مقایسه خواص کششی و نرخ کارسختی فولاد زنگ‌نزن آستنتی 304 ریزدانه و درشت دانه

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشجوی کارشناسی ارشد، دانشکده مهندسی مواد و متالورژی، دانشگاه علم و صنعت ایران، تهران، ایران.

2 استاد، دانشکده مهندسی مواد و متالورژی، دانشگاه علم و صنعت ایران، تهران، ایران.

3 استادیار، دانشکده مهندسی مواد و متالورژی، دانشگاه علم و صنعت ایران، تهران، ایران.

4 استادیار، دانشکده مهندسی شیمی و مواد، دانشگاه صنعتی شاهرود، شاهرود، ایران.

چکیده

در این پژوهش تاثیر اندازه دانه بر روی خواص کششی و رفتار کارسختی فولاد زنگ‌نزن آستنیتی 304 مورد بررسی قرار گرفت. به منظور دستیابی به این هدف، عملیات ترمومکانیکی با اعمال 75 درصد نورد سرد بر روی ورق اولیه فولاد زنگ‌نزن آستنیتی و به دنبال آن آنیل در دو دمای °C 1000 و 750 به منظور تولید ورق هایی با دو ریزساختار ریزدانه و درشت دانه انجام شد. میانگین اندازه دانه از μm 25 در نمونه اولیه به μm 93/1 در نمونه آنیل شده در دمای °C 750 و زمان min 90 (نمونه ریزدانه) کاهش یافت. همچنین  میانگین اندازه دانه در نمونه آنیل شده در دمای °C 1000 و زمان min 90 به μm 52/35 (نمونه درشت دانه) افزایش یافت. بررسی‌های ریزساختاری با استفاده از پراش اشعه ایکس و میکروسکوپ نوری انجام شد. آزمایش کشش نیز در سه جهت صفر، 45 و 90 درجه نسبت به جهت نورد بر روی نمونه ها انجام شد. مطابق نتایج این تحقیق، مقادیر استحکام تسلیم در سه نمونه اولیه، ریزدانه و درشت‌دانه به ترتیب 405، 733 و MPa 305 بدست آمد. اما درصد ازدیاد طول تا شکست  از 73 درصد در نمونه اولیه به 52 درصد در نمونه ریزدانه کاهش یافت. با بررسی رفتار کارسختی این فولاد، سه مرحله کارسختی یعنی؛ افت شدید تا رسیدن به یک مقدار حداقل، افزایش بعدی تا رسیدن به یک مقدار حداکثر و در نهایت افت نهایی تا شروع گلویی شدن در هر دو نمونه ریزدانه و درشت دانه مشاهده شد. نرخ کارسختی dσ/dε)) نمونه درشت دانه به دلیل بالاتر بودن نرخ استحاله آستنیت به مارتنزیت در این نمونه، بیشتر از نمونه ریزدانه بدست آمد.

کلیدواژه‌ها


عنوان مقاله [English]

Comparison of tensile properties and work hardening rate of fine and coarse-grained 304 austenitic stainless steel

نویسندگان [English]

  • Saeedeh Afshar 1
  • Hossein Arabi 2
  • Bagher Mohammad Sadeghi 3
  • Mohsen Karimi 4
1 MSc. Student, School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Tehran, Iran.
2 Professor, School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Tehran, Iran.
3 Assistant Professor, School of Metallurgy and Materials Engineering, Iran University of Science and Technology, Tehran, Iran.
4 Assistant Professor, School of Chemical and Materials Engineering, Shahrood University of Technology, Shahrood, Iran.
چکیده [English]

In this study, the effects of grain size on the tensile properties and the work-hardening behavior of 304 austenitic stainless steel was investigated. For this purpose, the thermomechanical processing was carried out by applying a 75% thickness reduction to the as-received 304 stainless steel sheet followed by annealing at two different temperatures of 750 and 1000 °C to produce sheets with two different fine- and coarse-grained microstructures. The average grain size decreased from 25 μm in the as-received matrix to 1.93 μm in the sample, which was annealed at 750 °C for 90 min (fine-grained sample). Also, the mean grain size of 35.52 μm (coarse-grained sample) was obtained after annealing at 1000 °C for 90 min. XRD and optical microscopy were used for characterizing the microstructure. The tensile tests were performed in the directions of 0°, 45°, and 90° to the rolling direction of the samples. The yield strength of as-received, fine-grained, and coarse-grained samples were obtained 405, 733, and 305 MPa, respectively. However, the total elongation decreased from 73% in the as-received sample to about 52% in the fine-grained sample. The work hardening behavior of both fine- and coarse-grained samples was observed in three stages: an initial sharp drop until a minimum value was reached, then an increase until a maximum value was reached, and finally a reduction in the work hardening rate until the beginning of necking. The work-hardening rate (dσ/dε) of the coarse-grained sample was higher than that of the fine-grained sample. This was due to the higher martensitic transformation rate in the coarse-grained sample.

کلیدواژه‌ها [English]

  • 304 austenitic stainless steel
  • Thermomechanical Processing
  • Grain Size
  • Work Hardening
  • Tensile Properties
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