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低合金钢经高热输入的焊接之后,可能产生热影响区(HAZ)粗晶区韧性的严重下降。这与HAZ 的组织转变有密切关系。本文采用光学金相、扫描电子显微镜和金属膜透射电子显微镜等方法,对正火状态14MnCuNiV 钢的HAZ 的显微组织和夹杂与韧性之间的关系进行了研究,主要结论如下:正火态的低合金钢经焊接热循环后,HAZ 粗晶区韧性均有不同程度的下降,热输入增高,HAZ 的脆性转变温度上升,韧性显著下降。当HAZ 组织在具有足够冲击韧性的转变温度时,带状硫化物对冲击值起了显著的破坏作用。但在材料本身具有较大脆性而出现准解理形貌时,带状夹杂不再具有主导作用。金属薄膜透射电镜分析表明,高热输入HAZ 的粒状贝氏体中存在挛晶马氏体的M-A 组织。这类组织是高热输入脆化的主要原因.低热输入HAZ 为板条马氏体+细粒状贝氏体组织,具有较好的低温韧性.本文利用HAZ 的非平衡态冷却条WF粒状贝氏体形成过程的机理,来解释不同焊接热输入对HAZ 粒贝小岛内M-A 组织产生条件的影响.这一解释在薄膜透射电镜分析中得到了证实.
Low-alloy steels with high heat input may cause a severe decrease in the toughness of the coarse-grained zone in the heat-affected zone (HAZ). This is closely related to the organizational change of HAZ. In this paper, the relationship between the microstructure and inclusions and the toughness of the HAZ in normalized 14MnCuNiV steel was investigated by means of optical metallography, scanning electron microscopy and metal film transmission electron microscopy. The main conclusions are as follows: After heat cycle of low alloyed steel, the toughness of coarse grain zone of HAZ decreased to some extent, the heat input increased, the brittle transition temperature of HAZ increased, and the toughness decreased significantly. Striped sulfides have a significant detrimental effect on impact values when the HAZ structure is at a transition temperature with sufficient impact toughness. However, when the material itself has a large brittleness and quasi-cleavage morphology appears, the ribbon inclusions no longer play a leading role. Transmission electron microscopy analysis of metal thin films shows that there is M-A tissue of tetraploid martensite in granular bainite of HAZ with high heat input. This kind of organization is the main reason of high heat input embrittlement.The low heat input HAZ is lath martensite + fine granular bainite, which has good low temperature toughness.In this paper, HAZ non-equilibrium cooling bar WF granular bainite Formation process to explain the effect of different welding heat inputs on the production of MA tissue in HAZ pellet islets This interpretation was confirmed by transmission electron microscopy (TEM).