为解决钢厂高强度船板钢连铸坯经常出现的中间裂纹等内部缺陷问题，从该钢种连铸坯中间裂纹区域获取试样，并对其进行了高温力学性能测试。结果表明，低温脆性区(即第三脆性区)的温度范围为750~925℃，在900~950℃温度区断口处存在较多液膜。综合断口形貌、液膜存在的温度范围以及断口纵断面金相组织等方面进行分析，认为950℃时塑性开始下降的主要原因是由于断口处存在液膜，并推断液膜的形成原因为晶界处形成了(FeS+FeO)或(MnS+FeS+FeO)低熔点共晶相。同时，该试样在750~950℃区间内塑性下降的发生机制可以大致归结为：900~950℃区间内由于低熔点共晶相液膜作用导致塑性下降；850~900℃之间由于低熔点共晶相液膜与晶界铁素体膜复合作用导致塑性下降；850℃以下由于晶界铁素体膜作用导致塑性下降。

In order to eliminate internal defects such as the intermediate crack in continuously cast slab of high-strength ship plate steel, the sample taken from the area of the intermediate crack was investigated by the high-temperature property test. The brittle zone of low temperature (ie the third brittle zone) was found in the range 750-925℃, and a lot of liquid film was found on the fracture in the range 900-950℃ through the test. On the basis of the feature of fracture, the existing temperature range of liquid film, the vertical-section metallographic structure of fracture and so on, the ductility decreasing first below 950℃ is due to the presence of the liquid film on the fracture, and it is deduced that the liquid film on the fracture is the result of the formation of the low-melting eutectic phase (FeS+FeO or MnS+FeS+FeO) at the grain boundary. Meanwhile, the formation mechanism of the ductility decreasing in the range of 750-925℃ can be roughly divided in the following three stages: in the range 900-950℃, the ductility decreasing is due to the liquid film; in the range 850-900℃, the ductility decreasing is due to the liquid film and the ferrite film at the grain boundary; below 850℃, the ductility decreasing is due to the ferrite film at the grain boundary.