共查询到20条相似文献,搜索用时 15 毫秒
1.
A. Bedolla-Jacuinde L. Arias B. Hernández 《Journal of Materials Engineering and Performance》2003,12(4):371-382
This work analyzes the rate of secondary carbides precipitation during the destabilization heat treatment of a 17% Cr white
iron. The experimental iron was characterized in the as-cast conditions to have comparable parameters with the heat treated
samples. Destabilization heat treatments were undertaken at temperatures of 900, 1000, and 1150 °C for between 5 min and 8
h; each sample was water quenched immediately after being taken out of the furnace. Characterization was carried out by optical
and electron microscopy, image analysis, and energy dispersive spectroscopy (EDS) microanalysis; hardness and microhardness
were also evaluated. It was found that most of the secondary carbides that precipitate (between 2–30% of the matrix volume)
precipitated in less than 2 h for the lowest destabilization temperature (900 °C). The secondary carbides volume fraction
was found to increase for lower destabilization temperatures and large soaking times. A very low carbide precipitation along
with a stabilization of the austenite phase occurred for heat treatments at 1150 °C. The results are discussed in terms of
the solubility of chromium and carbon in the austenite phase at the different treatment temperatures. 相似文献
2.
A. Bedolla-Jacuinde F. V. Guerra I. Mejía J. Zuno-Silva C. Maldonado 《International Journal of Cast Metals Research》2016,29(1-2):55-61
AbstractThis work analyses the secondary carbides precipitation during the destabilization of a 17% Cr White iron containing 195 ppm boron. The experimental iron was characterised in the as-cast conditions to have comparable parameters with the heat-treated samples. Destabilisation heat treatments were undertaken at temperatures of 825, 900 and 975 °C for 25 min; each sample was air-cooled after this soaking time. Characterisation was undertaken by optical and electronic microscopy, image analysis and energy dispersive spectroscopy microanalysis, hardness and microhardness were also evaluated. It was found that the volume fraction of secondary carbides precipitated is always higher for the lowest destabilisation temperature (825 °C) due to the lower carbon solubility in austenite at low temperatures. A much higher precipitation for the irons containing boron than that for the iron without boron at any destabilisation temperature was also noticed. For the iron containing boron, a density of 23 carbide particles per square micron was measured when destabilised at 825 °C, and it decreased to about 10 particles per square micron when destabilised at 975 °C. In the case of the alloy without boron additions, about 10 carbides per square micron were counted when destabilised at 825 °C and about 5 when destabilised at 975 °C. Higher volumes of carbides precipitation implies higher values of bulk hardness and microhardness in the alloys. The results suggest that boron works as a nucleant for the precipitation of secondary carbides; this is discussed in terms of the limited solubility of boron in iron and the formation of boron-rich precipitates found in the iron in the as-cast conditions. 相似文献
3.
采用药芯焊丝埋弧堆焊方法制备含有0.9%~3.0%C,15%~20%Cr,2.0%~3.0%V的高铬合金.借助光学显微镜、扫描电镜和X射线衍射等手段,研究其显微组织及碳化物分布形貌.结果表明,其显微组织由马氏体+铁素体+奥氏体+初生M7C3+(Fe,Cr)3C+TiC等相组成.通过优化药芯焊丝组份及调整堆焊速度,获得了沿堆焊表面垂直方向定向分布的初生M7C3型碳化物,电子能谱分析显示该碳化物为(Fe,Cr,V)7C3.此外,考察了碳含量对高铬堆焊合金硬度及耐磨粒磨损性能的影响.表明其耐磨性优良,其中15~25μm M7C3型初生碳化物颗粒有效阻碍磨粒的显微切削运动,显著改善了耐磨性. 相似文献
4.
对2.25Cr-1Mo-0.25V钢进行950 ℃淬火,再分别进行600 ℃和700 ℃回火,观察其显微组织和碳化物形貌,并测试了其耐蚀性。结果表明,2.25Cr-1Mo-0.25V钢在950 ℃淬火+ 600 ℃回火后具有较好的耐蚀性,而在950 ℃淬火+ 700 ℃回火后的耐蚀性变差,这是由于提高回火温度后大量合金碳化物析出,使合金元素流失,致使2.25Cr-1Mo-0.25V钢表面的氧化膜不能有效形成,导致耐腐蚀性下降。 相似文献
5.
A computer-controlled system for measuring electrical resistance has been developed and used to study the isothermal transformation
of austenite in a ductile iron (3.31 % C, 3.12 % Si, 0.22 % Mn, 0.55 % Cu). The ability of the technique to follow the isothermal
decomposition of austenite was established by measurements on an AISI4340 steel. The times at which the austenite decomposed
to primary ferrite, pearlite, and bainite were accurately detected. In the ductile iron, the formation of pearlite and of
bainite was easily detected, and an isothermal transformation diagram was constructed from the results. The temperature range
for the formation of bainite is especially important in producing austempered ductile iron (ADI) and was mapped. An initial
stage of decomposition of austenite to ferrite and high-carbon austenite is followed by a time delay; then the high-carbon
austenite decomposes to bainite. The formation of ADI requires austempering to a structure of ferrite and high-carbon austenite,
then quenching to retain this structure, thus avoiding the formation of bainite. This is achieved by isothermal transformation
into the time-delay region. For the ductile iron studied here, this time region was about 2.6 h at 400 °C and increased to
277 h at 300 °C. 相似文献
6.
High-carbon and high-chromium alloy steels are prone to pitting and intergranular corrosion, which reduces corrosion resistance. The precipitation behavior of the carbides of high-carbon and high-chromium alloy steels is one of the main factors affecting pitting and intergranular corrosion of stainless steel. In this study, 5Cr15MoV stainless steel was heated to 1,200℃ and then cooled by cooling rates varying from 25 to 150°C/min. The precipitation behavior of grain boundary carbides of 5Cr15MoV steel at different cooling rates, and its effect on the corrosion resistance of materials was studied. The results show that the carbides of 5Cr15MoV steel mainly precipitate along the grain boundaries, which leads to the formation of chromium-depleted zones near the grain boundaries and reduces resistance to intergranular corrosion. It has been found that a higher cooling rate shortens the width of the Cr-depleted zone near the boundary from 0.871 to 0.569 μm, reduces the Cr-concentration gradient near the grain boundary from 36.422% to 12.667%, and suppresses the nucleus growth rate of grain boundary carbides. As the cooling rate increases, the corrosion current density decreases from 13.29 to 2.42 μA/cm2. The corrosion rate is the lowest, while the cooling rate is 150°C/min. The corrosion rate decreases from 218.339 to 158.488 mm/a. The phenomenon of intergranular corrosion and pitting corrosion was found to be weakened; and thereby, it is shown that an intensive cooling rate can improve the corrosion resistance of 5Cr15MoV steel. 相似文献
8.
铬锰铜合金白口铸铁磨球材质,经930~1050℃正火处理,具有共晶碳化物+珠光体+弥散二次碳化物的微观结构,较好地适应于煤磨机中磨料磨损和腐蚀磨损的实际工况条件。装机运行试验证明,其抗磨耐蚀性能远优于中锰球铁材料。 相似文献
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采用药芯焊丝自保护明弧焊方法制备了含有11%~13%Cr、3.5%~3.8%C、2.1%~2.3%Nb、0.6%~0.7%B、0%~4.0%Mo (质量分数)且宏观硬度高达65 HRC的耐磨合金。采用光学显微镜、X-射线衍射仪和扫描电镜,研究了钼含量对其显微组织及耐磨性的影响。结果表明,随着钼含量增加,合金组织整体细化,形成了强韧性配合良好的奥氏体+针状马氏体复合基体以及韧性更好的M23(C,B)6+原位析出NbC耐磨相,脆性变态莱氏体Ld′的形成得到明显抑制。此外,湿砂磨粒磨损试验结果表明,适量Mo减小碳化物间隔尺寸及NbC颗粒脱落几率,显著改善耐磨性,但如加入过多,合金磨损机制会变为磨粒显微切削。 相似文献
11.
Siddhartha Sankar Mandal K. S. Ghosh 《International Journal of Cast Metals Research》2018,31(3):177-192
Destabilisation of as-cast chromium white iron with 16 wt-% chromium are performed by continuous destabilisation treatment for 4 h and short duration (0.66 h) cyclic destabilisation treatment at 900, 950, 1000, 1050, and 1100 °C. Continuous destabilisation causes secondary carbides precipitation from austenite which on slow cooling transforms to pearlite matrix. Cyclic destabilisation treatment causes similar precipitation of finer secondary carbides following shorter period austenitisation and a matrix containing martensite and retained austenite on forced-air cooling. After continuous destabilisation, hardness falls below the as-cast value (HV622); whereas it rises to HV950 after cyclic destabilisation treatment. The as-cast notched impact toughness (4.0 J) increases to 8.5 J or more after both continuous and cyclic destabilisation at 1050 and 1100 °C. Abrasive wear resistance after continuous destabilisation improves only at higher wear load (49.0 N), while after cyclic destabilisation it supersedes the as-cast and Ni-Hard IV performance at both low (19.6 N) and high (49.9 N) wear load. 相似文献
12.
Vinod Kumar 《Journal of Materials Engineering and Performance》2003,12(1):14-18
The presence of M7C3 carbide in white iron enhances its wear resistance because of high hardness. Scanning electron microscopy (SEM) revealed
its morphology as a pencil-like hexagonal structure. On the basis of the SEM observations, elemental distribution studies,
and differential thermal analysis (DTA) of some heat-treated hypoeutectic white irons alloyed with Cr, Mn, and Cu, it is concluded
that M7C3 carbides form as a result of attainment of a favorable condition in the liquid phase present at the austenite grain boundaries.
Segregation of phosphorus in the intercellular regions and formation of a copper-rich intermetallic is responsible for the
formation of this liquid phase. Austenite was found to nucleate first, followed by the nucleation and growth of M7C3 carbide in its vicinity, because of rejection of C and Cr during formation of austenite. The rosette structure generally
observed is formed from the joining of M7C3 carbides by precipitation of secondary carbides. 相似文献
13.
A series of experimental studies were conducted on the recrystallization of directionally solidified cobalt-base superalloy DZAOM. It is found that the secondary M23C6 precipitation influences the size and shape of the recrystal grains. When the annealing temperature is below 1 473 K, a large amount of the fine secondary M23C6 precipitations are distributed around the primary carbides, and such carbides impede the movement of grain boundary because the effect, the size and shape of recrystal grains become irregularly. When the temperature exceeds 1 473 K, the recrystal grains grow rapidly due to the dissolved secondary M23C6 precipitation. 相似文献
14.
柏广海 《稀有金属材料与工程》2016,45(10):2473-2479
本文系统地研究了不同加工工艺对Zr-1Nb-0.01Cu合金第二相粒子析出行为的影响。研究结果表明,随着冷轧和退火次数、中间退火温度和最终退火温度与时间的降低,第二相粒子的平均晶粒尺寸在减小。在温度高于640°C的中间退火过程中形成的β-Zr相在最终的退火过程中很难完全分解。由于Ostwald熟化效应,最终退火时间的延长会导致合金中尺寸较小的第二相粒子通过原子扩散合并成尺寸较大的第二相粒子。与其它加工工艺相比,降低中间退火温度在减小第二相粒子的尺寸方面更为有效。通过低温中间/最终退火(≤520°C)或者缩短退火时间(≤2h)可以获得平均晶粒尺寸小于50nm的第二相粒子。研究结果对调控Zr-Nb系合金第二相粒子的析出行为具有重要意义。 相似文献
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16.
研究了铌对高铬锰白口铸铁断裂韧度和耐磨性的影响规律。结果表明:在高铬锰白口铸铁中加入适量的铌,能提高断裂韧度和耐磨性,在使用较软磨料时,含铌0.5%的高铬白口铸铁,经650℃预处理和850℃淬火后,具有较好的耐磨性和断裂韧度的配合。 相似文献
17.
为研究铸造碳化钨粉末物性对激光熔覆陶瓷颗粒增强Fe基复合材料耐磨性能的影响,将不同制备方法和粒径的铸造碳化钨粉末添加到Fe基合金粉中,在45号钢表面进行激光熔覆以获得高硬度和高耐磨的合金化层。利用金相显微镜、扫描电子显微镜(SEM)、X射线衍射仪(XRD)、硬度计分别分析了合金化层的显微组织、物相组成以及显微硬度。利用轮式磨损试验机测试了其常温下的耐磨性能,并进行了比较。结果表明:熔覆层主要由莱氏体组成,碳化钨粉末的制备方法和粒径差异对复合材料的耐磨性能具有重要影响。等离子旋转电极雾化法制备的碳化钨粉末能起到最好的增强耐磨作用,粒径细的碳化钨粉末比粒径粗的粉末增强耐磨效果要好。 相似文献
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