ABSTRACT

An HSLA grade of structural steel was hot rolled using a coiling temperature of 500°C (CT500) or 540°C (CT540). As expected, the lower coiling temperature resulted in a more refined ferrite grain structure and a more dispersed distribution of smaller pearlite grains and carbides which formed along grain boundaries. Instrumented Charpy V-notch (CVN) tests were conducted and the CT500 material resulted in a higher ductile-brittle transition temperature, which was unexpected for the more refined microstructure. Damage evolution was characterized from the tested CVN specimens and revealed that a higher initial void/inclusion content for CT500 resulted in elevated void area fraction and void density values near the fracture surface of this material. Also, the refined distribution of carbides contributed to the higher void nucleation rate of CT500, which ultimately reduced the low temperature impact performance of this material.

摘要

使用 500°C (CT500) 或 540°C (CT540) 的卷取温度热轧 HSLA 等级的结构钢。正如预期的那样，较低的卷取温度导致更细化的铁素体晶粒结构和更分散的较小珠光体晶粒和沿晶界形成的碳化物的分布。进行了仪器化夏比 V 型缺口 (CVN) 测试，CT500 材料导致更高的韧脆转变温度，这对于更精细的微观结构来说是出乎意料的。从测试的 CVN 样品中表征了损伤演变，并表明 CT500 的初始空隙/夹杂物含量较高，导致该材料断裂表面附近空隙面积分数和空隙密度值升高。此外，碳化物的精细分布有助于 CT500 更高的空洞形核率，