note to users

NOTE TO USERS

Page(s) not included in the original manuscript and are unavailable from the author or university. The manuscript was scanned as received.

IX

This reproduction is the best copy available.

®

UMI Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

TORSION TEST: AN EFFECTIVE TOOL TO EVALUATE WIRE DUCTILITY

A Thesis Presented to The Faculty of the College of Graduate Studies Lamar University

In Partial Fulfillment of the Requirements for the Degree Master of Engineering Science by Nachiket Patil December 2006

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

UMI Number: 1446353

INFORMATION TO USERS

The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion.

®

UMI UMI Microform 1446353 Copyright 2008 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code.

ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

TORSION TEST: AN EFFECTIVE TOOL

TO EVALUATE WIRE DUCTILITY

NACHIKET PATIL

Approved:

V / 0 V /I A / A .

Malur N Srinivasan Supervising Professor

Kendrick T Aung Committee Member

Jiang Zhou Committee Member

Hsing-Wei Chu Chair, Department of Mechanical Engineering

Jack Hopperc Dean, College of Lamar University

>. Bradley jfean, College of Graduate Studies

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

© 2006 by Nachiket Patil

No part of this work can be reproduced without permission except as indicated by the “Fair Use” clause of the copyright law. Passages, images, or ideas taken from this work must be properly credited in any written or published materials.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

TORSION TEST: AN EFFECTIVE TOOL TO EVALUATE WIRE DUCTILITY By Nachiket Patil

ABSTRACT

Wire quality assessment is an important function. Torsion test is an easy, quick, and reliable method that effectively helps to gauge the wire quality, and hence the results are of utmost importance. Torsion test can reveal whether the specimen wire would perform as per the expectations or not. Flence, the Quality Control and Metallurgical team at Gerdau Ameristeel Beaumont (GAB) decided to establish and develop the use of wire torsion testing. Setting up of the required equipment was the first step; the next was preparing a fracture classification reference. A variety of samples, along with their fracture photographs, and ones from literature helped to prepare the reference manual. With this manual just by looking at the fracture photograph one can very easily ascertain approximately where in the manufacturing process the defect would have occurred. The addition of this capacity to the Metallurgical Laboratory at Gerdau Ameristeel Beaumont (GAB) greatly assists both the development of new grades and the improvement of those established.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

ACKNOWLEDGMENT

The author would like to express his sincere and greatest appreciation to Dr. Malur Srinivasan, his supervising professor, who allotted a great deal of time throughout the research. Without Dr. Srinivasan’s help he would not have completed thesis. Profound acknowledgment is also dedicated to Dr. Kendrick Aung and Dr. Jenny Zhou for their willingness to accept the position of committee member. The support of Gerdau Ameristeel Beaumont (GAB), Texas, is greatly acknowledged. The author is highly thankful to Dr. Bhaskar Yalamanchili for his help in getting him the project and supporting him until its end. The author is also very grateful for the guidance given by Mr. Peter Power. Without his valuable guidance he would not have completed the project within the stipulated time. Author would also like to thank Mr. Dan Lanham for his help in setting up the production runs for both rod and wire and Mr. Thad Boudreaux for his help in providing the specimen chemistry and lab services. The author would also like to thank Mr. Keith Cribbs and Mrs. Cathay Morton for helping him with the metallographic work. The author also thanks Gerdau Ameristeel management for granting the permission to carry out the project in their premises and supporting him in every possible way. He would also like to thank Carrollton Steel and Wire for their help in sending the samples and the torsion testing machine.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

Special thanks are due to the author’s father, mother, and sister for their understanding and encouragement in this study. The author appreciates the help of people who have directly or indirectly helped in the completion of his project.

iv

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

DEDICATION

This Thesis is dedicated to my family in Pune, India, for their support, love, inspiration, and encouragement.

v

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

TABLE OF CONTENTS

Page List of Tables............................................................................................................................ x List of Figures.......................................................................................................................... xi List of Sym bols.....................................................................................................................xiv Chapter 1. Introduction................................................................................................................... 1 2. Literature Review......................................................................................................... 3 2.1 Classification of SteelWire Rods......................................................................... 3 2.1.1 Low Carbon Steel Wire Rods....................................................................3 2.2.2 Medium Low Carbon Steel Wire Rods.................................................... 3 2.1.3 Medium High Carbon Steel Wire Rods....................................................4 2.1.4 High Carbon Steel Wire Rods...................................................................4 2.2 Wire Rod Production Process.............................................................................. 5 2.2.1 Melting........................................................................................................ 5 2.2.2 Refining and Tapping................................................................................ 6 2.2.3 Ladle Refining............................................................................................ 6 2.2.4 Casting........................................................................................................ 7 2.2.5 Rolling.........................................................................................................8 2.3 Wire Drawing............................................................................................................8 2.4 Cold Drawing and its Effect...................................................................................10 2.5 Dislocation Theory.................................................................................................. 10

vi

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

2.6 Evaluation of the Rate of Strain Hardening..................................................... 11 2.7 Controlled Cooling of Wire Rod....................................................................... 13 2.8 Effects of Cooling Rates on Physical Properties.............................................17 2.9 Effect of Cold Work on the Physical Properties..............................................18 2.10 Wire Drawing at Carrollton Steel and Wires..................................................19 2.11 Introduction to Torsion Test............................................................................20 2.12 Torsion Fracture Phenomenon.........................................................................22 2.13 Principal Plane and Principal Stress Theory.................................................22 2.14 Primary Causes for Failure.............................................................................. 28 2.14.1 Surface Defects.................................................................................. 28 2.14.2 Inclusions............................................................................................32 2.14.3 Delamination...................................................................................... 34 2.14.3.1 Shear Banding Formation....................................................34 2.14.3.2 Fracture Mechanics of Delamination..................................35 2.14.3.3 Stress Strain Curves............................................................. 37 2.15 Aging............................................................................................................................. 38 2.15.1 Quench Aging..................................................................................................... 38 2.15.2 Strain Aging........................................................................................................ 39 3. Scope of Present Investigation........................................................................................ 43 4

Experimental Procedure 4.1 Experimental Procedure..........................................................................................44 4.1.1 Carrollton Samples.........................................................................................44 4.1.2 Delta Sample Specifications......................................................................... 45

vii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

4.1.3 Bekaert Sample Specifications.....................................................................47 4.2 Experiment Procedure and Variables.......................................................................48 4.3 Test Equipments......................................................................................................... 53 4.4 Comparative Testing.................................................................................................. 55 5. Microstructure Analysis....................................................................................................56 5.1 Metallography...........................................................................................................56 5.1.1 Microscopy..................................................................................................... 57 5.1.2 Macroscopy..................................................................................................... 64 5.2 Desired Microstructure..........................................................................................65 5.3 Effect of Composition and Microstructure on Rate of Strain Hardening..........66 5.4 Discussion of Results......................

69

5.4.1 Intensity of Delamination............................................................................ 69 5.4.2 Ferrite Content.............................................................................................. 71 5.4.3 Martensite Traces..........................................................................................73 6. Results and Discussions....................................................................................................74 6.1 Torsion Test Results.................................................................................................. 74 6.2 Discussion of Results................................................................................................ 76 6.2.1 Minimum Twist Criteria................................................................................ 76 6.2.2 Entire Process Route.......................................................................................80 6.2.3 Delamination................................................................................................... 81 6.2.4 Torsion Failure Classification as Per Fracture Types.................................. 81 6.2.5 Manual............................................................................................................84 7. Conclusions........................................................................................................................ 86

viii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

LIST OF TABLES

Table

Page

4.1

Chemical Composition for Batch

1..

45

4.2

Chemical Composition for Batch

1....................................................................46

4.3

Chemical Composition for Batch

1....................................................................47

4.4 ASTM Standards............................................................................................................ 48 4.5 Recommended Tensile Forces To Be Applied to Wireduring TorsionTesting......... 51 4.6

Recommended Maximum Twisting Speeds...............................................................51

5.1 Typical Materials and Their Properties.......................................................................... 58 6.1 Batch #1 Test Results.....................................................................................................74 6.2 Batch #1 Test Results after Inducing Physical Defect on the Surface....................... 74 6.3 Batch #2 Test Results..................................................................................................... 75 6.4 Batch #3 Test Results.....................................................................................................75 6.5 Torsion and Strength Requirements..............................................................................76 6.6 Summary of Factors Affecting TorsionalProperties of High CarbonSteel Wire.......80

x

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

LIST OF FIGURES Figure

Page

2.1

Gerdau Ameristeel Beaumont, Texas, Process Flow Sheet........................... 5

2.2

Section through Wire Drawing Die.................................................................9

2.3

Basic Theory of Plastic Deformation.............................................................10

2.4

Two Mechanisms of Slip................................................................................11

2.5

Relationship between Tensile Strength of Cold Drawn Steel Wire and Reduction of Area by Wire Drawing........................................................... 12

2.6

The Stelmor® Deck Showing the Conveyer and the Laying Head Taken at Gerdau Ameristeel, Beaumont, Texas......................................................... 13

2.7

Effect of Cooling Rate and Austenite Grain Size on Ferrite Grain Size in AISI 1008,1022, and 1030 Steel Rods..................................................... 14

2.8

Effect of Cooling Rate and Austenite Grain Size on Pearlite Content in AISI 1008, 1022, and 1030 Steel Rods..................................................... 15

2.9

Effect of Cooling Rate and Austenite Grain Size on the Tensile Properties of AISI 1008 Steel R o d s.............................................................................. 17

2.10

Effect of Cold Work on the Physical Properties of Mild Steel.................... 18

2.11

Wire Drawing Setup at Carrollton Steel and Wires, Dallas, Texas.............19

2.12

Member Subjected to Axial Load.................................................................. 22

2.13

Member Subjected to Like Principal Stresses.............................................. 24

2.14

Ductile and Brittle (45 Degree) Failure Modes in Torsion Testing............ 26

2.15

Longitudinal Ductile Torsion Failures Resulting in a Helix Fracture.........27

2.16

Typical Lap Defect.............................

xi

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

28

2.17

SEM Picture of a Completely Flat, Ductile Fracture Surface.....................30

2.18

Surface Defect Tree........................................................................................31

2.19

SEM Picture View of a Cavity Left by an Undeformable Inclusion............33

2.20

Illustrative Scheme of Shear Banding Formation..........................................35

2.21

Applied Stresses in Torsion Test.................................................................... 35

2.22

Fracture Modes in Delamination.................................................................... 36

2.23

Schematic Diagram of Torsional Stress-Strain Curve..................................37

2.24

Dislocations Locked by Nitrogen.................................................................. 40

2.25

SEM Picture of a Typical Delamination Helix.............................................. 41

2.26

Delamination Tree........................................................................................... 42

4.1

Sketch Showing 90° Bend at Ends of Test Specimen................................... 50

4.2

Torsion Testing Machine at Gerdau Ameristeel, Beaumont (GAB)............53

4.3

Optical Microscope..........................................................................................54

4.4

Molding Machine........................................................................................... 54

4.5

Rough Polishing Machine............................................................................. 54

4.6

Fine Polishing Machine................................................................................. 54

5.1

Etching Reveals Grain Boundary in a Single-Phase Material...................... 61

5.2

Difference in Grain Orientation Produces Contrast Difference................... 62

5.3

Effect of Carbon Percentage on the Tensile Strength Gain..........................67

5.4

Photomicrograph of Pearlite (Dark Constituent) in a Low Carbon Wire Rod (1006) Taken at 500X........................................................................... 68

5.5

Cross Section of Wire Torsioned to Failure, Clearly Showing Shear Deformation Lines.........................................................................................69

xii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

5.6

Batch #2 Sample #1 Good Sample Showing Less IntenseDeformation Lines................................................................................................................ 70

5.7

Batch #2 Sample #3 Bad Sample Showing Intense Deformation Lines....70

5.8

Batch #2 Sample #3 Bad Samples Showing More Ferrite Locations

5.9

Batch #2 Sample #1 Good Samples Showing No Tracesof Ferrite..............72

5.10

Representative Figure Indicating Traces of Martensite.................................73

6.1

Typical Picture of a Wire Primarily Failing because of Surface

72

Defect..............................................................................................................77 6.2

Fractures Obtained on Batch #3 Samples..................................................... 78

6.3

Fractures Obtained on Batch #3 Samples; Showing a Typical Delamination-Type Fracture.........................................................................79

6.4

Torsion Failure Classifications......................................................................81

6.5

Normal Torsion Failure.................................................................................. 82

6.6

Torsion Fracture with Local Cracks..............................................................82

6.7

Torsion Fracture with Spiral Cracks All Along the Wire Length............... 83

xm

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

LIST OF SYMBOLS

Symbol

Description

C

Carbon

Mn

Manganese

P

Phosphorous

S

Sulfur

Si

Silicon

Cu

Copper

Ni

Nickel

Cr

Chromium

Mo

Molybdenum

Sn

Tin

xiv

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

Patil 1 CHAPTER 1 INTRODUCTION

Gerdau Ameristeel in Beaumont (GAB) was founded in 1976 and has been a predominant steel producer. It now produces wire rod for steel wires used to make nails, fencing of all sizes and types, bed springs, and many other products. Coiled rebar is used for construction applications. Its melt shop has the capacity to produce 720,000 tons per year, and the rolling mill operates with a 720,000 ton per year capacity (Yalamanchili, Nelson, Power, and Lanham 2000). The hot rolled rods are usually shipped to satisfy customer defined specifications in yield strength, tensile strength, and total elongation where they are cold drawn. The customers have found bundles of such cold drawn wires with similar tensile strength that varied widely in their torsional yield strengths. One bundle would produce uniform springs having a long fatigue life; another bundle would produce unsatisfactory springs with short life. Researchers have found that this variation is related directly to the orientation of the grain structure developed within the material during heat treatment in the wire mill. Hence the customers ship back the defective bundles to the manufacturers. Torsion test on these samples would help find the reason for the wire failure. Though the number of turns to failure by torsion in a test set-up cannot be related directly to the wire quality, the fracture type can definitely be. From the fracture type one can easily ascertain the probable cause of fracture.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

Patil 2 By studying a variety of samples and the literature available, one can conclude that the probable causes for torsion failure would be from surface defects, delamination, or inclusions. The microstructure analysis also revealed that microstructure governs the behavior of the cold drawn wires. The common causes for surface defects could be formation of seams, laps, slivers, mechanical damage, galling, and grazing. Delamination could be caused by aging, drafting practice, the ratio of yield strength to ultimate tensile strength, and other factors.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

Patil 3 CHAPTER 2 LITERATURE REVIEW

Steel is considered carbon steel when no minimum content is specified or required for aluminum, chromium, molybdenum, nickel, titanium, tungsten, vanadium, zirconium, or any other element added to obtain the required effect when the maximum content specified for the following elements does not exceed the percentages noted: manganese 1.65%, silicon 0.60%, copper 0.60%. Carbon steels contain only carbon as alloying element (American Iron and Steel Institute Committee Members 1977). Wire rods are semi-finished, hot rolled products (to an approximately round cross section) and are intended primarily for the manufacture of wire. They are produced in coils of one continuous length.

2.1 Classification of Steel Wire Rods Carbon Steel wire rods can be classified according to their carbon content as follows: 2.1.1 Low Carbon Steel Wire Rods They, by definition, contain less carbon than other steels usually,

90

Impact f .p .s .l

jy«i