افزودن تیتانیم روی فولاد کم آلیاژ استحکام بالا Effect of Titanium Addition on HSLA Steel

Study on the Mechanism of Strengthening and Toughening Effect

 of Titanium Addition on HSLA Steel 

مطالعه‌ی مکانیزم استحکام‌بخشی و اثر چقرمه‌سازی افزودن تیتانیم روی فولاد HSLA

ABSTRACT

Based on the determination of load variation against deflection by means of Instrumented Charpy Impact testing, the impact energy distribution of the High Strength Low Alloy (HSLA) steel containing Nb, Ni and Ti for pressure vessels at low temperature has been quantitatively studied. The total impact energy Et could be divided into two parts, Ei  and Ep. Ei is related to the base strength of the material in terms of the grain size and alloy addition, which is also found to be less influenced by the holding time of normalization process at 910℃. Whereas, Ep of Ni-Nb-Ti HSLA steel is strongly linked to the period of holding time. Thermodynamic kinetic investigation was  carried out to study the strengthening mechanism with metallurgical microstructure analysis. 

 

نیتروژن دهی یون-پلاسمایی فولاد ابزار ماشین آلات و قطعات

Ion-plasma nitriding of machines and tools parts instrumental steels

نیتروژن دهی یون - پلاسمایی فولاد ابزار ماشین آلات و قطعات 

ABSTRACT

Here introduced features of formation diffusion bond during ion nitriding in glow discharge plasma in gaseous mediums (mixture of nitrogen and argon). It is shown, that argon existing in saturated medium changes the nitriding process kinetics and the phase composition of the outer zone. Here presented investigation results on ion-plasma nitriding of instrumental steels, focused on microstructure and tool areas phase composition change, operating in most difficult conditions.

 

مارتنزیت پرآلیاژ در لایه سطحی غلتک های نورد

High-alloy martensite in the surfacing layer of

hot-rolling supporting rollers during the tempering process

مارتنزیت پرآلیاژ در لایه سطحی غلتک های پشتیبان نورد داغ در حین فرایند بازپخت

ABSTRACT

Flux-cored wire for surfacing hot-rolling supporting roller was developed and the specimens of surfacing layers were tempered at different temperatures. In order to characterize the high-alloy martensite in the surfacing layer during the tempering process, the microstructure and phase structure of the surfacing layer were analyzed, respectively. The nanoindentation hardness and phase transformation temperature of the high-alloy martensite were measured. The crystal structure of each phase was analyzed. The results show that the microstructure of the as-welded surfacing layer consists of martensite and retained austenite. Meanwhile, the high-alloy martensite with white reticular morphology is distributed on the crystal boundary. With increase of the tempering temperature, the high-alloy martensite disappears gradually, and the black reticular microstructure finally appears when the tempering temperature is 650 °C. The high-alloy martensite, whose average nanoindentation is 14.33 GPa, shows bulk morphology in field emission scanning electron microscope and starts to dissolve in the matrix at 420 °C. The contents of the alloy elements in the high-alloy martensite are higher than those in the normal one. However, the former decrease rapidly after tempering at 650 °C. The high-alloy martensite shows the body-centered tetragonal crystal structure, and the c-axis of the high-alloy martensite is longer than that of the normal one.

 

جوشکاری اصطکاکی-تلاطمی آلیاژ آلومینیوم به فولاد زنگ‌نزن

Friction stir welding of dissimilar Al 6013-T4 To

X5CrNi18-10 stainless steel

جوشکاری اصطکاکی-تلاطمی غیرهمجنس Al 6013-T4 به فولاد زنگ‌نزن X5CrNi  

ABSTRACT

The joining of dissimilar Al 6013-T4 alloy and X5CrNi18-10 stainless steel was carried out using friction stir welding (FSR) technique. The microstructure, hardness and fatigue properties of fiction stir welded 6013 aluminium alloy to stainless steel have been investigated. Optical microscopy was used to characterise the microstructures of the weld nugget, the heat affected zone (HAZ), thermo-mechanical affected zone (TMAZ) and the base materials. The results show that FSR can be used the joining of dissimilar Al 6013 alloy and X5CrNi18-10 stainless steel. Seven different zones of the microstructure in the welding are reported as follows: (1) parent stainless steel, (2) HAZ in the stainless steel at advancing side of weld, (3) TMAZ in the stainless steel at advancing side of weld, (4) weld nugget, (5) TMAZ in the Al alloy at retreating side of weld, (6) HAZ in the Al alloy at retreating side of weld and (7) parent Al alloy. A good correlation between the hardness distribution and the welding zones are observed. Fatigue properties of Al 6013-T4/X5CrNi18-10 stainless steel joints were found to be approximately 30% lower than that of the Al 6013-T6 alloy base metal.

 

میکروساختار و خواص سایشی فولاد ابزار

Microstructure and wear properties of AISI M2 tool steel

on RF plasma nitriding at different N2–H2 gas compositions

میکروساختار و خواص سایشی فولاد ابزار AISI M2

نیتروژن دهی پلاسمایی RF شده در ترکیب های مختلف از گازهای N2–H2

ABSTRACT

Wear behavior of quenched-tempered AISI M2 tool steel samples has been studied after plasma nitriding at different N2–H2 plasma gas flows containing 25, 50 and 75 sccm N2. Plasma nitriding was performed at 450 °C for 8 h under floating potential using a plasma reactor equipped with a radio frequency power generator. Microstructure, phase composition, nitrided layer thickness, hardness and surface roughness of the samples were studied using optical microscopy, X-ray diffraction, microhardness and surface profilometry measurements. Dry sliding wear resistance of samples was determined by performing ball-on-disc wear testes. The results revealed formation of mainly a diffusion zone at the 25 sccm N2–75 sccm H2 gas flow and mono-phase ε-Fe2–3N compound layer at higher N2 concentrations. Plasma nitriding increases near surface hardness up to 50% (about 1600HV0.025) irrespective of the N2:H2 ratio, where nitrided layer depth and surface roughness increase with increasing the N2 flow rate in the plasma gas. Depending on the nitrogen content, sliding wear resistance may be improved between 20 and 90% with respect to the un-nitrided substrate. Among the nitrided samples the maximum and minimum wear resistance was obtained at plasma gases containing higher and lower H2 fractions, respectively. Decreasing wear resistance with increasing N2 flow rate in the plasma gas attributed to formation of the hard and brittle compound (white) layer on the sample surface and development of residual stress profiles.

 

خواص سطحی فولاد کم آلیاژ نیتروکربوریزه شده Surface properties of low alloy steel

Surface properties of low alloy steel treated by

plasma nitrocarburizing prior to laser quenching process

خواص سطحی فولاد کم آلیاژ عملیات شده توسط نیتروکربوریزه کردن

پس از روش کوئینچ کردن با لیزر

ABSTRACT

Laser quenching (LQ) technique is used as a part of duplex treatments to improve the thickness and hardness of the surface layers of steels. The present study is to investigate the surface properties of low alloy steel treated by plasma nitrocarburizing (PNC) prior to a laser quenching process (PNC+LQ). The microstructure and properties of PNC+LQ layer determined are compared with those obtained by PNC and LQ processes. OM, XRD, SEM and EDS analyses are utilized for microstructure observation, phases identification, morphology observation and chemical composition detection, respectively. Microhardness tester and pin-on-disc tribometer are used to investigate the mechanical properties of the modified layers. Laser quenching of plasma nitrocarburized (PNC+LQ) steel results in much improved thickness and hardness of the modified layer in comparison with the PNC or LQ treated specimens. The mechanism is that the introduction of trace of nitrogen decreases the eutectoid point, that is, the transformation hardened region is enlarged under the same temperature distribution. Moreover, the layer treated by PNC+LQ process exhibits enhanced wear resistance, due to the lubrication effect and optimized impact toughness, which is contributed to the formation of oxide film consisting of low nitrogen compound (FeN0.076) and iron oxidation (mainly of Fe3O4).

 

فرآیند نیتروژن دهی پلاسمایی در فولاد قالب تزریق پلاستیک

A Study on Formation and Growth Mechanism of

Nitride Layers During Plasma Nitriding Process of

Plastic Injection Mold Steel

تحقیق روی مکانیزم رشد و تشکیل لایه های نیتریدی

حین فرآیند نیتروژن دهی پلاسمایی در فولاد قالب تزریق پلاستیک

ABSTRACT

Ion nitriding modifies composition of surface layer in steel used in plastic mold application and this consequently improves their lifecycle. In this study, pulsed plasma nitriding technique was used to produce a protecting hard layer on AISI P20 steel at three process temperatures of 450°C, 500°C, and 550°C for durations of 2.5, 5, 7.5, and 10 h at a constant gas mixture of 75% N2–25% H2. Surface morphology was studied by optical and scanning electron microscope and the phases formed on the surface layer were determined by X-ray diffraction (XRD). Elemental depth profile was measured by techniques including energy dispersive spectroscopy, wavelength dispersive spectrometer, and glow discharge spectroscopy and for identifying hardness profile, microhardness variations from surface to core of samples were recorded. Results showed that, thickness of compound layer of plastic mold steel AISI P20 was negligible. Moreover in ion nitriding of AISI P20, nitride were formed and grown in some preferred directions and upward diffusion of carbon and downward diffusion of nitrogen occurred during ion nitriding of AISI P20. XRD results showed that, ϵ-nitride is the dominant phase after plasma nitriding in all strategies. Furthermore, ion nitriding improved hardness of AISI P20 up to three times and as time and temperature increased, hardness and hardness depth of diffusion zone increased considerably.

 

الزامات پاکیزگی برای فولادهای X80 و X65 خط لوله جوشکاری‌شده

Steel cleanness requirements for X65 to X80

electric resistancewelded linepipe steels

الزامات پاکیزگی برای فولادهای X80 و X65 خط لوله جوشکاری‌شده

به روش مقاومت الکتریکی 

ABSTRACT

CONTROL OF OXIDES AND SULPHIDES : Clean steel practices at the BHP Steel Ltd, Flat Products plant have always been related to customers’ requirements and expectations. Monitors were developed for critical cleanness grades from either in-house tests or from customer supplied data. Some of these monitors have been in existence for nearly 20 years and have successfully guided process improvements both in steelmaking and in continuous slab casting, such as ladle opening with submerged shroud, vibration ladle slag detection, argon shielding of delivery systems, weir wall design, and quick melting  ux addition to the tundish on start up.

 

رشد سلولی و دندریتی Cellular and dendritic growth

Cellular and dendritic growth

رشد سلولی و دندریتی 

ABSTRACT

Many of the alloys used in practice, such as steel, aluminum-copper alloys, nickel-base and copper-base alloys, are single phase alloys, which means that the final product of solidification is a solid solution. Depending on the thermal and compositional field, cellular or, in most practical cases, dendritic morphology will occur. In other cases, even when the room temperature microstructure is mostly eutectic some primary phases solidify before the eutectic. They can be solid solutions, carbides, intermetallic phases, inclusions, etc. Their morphology affects mechanical properties, and thus, understanding how this morphology can be controlled is a mater of significant practical importance. A detailed discussion of primary phase growth, and in particular of dendrite growth, will be provided in the following sections.

 

عملیات حرارتی قطعات ریخته‎گری‎ بزرگ از فولاد 15Kh3M1FTsL

Heat Treatment of Large Castings from Steel 15Kh3M1FTsL

عملیات حرارتی قطعات ریخته‎گری‎ بزرگ از فولاد 15Kh3M1FTsL

ABSTRACT

The effect of heat treatment on mechanical properties, impact toughness, and cold-shortness threshold of cast steel 15Kh3M1FL is investigated. A heat treatment mode including homogenizing, air hardening, and high-temperature tempering of castings is suggested for commercial use.