奥氏体不锈钢的节镍

镍的需求持续大于供应，其价格居高不下，因此镍的最大消费者——不锈钢一直保持在高的价位。本文对节省50％以上镍的途径、节镍不锈钢与SUS304的性能比较作一评述，并对使用节镍不锈钢所引发的问题进行了讨论。节镍钢有下列4种：马氏体不锈钢、铁素体不锈钢、双相不锈钢和Cr—Mn-Ni奥氏体不锈钢。与SUS304相比，节镍不锈钢既有优势又有劣势，不过，它们很有可能替代SUS304。如果不锈钢所要求的性能按需求重新加以考虑，节镍不锈钢的应用有望进一步扩大。     

节镍型奥氏体不锈钢J5裂纹缺陷控制措施

节镍型奥氏体不锈钢是一种以氮代镍来获得稳定奥氏体组织的新钢种,它不仅可以节约镍资源,还可以提高不锈钢的综合性能,其应用范围广泛,主要用于制管、建筑装饰等行业。然而近年来随着应用范围的扩大,对其质量的要求越来越高,铸坯的裂纹问题更显突出,对下游工序的轧制造成了一定影响,同时对质量也产生较严重的影响。文章通过现场实践分析节镍型奥氏体不锈钢的裂纹缺陷原因,并针对性地采取对应措施,满足公司的质量要求和合同要求。     

氮对节镍奥氏体不锈钢高温变形的影响

通过热，力模拟实验机。进行氮含量不同的两种铸坯试样高温拉伸试验。绘制两种试样在不同温度下热变形的应力应变曲线、热变形屈服应力和峰值应力与变形温度的关系曲线、断面收缩率与变形温度的关系曲线；制备金相试样，观察热变形区域的组织变化。试验结果表明：氮含量高的试样容易发生动态回复，当温度高于1200℃，在较小的变形量下就可以通过动态回复使材料软化,降低晶界应力集中,从而获得很好的高温塑性，以便于材料热变形；而氮含量低的试样不容易发生动态回复,当温度高于1050℃,在足够的变形量下才能发生动态再结晶，降低晶界的应力集中。在拉伸试验中表现出相对较差的高温塑性。同时,氮含量高的试样奥氏体晶粒尺寸细小,而氮含量低的试样奥氏体晶粒尺寸较大。     

形变马氏体对304L奥氏体不锈钢显微组织和力学性能的影响

非稳态奥氏体不锈钢在经过变形后,极容易产生形变马氏体组织。本实验分析了固溶处理后304L奥氏体不锈钢在5%～50%轧制变形下马氏体显微组织的变化情况,测量了不同变形量下形变马氏体含量。同时分析不同形变马氏体含量对304L奥氏体不锈钢拉伸力学性能,得到形变马氏体含量对材料拉伸力学性能的影响关系。     

节镍奥氏体不锈钢镜面抛光问题研究

节镍奥氏体不锈钢具有优异的机械性能、一定的耐蚀性能以及较低的成本,在面板、制品和构件等领域应用广泛,但是由于其成分的替代,牺牲了部分耐蚀性,冷轧过程中容易产生腐蚀,导致下游用户难抛光。研究了节镍奥氏体不锈钢生产工艺,取样分析表面缺陷的形成原因,结果表明,通过调整脱脂工艺和退火温度,可以改进和减少表面缺陷,降低表面粗糙度,实现了市场上用户需求的粗糙度要求,满足了镜面抛光用途用户的需求。     

增氮节镍型316奥氏体不锈钢的耐冲蚀性能

采用30 kg真空感应炉熔炼了试验用316钢(/%:0.04C,0.36Si,2.00Mn,0.009P,0.024S,17.74Cr,11.74Ni,2.56Mo)以及采用常压充氮和加入氮化合金熔炼了试验用增氮节镍型316钢(/%:0.04C,0.25Si,1.86Mn,0.012P,0.021S,16.90Cr,8.18Ni,2.64Mo,0.36N),经锻造和轧制成4 mm带材,并经1 100℃1 h固溶处理。借助电子天平、扫描电镜以及自制的砂浆冲蚀磨损试验装置,对试验钢的冲蚀磨损率以及冲蚀磨损后的表面形貌进行了表征与分析。结果表明,两种试验奥氏体不锈钢的磨损率随着冲蚀角度的增大,出现了先上升,后下降,再上升的趋势,在45°与90°出现了两个峰值,当冲蚀角度为90°时,磨损率达到最大值;两种奥氏体不锈钢的冲蚀磨损率随着冲蚀速度和冲蚀时间的增加而增大。在相同的冲蚀条件下,增氮节镍型316奥氏体不锈钢具有较优的耐冲蚀磨损性能和较低的冲蚀磨损率。     

Strain induced martensite formation in stainless steel

The Conversion Electron and X-ray Mössbauer studies of the surface of Type 316 stainless steel at 400 K, 300 K, and 100 K show that both the substitutional and interstitial elements perturb the cubic symmetry at the iron site. The single peak of austenite is a superposition of at least five quadrupole split doublets whose magnitudes and intensities depend on the type and concentration of the impurity elements. However, when the surface of the stainless steel is plastically deformed, a layer of martensite about 5000 Å thick is formed on the austenite base. This layer consists of a mixture of 31 pct martensite with the rest being the original austenite. The magnetic environment of the iron in this martensite is controlled by the concentration of alloying elements, and the distribution of the hyperfine fields is determined by the number of nearest and next nearest neighbor impurity atoms. The magnetic field decreases linearly at first as the number of nearest neighbors increases and then follows a nonlinear trend for a number of nearest neighbors. The temperature dependence of the sublattice magnetization is different for each number of neighbors, and a Curie temperature has been estimated for each site.     

Strain induced martensite formation in stainless steel

The Conversion Electron and X-ray M?ssbauer studies of the surface of Type 316 stainless steel at 400 K, 300 K, and 100 K show that both the substitutional and interstitial elements perturb the cubic symmetry at the iron site. The single peak of austenite is a superposition of at least five quadrupole split doublets whose magnitudes and intensities depend on the type and concentration of the impurity elements. However, when the surface of the stainless steel is plastically deformed, a layer of martensite about 5000 ? thick is formed on the austenite base. This layer consists of a mixture of 31 pct martensite with the rest being the original austenite. The magnetic environment of the iron in this martensite is controlled by the concentration of alloying elements, and the distribution of the hyperfine fields is determined by the number of nearest and next nearest neighbor impurity atoms. The magnetic field decreases linearly at first as the number of nearest neighbors increases and then follows a nonlinear trend for a number of nearest neighbors. The temperature dependence of the sublattice magnetization is different for each number of neighbors, and a Curie temperature has been estimated for each site.     

Chromium depletion and martensite formation at grain boundaries in sensitised austenitic stainless steel

A microstructural and compositional investigation of grain boundary precipitation and martensite formation in sensitised 304 stainless steel has been conducted. Grain boundary depletion of chromium has been quantified in terms of sensitisation time, temperature and boundary type by energy dispersive X-ray microanalysis in the transmission electron microscope. Chromium depleted profiles measured in grain boundary vicinities are sometimes asymmetrical and correlate with the expected profiles generated by growth of semicoherent and incoherent carbide interfaces. The depletion of chromium promotes martensite formation within near-grain boundary regions and this transformation has been directly studied by in situ cold stage microscopy down to − 150°C. Transformation occurs at the most severely depleted boundaries and initiation is favoured at slip band-boundary intersection points and along grain boundaries whose plane orientation matches that of the martensite habit plane. The preferential formation of grain boundary martensite could be an important factor in the stress corrosion and environment sensitive failure of this material.     

The effects of deformation induced martensite on the sensitization of austenitic stainless steels

This paper compares the effects of deformation which induces martensite in austenitic stainless steel with deformation which does not on the sensitization and corrosion susceptibility of these alloys. We show that deformation which induces martensite causes rapid sensitization at temperatures below 600 °C, leads to extensive transgranular corrosion, and can produce rapid healing. The martensite is also an area of extensive carbide precipitation. Deformation alone noticeably increases the kinetics of sensitization only at temperatures where undeformed samples are readily sensitized. Without the presence of martensite, intergranular corrosion is always the predominant corrosion path, rapid healing is not observed, and most carbides precipitate along the grain boundaries.     

超级奥氏体不锈钢的高温变形行为

 为了研究超级奥氏体不锈钢Cr20Ni24Mo6N钢的高温变形行为,采用Gleeble热模拟试验机进行了等温压缩试验,建立了合金的热加工图。结果表明,当变形温度为1 000～1 200 ℃时,Cr20Ni24Mo6N钢的流变曲线表现出典型的“加工硬化＋动态再结晶软化”特点;Cr20Ni24Mo6N钢的热激活能[Q]为678.656 kJ/mol。通过加工图与微观组织综合分析得出,超级奥氏体不锈钢Cr20Ni24Mo6N的合适热加工工艺为,应变速率10 s－1左右,应变量0.5～0.8,变形温度1 150～1 200 ℃。     

Hydrogen induced ductility losses in austenitic stainless steel welds

The effect of hydrogen on the tensile behavior of austenitic stainless steel welds was studied in two AISI 300 series alloys and two nitrogen strengthened alloys. The microstructure of these welds typically contained several percent ferrite in an austenite matrix. Hydrogen was found to reduce the ductility of all welds; however, the severity of ductility loss increased with increasing tendency to deform via a planar slip mode. In materials exhibiting large degrees of slip planarity, 304L and 308L, hydrogen changed the fracture mode from dimple rupture to a mixed mode of ductile and brittle fracture associated with the austenite-ferrite interface. The two alloys, 22-13-5 and 309S, which tend to deform by cross slip mechanisms, showed smaller losses in ductility even though hydrogen assisted the ductile rupture process by aiding void growth and coalescence, without changing the fracture mode. Varying the amount of ferrite from approximately one to 10 pct had no significant effect on performance in hydrogen.     

In situ observations of the formation of martensite in stainless steel

Specimens of stainless steel have been deformed at room temperature, or cooled to below M_s in an HVEM and the formation of martensite observed. The M_s temperature, orientation relationships and habit planes of the martensites formed in specimens thicker than 0.5 μm were found to be identical to those of the bulk material. It has been shown that the ϵ-martensite occurs in regions where appropriately, but usually irregularly, spaced stacking faults are formed, while α-martensite nucleation is associated with dislocation pile-ups on the active slip plane.     

Structure and strength of low-nickel stainless steel alloyed with nitrogen

New X19H6 10AM2 low-nickel steel is characterized by very high strength after hot rolling and quenching from the austenitic region. Accordingly, it performs well in the climatic conditions of the Arctic and Antarctic. The strength is higher than that of traditional X18H10 stainless steel on account of additional solid-solution strengthening. For traditional X18H10 stainless steel alloyed with nitrogen (up to 0.18%), the mechanical properties are lower but still high, while the thermal and mechanical stability of the austenite is lower. Such steel may be used at less challenging temperatures and loads.     

Damping properties of austenitic stainless steels containing strain-induced martensite

Damping properties of two austenitic stainless steel grades, EN 1.4318 and EN 1.4301, were investigated. The test materials were cold rolled to different reductions and damping capacity was measured as a function of temperature with an internal friction method. Microstructures of the test materials were studied by means of X-ray diffraction (XRD) and magnetic measurements. The results showed that damping capacity of the studied materials depended on the amounts of strain-induced ε- and α′-martensite phases. At temperatures around 0 °C, highest damping capacity was achieved with cold rolling reduction of 10 to 15 pct. This behavior is related to the existence of ε-martensite and stacking faults. Internal friction peak due to α′-martensite phase was present at the temperature of 130 °C. Strain aging heat treatment at 200 °C for 20 minutes decreased the damping capacity in the entire studied temperature range.