共查询到18条相似文献,搜索用时 125 毫秒
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用金相方法验证了晶粒边界腐蚀法的可靠性,并对测定奥氏体本质晶粒度的有关方法及其实验条件进行了讨论和分析。结果表明:网状铁素体法和网状珠光体(屈氏体)法是准确的:晶粒边界腐蚀法也是准确的;暴露氧化法在一定条件下还是适用的;渗碳法所显示的奥氏体晶粒度是真实的,但是这个晶粒度并非原始钢材的奥氏体本质晶粒度,一般比晶粒边界腐蚀法的结果偏粗。认为,目前采用的以930℃的温度作为考核奥氏体本质晶粒度的实验条件仅对渗碳钢适用,对其它类钢种是不适用的和脱离实际的。因此,对调质钢、低碳马氏体和超高强度钢以及进行 C—N 共渗的钢种,推荐采用比各相应钢种正常淬火温度高20—30℃的温度制度作为考核奥氏体本质晶粒度的实验条件.文中还对电渣钢和电炉钢奥氏体本质晶粒度之间可能产生的差异及改善粗晶和混晶的有关方法等问题也进行了讨论和分析. 相似文献
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H13晶粒度测试试验 总被引:1,自引:0,他引:1
钢的晶粒度直接影响着钢的机械性能和工艺性能,清晰地显示和正确的评定晶粒度级别不仅是标准规定的要求,也直接影响着钢的实物质量。使用氧化法或淬火法代替渗碳法检测H13(4Cr5MoSiV1)晶粒度,效果良好,大大缩短了检验周期,节约了人力物力,检验质量得到显著改善。 相似文献
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在转炉长流程生产工艺条件下,研究了铝含量、氮含量和铝氮比对轿车用20Mn Cr5渗碳钢晶粒度混晶的影响。结果表明,在规定的热处理工艺条件下,20Mn Cr5渗碳齿轮钢产生混晶的主要原因是钢中氮含量偏低。当20Mn Cr5钢中铝含量≥0.025%且铝氮比≥3时,可以达到轿车渗碳钢对奥氏体晶粒度的要求。 相似文献
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12Cr2Ni4A奥氏体晶粒粗大原因浅析 总被引:1,自引:0,他引:1
由于钢中酸溶铝含量极大影响奥氏体晶粒度,故用渗碳法检验12Cr2Ni4A钢的奥氏体晶粒度,要保证奥氏体晶粒度检验合格。必须使钢的铝含量在一定的范围之内。 相似文献
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实验研究了加热温度和保温时间对具有不同AlN析出状态的SCr420H齿轮钢的奥氏体晶粒长大行为的影响。用Thermo-Calc热力学计算软件计算了实验钢AlN析出相的平衡溶解规律,并用场发射透射电子显微镜研究了实验钢中AlN的析出行为。结果表明,热轧空冷态的试样在950~1 050℃渗碳0.5 h均出现混晶,奥氏体平均晶粒度级别低于5级。经过1 210℃固溶水淬处理的试样在950~1 000℃渗碳0.5~6 h和在1 050℃渗碳0.5~2 h奥氏体晶粒均不发生长大,晶粒度级别在9.5~10级;在1 050℃渗碳2 h以后开始出现异常晶粒长大。试样经1 210℃固溶水淬后在700℃等温1 h水冷处理,可使其在1 050℃渗碳8 h而不发生异常晶粒长大或混晶,奥氏体晶粒平均尺寸为14μm,晶粒度级别为9.4级。试样在渗碳过程中的奥氏体晶粒长大行为主要受钢中第二相AlN的溶解度和熟化速率控制。固溶后在1 050℃渗碳0.5 h的试样中AlN析出相尺寸均小于80 nm,平均尺寸为27.8 nm,渗碳2.5 h的试样中出现了尺寸大于100 nm的AlN粒子,数量占比为14.3%,AlN粒子的平... 相似文献
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目前,在我国执行标准中对30CrMnSiA、40CrNiMoA和38CrA等调质用钢要求检验奥氏体(以下简称A体)本质晶粒度。A体本质晶粒度在YB27—77标准定义是:“当钢加热超过临界点以上某一个规定温度(930℃)时所具有的A体晶粒。A体晶粒度表示钢的A体晶粒在规定温度下长大的倾向”[1]在这基本定义的要求下,不管什么钢种,其实际热处理条件如何都要在930℃温度下,衡量A体晶粒度大小并由此鉴定钢材质量的好坏,这是不科学的。回顾A体晶粒度的研究历史就不难看出“本质晶粒度”的引入首先从渗碳钢开始的。 相似文献
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轨道交通用高端齿轮钢往往要求长时间高温渗碳处理以提高其表面硬度与耐磨性,利用合适的铝、氮含量实现AlN粒子对奥氏体晶界的有效钉扎对保证齿轮的晶粒度、力学性能与尺寸精度至关重要。在通常的渗碳温度下,AlN已经发生了部分固溶,为了保证高温渗碳后奥氏体晶粒细小,齿轮钢中的酸溶铝质量分数一般需要保持在0.02%~0.055%以保证析出足量细小的AlN第二相粒子来钉扎晶界,且氮质量分数要求为0.01%~0.016%。这一元素含量范围较广,因此有必要研究钢在高温渗碳时所需要的恰当铝氮积与铝氮比,也就是钢中w(Al)与w(N)的乘积和比值的取值范围,还需要研究AlN粒子对于奥氏体的钉扎作用。针对不同含铝含氮轨道交通用齿轮钢进行了伪渗碳试验与AlN第二相粒子Ostwald熟化和Gladman钉扎模型计算研究,揭示了奥氏体晶粒不均匀性因子Z与加热温度T的定量关系式。研究了含铝含氮齿轮钢高温保温过程奥氏体晶粒半径RA的变化规律,以及不同铝氮积和铝氮比对奥氏体晶粒生长的影响。结果表明,加热温度T在1 173~1 273 K范围内,此类微合金高强钢的奥氏体晶粒长大不均匀性因子服从线性规律... 相似文献
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李学富 《冶金标准化与质量》1996,(Z1)
1 中外晶粒度测定方法标准中晶粒度的叫法 经查阅中、俄、美、日、德、法、英及ISO晶粒度测定法标准,各国对晶粒度的叫法有: (1)GB6394—86只规定了“晶粒度是指晶粒大小的程度”,并规定了晶粒度的六种显示方法:(a)渗碳法;(b)网状铁素体法;(c)氧化法;(d)直接淬火硬化法;(e)网状渗碳体法;(f)网状珠光体(屈氏体)法。 相似文献
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High temperature carburization is becoming more and more attractive because it can remarkably reduce processing time and increase productivity. However, the commonly used gear steels which are microalloyed by Al are not suitable for high temperature carburization due to abnormal grain coarsening. The gear steel 20CrMnTiNb, which is microalloyed with 0. 048% Nb and 0. 038% Ti, has been compared with the gear steel 20CrMn in terms of microstructure in the case of hardened layer and in the core after carburizing at 1000 °C for 4 h and mechanical properties after carburizing and pseudo-carburizing. The results indicate that the fine austenite grains exist in the carburized case of 20CrMnTiNb steel, while there is abnormal coarsening and duplex grain structure in the case and core of steel 20CrMn. The average prior austenite grain sizes are 19.5 and 34.2 μm for the steels 20CrMnTiNb and 20CrMn, respectively. In addition, the mechanical properties of 20CrMnTiNb steel are superior to those of 20CrMn steel. In particular, the HV hardness of the former is higher than that of the latter by about 40–70 in the range of less than 0.7 mm in depth. Therefore, the steel 20CrMnTiNb is suitable for high temperature carburization. 相似文献
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A. I. Ul'yanov R. G. Faizullin A. I. Zvonarev 《Powder Metallurgy and Metal Ceramics》1993,32(7):618-621
The effect of the carburization time (0.5–2.0 h) on the magnetic and electric properties, the structural state, and the hardness of 30N2M steel was studied. The mechanical and physical properties of carburized steel are compared to those of conventionally sintered steel. The problems of magnetic structural analysis of carburized steel are discussed. It is concluded that in order to determine indirectly the hardness of articles made of powdered steel it is necessary to construct calibration curves of HB(Hc) for carburized and sintered 30N2M steel.Translated from Poroshkovaya Metallurgiya, No. 7(367), pp. 67–70, July 1993. 相似文献
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T. N. Prasanthi Cheruvathur Sudha V. Thomas Paul N. Sivai Bharasi S. Saroja M. Vijayalakshmi 《Metallurgical and Materials Transactions A》2014,45(10):4220-4234
Mod. 9Cr-1Mo is used as the structural material in the steam generator circuit of liquid metal-cooled fast breeder reactors. Microstructural modifications on the surface of this steel are investigated after exposing to flowing sodium at a temperature of 798 K (525 °C) for 16000 hours. Sodium exposure results in the carburization of the ferritic steel up to a depth of ~218 µm from the surface. Electron microprobe analysis revealed the existence of two separate zones with appreciable difference in microchemistry within the carburized layer. Differences in the type, morphology, volume fraction, and microchemistry of the carbides present in the two zones are investigated using analytical transmission electron microscopy. Formation of separate zones within the carburized layer is understood as a combined effect of leaching, diffusion of the alloying elements, and thermal aging. Chromium concentration on the surface in the α-phase suggested possible degradation in the corrosion resistance of the steel. Further, concentration-dependent diffusivities for carbon are determined in the base material and carburized zones using Hall’s and den Broeder’s methods, respectively. These are given as inputs for simulating the concentration profiles for carbon using numerical computation technique based on finite difference method. Predicted thickness of the carburized zone agrees reasonably well with that of experiment. 相似文献
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