根据JIS Z2275-1978对FB780MP热轧钢板进行平面弯曲疲劳试验，并运用最小二乘法对试验数据进行拟合，获得了在对称循环应力下的疲劳经验公式。结果表明：FB780MP热轧钢板在加载频率为25 Hz、循环载荷比R=-1条件下的疲劳极限为377.6 MPa；运用最小二乘法拟合出的疲劳经验公式为σ=-36.56lnN+852.11；疲劳试样裂纹源区未发现夹杂或加工缺陷，断面形貌特征与设定的试验条件相符合。

According to JIS Z2275-1978, the plane bending fatigue test of FB780MP hot rolled steel plate was carried out. The least square method was used to fit the test data, and the fatigue empirical formula under symmetrical cyclic stress was obtained. The results show that the fatigue limit of the FB780MP hot rolled steel plate was 377.6 MPa under loading frequency 25 Hz and cyclic load ratio R=-1. The fatigue empirical formula fitted by least square method was σ=-36.56lnN+852.11. No inclusions or processing defects were found in the crack source zone of fatigue samples, and the characteristics of fracture surface morphology were in accordance with the set test conditions.