EFFECT OF Al, Ti AND B ADDITION ON THE LOW-TEMPERATURE TEMPERING EMBRITTLEMENT OF Cr-Mn CASE-HARDENING STEEL

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  • Mr-Cr肌焼鋼の低温焼戻脆性に及ぼすAl, Ti及びBの影響
  • Mn-Cr肌焼鋼の低温焼戻脆性に及ぼすAl,Ti及びBの影響
  • Mn-Crハダショウコウ ノ テイオン ヤキモドシゼイセイ ニ オヨボス Al , Ti オヨビ B ノ エイキョウ

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Description

The cause of the hard tempered martepsite brittleness which has come to be known as "500°F embrittlement" has not been explained until today. The phenomenon was much relatd to the deoxidation, nitrogen-fixation, and austenite grain size of steel. The tempering characteristics of the steel plays a major role in the development of embrittlement. This investigation consists of a stuay of the effect of Al, Ti and B addition on the impact-resistance and an electron micrgscopic study of the manganese-chromium case hardening steel when tempered between 120° and 420°C. The results obtained are as follows:<BR>(1) The Al-Ti (0.05-0.10%) addition markedly improves the impact values during tempering at these temperatures, especially with Ti addition the benefibal effect in the ternperature range of embrittlement is distinct.<BR>(2) The tempering embrittlement temperqture is not changed with the Al or Al-Ti addition and it occures at 300°C to 360°C; however in the case of Al-Ti-B addition it is the temperature range at 300°C to 420°C<BR>(3) The impact minimum occurs in 20 to 30 minutes at the tempering embrittlement temperatures and the value is decreased with keeping time at 300°C, it is almost constant up to 10h at 360°C.<BR>(4) The transition temperature is lowered by the Al, Ti and Al-Ti-B additiop; with the Al (0.04%), Ti(0.10%) and Al-Ti (0.06%)-B addition it falls down to 0°C-10°C.<BR>(5) It is obeerved that the embrittlement arises from a precipitation of elongated thin cementite network along ferrite grain boundaries, with the B addition the formation is obserVed at the higher tempering temperature.

Journal

  • Tetsu-to-Hagane

    Tetsu-to-Hagane 42 (4), 318-326, 1956

    The Iron and Steel Institute of Japan

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