时效处理对超级双相不锈钢00Cr29Ni6Mo2N组织和耐点蚀性的影响

采用扫描电镜和X射线能谱仪研究了00Cr29Ni6Mo2N超级双相不锈钢1080 ℃ 30 min固溶+650~1 000℃ 60 min时效后的显微组织。试验结果表明,在奥氏体和铁素体相界面上析出了Cr₂N和σ相两种析出相,同时发现少量的Cr₂N在铁素体相内。Cr₂N析出优先于σ相,增加时效温度和时间对Cr₂N的析岀量没有显著影响,但σ相含量随着时效温度的升高先增加后减少,850 °C时效σ-相面积百分含量最大,达5. 8%,同时在给定时效温度下随时效时间增加σ-相含量增加。Cr₂N和σ相的析出均降低了00Cr29Ni6Mo2N超级双相不锈钢的耐点蚀性能。     

超级双相不锈钢S32760凝固过程Thermo-Calc热力学软件的应用

利用Thermo-Calc热力学计算软件得到S32760（022Cr25Ni7Mo3WCuN）超级双相不锈钢凝固过程中的相图,确定了S32760双相钢是FA （铁素体-奥氏体）凝固模式,通过改变奥氏体和铁素体的形成元素的含量,确定在不同的化学成分下的热加工性能、Cr₂N和σ相析出温度,得到S32760双相钢热加工温度区间随着奥氏体形成元素C、N、Ni、Mn含量的增加而变大,随着铁素体形成元素Si、Cr、Mo含量的增加而减小,而W对热加工性能没有影响。根据热力学计算,确定了最优的化学成分（/%:0.022C,0.30Si,0.80Mn,25.60Cr,6.20Ni,0.54Cu,3.50Mo,0.54W,0.27N）,S32760双相钢最佳热塑性温度为1195℃, Cr₂N相的析出温度为1050℃, σ相析出温度为1020℃,热加工区间为145℃,并且通过了后续的现场实践验证。     

氮含量对无镍奥氏体不锈钢平衡相转变的影响

高氮铬锰奥氏体不锈钢有着极为广泛的应用前景,然而氮含量对其相转变的影响尚不十分清晰。设计并冶炼了氮质量分数为0.02%～1.20%的试验钢,对各钢的平衡相转变进行了热力学计算,对δ铁素体和Cr₂N的形貌进行了观察。结果表明,钢中δ铁素体的最大析出量随着氮含量的升高而降低,当氮质量分数超过1.05%后,无δ铁素体析出。获得了试验钢加热时δ铁素体的析出温度与氮含量的关系式。随着氮含量的升高,试验钢在冷却时Cr₂N的析出温度逐渐升高,并获得了其定量关系式。在GN04钢中,1 200 ℃等温2 h后的δ铁素体主要沿三叉晶界分布。Cr₂N析出优先在晶界形成,然后朝着晶内发展。在相同等温条件下,试验钢中Cr₂N的析出量随着氮含量的升高而增大,且层片间距随之减小。     

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.     

18Mn18Cr高氮钢析出相特征及形成机制

通过金相显微镜、扫描电镜、电子探针显微分析、透射电镜及热力学计算软件研究C和N含量对铸态及时效态18Mn18Cr高氮钢析出相特征及形成机制的影响.研究发现在铸态,随C/N质量比降低,析出相依次为Cr₂₃C₆相、σ相和Cr₂N相.增加C或N含量可分别促进Cr₂₃C₆相和Cr₂N相析出.C和N含量影响实验钢凝固模式及不稳定铁素体相共析分解产物.18Mn18Cr0.44N钢凝固模式为AF模式,不稳定铁素体相共析分解反应为δ→σ+γ₂（0.025% C）和δ→γ₂+Cr₂₃（C_xN_y）₆（x/y>1）（0.16% C）;18Mn18Cr0.72N钢凝固模式为A模式,晶界处存在少量颗粒状Cr₂N相.在固溶时效态,实验钢仅析出片层状的Cr₂N_0.39C_0.61相.随C+N含量增加,片层状析出相体积分数和片层间隙增加,析出孕育时间减少.      

S31254超级奥氏体不锈钢析出相演变及微观表征

利用热力学计算了S31254超级奥氏体不锈钢在500~1 200 ℃温度范围内的平衡态析出相,并结合热模拟试验、扫描电镜、透射电镜等方法,对不同析出物的析出行为进行了表征和分析。结果表明,S31254不锈钢奥氏体基体中可存在的第二相包括σ、χ、Laves等金属间相,Cr₂N、π型氮化物相以及M₂₃C₆型碳化物相,高Mo、高N、高Cr含量是该钢析出相种类复杂的主要原因;试验钢具有高的第二相析出倾向,σ相开始析出温度约为1 150 ℃,而在900~800 ℃区间可发现χ相和σ相的转变,χ相更易作为一种稳定相存在;析出相的析出位置和形貌呈现不同特点,晶界析出主要为σ相、χ相和Laves相,而晶内主要有呈针状和块状分布的χ相和呈棒状析出的Cr₂N相。     

高锰高氮不锈钢10Cr21Mn16NiN线材开发

介绍了10Cr21Mn16NiN钢线材成分设计、增氮原理、冶炼工艺、轧制和固溶工艺、Cr₂N相析出的生产工艺。采用30 t AOD精炼,吹氮气增氮,精炼后期加氮化锰。轧制时采用1 240 ℃加热、控轧控冷,保证了盘条表面质量,避免了中心缩孔等问题;固溶温度应控制在1 100 ℃左右,且保温30 min后快冷,可防止Cr₂N相析出。成功生产出表面质量和性能优良的10Cr21Mn16NiN不锈钢线材。     

2205双相不锈钢夹杂物水平改善

双相不锈钢中夹杂物含量高低是影响其热塑性的一个重要因素。用光学显微镜和扫描电镜对2205双相不锈钢同期生产的板坯、热轧卷夹杂物进行分析。结果表明,2205双相不锈钢板坯和热轧卷中存在大于20μm的夹杂物,夹杂物以CaO-SiO2-Al2O3-MgO为主,Al质量分数为30%左右,Mg质量分数为10%左右,夹杂物变形能力差。通过控制炼钢过程工艺,以及实施夹杂物变性处理、提高LF弱吹时间、控制浇铸等措施,有效改善了钢中夹杂物水平。改进后,板坯中夹杂物都小于15μm,热轧卷中脆性夹杂物减少,夹杂物都发生了明显变形,夹杂物中Al2O3和MgO含量下降,CaO含量增加。     

开轧温度对铌微合金化热成型钢氢致延迟开裂性能的影响

通过动态充氢恒载荷、氢渗透等实验研究轧制工艺对铌合金化热成型钢的氢致延迟开裂性能的影响.随着开轧温度从1000℃降低到950℃,热成型钢的氢扩散系数降低,氢致延迟开裂性能提高,耐腐蚀性能下降.透射电镜观察发现开轧温度为1000℃时MX型析出相尺寸为30 nm;开轧温度为950℃时热成型钢的MX型析出相尺寸为5 nm左右,可以观察到直径为50 nm Cr₂C₃析出相.作为氢陷阱的纳米析出相是提高实验钢氢致延迟开裂性能的主要因素.析出相不同的原因是开轧温度为1000℃时MX型析出相发生熟化现象,进一步抑制Cr₂C₃的析出.      

2205双相不锈钢热轧裂边成因分析与改善

论述了2205双相不锈钢热轧裂边问题与精炼炉添加高铅萤石有关,过量的铅元素残留于钢液中,导致钢坯热塑性恶化而产生热轧裂边缺陷,通过管控精炼炉所添加萤石中的铅含量,2205双相不锈钢热轧裂边问题得到有效解决。     

Fracture toughness of the lean duplex stainless steel LDX 2101

Fracture toughness testing was performed on the recently developed lean duplex stainless steel LDX 2101 (EN 1.4162, UNS S32101). The results were evaluated by master curve analysis, including deriving a reference temperature. The master curve approach, originally developed for ferritic steels, has been used successfully. The reference temperature corresponds to a fracture toughness of 100 MPa√m, which characterizes the onset of cleavage cracking at elastic or elastic-plastic instabilities. The reference temperature, T ₀, was −112 °C and −92 °C for the base and weld materials, respectively. In addition, the fracture toughness is compared with impact toughness results. Complementary crack tip opening displacements (CTODs) have also been calculated. The toughness properties found in traditional duplex stainless steels (DSS) are generally good. The current study verifies a high fracture toughness for both base and weld materials and for the low alloyed grade LDX 2101. Even though the fracture toughness was somewhat lower than for duplex stainless steel 2205, it is still sufficiently high for most low-temperature applications.     

Comparative research on the mechanical property and precipitation of the 2101 and 2205 duplex stainless steels

The mechanical property and precipitation of the 2101 and 2205 duplex stainless steels were investigated.The results show that with nitrogen-content increasing from 0.12% to 0.26% to partly replace nickel,the yield strength of the 2101 steel gains an increase of 80 MPa whilst its elongation proportion keeps unchanged.The impact energy at a low temperature is obviously reduced.The temperature at which the impact energy starts decreasing is lower than 20℃,-20℃ and-40℃ for the 2101 steels containing 0.5%Ni,1.5%Ni and 2.5%Ni respectively,whereas it is-70℃ for the 5%Ni-containing 2205 steel.The nose temperature of precipitation is 700℃ for the 2101 steel and 850℃ for the 2205 steel.The scanning electronic microscope(SEM),the transmission electron microscope(TEM)and the X-ray diffraction(XRD)analyses show that the drop in the impact energy of the 2101 steel can be mainly attributed to the precipitation of Cr2N upon ageing while it is attributed to the sigma phase for the 2205 steel.     

2205双相不锈钢连铸坯的高温组织和高温力学性能

对2205双相不锈钢连铸坯进行高温短时拉伸试验,分析了抗拉强度、断面收缩率随温度的变化情况。观察了试验温度为1 300、1 050、950、850℃下试样的高温组织及断口形貌。结果表明,在1 150～1 350℃温度范围内,双相不锈钢试样具有很好的塑性;在1 000～1 100℃时,较高的应变速率抑制了软化作用的进行,使双相不锈钢出现第Ⅱ脆性温度区,同时试样中存在的疏松和细小析出物进一步加剧了裂纹的发展。第Ⅲ脆性区产生的原因是由于在奥氏体晶界上析出了氮化物、碳氮化物等细小析出物造成晶界脆化。     

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.     

Delaminations by Cleavage Cracking in Duplex Stainless Steels at Sub-zero Temperatures

Impact toughness testing was conducted on 10 and 30 mm plates of 2205 together with a 30 mm plate of LDX 2101^® duplex stainless steel (DSS). The testing temperatures were between 153 K (?120 °C) and room temperature. Interrupted fracture toughness tests of the 10 mm plate and a 50 mm plate of 2205 were also performed. The conclusion from the fractographic investigation was that the delaminations that occur in hot-rolled DSSs were cleavage fractures. The toughness anisotropy can be explained by the cleavage fracture and the appearance of the microstructure. The result from the interrupted fracture toughness test revealed that the delaminations initiated prior to the maximum force plateau and propagated ahead of the stable crack growth during testing. Estimated upper limit for the fracture delamination initiation toughness at sub-zero temperatures for the 2205 base metal according to the crack-tip opening displacement method was 28 to 61 μm for the 10 mm plate, 70 to 106 μm for the 30 mm plate and below 100 μm for the 50 mm plate.