اثر دمای آنیل میان بحرانی فولاد دوفازی SAPH440 بر رفتار کششی آن

نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه مهندسی متالورژی و مواد، دانشگاه فردوسی مشهد، مشهد ایران

2 گروه مهندسی متالورژی و مواد، دانشگاه فردوسی مشهد، مشهد، ایران.

3 گروه مهندسی متالورژی و مواد، دانشگاه فردوسی مشهد. مشهد. ایران.

چکیده

فولادهای دوفازی فریتی-مارتنزیتی به دلیل دارا بودن خواصی مکانیکی قابل توجه نظیر استحکام کششی بالا و شکل پذیری مناسب دارای کاربرد گسترده‏ در صنایع خودروسازی هستند. روشن است که خواص مکانیکی این فولادها وابسته به ویژگیهای ریز ساختاری آنها از جمله کسر حجمی فازهای مختلف و چگالی نابجایی در این فازها بوده که این مشخصه های ریز ساختاری، تابعی از تاریخچه ترمومکانیکی می‏باشند. هدف از این پژوهش، بررسی اثر ریزساختار فولاد فریتی-مارتنزیتی JIS-SAPH440 بر مشخصه های رفتار کششی این فولاد نظیر استحکام کششی و نمای حساسیت تنش سیلان به نرخ کرنش آن می‏باشد. به این منظور، پس از انجام آنیل میان بحرانی در دماهایی بین 750 الی 790 درجه سانتی گراد به مدت 30 دقیقه، رفتار سیلان فولاد مذکور توسط آزمون کشش در دمای محیط در دو نرخ کرنش متفاوت مورد بررسی قرار گرفت. همچنین تحولات ریزساختاری این فولاد توسط میکروسکوپهای نوری و الکترونی روبشی و آزمون پراش اشعه ایکس، مورد مطالعه قرار گرفت. نتایج نشان داد که افزایش دمای آنیل میان بحرانی از 750 به 790 درجه سانتی گراد سبب افزایش کسرحجمی فاز مارتنزیت از 31 درصد به 45 درصد و همچنین افزایش چگالی نابجایی ها در فاز فریت از 1015 × 5 بر متر مربع به 1016 × 54/1 بر متر مربع شد. این تغییرات، سبب شد که استحکام کششی فولاد مذکور از حدود 800 مگاپاسکال به حدود 1100 مگاپاسکال افزایش یابد و در مقابل، نمای حساسیت نرخ کرنش به تنش سیلان کاهش یافته و به مقادیر ناچیز برسد.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Effect of Intercritical Annealing Temperature on the Tensile Behavior of JIS-SAPH440 Steel

نویسندگان [English]

  • Mehran Salehifar 1
  • hasan farshidi 2
  • mohamad mazinani 3
1 1- M. Sc. Graduate, Ferdowsi University of Mashhad, Mashhad, Iran.
2 Department of Material Science and Engineering,, Ferdowsi University of Mashhad, Mashhad, Iran.
3 Department of Material Science and Engineering,, Ferdowsi University of Mashhad, Mashhad, Iran.
چکیده [English]

Ferritic-Martensitic dual-phase steels are widely used in car manufacturing industries because of their attractive mechanical properties like significant tensile strength and good formability. It is clear that the mechanical properties of these steels are dependent on their microstructural characteristics like the fraction of different phases and the dislocation density of each phase, and these characteristics are affected by the thermomechanical history.  The aim of this work is to investigate the effect of the microstructure of the Ferritic-Martensitic SAPH440 steel on its tensile behavior like the tensile strength and the strain rate sensitivity of flow stress. For this purpose, the steel is subjected to inter-critical annealing at different temperatures between 750 ºC to 790 ºC and then, it is subjected to the tension test at room temperature using two different strain rates. Also, the microstructure evolutions of this steel are studied using optical microscopy, scanning electron microscopy, and X-ray diffraction. Results show that the increase of the intercritical annealing temperature from 750 ºC to 790 ºC causes an increase of the martensite fraction from 31% to 45% and the increase of dislocation density of ferrite from 5×1014 to 1.54×1016. These variations cause the increase of the tensile strength from 800 MPa to 1100 MPa while the strain rate sensitivity of the flow stress decreases to a negligible amount.

کلیدواژه‌ها [English]

  • Dual-phase steel
  • Ferritic-Martensitic
  • Tensile behavior
  • Dislocation density
  • Martensite fraction

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