Effect of cryogenic treatment on the mechanical properties of some quenched and tempered steel

مقدم أطروحة جامعية

al-Nayir, Muhammad Hamid M.

مشرف أطروحة جامعية

al-Tai, Abbas A. Husayn

الجامعة

جامعة أم درمان الإسلامية

الكلية

كلية العلوم الهندسية

القسم الأكاديمي

قسم الهندسة الميكانيكية

دولة الجامعة

السودان

الدرجة العلمية

ماجستير

الملخص الإنجليزي

- This thesis describes a study of the cryogenic treatment effect on the mechanical properties of some quenched and tempered steels.

Four different types of steels with different chemical composition were used medium carbon low alloy, medium carbon low alloy (special), high carbon low alloy and high carbon high alloy.

The aim is to determine the response of these different steel to cryogenic treatment. Standard shaped specimens prepared from each steel type for tensile and impact tests.

These specimens were quenched and tempered, then insulated with parafine wax to prevent thermal shock, and soaked in liquid nitrogen for 24 Hours. Hardness, toughness and tensile properties were then measured before and after cryotreatment. The tests results indicated that improvement in hardness was generally low, but the response of medium carbon low alloy steel was nearly double in comparison to those of high carbon steel. For tensile strength, the result was different, where the response of high carbon steels was better than those of a medium carbon.

However the general improvement was still low. As for toughness, all four steel types indicated positive response, in which high carbon steel (tool and die steel and high speed steel) showed greater improvement (~ 50% to 140 %), and when the specimens were subjected to a postcryo tempering the toughness improved by 250% to 280% without appreciable loss in hardness. The high enhancement in toughness due to cryotreatment may attribute to the development of a more uniform, refined microstructure with greater density.

Also, the formation of micro-fine carbides, which take up the space in the micro-voids, results in a much denser and coherent structure of the tool steel.

The further improvement in toughness due to postcryo tempering can be attributed to the removal of residual stresses raised by the prolonged cryogenic treatment, and to the slight decrease in hardness.

The general conclusion of the present work is that cryogenic treatment could further improve all mechanical properties achieved by heat treatment at the same time.

التخصصات الرئيسية

الهندسة الميكانيكية

الموضوعات

• الخواص الميكانيكية
• سبائك الصلب

عدد الصفحات

168

قائمة المحتويات

• APA
• MLA
• AMA

لغة النص

الإنجليزية

نوع البيانات

رسائل جامعية

رقم السجل

BIM-364301