Influence Of Chemical Composition And Heat Treatment Process On Microstructure And Mechanical Properties Of45CrNiMo Steel

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.