194 論文鉄と鋼 Tetsu-to-Hagané Vol. 103 (2017) No. 4 SUJ2 材の焼入れ組織に及ぼす高周波誘導加熱条件の影響 Influence of Induction Heating Condition on Quenched Structure of

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1 194 論文 SUJ2 材の焼入れ組織に及ぼす高周波誘導加熱条件の影響 Influence of Induction Heating Condition on Quenched Structure of JIS-SUJ2 Steel Hiroshi Yuki, Miyu Sato and Chikara Ohki Synopsis : When JIS-SUJ2 steel is hardened by induction heating, high temperature austenitizing is applied in order to achieve high productivity. In this case, SUJ2 is quenched from the single-phase austenite zone. As a result, the properties of SUJ2 may be different from the conventional furnace process involving SUJ2 quenched from the two-phase austenite / cementite zone. In this study, we experimentally investigated the relation between the amount of undissolved carbide, austenitizing temperature, and duration. Additionally, we developed a prediction formula for undissolved carbide in the single-phase austenite zone. The formula is consists of the Arrhenius equation and the Kolomogorov-Johnson-Mehl-Avrami equation. Subsequently, the effect of austenitizing temperature and amount of undissolved carbide on hardness, retained austenite content, prior-austenite grain size, and martensite block size were investigated. Key words: heat treatment; bearing steel; induction heating; grain size; retained austenite. 1. 緒言 JIS-SUJ2 SUJ2 SUJ2 SUJ SUJ2 SUJ ,5,6 X Dilatometer J-STAGE Received on Jun. 24, 2016 ; Accepted on Nov. 25, 2016 ; J-STAGE Advance published on Dec. 28, NTN Advanced Technology R&D center, NTN Corporation, Hidamarinooka Kuwana Mie Corresponding author : hiroshi_yuuki@ntn.co.jp DOI : 20

SUJ2 195 2. 実験方法 2 1 均熱温度および残留炭化物量を変更した試験片作製方法 Table 1 SUJ2 Fig.1 60.3 mm 53.7 mm 15.3 mm 103 mm 74 mm 22 mm 80 khz 1300 Arms Fig.2 900 57 s 70 H 0.

1 mm X α 211 γ 220 2 4 脱炭量測定 Fig.3 0.5 mm EPMA 2 m 2 m Table 1. Chemical Composition of the SUJ2 steel used in the present study (mass%). C Si Mn P S Ni Cr Mo Cu 1.02 0.31 0.

2 SUJ 実験方法 2 1 均熱温度および残留炭化物量を変更した試験片作製方法 Table 1 SUJ2 Fig mm 53.7 mm 15.3 mm 103 mm 74 mm 22 mm 80 khz 1300 Arms Fig s 70 H 0.14 cm h s % s s s 2 2 組織観察方法 Fig.3 SEM ASTM 10 FE-SEM/EBSD 2 3 残留オーステナイト測定 0.1 mm X α 211 γ 脱炭量測定 Fig mm EPMA 2 m 2 m Table 1. Chemical Composition of the SUJ2 steel used in the present study (mass%). C Si Mn P S Ni Cr Mo Cu Fig. 2. Temperature variation during induction heating. Fig. 1. Photograph of a test piece. (Online version in color.) Fig. 3. Schematic illustration of the observed cross-section. 21

196 3. 実験結果 3 1 均熱温度保持時間と残留炭化物量の関係 Fig.4 900 70 s Fig.5 11 Kolomogorov-Johnson-Mehl- Avrami 12 1 2 1 2 f K t s T R n A Q 15.6% 7860 kg/m 3 7680 kg/m 3 13 0% Fig.5 1 2 n A Q T t s M % 3 3 Fig.

3 実験結果 3 1 均熱温度保持時間と残留炭化物量の関係 Fig s Fig.5 11 Kolomogorov-Johnson-Mehl- Avrami f K t s T R n A Q 15.6% 7860 kg/m kg/m % Fig n A Q T t s M % 3 3 Fig.6 3 R 均熱温度および残留炭化物量が材料組織に及ぼす影響 % % 3 6 Fig.7 Fig. 4. Undissolved carbide particles observed by SEM. Fig. 6. Comparison between experimental and predicted values of undissolved carbide fraction(%), according to the formula (3). Fig. 5. Undissolved carbide fraction of all tested conditions, as a function of the duration time with various heating temperatures. Fig. 7. Influence of austenitizing temperature and undissolved carbide fraction on retained austenite content. 22

SUJ2 材の焼入れ組織に及ぼす高周波誘導加熱条件の影響度が高いほどおよび残留炭化物量が少ないほど残留オート中での炭素の拡散係数は非常に大きい 14 ため固溶炭素ステナイト量が多くなる傾向となった同一の残留炭化物が十分拡散し均熱温度が 900 950 の場合と同等の硬さ量の場合均熱温度が高い方ほど残留オーステナイト量がが得られていると考えられる多い傾向にあった Fig.

10 に結晶粒度測定結果を示す残残留炭化物量が少ないほど硬くなる傾向にある均熱温度留炭化物量が多くなるほど結晶粒度番号が大きくなる傾が 950 の場合残留炭化物量 12% の場合よりも 8% の場向にあるが残留炭化物量 4% の場合でも結晶粒度番号は 9 合の方が硬いが 4% の場合は逆転するこれは残留オー番程度であり炭化物のピン止め効果により結晶粒の粗大

4 SUJ2 材の焼入れ組織に及ぼす高周波誘導加熱条件の影響度が高いほどおよび残留炭化物量が少ないほど残留オート中での炭素の拡散係数は非常に大きい 14 ため固溶炭素ステナイト量が多くなる傾向となった同一の残留炭化物が十分拡散し均熱温度がの場合と同等の硬さ量の場合均熱温度が高い方ほど残留オーステナイト量がが得られていると考えられる多い傾向にあった Fig.9 に均熱温度を 900 とした場合の旧オーステナイト Fig.8 に硬さ測定結果を示す均熱温度が 900 の場合結晶粒を例示する Fig.10 に結晶粒度測定結果を示す残残留炭化物量が少ないほど硬くなる傾向にある均熱温度留炭化物量が多くなるほど結晶粒度番号が大きくなる傾が 950 の場合残留炭化物量 12% の場合よりも 8% の場向にあるが残留炭化物量 4% の場合でも結晶粒度番号は 9 合の方が硬いが 4% の場合は逆転するこれは残留オー番程度であり炭化物のピン止め効果により結晶粒の粗大ステナイト量の割合が増大することに起因すると考えられ化を抑制できている均熱温度が高いほど結晶粒は大きくる均熱温度 1000 の場合残留炭化物量が多いすなわなるがその差は微少であり本実験範囲内では均熱温度ち固溶炭素量が少ない場合でも高硬さであった均熱温度の結晶粒度に及ぼす影響は小さいと言えるが 1000 の場合は均熱時間が非常に短いがオーステナイ Fig.11 に均熱温度 900 とした場合のマルテンサイトの Fig. 8. I nfluence of austenitizing temperature and undissolved carbide fraction on hardness. Fig. 10. I nfluence of austenitizing temperature and undissolved carbide fraction on prior-austenite grain size. Fig. 9. Prior-austenite grain structures of samples heated at 900 C. Dissolved carbide fraction : (a) 4%, (b) 8%, and (c) 12%. Fig. 11. Martensite IPF maps of samples heated at 900 C. Dissolved carbide fraction: (a) 4%, (b) 8%, and (c) 12% (Online version in color.)

198 5 1 Table 2 Fig.12 8% 4% 12% 3 3 脱炭量 Fig.13 900 EPMA 2 m ε Table 2. Martensite block size determined from IPF maps.

5 Table 2 Fig.12 8% 4% 12% 3 3 脱炭量 Fig EPMA 2 m ε Table 2. Martensite block size determined from IPF maps. Temperature ( C) Undissolved carbide (%) Martensite block size (μm) Max Min. Ave Fig.14 12% 4% 8% 8% 0.02 mm 4% 0.08 mm 4. 考察 SUJ2 3 1 n n K Kolomogorov-Johnson-Mehl-Avrami ln ln 1/1-f ln t Fig.5 Fig.15 Fig. 12. Influence of austenitizing temperature and undissolved carbide fraction on martensite block size. Fig. 14. Influence of austenitizing temperature and undissolved carbide fraction on maximum decarburization depth. Fig. 13. Carbon concentration profiles of samples heated at 900 C. Dissolved carbide fraction : (a) 4%, (b) 8%, and (c) 12%. (Broken lines indicate average carbon concentration in each case) 24

6 SUJ2 199 n K Table n 900 n SUJ mass%c Acm n FactSage 900 Fig % 900 n n n n 2 1 n Fig 結言 JIS-SUJ % Table 3. Values of n and K in fomula (2) for different austenitizing temperatures determined from the plots shown in Fig.15. Temperature ( C) n K Fig. 16. Equilibrium phase diagram of SUJ2 steel. Fig. 15. Plots of ln ln(1/(1-f)) vs ln t for different austenitizing temperature. (a) 900 C, (b) 950 C, and (c) 1000 C. 25

7 SUJ2 M % T K t s % 3 8% 4% 12% 0.35 m 文 1 ) V.Rudnev, D.Loveless, R.Cook and M.Black: Handbook of Induction Heating, Marcel Dekker, New York, (2003), ) S.Shiko, K.Okamoto and S.Watanabe: Tetsu-to-Hagané, 54(1968), ) M.Ueno, T.Mitsuhashi and Y.Nakano: Tetsu-to-Hagané, 41(1955), ) M.Ueno and Y.Nakano: Tetsu-to-Hagané, 43(1957), ) K.Monma, R.Maruta, T.Yamamoto and Y.Wakikado: J. Jpn. Inst. Met., 32(1968), ) K.Monma, R.Maruta, T.Yamamoto and Y.Wakikado: J. Jpn. Inst. Met., 32(1968), ) J.Epp, H.Surm, O.Kessler and T.Hirsch: Metall. Mater. Trans. A, 38(2007), ) J.Epp, H.Surm, O.Kessler and T.Hirsch: Acta Mater., 55(2007), ) W.Song, P.Choi, G.Inden, U.Prahl, D.Raabe and W.Bleck: Metall. Mater. Trans. A, 45(2014), ) JIS G 0551: Steel-Micrographic determination of the apparent grain size, (2013). 11) T.Fujita and N.Suzuki: NTN Tech. Rev., 80(2012), ) J.Burke: The Kinetics of Phase Transformations in Metals, Pergamon Press, New York, (1965), ) (2015), ) C.Wells, W.Batz and R F.Mehl: Trans. AIME, 188(1950), ) M.Hillert, K.Nilsson and L.-E.Torndahl: J. Iron Steel. Inst., 209(1971), 49. 献 26

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194 論 文 鉄と鋼 Tetsu-to-Hagané Vol. 103 (2017) No. 4 SUJ2 材の焼入れ組織に及ぼす高周波誘導加熱条件の影響 Influence of Induction Heating Condition on Quenched Structure of

194 論文鉄と鋼 Tetsu-to-Hagané Vol. 103 (2017) No. 4 SUJ2 材の焼入れ組織に及ぼす高周波誘導加熱条件の影響 Influence of Induction Heating Condition on Quenched Structure of