Effect of sigma phase precipitation on microstructure and properties of cast ZG0Cr26Ni5Mo3Cu3 duplex stainless steel under different heat treatments

ZG0Cr26Ni5Mo3Cu3 Duplex Stainless Steel （DSS） was solution treated at 1,060 ℃ for 3 h,followed by water cooling. Tempering treatments were conducted at 720, 750 and 780 ℃, respectively, for 16 h,followed by air cooling. The microstructures of ZG0Cr26Ni5Mo3Cu3 duplex stainless steel samples treated at different tempering temperatures were observed by scanning electron microscope （SEM） and energy dispersal spectroscopy （EDS）, and the phase consitutions were analyzed using X-ray diffraction （XRD）. The effects of the precipitation of sigma （σ） phase on the duplex phase percentage, hardness, impact toughness and corrosion resistance of the DSS were studied. Results showed that microstructures of ZG0Cr26Ni5Mo3Cu3 after solution treatment consists of ferrite （α） phase and austenite （γ） phase; after being tempered at different temperatures,σ phase appeared due to a eutectoid-type reaction of α→σ＋γ2 during tempering treatment. It was observed that σ phase distributed along the grain boundary. The volume fraction of σ and γ phases increased with increasing tempering temperature in the range of 720 to 780 oC, whereas the volume fraction of α phase showed the opposite trend. When the percentage of σ phase increased, the hardness of steel also increased. In the solution treated steel, hardness was measured to be only 244.0 HB, because σ phase did not appear. However, itincreased to 391.8 HB when the DSS was tempered at 780 oC because a great of deal of σ phase appeared. The impact toughness and corrosion resistance of DSS decreased when the percentage of σ phase increased.

Sigma Phase Precipitation and Properties of Super-duplex Stainless Steel UNS S32750 Aged at the Nose Temperature

The nose temperature for σ-phase precipitation in super-duplex stainless steel （SDSS） UNS S32750 was evaluated by hardness method.Color-optical microscopy,scanning electron microscopy,energy spectrum analysis,impact and corrosion testing were carried out to investigate characteristics of microstructure and properties of the SDSS aged at the nose temperature.The experimental results indicate that the nose temperature of precipitation is 920℃ and aging at this temperature tiny σ phases can precipitate at phase interfaces or ferrite grain boundaries within 2min.Prolonging aging duration the amount ofσ-phase increases and a dual structure with σ and γ is obtained when aging for 120min.The precipitation ofσ-phase leads to severe deterioration in impact toughness （longitudinal/transverse direction） and corrosion resistance of SDSS.

Thermal aging effect on 2205 duplex stainless steel

： The effect of isothermal aging treatment on the mechanical and corrosion properties of 2205 duplex stainless steel was investigated by means of impact toughness test and micro-hardness measurement in combination with the critical pitting temperature （CPT） technique. The corresponding fractography of the steel was then observed after the impact toughness test. The results demonstrated that, at the critical temperature for precipitation of the sigma （σ） phase, e. g., 850 ℃, the impact toughness decreased rapidly and the micro-hardness increased gradually with increasing aging time. The CPT decreased from 61 to 15 ℃ as the aging time increased from 4 rain to 8 h. In addition, optical microscopy, transmission electron microscope （TEM） and X-ray diffraction studies showed that the ferrite in the steel transformed into secondary austenite and σ phase.

Effect of multiple heat treatments on fracture property of centrifugal casting stainless steels Z3CN20.09M with long-term thermal aging degradation

It is of great significance to investigate effect of multiple heat treatments on fracture property of centrifugal casting stainless steels Z3CN20.09M cut from pump casing with long-term thermal aging degradation for nuclear power plants to consider actual operation of nuclear power plants.Both multiple heat treatments and accelerated thermal aging experiment at the same temperature of 400℃ for different time were successively carried out on centrifugal casting stainless steels Z3CN20.09M in order to examine the metallographic modification and impact properties.Finally,an additional investigation on the related fracture properties was carried out,in which the critical initial fracture toughness Ji was determined by stretch zone width and 0.2 mm offset line methods.These results indicated that the multiple heat treatments led to the dispersed distribution of ferrite phases in austenite matrix and thus microhardness increased,but impact energy exhibited a decreasing tendency significantly.After long-term aging,the metallographic structure remained almost unchanged,but the size of ferrite phases showed a slight increasing trend because of spinodal decomposition in ferrite phases and G-phase precipitation.In addition,centrifugal casting stainless steels Z3CN20.09M with multiple heat treatments exhibited the higher microhardness,Charpy impact toughness,critical initial fracture toughness J_(IC)(J-integral determined by 0.2 mm offset line method),and J_(SZW)(J-integral determined by stretch zone width method)than those with primary heat treatment,while the specific number of the heat treatment had a low influence on fracture toughness.

CF-8M铸造不锈钢主管道的热老化脆化行为研究

为了评价和预测铸造奥氏体不锈钢(CASS)材料服役期限内的热老化脆化程度,通过对美国的阿贡实验室(ANL)预测模型的研究和分析,以及在400℃下对核级CF-8M主管道材料实施了10 000 h的加速热老化试验,研究了CF-8M材料在不同热老化时间下拉伸性能、冲击性能和微观组织的变化规律,以冲击能作为表征热老化脆化程度的参数,获得了CF-8M材料的热老化脆化预测关系式,并与ANL模型的预测结果进行了对比和分析。结果表明,在加速热老化试验周期内随着热老化时间的增加,CF-8M材料的室温和高温(350℃)0.2%塑性延伸强度变化缓慢,抗拉强度缓慢增加;室温冲击能迅速下降,8 000 h以后冲击能下降趋势接近饱和状态;ANL模型对试验对象在加速老化试验周期内的冲击能预测结果不保守。CF-8M材料加速热老化10 000 h即等效服役30.49 a,其热老化脆化程度接近于热老化饱和状态。

核电管道不锈钢中σ相的退火消除及脆性恢复

在获得σ相析出显著恶化核电主管道铸造奥氏体不锈钢Z3CN20.09M冲击韧性的基础上,采用等温退火、光学显微镜（OM）、扫描电镜（SEM）等研究了消除σ相的热处理工艺及机理。结果表明：850-1000℃等温退火一定时间,σ相可完全消除,此温度范围内发生σ→α转变,但退火温度越低,所需时间越长,反之越短。这是因为温度低,合金元素扩散速率低,相转变缓慢;而温度升高,合金元素扩散速率加快且相转变驱动力提高,σ相转变速率增加,转变时间缩短。综合考虑,950℃等温退火0.5h为最佳热处理工艺参数。经此工艺处理后,时效（含σ相）试样的力学性能得到完全恢复,σ相的脆化影响消除。

高温时效对2507超级双相不锈钢组织和性能的影响

对2507超级双相不锈钢在920℃进行了不同保温时间的时效处理,采用光学显微镜、扫描电镜、X射线衍射仪和能谱仪分析了不同时效状态下的组织演变规律,通过硬度试验和冲击试验研究了时效时间对2507超级双相不锈钢性能的影响。结果表明,920℃时效处理时,大量的σ相沿γ/α及α/α晶界析出,并向铁素体内部长大,其形成机理为铁素体共析转变成σ相和二次奥氏体γ2;在时效5 min内σ相的析出速率最快,随着时效时间的延长,σ相的含量增加,但析出速率逐渐变小;σ相的出现严重降低了超级双相不锈钢的冲击韧性,并且使其硬度明显增加,冲击功和硬度值的大小与σ相析出量有关,当920℃时效30 min时,σ析出相的含量接近于28%,对应双相不锈钢的冲击功和硬度值分别为6 J和376 HB。

固溶温度对2205双相不锈钢焊缝组织与韧性的影响

对采用等离子弧焊(PAW)打底+熔化极氩弧焊(MIG)盖面的2205双相不锈钢平板焊接接头分别进行不同温度的固溶处理,并对热处理后的焊缝部位进行奥氏体和铁素体的两相比例检测,以及显微组织分析及低温冲击韧性检测。结果表明:随固溶温度上升,焊缝铁素体含量逐渐增多;低温冲击韧性值单调升高。当固溶温度低于1000℃时,因σ相的析出,导致焊缝冲击韧性急剧下降。

镍对Cr-Ni-Si系铸造不锈钢性能的影响

研究了Cr Ni Si系耐浓硝酸铸造不锈钢的化学成分、耐蚀性、冲击韧性。试验结果表明 ,含 7%Ni的铁素体 奥氏体双相钢 。

多元合金化双相铸造不锈钢Cr22Ni5Mo4Cu3.5的组织与性能

试验结果表明，所研制的Ｃｒ２２Ｎｉ５Ｍｏ４Ｃｕ３．５钢，经１０５０℃×２ｈ水冷固溶处理后，具有良好的耐均匀腐蚀性能，较好的抗晶间腐蚀与抗点蚀能力。此外，新型钢还具有良好的综合力学性能和工艺性能。

时效处理对S32750双相不锈钢显微组织和力学性能的影响

对S32750双相不锈钢进行了1 070℃×3 min水冷固溶处理,随后分别在300℃、350℃、400℃、500℃、800℃和850℃时效处理3 h,以及在350℃分别时效3 h和7 h。研究了时效工艺对该不锈钢显微组织和力学性能的影响。结果表明,该双相不锈钢在400℃、800℃和850℃时效处理后,有析出相产生,导致钢的冲击韧度降低;在350℃短时间时效处理后,没有明显的析出相产生,随着时效时间的延长,析出相逐渐增多,导致钢的冲击韧度下降。此外,由于S32750双相不锈钢有很强的晶间物析出倾向,应严格控制时效的温度和时间。

固溶处理的冷却对S32750双相不锈钢组织和力学性能的影响

对尺寸为30 mm×30 mm×300 mm的S32750双相不锈钢试样进行了1 070℃保温1.5 h、随后分别炉冷、空冷、5×10~5 Pa氮气冷却、油冷和水冷的固溶处理。检测了试样的显微组织和力学性能。结果表明:在真空炉中炉冷固溶处理的S32750钢中出现了脆性相,影响钢的冲击性能;当以大于空冷的速度冷却后,钢为两相组织,并且随着冷却速度的进一步增大,钢的冲击韧度也缓慢增加,但抗拉强度和屈服强度随冷却速度增大的变化不明显。

耐浓硝酸铸造不锈钢冲击韧性、耐蚀性与断口形貌的关系

设计了用于浓硝酸介质的铸造不锈钢化学成分及其金相组织，研究了钢的冲击韧性、耐蚀性和断口形貌。试验结果表明：含６．９６％Ｎｉ的铁素体－奥氏体双相铸造不锈钢，具有良好的韧性和在浓硝酸介质条件下的耐腐蚀性能。

ZG 1Mn19Ni3Al 铸焊结构低温性能研究

通过化学成分设计和金相组织设计，开发了一种适用于与１６Ｍｎ钢组成铸焊结构的新铸钢ＺＧ１Ｍｎ１９Ｎｉ３Ａｌ。研究了这两种材料组成的焊板在常温、低温（－１９６℃）下的力学性能和冲击断口形貌。试验结果表明，夹杂物和焊接线能量对其低温冲击韧性有着显著的影响。

新型低镍铸造不锈钢DSS-1的组织和磨蚀性

具有双相组织的新型铸造不锈钢DSS 1(0 .5C 2Si 1.5Mn 2 5Cr 5 .5Ni 2Mo 2 .5Cu) ,在含有固相颗粒的高温碱介质中具有良好的耐腐蚀与耐磨蚀性能。此外 ,该钢还具有较好的力学性能和铸造性能。

冲击载荷的变化对铸态复相耐磨钢磨粒磨损特性的影响

在动载三体磨粒磨损条件下 ,试验研究了冲击载荷的变化对铸态复相耐磨钢动载磨粒磨损特性的影响。结果表明 ;在给定的低铬铸铁下试样条件下 ,当冲击载荷较小时 ,铸态复相耐磨钢具有良好的冲击耐磨性。

甲烷-乙烯液体馏份输送泵用0.1C-20Mn-3.5Ni铸钢

－115～－165℃温度下在CH4＋C2H4液体中使用的新型铸钢0．1C－20Mn－3．5Ni的金相组织、断口形貌和力学性能的试验结果表明，γ＋ε构成的双相组织具有良好的低温力学性能。

回复处理对热轧态 Si-Mn 双相钢的低温冲击韧度的影响

研究了热轧态Ｓｉ－Ｍｎ双相钢的低温冲击韧度。试验结果表明热轧态Ｓｉ－Ｍｎ双相钢经４９０℃回复９０ｍｉｎ后，低温冲击韧度显著提高。

氧对00Cr13Ni5Mo熔敷金属组织和韧性的影响

文中研究了MAG焊保护气体氧含量变化对00Cr13Ni5Mo熔敷金属中氧化物夹杂类型、尺寸、数量、分布和残余奥氏体、逆变奥氏体含量以及冲击韧性的影响.结果表明,Si-Mn-O,Si-Mn-Al-O复合氧化物夹杂是导致00Cr13Ni5Mo熔敷金属冲击韧性下降的主要原因.氧化物夹杂对00Cr13Ni5Mo熔敷金属回火过程中产生的逆变奥氏体具有抑制作用,随着氧化物夹杂的增加,逆变奥氏体含量呈减少趋势.

核电用大型铸造泵壳密封面相控阵超声无损检测研究

由于核电用大型铸造泵壳材料CF8双相不锈钢为粗晶组织,超声波检测缺陷的难度大。采用双晶（线阵）探头＋相控阵超声检测方法,对含有埋深25~35 mm准3 mm平底孔的对比试块和实际铸件分别进行了检测。结果表明：平底孔深度的检测最大误差为1.4%,平均误差为0.6%,说明该方法的检测可靠性较高。检测结果可为后续缺陷修复处理提供依据。