 4. Considerg composition 3 4, presence copper phosphus must have duced susceptibility to temper brittleness steel. effect time on Fig. 3 Effects 100hr. copper phosphus steels on temper 300- is shown Fig. 5. After about 100hr, ATrS already reached a surion value specimen 2, but 3 4, still creased with time. So difference degree depended
Masayoshi Hasegawa, Nobuya Nakajima, Nobuharu 644 Fig. 5 Effect time on Kusunoki Kazuhiro Suzuki temper steels. largely upon composition, especially copper phosphus, time temperure. It was well known th one facts affected degree temper was austenite gra size(13). In quenched tempered ste, transition temperures 1 3 raised a little as austenite gra size crease from ASTM 6 to 3 as shown Fig. 6. After beg 100hr, although Fig. 6 Effect pri austenite gra size on Charpy transition temperure 1 3. aus- tenite gra size did not fluence temper specimen 1, existence copper caused transition temperure specimen 3 to be highly sensitive to gra size he trement conditions examed. 4. Microstructures microstructures observed by means optical microscopy scanng type electron microscopy (SEM). microstructures 1 to 4 as quenched tempered all tempered martensite shown Photo. 1, after, carbides produced gra boundary tempered martensite. Sce no difference was observed between, copper phosphus nurally had no effect on optical microphotographs. Fractographs impact-fractured surface obtaed with SEM. brittle fracture surface quenched tempered was quasicleavage one th was ten obtaed a tempered martensite structure. After trement, 1 2 consisted quasi-cleavage fracture but tergranular fracture was also observed 3 4. 5. Auger electron spectroscopy technique Auger electron spectroscopy was used to measure segregion elements. Pre-notched samples-6.35mm (1/4.) diameter 25.4mm (1.) long- held a evacued chamber a pressure 3 10-9 Tr. mely -170. a In temperure this chamber, a approxihammer fractured sample notch surface was provided analysis composition. result analysis usg 3 4 is shown Fig. 7. Comparg curves (b) with (a) specimen 3, three peaks which cresponds to copper can be seen specimen. Specimen contag 0.37 copper demonstred th copper segreged to gra boundary by. As shown curves (c) (d) specimen 4 only change imptance appears to be phosphus le.
Effects Cu P on Temper Photo. Photo. 2 Scanng 1 Embrittlement Microstructures electron ASTM microscope fractographs Steel 645 steels. steels. (a) Specimen 4 after ( 1000hr) tested -65 (b) Specimen 3 after (400 1000hr) tested -45 (c) Specimen 3 after ( 1000hr) tested -35 ( 1000 3/5) (2) maximum re was Ⅲ. Conclusion Discussion Evalug temper ASTM steels with without copper phosphus, results obtaed are summarized as follows: (1) With, effect phosphus on temper was observed, content copper also showed same behavi as effect phosphus. obtaed bearg specimen 300 to copper phosphus- temperures. (3) In this temperure range, creased with time. (4) By trement, mode fracture surface was changed from quasicleavage to tergranular specimen contag copper phosphus. (5) After prolonged heg, concen-
Masayoshi Hasegawa, Nobuya Nakajima, Nobuharu Kusunoki Kazuhiro Suzuki 646 would occur after long time use even temperures lower than temperure range this vestigion. This phenomenon is a quite terestg problem from pots view metallurgical engeerg safety, so th furr experiments are beg carried out on followg: (1) prolonged lower temperures, (2) an quench-temper low alloy steels, such as ASTM A542, (3) allowable lower limit copper phosphus content, (4) detailed mechanism behavi copper phosphus on. Acknowledgment Fig. 7 Auger tied ( spectra non-embrittled 1000hr) steels used this study melted Yawa Technical Research Laby co-operive irradiion test sponsed by Japan Atomic Energy Research Institute Auger electron spectroscopy was permed Foundamental Research Laby Nippon Steel Cp. auths wish to thank Mr. Keiji Shimokawa Dr. Mitsuru Tano Cp. ir cooperion. embrit- ASTM steels. REFERENCES trion copper phosphus on fracture surface was observed by Auger electron spectroscopy. detailed mechanism by which copper produces temper remas almost unknown. In steel, copper has large solubility austenite structure. Although equilibrium solubility not has been copper α-iron defitely below established, it is thought to be very small(14). When a steel contag a small amount copper is quenched tempered, copper might be dissolved tempered martensite. Sce diffusion re copper gradually is very low, a long time it must precipite α-iron(15) (17). To cause temper by copper, a prolonged is necessary tempered martensitic structured steel such as specimen used this study. Temper caused by presence copper steel will be duced not by a temperg trement but by a prolonged heg operg temperure. In steel used nuclear, react turbes he enge plants, this (1) J. H. Hollomon:Trans.ASM,36 (1946),473. (2) B. C. Woodfe:J. Iron SteelInst., 173(1953), 229. (3) P. A. Restao C. J. McMahon:Trans.ASM, 60 (1967),699. (4) A. Preece R. D. Carter: J. Iron SteelInst., 173(1953),387. (5) J. R. Low,Jr., D. F. Ste,A. M. Turkalo, R. P. Lace: Trans. Met. Soc. AIME, 242 (1968),14. (6) W. Steven K. Balajiva:J. Iron SteelInst., 179(1959),141. (7) D. F. Ste,R. E. Weber, P. W. Palmberg: J. Metals,23 (1971),39. (8) R. Viswanhan:Met. Trans.,2 (1971),809. (9) D. F. Ste,A. Joshi, R. P. Lace:Trans. ASM, 62(1969),776. (10)L. E. Steele: AtomicEnergyReview,7 (1969), 122. (11)F. A. Smidt,Jr.: Met. Trans.,3 (1972),2065. (12)J. R. Hawthne:ASTMSTP 484(1970),96. (13)J. M. Capus:J. Iron SteelInst., 182 (1962),922. (14)H. A. Wriedt L. S. Darken: Trans. Met. Soc.AIME,218(1960),30. (15)M. S. An R. P. Agarwala:J. Appl. Phys., 37 (1966),4248. (16)E. Hnbgen R. C. Glenn: Trans. Met. Soc.AIME,218(1960),1064. (17)E. Hnbgen:Acta. Met.,10 (1962),525.