时效对超级双相不锈钢析出相演变的影响

通过在850℃时效处理研究了S32750超级双相不锈钢析出相的析出行为。采用Thermo-Calc热力学软件预测析出相及相组成,采用OM,FE-SEM和EDS对S32750超级双相不锈钢铸坯不同时效状态下的样品进行全面分析,利用K-J-M-A模型进行σ相析出动力学拟合。实验结果表明：850℃时效过程中,σ相优先在铁素体内部和双相晶界处析出,直至铁素体相耗尽;σ相的析出动力学控速环节主要是：初始阶段形核控速和时效40 min后的元素扩散控速;除σ相外,时效过程中还会析出χ相和Cr2N相。其中χ相属于亚稳定相,主要在时效前期析出,随着时效时间的延长最终转化成σ相。     

时效条件下2205双相不锈钢中的析出相分析及其对冲击性能的影响

研究采用光学显微镜(OM)、扫描电镜(SEM)、能谱分析(EDS)和透射电镜(TEM)等试验技术,分别对2205双相不锈钢在700、750℃时效处理0.5、12、h后组织中的析出相进行分析。结果表明:在700℃时效处理的条件下,2205双相不锈钢的析出相主要是Cr2N和χ相;750℃时效处理的条件下,析出相主要由Cr2N、χ相以及σ相组成。结合室温冲击功的测量结果,随着时效时间的延长,该钢的冲击功明显降低;在相同时效时间条件下,与700℃时效处理相比,经750℃时效处理后的2205双相不锈钢冲击功较低,这主要是由于组织中σ相的析出造成的。     

2209双相不锈钢焊缝的析出及对冲击性能的影响

 对2209双相不锈钢焊缝在690℃进行不同时间时效处理,采用了透射(TEM)、相分析、冲击测试等手段,研究了析出相的形貌、分布及其类型和含量以及析出相对冲击功的影响。结果表明,析出相为M23C6和σ相,主要在铁素体和奥氏体晶界和铁素体内析出。随着时效时间的延长,析出相逐渐长大并增多,冲击功逐渐降低。在扫描电镜下观察冲击断口形貌为韧窝和准解理,断裂类型由韧性到脆性断裂。     

热加工图对节约型双相不锈钢2101表面裂纹的预测

采用THEMOMASTER-Z热模拟试验机对节约型双相不锈钢2101在变形温度950～1150℃、应变速率0.01～30s-1及真应变0.8的条件下进行高温压缩试验。在较低变形温度或较高应变速率区域变形时,试验钢在环形拉应力的作用下,在试样鼓肚处易出现与压缩轴呈45 的表面裂纹。利用试验数据分别采用动态材料模型理论和塑性功方法构建热加工图对试验钢表面裂纹进行预测。基于动态材料模型构建得到的热加工图与试验钢表面裂纹存在较大差别,而基于塑性功方法构建得到的热加工图对压缩试样表面裂纹的预测结果与试验结果基本吻合。     

2205双相不锈钢中σ相的析出规律

研究了2205双相不锈钢中σ相的析出规律及原始组织对析出规律的影响.分别对铸态试样和热轧态试样进行了不同工艺条件的固溶处理实验,并对实验后试样进行了显微组织的观察和分析.结果表明,2205双相不锈钢中σ相析出的鼻尖温度为850℃;变形会使σ相的析出温度升高,孕育期缩短,析出速度增大;工业生产2205双相不锈钢热轧卷板时轧件终轧后应采用较快冷却速度冷却到卷取温度,以避免σ相的析出给热轧卷板开卷及后续工序带来困难.     

马氏体时效不锈钢时效析出相及位向关系的研究

系统研究了Custom 465钢510℃时效析出相及相关的位向关系,结果表明:Ni3Ti是钢的主要时效析出相,析出相为杆状,杆的长度方向与马氏体基体的[111]M方向一致;(011)M///(0001)Ni3Ti、[111]M//[1120]Ni3Ti是马氏体和Ni3Ti金属间化合物确切的位向关系,这种位向关系使Ni3Ti在马氏体基体内出现12种可能的亚型.     

In Situ Observation of Surface Electrochemical Activities of Lean Duplex Stainless Steel LDX 2101

The surface electrochemical corrosion activity of the economic lean duplex stainless steel LDX2101 was investigated in situ in chloride solution with a combination of long working distance microscope (LWDM) and electrochemical techniques. In addition, the site and chemical composition of the electrochemical active points on the specimen surface were also determined with integrated scanning electron microscope/energy dispersive X‐ray spectroscope (SEM/EDS) system. The results demonstrated that: (i) The reaction of α → Cr₂N + γ₂ precedes that of α → σ + γ₂ when LDX2101 was aged at 700°C. (ii) The initiation sites of electrochemical active points could be determined by LWDM in combination with potentiostatic pulse technique (PPT). (iii) The sites of electrochemical active points were found to change from inclusions (MnS/Al₂O₃) to secondary austenite phase (γ₂), with the increase of aging time at 700°C.     

Weldability Aspects of a Newly Developed Duplex Stainless Steel LDX 2101

Duplex grades have, due to balanced chemical compositions of both filler and base metals, a weldability that allows for successful welding using a majority of the technically relevant techniques of today. In order to fulfil the performance requirements several aspects must be considered. In the heat affected zone (HAZ) the austenite reformation must be reasonably high and in the weld metal the microstructure must be stable so that e.g. high productivity welding and multi‐pass welding are possible, without precipitation of detrimental phases in previous passes. This paper addresses the effect of alloying elements and thermal cycles on phase balance in the high temperature HAZ (HTHAZ) of the newly developed lean duplex grade LDX 2101 (EN 1.4162, UNS S32101). Bead‐on‐plate welds and simulated weld structures have been produced and investigated using metallography, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results are analysed using the thermodynamic database Thermo‐Calc and a model for phase transformation based on a paraequilibrium assumption for ferrite‐austenite transformation. In the temperature region outside the paraequilibrium domain, growth controlled by diffusion of substitutional elements was considered. The analysis follows a model by Cahn regarding grain boundary nucleated growth and the Hillert‐Engberg model on kinetics of spherical and planar growth.     

Effect of Aging on the Fracture Behavior of Lean Duplex Stainless Steels

The influence of aging in the range of 550 °C to 850 °C for 5 to 120 minutes on the impact fracture behavior of 2101 and 2304 lean duplex stainless steels (DSS) was investigated in the present study. The 2304 steel displayed ductile behavior irrespective of aging conditions. In contrast, the 2101 steel displayed a ductile behavior only in the case of aging for 5 minutes at 550 °C and 650 °C, whereas in all other cases, it fractured in a brittle manner. The brittle fracture behavior of the 2101 steel has been attributed to the precipitation of small black particles at the α/α and α/γ grain boundaries (nitrides), which form paths for easy crack propagation. In the 2304 steel, such particles precipitated at 750 °C and 850 °C, but they were located inside the austenitic grains because of the formation of secondary austenite. They therefore did not embrittle the steel. The larger Ni content of the 2304 steel favored the formation of the secondary austenite that is absent in the 2101 steel.     

Crack Properties of Lean Duplex Stainless Steel 2101 in Hot Forming Processes

The crack behavior of LDX 2101 by hot compression tests in the temperature range of 950 to 1150 ℃ and strain rate range of 0.01 to 30 s-1 was studied.The hot workability map of LDX 2101 was constructed and the alloy exhibited a better crack resistance at higher temperature and lower strain rate.Microvoids initiated and coalesced into crack at subsurface on the equatorial plane of bulge surface under secondary tensile condition.The cracks were orientated at an angle of approximately 45° with respect to the c...     

Development of a Lean Duplex Stainless Steel

The classic series of duplex stainless steels shows very high corrosion resistance and can be used for very demanding applications. A new lean duplex steel, LDX 2101® (EN 1.4162, UNS S32101), has been developed with corrosion resistance on a par with standard austenitic grades. Application areas include: structural components, chemical industry, tanks and containers. The steel was designed to have equal amounts of ferrite and austenite in annealed condition and with an austenite that is stable against strain‐induced martensite. Thanks to its high nitrogen content, the steel has a fast austenite reformation when subjected to thermal cycling, e.g. welding. Unlike conventional duplex grades, the formation of intermetallic phase is very sluggish, although precipitation of nitrides and carbides has a certain impact on material properties after exposure in the temperature range 600 to 800°C. The precipitation behaviour after different isothermal treatments is described and its influence on different product properties is shown. A good agreement was found between impact toughness and corrosion resistance for a wide range of thermal treatments.     

固溶处理对铸态2101双相钢腐蚀性能的影响

通过电化腐蚀学实验研究了900～1190℃固溶处理对铸态2101双相钢(/%:0.02C,0.69Si, 5.00Mn, 0.0015S,0.022P,21.42Cr, 1.66Ni, 0.31Mo, 0.48Cu, 0.25N)腐蚀性能的影响。EIS阻抗谱图、等效电路极化电阻值和Tafel曲线均表明,同一固溶温度下,固溶时间越长钢的耐蚀性越好。通过组织形貌电镜图及测定组织中γ相面积比和晶粒度得到,固溶处理30 min和2 h后γ相面积比和单位面积γ晶粒个数随着固溶温度的增加都呈先升高后降低的趋势,在970℃时组织最为细密,固溶2 h后组织比固溶30 min的更为细密。组织致密度高,析出氮化物少,则2101双相不锈钢的耐蚀性好,该钢最佳固溶工艺为970℃和2 h。