Microstructural Evolution and Change in Hardness of S30432 Heat‐resistant Steel during Creep at 650 °C

The microstructural evolution of S30432 heat‐resistant steel during creep at 650 °C and its effect on the change in hardness was investigated. The change of hardness during creep of S30432 at 650 °C can be divided into three stages. These are related to the precipitation and coarsening of ε‐Cu and M₂₃C₆ carbides, decrease in the number of twins and increase in grain size. The precipitation of ε‐Cu dominantly contributes to the significant hardening at stage I, and the coarsening of ε‐Cu is the key factor to decrease the hardness at stage II. At stage III, the hardness hardly changes since the microstructure of S30432 tends to be stable in the long‐term creep range.     

00Cr25Ni35AlTi合金时效处理中M23C6析出行为

 对经550~950 ℃时效处理后的00Cr25Ni35AlTi合金M23C6相的析出行为进行了研究。结果表明,在本温度范围内时效处理,合金组织中M23C6相主要在晶界、孪晶端部析出,并与晶界一侧的基体保持共格关系,共格孪晶界、晶粒内部没有发现M23C6。在550~850 ℃范围随着温度的升高,M23C6的数量增加并发生长大,形貌由细柱状向薄片状、大颗粒状转变。在850~950 ℃范围M23C6开始溶解,数量减少。     

Dependence of Accelerated Creep Rate at 580 °C and Room Temperature Yield Stress for Two Creep Resistant Steels

Two creep resistant steels, P91 and X20, were tempered for 17520 h at 650 °C or 8760 h at 750 °C to study the growth and redistribution of carbide precipitates in martensite. On specimens annealed for a different time, yield stress at room temperature and accelerated creep rate at 580 °C were determined. With increasing yield stress in the range from 350 to 650 MPa the accelerated creep rate decreased continuously by about 2 orders of magnitude from 8·10^?7 s^?1 to 5·10^?9 s^?1. For equal yield stress, the creep rate was slightly lower for the steel P91 than for the steel X20.     

Growth Kinetics of Laves Phase and Its Effect on Creep Rupture Behavior in 9Cr Heat Resistant Steel

The effects of Laves phase formation and growth on creep rupture behaviors of P92 steel at 883 K were studied.The microstructural evolution was characterized using scanning electron microscopy and transmission elec-tron microscopy.Kinetic modeling was carried out using the software DICTRA.The results indicated Fe2 (W,Mo) Laves phase has formed during creep with 200 MPa applied stress at 883 K for 243 h.The experimental results showed a good agreement with thermodynamic calculations.The plastic deformation of laths is the main reason of creep rupture under the applied stress beyond 160 MPa,whereas,creep voids initiated by coarser Laves phase play an effective role in creep rupture under the applied stress lower than 160 MPa.Laves phase particles with the mean size of 243 nm lead to the change of creep rupture feature.Microstructures at the vicinity of fracture surface,the gage portion and the threaded ends of creep rupture specimens were also observed,indicating that creep tensile stress enhances the coarsening of Laves phase.     

5Cr21Mn9Ni4Nb2WN耐热钢M(CN)和M23(CN)6的可逆析出反应

通过扫描电镜(SEM)、透射电镜(TEM)和选区电子衍射分析(EDA)、能量色散X-射线衍射分析(EDAX)等技术研究了5Cr21Mn9Ni4Nb2WN耐热钢锻态,1200℃ 120 min水冷固溶,+1030℃ 20~240 min水冷固溶状态,再经1220℃ 20~240 min水冷固溶状态的晶内和晶界面上碳化物相、显微组织和力学性能。结果表明,5Cr21Mn9Ni4Nb2WN钢在1030℃固溶时晶界晶内不但有粒状M₂₃(CN)₆析出,同时M(CN)块作为补充碳源发生了向M₂₃(CN)₆的退化反应,其室温冲击功急剧下降,但对钢的屈服强度影响不大;再经在1220℃固溶处理时出现M₂₃(CN)₆向M(CN)的逆析出反应,该钢又显示出较高的室温冲击功。     

高速钢M2中共晶碳化物M_2C的性质和形态

采用砂型和金属型铸造制备M2高速钢铸锭,研究了共晶碳化物M2C性质和形态随冷却速度的变化规律。结果表明,冷速加快,促进共晶M2C由平直片层状变为弯曲棒状,并使碳化物中合金元素含量降低,基体合金含量升高。不同形态M2C热分解性质差异较为明显:片层状M2C分解产生的MC多分布在碳化物内部,形成大量M6C+MC复合碳化物;棒状M2C起始分解温度低于片层状M2C,MC多形成于碳化物和基体界面处,高温加热时易与M6C分离,使复合碳化物数量减少。共晶M2C热分解性质的差异与冷速不同引起的合金元素分布变化有关。     

Influence of Precipitates Size and Distribution on Room Temperature Mechanical Properties and Accelerated Creep of X20CrMoV121

The effect of microstructure on creep resistance of the low carbon chromium steel X20CrMoV121 after 100‐hours of static‐load test at a temperature of 580 °C and constant stress of 170 MPa was investigated. The specimens for the experiments were extracted from steam pipes of a steam power plant and heat treated. The effect of isothermal annealing on the microstructure and hardness as well as the kinetics of the precipitation of the carbide particles were determined.     

C和N含量及终锻温度对38MnVS6性能和组织的影响

通过显微组织定量统计、高分辨透射电镜及热力学计算等手段,研究了成分微调及终锻温度对38MnVS6非调质钢力学性能和显微组织的影响。结果表明,通过降C增N处理和降低终锻温度,实验钢屈服强度得到一定提高,塑韧性得到明显改善,室温冲击功由52 J增加至83 J。其作用机制为降C使铁素体体积分数增加,塑韧性得到改善;而增N后提高了钢的析出强化作用,弥补降C带来的强度损失;随着终锻温度的降低,铁素体数量增加且尺寸减小,细晶强化及韧化作用得到进一步提高。两方面综合作用使得实验钢强度保持稳定,而冲击韧性提高。