خواص مکانیکی و ساختاری آلیاژ استحکام بالای AISI 4340

Mechanical properties and microstructural features of AISI 4340

high-strength alloy steel under quenched and tempered conditions

خواص مکانیکی و ویژگی‎های ریزساختاری آلیاژ استحکام بالای AISI 4340

تحت شرایط کوئنچ و بازپخت 

ABSTRACT

In this work, the mechanical properties and microstructures of AISI 4340 high strength alloy steel under different tempering conditions are investigated. The specimens are quenched and tempered to a martensite structure and loaded to fracture at a constant strain-rate of 3.3×10−4 s−1 by means of a dynamic material testing machine (MTS 810). The mechanical properties and strain-hardening exponent are considered as function of the tempering conditions. The morphological features of the as-quenched martensite and their evolution during tempering are described. Fractographs of the specimens are also made in order to analyse their fracture and embrittlement mechanisms. The results indicate that the mechanical properties and microstructural features are affected significantly by tempering temperature and holding time. The strength and hardness of tempered martensite drop as the tempering temperature and holding time are increased. However, the ductility increases with increasing tempering temperature and holding time, except when tempered martensite embrittlement occurs. Microstructural observations reveal that the carbide precipitates have a plate-like structure at low temperatures, but are spheroid-like at high temperatures. Under the tested conditions, the fracture appearances show that the material failed in a ductile manner except for the case of tempering at 300°C, where tempering martensite embrittlement occurs due to the existence of retained interlath austenite..

 

مقدمه ای بر دایکست با فشار بالا و عیوب رایج در دایکست

Introduction Of High Pressure Die-Casting

And Common Defects In Die-Casting

مقدمه ای بر دایکست با فشار بالا و عیوب رایج در دایکست 

ABSTRACT

Die casting is a manufacturing process that can produce geometrically complex metal parts through the use of reusable molds, called dies. The die casting process involves the use of a furnace, metal, die casting machine, and die. The metal, typically a non-ferrous alloy such as aluminum or zinc, is melted in the furnace and then injected into the dies in the die casting machine. There are two main types of die casting machines - hot chamber machines (used for alloys with low melting temperatures, such as zinc) and cold chamber machines (used for alloys with high melting temperatures, such as aluminum). The differences between these machines will be detailed in the sections on equipment and tooling. However, in both machines, after the molten metal is injected into the dies, it rapidly cools and solidifies into the final part, called the casting. 

 

مقایسه جوشکاری EBW و اتصال خود فشاری حرارتی برای آلیاژ Ti6Al4V

A comparative study on electron beam welding and

rigid restraint thermal self-compressing bonding for Ti6Al4V alloy

بررسی مقایسه ای جوشکاری پرتوی الکترونی

و اتصال خود فشاری حرارتی سخت مقیدشده برای آلیاژ Ti6Al4V

ABSTRACT

This study focuses on the influence of joining method difference on the joint microstructure and properties. Unlike vacuum electron beam welding (EBW) utilizing electron beam as fusion heat source, rigid restraint thermal self-compressing bonding (TSCB), a new solid-state bonding method proposed by authors, employs vacuum electron beam as the non-melt heat source to bond materials in this work. Meanwhile, a comparative study on the microstructure and mechanical properties of EBWjoint and rigid restraint TSCB joint was conducted to investigate the effect of this difference on joint microstructure and properties. Results show that compared with EBW joints, the rigid restraint TSCB joints as solid-state joints are homogeneous in terms of microstructure and microhardness profile. Strength of both joints are comparable with that of base metal, but the elongation of the rigid restraint TSCB joint is more close to that of base metal. Rigid restraint TSCB joint has better combination of strength and ductility.

 

اثر اندازه نمونه بر ریزساختار فاز بین فلزی Al2Cu

Effect of sample size on intermetallic Al2Cu microstructure and

orientation evolution during directional solidification

اثر اندازه نمونه بر ریزساختار فاز بین فلزی Al2Cu

و روند جهت گیری آن در حین انجماد جهت دار

ABSTRACT

Al-40% Cu hypereutectic alloy samples were successfully directionally solidified at a growth rate of 10 μm/s in different sizes (4 mm, 1.8 mm, and 0.45 mm thickness in transverse section). Using the serial sectioning technique, the three-dimensional (3D) microstructures of the primary intermetallic Al2Cu phase of the alloy can be observed with various growth patterns, L-shape, E-shape, and regular rectangular shape with respect to growth orientations of the (110) and (310) plane. The L-shape and regular rectangular shape of Al2Cu phase are bounded by {110} facets. When the sample size was reduced from 4 mm to 0.45 mm, the solidified microstructures changed from multi-layer dendrites to single-layer dendrite along the growth direction, and then the orientation texture was at the plane (310). The growth mechanism for the regular faceted intermetallic Al2Cu at different sample sizes was interpreted by the oriented attachment mechanism (OA). The experimental results showed that the directionally solidified Al-40% Cu alloy sample in a much smaller size can achieve a well-aligned morphology with a specific growth texture.

 

بررسی مواد کامپوزیتی زمینه آلومینیم تقویت شده با نانولوله های کربنی

Investigation of carbon nanotube reinforced

aluminum matrix composite materials

بررسی مواد کامپوزیتی زمینه آلومینیم تقویت شده با نانولوله های کربنی

ABSTRACT

We have increased the tensile strength without compromising the elongation of aluminum (Al)–carbon nanotube (CNT) composite by a combination of spark plasma sintering followed by hot-extrusion processes. From the microstructural viewpoint, the average thickness of the boundary layer with relatively low CNT incorporation has been observed by optical, field-emission scanning electron, and high-resolution transmission electron microscopies. Significantly, the Al–CNT composite showed no decrease in elongation despite highly enhanced tensile strength compared to that of pure Al. We believe that the presence of CNTs in the boundary layer affects the mechanical properties, which leads to well-aligned CNTs in the extrusion direction as well as effective stress transfer between the Al matrix and the CNTs due to the generation of aluminum carbide.

 

انواع خوردگی Corrosion

Corrosion

خوردگی 

ABSTRACT

Corrosion is often associated with welded structures, since the microstructure, properties, and composition of the weld metal and HAZ may be quite different than those of the base metal. Corrosion takes a number of forms, as described in the  following section, and may result in general (uniform), localized, or microstructurespecific attack.

Often, the corrosion rate associated with welds is much higher than the base metal. The reason for this is usually a combination of the effect of microstructure and residual stress. Highly stressed regions surrounding welds may result in accelerated corrosion relative to the base metal. For example, the spot welds in automotive steels are normally the first place where corrosion attack takes place in car bodies.

 

پیشرفت‌ها در فناوری پالایش فولاد و چشم‌انداز آینده

Advances in Steel Refining Technology and Future Prospects

پیشرفت‌ها در فناوری پالایش فولاد و چشم‌انداز آینده

ABSTRACT

By the 1980s, Nippon Steel Corporation established a separated refining process based on hot-metal pretreatment,2) whereby the contents of silicon, sulfur, and phosphorus in hot metal were decreased before the decarburization in converters, using torpedo ladle cars, hot-metal ladles, or converters as the reaction vessels. Thereafter, technical developments such as the following were achieved:
separation of desulfurization from the other hot-metal pretreatment; separate processing of hot-metal dephosphorization from decarburization; development of hot-metal dephosphorization using converters as the reaction vessels and not requiring fluorine; improvement in reaction efficiency of these processes; recycled use of slag; adjustment of silicon content in hot metal in case of excessively high Si; and increase in converter capacity for hot-metal dephosphorization in converters.

 

فرایند انجماد و ساختار ریختگی در ریخته گری شمش

Solidification and Processes and Cast Structures

فرایند انجماد و ساختار ریختگی

ABSTRACT

This swction deals with three tranitional solidificationprocesses: ingot casting, continous casting, and welding. however, the last to processe hold a key importance in todays technology. almost entire molten metal is cast into solid state by either the traditional ingot casting or reatively modern continuous casting. the development of the ingot and continuously cast structure as well as fusion welding structure and weld cracking are briefly described.

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چقرمگی شکست یک فولاد ضدزنگ سوپر داپلکس جوشکاری شده

Fracture toughness of a welded super duplex stainless steel

چقرمگی شکست یک فولاد ضدزنگ سوپر داپلکس جوشکاری شده

ABSTRACT

Fracture toughness testing was conducted on standard single-edge notched bend bar specimens of base and weld metal. The material was the SAF 2906 super duplex stainless steel. The aim was to evaluate the susceptibility for brittle failure at sub-zero temperatures for the base and weld metal. The base metal was tested between −103 and −60 °C and was evaluated according to the crack-tip opening displacement method. The fracture event at and below −80 °C can be described as ductile until critical cleavage initiation occurs, which caused unstable failure of the specimen. The welding method used was submerged arc welding with a 7 wt% nickel filler metal. The welded specimens were post-weld heat treated (PWHT) at 1100 °C for 20 min and then quenched. Energy-dispersive X-ray spectroscopy analysis showed that during PWHT substitutional element partitioning occurred which resulted in decreased nickel content in the ferrite. The PWHT weld metal specimens were tested at −72 °C. The fracture sequence was critical cleavage fracture initiation after minor crack-tip blunting and ductile fracture.

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رفتار زینترینگ و مقاومت هیدروژنی دولومیت واکنشی

Sintering, consolidation, reaction and crystal growth by

the spark plasma system (SPS)

رفتار زینترینگ و مقاومت هیدروژنی دولومیت واکنشی

ABSTRACT

Sintering of raw dolomite and hydroxides derived from dolomite was carried out in the temperature range 1350–1650 °C. The hydroxide derived from dolomite was developed through pre-calcination of dolomite followed by its hydration. For hydroxide development, after precalcination one sample was air-quenched and the other powder was furnace cooled before hydration. The air quenched samples showed better densification than that of the furnace cooling process at the same temperature. Fe2O3 addition enhances sintering by liquid formation at higher temperature. The grain size of doloma with Fe2O3 addition is bigger than that without additive. Hydration resistance was related to densification and grain size of sintered dolomite.

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