实际生产中检测18Ni(250)钢的伸长率并不高,当钢板厚度为1.4 mm时,其伸长率在4%左右,似乎其塑性很差,接近于脆性材料。通过对不同厚度的18Ni(250)钢板进行拉伸试验，研究了该钢伸长率较低的原因。结果表明: 该钢伸长率有尺寸效应,即伸长率随着拉伸试样截面尺寸的减小而减小; 该钢塑性很好,其伸长率反映的塑性是一个假象。

The elongation ratio of 18Ni(250) steel is low in actual test. When the steel is as thin as 1.4mm, the elongation ratio of it is only at 4% around, as if its plasticity is very bad and it approaches brittle materials. Series tensile test were carried out to find the reason for lower elongation ratio of the steel with different thickness 18Ni(250) steel plate as samples. The results show that 18Ni(250) steel has a size effect phenomena, that is its elongation ratio decreased with the decrease of the sectional dimension of the tensile samples. The plasticity of this steel is very fine in fact, and the plasticity of it reflected by its elongation ratio is a feint.