مهندسی مکانیک مدرس

مهندسی مکانیک مدرس

اثر نوع فرایند آستنیته کردن بر قابلیت ماشینکاری چدن نشکن آستمپر با زمینه دوفازی

نوع مقاله : پژوهشی اصیل

نویسندگان
دانشگاه رازی
چکیده
هدف اصلی این تحقیق مشخص کردن فرایند آستنیته کردن مناسب برای دست‌یابی به چدن نشکن آستمپر با زمینه دوفازی دارای بهترین قابلیت ماشینکاری ممکن است. در این راستا نمونه‌های چدن نشکن فریتی کم آلیاژ با ریخته­گری تهیه گردید. ابتدا به منظور ایجاد مخلوط دو فازی فریت و آستنیت با درصدهای مختلف فاز آستنیت، نمونه‌ها تحت یکی از دو فرایند: الف) آستنیته جزئی (حرارت دهی در دمای oC 870 به مدت 5 تا 60 دقیقه) و یا ب) آستنیته بین بحرانی(حرارت دهی در دماهای oC 750-765-780 و oC 800 به مدت 60دقیقه) قرار گرفتند و بعد از آن در نمک مذاب با دمای oC 350 به مدت یک ساعت آستمپر شدند. نیروی برش طی روتراشی با ماشین تراش مجهز به دینامومترنیرو به عنوان معیار پذیرفته شده برای بررسی قابلیت ماشینکاری اندازه‌گیری شد. مطابق نتایج به دست آمده، با افزایش زمان آستنیته جزئی و یا دمای آستنیته بین بحرانی، درصد فاز سخت آسفریت زیاد شد، اما نیروی برش در ابتدا کاهش و سپس افزایش یافت. در یک درصد یکسان فاز آسفریت، تراشکاری نمونه‌های تهیه شده با فرایند آستنیته جزئی در مقایسه با نمونه‌های به دست آمده با فرایند آستنیته بین بحرانی، با نیروی برش کمتری همراه بود. به طور کلی می‌توان نتیجه‌گیری نمود که بیشترین قابلیت ماشینکاری چدن نشکن آستمپر شده در دمایoC 350 هنگامی حاصل می شود که دما و زمان آستنیته کردن به ایجاد زمینه با ساختار دوگانه حاوی 3 ± 39 درصد حجمی فاز آسفریت منجر گردد.
کلیدواژه‌ها

موضوعات


عنوان مقاله English

Effects of austenitizing type on machinability of austempered ductile irons with dual matrix structure

نویسندگان English

Mohsen Sabzalipour
Ali Mohammad Rashidi
Engineering Faculty, Razi University
چکیده English

The main goal of present work is to identify the appropriate austenitising category to achieve the austempered ductile irons with dual matrix structure having the best possible machinability. In this regard, specimens of low-alloyed ferritic spheroidal graphite cast iron were prepared by casting process. In order to obtain a mixed ferrite-austenite structures having different volume fraction of austenite phase, samples were subjected to one of two processes: a) partial austenitising at 870 oC for various times (5 to 60 min) or b) intercritical austenitising at various temperatures (750, 765, 780 and 800 oC) for 60 minutes. After that they were austempered in molten salt at a temperature of 350 oC for one hour. During turning with a lathe equipped with a force dynamometer, the cutting forces of the workpieces were measured as a general adopted criterion for machinability investigation. According to the obtained results, with the increase of partial austenitising time or intercritical austenitising temperature, the volume fraction of the ausferrite phase increased, but the cutting force decreased initialy and then increased. For a certain percentage of the ausferrite phase, the turning of samples prepared with partial austenitising process was associated with lower cutting force, compared to the samples obtained by the intercritical austenitising process. In general, it can be concluded that the maximum machinability of dual matrix ductile iron austempered at 350 oC is achieved when the selected austenitising temperature and time results to creation dual matrix structure containing 39 ± 3 Vol% ausferrite phase

کلیدواژه‌ها English

austempered ductile iron
cutting force
Intercritical Austenitising
Machinability
Partial Austenitising
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