The Effect Of Tensile Stress On Transformation Microstructure And Hardness Of HQ785 Steel

In recent years, new steel based on low carbon bainite is developing in both domestic and overseas, and the carbon content of this steel is declined dramatically(commonly about 0.05%) , and has high intensity, plasticity and toughness, and welding performance. But there are many problems, such as obdurability , organization control and fine because of its short development time, so it is difficult for this steel to develop and use, and it is need to fully extended in seriation, production control technology , new kinds and usesge range.In this paper ,the experimental materials for low carbon bainite steel is HQ785, use Gleeble-3500 hot/force simulation test enginery plus one-way tensile stress of the phase change experiment, at the same time by optical microscope,Scanning electron microscopy (sem) , transmission electron microscope (tem) observing the influence of organization morphology under tensile stress, but also use vickers hardness tester for different technology organization hardness measured, and the experimental results are discussed as follows:1. The effect of applied stress on the austenitic transformationNo stress effect, the average austenite grain size which after austenitic phase change is small, and on a kind of uniformity; When the stress on smaller, Average grain size has a modest reduction of the trend,then the average grain size increase as the stress increases,nonuniform also will increase; When applied to sample the transient stress, austenitic grain size reduced significantly, and no stress and applying the samples for stress, compared with transient stress the austenitic organization is the most trivial, nonuniform is also reduce; Along with the increase of stress, vickers hardness in gradually rise, compared with sustained stress,the hardness which under transient is low.2. The effect of applied stress on the microstructure of continuous cooling transformation With the increase of stress, Bs points also increased significantly. No stress, the length and width of the attrib wattle are differentials, grain boundary with a lot of retained austenite; Imposed after stress, the organization attrib wattle was refined, the amount of retained austenite significantly reduced; Exert transient stress, attrib wattle is the most narrow and nearly parallel. Along with the increase of stress, vickers hardness in gradually rise, compared with sustained stress,the hardness which under transient is low.3. The effect of applied stress on the bainite microstructureNo stress, grains is small; Grain size becomes larger as the applied stress increase, the retained austenite or rich carbon M-A island which between the batten are also reduce gradually, and gathered to grain boundary, Bainite attrib wattle also presents the widened trend; Compared with sustained stress,the grain size which obtained under exert transient stress is smaller, and more uniform, bainite attrib wattle also relatively narrow.At the same time, it is also observed that the microstructure morphology of bainite inherited the characteristics morphology of the austenitic microstructure.