【摘要】：碳素結(jié)構(gòu)鋼在工業(yè)生產(chǎn)中被廣泛應(yīng)用于制造各種機(jī)械零件。但是碳素結(jié)構(gòu)鋼硬度低,耐蝕性差,所以需要對(duì)碳素結(jié)構(gòu)鋼機(jī)械零件進(jìn)行表面處理。目前,鹽浴滲氮技術(shù)可以顯著提高碳素結(jié)構(gòu)鋼機(jī)械零件的表面硬度,耐磨性和耐蝕性。但是在常規(guī)鹽浴滲氮溫度條件下,滲氮鹽浴中分解產(chǎn)生活性氮原子的速率較慢。為了使鹽浴滲氮后的零部件獲得有效的滲層厚度,就需要顯著的增加保溫時(shí)間,所以常規(guī)鹽浴滲氮的效率較低。本文采用調(diào)質(zhì)態(tài)35鋼和45鋼為實(shí)驗(yàn)材料,探索研究了高溫鹽浴滲氮、稀土鹽浴滲氮和鹽浴預(yù)氧化的催滲效果和機(jī)理。采用金相顯微鏡(OM)、掃描電子顯微鏡(SEM)、維氏硬度計(jì)、X射線衍射儀(XRD)和電化學(xué)工作站等分析儀器對(duì)鹽浴滲氮處理后試樣的截面組織、硬度、物相結(jié)構(gòu)和耐蝕性進(jìn)行了測(cè)試和分析。高溫快速鹽浴滲氮研究表明,適當(dāng)提高滲氮溫度可以顯著縮短鹽浴滲氮的保溫時(shí)間,提高滲氮速度。經(jīng)660℃×20 min高溫鹽浴滲氮工藝處理后化合物層厚度與560℃×140 min常規(guī)鹽浴滲氮基本相同。同時(shí)高溫鹽浴滲氮后化合層與擴(kuò)散層之間還形成了殘余奧氏體層,增加了高溫鹽浴滲氮處理后樣品的耐蝕性。此外,高溫鹽浴滲氮處理后滲層中還含有γ'-Fe4N相,可以進(jìn)一步提高滲層的硬度。通過(guò)動(dòng)力學(xué)分析,660℃高溫鹽浴滲氮工藝處理過(guò)程中氮原子的擴(kuò)散系數(shù)為27.63×10-14 m2·s-1,是560℃常規(guī)鹽浴滲氮的10倍以上。同時(shí),相比于常規(guī)鹽浴滲氮工藝,高溫鹽浴滲氮工藝處理后活性氮原子的擴(kuò)散激活能顯著降低。稀土鹽浴滲氮研究表明,在5 wt.%最佳的稀土添加量條件下,經(jīng)560℃×120 min稀土鹽浴滲氮處理后化合物層厚度為18.5μm,比相同溫度和時(shí)間的常規(guī)鹽浴滲氮提高約40%。同時(shí)具有更高的截面硬度和耐蝕性。通過(guò)XRD和EDS分析表明,稀土鹽浴滲氮處理后稀土La原子會(huì)滲入到試樣表層。此外,EDS分析表明,稀土鹽浴滲氮處理后滲層中活性氮原子濃度和擴(kuò)散的距離均要高于常規(guī)鹽浴滲氮。鹽浴預(yù)氧化研究表明,在預(yù)氧化溫度和時(shí)間均為350℃×45 min時(shí),鹽浴預(yù)氧化+鹽浴滲氮處理后的化合物層厚度從空氣預(yù)氧化+鹽浴滲氮的13.2μm增加到20.8μm。同時(shí)在相同的預(yù)氧化和滲氮工藝參數(shù)條件下,鹽浴預(yù)氧化+鹽浴滲氮處理后表面硬度要小于空氣預(yù)氧化+鹽浴滲氮。但是有效硬化層更厚,同時(shí)耐蝕性也得到了進(jìn)一步提高。在相同的預(yù)氧化溫度和時(shí)間的條件下,鹽浴預(yù)氧化處理后樣品表面可以生成更多的Fe3O4相。動(dòng)力學(xué)分析表明,鹽浴預(yù)氧化工藝處理后的活性氮原子擴(kuò)散系數(shù)提高約2倍。同時(shí),擴(kuò)散激活能從空氣預(yù)氧化鹽浴滲氮工藝的216 kJ/mol降低到158 kJ/mol。
[Abstract]:Carbon structural steel is widely used in manufacturing various mechanical parts in industrial production. But the hardness of carbon structural steel is low and the corrosion resistance is poor, so it is necessary to treat the mechanical parts of carbon structure steel. At present, salt bath nitriding technology can significantly improve the surface hardness, wear resistance and corrosion resistance of carbon structural steel mechanical parts. However, the rate of decomposition of active nitrogen atoms in nitriding salt bath is slower under conventional salt bath nitriding temperature. In order to obtain effective thickness of nitriding layer after salt bath nitriding, it is necessary to increase the holding time significantly, so the efficiency of conventional salt bath nitriding is low. In this paper, the effect and mechanism of high temperature salt bath nitriding, rare earth salt bath nitriding and salt bath preoxidation were studied by using tempered 35 steel and 45 steel as experimental materials. (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD) and electrochemical workstation were used to analyze the microstructure and hardness of the samples after nitriding in salt bath. The phase structure and corrosion resistance were tested and analyzed. The research of high temperature and fast salt bath nitriding shows that proper increase of nitriding temperature can significantly shorten the holding time of salt bath nitriding and increase the nitriding speed. The thickness of compound layer treated by high temperature salt bath nitriding at 660 鈩，

本文編號(hào)：2419377