本文選題：糊狀區(qū)保溫 + 顯微組織�。� 參考：《昆明理工大學》2017年碩士論文

【摘要】：不銹鋼是日常生產(chǎn)生活中最常見的一種金屬,因其良好的力學性能和優(yōu)異的耐蝕性得到廣泛應用。對不銹鋼進行氮化處理,以氮代鎳,既能保證不銹鋼的各項性能,又能節(jié)約資源,因此受到了廣泛的關注。常見的不銹鋼氮化技術主要是液相滲氮和固相滲氮,但是液相滲氮存在滲氮效果較差,且工藝復雜的問題,固相滲氮時滲氮時間長,且滲氮層厚度有限。本研究對滲氮工藝進行改進,提出一種新的滲氮方法,糊狀區(qū)保溫滲氮工藝。主要是利用糊狀區(qū)溫度范圍內(nèi),固液兩相區(qū)共存的特點,進行一定時間的保溫,使氮氣有充分的時間溶入液相,并擴散至奧氏體相,最終提高室溫組織中的氮含量。通過實驗及理論研究,本文最終得出以下結論:(1)糊狀區(qū)保溫過程中,氮含量隨著保溫時間的增加逐漸提高,當?shù)獨鈮毫?.1MPa時,氮含量可從0.17%提高到0.23%,而氣孔率則從1.86%降至1.37%;當?shù)獨鈮毫?.4MPa時,氮含量由0.29%提高到0.37%,氣孔率從1.41%降到1.06%。說明糊狀區(qū)保溫工藝可以有效提高鋼中的氮含量,同時能夠降低鑄錠中的氣孔率。(2)探究了糊狀區(qū)保溫過程中組織隨氮含量的變化,表明在糊狀區(qū)保溫過程中,氮在鋼液中不斷溶解會使組織中的鐵素體發(fā)生等溫相變,一部分鐵素體與液相發(fā)生包晶反應生成奧氏體,另一部分由固態(tài)相變變?yōu)閵W氏體;液相中的氮達到一定含量后,會在隨后的冷卻中直接轉變?yōu)閵W氏體。(3)闡述了糊狀區(qū)保溫增氮的機理:一方面,糊狀區(qū)增氮促使鐵素體向奧氏體轉變,奧氏體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轉變?yōu)閵W氏體,增加了室溫組織中的奧氏體含量。(4)高氮奧氏體不銹鋼在變形量小于2%時候,氮含量的增加能顯著提高奧氏體不銹鋼的屈服強度;當變形量超過5%以后,試樣中可能有形變馬氏體產(chǎn)生,使得氮含量較低的試樣應力值顯著增大,而氮含量較高的試樣中,強化仍以加工硬化為主。
[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.
【學位授予單位】：昆明理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG142.71;TG156.82

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