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Effect of reduction pretreatment process on evolution of micro-porosity in 42CrMo billet

Journal of Iron and Steel Research International 2021年第4期28卷 413-423页

作者： Zhen Ning Wei Yu Hong-qiang Liu Qing-wu Cai Collaborative Innovation Centre of Steel Technology University of Science and Technology BeijingBeijing 100083China HBIS Group Co. Ltd.Shijiazhuang 050000HebeiChina

Reduction pretreatment(RP)process,which is implemented after the billet is completely solidified,is an alternative process to further improve billet *** element method and experiment were used to investigate the effect of the RP process on the internal quality of 42CrMo *** ultrasonic testing technology was used to study the influence of the RP process on the *** a three-dimensional finite element model,the mechanism of the RP process on the porosity closure was *** experimental results show that the RP process eliminates the macro-porosities of the billet *** number of micro-porosities in the billets is effectively reduced,and the increase in deformation contributes to the reduction in *** with isothermal rolling,the RP process leads to a larger equivalent strain and hydrostatic integration in the billet center because of the temperature gradient,and the effect of the temperature gradient is greater with the increase in *** closure effect of micro-porosity is related not only to the stress state,but also to the distribution of *** increase in three-dimensional compressive stress is beneficial to the porosity *** the micro-porosities distributed densely,excessive stress could induce micro-porosity coalescence,which has the risk of inducing cracks.

关键词： Reduction pretreatment Temperature gradient Large deformation micro-porosity Ultrasonic testing

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Relationship between micro-porosity and tensile properties of 6063 alloy

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China Foundry 2013年第1期10卷 29-33页

作者： Li Xiehua He Lizi Zhu Pei Cao Yiheng Guo Yaping Cui Jianzhong Key Lab of Electromagnetic Processing of Materials Ministry of EducationNortheastern University Chalco Ruimin Corporation Limited

The micro-porosity is usually present in the as-cast microstructure, which decreases the tensile strength and ductility and therefore limit the application of cast aluminum parts. Although much work has been done to investigate the effects of various casting parameters on the formation of porosity in various aluminum alloys, up to now, little information has been available for the relationship between micro-porosity and tensile properties of 6063 alloy. In this study, the influences of size and area fraction of micro=porosity on the tensile properties and fracture behavior of 6063 aluminum alloy were investigated by means of tensile testing, optical microscopy （OM）, and scanning electron microscopy （SEM）. The tensile tests were conducted in air at 100 ℃, 200 ℃ and 300 ℃, respectively. Results show that the large micro-porosity with sizes between 100 pm and 800μm located at the center and top of the ingot, while the small micro-porosity with size between 2 IJm and 60 μm distributed at the edge and bottom of the ingot. The area fraction of micro-porosity at the center of the ingot is much bigger than that at the edge of the ingot. When tested at 100 ℃, with the decrease in the area fraction of micro-porosity from the top of the ingot to the bottom of the ingot, the ultimate tensile strength, yield strength and the elongation are increased from 82 to 99 MPa, 32 to 66 MPa and 7% to 11%, respectively. When the temperature is no more than 200 ℃, the strain hardening exponent decreases with an increase in the area fraction of micro-porosity; while the deviation disappears when the temperature reaches 300 ℃. The fracture mode of the alloy is greatly influenced by the size and area fraction of the micro-porosity.

关键词： 6063 alloy micro-porosity tensile properties fracture

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Investigation on Structure and Properties of Brass Casting

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Journal of Materials Science & Technology 2008年第3期24卷 299-301页

作者： M.M.Haque A.A.Khan 53100 Kuala Lumpur Department of Manufacturing and Materials Engineering Kulliyyah of Engineering Gombak International Islamic University Malaysia(IIUM)

In this work,alpha(α)brass was poured in green sand mould and metallic chill mould at about 1050℃. Sand casting method and metallic chill casting method are representing the slow and fast cooling rates of the castings,*** slow cooling rate in the sand mould produces larger grains,while the metallic chill mould produces smaller grains in the *** the grain size decreases,the strength of the cast brass increases;micro-porosity in the casting decreases and the tendency for the casting to fracture during solidification ***,the faster cooling rate casting offers higher strength,density and hardness compared to the slow cooling rate casting.

关键词： Green sand Chill mould micro-porosity Solidification

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Solidification microstructure of centrifugally cast Inconel 625

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China Foundry 2017年第4期14卷 304-312页

作者： Silvia Barella Andrea Gruttadauria Carlo Mapelli Davide Mombelli Paolo Taiana Matteo Bosatra Alberto Morini Dipartimento di Meccanica Politecnico di Milanovia La Masa 120156 MilanoItaly Fondinox via Marconi 42/4826010 Sergnano(CR)Italy

Centrifugal casting is a foundry process allowing the production of near net-shaped axially symmetrical components. The present study focuses on the microstructural characterization of centrifugally cast alloys featuring different chemical compositions for the construction of spheres applied in valves made of alloy IN625 for operation at high pressure. Control of the solidification microstructure is needed to assure the reliability of the castings. Actually, a Ni-base superalloy such as this one should have an outstanding combination of mechanical properties, high temperature stability and corrosion resistance. Alloys such as IN625 are characterised by a large amount of alloying elements and a wide solidification range, so they can be affected by micro-porosity defects, related to the shrinkage difference between the matrix and the secondary reinforcing phases(Nb-rich carbides and Laves phase). In this study, the microstructure characterization was performed as a function of the applied heat treatments and it was coupled with a calorimetric analysis in order to understand the mechanism ruling the formation of micro-porosities that can assure alloy soundness. The obtained results show that the presence of micro-porosities is governed by morphology and by the size of the secondary phases, and the presence of the observed secondary phases is detrimental to corrosion resistance.

关键词： alloy IN625 centrifugal casting solidification defects Nb carbides Laves phases micro-porosity corrosion

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