粉末冶金双相不锈钢中显微结构的控制

含铬质量百分比11%的粉末冶金不锈钢高温时具有奥氏体/铁素体双相结构,冷却后奥氏体转变为马氏体,而铁素体不转变,控制马氏体与铁素体的比例,可改变材料的性能,因而可根据需要控制生产粉末冶金奥氏体/铁素体双相不锈钢材料的性能,使这些双相钢既具有马氏体材料的高强度和硬度,又具有铁素体钢的抗腐蚀、塑性和焊接性能。调节马氏体与铁素体的比例可以通过改变材料的化学成分实现,一般对于锻造材料来说公式(1)表示了合金元素与Km 值之间的关系,式中正号表示增加铁素体,负号表示增加马氏体,Km 值<8为10 0 %马氏体,Km 值>10为10 0 %铁素体,Km …     

热处理工艺对SAF2205和SAF2304不锈钢晶间腐蚀和孔蚀的影响

双相不锈钢是铁、铬、镍的合金，其室温组织通常为50％的奥氏体和50％的铁素体。双相不锈钢同时具有高强度和耐腐蚀性能，而这是普通单相奥氏体或铁素体不锈钢所不具备的。与奥氏体不锈钢相比，双相不锈钢具有更好的耐局部和应力腐蚀的性能，尤其是在含氯离子的热腐蚀环境中。与铁素体不锈钢相比，双相不锈钢具有更好的成型性能、焊接性能及韧性。正是由于这些优良性能，双相不锈钢被越来越多地应用于海洋环境、石化工业和石油提炼业。尽管双相不锈钢早在20世纪30年代就已被开发出来，但直到高合金双相不锈钢的出现才使其得到广泛应用。这是因为早期的双相不锈钢难于进行热加工并且经焊接和热处理后易发生晶间腐蚀。     

双相钢中相硬化和相软化现象

本文对铁素体加马氏体及奥氏体加马氏体两类双相钢中软相(铁素体、奥氏体)的相硬化及硬相(马氏体)的相软化现象进行了研究。结果表明,软相的硬化及硬相的软化是双相钢中普遍存在的现象。在铁素体—马氏体双相钢中,铁素体的相硬化原因是奥氏体向马氏体转变时由于体积效应致使铁素体产生塑性变形,造成较高的位错密度,从而提高了硬度。马氏体相软化的原因较为复杂:①双相钢中马氏体内孪晶数量较相同含碳量的单相马氏体为少;②马氏体内靠近铁素体处位错密度偏低。在马氏体岛内存在一些不规则形状的铁素体微区,也是造成马氏体实测硬度偏低的一个原因。     

近年来国外不锈钢发展状况

由于ＡＯＤ和ＶＯＤ精炼技术和连铸技术在不锈钢生产上的应用,促进了不锈钢钢种和产量的发展。本文简单介绍了近年来国外不锈钢生产现状,并较详细地以马氏体、铁素体、奥氏体、双相和沉淀硬化型不锈钢五大系列分门别类地举例说明了国外不锈钢钢种的发展状况。     

烧结双相不锈钢的相结构和强韧性

研究了粉末烧结双相不锈钢及其时效后的相结构和强韧性。结果表明,在316L粉末中添加4%(wt)St,用粉末烧结法可以获得奥氏体加18%(Vol)铁素体的双相不锈钢。该双相不锈钢在800℃时效时,沿奥氏体和铁素体界面析出条状σ相,使双相不锈钢的硬度增加,塑性下降。     

国内最新不锈钢图书出版发行《不锈钢概论》

《不锈钢概论》介绍了不锈钢的化学成分、组织结构和性能特点等基础知识；马氏体、铁素体、奥氏体、α＋γ双相和沉淀硬化五大类不锈钢国内外的最新进展、性能特点、生产和应用中的难点以及解决的途径；在不锈钢生产中，如何有效地进行不锈钢的质量控制；在不锈钢的应用中，不锈钢产生腐蚀破坏的原因、常见形态和防止措施，如何正确选择和合理使用不锈钢等内容。     

F201新型不锈钢研制报告

1.铁素体不锈钢发展概况从1886年发现铬具有不锈特性,先后生产出马氏体不锈钢、铁素体不锈钢、奥氏体不锈钢、双相不锈钢四大类,不锈钢的发展已有一百多年的历史了。 F201属于铁素体型不锈钢。铁素体型不锈钢出现比较早,在二十年代初期和马氏体不锈钢相继产生,其次才是奥氏体不锈钢,     

双相不锈钢中的相变:金相和磁性质研究

用金相和不同的无损磁试验对商业低合金双相不锈钢及超级双相不锈钢因热处理和冷加工产生的显微结构过程进行了研究。在双相不锈钢(DSS)和超级双相不锈钢(SDSS)中,亚稳态的铁素体由于热处理可以分解为σ相和二次奥氏体相。这些显微结构的改变显著影响着钢材的机械性能、耐腐蚀性能和磁特性。磁性测量使得破坏性实验中获取的谐频和机械性能存在定量关系。在低合金双相不锈钢中,当低含量的Ni被N和Mn取代后,可能导致奥氏体相的不稳定性,奥氏体相容易转变为亚稳态的马氏体相,而SDSS奥氏体会更加稳定。通过室温冷轧(10%～85%压下率)的方法进行固溶退火材料的塑性变形研究,2101材料仅考察了轧制条件,而冷轧2507样本还进行了热处理。冷轧样品用光学显微镜(OM)、扫描电子显微镜(SEM)、X-射线衍射(XRD)和磁试验进行了研究。还对双相不锈钢样品进行了三种不同的磁试验,以确定其磁性能。结果表明冷轧对晶粒的大小和形状有一定影响,磁测试结果还显示2101样品中存在马氏体。     

某些沉淀硬化不锈钢的金属学问题(续)

1.马氏体相变为了保证本类型钢的特点,应严格控制Ms温度,因而合金元素作用很关键。譬如Cr、Mo和Si对奥氏体有双重作用。笔者们参考了Eichelmann及Monkman计算奥氏体不锈钢公式(15)。Yeo对Fe-22.5%Ni合金中各元素对Ms温度影响数据,结合实验室工作,得出PH15-7Mo半奥氏体沉淀硬化不锈钢,在固溶状态下Ms温度的关系式(11)     

焊后热处理对沉淀硬化不锈钢15-7Mo焊接接头组织性能的影响

研究了4种不同的焊后热处理工艺对半奥氏体沉淀硬化不锈钢15-7Mo焊接接头组织性能的影响.结果表明:焊接接头不进行热处理或时效热处理的焊接系数低于0.7,焊接接头进行调整+时效热处理后的焊接系数可达0.9,而对焊接接头进行固溶+调整+时效热处理后焊接系数接近1.接头不进行热处理或者是仅时效热处理时,薄弱区为熔合线靠近母材的区域,组织为奥氏体和少量的铁素体.进行调整+时效热处理或固溶+调整+时效热处理时,熔合线靠近母材侧的组织为板条马氏体、少量的铁素体和沉淀析出相,焊缝的组织为板条马氏体和沉淀析出相,薄弱区消失,焊接系数大幅度提高.     

用等离子旋转电极工艺生产高氮钢

为了寻求高效、经济的高氮钢生产工艺,用等离子旋转电极工艺(PREP)生产高氮钢并测试了所生产的几种典型高氮钢的性能。结果表明,氮可显著地提高奥氏体不锈钢1．4301的室温及高温强度;氮可以提高马氏体不锈钢的强度。为保证高氮马氏体不锈钢的淬透性,应根据氮含量适当降低其碳含量或提高铬含量。对于铬含量为17％的马氏体不锈钢1．4122,其碳和氮的总含量不应超过0．65％;当氮含量达到0．24％时,铁素体不锈钢1．4016转变成为马氏体钢,其强度高于碳和氮的总含量与其相当的普通马氏体不锈钢1．4122。     

Formability of stainless steel

The forming behavior of austenitic stainless steels (types 201, 301, and 304) and ferritic stainless steels (types 437, 439, 444, and 468) was investigated. The tensile behavior and the forming-limit diagrams (FLDs) for these grades were determined. The ferritic alloys behave similarly to plain carbon steels and are relatively insensitive to small variations of strain rate and temperature. The formability of the austenitic alloys is influenced greatly by martensitic transformation during straining. The fraction of martensite transformed as a function of strain was found to be very sensitive to temperature, which, in turn, depends on the strain rate at typical testing rates (10⁻³ to 10⁻¹/s). At low rates (when the specimen remains near room temperature), the formability of the austenitic alloys is markedly improved by transformation strengthening. The enhancement of formability is largest on the biaxial side of the FLD, because the fraction martensite transformed was found to depend on the absolute thickness strain, which is maximized in the balanced biaxial strain state.     

Nb对0Cr11铁素体不锈钢组织和性能的影响

 铁素体不锈钢与奥氏体不锈钢相比具有成本低、热膨胀系数低和耐应力腐蚀等优点,所以被广泛应用到汽车排气系统、家用电器和建筑等领域。研究了不同的Nb含量对铁素体不锈钢显微组织和力学性能的影响。研究结果表明：Nb有细化晶粒的作用,随着Nb含量的增加,晶粒的平均尺寸减小;由于合金元素Nb和Ti的加入,形成了TiN、NbC 和 Fe2Nb析出相,其透射电镜观察结果与Thermal calc计算结果一致;材料的抗拉强度和显微硬度随着Nb含量的增加而增加,这是由于Nb的固溶强化和析出强化共同作用的结果。     

Phase and structural transformations in corrosion-resistant steels upon high-pressure torsion and heating

High-pressure torsion (HPT) at a pressure of 6 GPa and room temperature is found to form a nanocrystalline structure in corrosion-resistant austenitic 05Kh15N9D2TAMF and 08Kh18N10T steels and a submicrocrystalline structure in corrosion-resistant ferritic 08Kh18T1 steel and armco iron. X-ray diffraction analysis of both austenitic steels reveals the γ → α and γ→ ?→ α martensitic transformations during HPT at room temperature. After HPT, the strain hardening in the austenitic and ferritic steels is approximately the same and mainly determined by nano- and submicrocrystalline structures, and the role of alloying and phase composition weakens. The thermal stability of the hardening in the austenitic and ferritic steels is almost the same, ～400°C. As a result of HPT, the austenitic 08Kh18N10T and ferritic 08Kh18T1 steels acquire an axial texture with the predominant 〈211〉_γ direction in austenite and the 〈110〉_α and 〈311〉_α directions in martensite and ferrite, respectively. The axial texture is retained in both steels up to a heating temperature of 750°C.     

High temperature creep-fatigue design

Generation IV fission and future fusion reactors envisage development of more efficient high temperature concepts where materials performances are key to their success. This paper examines different types of high temperature creep-fatigue interactions and their implications on design rules for the structural materials retained in both programmes. More precisely, the paper examines current status of design rules for the stainless steel type 316L(N), the conventional Modified 9Cr-1Mo martensitic steel and the low activation Eurofer steel. Results obtained from extensive high temperature creep, fatigue and creep-fatigue tests performed on these materials and their welded joints are presented. These include sequential creep-fatigue and relaxation creep-fatigue tests with hold times in tension, in compression or in both. Effects of larger plastic deformations on fatigue properties are studied through cyclic creep tests or fatigue tests with extended hold time in creep. In most cases, mechanical test results are accompanied with microstructural and fractographic observations. In the case of martensitic steels, the effect of oxidation is examined by performing creep-fatigue tests on identical specimens in vacuum. Results obtained are analyzed and their implications on design allowables and creep-fatigue interaction diagrams are presented. While reasonable confidence is found in predicting creep-fatigue damage through existing code procedures for austenitic stainless steels, effects of cyclic softening and coarsening of microstructure of martensitic steels throughout the fatigue life on materials properties need to be taken into account for more precise damage calculations. In the long-term, development of ferritic/martensitic steels with stable microstructure, such as ODS steels, is proposed.     

近代超级不锈钢的发展

不锈钢的近代发展目标是超级不锈钢－超级奥氏体,超级铁素体,超级复相不锈钢。这些钢可在大范围内解决局部腐蚀问题并在某些用途中可替代钛和镍基合金。     

Evaluation of the elastic modulus of steels

Literature data on the physical properties of steels have been collected and put into a database. The elastic modulus of steels has been analyzed as a function of composition. An overview over former studies is given. The steels have been investigated in three groups, martensitic and ferritic steels, ferritic steels separately, and austenitic steels. For the last two groups, a thermodynamic analysis with Thermo‐Calc has been performed. Regression analysis on the influence of composition on the elastic modulus was then carried out. The results for ferritic steels reveal that cementite has no effect on the elastic modulus, whereas Cr, Mo, Si, Mn, and Cu increase it. The elastic modulus of austenitic steels is reduced by Ni and Mo and increased by N, NbC, TiC, and Cr. Cr₂₃C₆, while statistically significant in the analysis, has no effect on the elastic modulus of austenitic steels. The regression coefficients found can be used to predict the elastic modulus of steels with known composition.     

Microstructural Evolution of Dissimilar Metal Welds Involving Grade 91

Metallurgical and Materials Transactions A - Dissimilar metal weld failures between low alloy Cr-Mo ferritic steels and austenitic stainless steels made with Ni-base filler metals are typically...     

Stress corrosion cracking of stainless steels

The similarities and differences in the stress corrosion cracking response of ferritic and austenitic stainless steels in chloride solutions will be examined. Both classes of materials exhibit a cracking potential: similar transient response (to loading) of the potential in open circuit tests or the current in potentiostatic tests and similar enrichment of chromium and depletion of iron in the film associated with localized corrosion processes. The ferritic steels are more resistant to localized corrosion than are the austenitic steels, which is responsible for the difference in the influence of prior thermal and mechanical history on cracking susceptibility of the two types of steel. Similarities in the fractography of stress corrosion cracks and those produced by brittle delayed failure during cathodic charging of the ferritic steels indicate that hydrogen embrittlement is involved in the failure process.     

Effect of Welding Processes and Consumables on Tensile and Impact Properties of High Strength Quenched and Tempered Steel Joints

Quenched and tempered steels are prone to hydrogen induced cracking in the heat affected zone after welding. The use of austenitic stainless steel consumables to weld the above steel was the only available remedy because of higher solubility for hydrogen in austenitic phase. In this investigation, an attempt was made to determine a suitable consumable to replace expensive austenitic consumables. Two different consumables, namely, austenitie stain less steel and low hydrogen ferritic steel, were used to fabricate the joints by shielded metal are welding （SMAW） and flux cored arc welding （FCAW） processes. The joints fabricated by using low hydrogen ferritic steel consumables showed superior transverse tensile properties, whereas joints fabricated by using austenitic stainless steel consumables exhibited better impact toughness, irrespective of the welding process used. The SMAW joints exhibited superior mechanical and impact properties, irrespective of the consumables used, than their FCAW counterparts.