新聞資訊
等溫淬火低合金貝氏體球墨鑄鐵的回火組織與性能
發(fā)布人：上海艾荔艾合金股份有限公司www.shailiai.cn
更新時間：2016-05-01
對3.55C-1.95Si-0.36Mn-3.58Ni-0.708Cu-0.92Mo-0.65Cr (質(zhì)量分?jǐn)?shù), %)低合金貝氏體球墨鑄鐵實施等溫淬火及不同溫度的回火熱處理工藝, 采用 OM, EPMA, SEM, TEM 以及 XRD研究了回火溫度對等溫淬火低合金貝氏體球墨鑄鐵的組織演變過程的影響, 并對力學(xué)性能和耐磨性進(jìn)行了測試與分析.
等溫淬火低合金貝氏體球墨鑄鐵的回火組織與性能TEMPERED MICROSTRUCTURE AND MECHANICAL PROPERTIES?OF AUSTEMPERED LOW ALLOYED BAINITIC DUCTILE IRON
對3.55C-1.95Si-0.36Mn-3.58Ni-0.708Cu-0.92Mo-0.65Cr (質(zhì)量分?jǐn)?shù), %)低合金貝氏體球墨鑄鐵實施等溫淬火及不同溫度的回火熱處理工藝, 采用 OM, EPMA, SEM, TEM 以及 XRD研究了回火溫度對等溫淬火低合金貝氏體球墨鑄鐵的組織演變過程的影響, 并對力學(xué)性能和耐磨性進(jìn)行了測試與分析. 結(jié)果表明, 回火過程組織演變的物理機(jī)制包括孿晶馬氏體及其位錯亞結(jié)構(gòu)的回復(fù)與再結(jié)晶軟化、殘余奧氏體分解、馬氏體中過飽和碳的脫溶與相變以及共晶滲碳體的轉(zhuǎn)變等過程. 隨著回火溫度的升高, 等溫淬火低合金貝氏體球墨鑄鐵基體的顯微硬度和宏觀硬度及抗壓強度逐漸降低. 在 450 ℃回火后, 共晶滲碳體的顯微硬度出現(xiàn)最低值, 其原因是在此溫度下共晶滲碳體的亞片層有 α 相析出, 此時, 低合金貝氏體球墨鑄鐵的壓縮率最高, 塑性提高; 在 600 ℃回火時, 其力學(xué)性能明顯惡化. 在干砂/橡膠輪磨損條件下, 450 ℃回火后的等溫淬火低合金貝氏體球墨鑄鐵具有較好的耐磨性. 磨損形貌觀察表明, 其磨損機(jī)制為塑性變形疲勞磨損和顯微切削, 塑性變形疲勞機(jī)制對耐磨性的貢獻(xiàn)大于切削破壞機(jī)制, 在 450 ℃回火析出的彌散 Mo2C 對耐磨性也有一定貢獻(xiàn).?
Austempered bainitic ductile cast iron has been widely used in machinery components and parts due?to its low fabrication cost, excellent mechanical properties, and abrasive wear resistance. In order to get a fine?bainitic matrix, austempering process is usually adopted which consists of austenitizing temperature,?austempering temperature and time. For quenched ductile cast iron, tempering plays important role in subsequent?heat treatment process. However, less attention has been paid on the microstructural evolution and mechanical?properties of the austempered bainitic ductile iron after tempering treatment. Thus, in this work,?3.55C-1.95Si-0.36Mn-3.58Ni-0.708Cu-0.92Mo-0.65Cr (mass fraction) bainitic ductile iron was subjected to?austempering and subsequent tempering treatment, and the effect of tempering on microstructures and properties?has been investigated by using OM, EPMA, SEM, TEM and XRD. The microstructural evolution during?tempering has been investigated, and mechanical properties and wear resistance have also been measured and?analyzed. The results show that microstructural evolution of the bainitic ductile iron during tempering contains?recovery and recrystallization softening processes of twin martensite and dislocation substructure, decomposition?of retained austenite, dissolution of supersaturated carbon and phase transformation in martensite and?transformation in eutectic cementite. With increasing tempering temperature, there is a gradual decrease in micro-?and macro-hardness of substrate microstructure and compressive strength of austempered low alloying bainitic?ductile iron. When the bainitic ductile iron was tempered at 450 ℃, the eutectic cementite has lowest?micro-hardness value due to the precipitation of α phase in its slice layer and the compressive ratio is thus higher.?The mechanical properties of the austempered low alloyed bainitic ductile iron was even worse when tempered at?600 ℃. Under the wear condition of dry sand/rubber wheel, the austempered low alloying bainitic ductile iron?possesses the best wear resistance when tempered at 450 ℃. The worn morphology observation by SEM?indicates that the worn surfaces were caused by plastic deformation and micro-cutting. The plastic deformation?plays an important role in wear process, while the precipitated and finely distributed Mo2C contributes a lot to the?improvement of wear resistance when tempered at 450 ℃.?
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