Microstructure and Mechanical Properties of B-Bearing Austenitic Stainless Steel Fabricated by Laser Metal Deposition In-Situ Alloying

In the field repair application of laser metal deposition(LMD),the kinds of powder materials that can be used are limited,while the equipment components are made of various materials.Hence many components have to be repaired with heterogeneous materials.However,it is difficult to match the mechanical properties between the repaired layer and the substrate due to the diff erent materials.Based on the high flexibility of raw materials and processes in LMD,an in-situ alloying method is proposed herein for tailoring the mechanical properties of LMDed alloy.Using diff erent mixing ratios of Fe314 and 316 L stainless steel powders as the control parameter,the microstructure and mechanical properties of B-bearing austenitic stainless steel fabricated by LMD in-situ alloying with diff erent proportions of Fe314 and 316 L particles were studied.With the increase in the concentration of 316 L steel,the volume fraction of the eutectic phase in deposited B-bearing austenitic stainless steel reduced,the size of the austenite dendrite increased,the yield strength and ultimate tensile strength decreased monotonically,while the elongation increased monotonically.Moreover,the fracture mode changed from quasi-cleavage fracture to ductile fracture.By adding 316 L powder,the yield strength,tensile strength,and elongation of deposited B-bearing austenitic stainless steel could be adjusted within the range of 712 MPa–257 MPa,1325 MPa–509 MPa,and 8.7%–59.3%,respectively.Therefore,this work provides a new method and idea for solving the performance matching problem of equipment components in the field repair.

Microstructure and mechanical properties of similar and dissimilar metal gas tungsten constricted arc welds:Maraging steel to 13-8 Mo stainless steel

Maraging steel (250) and 13-8 Mo stainless steel plates were joined by gas tungsten constricted arc welding(GTCAW) process in similar and dissimilar metal combinations using 13-8 Mo stainless steel filler wire. The similar and dissimilar metal welds made in solutionized condition were subjected to standard post weld hardening treatments direct ageing at 485 ℃, soaking for 31/2 hours followed by air cooling(ageing treatment of maraging steel) and direct ageing at 510 ℃, soaking for 4 h followed by air cooling(ageing treatment of 13-8 Mo stainless steel). The joint characterization studies include microstructure examination, microhardness survey across the weldments and transverse weld tensile test.Similar and dissimilar metal weldments responded to both the post weld ageing treatment. After post weld aging, increase in yield strength, UTS and slight reduction in % elongation of similar and dissimilar metal were observed. The observed tensile properties were correlated with microstructure and hardness distribution across the welds.

Microstructures and mechanical properties of laser-welded TiNi shape memory alloy and stainless steel wires

The Nd ： YAG laser welding was used to join the TiNi shape memory alloy and AISI304 stainless steel wires. The microstructural features of the dissimilar material joint were analyzed. The tensile and hardness tests were carried out to examine the mechanical properties and microhardness distribution of the welded joint. The results show that the joint has the non-homogeneous microstructure and element distribution. The brittle phases such as Fe2 Ti , Fe Ti , Cr2 Ti , Ti3 Ni4, Feo 2 Ni4.s Ti5 and TiN mainly segregate in rich Ti region of fusion zone. The laser-welded joint has the tensile strength of 298 MPa with the elongation of 3.72 % and exhibits the brittle fracture features on the fracture surfaces. The reasons for low joint strength were discussed in this investigation.

Microstructures and properties of capacitor discharge welded joint of TiNi shape memory alloy and stainless steel

Microstructures and properties of capacitor discharge welded （CDW） joint of TiNi shape memory alloy （ SMA ） and stainless steel （SS） were studied. The fracture characteristics of the joint were analyzed by means of scanning electron microscope （ SEM）. Microstructures of the joint were examined by means of optical microscope and SEM. The results showed that the teusile strength of the inhomogeneous joint （ TiNi-SS joint） was low and the joint was brittle. Because TiNi SMA and SS melted, a brittle as-cast structure and compound were formed in the weld. The tensile strength and the shape memory effect （SME） of TiNi-SS joint were strongly influenced by the changes of composition and structure of the weld. Measures should be taken to prevent defects from forming and extruding excessive molten metal in the weld for improving the properties of TiNi-SS joint.

A short review on the role of alloying elements in duplex stainless steels

Duplex stainless steels consisting of ferrite and austenite are widely used due to their excellent mechanical properties and corrosion resistance.Compared with ferritic stainless steels,duplex stainless steels have better plasticity,toughness,and welding performance.They also possess higher strength and better resistance to stress,pitting,and crevice corrosion than austenitic stainless steels.In addition to the above-mentioned properties,there are cost-saving advantages in duplex stainless steels due to their lower nickel content.Today,the types of duplex stainless steel are mainly divided into four categories:lean duplex stainless steel,standard duplex stainless steel,super duplex stainless steel,and hyper duplex stainless steel.Alloying design of duplex stainless steel is an important strategy to achieve high performance.In the last two decades,significant progress has been made in both theoretical calculations and experiments.By adjusting alloying elements such as chromium,nickel,molybdenum,nitrogen,copper,tungsten and rare earth,etc.,the mechanical properties and/or corrosion resistance of the duplex stainless steels can be further improved.Summarizing the comprehensive progress of alloying design of duplex stainless steel is of great significance in providing a data basis for establishing the corresponding relationship between chemical compositions and properties.Therefore,this paper reveals the specific roles of alloying elements in the duplex stainless steels and provides a reference for alloying design with different performance requirements.

Microstructural evolution and mechanical properties of friction stir-welded C71000 copper–nickel alloy and 304 austenitic stainless steel

Dissimilar joints comprised of copper–nickel and steel alloys are a challenge for manufacturers in modern industries, as these metals are not thermomechanically or chemically well matched. The present study investigated the effects of tool rotational speed and linear speed on the microstructure and mechanical properties of friction stir-welded C71000 copper–nickel and 340 stainless steel alloys using a tungsten carbide tool with a cylindrical pin. The results indicated that a rotational-to-linear speed ratio of 12.5 r/mm did not cause any macro defects, whereas some tunneling defects and longitudinal cracks were found at other ratios that were lower and higher. Furthermore, chromium carbide was formed on the grain boundaries of the 304 stainless steel near the shoulder zone and inside the joint zone, directing carbon and chromium penetration toward the grain boundaries. Tensile strength and elongation percentages were 84% and 65% of the corresponding values in the copper–nickel base metal, respectively.

Effect of welding process on the microstructure and properties of dissimilar weld joints between low alloy steel and duplex stainless steel

To obtain high-quality dissimilar weld joints, the processes of metal inert gas （MIG） welding and tungsten inert gas （TIG） welding for duplex stainless steel （DSS） and low alloy steel were compared in this paper. The microstructure and corrosion morphology of dissimilar weld joints were observed by scanning electron microscopy （SEM）; the chemical compositions in different zones were detected by en- ergy-dispersive spectroscopy （EDS）; the mechanical properties were measured by microhardness test, tensile test, and impact test; the corro- sion behavior was evaluated by polarization curves. Obvious concentration gradients of Ni and Cr exist between the fusion boundary and the type II boundary, where the hardness is much higher. The impact toughness of weld metal by MIG welding is higher than that by TIG weld- ing. The corrosion current density of TIG weld metal is higher than that of MIG weld metal in a 3.5wt% NaC1 solution. Galvanic corrosion happens between low alloy steel and weld metal, revealing the weakness of low alloy steel in industrial service. The quality of joints pro- duced by MIG welding is better than that by TIG welding in mechanical performance and corrosion resistance. MIG welding with the filler metal ER2009 is the suitable welding process for dissimilar metals jointing between UNS $31803 duplex stainless steel and low alloy steel in practical application.

Tuning Cr-rich nanoprecipitation and heterogeneous structure in equiatomic CrFeNi medium-entropy stainless alloys

High-/medium-entropy stainless alloys(HESAs/MESAs)are a new kind of alloys with great potential to combine excellent properties from high-/medium-entropy alloys(HEAs/MEAs)and stainless steels.A CrFeNi MESA was chosen to investigate its microstructures and mechanical behaviors.After homogenization,the strength and ductility of CrFeNi MESAs with single-phase face-centered-cubic(fcc)structure were higher compared with those of Fe_(100−x-y)Cr_(x)Ni_(y)austenitic stainless steels.Cr-rich body-centered-cubic(bcc)precipitates and heterogeneous structure were introduced by cold rolling and annealing at 800℃.Rolling at 700℃ results in higher dislocation density and the occurrence of lamellar Cr-rich bcc precipitates.High-density dislocations and fcc grains with heterogeneous structure,together with Cr-rich bcc precipitates,contribute to a yield strength improvement of about 50 MPa,and appreciable tensile yield strength of~540 MPa and fracture strain of~20%are obtained.It reveals that not only compositional variations but also grain size and phase structure tuning can be utilized for achieving desired mechanical properties.

Influences of different filler metals on electron beam welding of titanium alloy to stainless steel

Electron beam welding experiments of titanium alloy to stainless steel were carried out with different filler metals, such as Ni, V, and Cu. Microstructures of the joints were examined by optical microscopy, scanning electron microscopy and X-ray diffraction analysis. Mechanical properties of the joints were evaluated according to tensile strength and microhardness. As a result, influences of filler metals on microstructures and mechanical properties of electron beam welded titanium-stainless steel joints were discussed. The results showed that all the filler metals were helpful to restrain the Ti-Fe intermetallics. The welds with different filler metals were all characterized by solid solution and interfacial intermetallics. For each type of the filler metal, the type of solid solution and interfacial intermetallics depended on the metallurgical reactions between the filler metals and base metals. The interfacial intermetallics were Fe2Ti＋Ni3Ti＋NiTi2, TiFe, and Cu2Ti＋CuTi＋CuTi2 in the joints welded with Ni, V, and Cu filler metals, respectively. The tensile strengths of the joints were dependent on the hardness of the interfacial intermetallics. The joint welded with Ag filler metal had the highest tensile strength, which is about 310 MPa.

Electron beam welding of 304 stainless steel to QCr0.8 copper alloy with copper filler wire

Electron beam welding （EBW） of 304 stainless steel to QCr0.8 copper alloy with copper filler wire was carried out. Orthogonal experiment was performed to investigate the effects of process parameters on the tensile strength of the joints, and the process parameters were optimized. The optimum process parameters are as follows：beam current of 30 mA, welding speed of 100 mm/min, wire feed rate of 1 m/min and beam offset of-0.3 mm. The microstructures of the optimum joint were studied. The results indicate that the weld is mainly composed of dendriticαphase with little globularεphase, and copper inhomogeneity only occurs at the top of the fusion zone. In addition, a melted region without mixing exists near the weld junction of copper side. This region with a coarser grain size is the weakest section of the joints. It is found that the microhardness of the weld decreases with the increase of the copper content in solid solution. The highest tensile strength of the joint is 276 MPa.

Electron beam welding of Ti-15-3 titanium alloy to 304 stainless steel with copper interlayer sheet

Electron beam welding of Ti-15-3 titanium alloy to 304 stainless steel with a copper sheet as interlayer was carried out.Microstructures of the joint were studied by optical microscopy(OM),scanning electron microscopy(SEM) and X-ray diffractometry(XRD).In addition,the mechanical properties of the joint were evaluated by tensile test and the microhardness was measured.These two alloys were successfully welded by adding copper transition layer into the weld.Solid solution with a certain thickness was located at the interfaces between weld and base metal in both sides.Regions inside the weld and near the stainless steel were characterized by solid solution of copper with TiFe2 intermetallics dispersedly distributed in it.While weld near titanium alloy contained Ti-Cu and Ti-Fe-Cu intermetallics layer,in which the hardness of weld came to the highest value.Brittle fracture occurred in the intermetallics layer when the joint was stretched.

等离子弧焊梯度材料增材制造微观组织和性能研究

目的研究等离子弧焊工艺增材制造SS 316L不锈钢和Inconel 625镍基合金梯度材料的微观组织和力学性能。方法采用非同轴送丝的等离子弧焊的方式分别制备了采用梯度过渡和没有采用梯度过渡的SS 316L不锈钢与Inconel 625镍基合金电弧增材制造样件,在将实验数据线性归一化后,研究了2种样件在不同位置、不同方向的微观组织与力学性能。结果随层数的增多,采用了梯度过渡的样件底部各层热输入逐层减小,底部增材制造过程更稳定,而没有采用梯度过渡的样件在2种金属的连接区域粗糙度较大且层间成形不均匀。2种样件的显微硬度随层高的增加呈上升趋势,其中在30%(体积分数,下同)Inconel 625/70%SS 316L到20%Inconel 625/80%SS 316L的特定过渡区中梯度过渡样件显微硬度突然下降,因为该区域有Mo、Nb元素明显偏析,因此判断产生了Laves相。结论通过等离子弧焊工艺可得到薄而均匀的SS 316L不锈钢与Inconel 625镍基合金电弧增材制造样件,梯度过渡材料具有较多的柱状枝晶和较少的等轴枝晶,且晶区结构更加均匀,导致显微硬度值增加,进而提升了产品的性能。因此采用梯度过渡材料同时避免特定过渡区(30%Inconel 625/70%SS 316L到20%Inconel 625/80%SS 316L)能有效提高此工艺的产品性能。

Effect of electrode morphology on steel/aluminum alloy joint

Microstructure characteristics of dissimilar-metal resistance spot welded joints of SUS301 L austenitic stainless steel and 6063-T6 aluminum alloy, and effects of electrode morphology were studied. Results indicated that welded joints of dissimilar materials between austenitic stainless steel and aluminum alloy had characteristics of welding-brazing. The aluminum nugget consisted mainly of the cellular crystal, cellular dendrites and dendrites. The interface between austenitic stainless steel and aluminum alloy had a two-layered structures:a flat front surface θ-Fe_2Al_5 on the steel side and a serrated morphology θ-FeAl_3 on the aluminium alloy side, and it was the weakest zone of the joints. The electrode morphology had great effects on spot welded joints of stainless steel and aluminum alloy. The custom electrodes were a planar circular tip electrode with tip diameter of 10 mm on the stainless steel side and a spherical tip electrode with spherical radius of 35 mm on the aluminum alloy side. When the custom electrodes were used, the nugget diameter, tensile shear load and indentation ratio of spot welded joint were 7.22 mm, 3 606 N and 10.71%, respectively. The nugget diameter and joint tensile shear load increased by 34% and 102% respectively, and the indentation ratio decreased by 65% compared with the F-type electrodes(nugget diameter: 5.384 mm, tensile-shear load 1 783 N, indentation rate 30.94%). Therefore, it was more favorable to use the custom electrodes for improving the mechanical properties and appearance quality of resistance spot welded joints of stainless steel and aluminum alloy.

Strengthening mechanism of steels treated by barium-bearing alloys

The deoxidation, desulfurization, dephosphorization, microstructure, and mechanical properties of steels treated by barium-bearing alloys were investigated in laboratory and by industrial tests. The results show that barium takes part in the deoxidation reaction at the beginning of the experiments, generating oxide and sulfide compound inclusions, which easily float up from the molten steel, leading to the rapid reduction of total oxygen content to a very low level. The desulfurization and dephosphorization capabilities of calcium-bearing alloys increase with the addition of barium. The results of OM and SEM observations and mechanical property tests show that the structure of the steel treated by barium-bearing alloys is refined remarkably, the lamellar thickness of pearlitic structure decreases, and the pearlitic morphology shows clustering distribution. Less barium exists in steel substrate and the enrichment of barium-bearing precipitated phase mostly occurs in grain boundary and phase boundary, which can prevent the movement of grain boundary and dislocation during the heat treatment and the deformation processes. Therefore, the strength and toughness of barium-treated steels are improved by the effect of grain-boundary strengthening and nail-prick dislocation.

石墨管与不锈钢管钎焊接头的组织和残余应力

为使石墨材料能够在空间核电散热装置中更充分地发挥其价值,本文采用BNi-2钎料真空钎焊连接等静压石墨管和304不锈钢管,研究了石墨/BNi-2/不锈钢接头在1010℃、保温90 min条件下的显微组织和不同冷却工艺对接头残余应力的影响。研究表明:在1010℃,保温90 min条件下,钎焊接头致密无裂纹,Cr元素在石墨侧与石墨基体反应形成Cr_(7)C_(3)反应层,在不锈钢侧形成了σ-FeCr扩散层,界面接头组成为石墨/Cr_(7)C_(3)/Ni(s,s)+Ni_(3)Si/σ-FeCr/不锈钢;经缓冷工艺处理的接头,常温剪切强度为28.38 MPa,比炉冷处理的接头剪切强度提高了22%;有限元数值分析结果表明,采用缓慢冷却的钎焊工艺可以有效缓解钎焊接头在冷却过程中产生的残余应力,符合剪切实验结果。

Effect of Ni and Mn on the Mechanical Properties of 22Cr Microduplex Stainless Steel

The tensile properties of 22Cr–2Ni–4Mn–0.2N micro-duplex stainless steels with different Ni and Mn contents were investigated. Duplex stainless steels were vacuum induction melted and hot rolled, then annealed at 1,000–1,100 °C, at which temperature both the austenite and ferrite phases were stable. The volume fraction of the ferrite phase was markedly affected by the alloying elements of Mn and Ni; 1 wt% of Mn was equivalent to 0.4 wt% of Ni. All of the steels tested at room temperature showed the common strain-hardening behavior, while the steels tested at lower temperatures（-30 or-50 °C）showed a distinct inflection point in their stress–strain curves, which resulted from the transformation of the austenite to straininduced martensite. The onset strain（e0） of the inflection point in the stress–strain curve depended on the Md30 value of the steel. Testing at lower temperatures resulted in smaller e0 and consequently higher strengths and fracture strains（ef）. The tensile behavior was examined from the perspective of austenite stability of the micro-duplex stainless steels with the different Ni and Mn contents.

316L不锈钢蜂窝夹芯结构的抗爆性能研究与优化

为探究316L不锈钢蜂窝夹芯结构抗爆性能,设计了一种蜂窝夹芯结构,并采用316L不锈钢粉末通过选区激光熔融(selective laser melting,SLM)制备,同时采用该方法制备等面密度实心板作为对照组。通过静爆实验、LS-DYNA仿真实验得到该结构在近场静爆载荷下的力学行为,并且对应力波在其中的传播方式进行探究以明确其抗爆原理。同时在此基础上利用Optistruct对该结构进行拓扑优化以及结构优化,以期进一步提升抗爆性能。研究结果表明,多孔夹芯结构相比传统实心面板背板挠度降低13.2%,抗爆性能有所提升。建立的流固耦合数值模型描述了静爆实验的3个阶段,即冲击波传播阶段、流固耦合阶段和惯性作用阶段;明确静爆实验中靶板中心处“川”字形裂纹产生是残余芯层挤压导致的,芯层变形失效机理为蜂窝板平面内拉伸撕裂。Optistruct优化结果呈现三角形骨架和圆形孔洞交替波纹板结构,优化后波纹芯靶板相比优化前传统蜂窝夹芯板在相同的爆炸载荷下背板挠度降低25.4%,板后压力峰值降低17.6%,抗爆性能提升明显。相比蜂窝板,圆孔结构可以使背板挠度降低38.1%,三角孔结构可以使板后压力峰值降低22.4%。

Ti-6Al-4V合金添加对原位合金化增材制造15-5PH不锈钢显微组织与力学性能的影响

研究了不同Ti-6Al-4V合金粉末添加对原位合金化增材制造15-5PH不锈钢显微组织和力学性能的影响,结合金相及背散射电子衍射显微组织、X射线衍射、扫描电镜断口及拉伸实验分析了原位合金化增材制造15-5PH不锈钢的晶粒细化机制及强韧化机理。结果表明:Ti-6Al-4V原位合金化后15-5PH不锈钢组织发生了等轴转变,显著细化晶粒的同时降低了织构强度,同时通过抑制马氏体相变使位错密度降低。15-5PH+0.8%Ti-6Al-4V和15-5PH+1.6%Ti-6Al-4V合金的屈服强度分别达1069 MPa和1021 MPa,远高于15-5PH不锈钢(680 MPa),且合金的延伸率明显提升,其较高的屈服强度和延伸率主要源于晶粒细化及内部位错密度的降低。

Influence of Vanadium Element on Microstructure of Electron Beam Welded Titanium Alloy to Stainless Steel Joint

Electron beam welding experiments of titanium alloys with different vanadium content to stainless steel,as well as alpha titanium to stainless steel using vanadium sheets as filler metal and transition portion were carried out.Microstructures of the joints were examined by scanning electron microscope.The properties were evaluated by microhardness and tensile strength.It was shown that electron beam welding is not feasible due to the brittle Ti-Fe intermetallics with high hardness.Increase of vanadium content in base metal can restrain but can't avoid the formation of cracks.When vanadium content was too large,the joint was embrittled by FeTi compound with supersaturated V and also cracked after welding.Crack free joint was achieved by using vanadium transition portion which can prevent the contact of Ti and Fe elements.However,the formation of brittle σ intermetallics reduced the tensile strength of the joint,only up to 134MPa.