構造用 金屬材料의 展性破壞에 對한 硏究

Abstract

構造用 金屬材料로서 오스테나이트 스테인레스 강판을 壓延方向에 대하여 여러 가지 方向으로 引張試驗한 結果 상당한 量의 異方性이 檢出되었다.

異方性은 變形速度와 引張方向에 따라 달라졌다. 異方性의 尺度인 平面塑性 變形比는 變形速度가 增加함에 따라 어떤 臨界變形速度 이상에서 급격하게 增加하였다. 이것은 塑性變形機構가 臨界變形速度에서 結晶粒果 미끄러짐으로부터 결정 슬립으로 變化되는 것을 의미한다.

넥킹이 시작될 때 확산넥킹 변형율(??)과 加工硬化指數(n??)사이에는 아래와 같은 關係가 成立함을 塑性理論에 의하여 誘導하였고 實驗에 의하여 確認하였다.

n??=??+상수

部分的으로 軟化熱處理한 오스테나이트 스테인레스 壓延鋼板의 引張軸에 對한 破面角度는 異方性과 板材두께가 增加함에 따라 增加하였다.

A reasonably high anisotropy was detected by tension tests with various tensile direction of austenitic stainless steel plate as a structural material.

Anisotropy was a function of strain rate and the degree between load axis and rolling direction of austenitic stainless steel plates. Plastic strain ratio which is reflective of anisotropy increased sharply at some ciritical strain rate with increasing strain rate. The operative deformation mechanism at this critical strain rate was considered to change from grain boundary sliding to crystallographic multiple slip.

Following expression between diffuse necking strain (??) and the strain hardening exponent (n??) at plastic instability conditions was dereved by the theory of plasticity and confirmed by experiment.

n??=??+constant

The degree between load axis and fracture plane of partially softened austenitic stainless steel increaed with increasing anisotropy and thickness of plate.

A reasonably high anisotropy was detected by tension tests with various tensile direction of austenitic stainless steel plate as a structural material.

Anisotropy was a function of strain rate and the degree between load axis and rolling direction of austenitic stainless steel plates. Plastic strain ratio which is reflective of anisotropy increased sharply at some ciritical strain rate with increasing strain rate. The operative deformation mechanism at this critical strain rate was considered to change from grain boundary sliding to crystallographic multiple slip.

Following expression between diffuse necking strain (??) and the strain hardening exponent (n??) at plastic instability conditions was dereved by the theory of plasticity and confirmed by experiment.

n??=??+constant

The degree between load axis and fracture plane of partially softened austenitic stainless steel increaed with increasing anisotropy and thickness of plate.