بررسی تاثیر عملیات زیرصفرعمیق بر ریز ساختار ، مقاومت سایشی و خواص کششی فولاد GOST9HF در دماهای تمپر 150 تا 650 درجه سانتیگراد
محورهای موضوعی : عملیات حرارتی
کامران امینی
1
(
دانشیار، مرکز تحقیقاتی مهندسی پیشرفته، واحد شهر مجلسی، دانشگاه آزاد اسلامی، مجلسی، اصفهان، ایران
)
کلید واژه: ریز ساختار, سختی, عملیات زیر صفر عمیق, دمای تمپر,
چکیده مقاله :
عملیات زیر صفر در سالهای اخیر جهت بهبود مقاومت سایشی و سختی فولادهای ابزار توصیه شده است. این عملیات قبل از عملیات تمپر و بعد از کوئنچ بر روی فولاد انجام میگردد. در تحقیق حاضر تاثیر عملیات زیرصفر عمیق بر روی فولاد GOST9HF بررسی میگردد. بدین منظور دو نمونه کوئنچ- تمپر و کوئنچ- زیر صفر به مدت 48 ساعت- تمپر آماده سازی شده و تاثیر عملیات زیرصفر بر میزان آستنیت باقیمانده، رسوب کاربیدهای ریز، سختی، استحکام و مقاومت سایشی با انجام آزمایشهای پراش پرتو ایکس، بررسی ساختار توسط میکروسکوپ الکترونی روبشی، میکروسکوپ الکترونی عبوری، سختی سنجی، کشش و سایش به روش پین بر روی دیسک بررسی میگردد. نتایج نشان داد در نمونه های زیر صفر شده در مقایسه با نمونه کوئنچ- تمپردر تمام دماهای تمپر (150 درجه سانتیگراد تا 650 درجه سانتیگراد ) سختی، مقاومت سایشی و خواص کششی بالاتر است. ضمن آنکه با افزایش دمای تمپر در هر دو نمونه سختی، مقاومت سایشی و خواص کششی به دلیل نرم شدن ساختار و رشد دانه ها کاهش می یابد. دلیل بهبود خواص در نمونه زیرصفر شده حذف آستنیت باقیمانده، رسوب کاربیدهای ریز و یکنواخت تر این کاربیدها است. به نحوی که عملیات زیر صفر باعث کاهش میزان آستنیت باقیمانده از 12% در نمونه کوئنچ – تمپر به کمتر از 1% در نمونه زیرصفر شده می شود. همچنین عملیات زیر صفر باعث افزایش کسر حجمی کاربیدها به میزان 52% میگردد.
In recent years, cryogenic-treatment is considered in order to improve of wear and hardness resistance of tool steels. Cryo-treatment is performed on steel before and after of tempering and quenching treatment, respectively. In this research, the effect of deep cryogenic treatment is investigated on the GOS9HF-steel. In this regard, the quenched-tempered and quenched-Cryo-treated samples are prepared after tempering treatment for 2hrs. then, impact of Cryo-treatment on value of retained austenite, fine carbide precipitations are evaluated by XRD, SEM and the amount of hardness, strength and wear resistance are measured by micro-hardness, tensile and wear tests. The wear test is conducted by pin-on-disc method. The results indicated that the amount of hardness and properties of wear and tensile in the Cryo-treated sample were rather than the quenched-tempered samples at all of tempering temperatures (i.e. from 150 to 650˚C). Additionally, with increase of tempering temperature, the amount of hardness, wear behavior and tensile property are decreased in both of Cryo-treated and quenched-tempered samples. This can be attributed to the softening of microstructure and the growing of grain sizes. Moreover, it was obvious that improving of Cryo-treated samples are related to the removing of retained austenite, precipitation of fine carbides and more appropriate distribution of these carbides. It is cleared that the Cryo-treatment causes to decrease of value of retained austenite from 12% to below of 1% at quenched-tempered and Cryo-treated samples, respectively. Finally, Cryo-treatment causes to increase of volume fracture of carbides to 52%.
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