KINETICS OF TEMPER EMBRITTLEMENT IN 2.25Cr-1Mo STEEL USED FOR HOT-WALL HYDROFINING REACTORS

Based on the theory of grain boundary segregation, a kinetics model of temper em-brittlement caused by long-term service for hot-wall hydrofining reactors was studied.The kinetics model was applied to phosphorus (P) segregation in 2.25Cr-1Mo steelused for a hot-wall hydrofining reactor, and the kinetics of grain boundary segrea-tion of impurity P in the steel exposed to the process environment of the hydrofiningreactor was calculated on the basis of the model. The Auger electron spectroscopytest was performed in order to determine the grain boundary concentration of P. Theexperimental result is agreement with the theoretical calculated data. The results showthat the kinetics equation is reasonable for predicting the levels of grain boundarysegregation of impurity P in 2.25Cr-1Mo steel used for hot-wall hydrofining reactors.     

Intergranular fracture on fatigue fracture surface of 2.25Cr-1Mo steel at room temperature in air

Low-alloy steels serving for a long time at high temperature (∼500 °C) are very sensitive to temper embrittlement due to segregation of various trace elements at prior austenite grain boundaries and/or carbide/matrix interfaces. This type of segregation in combination with various environmental effects can adversely affect the fracture resistance and fatigue crack propagation rate with subsequent change in the fracture morphology of low-alloy steels. The present work describes the effects of heat treatments on impurity element segregation and its subsequent effects on fatigue fracture behavior of 2.25Cr-1Mo steel under different environmental conditions and temperatures. It has been found that either prior impurity element segregation caused during the heat treatment or hydrogen-induced embrittlement due to the presence of water vapor in laboratory air alone cannot produce intergranular fracture on the fatigue surfaces of 2.25Cr-1Mo steel at room temperature in air. The occurrence of intergranular fracture on the fatigue surfaces results from the combined effect of impurity element segregation-induced grain boundary embrittlement and hydrogen-induced embrittlement, and that the proportion of intergranular fracture is a function of prior impurity element segregation provided that the grain boundary segregation level exceeds a certain critical value.     

2.25Cr-1Mo-0.25V钢焊缝冲击性能和显微组织分析

进行了2.25Cr-1Mo-0.25V钢的焊条电弧焊试验,测定其焊缝的成分和冲击吸收功,进行了金相及启裂源观察,对冲击吸收功较低的样品进行脱脆处理.结果表明,冲击吸收功较低的焊缝的Mn,Si,Mo及其杂质元素含量相对较高,Mn,Si,Mo等元素促进杂质元素在晶界上的偏聚,致使晶界性能变坏,断口以沿晶断裂为主,冲击吸收功降低,脱脆处理后,冲击韧性恢复说明焊缝存在高温回火脆性,导致高温回火脆性是由于杂质元素在晶界上的偏聚,因此研制焊条时要严格控制Mn,Si,Mo和杂质元素的含量.     

2.25Cr-1Mo与2.25Cr-1Mo-0.25V钢冷却转变对比分析

采用相变仪、光学显微镜及扫描电镜研究了2.25Cr-1Mo和2.25Cr-1Mo-0.25V钢冷却转变过程,并分析了钒对其冷却转变的影响。结果表明,与2.25Cr-1Mo钢的CCT曲线相比,2.25Cr-1Mo-0.25V钢铁素体转变区及贝氏体转变区均向右移,并且在现有试验条件下已无法观察到珠光体转变区;钒添加到2.25Cr-1Mo钢中,能够提高钢的淬透性,2.25Cr-1Mo-0.25V钢在48 000 ℃/h冷速下能生成部分马氏体;钒能够细化钢板显微组织,与2.25Cr-1Mo钢相比,2.25Cr-1Mo-0.25V钢在800 ℃/h冷速下组织更为细小。     

Influence of Prior Austenite Grain Size on the Degree of Temper Embrittlement in Cr-Mo Steel

Reversible temper embrittlement has been frequently observed in many different low alloy steels serving at high temperature, e.g. order of 500 °C. This type of embrittlement can change the brittle transgranular fracture mode to intergranular decohesion with subsequent change in fracture stress and fracture toughness. The present paper deals with the influence of the prior austenite grain size and isothermal aging time on the degree of embrittlement of 2.25Cr-1Mo steel, which is very popular for its use in power generating and other petrochemical industries. In this research work, the specimens of 2.25Cr-1Mo steel were treated in three different austenitizing temperatures along with different isothermal embrittling time periods. Then the induced degree of embrittlement was characterized by the fracture stress values at −196 °C and area fraction of intergranular failure. The outcome of the experimental results shows that the increase in austenite grain size and/or isothermal embrittling time severely weakens the grain boundary cohesive strength leading to brittle intergranular failures and thus to a greater degree of temper embrittlement.     

Grain Boundary Segregation Behavior in 2.25Cr-1Mo Steel During Reversible Temper Embrittlement

Low alloy steels serving for a long time at high temperature, e.g., around 500 °C, are very sensitive to temper embrittlement due to segregation of various trace elements at prior austenite grain boundaries and/or carbide/matrix interfaces. This type of segregation in combination with various environmental effects can adversely affect the fracture resistance and fatigue crack propagation rate with subsequent change in fracture morphology of low alloy steels. This article describes the segregation behavior of various elements in 2.25Cr-1Mo pressure vessel steel investigated by AES, FEG-STEM, SEM, and EDS analyses. As confirmed by AES and FEG-STEM, phosphorus is found to be the main embrittling element for isothermal embrittlement. Sulfur and Mo segregation is only evident after longer embrittlement times. In the step-cooling embrittlement, phosphorus is still found to be the main embrittling element, but heavy segregation of sulfur in some isolated intergranular facets was also observed. For P segregation, a Mo-C-P interaction is observed, while sulfur segregation is attributed to site competition between sulfur and carbon atoms.     

加氢反应器用2.25Cr-1Mo钢锻件的热处理

本文通过解剖一只由 2 8t钢锭锻制的 2 .2 5 Cr- 1Mo钢试验件 ,测试了锻件不同部位的组织、晶粒度和不同部位、不同方向的力学性能 ,研究了回火参数及奥氏体化后的冷却速度对力学性能的影响 ,讨论了化学成分、奥氏体化温度对力学性能的影响。最后用两个典型锻件的生产实例 ,证明了壁厚347mm以下的加氢反应器用 2 .2 5 Cr- 1Mo钢锻件的热处理工艺是可行的。     

Microstructural Effects on Fracture Behavior of Ferritic and Martensitic Structural Steels

The effect of microstructure on fracture behavior of 1Cr-0.5Mo and 9Cr-1Mo structural steels was evaluated. 1Cr-0.5Mo steel is used in steam pipes and superheater tubes of power stations. Its microstructure is typically comprised of bainite in a pre-eutectoid ferrite matrix with an average grain size of 10 μm. 9Cr-1Mo steel was developed for applications in steam power stations and as a candidate structural material for first-wall and blanket components of future fusion reactors. Its microstructure consisted of a fully martensitic structure with a prior austenite grain size of 25 μm. The fracture properties were measured using instrumented impact testing at temperatures between ?196 and 300 °C. The total impact fracture energy, the crack initiation and propagation energy, the dynamic yield strength, the brittleness temperature, and the cleavage fracture stress were measured. The bainitic-ferritic alloy steel exhibited much higher resistance to ductile fracture at high test temperatures, while its resistance to brittle fracture at low test temperatures was reduced compared to that of the fully martensitic alloy steel. The results were discussed in terms of the chemical composition and microstructure of the two steel types.     

2.25Cr-1Mo不锈复合钢板厚壁容器的焊接

主要介绍了2.25Cr-1Mo不锈复合钢板的焊接工艺试验和工艺评定，阐明了2.25Cr-1Mo锈复合钢板焊接工艺的可行性，实践证明，该工艺能满足使用要求。     

P91与10GrMo910异种钢焊接接头特性分析

通过冲击韧度和显微硬度测试及金相组织观察,研究了采用2.25Cr-1Mo型和5Cr-0.5Mo型两类国产焊接材料,按实际焊接要求制备的P91钢与10CrMo910钢异质焊接接头,在二次回火前后的特性.结果发现,焊接接头的韧性受所用焊接材料和焊后热处理条件影响,用2.25Cr-1Mo型焊接材料所焊接头韧性较高,而用5Cr-0.5Mo型焊接材料所焊接头韧性较差,焊后二次回火处理在一定程度上能改善接头组织,提高接头韧性.由于组织变化和碳迁移的原因,在接头异质界面熔合线两侧产生了较大的硬度差,二次回火使接头硬度整体下降,但几乎不影响其分布规律.在靠近P91钢侧的焊缝中存在未混合区.     

氢在2.25Cr—1Mo耐热钢中的扩散规律

采用电化学渗氢的方法研究了加氢反应器简体2．25Cr－1Mo钢中氢的扩散现律试样的厚度低于1．6mm时，随着厚度的增加，扩散系数D值增大；当厚度大于1．6mm后，D值稳定不变实验测得温度与扩散系数的关系为此式可用于在运行状态下的加氢反应器器壁中氢渗透原子氢浓度分布的计算     

2.25Cr-1Mo钢氢致开裂行为及回火脆对抗氢致开裂性能的影响

    采用电解充氢方法分别对回火脆态和脱脆态2.25Cr-1Mo钢氢致开裂行为进行实验研究,通过甘油测氢法测定了2.25Cr-1Mo钢发生裂纹扩展时钢中扩散的平均氢浓度.为进一步了解回火脆对抗氢致开裂性能的影响,利用有限元软件分别对氢在回火脆态与脱脆态2.25 Cr-1Mo钢中的扩散过程进行模拟分析,系统研究了在应力-氢环境交互作用下裂纹尖端周围的氢扩散规律,并给出了裂纹扩展时裂尖局部位置的氢浓度大小.     

Effect of Plasma Sprayed Yttria Stabilized Zirconia(YSZ) Coating for High Temperature Oxidation Resistance of Low Alloy Steel

This paper investigates the influence of YSZ coating on high temperature oxidation behaviour of low alloy 2.25 Cr-1 Mo steel. The YSZ powder was plasma sprayed coated over 2.25 Cr-1 Mo steel substrate. The isothermal oxidation test of the coated and uncoated specimen was carried in air oxidation environment at 900°C. The weight changes of the specimen were measured at different intervals. The oxidation rate and reaction kinetics were studied and the post corroded scales were characterized in SEM, EDS and XRD. The results clearly indicate that YSZ coated specimen significantly improves the oxidation resistance as compared to uncoated specimen. The improvement of oxidation resistance in presence of YSZ coating can be attributed to the changed mechanism of scale growth from outer cation migration to inner anion migration. The detail mechanism of the oxidation behaviour in presence of YSZ coated and uncoated specimen is discussed in this paper.     

2.25Cr-1Mo加氢反应器过渡段调质工艺的优化

在2.25Cr-1Mo加氢反应器过渡段常规调质工艺中增加亚温淬火,改善了大锻件的内部组织,细化了晶粒,提高了锻件的抗回火能力,使模拟焊后热处理(PWHT)后的力学性能显著提高.     

固溶态不锈钢在尿素生产介质中的晶间腐蚀与磷(硅)的晶界富集

用扫描电镜、透射电镜能谱和俄歇能谱等研究了尿素厂汽提塔内实际腐蚀部件的腐蚀形态和机理。结果发现:固溶态的316L 不锈钢发生了晶间腐蚀,并伴生全面腐蚀和晶粒脱落,因而晶间腐蚀不深;其晶界区并不贫铬但富集磷、硅,晶界磷含量比钢中平均含量高二个数量级;而同样介质条件下未遭受晶间腐蚀的固溶态00Cr25Ni22Mo2N 高纯不锈钢却未见磷、硅的晶界富集。故认为磷(硅)的晶界富集是固溶态316L 不锈钢在尿素生产介质中产生晶间腐蚀的重要原因之一.     

Mechanical properties and microstructural evolution of modified 9Cr-1Mo steel after long-term aging for 50,000 h

The mechanical properties and microstructural evolution of modified 9Cr-1Mo steel have been studied to investigate steel property changes after long-term isothermal aging at 600 °C for 50,000 h. The microhardness and strength were maintained constantly after aging but the impact energy was dramatically reduced by 62 % during the aging period. From the viewpoint of microstructural evolution after the aging process, Cr-enrichment and Fe-depletion took place within the M₂₃C₆-type precipitates in the as-aged steel and V-depletion also happened within the VX-type precipitates after aging. In addition, the precipitates of the M₂Mo-type Laves phase and the segregation of the impurity atoms would be formed during the long-term aging period. It was considered that the sharp reduction of the impact energy could be related to the formation of the Laves phases and the impurity segregation after aging at 600 °C. The phase stability was also verified by the specific heat results up to 950 °C from a DSC test. It was concluded from this study that the modified 9Cr-1Mo steel would keep its microstructural stability at 600 °C during the long-term aging period of 50,000 h, which was equivalent to the in-service life of the SFR fuel cladding.     

2.25Cr-1Mo-0.25V钢的热变形行为及其形变组织

采用Gleeble3500热模拟试验机对加氢反应器用2.25Cr-1Mo-0.25V钢进行不同变形温度、不同应变速率的热压缩变形试验,并分析和讨论了再结晶组织的演变规律。结果表明,该钢高温流变应力和峰值应变随变形温度的降低和应变速率的提高而增大,确定了热变形激活能和热变形方程;再结晶晶粒的数量随应变量的增加而增加;变形温度越高,应变速率越小,再结晶现象更容易发生,并且进行的更完全。     

EFFECT OF Cr ON P GRAIN BOUNDARY SEGREGATION IN LOW ALLOYED STEELS

碳与杂质在晶界呈相互排斥,而碳为更强的晶界活性元素,因此杂质在晶界的偏聚受碳在α相中固溶度的控制.合金元素的加入使碳的固溶度降低,从而促进了杂质元素的偏聚.按照这个理论,本文对Guttmann的模型作进一步推广,提出了一个定量的模型.由此计算碳钢及铬钢中磷的晶界偏聚与实验结果符合得很好。     

2.25Cr-1Mo与0Cr18Ni9钢焊接工艺研究

在筒体母材为2.25Cr-1Mo钢的大型压力容器生产制造过程中,常涉及到0Cr18Ni9不锈钢内构件与筒节2.25Cr-1Mo钢的焊接。阐述了采用药芯气体保护焊(FCAW)方法焊接该类异种钢的有关工艺要素。通过试验分析了如何调整工艺以改善焊接接头易出现脆化组织的情况,以使接头性能满足产品设计要求。     

高Mo的316L堆焊技术在2.25Cr-1Mo-0.25V钢制容器上的应用

在2.25Cr-1Mo-0.25V钢制容器上进行Mo含量超过2.5%的316L双层堆焊时,研究了经过705℃保温32 h热处理后堆焊层中铁素体数很低时如何确保180°弯曲试验无缺陷,为2.25Cr-1Mo-0.25V钢制容器堆焊高Mo含量的309MoL+316L双层堆焊工艺的应用提供了参考。