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Effects of aging treatment on microstructure and mechanical properties of Cr25Ni35Nb and Cr35Ni45Nb furnace tube steel

Limin SHEN

金属学报(英文版)

Cr25Ni35Nb and Cr35Ni45Nb alloys are usually used in the ethylene cracking furnaces. However, premature failure of furnace tubes often occurs ahead of design life due to elevated temperature exposure conditions (1050--1100 ℃) and aggressive service environment. Effects of exposure temperature and time on microstructure and mechanical properties of Cr25Ni35Nb and Cr35Ni45Nb steel at aging temperature (1200 ℃) with various exposure time were simulated different service times at 1050 ℃. Change of mechanical properties at room temperature and elevated temperature (900℃) of the aged Cr25Ni35Nb and Cr35Ni45Nb steel were investigated. Under exposure at 1200 ℃, ultimate tensile and yield strength, elongation of Cr35Ni45Nb steel increase initially and then decrease, however, strength and ductility of Cr25Ni35Nb steel decrease with aging time increasing. Large amount of fine secondary carbide particles precipitated and dispersed in matrix of Cr35Ni45Nb steel, which increased strength and ductility for dispersion strengthening. However, the effect of the dispersion strengthening is weakened by needle-like secondary carbides. Strength and ductility decreased with fine secondary carbide particles growing. For Cr25Ni35Nb steel, few fine secondary carbide particles precipitated and dispersed in the matrix, and needle-like secondary carbides generated in the matrix, which causes strength and ductility decreased with aging time increasing.

关键词: Aging treatment

焊接及热处理对T250马氏体时效钢薄壁旋压圆筒性能的影响

张黎旭 , 吴军 , 胡春海 , 温树斌 , 邵芬

宇航材料工艺 doi:10.3969/j.issn.1007-2330.2014.03.023

采用脉冲TIG焊对T250马氏体时效钢薄壁旋压圆筒进行焊接,通过优化焊接工艺参数,得到了外观成形良好,内部缺陷达到QJ175-93 0级标准要求的焊缝.在焊前和焊后对T250马氏体时效钢薄壁旋压圆筒进行了热处理,研究了热处理对焊接接头金相组织、显微硬度、角变形和力学性能的影响.结果表明:时效处理后,焊缝金属枝晶晶界中存在逆转变奥氏体组织,显微硬度低于母材;熔合线附近焊接热影响区晶粒长大,最大处晶粒约为基材的6倍;焊前时效处理大幅度减小了焊接接头角变形;在焊后对试样进行500℃时效处理的情况下,焊前时效处理使焊接接头抗拉强度和弯曲角都有所提高;焊前对旋压圆筒进行500℃时效处理,焊后进行500℃时效处理,得到了最佳焊缝强韧性匹配.

关键词: T250马氏体时效钢 , 时效处理 , 金相组织 , 力学性能

Improvement of Toughness of Ultrahigh Strength Steel Aermet 100

Liuding WANG , Laizhu JIANG , Ming ZHU , Xiao LIU , Wangmin ZHOU

材料科学技术(英文)

The influence of double aging on the microstructure and mechanical properties of ultrahigh strength steel Aermet 100 was analyzed. Under the double aging, there is no apparent decrease in the strength of steel. However, the impact fatigue life can be prolonged by 35.5% and dynamic fracture toughness be raised by 22.6% respectively, as compared with the normal aging. Based on the observation of microscopic structure, the physical mechanism of the prolongation of impact fatigue life and the enhancement of stability of the reverted austenite, AR, is analyzed further. The results show that this new technique is a breakthrough of combination optimization between strength and toughness for Aermet 100 steel. In the light of the current understanding on this subject, the volume fracture of soften and tough AR formed in process of heat preservation at higher temperature of double aging increases drastically. Moreover, during the treatment of lower temperature of double aging, the carbon separating from the martensitic ferrite will diffuse into AR, resulting that the martensitic brittleness decreases and the stability of AR increases.

关键词: Ultrahigh strength steel , null , null , null

Effect of Aging on Microstructure and Mechanical Property of 1900 MPa Grade Maraging Stainless Steel

Kai LIU

材料科学技术(英文)

The 18%Ni alloy steels provide high strength and toughness, while age-hardenable or PH stainless steels also have good corrosion resistance. This paper focuses on an investigation of the heat treatment, mechanical properties and microstructural development of a new maraging stainless steel. It is reported that the heat treatment process should consist of solution treatment and cryogenic cooling to attain a fully martensitic structure, followed by aging at 813 K. This heat treatment resulted in an ultimate tensile strength of over 1900 MPa combined with good impact toughness. Transmission electron microscopy is used to show that, for the peak-aged condition (813 K/4 h), nano-sized precipitates, e.g. Ni3Mo and/or R-phase, and a high density of dislocations were uniformly dispersed in the lath martensite matrix. The calculated yield strength, based on a revised Orowan mechanism, is in good agreement with the test data. The steel studied has an ultimate tensile strength over 1900 MPa, excellent fracture toughness, and good resistance against over-aging and relatively good corrosion resistance as well.

关键词: Maraging stainless steels , steels , Precipitation , High , stren

Optimal Selection and Control for Precipitation of α2 Phase in Near α High Temperature Ti Alloys during Aging Treatment

Jun ZHANG , Qingjiang WANG , Yuyin LIU , Li LI , Dong LI

材料科学技术(英文)

The characteristic of the precipitation and growth of α2 ordered phase during aging treatment in near αTi alloys have been investigated in terms of the influences of aging temperature, aging time and aging manner. The results exhibit that aging temperatures influence the distribution ofα2 phase precipitated and cause the changes in growth speed ofα2 phase. For various aging temperatures, the time to finish precipitation ofα2 phase is different. The facts that various distribution characteristics and growth speed ofα2 ordered phase are caused by changed aging condition imply optimal selection and control for precipitation ofα2 ordered phase reachable. Some discussions on adoptable aging steps are presented.

关键词: α2 ordered phase , null , null

Effect of Aging Treatment on Microstructural and Mechanical Characteristics of PEO Coatings on Mg-Al Alloy

S.Y.Chang , Y.L.Kim

材料科学技术(英文)

Cast Mg-6 wt pct Al alloy solution-treated at 683 K for 16 h and aged at 498 K was coated by plasma electrolytic oxidation (PEO) method. The Mg-6 wt pct Al alloy aged for 16 h exhibited the highest microhardness and wear resistance. After PEO coating, however, the microhardness and wear resistance of coatings on Mg-6 wt pct Al alloy showed a tendency to decrease with increasing aging time, which was in aggrement with the change of thickness with aging time. In addition, the coatings on solution-treated Mg-6 wt pct Al alloy had better microhardness and wear resistance than those on aged Mg-6 wt pct Al alloys. Consequently, it can be understood that the aging treatment has a deleterious influence on the mechanical properties of coatings on Mg-6 wt pct Al alloy.

关键词: Cast Mg-6 wt pct Al , null , null

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