氮含量对Cr10Mn9Ni0.7合金组织和力学性能的影响

发布时间：2018-05-06 23:03

本文选题：糊状区保温 + 显微组织　；参考：《昆明理工大学》2017年硕士论文

【摘要】：不锈钢是日常生产生活中最常见的一种金属,因其良好的力学性能和优异的耐蚀性得到广泛应用。对不锈钢进行氮化处理,以氮代镍,既能保证不锈钢的各项性能,又能节约资源,因此受到了广泛的关注。常见的不锈钢氮化技术主要是液相渗氮和固相渗氮,但是液相渗氮存在渗氮效果较差,且工艺复杂的问题,固相渗氮时渗氮时间长,且渗氮层厚度有限。本研究对渗氮工艺进行改进,提出一种新的渗氮方法,糊状区保温渗氮工艺。主要是利用糊状区温度范围内,固液两相区共存的特点,进行一定时间的保温,使氮气有充分的时间溶入液相,并扩散至奥氏体相,最终提高室温组织中的氮含量。通过实验及理论研究,本文最终得出以下结论:(1)糊状区保温过程中,氮含量随着保温时间的增加逐渐提高,当氮气压力为0.1MPa时,氮含量可从0.17%提高到0.23%,而气孔率则从1.86%降至1.37%;当氮气压力为0.4MPa时,氮含量由0.29%提高到0.37%,气孔率从1.41%降到1.06%。说明糊状区保温工艺可以有效提高钢中的氮含量,同时能够降低铸锭中的气孔率。(2)探究了糊状区保温过程中组织随氮含量的变化,表明在糊状区保温过程中,氮在钢液中不断溶解会使组织中的铁素体发生等温相变,一部分铁素体与液相发生包晶反应生成奥氏体,另一部分由固态相变变为奥氏体;液相中的氮达到一定含量后,会在随后的冷却中直接转变为奥氏体。(3)阐述了糊状区保温增氮的机理:一方面,糊状区增氮促使铁素体向奥氏体转变,奥氏体含量的增多增加了合金中氮的溶解度;另一方面,氮含量的提高促使液相直接转变为奥氏体,增加了室温组织中的奥氏体含量。(4)高氮奥氏体不锈钢在变形量小于2%时候,氮含量的增加能显著提高奥氏体不锈钢的屈服强度;当变形量超过5%以后,试样中可能有形变马氏体产生,使得氮含量较低的试样应力值显著增大,而氮含量较高的试样中,强化仍以加工硬化为主。
[Abstract]:Stainless steel is one of the most common metals in daily life. It is widely used because of its good mechanical properties and excellent corrosion resistance. Nitridation of stainless steel with nitrogen instead of nickel can not only guarantee the properties of stainless steel, but also save resources, so it has been paid more and more attention. The common nitriding technology of stainless steel is mainly liquid phase nitriding and solid phase nitriding. But liquid phase nitriding has some problems such as poor nitriding effect and complicated process. The nitriding time is long and the thickness of nitriding layer is limited during solid phase nitriding. In this study, the nitriding process was improved, and a new nitriding method was put forward. It is mainly made use of the characteristic of coexistence of solid and liquid two phases in the temperature range of the paste zone to hold heat for a certain time so that nitrogen can be dissolved into liquid phase and diffused into austenitic phase, and the nitrogen content in the microstructure at room temperature will be increased. Through experimental and theoretical research, the following conclusion is drawn: during the heat preservation process of the paste zone, the nitrogen content increases gradually with the increase of the holding time, when the nitrogen pressure is 0.1MPa, The nitrogen content increased from 0.17% to 0.23%, while the porosity decreased from 1.86% to 1.37%, and when the nitrogen pressure was 0.4MPa, the nitrogen content increased from 0.29% to 0.37%, and the porosity decreased from 1.41% to 1.066.When the nitrogen pressure was 0.4MPa, the nitrogen content increased from 0.29% to 0.37%. The results show that the gelatinized zone heat preservation process can effectively increase the nitrogen content in steel, and decrease the porosity of ingot at the same time) the change of microstructure with nitrogen content in the heat preservation process of paste zone is explored, which indicates that in the heat preservation process of paste zone, the change of microstructure with nitrogen content is discussed. The continuous dissolution of nitrogen in liquid steel will cause the isothermal transformation of ferrite in the microstructure. Some ferrite react with the liquid phase to form austenite, the other part changes from solid phase transformation to austenite. The mechanism of nitrogen increasing in the paste region is explained: on the one hand, the nitrogen increasing in the paste region promotes the transformation of ferrite to austenite, and the increase of austenite content increases the solubility of nitrogen in the alloy. The increase of nitrogen content leads to the direct transformation of liquid phase to austenite, which increases the austenite content in the room temperature microstructure. The yield strength of austenitic stainless steel can be significantly increased by the increase of nitrogen content when the deformation amount of high nitrogen austenitic stainless steel is less than 2%. When the amount of deformation exceeds 5%, there may be deformed martensite in the sample, which makes the stress value of the sample with lower nitrogen content increase significantly, but the strengthening of the sample with higher nitrogen content is still mainly work hardening.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.71;TG156.82

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