Influence of grain refining elements on mechanical properties of AISI 430 ferritic stainless steel weldments – Taguchi approach

The effect of grain refining elements such as copper, titanium and aluminum on transverse tensile strength, ductility, impact toughness, microhardness and austenite content of AISI 430 ferritic stainless steel welds through Gas Tungsten Arc Welding (GTAW) process in as-welded condition was studied. Taguchi method was used to optimize the weight percentage of copper, titanium and aluminum for maximizing the mechanical properties and austenite content in the weld region of ferritic stainless steel welds. Based on Taguchi orthogonal array the regression equations were developed for predicting the mechanical properties of ferritic stainless steel welds within the range of grain refining elements. The observed mechanical properties and austenite content have been correlated with microstructure and fracture features.     

Tensile and Impact Properties of Shielded Metal Arc Welded AISI 409M Ferritic Stainless Steel Joints

The present study is concerned with the effect of filler metals such as austenitic stainless steel, ferritic stainless steel and duplex stainless steel on tensile and impact properties of the ferritic stainless steel conforming to AISI 409M grade. Rolled plates of 4 mm thickness were used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure and fracture surface morphology of the joints fabricated by austenitic stainless steel, ferritic stainless steel and duplex stainless steel filler metals were evaluated and the results were reported. From this investigation, it is found that the joints fabricated by duplex stainless steel filler metal showed higher tensile strength and hardness compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Joints fabricated by austenitic stainless steel filler metal exhibited higher ductility and impact toughness compared with the joints fabricated by ferritic stainless steel and duplex stainless steel filler metals.     

Structure and properties of ion-nitrided stainless steels

The structure and properties of ion-nitrided layers on several stainless steels, 410 martensitic stainless steel, 430 ferritic stainless steel and 321 austenitic stainless steel, has been studied under varying process conditions with microhardness-depth correlations, optical microscopy and transmission electron microscopy. The process variables studied include time (2 to 10 h) and temperature (400 to 600° C). The highest case depth values and hardness levels were observed in martensitic stainless steels. The lowest case depths were observed in austenitic stainless steel. In general, the behaviour of matensitic and ferritic stainless steels were similar. All three steels showed increasing case depths and decreasing surface hardnesses with increasing ion-nitriding temperatures and times. Nitriding depth was found to be parabolic with ion nitriding time in all three steels at all ion-nitriding temperatures investigated, the nitriding reaction being faster in martensitic stainless steel than the others. Electron microscopy showed that almost no structural difference arises in the core of ferritic and austenitic stainless steels whereas recrystallization of the martensitic structure was observed in the core of martensitic steel following ion nitriding. Electron microscopy results also showed that ion nitriding produces platelets or disc-shaped precipitates on {001} matrix planes, coherent with the matrix. These platelets showed a striated morphology which is thought to be the result of the elastic strain in the matrix.     

Microstructure and Fracture Morphology in the Welding Zone of Cr18Mo2 Ferritic Stainless Steel

Microstructure, precipitates and fracture morphology in the weld metal and the heat-affected zone (HAZ) of Cr18Mo2 ferritic stainless steel have been studied by means of metalloscope, SEM,TEM and X-ray diffractometer. Experimental results indicate that crystalline grain coarsening in HAZ is one of the reason resulting in the embrittlement fracture in the welding zone of the ferritic stainless steel. Some precipitates (TiC, TiN and Cr2N) in the steel promote production and development of the brittle cracks. In practical applications. the welding heat input should be as small as possible to prevent embrittlement caused by HAZ grain coarsening.     

Microdeformation Behaviour of a Ferritic-Austenitic Duplex Stainless Steel

Microdeformation of ferritic and austeniticgrains in a ferritic-austenitic duplex stainless steelhave been observed in-situ by SEM with photoetch.The plastic deformation behaviour of austeniticgrains are similar to ferritic grains for hydrogenuncharged specimens,it follows Mileiko'sstrain-equal model.But it will be changed when thespecimens are hydrogen charged.     

超级铁素体不锈钢表面超疏水结构的制备及其耐腐蚀性能

将多巴胺的自发聚合反应与低表面能物质ODA和PFDT结合,在超级铁素体不锈钢表面制备了均匀致密的超疏水薄膜.用水雾凝聚实验、扫描电子显微镜(SEM)和X射线能谱分析(EDS)等手段表征了涂层修饰前后的润湿性、表面形貌以及化学结构,并使用三电极体系电化学工作站测试了超级铁素体不锈钢表面修饰前后涂层的阻抗谱和极化曲线.结果...     

低铬铁素体不锈钢晶间腐蚀敏感性的测试方法及性能

研究了爆炸复合板复层06Cr13R低铬铁素体不锈钢的晶间腐蚀敏感性测试方法及性能。结果表明：电化学动电位扫描法（双环EPR法）适合用于爆炸复合板复层06Cr13R低铬铁素体不锈钢晶间腐蚀敏感性的检测,其试验结果与草酸电解侵蚀法对应较好;06Cr13R低铬铁素体不锈钢的晶间腐蚀敏感性与铬-镍奥氏体不锈钢不同,其晶间腐蚀敏感性出现在910℃正火处理后,甚至强制吹风急冷条件下也无法避免,而经过800℃退火处理后,其晶间腐蚀敏感性可减轻。     

1.4003铁素体不锈钢与Q235-C钢焊接接头的组织和力学性能

采用室温拉伸、不同温度冲击、硬度及金相检验等分析方法对用熔化极混合气体保护焊焊接的1.4003铁素体不锈钢与Q235-C钢焊接接头的显微组织和性能进行了研究.试验结果表明:该焊接接头的抗拉强度与母材相当,焊缝的冲击性能略低于母材,1.4003铁素体不锈钢的热影响区(HAZ)冲击性能较差,焊缝为奥氏体+铁素体双相组织;Q235-C钢的熔合区出现明显界限,1.4003铁素体不锈钢焊接热影响区为晶粒粗大的单一铁素体组织.     

含Cu抗菌不锈钢的工艺与耐蚀性能

与普通0Cr17铁素体不锈钢和0Cr18Ni9奥氏体不锈钢相比，含铜铁素体和奥氏体抗菌不锈钢均具有良好的冷热加工性能和焊接性能．通过提高浇铸温度，抗菌不锈钢能保持良好的铸造性能．奥氏体抗菌不锈钢的抗应力腐蚀性能比0Cr18Ni9不锈钢有很大的提高，而铁素体抗菌不锈钢比0Cr17有明显的下降．与相应的普通不锈钢相比，两种类型抗菌不锈钢的耐点蚀性能均略有下降．     

FRACTOGRAPHIC ANALYSIS IN THE UNDERSTANDING OF CORROSION FATIGUE MECHANISMS

Fractographic analyses have been used to explain the cyclic crack growth behaviour of A533-B, Ducol W30, a C-Mn steel and type 304 stainless steel in simulated light water reactor environments at ambient temperature. Fractographic observations have offered an explanation for anomalous crack growth behaviour and have also indicated where micro structural or environmental variables dominate in producing certain fracture modes and crack growth rates. An understanding of the operative corrosion fatigue mechanisms has been formulated through these fractographic analyses. Environmental crack growth in the ferritic steels has been described by a model involving both anodic dissolution and hydrogen embrittlement. Conditions where only one of these mechanisms would dominate have been identified and limits to their effect postulated. A crystallographic mode of failure observed in the austenitic type 304 stainless steel has also been explained by a selective dissolution process.     

Metallurgical changes and mechanical behaviour during high temperature aging of welds between Alloy 800 and 316LN austenitic stainless steel

Abstract

In the use of ferritic to austenitic stainless steel transition joints for power plant applications, the difference in coefficients of thermal expansion constitutes a serious problem. One way to mitigate this is to use a trimetallic configuration by interposing a material with a coefficient of thermal expansion intermediate between the ferritic and austenitic steels. Modified 9Cr - 1Mo steel has been joined to 316LN austenitic stainless steel using Alloy 800 as an intermediate piece. In the work herein reported, welds between Alloy 800 and 316LN have been produced using Inconel 182 filler material. These have been subjected to high temperature exposure for up to 5000 h at 625 ° C. Results have shown that up to 500 h of aging the structure and mechanical properties remain unaffected. On treatment for 2000 and 5000 h, however, there is a noticeable increase in hardness and reduction in toughness. These have been found to be caused by precipitation of Ni₃Ti and carbide phases including NbC and M₂₃C₆.     

Effects of deformation on hydrogen degradation in a duplex stainless steel

Hydrogen embrittlement of annealed, 20 and 40% cold worked 2205 duplex stainless steels has been evaluated using electrochemical permeation measurement, hydrogen microprint technique and tensile test in this study. Due to hydrogen transport in 2205 duplex stainless steel is mainly lattice diffusion in ferritic phase, more hydrogen distribution, higher permeation rate and effective diffusion in ferritic phase were detected. Hydrogen trapping and mechanical property effects were studied for cold worked specimens. Fractographic investigation revealed that hydrogen absorption promoted transgranular fracture in cold worked specimens. These results exhibits that the cold worked duplex stainless steels are more susceptible to hydrogen embrittlement.     

Cleavage fracture in 26Cr–1Mo ferritic stainless steel

Abstract

Cleavage fracture of a 26Cr–1Mo ferritic stainless steel has been studied using fatigue precracked specimens. The parameters determined were fracture toughness, cleavage fracture strength, and effective surface energy of ferrite. The results have been compared with earlier results on notched specimens.

MST/185     

活性剂对铁素体不锈钢A-TIG接头熔深及组织性能研究

目的 选用430铁素体不锈钢作为研究对象,对比研究添加SiO2、TiO2、Cr2O3和未添加活性剂对A-TIG焊接接头显微组织和力学性能的影响。方法 采用3种活性剂涂覆在430铁素体不锈钢上进行A-TIG试验,分析活性剂对接头熔深、组织、性能、元素含量的影响情况。结果 同一焊接工艺参数下,活性剂的加入均能提高焊缝的熔深和深宽比,减少熔宽;其中,SiO2为活性剂时获得了最佳的焊缝几何形貌。同时,对比常规TIG焊接(未添加活性剂)接头的显微组织及力学性能可知,活性剂的加入并未改变焊接接头的显微组织且无新相的生成;活性剂的添加能够细化接头组织,从而使得接头硬度有所提高。结论 活性剂的加入能够显著增加铁素体不锈钢TIG焊缝熔深,改善接头组织,提高接头硬度。     

A new ferritic stainless steel with improved thermo-mechanical fatigue resistance for exhaust parts

Abstract

Over the past few years, car manufacturers have been considering ever higher service temperatures for the engine in order to comply with the constraints of depollution standards. The requirements in terms of exhaust gas temperature could easily reach and overtake the limits of common stainless steel grades used for such applications in the coming years.

A new ferritic stainless steel – named K44X – with increased high temperature resistance has therefore been developed to withstand service temperature up to 1000 °C. K44X belongs to EN 1.4521 and AISI 444 classifications and is composed of approximately 19% Cr, 2%Mo and 0.6% Nb. This specific composition leads to better mechanical properties, higher creep and fatigue resistance than EN 1.4509, while keeping comparable weldability and formability. Its coefficient of thermal expansion is lower in comparison to austenitic stainless steel grades and its resistance to cyclic oxidation is improved significantly.

High-temperature properties (mechanical properties, creep, cyclic oxidation resistance, and high cycle fatigue) of K44X are presented in this paper and compared with common ferritic and austenitic stainless steels used in the hot end of exhaust lines. A thermal fatigue test – designed to reproduce exhaust manifold service conditions – has also been carried out with the highest temperatures of the cycle in the range of 850–1000 °C. The results of these thermal fatigue tests were compared with the above-mentioned stainless steels. A thermal fatigue damage criterion was then identified based on these experimental results and using a cyclic behaviour law obtained from isothermal low cycle fatigue tests.     

Heat-affected zone oxidation properties in AISI 430 ferritic stainless steel welds

High temperature corrosion of ferritic stainless steel weldments has not previously been studied. This paper is an attempt to standardize a method for assessing the oxidation properties of the heat-affected zone (HAZ) of ferritic stainless steel welds. A weld thermal cycles simulator was used to model HAZ representative microstructure specimens, and the oxidation kinetics of both the base metal and selected HAZ specimens then studied by oxidizing the specimens at 950°C and 1 atmosphere in purified oxygen using a thermogravimetric rig. The oxidation mechanisms of both base metal and HAZ from representative specimens of the AISI 430 steel were studied using optical microscopy, scanning electron microscopy and energy dispersive X-ray analysis. The oxidation kinetics and morphology of both HAZ and base metal samples are reported.     

碳氮含量对含钒铁素体不锈钢高温性能的影响

为研究碳氮含量对其高温热拉伸及热压缩性能的影响,以含钒铁素体不锈钢为实验材料,采用Gleeble3500试验机进行热模拟实验,并对热压缩后试样的显微组织进行了金相观察和SEM检测,对析出相采用TEM分析.结果表明:钒元素的加入在一定程度上提高了材料的高温性能;在实验设计的成分范围内,较高的氮含量和低的碳含量组合能在保证材料韧塑性的前提下提高强度;热压后缓冷至室温,材料中将出现部分马氏体组织.     

Methods to overcome embrittlement problem in 9Cr–1Mo ferritic steel and its weldment

This article presents the issues that need to be addressed in ferritic steel, for their use in nuclear core, namely, the embrittlement and type IV cracking of weldment. It has been established that the ferritic steels possess a significantly higher resistance to radiation damage as compared to the present generation austenitic stainless steels and the creep behavior is satisfactory for applications up to 873 K. The major challenges that need to be addressed are the poor creep resistance of the weld joints and embrittlement of ferritic steels. This article describes the efforts taken at IGCAR to overcome the embrittlement problem by impurity control, grain boundary engineering or design of suitable thermomechanical treatments in a 9Cr–1Mo ferritic steel.     

Using strain rate sensitivity measurements to determine phase relations in A430 stainless steel

Precision strain rate sensitivity measurements have been used to determine the solid solution component of interstitials in ferritic stainless steel. The measurements are based on activation volume of dislocation-solute interaction. Under an instantaneous strain rate change, a load drop occurs which is inversely proportional to the activation volume. By correlating the measured response with heat treatments a pseudo-binary Nb(C,N) solvus was determined. Such a phase diagram for a specific stainless steel alloy is useful for delineating hot-working conditions. The technique was also able to detect the presence of fine Guinier-Preston zone type of precipitates that formed during quenching and were aligned with the {001} planes of the matrix.     

MECHANISMS AND FACTORS THAT INFLUENCE POSTWELD INTERGRANULAR UNDERCLAD CRACKING

Abstract— Forged components of ferritic steel can be protected by a welded austenitic stainless steel clad. Intergranular cracking can take place in the ferritic phase close to the ferritic austenitic interface. After developing a technique for fabrication of these cracks, the formation conditions are studied. Auger electron spectroscopy investigations of specimens containing a real crack opened inside the vacuum chamber are used for interpretation. Sulphur segregations embrittle the grain boundaries which are cracked by residual and thermal stresses during the postweld heat treatment.