耐熱沃斯田鐵系不鏽鋼的機械性質 與抗腐蝕能力;Mechanical properties and corrosion resistance of heat-resistant Austenitic stainless steel

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Title:	耐熱沃斯田鐵系不鏽鋼的機械性質與抗腐蝕能力;Mechanical properties and corrosion resistance of heat-resistant Austenitic stainless steel
Authors:	何旻璋;Ho, Min-Chang
Contributors:	機械工程學系
Keywords:	低鎳沃斯田鐵不鏽鋼;碳化物;機械性質;無析出帶(PFZ);抗腐蝕性;Low nickel stainless steel;carbide;mechanical properties;precipitation free zone (PFZ);corrosion resistance
Date:	2020-08-20
Issue Date:	2020-09-02 19:14:55 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究探討EN系列和低鎳沃斯田鐵不鏽鋼分別在鑄態、熱循環及熱處理後的不鏽鋼機械性質與抗腐蝕能力的影響。實驗使用EN系列和低鎳沃斯田鐵不鏽鋼的拉伸試棒，分成鑄態、三次熱循環、十次熱循環及熱處理，再按照JIS Z2201 13B規範加工成拉伸試棒進行拉伸及量測，後續分析鑄態與熱循環及熱處理對材料微結構與機械性質的影響。將拉伸試驗完的試棒縱剖進行研磨及拋光，利用光學顯微鏡(OM)觀察基地與析出物的微結構，並利用影像分析軟體分析碳化物顆粒的數量、尺寸及分佈，探討碳化物顆粒對合金機械性質的影響。透過掃描式電子顯微鏡(SEM)，判斷析出物的類型，利用ｘ光粉末繞射儀(XRD)所產生的繞射峰印證析出物的種類，以及利用恆電位儀分析試棒的抗腐蝕能力與腐蝕速率。實驗結果顯示，全部試棒皆符合規範要求，其中常溫機械性質由於析出MC碳化物，以LNSS試棒8最為突出(YS:292MPa、UTS:499MPa及EL:29%)；高溫機械性質以鎳含量較高的EN1.4848最佳(YS:30.9 MPa、UTS:32MPa及EL:51%)；而經過三次熱循環後，回溶於基地的碳化物經過風冷後析出，使碳化物總顆粒數增加，高溫機械性質呈現提高的趨勢；當經過十次熱循環後，EN1.4849機械性質均提高，主因是碳化物總顆粒數經過三次熱循環後數量先增加後漸少，而熱循環後，碳化物在基地或晶界析出，會產生無析出帶(PFZ)，無析出帶(PFZ)對EN系列和低鎳沃斯田鐵不鏽鋼機械性質與抗腐蝕能力影響最大，在晶界上連續分佈的析出物會降低沃斯田鐵不鏽鋼的延伸率及韌性。 ;This study investigated the effects of mechanical properties and corrosion resistance of EN series and low nickel stainless steels in as-cast, thermal cycling, and heat-treated steels, respectively. EN series and low nickel stainless steel tensile test were used in the experiment, divided into as-cast, three thermal cycles, ten thermal cycles and heat treatment, and then processed into tensile test according to JIS Z2201 13B specifications for stretching and volume measurement. Subsequently,analysed the effect of as-cast and thermal cycling and heat treatment on the microstructure and mechanical properties of the material. Grinded and polished the longitudinal section of the sample after the tensile test, observed the microstructure of the base and precipitates with an optical microscope (OM), and analyzed the number, size and distribution of carbide particles using image analysis software to research carbide particles effect on the mechanical properties of the alloy. Through scanning electron microscopy (SEM), determined the type of precipitate, used the diffraction peak produced by X-ray powder diffractometer (XRD) to confirm the type of precipitate, and use the potentiostat to analyze the corrosion resistance and the speed of the corrosion rate. The experimental results showed that all the test bars meet the requirements of the specification, among which the LNSS test bar 8 is the most prominent at room temperature mechanical properties (YS: 292MPa, UTS: 499MPa and EL: 29%); the high temperature mechanical properties are the best with EN1.4848 (30.9 MPa) , UTS: 32MPa and EL: 51%); What’s more, after three thermal cycles, the mechanical properties of high temperature showed an increasing trend; after ten thermal cycles, the mechanical properties of EN1.4849 all improved.The main reason is that after three thermal cycles,the total number of carbide particles first increases and then decreases. After thermal cycling, carbides precipitate at the base or grain boundaries, which will produce precipitation free zone (PFZ).PFZ has the greatest influence on the mechanical properties and corrosion resistance of EN series and low nickel stainless steel, and the continuous distribution of precipitates on the grain boundaries will reduce the elongation and toughness of the stainless steel.
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