超高強度耐磨鋼板熱處理對機械性質的影響

Abstract

本實驗之主要目的乃在於尋求四種耐磨鋼：包括三種Fe-xNi-1.5%Cr-0.5%Mo(x分別為3、5及7%)及一種改良焊接性的Fe-5Ni%-1.0%Cr-0.5%Mo的最佳熱處理條件，其中包括了沃斯田鐵化溫度、淬火速率、深冷處理、回火溫度、等因素之配合。 經由機械性質(硬度、衝擊值)之測試及顯微組織(OM、TEM、SEM)的觀察來探討顯微組織與機械性質之關係，來瞭解回火組織之變態情形，進而掌握機械性質之變化，尤其是在回火組織中的碳化物析出的位置、種類、分佈與大小，其變化左右著硬度及韌性值。 實驗結果顯示Ni-Cr-Mo鋼經850℃ × 30min沃斯田鐵化油淬火後於液態氮深冷10min，再經150~175℃×1hr回火可得到高硬度並保有足夠韌性。回火於250℃~500℃左右會發生回火麻田散鐵脆性(TME)，其原因為麻田散鐵板條界面的殘留沃斯田鐵變態析出雪明碳鐵所造成。 另外殘留沃斯田鐵的測定實驗，由於量很少，無法利用XRD分析之，於是利用磁性計測量之。經測量發現如果深冷天數延緩越久則殘留沃斯田鐵有穩定化的趨勢，以及合金中鎳含量提高則殘留沃斯田鐵量也會隨之增加。

The purpose of the this work is to determine the best heat-treatment condition (including the austenitizing temperature, quenching rate, subzero treatment and tempering temperature ) the four wear-resistance steels (Fe-xNi-1.5%Cr-0.5%Mo,x equals 3、5 and 7% , and Fe-5Ni%-1.0%Cr-0.5%Mo). The correlation between microstructure and mechanical properties will be discussed by optical microscope (OM), transmission electron microscope (TEM) and scanning electron microscope (SEM). The experiment finds that the toughness and hardness are seriously influenced by the distribution and morphology of the carbide precipitates in the tempered structure. The results show that the Ni-Cr-Mo steels can obtain high hardness and maintain good toughness by the way of oil-quenched from 850℃, subzero-treated in liquid nitrogen for 10 minutes and tempered at 150~175℃. On the contrary , tempered martensite embrittlement (TME) occurred at 250~500℃ because of retained austenite at the martensite lath boundary transformed to cementite. Finally we want to figure out the quantity of the retained austenite in this experiment but the content of retained austenite is too little to determine by X-ray diffractometer(XRD) . So that the retained austenite was analyzed by magnetometry. The results show that the retained austenite will be stabilized when the delay-time of subzero-treatment is increased. However the more the addition of nickel in the alloy,the more increase the amount of retained austenite.