3ナイロン結晶には, 前報で報告した結晶型の他に, 三つの結晶型が見出された。ここでは, 結晶I, II, III, IVと呼ぶことにする。Iは延伸繊維, o-ジクロルベンゼン重合溶媒中で得られた重合体に見出される結晶型で, この特徴は, 他の結晶型に比べて (200) 面が強いことにある。IIは, 未延伸糸, 再沈試料などに見出される結晶型で, 面反射はIと同位置に現われるが, 強度が異なる。IIは延伸するとIに変わる。IIIは無機塩添加重合物に見出され, 面反射はIと同位置に現われるが反射強度が異なっている。I, II, IIIにおいては, 赤外分光学的に分子鎖はいずれも伸び切った形態にあった。IVは, I, II, IIIを融点直下より急冷すると得られる, いわゆるSmectic Hexagonalに対応するものであり, 沸水処理でIに転換した。γ型結晶は存在しなかった。

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Residual stresses and angular distorsions are very important probrems in welding design and fabrication. In the previous reports it was shown that the materials with a martensitic transformation at low temperature were effective to the reduce residual stress and anguler distorsion in welding.
In this report the effects of transformation on prevention against crack in welding were examined by use of restraint thermal cycle test and constraint crack test. The results are shown as follows;
(1) The materials with transformation at low temperature were effective to reduce residual stresses in stress concetration area and to prevent cracks in welding.
(2) As the result of the stress consentration test (mild steel was broken in the midst of cooling by this test method), it was possible to prevent a crack or a failure at the stress concentration area by use of the materials with the transformation at low temperature. In this case, the transformation superplasticity was more effecive than transformation expansion to release the stress concentration.
(3) The M_s temperature of the materials with the transformation at low temperature (there was no crack by use of these materials in this test) was less than 200°C. But a dilution from a base metal raised the transformation temperature and the free thermal contraction curve changed. Therefore in welding practices, the change of transformation temperature by the dilution from base metal is also important.

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