Low temperature thermo mechanical treatment

Dissertant

Kazim, Hiyam Abd al-Razzaq

University

University of Technology

Faculty

-

Department

Department of Production Engineering and Metallurgy

University Country

Iraq

Degree

Ph.D.

Degree Date

2006

English Abstract

The aim of this research is to improve the strength, hardness with ductility, and toughness properties of tool steel (AISI H-13) by hot working in order to change its shape and refine the microstructure, the LTMT named au forming technique is applied.

A group of (AISI H-13) low alloy tool steel specimens were prepared, which contain 0.4 % C and 5 % Cr.

For studying the behavior of the H-13 tool steel during the hot working, the H-13 tool steel was deformed at various amount of deformation (35, 40, and 45 %) by using one-step hammer forging (3 ton capacity) at different temperature (400, 500, 600, and 700 C°).

then the steel was thermally treated (tempering) after the mechanical treatment at 550˚C.

Mechanical tests (tensile, hardness, and impact) were applied to the unformed H-13 tool steel, as well as specimens amasses by using (XRD), furthermore microstructural analysis were done to define the microstructural component of the au formed tool steel after LTMT.

From the results, it was found that the deformation during the au forming process introduces changes in the microstructure by the transformation of austenite to granular bainitic package structure; consist of (fine alloy carbide precipitations, ferrite, and retained austenite) in a matrix of marten site.

Increasing the amount of deformation means increasing the fine alloy carbide precipitations and consequently increasing the values of mechanical properties, this was also obtained from the analysis of XRD.

Through the XRD analysis we can see that increasing the amount of deformation leads to increasing the amount of fine alloy carbide precipitations.

Mechanical tests results showed that the mechanical properties (the tensile strength, hardness, and ductility) increased with increasing the amount of deformation.

In addition, it has been found that the impact toughness increased too.

The improvement during the ausfonning process apparently results from the formation of bainitic package and the precipitation of a fine dispersion of alloy carbides.

Through the mechanical tests, it was found that the deformation temperature affects the mechanical properties values by lowering these values with increasing the deformation temperature because of the greater strain hardening induced in the austenite.

The visual examination of fractured section of tensile and impact test specimens revealed three types of fracture : Inclined, cup-cone and cleavage fracture.

Inclined fracture has been observed in metal exposed to 35 % deformation, cup-cone fracture has been observed in metal exposed to 40 % deformation, cleavage fractures has been observed in metal exposed to 45 % deformation.

Main Subjects

Mechanical Engineering

Topics

• Mechanical properties

• APA
• MLA
• AMA

Language

English

Data Type

Arab Theses

Record ID

BIM-305932