تاثیر فرآیند ترمومکانیکی بر روی فولادهای بینیتی نانوساختار کربن متوسط

نوع مقاله: مقاله پژوهشی

نویسندگان

1 پژوهشکده فناوری نانو و مواد پیشرفته، پژوهشگاه مواد و انرژی، کرج، ایران

2 پژوهشکده نانو، پژوهشگاه مواد و انرژی، مشکین دشت، ایران

چکیده

در سال‌های اخیر تلاش‌های زیادی برای توسعه‌ی نسل جدیدی از فولادها تحت عنوان فولادهای نانوساختار بینیتی انجام شده است. اندازه دانه آستنیت اولیه از پارامترهای موثر در تشکیل ریزساختار بینیتی می‌باشد. فرآیند مارتنزیت از جمله فرآیندهای ترمومکانیکی پیشرفته است که مشتمل بر نورد سرد ریزساختار مارتنزیتی و آنیل متعاقب آن می‌باشد. در این پژوهش سعی شده است تا تاثیر تلفیق فرآیند مارتنزیت و فرآیند آستمپرینگ بر روی ریزساختار و خواص مکانیکی فولادهای نانوساختار بینیتی بررسی شود. فولا مورد استفاده در این پژوهش از نوع کربن متوسط و آلومینیوم بالا بوده که طراحی و سپس ریخته‌گری شده و در نهایت نورد داغ شده است. این فولاد در دمای °C 1030 به مدت 20 دقیقه آستنیته شده و سپس در آب کوئنچ گردید تا ساختار مارتنزیت حاصل گردد. نمونه‌ها به میزان 20 درصد توسط نورد سرد کاهش مقطع داده شده و سپس در دمای °C 600 به مدت 20 دقیقه آنیل شدند. نمونه‌ها مجددا در دما و زمان مشابه آستنیته شده و در دمای °C 340 تحت عملیات آستمپرینگ قرار گرفتند. بررسی‌های ریزساختاری با استفاده از پراش پرتو ایکس، میکروسکوپ‌های نوری و الکترونی روبشی انجام گرفت و به منظور ارزیابی خواص مکانیکی از آزمون کشش استفاده شد. به دلیل تشدید نرخ استحاله بینیتی و تغییرات کم اندازه دانه آستنیت اولیه تفاوت زیادی در خواص مشاهده نشد. استحکام کشش نهایی برای نمونه‌ها با اندازه دانه بزرگ (47 میکرومتر) 1279مگاپاسکال با ازدیاد طول 23 درصد و برای نمونه‌ها با اندازه دانه ریزتر (33 میکرومتر) 1231 مگاپاسکال با ازیاد طول 19 درصد به دست آمد.

کلیدواژه‌ها


عنوان مقاله [English]

The effect of thermomechanical process on the nanobainitic medium carbon steels

نویسندگان [English]

  • alireza kolahi 1
  • Meysam Pourshadloo 2
  • yahya palizdar 1
1 Department of Nanotechnology and Advanced Materials, Materials and Energy Research Center (MERC), Karaj, Iran.
2 insitute of materials and energy (MERC), meshkin-dasht, iran
چکیده [English]

The austenite grain size has a significant influence on phase transformation and mechanical properties of bainitic steels. The martensite treatment including cold rolling and subsequent annealing of microstructures with high percentage of martensite is one of the most effective thermo-mechanical methods for the grain refinement in steels. The present study aims to investigate the effects of thermomechanical and austempering processes on the microstructure and mechanical properties of the medium carbon high aluminium nanobainitic steel. In this regard, nanostructured bainitic steels with lower carbon content (0.45 wt%) than conventional supper bainitic steel were cast and hot rolled. To obtain the bainitic structure the specimens were austenitized at 1030 °C for 20 min and quenched in water. The specimens were subjected to 20% reduction in thickness by cold rolling and subsequent annealing at 600 °C for 20 min. The specimens were austenitized and transformed isothermally at 340 °C and finally were quenched in water. The microstructure was characterized by X-ray diffraction (XRD), optical (OM) and field emission scanning electron microscopy (FESEM) as well as tensile test for mechanical properties. The results showed that no significant changes were obtained in properties due to the increase in the rate of bainitic transformation and low changes in the austenite grain size. For specimens with a coarse austenite grain size (47 µm) the strength of 1279 MPa and elongation of 23% and for specimens with a fine austenite size (33 µm) the strength of 1231 MPa with a elongation of 19%, were obtained.

کلیدواژه‌ها [English]

  • Bainitic Steel
  • Nano structure
  • Martensite process
  • Medium carbon high aluminum steel
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