微量元素对大型船用柴油机连杆疲劳强度的影响

Effect of trace elements on fatigue strength of connecting rods for large marine diesel engine

通过调整Cr、Ni、Si等微量元素、降低终锻温度,提高心部变形量,解决了大锻件心部晶粒度不均匀、疲劳强度低的难题,使锻件内部质量满足设计要求。运用Gleeble热模拟试验机,对不同成分的S30Mn钢进行对比,测得在加热条件下的临界转变温度值和不同冷却速率的相变温度值,并绘制了CCT图,确定了精确的材料参数。探讨了微量元素在S30Mn钢中的强化机理,针对连杆,Cr、Ni、Si等微量元素能够更有效地固溶于基体组织,从而推迟γ相向珠光体的转变温度40℃,甚至在较低的冷却速度(0.05℃·s-1)下,γ相仍能有效地向珠光体转变,使得珠光体片层间距变薄、晶粒更加细化。经过对比试验可知,调整微量元素并优化锻造工艺后,产品的力学性能、心部晶粒度及疲劳强度均有明显地提高。

The problems of uneven grain size and low fatigue strength in the center of heavy forgings were solved,and the internal quality of forgings met the design requirements by adjusting the trace elements of Cr,Ni,Si etc.,reducing the final forging temperature and increasing the center deformation.To determine the material parameters accurately,the S30 Mn steels with different chemical compositions were compared by Gleeble thermal simulator,the critical transition temperature under the heating condition and the phase transition temperature under different cooling rates were measured,and the CCT diagram was drawn.The strengthening mechanism of the trace element in S30 Mn steel was studied,the trace elements of Cr,Ni,Si could be solid soluted in the matrix-structure more effectively to delay the transforming temperature ofγphase to pearlite by 40℃,theγphase could still transform to pearlite effectively at a low cooling speed of 0.05℃·s-1,the lamella distances of pearlite turned thin,and the grain size refined more.The results show that after adjusting the trace elements and optimizing forging process,the mechanical properties,core grain size and fatigue strength of products are improved significantly.