【作者】 杨丽；

【导师】 朱景川；

【作者基本信息】 哈尔滨工业大学 ， 材料工程， 2014， 硕士

【摘要】 曲轴用钢45CrNiMo经调质热处理后，出现大量力学性能偏低的现象，主要是冲击性能不符合标准要求，存在安全隐患，严重影响曲轴的使用。冲击功偏低的主要原因，一方面是部分元素形成化合物停留在晶界，破坏钢的连续性，比如磷、硫、钛等元素在晶界形成化合物析出；另一方面热处理工艺使组织出现超大块的珠光体团。本文应用回归分析、人工神经网络、断口分析以及正交试验等方法，研究了化学成分、热处理制度对力学性能的影响。首先基于54炉45CrNiMo钢生产冶炼与检验数据，分别采用回归分析与神经网络法分析了化学成分对力学性能的影响规律。通过回归分析发现化学成分对材料力学性能的影响是多种元素共同作用的结果；钢中硫、磷、钛的含量对冲击性能的影响和危害程度最大，在硫含量小于0.005%，磷含量不大于0.007%时，冲击韧性的值均大于30J；钛含量超过0.02%时会使钢的冲击韧性降低，当钛含量小于0.01%，会起到弥散强化的作用，因此钢中钛的含量控制在一定的范围，不仅可以防止出现热送裂纹，又对冲击性能的影响不大；进一步建立了化学成分与冲击功和拉伸性能的神经网络定量模型，反映了各元素的综合作用，并能进行性能定量预测与成分反向控制。随后研究了中碳调质曲轴用钢45CrNiMo的奥氏体化与连续冷却转变行为，并进一步研究了正火预处理和最终调质热处理工艺与钢的力学性能之间的变化关系。分析了热处理工艺对铁素体和珠光体组织组成的影响，及其对拉伸与冲击性能的影响规律，确定了适宜的奥氏体化温度与调质热处理工艺。对45CrNiMo钢的冲击断口形貌分析表明，冲击值大于30J的试样，塑性区面积较大，先共析铁素体含量较多，珠光体含量较少；冲击值偏低试样的塑性区面积较小，先共析铁素体含量较少，而珠光体含量较多。说明先共析铁素体含量的控制对提高冲击性能有很大作用。上述化学成分与力学性能关系模型以及组织转变规律对该类钢的冶炼生产与热处理组织控制具有重要的指导意义。更多还原

【Abstract】 A large number of low mechanical properties phenomenons，Most of which arethe impact toughness not meeting the standard, appears in45CrNiMo, the crankshaftsteel, after tempering heat treatment. These cause serious hidden danger, whichinfluence the use of the crankshaft. The main reason for the low impact energy, onthe one hand, is that some of the elements formed the chemical compounds in grainboundary, destroying the continuity of steel, such as phosphorus, sulfur, titanium; onthe other hand, heat treatment process causes large piece of pearlite appear in themicrostructure. In this paper, the influence of the chemical composition and heattreatment process on the mechanical properties was studied using regressionanalysis, artificial neural network, fracture analysis and orthogonal test method.Firstly, based on the smelting and testing data of54furnaces of steel, analysisof regression and ANN is used to analyze the influence rule of chemical compositionon the mechanical properties. It is found through the analysis that the performanceof mechanics of materials is not affected by an element or two elements, but is theresult of a variety of elements together. It is concluded that sulfur, phosphorus andtitanium are the Most harmful elements in the steel. When the sulfur content is lessthan0.005%, phosphorus content is not More than0.007%, the impact toughnessvalues is greater than30J. If the titanium content is More than0.02%, the impacttoughness of the steel would reduce. The titanium content which is less than0.01%,will have the effect of dispersion strengthening. So the content of titanium in steelshould be controlled in a certain range, in which not only can prevent the hot crack,but also do not have negative influence to the impact performance. Furthermore, theANN Model of the effects of chemical composition on the mechanical properties isbuilt, which reflects the effects of different elements’ combined action, and is able tomake quantitative prediction of the performance and control the compositionreversely.Then the austenitizing and continuous cooling transition of the medium carbonalloy crankshaft steel45CrNiMo is studied. The relationship between normalizingpretreatment and final processing of quenching and tempering and the mechanicalproperties of the steel is also investigated in this paper. The influence of heattreatment to the ferrite and pearlite content and influence rule of the content to theimpact toughness is studied, the optimum austenitizing temperature is determined.The analysis of the fracture surface of45CrNiMo steel showed that the plasticarea is bigger and the ferrite content is higher in the sample of w hich the impact toughness is bigger than30J. The ferrite content and the plastic area are smaller inthe samples of which the impact toughness is lower.Above-mentioned Model of chemical composition and mechanical propertiesand the phase transition rule has significant guiding importance on the smelting andheat treatment microstructure control.更多还原