Abstract: The cold heading cracked samples and Φ 12 mm hot-rolled wire rods of SWRCH35K steel are inspected by optical microscope. Analysis results show that the reason for cold heading cracking is full decarburized layer exist on the surface of hot-rolled wire rod, led to decrease of strength, resulting in stress cracking of the surface layer during the cold upsetting process. By decreasing billet heating temperature from original 1 000 〜1 150 °C  to 950 〜1 050 °C , controlling air-fuel ratio 0. 4 ~0. 6, and decreasing billet total heating time from original 95 ~212 min to 95 ~ 158 min, the full decarburized layer of SWRCH35K steel hot-rolled wire rod is effectively eliminated, and the cold heading cracking in the production process of bolts and nuts is avoided.

摘要： 釆用光学显微镜对SWRCH35K钢冷徵开裂样品和Φ12 mm热轧盘条进行高倍检验。分析表明，冷镦开裂原因为热轧盘条表面存在完全脱碳层，导致强度下降，致使表层基体受冷锹成型过程中应力作用产生开裂。 通过将钢坯加热温度从原1000 ~1 150 °C降至950 - 1 050°C 空燃比控制在0.4-0. 6,总加热时间由原95 ~ 212 min降至95 - 158 min,有效消除了 SWRCH35K钢热轧盘条的完全脱碳层，避免了螺栓、螺母的冷镦开裂。

关键词: 冷镦开裂螺栓、螺母, SWRCH35K钢, 完全脱碳层, 加热工艺