ABSTRACT The mechanical properties of two different carbon equivalent (4.0、3.7)ductile cast irons after austempered treatment in 360℃ and 390℃ were investigated. Added Ni in the CE4.0 ductile cast irons were compared with no Ni ones. Used image analysis system to analysis graphite parameter. X-ray diffraction was used to evaluate retain austenite fraction. SEM was applied for micro-graph observation of etched specimens of ADIs. Experimental results showed that Ni additions had not remarkable effect on nodularity, nodule count and mechanical properties. Effect of elongation by austempered time in 390℃ was more remarkable than in 360℃. Under same nodule count and treatment, the tested elongations increased by the nodular graphite diameter decreased. Ultra tensile strength (UTS) was associated with nodularity increased, but UTS increased little. Increasing nodule count, the tested elongations had a increased trend. Increasing graphite area fraction reduced both UTS and tested elongations. Increasing the diameter of nodular graphite decreased tested elongations. The mechanical properties of this study applied for ASTM A-897-90 standard, the heat treatment processes had two methods:(1)specimens were preheated at 550℃ for 15 min and asutenitized at 900℃ for 90 min, after which they were quenched in a salt bath at 360℃ for 120 min. After the austempered treatment, specimens were then air-cooled to room temperature. After this method the mechanical properties can reach ASTM A-897-90 1200/850/4 grade standard.(2)specimens were preheated at 550℃ for 15 min and asutenitized at 900℃ for 90 min, after which they were quenched in a salt bath at 360℃ for 60 min. After the austempered treatment, specimens were then air-cooled to room temperature. After this method the mechanical properties can reach ASTM A-897-90 1050/700/7 grade standard. Keyword:processing variables , low carbon equivalent, graphite, ADI.
總目錄
總目錄.......................................................................................................Ⅰ
表目錄..................................................................................................... Ⅳ
圖目錄..................................................................................................... Ⅴ
第一章 緒論.............................................................................................1
1-1研究背景與動機.................................................................................1
1-2研究目的.............................................................................................2
第二章 文獻回顧.....................................................................................3
2-1 沃斯回火球墨鑄鐵(ADI)之發展與簡介........................................3
2-1-1 沃斯回火球墨鑄鐵(ADI)之發展.................................................3
2-1-2 沃斯回火球墨鑄鐵(ADl)簡介.....................................................3
2-2 ADI之製程......................................................................................5
2-3 球墨鑄鐵的成核與成長...................................................................6
2-3-1球墨鑄鐵的成核...........................................................................6
2-3-2球墨鑄鐵的成長.....................................................................9
2-4球墨變數對球墨鑄鐵之影響...........................................................15
2-4-1球墨數與球化率的影響..............................................................15
2-4-2球墨的型態及其成因.................................................................16
2-4-3球墨的退化(或惡化)型態及其成因...........................................17
2-5 主要元素與合金添加對ADI之影響............................................19
2-5-1碳當量(Carbon equivalent)..........................................................20
2-5-2矽(Silicon)...................................................................................21
2-5-3錳(Manganese).............................................................................22
2-5-4鉬(Molybdenum)..........................................................................23
2-5-5鎳(Nickel)和銅(Copper)..............................................................23
2-5-6鎂(Magnesium)............................................................................24
2-5-7硫(Sulfur).....................................................................................25
2-5-8磷(Phosphorus)............................................................................25
2-5-9合金的添加對沃斯回火熱分析的影響.....................................26
2-5-10合金偏析的改善.......................................................................26
2-6 鑄造參數對球墨鑄鐵的影響........................................................27
2-6-1接種與球化處理的影響..............................................................27
2-6-2保持時間(holding time)與澆注溫度(pouring temperature)的影響 ...............................................................................................................28
2-7 沃斯田鐵化溫度及時間對ADI之影響....................................28
2-8 恆溫變態之探討—ADI二階段相變化.....................................29
2-8-1 第一階段相變態(γο→α+γhc) .........................................29
2-8-2 第二階段相變態(γhc→α+carbide)....................................30
2-9 高、低溫回火相變態......................................................................31
2-9-1高溫回火......................................................................................31
2-9-2低溫回火......................................................................................31
2-10影響ADI基地硬度之因素............................................................31
2-10-1碳(C)之影響.........................................................................31
2-10-2 錳(Mn)之影響............................................................32
2-10-3 鎳(Ni)與銅(Cu)之影響.........................................32
2-10-4 沃斯回火時間、溫度與殘留沃斯田鐵之影響..............32
2-10-5 球墨大小之影響..............................................................33
2-10-6 熱機處理(Thermomechanical Treatment)之影響...........33
2-10-7 冷卻時間(Roling Time:AC3→733K)之影響....................33
2-10-8 碳化物形態之影響..........................................................34
第三章 實驗步驟..........................................................................36
3-1 球墨鑄鐵澆鑄...............................................................................36
3-2 試件製作.......................................................................................37
3-3 熱處理...........................................................................................37
3-4 機械性質測試...............................................................................37
3-4-1 拉伸試驗..................................................................................37
3-4-2 衝擊試驗..................................................................................38
3-5 金相觀察.......................................................................................38
3-5-1 ADI試片之金相觀察..............................................................38
3-5-2 球墨數與顆粒尺寸之分析......................................................39
第四章 結果與討論.............................................................................40
4-1 鑄態組織........................................................................................40
4-2 球墨參數的影響............................................................................41
4-2-1碳當量與球墨數之關係..............................................................41
4-2-2球墨粒度......................................................................................42
4-2-3機械性質的影響.........................................................................43
4-3機械性質的探討.............................................................................46
4-3-1 碳含量的影響............................................................................46
4-3-2 沃斯回火的影響........................................................................47
4-3-3不同球墨數、相同碳當量的影響........................................48
4-3-4相同球墨數及熱處理條件下之變異性....................................49
4-4 理想機械性質之熱處理條件..........................................................51
4-5合金元素的影響......................................................................52
4-6顯微組織觀察..........................................................................52
4-7改良式沃斯回火球墨鑄鐵之金相觀察..................................53
第五章 結論與建議.................................................................................56
5-1 結論..................................................................................................56
5-2 建議..................................................................................................57
參考文獻...............................................................................................58
表目錄
表2-1 The Applications of ADIs........................................................65
表2-2 Standards of ADIs....................................................................66
表3-1 Chemical compositions of material 1-5 used in this study.......67
表3-2(a) Chemical compositions of inoculants.......................................67
表3-2(b) Chemical compositions of spheroidizers..................................67
表4-1 Mechanical properties of as-cast Y-block casting....................68
表4-2 Parameter of Graphite in this study(tensile test species)..........69
表4-3 Parameter of Graphite in this study(impact test species).........72
表4-4 Mechanical properties of material 1-5 used in this study.........75
表4-5 Mechanical properties of material with same nodule count.....78
圖目錄
Fig.2-1 Manufacturing processes of ADIs...........................................80
Fig.2-2 (a) Comparsion of tensile strengths and elongations of different Material.(b) Comparsion of mechanical properties of ADIs and other casting material..............................................................81
Fig.2-3 Various manufacturing processes of ADIs..............................82
Fig.2-4 Hexagonal structure of graphite..............................................83
Fig.2-5 Nucleation and growth mechanism of graphite in molten treated with spheroidizer.....................................................................83
Fig.2-6 (a)formation mechanism of Mg gas bubble in liquid iron.(b) Nucleation and growth mechanism of graphite in gas bubble.84
Fig.2-7 Scheme of relationship between growth rate and undercooling for (0001)plane and (1010) plane of graphite during spheroidal growth, where Rp–(1010) plane, two-dimensional nucleation controlled growth.R`p -(1010) plane, continuous growth.R –plane, screw dislocation controlled growth.R`B-(0001) plane,continuous growth.....................................................................................84
Fig.2-8 Structure of circumferentially growing SG in the FeSiRe-treated cast iron (Sample 1,TE,SEM)(a)Micrograph of the SG;(b)AFG at the center of the SG ; (c)The periphery of SG formed by graphite flakes branching frequently and growing circumferentially; (d)Around head of CVG formed by twin/tilt.(e)Schematic representatio of Fig.3d.............................................................85
Fig.2-9 Morphologies of SG in cast irons(DE.SEM)(a)The SG consisting of pyramids growing spirally around periphery(Sample 4, treated with MgTiRE, quenched after slow cooled),(b)The onion type SG.(Sample 3 ,treated with FeSiREMg,green casting, section thickness : 15 mm),(c) The onion type SG.(Sample 2 ,treated with Cu-Mg , green casting, section thickness : 15 mm)........86
Fig.2-10 Structure of ribbed SG(Sample 5, treated with MgTiRE, green
casting, section thickness : 10 mm,TE,SEM)(a)A degenerated
ribbed SG ; (b)AFG at the center of the SG.........................86
Fig.2-11 Schematic representation of radial SG..................................87
Fig.2-12 Schematic representation of growth process of duplex SG..87
Fig.2-13 Structure of duplex SG in FeSiRE-treated cast iron.(Sample
1,green casting , section thickness : 15 mm,TE,SEM)(a)duplex
SG with circumferentially growing interior spherulite and A
spirally growing outer shell ; (b) The circumferentially growing
interior spherulite ; (c) The nodular nucleus of the SG and
center part of the spherulite formed by graphite flakes growing
circumferentially from the nodular nucleus..........................88
Fig.2-14 Relationship between the type of austinite and the shape of the
graphite spheroids.................................................................88
Fig.2-15 Isothermal growth mechanism of graphite in austenite shell,(a)
In contacted with residual austenite as graphite growth. (b)
Graphite that bounded by austenite ring. (c)Bull-eye
structure.................................................................................89
Fig.2-16 Micro-segreations of alloying elements................................90
Fig.2-17 (a)Summary of the UTS vs. wt% Mn of austempered casting .
The lines refer to average values at the top and the bottom. The
individual points represent the extremes(i.e.the best and worst
properties at the bottom and top. repectively)(b) Summary of
the percent elongation vs. wt% Mn of austempered casting .The
lines refer to average values at the top and the bottom. The
individual points represent the extremes (i.e.the best and worst
properties at the bottom and top. repectively)........................91
Fig.2-18 (a)Effect of molybdenum on mechanical properties of ADIs (b)
Effect of nickle on mechanical properties of ADIs................92
Fig.2-19 Effect of phosphorus on mechanical properties of ductile iron...........................................................................................93
Fig.2-20 Effect of Allying elements addition and nodule count on the
types and distributions of ferrite............................................93
Fig.2-21 Effect of temperature on inoculated conditions.....................94
Fig.2-22 Relationship between optimum pouring temperature and section
thickness................................................................................94
Fig.2-23 (a)Effect of austenitizing temperature and time on concentration
of cabon. (b) Effect of austenitizing temperature on TTT
diagram……………..……………………………………....95
Fig.2-24 The first stage phase transformation of ADIs…………........96
Fig.2-25 Schematic microstructures of two stage phase transformations of
ADIs and steel……………………………………………...97
Fig.2-26 Relationship between austempered time,ferrite and high carbon
austenite………………………………………………….....98
Fig.2-27 Schematic microstructures of ADIs with high isothermal holding temperature(350C). (b) Schematic microstructures of ADIs with low isothermal holding temperature (<=350C)….99
Fig.2-28 Relation between C content and mechanical properties…..100
Fig.2-29 Relation between Mn content and retained austenite……..100
Fig.2-30 Influence of Mn content on mechanical properties of ADIs.101
Fig.2-31 Ni vs. Cu response surface of Rockwell hardness for diam.30
mm specimens……………………………………………….101
Fig.2-32 Influence of austempering time and temperature on hardness and
retain(stabilized) austenite…………………………………...102
Fig.2-33 Effect of austempering time and spherodial graphite size on
Hardness(Austempering temperature : 673 K)………………102
Fig.2-34 Effect of austempering time on retained austenite(Austempering
temperature : 673 K)…………………………………………103
Fig.2-35 Relationship between Vickers hardness and reduction ratio..103
Fig.2-36 Relationship between Vickers hardness and austempering
time…………………………………………………………..104
Fig.2-37 Relationship between hardness and cooling time from AC3 to
773K…………………………………………………………104
Fig.2-38 Secondry electron image and EDS spectrum of inclusion and graphite at different positions in a rapid cooled specimen.(A)near chilled surface.(B)0.6mm inner from surface.(C) 2.5 mminner from surface...........................................................................104-1
Fig.3-1 ASTM A439 Y-block pattern..............................................105
Fig3-2 Dimensions of (a) tensile test specimen (b)impact test
specimen .............................................................................105
Fig 4-1 Ferrite content (80%) of DI-1,S1.........................................106
Fig 4-2 Ferrite content (45%) of DI-1,S3.........................................106
Fig 4-3 Ferrite (35%) and carbide(10%) contents of DI-5,S3..........107
Fig4-4 Relationship between nodule count and nodular graphite
diam.....................................................................................107
Fig 4-5 Relationship between UTS and Nodularity.........................108
Fig 4-6 Microstructure of DI-4........................................................109
Fig 4-7 Relationship between Elongation and Nodularity...............110
Fig 4-8 Relationship between UTS and Nodule count.....................111
Fig 4-9 Microstructures of DI-2 after austempered 390℃1 hr......112
Fig 4-10 Microstructures of DI-3 after austempered 390℃1 hr......112
Fig 4-11 Relationship between Elongation and Nodule count...........113
Fig 4-12 Relationship between UTS and Graphite area.....................114
Fig 4-13 Relationship between Elongation and Graphite area...........115
Fig 4-14 Relationship between UTS and Nodular Graphite dia.........116
Fig4-15 Relationship between Elongation and Nodular Graphite
dia........................................................................................117
Fig 4-16 Microstructure of DI-3 after austempered 390℃1 hr.......118
Fig4-17 Relationship between unreact Austinte and Graphite
Factor...................................................................................119
Fig4-18 Relationship between unreact Austinte and Austempered
time,390℃...........................................................................120
Fig4-19 Relationship between unreact Austinte and Austempered
time,360℃...........................................................................121
Fig4-20 Relationship between UTS and Austempered time.............122
Fig4-21 Relationship between Impact energy and Austempered
Time.....................................................................................123
Fig 4-22 Relationship between Elongation and Austempered time....124
Fig 4-23 Relationship between UTS and Austempered temperature..125
Fig4-24 Relationship between Elongation and Austempered
Temperature.........................................................................126
Fig4-25 Relationship between UTS and Elongation in various
Nodule count,390℃............................................................127
Fig4-26 Relationship between UTS and Elongation in various
Nodule count,360℃............................................................128
Fig4-27 Microstructures of DI-1 after Austempered 390℃1 hr.......129
Fig4-28 Microstructures of DI-2after Austempered 390℃2 hr…....129
Fig4-29 Microstructures of DI-5(S2) after Austempered 390℃2
hr…………………………………………………………..130
Fig4-30 Microstructures of DI-5(S1) after Austempered 390℃2 hr..130
Fig4-31 Optical micrographs of CE3.7 after cooling from 900℃to
760℃ in 12 min, 200X(V/A=1.67)................................131
Fig4-32 Optical micrographs of CE4.0 after cooling from 900℃to
760℃ in 12 min, 200X(V/A=1.67)................................131
Fig4-33 Optical micrographs of CE3.7 after cooling from 900℃to
760℃ in 12 min and keep 3 min, 200X(V/A=1.67)......132
Fig4-34 Optical micrographs of CE4.0 after cooling from 900℃to
760℃ in 12 min and keep 3 min, 100X(V/A=1.67)......132
Fig4-35 Optical micrographs of CE3.7 after cooling from 900℃to
760℃ in 12 min and keep 3 min, 200X(V/A=2.29)......133
Fig4-36 Optical micrographs of CE4.0 after cooling from 900℃to
760℃ in 12 min and keep 3 min,100X(V/A=2.29).......133
Fig4-37 Optical micrographs of CE3.7 after cooling from 900℃to
760℃ in 12 min and keep 3 min, 1000X(V/A=1.67).....134
Fig4-38 Optical micrographs of CE4.0 after cooling from 900℃to
760℃ in 12 min and keep 3 min, 1000X(V/A=1.67).....134
Fig4-39 Relationship between Strength and Elongation,360℃............135
Fig4-40 Relationship between Strength and Elongation,390℃............135
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