Weld overlay cladding of high strength low alloy steel with austenitic stainless steel – Structure and properties

The present work aims at studying structure–property correlations in a weld overlay clad high strength low alloy steel with austenitic stainless steel of American Institute for Steel and Iron (AISI) 347 grade. Optical microscopy studies revealed that the interface between the two steels was nearly flat. The base plate had ferrite plus bainite microstructure adjacent to the interface and tempered bainite/martensite structure away from the interface. Grain coarsening and decarburization were observed near the interface. The stainless steel exhibited austenite dendritic structure. Tensile strength, notch-tensile strength and charpy impact energy of the base plate were found to be higher than those for the interface. The microhardness was observed to be maximum on the clad layer near interface. The shear bond strength of the weld overlay-interface was higher than the shear strength of the base plate. Fractography was carried out using scanning electron microscope on tensile, notch-tensile and shear bond test specimens of the interface as well as shear test specimens of the base plate. It revealed the presence of predominantly dimpled rupture. Charpy impact specimens of the interface failed in mixed mode while impact specimens of the base plate failed in ductile mode. Electron probe microanalysis across the bond interface indicated linear change in concentrations of Cr, Ni, Mn, Cu, Mo, Nb and Si between the levels appropriate to the clad layer and base metal.     

316L-Q345R不锈钢复合板性能评价

从微观组织和显微硬度两方面对真空热轧316L-Q345R不锈钢复合板试样性能进行评价。采用电子显微和能谱分析技术,对试样进行微观组织特征观察和成分含量测定,研究相结构及成分变化规律。通过硬度测试仪对复合板界面附近硬度进行测量,研究微观组织与硬度关系。结果表明:热轧后复合板Q345R侧显微组织以铁素体和珠光体为主,316L侧显微组织为单一奥氏体,一部分晶粒呈孪晶状态,Q345R低合金钢和316L不锈钢经过热轧可良好复合,复合界面平直;界面两侧元素存在扩散现象,不锈钢中Cr,Ni元素向低合金钢侧扩散,在界面形成富Cr,Ni薄层,低合金钢中C向不锈钢侧产生少量迁移;在复合界面处的硬度值较大,低合金钢侧远离界面位置复合板硬度与Q345R本身硬度值接近,而从界面到不锈钢侧硬度呈现先下降后上升至稳定的趋势。     

爆炸复合板与轧制复合板界面结构的研究

用透射电镜、扫描电镜和能谱仪等手段对爆炸和轧制复合板界面组织、相结构和成分变化进行了研究。结果发现爆炸复合是由周期性熔化和非熔化构成的波状复合面，它比轧制扩散复合形成的平面积多１／３左右。两种复合方式都有越过界面的元素扩散，爆炸态扩散范围在２５μｍ左右；轧制态Ｆｅ、Ｎｉ、Ｃｒ元素扩散范围在５０μｍ左右，碳元素越过纯Ｎｉ层向不锈钢侧的扩散范围为１００μｍ左右，在此区域发现沿晶界连续析出有Ｍ２３Ｃ６型碳化物。     

Direct metal deposition (DMD) of H13 tool steel on copper alloy substrate: Evaluation of mechanical properties

H13 tool steel powder was clad on copper alloy substrate both directly and using 41C stainless steel (high Ni steel) powder as a buffer layer by direct metal deposition (DMD). Cu-steel bimetallic die casting and injection molding tools are of high interest for reduction of cycle time by efficient heat extraction due to high thermal conductivity of copper. The mechanical properties of these bimetallic structures were investigated in terms of bond strength, impact energy and fracture toughness. The bond interfaces of these claddings showed porous and crack free transition regions. The bond strength was higher in the directly clad H13 tool steel compared to the H13 tool steel clad with 41C stainless steel as buffer layer. The fracture morphology in tensile test specimens showed ductile dimple fracture. Presence of necking just below the interface depicted the softening of substrate in heat affected zone (HAZ) during cladding. The Charpy impact energy is little higher in the 41C stainless steel buffered specimens compared to the directly clad H13 tool steel specimens but the fracture toughness results showed reduction of fracture toughness in the 41C stainless steel buffered specimens due to the low strength in the tensile test. However the fracture toughness value was in the ductile region for both deposits.     

Effect of heat treatment on interface microstructure and bond strength in explosively welded Ti/304L stainless steel clad

Abstract

The effects of heat treatment on the microstructure and bond strength at the interface of explosively welded titanium/304L stainless steel clad have been investigated. The microstructure of the clad interface were examined using optical and scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) techniques. At 700°C, the formation of intermetallic phases σ and Fe₂Ti besides β-Ti were confirmed, while in samples, heat treated at 800°C and 900°C, other intermetallic phases such as λ and FeTi, NiTi, NiTi₂ phases were detected in addition to σ and Fe₂Ti phases. The shear test results show that the shear strengths of heat treated samples are overall significantly lower than that of stress relieved samples. This could be due to the formation of brittle intermetallic phases at the interface. Despite of formation of the intermetallic phase at 700°C, the shear strength of the sample is still more than the minimum standard amount of 137·9 MPa. It is also observed that the higher the heat treatment temperature, the lower the interface shear strength, which can be explained by the fact that the volume fraction of intermetallics increases with increasing temperature. The shear strength values of heat treated samples are lower than those of diffusion bonded clads. This could be attributed to the fact that the total widths of intermetallic layers achieved in heat treated samples are larger than those of for diffusion bonded ones.     

Finite element analysis of the effect of welding heat input and layer number on residual stress in repair welds for a stainless steel clad plate

Stainless steel clad plate is widely used in petroleum, chemical and medicine industries due to its good corrosion resistance and high strength. But cracks are often formed in clad layer during the manufacture or service, which are often repaired by repair welding. In order to ensure the structure integrity, the effects of residual stress need to be considered. The objective of this paper is to estimate the residual stress and deformation in the repair weld of a stainless steel clad plate by finite element method. The effects of heat input and welding layer number on residual stresses and deformation have been studied. The results show that large residual stresses have been generated in the repair weld. The heat input and layer number have great effects on residual stress distribution. With the heat input and welding layer number increasing, the residual stresses are decreased. Using multiple-layer welding and higher heat input can be useful to decrease the residual stress, which provides a reference for optimizing the repair welding technology of this stainless steel clad plate.     

Interfacial precipitation in hot isostatically pressed diffusion bonds of 17-4 PH stainless steel

Abstract

The embrittlement of hot isostatically pressed (hipped) diffusion bonds manufactured from 17-4 PH stainless steel has been investigated by Auger electron spectroscopy (AES) of in situ fracture specimens. Depth profiling by AES has revealed copper precipitation at the interface of the diffusion bond. This precipitation, up to a few monolayers in thickness, occurs during the ramp up to temperature and pressure of the hot isostatic pressing (hipping) cycle and is not readily removed by subsequent heat treatment. This effect is explained in terms of the metallurgical characteristics of copper within the steel. Results suggest that the extent of the precipitation decreases with increasing process temperature. In the case of PH 13-8 Mo stainless steel, where the precipitation hardening phase is NiAl, the interface is weakened by sulphur segregation and the formation of oxide particles.     

镍-不锈钢复合板轧制过程中界面的结合机制

采用轧制终止取样法对镍-不锈钢热轧复合板轧制过程中的界面成分、界面组织以及界面处的氧化物进行了表征,研究了轧制过程中界面的结合机制并根据热力学原理解释了高温下选择性内氧化的机理.将复合板坯加热至1200℃,保温120 min后进行轧制,分别在轧制3、5、7道次后中断轧制快速水冷,随后进行取样观察.结果 表明,轧制3道次...     

Microstructural control by secondary processing of strip cast low carbon steel

Abstract

The secondary processing of low carbon steel strip produced by twin roll casting was investigated to examine its effect on microstructural development and mechanical properties. The as cast microstructure is predominantly acicular ferrite with regions of bainitepearlite and polygonal ferrite. Deformation at temperatures below Ar1 produces a heterogeneous microstructure with regions of moderately deformed acicular ferrite adjacent to highly deformed regions containing shear bands. Cold rolled and warm rolled steels show similar behaviour to conventional hot band in that dynamic recovery during warm rolling results in sluggish recrystallisation and produces a coarse final grain size. However, the initial as cast microstructure recrystallises at a slower rate than conventional hot band and produces a weaker recrystallisation texture. This can be attributed to the heterogeneous microstructure of the as cast strip such that, after rolling, nucleation occurs within shear bands and more ill defined sites, which results in nucleation of randomly oriented grains thereby producing a weak final texture. It was found that austenitising the as cast strip followed by rolling in the vicinity of Ar3 produces a uniform distribution of equiaxed, ultrafine ferrite UFF grains throughout the thickness of the strip. The production of UFF by twin roll casting and subsequent rolling represents a simple processing route for the production of fine grained low carbon sheet steel products.     

Vacuum Hot Rolling Preparation of a Stainless Steel Clad Plate and Its Numerical Simulation

Strength of Materials - Vacuum hot rolling was used to prepare stainless steel clad plate samples. As a key process parameter, force analysis of the compound deformation process was conducted for...     

Microstructure evolution and impact toughness of sandwich structured composite prepared by centrifugal casting and hot rolling process

A sandwich structured composite containing a hypereutectic high chromium cast iron (HCCI) core and low carbon steel (LCS) claddings was successfully fabricated by centrifugal casting and hot rolling process, and then a series of heat treatments were employed to optimise the performance of the composites. The evolution of microstructures and microhardness of as cast, hot rolled and heat treated specimens were investigated. The results showed that the interfaces combined well with a good metallurgical bonding before hot rolling. Etuectic carbides are crushed, refined obviously and become more isolated. There is not obvious break between primary carbides. The hardness of hot rolled HCCI is 62 HRC, which is higher than that of as cast HCCI (56 HRC) due to the broken and diffusely distributed carbides. The hardness of hot rolled HCCI can reach up to 69 HRC or above after air quenching. The average impact toughness of LCS/HCCI composite could reach up to 10·1 J cm^?2, which was almost three times that of the as cast sample. Glide lamellas were observed among the interface due to the stagger of LCS and HCCI.     

Effect of thermal ageing on microstructure,mechanical properties,and fracture behaviour of 50 % cold rolled duplex stainless steel (alloy 2507)

The paper deals with cold rolling and ageing on microstructure and mechanical properties of 2507 duplex stainless steel. Microstructure depicts acicular/Widmanstätten austenite and δ-ferrite with dissimilar volume fraction (∼0.55 for ferrite and ∼0.45 for austenite). Cold rolling and ageing at 950 °C, 1000 °C and 1050 °C result in equiaxed austenite for samples solution treated at 1040 °C and elongated at 1300 °C. By lowering ageing temperature from 1050 °C to 950 °C, structure becomes finer from ∼20 μm to <10 μm grain size. The sigma (σ) phase appears after ageing at 950 °C. Micro-hardness reveals maximum hardness for the hot rolled, solutionized (1040 °C) water quenched, and cold rolled (50 %) sample (380 HV_δF 100 and 430 HV_γ 100), whereas the tensile results reveal the hot rolled, solution treated (1300 °C, 1040 °C), cold rolled and aged at 950 °C samples show higher strength (yield strength=625 MPa, 567 MPa and ultimate tensile strength=892 MPa, 826 MPa) and lower ductility (23 %, 32 %) due to the σ-phase. The solution treated (1040 °C), cold rolled, aged at 1050 °C sample exhibits attractive strength and ductility combination (∼30 GPa %). Fractography supports the tensile results.     

热轧后退火对超纯Cr17钢成形性能的影响

为了揭示热轧后退火对超纯Cr17铁素体不锈钢冷轧退火板成形性能的影响,以1种铌、钛双稳定化超纯Cr17铁素体不锈钢的热轧板和热轧退火板为实验材料,分别进行相同的冷轧及退火处理,对其组织、织构演变和成形性能进行了对比研究.研究结果表明,热轧后退火对冷轧退火板的组织、织构和成形性能影响很大.与不退火相比,退火能够使冷轧退火...     

不同压缩比2205双相不锈钢轧制复合板组织及性能对比研究

研究了不同压缩比2205双相不锈钢轧制复合板界面和复层的组织和性能。结果表明,压缩比为4和6的复合板复层均由奥氏体和铁素体组成,奥氏体和铁素体相界呈锯齿状;基层和复层界面处碳钢侧为单一铁素体,不锈钢侧可见一条不连续黑色条带;相比压缩比为4的复合板,压缩比为6的复合板复层铁素体含量更高,奥氏体γ相尺寸更小更长,耐腐蚀性更好,但强度无明显差异;基层和复层界面更平整,结合力更低。     

热轧后退火对超纯铁素体不锈钢表面皱折的影响机理

以一种铌、钛双稳定化超纯Cr17铁素体不锈钢的热轧板和热轧退火板为初始材料,分别经相同的冷轧及退火处理,从显微组织演变、微织构演变的角度研究了热轧后退火对成品板表面皱折的影响机理.研究结果表明,与热轧后不退火相比,热轧后退火可使冷轧退火板的最大皱折高度和平均皱折高度分别降低37.0%、35.6%.热轧后退火有利于热轧板...     

Vacuum hot roll bonding of titanium alloy and stainless steel using nickel interlayer

Abstract

Vacuum hot roll bonding of titanium alloy and stainless steel using a nickel interlayer was investigated. No obvious reaction or diffusion layer occurs at the interface between stainless steel and nickel. The interface between titanium alloy and nickel consists of an occludent layer and diffusion layers, and there are the intermetallic compounds (TiNi₃, TiNi, Ti₂Ni and their mixtures) in the layers. The total thickness of intermetallic layers at the interface between titanium alloy and nickel increases with the bonding temperature, and the tensile strength of roll bonded joints decreases with the bonding temperature. The maximum tensile strength of 440·1 MPa was obtained at the bonding temperature of 760°C, the reduction of 20% and the rolling speed of 38 mm s^–1.     

扫描电镜在热轧板表面氧化铁皮分析中的应用

用扫描电镜(SEM)及能谱分析(EDS)、X射线衍射(XRD)等方法对精轧前采用及未采用除鳞系统(FSB)的两种工艺下的热轧板表面的氧化铁皮作了对比分析。结果表明，两种工艺下的热轧板表面氧化铁皮结构均由三种铁的氧化物FeO、Fe3O4和Fe2O3构成；在靠近基板到表层的氧化铁皮中三种铁的氧化物按FeO，Fe3O4和Fe2O3顺序逐渐增多，且内层的结构成分以氧化亚铁为主。FeO含量较少的氧化铁皮层与钢板基体结合比较疏松，容易去除。精轧前采用FSB除鳞系统工艺并不能显著缓解热轧板表面的氧化铁皮缺陷问题，通过对热轧生产工艺的优化调整可解决热轧氧化铁皮去除难的问题。     

轧制工艺对316L不锈钢组织和耐蚀性能的影响

为探索改善不锈钢耐腐蚀性能的途径,对316L不锈钢施加相同变形量的同步轧制和异步轧制,利用X射线衍射、透射电镜观察、电化学测量和扫描电镜表面观察研究了轧制工艺对钢的显微组织和腐蚀性能的影响.结果表明,经过异步轧制后显微组织中出现大量孪晶界,优化了晶界结构,在酸性介质中的晶间腐蚀敏感性明显减轻;而经过同步轧制后,样品呈现出高位错密度的显微组织,在酸性介质中的耐腐蚀性能降低.异步轧制后耐蚀性能得到改善是由于大量孪晶界的形成优化了晶界结构.     

Research on explosive welding of aluminum alloy to steel with dovetail grooves

In order to explore a new method for the explosive welding of aluminum alloy to steel, a 5083 aluminum alloy plate and a Q345 steel plate with dovetail grooves were respectively employed as the flyer and base plates. The parameters adopted in the explosive welding experiment were close to the lower limit of weldable window of 5083 aluminum alloy to Q345 steel. The bonding properties of 5083/Q345 clad plate were studied through mechanical performance tests and microstructure observations. The results showed that the aluminum alloy and steel plates were welded under the actions of metallurgical bonding and meshing of dovetail grooves. The tensile shear strength of 5083/Q345 clad plate met the requirements of the bonding strength of Al/Fe clad plate. The interfaces between aluminum alloy and the upper and lower surfaces of dovetail grooves were mainly welded through direct bonding, and discontinuous molten zone emerged in the local region; while the interface between aluminum alloy and the inclined surface of dovetail grooves was bonded by continuous molten layer. The brittle intermetallic compounds FeAl₂ and Al₅Fe₂ were generated at the bonding interfaces of 5083/Q345 clad plate. The fracture surface of the tensile specimen exhibited ductile and quasi-cleavage fractures.     

铜/不锈钢加筋板爆炸焊接工艺实验

随着我国核电新能源的发展,新型材料的需求也在不断的增加,铜/不锈钢加筋板是其中一种,具有重要工程应用价值,目前无法用常规的冷、热加工工艺进行生产。通过爆炸焊接法,采用一种新的"凸台式"装药形式,在支撑模板设计及其填充方案、工装等方面进行了深入研究,优化了焊接参数,并对成品的结合界面进行了剪切强度测试、金相观测、电镜扫描和显微硬度测试。检测结果表明:铜/不锈钢焊接结合面为波状冶金结合界面,在波峰两侧存在含金属氧化物的"冠状"漩涡,结合界面附近的晶粒被拉长变细,显微硬度显著升高,界面结合强度超过铜材。