Improving the steam temperature and the pressure of the boiler applied in the thermal power could enhance the coal-fired efficiency and reduce the emission of harmful gases. Due to the dual impact of dwindling fossil resources and an exacerbated global greenhouse effect, it is critical to develop new heat-resistant boiler materials for ultra super-critical (USC) units at temperatures of 650oC and higher. With great thermal conductivity, good fatigue resistance, and low cost, martensitic heat-resistant steel G115, based on P92 steel applied in 600oC USC units, is a promising steel to be applied to this among all candidate materials. This paper introduces the main chemical composition and the microstructure feature of G115 steel, and the research progress in the areas of microstructure stability, creep performance, fatigue resistance, steam oxidation resistance, and industrial pipe production are summarized, with a focus on the role of Cu-rich phase in G115 steel. Finally, some key points on G115 steel are proposed to provide ideas for future research.

提高火电机组中耐热锅炉的蒸汽温度和压力参数可以有效提升燃煤效率，减少有害气体排放。受煤炭资源紧缺和温室效应的双重影响，发展650℃及更高温度超超临界(ultra super-critical，USC)机组中的耐热锅炉材料已迫在眉睫。我国在600℃ USC机组用耐热材料P92钢基础上研发的马氏体耐热钢G115有望成为优选材料之一。本文介绍了G115钢的成分特点、形貌特征，综述了其在组织稳定性、蠕变性能、抗疲劳性能、抗蒸汽氧化性能以及工业管材制备等方面的研究进展，重点归纳了G115钢中富Cu相的作用，展望了未来研究重点，以期为更深入研究G115钢提供可行思路。

The heat transfer component is a major component of a nuclear power plant, the safety and service life of which are determined based on the long-term creep performance of the heat-transfer pipe material. Several long-term creep tests are usually required to determine the creep life of the heat-transfer pipe materials, which considerably restrict the evaluation efficiency of the material service performance. The objective of this study is to investigate the feasibility of accelerated creep test (ACT) to reduce the time required for evaluating the creep properties of materials. A alumina-forming austenitic (AFA) stainless steel was prepared, and the ACT was performed on a Gleeble thermal simulator. Based on the ACT developed and realized on the Gleeble thermal simulator, damage accumulation was realized by applying elastic-plastic tensile and compressive strains on the ACT specimen to simulate the accelerated changes in the microstructure of the alloy that can be usually observed during a conventional creep test (CT). The average stress with respect to all the cyclic stress relaxation stages in the ACT was considered to be the initial stress of the conventional CT, and a creep fracture test was conducted on the alloy sample. Results revealed that the ACT accelerated the microstructure evolution of the precipitated phases, dislocations, twins, and so on in a short time. Nevertheless, the repeated generation and annihilation of a large number of dislocations in the AFA alloy during the ACT provided the nucleation point and reduced the driving force associated with the nucleation of the precipitated second phase, including the Laves phase. In addition, the cyclic strain applied during the ACT will reduce the strengthening effect of the nanoscale deformation twins in the AFA alloy, resulting in differences in the evaluation effect. Thus, ACT is useful for the efficient evaluation of the creep properties of materials; however, the optimal range of test parameters must be further investigated.

Lightweight Fe-Mn-Al-C steels are promising candidates for automobile structural materials and have gained increased scientific and commercial interest owing to their outstanding mechanical properties and low density. To date, several studies have been conducted to illustrate the mechanism of phase transformation, strengthening, and strain hardening under solution and aging state. Moreover, prestrain before aging as a low-cost and simple method to tailor precipitates and control properties has been widely reported; however, it has been barely investigated in the Fe-Mn-Al-C alloy system. Therefore, in this study, the effects of pre-cold rolling and two-step aging on the microstructure and mechanical properties of Fe-30Mn-11Al-1.2C (mass fraction, %) austenitic low-density steel are investigated using EBSD, TEM, and universal testing machine. Results showed that the yield strength (YS) significantly increased via the two-step aging from 580 MPa (at solution state) to 1120 MPa, but the uniform elongation (UE) sharply decreased to approximately 0. However, after the pre-cold rolling and two-step aging, the YS of the material further improved to 1220 MPa, and the UE significantly increased to 18.2%, which implies an improvement in the comprehensive mechanical properties of the material. According to the microstructure analysis, the increase in YS after the two-step aging was caused by the ordering strengthening effect of κ' carbide. Further, the pre-cold rolling could introduce heterogeneous nucleation sites, inducing intragranular precipitation. The combination of the precipitation strengthening of the precipitates and deformation strengthening induced via the pre-cold rolling further increased the YS of the material. Moreover, these intragranular precipitates could improve the work hardening capability, which is the root cause of the high plasticity of materials. This process provides a novel idea for improving the performance of austenitic low-density steels.

为探究近服役温度时效行为对ODS钢微观组织和力学性能的影响，通过SEM、TEM和拉伸性能测试等方法，研究了9Cr ODS钢在700℃时效不同时间后的碳化物(M23C6)、纳米氧化物演变和力学性能变化。结果表明：在时效初期(≤ 200 h)，M23C6在晶界处呈条带状快速析出并聚集长大，纳米氧化物无明显变化；在时效中期(200和1000 h)，M23C6和纳米氧化物稳定长大；在时效后期(2000和3000 h)，M23C6达到亚微米级，纳米氧化物的平均尺寸和数密度趋于稳定，与初始态相比，其平均尺寸的增长率为19.7%，数密度的下降率为27.1%。因纳米氧化物对不断增殖位错的钉扎，在部分晶粒内出现了位错胞和回复亚晶。9Cr ODS钢的拉伸强度在时效初期快速下降。在时效中后期，虽然纳米氧化物平均尺寸增加、数密度降低，但其钉扎作用仍然显著，以及基体中不断增殖的位错使得材料的拉伸强度维持稳定，延伸率在时效1000和2000 h期间处于低谷。

S31042 steel is a typical 25Cr-20Ni-type austenitic heat-resistant steel with excellent oxidation and corrosion resistance, and its creep rupture strength can be improved by the addition of Nb and N. This austenitic steel is widely used in superheater and reheater in ultrasupercritical power plants. At high temperatures, its performance is associated with the formation and evolution of Z, MX, and M23C6 phases. Till date, few studies have addressed the precipitation behavior of the Z phase in austenitic steel and the reinforcing mechanism of different M23C6 phases remains unclear. To clarify this, the ageing treatment of S31042 steel was performed at 1050oC, and the evolution behavior, thermal stability, and strengthening mechanism of the precipitates during creep tests were investigated. Furthermore, the relation between precipitate evolution and high-temperature performance was elucidated via OM, SEM, TEM, and creep tests. The supersaturation degree of the alloying components in solution-treated S31042 steel decreased after ageing at 1050oC and the driving force for M23C6 phase formation became smaller, resulting in a discontinuous distribution of the rod-like M23C6 phase along the austenite grain boundaries during the creep tests. At high stress levels, this discontinuous distribution of the rod-like M23C6 phase along the austenite grain boundaries increased the resistance to grain boundary sliding without changing the ductility, thus improving the rupture ductility of the steel. At low stress levels, the strengthening effects of the M23C6 phase discontinuously distributed along the austenite grain boundaries in aged steel were not as strong as those in solution-treated steel.

以S31042奥氏体耐热钢为研究对象，采用短时高温时效处理后在700℃下对其进行长期蠕变性能测试。通过OM、SEM和TEM等手段表征了S31042钢蠕变过程析出相的类型和演化规律，并利用蠕变实验分析了高温时效处理对S31042钢高温性能的影响。结果表明，经1050℃时效10 h处理后，S31042钢组织中析出大量尺寸在100 nm左右的Z相，降低了固溶态S31042钢中合金元素Cr和Nb的过饱和度，减小了M23C6相的形核驱动力，将蠕变过程晶界上析出M23C6相的形态由连续的链状调控为断续的短棒状。短棒状M23C6相的形成能够在不影响材料塑性的前提下，增大晶界滑动的阻力，改善材料的持久塑性。

采用DSC、TEM、导电率和力学性能等测试方法，研究了不同冷轧变形量对Cu-3.0Ni-0.60Si-0.16Zn-0.15Cr-0.03P (质量分数，%)合金组织性能与析出行为的影响，旨在通过工艺调控提升该合金的综合性能。通过对比不同冷轧变形后合金的开始析出温度和再结晶温度以及时效后合金的组织性能，确定了高性能Cu-Ni-Si系合金的形变-时效工艺参数，明确了冷轧变形量对合金时效析出动力学的影响规律和强化相析出的调控机制；合金经过95%冷轧+ 450℃、60 min形变热处理后获得了显著优于现有Cu-Ni-Si合金(如C70250)的性能，其抗拉强度为(841 ± 10) MPa，导电率为(52.2 ± 0.3)%IACS。

随着现代工业中交通、电气、航空航天、电子等领域的快速发展，对铜合金的性能要求越来越高。强度和导电率是相互矛盾的性质，实现铜合金兼具高强度和高导电率是现代铜工业发展的重要课题。采用真空熔炼、低温轧制、时效处理等工艺制备了Cu-1Cr-0.2Zr-0.25Nb (质量分数，%)合金，研究了低温轧制对Cu-1Cr-0.2Zr-0.25Nb合金显微组织、力学性能和导电性能的影响，分析了时效工艺对析出相种类、形貌和分布的影响。结果表明，Cu-1Cr-0.2Zr-0.25Nb合金主要由Cr相、富Zr相、Cr2Nb相及Cu基体相组成。450℃短时(30 min)时效后Cu-1Cr-0.2Zr-0.25Nb合金即可析出纳米级fcc结构的Cr析出相，在长时间(300 min)时效后，会形成bcc结构的Cr析出相。Cu-1Cr-0.2Zr-0.25Nb合金经过低温轧制和时效处理后，在Cu基体中形成了纳米析出相、纳米变形孪晶和位错等混合组织并获得了优异的综合性能。低温轧制Cu-1Cr-0.2Zr-0.25Nb合金450℃时效30 min后，抗拉强度为700 MPa，导电率为73.29%IACS；450℃时效300 min后，导电率可达79.81%IACS，此时，抗拉强度、屈服强度和硬度分别为646 MPa、606 MPa和212 HV。结合实验结果和对强度贡献计算表明，位错强化和析出强化是Cu-1Cr-0.2Zr-0.25Nb合金的主要强化机制。

Owing to their attractive structure and mechanical properties, high-entropy alloys (HEAs) and medium-entropy alloys (MEAs) have attracted considerable research interest. The strength of HEAs/MEAs with a single face-centered cubic (FCC) phase, on the other hand, requires improvement. Therefore, in this study, we demonstrate a strategy for increasing the room-temperature strength of FCC-phase HEAs/MEAs by tuning cryo-pre-straining-induced crystal defects via the temperature-dependent stacking fault energy-regulated plasticity mechanism. Through neutron diffraction line profile analysis and electron microscope observation, the effect of the tuned defects on the tensile strength was clarified. Due to the cryo-rolling-induced high dislocation density, mechanical twins, and stacking faults, the room-temperature yield strength of an equiatomic CoCrFeNi HEA was increased by ∼290%, from 243 MPa (as-recrystallized) to 941.6 MPa (30% cryo-rolled), while maintaining a tensile elongation of 18%. After partial recovery via heat treatment, the yield strength and ultimate tensile strength decreased slightly to 869 and 936 MPa, respectively. Conversely, the elongation increased to 25.6%. The dislocation density and distribution of the dislocations were found to contribute to the strengthening caused by forest dislocations, which warrants further investigation. This study discussed the possibility of developing single-phase high-performance HEAs by tuning pre-straining-induced crystal defects.

Owing to the excellent combination of specific strength and ductility, medium Mn steels (MMSs) with Mn contents of 3%-12% (mass fraction) are considered the most promising candidates for the third-generation advanced high-strength steel. The combination of excellent strength-ductility is mainly attributed to the active transformation-induced plasticity effect of the metastable retained austenite during deformation. Therefore, producing a considerable amount of retained austenite with reasonable stabilities in the steel by various heat treatment schedules is always important. In this study, granular- and lamellar-structured retained austenites were developed in a cold-rolled 0.15C-5Mn MMS by introducing a technical process of precontrolling ferrite recrystallization in the annealing schedule. The microstructures of the annealed samples were analyzed using SEM, EBSD, and TEM. The results show that duplex microstructures comprising various amounts of recrystallized ferrite and fresh martensite can be obtained in the cold-rolled MMS when controlling the occurrence of recrystallization at different intercritical temperatures by a preannealing process. When this microstructure is used for the final austenite reverted transformation annealing, the resultant ultrafine duplex microstructure with recrystallized ferrite and two types of heterogeneous retained austenite, i.e., lamellar and granular, is produced. The heterogeneous-structured austenite shows more sensitivity to increasing strain, i.e., various mechanical stabilities, which enable an excellent strength-ductility combination and reduced Lüders strain in the cold-rolled medium Mn steel.

为探究铁素体再结晶对冷轧中锰钢微观组织与力学性能的影响规律，以0.15C-5Mn (质量分数，%)冷轧中锰钢为研究对象，采用两步临界区退火的热处理方法，利用SEM、TEM和EBSD等表征手段和力学性能测试方法，研究了铁素体再结晶调控对冷轧中锰钢多样化残余奥氏体形成及其力学性能的影响。结果表明，通过在不同温度预先调控冷轧中锰钢中的铁素体再结晶，可获得由不同比例的等轴状再结晶铁素体和马氏体组成的双相细晶组织。经常规退火处理后，在终态组织中形成了不同体积分数的超细晶再结晶铁素体和呈等轴状/板条状形貌的多样化细晶残余奥氏体，使中锰钢在拉伸变形过程中表现出多样化的TRIP效应，在提升冷轧中锰钢强塑性能的同时，其Lüders变形也获得改善。

The oxidation behavior and mechanism of as-received and 30 % cold-rolled alumina-forming austenitic (AFA) steel were investigated in dry air at 700 °C. The results show that the mass gain per unit area curves of as-received and 30 % cold-rolled steels subject to near-parabolic law before 100 h oxidation time. Two samples both show higher high-temperature oxidation resistance due to the formation of dense Al2O3 oxide scale. Gradual spallation of outer scale results in the formation of continuous and dense alumina scale. Dislocations can act as short-circuit diffusion channel for the diffusion of Al from alloy matrix to surface, and also provide nucleation sites for B2-NiAl phase, which ensure the continuous formation of Al2O3 scale.