2Cr-1Mo钢热处理特性及其强韧化机制

本文采用光学显微镜、扫描电镜、透射电镜和定量金相等试验手段，主要研究了Ｃｒ－１Ｍｏ钢正火处理后显微组织对钢强韧性的影响。在奥氏体化处理后冷却过程中（１００～１℃／ｍｉｎ），共得到四种显微组织─—粒状贝氏体，细珠光体，典型的片层状珠光体和先析铁素体，该钢先析铁素体临界冷速约为６０℃／ｍｉｎ，冷速高于６０℃／ｍｉｎ获得的组织为完全粒状贝氏体组织。试验结果表明，显微组织的类型及其含量的变化是造成Ｃｒ－１Ｍｏ钢强韧性能变化的主要原因。     

合金元素和垂直离心浇注条件对HSS钢显微组织和力学性能的影响

研究了合金元素和垂直离心浇注条件对 HSS钢的显微组织和力学性能 (包括高速钢的硬度和耐磨性 )的影响。用硬度和耐磨试验评测采用重力浇注和垂直离心浇注工艺生产的高速钢的力学性能。随着钢中钒含量的增加 ,其硬度增加。发现 MC碳化物的数量随钒和铌含量的提高而增加 ,而 M3C碳化物的数量却随之减少。离心浇注的旋转速率增加时 ,由于冷却速率提高 ,碳化物变细而且 M7C碳化物的数量减少合金元素和垂直离心浇注条件对HSS钢显微组织和力学性能的影响@茅益明     

冷轧工作辊用半高速钢中碳化物的溶解和析出

采用X射线衍射分析、TEM组织观察和电子衍射分析,对新型半高速钢在加热和冷却及回火过程中碳化物的溶解和析出行为进行了研究。结果表明,退火状态下钢中含有MC、M6C和M7C3型碳化物;淬火加热时M6C和M7C3型碳化物全部溶解,回火过程中析出MC、M2C、M6C和M7C3型碳化物,当回火温度为520℃时出现硬度峰值,此时Mo2C的弥散强化起主要作用。     

热处理工艺对2.25Cr1MoR钢组织和力学性能的影响

本文研究了热处理工艺对2.25C r1M oR钢组织和力学性能的影响。结果表明,该钢在780℃时可获得良好的强韧化效果和较高的抗回火脆性能力,在此基础上得到了该钢板生产制造的热处理工艺参数。实践证明,该工艺合理可行。     

钒微合金化中碳铁素体-珠光体钢的显微组织和力学性能

对含C>o.4％的铁素体-珠光体钢用钒微合金化后的显微组织、先共析铁素体和铁素体-珠光体中的析出情况以及它们对力学性能的影响进行了深入研究。试验钢的基本成分为Fe-O.4C-0.32Si-O.85Mn。试样经1250°C奥氏体后,连续冷却(分快冷和慢冷)或等温退火处理。试样中测得的显微组织参数如下表。     

M7钢轧制劈头分析及工艺改进

采用显微电镜、扫描电镜对M7钢热轧后劈头处的金相组织进行了观察,分析了M7钢轧制劈头的产生原因,优化了钢锭的加热工艺参数。研究表明,M7钢产生轧制劈头的主要原因是碳化物组织分解破碎不充分;延长钢锭加热时间后,该钢的碳化物分解破碎情况明显改善,M7钢方坯轧制顺利,无劈头现象产生。与工艺优化前相比,轧制成材率提高31%。     

喷射成形M3型高速钢碳化物组织特征与加热过程演化

采用常规铸造和喷射成形工艺分别制备了M3型高速钢铸坯和沉积坯.利用扫描电子显微镜、X射线能谱和X射线衍射等分析方法对冷却速度对合金的显微组织的影响,加热温度对M3高速钢中M₂C共晶碳化物分解行为的影响,以及热加工变形后铸态和沉积态组织的变化进行了研究.结果表明:铸态合金含有粗大的一次枝晶和M₂C共晶碳化物,而喷射成形沉积坯主要为等轴晶且碳化物细小均匀;冷却速度的提高极大地抑制了碳化物的析出和晶粒长大;加热温度的提高有利于M₂C共晶碳化物分解,过高的温度使得分解后的M₆C长大,不利于合金性能的提高;沉积坯经恰当的预热处理和热变形可以获得理想的变形组织.      

不同冷却制度下X100管线钢组织特征及力学性能

采用热模拟试验机和试验轧机研究了X100管线钢连续冷却相变规律及不同冷却制度下显微组织特征及力学性能变化规律.研究结果表明:随冷却速度升高及终冷温度降低,试验钢显微组织由针状铁素体过渡至板条贝氏体及马氏体,非淬火条件试验钢中马氏体岛或M-A岛为微孪晶马氏体;轧制后直接以30℃/s冷却至450℃左右时,试验钢具有良好强韧...     

回火工艺对COST-FB2转子钢组织与性能的影响

利用OM、SEM和TEM等手段研究了回火工艺对COST-FB2转子钢的显微组织与力学性能的影响,结果表明:570℃一次回火后,马氏体板条内有杆状Fe3 C和细小颗粒状的MX,板条界有少量颗粒状碳化物析出;700℃二次回火后,板条内杆状Fe3 C和板条界上颗粒状碳化物消失或转变成M23 C6型碳化物.经570℃一次回火,...     

38Si7钢的强韧化处理

研究了３８Ｓｉ７钢强韧化处理的显微组织和性能。试验结果表明：３８Ｓｉ７钢经强韧化处理后,与常规热处理相比,在强度相当的同时,冲击韧性有显著提高。文章详细分析和讨论了３８Ｓｉ７钢的强韧化机理。     

Bainitic chromium-tungsten steels with 3 Pct chromium

Previous work on 3Cr-1.5MoV (nominally Fe-3Cr-2.5Mo-0.25V-0.1C), 2.25Cr-2W (Fe-2.25Cr-2W-0.1C), and 2.25Cr-2WV (Fe-2.25Cr-2W-0.25V-0.1C) steels indicated that the impact toughness of these steels depended on the microstructure of the bainite formed during continuous cooling from the austenitization temperature. Microstructures formed during continuous cooling can differ from classical upper and lower bainite formed during isothermal transformation. Two types of nonclassical microstructures were observed depending on the cooling rate: carbide-free acicular bainite at rapid cooling rates and granular bainite at slower cooling rates. The Charpy impact toughness of the acicular ferrite was considerably better than for the granular bainite. It was postulated that alloying to improve the hardenability of the steel would promote the formation of acicular bainite, just as increasing the cooling rate does. To test this, chromium and tungsten were added to the 2.25Cr-2W and 2.25Cr-2WV steel compositions to increase their hardenability. Charpy testing indicated that the new 3Cr-W and 3Cr-WV steels had improved impact toughness, as demonstrated by lower ductile-brittle transition temperatures and higher upper-shelf energies. This improvement occurred with less tempering than was necessary to achieve similar toughness for the 2.25Cr steels and for high-chromium (9 to 12 pct Cr) Cr-W and Cr-Mo steels.     

Degradation of mechanical properties of Cr-Mo-V and 2.25Cr-1Mo steel components after long-term service at elevated temperatures

The influence of operating temperature on in-service degradation of mechanical properties of high temperature stream turbine components has been investigated. Material samples for this study were taken from a Cr-Mo-V rotor and several 2.25Cr-1Mo cast steel components which had operated over 200,000 hours. The test results revealed that the degree of in-service degradation of strength, toughness, and the fracture appearance transition temperature of both steels were very sensitive to the service temperature. Both steels softened only when they were exposed at a temperature greater than 454°C (850°F) and the degree of softening increased with further increase in service temperature. In Cr-Mo-V steel, the loss in strength was accompanied by an improvement in ductility and toughness. Despite softening of 2.25Cr-1Mo steel in service, elevated temperature exposure resulted in a marked decrease in ductility and toughness. The loss of toughness in this steel was in part irreversible. In contrast, a severe increase in fracture appearance transition temperature, due to reversible temper embrittlement, occurred in both steels at a service temperature of around 427°C (800°F), but not at the highest service temperature. In fact, the Cr-Mo-V steel did not temper embrittle as a result of service exposure at the highest operating temperature investigated. These results are rationalized in terms of changes in microstructure and grain boundary chemistry that occur in service as a function of operating temperature.     

Evolution of Carbide Precipitates in 2.25Cr-1Mo Steel during Long-Term Service in a Power Plant

Carbide precipitation from the steel matrix during long-term high-temperature exposure can adversely affect the fracture toughness and high-temperature creep resistance of materials with implications on the performance of power plant components. In the present work, carbide evolution in 2.25Cr-1Mo steel after long-term aging during service was investigated. Boiler pipe samples of this steel were removed from a supercritical water-cooled coal-fired power plant after service times of 17 and 28 years and a mean operational temperature of 810 K (537 °C). The carbide precipitation and coarsening effects were studied using the carbon extraction replica technique followed by analysis using transmission electron microscopy and energy dispersive X-ray spectroscopy. The carbides extracted using an electrolytic technique were also analyzed using X-ray diffraction to evaluate phase transformations of the carbides during long-term service. Small ball punch and Vickers hardness were used to evaluate the changes in mechanical performance after long-term aging during service.     

钛—硼和铝—硼处理对抗氢蚀1.25Cr—0.5Mo钢使用性能的影响

对Ａｌ－Ｂ或Ｔｉ－Ｂ处理的１．２５Ｃｒ－０．５Ｍｏ钢的研究结果表明：（１）Ａｌ－Ｂ和Ｔｉ－Ｂ处理明显增加了１．２５Ｃｒ－０．５Ｍｏ的淬透性，强度及塑、韧性；（２）Ａｌ－Ｂ和ＴｉＢ处理均使．２５Ｃｒ－０．５Ｍｏ钢的抗氧性能明显提高，当Ｂ含量相当时，Ｔｉ－Ｂ处理钢的抗氢蚀性能优于Ａｌ－Ｂ处理钢；（３）Ｂ含量较高时，钢的抗氧蚀性能较强，但塑、声望生及回火性能却相对较差，因此，较低含量Ｂ处理更有利于材料综     

The postweld heat-treatment response of simulated coarse-grained heat-affected zones in a new ferritic steel

The tempering behavior of simulated coarse-grained (CG) heat-affected zones (HAZs) in two ferritic alloy steels, 2.25Cr-1Mo and HCM2S, was investigated. The hardness of HCM2S was found to be stable at longer times and higher temperatures than the 2.25Cr-1Mo steel, even though the “as-welded” hardnesses were approximately equal. Both materials reached a peak secondary hardness after tempering for 5 hours at 575 °C. The increase in hardness of the 2.25Cr-1Mo steel was due to precipitation of Fe-rich M₃C carbides within the prior-austenite grains, whereas the secondary hardening in HCM2S was due to a fine dispersion of intragranular, W-rich carbides. The HCM2S steel retained its hardness at longer times and higher temperatures than 2.25Cr-1Mo steel, because of the precipitation of intragranular, W-rich carbides and V-rich MC carbides that stabilized the lath structure. This study shows that HCM2S should not be heat treated in the same way as 2.25Cr-1Mo steel and also provides a basis for defining the postweld heat treatment (PWHT) of HCM2S.     

2.25Cr-1Mo合金钢回火脆化过时效现象的研究

研究了2.25Cr-1Mo合金钢在回火温度下时效处理时,发生回火脆化和回火脆化的过时效反偏聚现象。应用非平衡偏聚的动力学理论,确定了成分(%)为0.15C、2.32Cr、0.95Mo、0.009P的2.25Cr-1Mo合金钢在650℃140 h回火时钢中磷的非平衡晶界偏聚规律。试验得出,2.25Cr-1Mo合金钢650℃磷非平衡偏聚的临界时间t_c为20 h,晶界磷的原子浓度,由初始状态的0.016%提高至最大值2.79%。根据试验数据进行的动力学计算,得出的计算曲线与试验结果吻合,验证了非平衡晶界偏聚空位-复合体模型的扩散机制。     

An assessment of creep deformation and fracture behavior of 2.25Cr-1Mo similar and dissimilar weld joints

The evaluation of the creep deformation and fracture behavior of a 2.25Cr-1Mo steel base metal, a 2.25Cr-1Mo/2.25Cr-1Mo similar weld joint, and a 2.25Cr-1Mo/Alloy 800 dissimilar weld joint at 823 K over a stress range of 90 to 250 MPa has been carried out. The specimens for creep testing were taken from single-V weld pads fabricated by a shielded metal arc-welding process using 2.25Cr-1Mo steel (for similar-joint) and INCONEL 182 (for dissimilar-joint) electrodes. The weld pads were subsequently given a postweld heat treatment (PWHT) of 973 K for 1 hour. The microstructure and microhardness of the weld joints were evaluated in the as-welded, postweld heat-treated, and creep-tested conditions. The heat-affected zone (HAZ) of similar weld joint consisted of bainite in the coarse-prior-austenitic-grain (CPAG) region near the fusion line, followed by bainite in the fine-prior-austenitic-grain (FPAG) and intercritical regions merging with the unaffected base metal. In addition to the HAZ structures in the 2.25Cr-1Mo steel, the dissimilar weld joint displayed a definite INCONEL/2.25Cr-1Mo weld interface structure present either as a sharp line or as a diffuse region. A hardness trough was observed in the intercritical region of the HAZ in both weld joints, while a maxima in hardness was seen at the weld interface of the dissimilar weld joint. Both weld joints exhibited significantly lower rupture lives compared to the 2.25Cr-1Mo base metal. The dissimilar weld joint exhibited poor rupture life compared to the similar weld joint, at applied stresses lower than 130 MPa. In both weld joints, the strain distribution across the specimen gage length during creep testing varied significantly. During creep testing, localization of deformation occurred in the intercritical HAZ. In the similar weld joint, at all stress levels investigated, and in the dissimilar weld joint, at stresses ≥150 MPa, the creep failure occurred in the intercritical HAZ. The fracture occurred by transgranular mode with a large number of dimples. At stresses below 150 MPa, the failure in the dissimilar weld joint occurred in the CPAG HAZ near to the weld interface. The failure occurred by extensive intergranular creep cavity formation.     

Characterization of (Nb,Ti, Mo)C Precipitates in an Ultrahigh Strength Martensitic Steel

A study on ultrahigh strength steel plate subjected to novel thermo-mechanical control process was presented. The mechanical properties examination showed that the investigated steel exhibited excellent combination of ultra-high strength( 2 200 MPa) and toughness( 26 J). The microstructure of the experimental steel was observed by scanning electron microscope and transmission electron microscope. Desired martensitic lath with width of about 180- 250 nm was obtained. Nanostructured carbide precipitates with sizes of 20-50 nm,which contained Nb,Ti and Mo,were observed in the lath martensitic microstructure,and confirmed to be MC-type carbides with B1 structure by means of selected area electron diffraction.The compositional characteristics revealed by energy dispersive X-ray spectrometer mapping implied that the carbide forming elements Nb,Ti and Mo distributed in the precipitates evenly. Three-dimensional atom probe tomography reconstruction further indicated that Mo incorporated into the precipitates without enrichment in the carbide-matrix interface and probably substituted for Nb and Ti to form the( Nb,Ti,Mo) C carbides.     

Fine carbide-strengthened 3Cr-2WVTa bainitic steel

Both the 3Cr-3WV and the 3Cr-2WVTa steels exhibit an acicular bainite microstructure under the normalized and the normalized-and-tempered condition. The addition of Ta to the 3Cr-3WV steel substantially decreases the prior austenite grain size, but it has little effect on the bainite packet size. Fine TaC precipitates are formed in the normalized 3Cr-3WVTa specimen. After further tempering of 3Cr-3WVTa steel, fine TaC particles are further precipitated and dispersed within grains. The carbides at the prior austenite grain boundaries in the Ta-containing steel are much smaller than those in the steel without Ta. Tensile tests and fracture toughness (K _IC ) tests have been performed on both the 3Cr-3WV and 3Cr-3WVTa steels at room temperature. The 0.2 pct yield strength of the Ta-containing steel is higher than that of the steel without Ta, especially under the normalized-and-tempered condition. The 3Cr-3WVTa steel is primarily strengthened by a secondary-phase precipitation mechanism represented by the formation of fine carbides after tempering. The 3Cr-3WVTa steel exhibits higher fracture toughness than the 3Cr-3WV steel. The toughening mechanism is also discussed based on the dependence of the calculated fracture stress upon the carbide size and the bainite packet size.