Abrasion-Resistant White Cast Iron 25 -ASTM A532_A532M

Abrasion-Resistant White Cast Iron 25

-ASTM A532_A532M

 

  • 5.4 Bimetal composite material and composite casting process

Many parts are in the field of not only high stress but also high impact load abrasive wear. In view of the fact that it not only require good abrasion resistance but also require good strength and toughness. The compound casting process makes the casting a composite with two kinds of material properties at the same time. The process is with high chromium white cast iron-steel bimetal composite material. Which greatly improves the service life time of the vulnerable parts.

 

High chromium white cast iron and cast steel bimetal composite material play the good antiwear properties. It has the same abrasion resistant property of high chromium white cast iron. At the same time it also played a good strong toughness of cast steel, parts abrasion and impact resistance. So that it can ensure the safety in the process of using reliability and durability. With bimetal composite casting technology we can produce a large variety of compound castings. Such as ball mill liner (Ø  5m x Ø 15.6m), large excavator bucket teeth. And also various specifications of jaw crusher jaw plate, various hammer head, board hammer and so on. Its lifetime is 4~8 times higher than that of a single high manganese steel.

Abrasion-Resistant White Cast Iron 24 -ASTM A532_A532M

Abrasion-Resistant White Cast Iron 24

-ASTM A532_A532M

 

  • 5.3 Rational selection of matrix structure of high chromium white cast iron continued.

 

The results of the wear surface analysis show that in martensite + bainite + austenite matrix. Maybe the impact fatigue exfoliation is obviously smaller than martensite matrix.  Furthermore the microcrack is smaller than martensite. Which is related to the distribution of martensite + bainite + austenite basic tissue. It seems like it is easy to produce the crack initiation of carbide.

Surrounded by bainite austenite is surrounded by bainite. And martensite is located in the region of austenite transformation away from bainite. Even if the carbide microcracks occur in the impact abrasive wear. The surrounding matrix is bainite and austenite with a certain impact resistance. And the austenite has a good passivation on the crack. As a result which makes the crack difficult to expand. In conclusion it does not crack quickly like martensite to form a net and accelerates the fatigue exfoliation of the matrix.

The results of the study and the field contrast test show that the martensitic matrix shows good abrasion resistance in low stress abrasive wear. While martensitic + bainite + austenite structure shows good abrasion resistance and impact fatigue resistance in high stress and impact load abrasive wear.

Abrasion-Resistant White Cast Iron 23 -ASTM A532_A532M

Abrasion-Resistant White Cast Iron 23

-ASTM A532_A532M

  • 5.3 Rational selection of matrix structure of high chromium white cast iron

First of all many manufacturers prefer to choose the tempered martensite when choosing the matrix structure of high chromium white cast iron. No matter the working condition and the stress state of the castings. Even the less the retained austenite in the matrix is better. The retained austenite can be regarding as the defect of the structure. And even as the standard of the product’s disqualification.

Due to the research results show that the wear behavior of the matrix is different in different wear systems. As a result we can select the matrix according to the wear characteristics and the stress state of the parts. That  so as to maximize the potential of the material.

The test results show that the martensitic matrix displays the best abrasion resistance under low stress abrasive wear condition. No matter it is high chromium white cast iron or medium chromium white cast iron. Followed by martensite + bainite + austenite complex matrix. Then it is bainite + austenite. And probably the worst is austenite.

The results of the field assessment confirmed this conclusion. Martensite + bainite + austenite complex matrix of medium chromium white cast iron grinding ball shows the best wear resistance on the gold ball mill. And also shows the minimum crushing rate. Analysis of wear morphology shows that grinding ball wear belongs to abrasive wear which is mainly fatigue peeling mechanism. In conclusion improving the anti fatigue ability of grinding balls is the best way to improve wear resistance and reduce crushing rate of grinding balls.

The results of the wear surface analysis show that in martensite + bainite + austenite matrix. Maybe the impact fatigue exfoliation is obviously smaller than martensite matrix.  Furthermore the microcrack is smaller than martensite. Which is related to the distribution of martensite + bainite + austenite basic tissue. It seems like it is easy to produce the crack initiation of carbide.

Abrasion-Resistant White Cast Iron 22 -ASTM A532_A532M

Abrasion-Resistant White Cast Iron 22

-ASTM A532_A532M

  • 5.2 Casting process and quality of castings

There are many factors influencing casting quality. And also casting process is the most important factor affecting casting quality. It is not difficult to see from table 13 that the related casting technology. Such as strengthening cooling, reducing inclusions, strengthening the full filling of castings. And improving the strength and toughness of white cast iron (bimetal compound casting process). Consequently it can significantly improve the performance of high chromium white cast iron. Generally speaking, the quality of castings can be improved by means of wet type, metal type, external cold iron. Same process as adding heat preservation on pour system and adding filter screen in gating system.

Table 13 Influence of several casting methods on the performance of high chromium cast iron products

casting method Products Performance
Lifetime comparison Damage type
Wet casting Blade of shot blasting machine high
Dry mold casting low
Working face with external cold iron Ø1.83M to 3.5m ball mill liner 1.3-1.5
Do not add cold iron 1 Most of them are broken
Metal type Grinding ball Ø30mm~120mm 1.3-1.4 Low crushing rate, roundness
Sand mold 1 High crushing rate, loss of circle
Filter network Impellers of impurity pump 1.3-1.5 Uniform wear
Non filter net 1 Concentrated wear, perforation
Heat insulating casting head Various grinding ball high Roundness
No insulating casting head low Big tends of loss of roundness
Bimetal compound casting Large ball mill liner 2-3
Single metal 1 Break off

Abrasion-Resistant White Cast Iron 21 -ASTM A532_A532M

Abrasion-Resistant White Cast Iron 21

-ASTM A532_A532M

 

  1. C. Effects of modification on grain boundary metallurgical quality of high chromium white cast iron

First of all there are many factors that affect the grain boundary metallurgical quality of high chromium white cast iron. Furthermore the content and morphology of inclusions seems like the most influential factors. The analysis results show that the main inclusions are sulfide and oxide or silicate. Which are in the grain boundary of high chromium white cast iron. In addition sulfide and oxide are most sensitive to the mechanical properties.  Furthermore it is not difficult to see from table 11 that SI and S III modifiers significantly reduce oxygen and sulfur content.  Thus seems like significantly reducing the grain boundary inclusions.

 

Especially relevant in table 12 shows the effect of different modifiers on impact value and probably small energy impact value also.

Table 12 Effect of different modifiers on impact value and small energy impact value

Batch No. Chemical composition % Modifier type Impact value

αk

/ J. ·cm – 2

Small energy multiple shocks / times

(impact power is 117J)

Grinding ball

Test / times

Hardness

HRC

C S Si Mn Cr Cu
0-1 2.49 0.047 0.85 1.55 15.6 Fe – Mg – Ba – Ca 7.08, 8.75 56
1-1 2.75 0.047 1.18 1.47 15.5 7.9 , 7 , 7.9 57
2-1 2.61 0.048 0.83 1.55 16.3 0.73 SiC 7.2 , 5.6 57
2-2 2.52 0.048 0.91 0.39 10.9 0.32 8.5 , 8 56
2-3 2.49 0.047 0.85 1.55 15.6 0.53 9 , 10.5 56
3-1 2.49 0.047 0.85 1.55 15.6 SI 56
3-2 2.49 0.047 0.85 1.55 15.6 11.4, 12.4 56
3-3 2.49 0.047 0.85 1.55 15.6 0.71 9.5 ,12.6 ,12.3 56
3-4 2.49 0.047 0.85 1.55 15.6 0.32 12.2, 13.2 56
3-5 2.49 0.047 0.85 1.55 15.6 0.51 11.5, 9.5, 13.2 34100 3250 56
4-1 2.49 0.047 0.85 1.55 15.6 S Ⅲ 8.3 , 10 , 10 56
4-2 2.49 0.047 0.85 1.55 15.6 0.71 56
4-3 2.49 0.047 0.85 1.55 15.6 0.32 10.6 , 9.6 56
4-4 2.49 0.047 0.85 1.55 15.6 0.57 11 , 10.4 56
4-5 2.49 0.047 0.85 1.55 15.6 0.53 11 , 12.4 56
5-1 2.49 0.047 0.85 1.55 15.6 0.51 Molten iron 5.3 , 6.3 20500 1350 56
5-2 2.49 0.047 0.85 1.55 15.6 0.53 5.4 , 5.7 56

Abrasion-Resistant White Cast Iron 20 -ASTM A532_A532M

Abrasion-Resistant White Cast Iron 20

-ASTM A532_A532M

 

  1. C. Effects of modification on grain boundary metallurgical quality of high chromium white cast iron

First of all there are many factors that affect the grain boundary metallurgical quality of high chromium white cast iron. Furthermore the content and morphology of inclusions seems like the most influential factors. The analysis results show that the main inclusions are sulfide and oxide or silicate. Which are in the grain boundary of high chromium white cast iron. In addition sulfide and oxide are most sensitive to the mechanical properties.  Furthermore it is not difficult to see from table 11 that SI and S III modifiers significantly reduce oxygen and sulfur content.  Thus seems like significantly reducing the grain boundary inclusions.

 

Especially relevant in table 12 shows the effect of different modifiers on impact value and probably small energy impact value also.

 

Table 11  The effect of modification on sulfur content and oxygen content

Modifier type Amount of addition  % sulfur content  % oxygen content x10-6
SI 0 0.065 84
SI 112 0.035 45
SI 115 0.028 32
S Ⅱ 0 0.08 79
S Ⅲ 110 0.038 47
S Ⅲ 112 0.023 22

Abrasion-Resistant White Cast Iron 19 -ASTM A532_A532M

Abrasion-Resistant White Cast Iron 19

-ASTM A532_A532M

  1. B. Effects of modifier and modification on the morphology of as cast carbides

The effects of modifier type and modification on austenitic characteristics and carbide perimeter are shown in Table 9 and table 10 respectively.

Table 9  Effects of metamorphism on austenite properties (same field of view)

Sample number Modifier type The total area of austenite

A/ mm2

Austenite grain number / piece Nominal diameter of austenite  α/mm
1 SI 01865294 E – 02 21 01202989 E – 01
2 SI 01952776 E – 02 25 01195220 E – 01
3 S Ⅲ 01970025 E – 02 23 01205366 E – 01
4 S Ⅲ 01763587 E – 02 26 01171373 E – 01
5 Unmetamorphosed 01107800 E – 01 14 01277488 E – 01
6 Unmetamorphosed 01107042 E – 01 11 01311946 E – 01

 

Table 10  Effect of modification on the perimeter of carbides

Sample number Modifier type The total area of austenite

A/ mm2

Total carbide perimeter P / mm Carbide shape factor

P∶A

1 SI 01149494 E – 01 3151213 2341940
2 SI 01149494 E – 01 3158571 2051842
3 S Ⅲ 01142976 E – 01 2194304 2061564
4 S Ⅲ 01134971 E – 01 2195316 2181799
5 Unmetamorphosed 01142476 E – 01 2182331 1981160
6 Unmetamorphosed 01142476 E – 01 1179655 1261102

Abrasion-Resistant White Cast Iron 18 -ASTM A532_A532M

Abrasion-Resistant White Cast Iron 18

-ASTM A532_A532M

  1. 5. The process to improve the performance of abrasion resistant castings

Now the process of producing high chromium white cast iron is introduced as a sample.

  • 5.1 In the furnace adopt the comprehensive modification process to purify molten iron. Hence the process will improve grain boundary metallurgical quality.

The main factors affecting the toughness of the high chromium white cast iron with the same composition are:

(1) the shape, distribution and size of the carbide.

(2) the metallurgical quality of the grain boundary.

(3) the micro porosity.

(4) the grain degree.

(5 )the composition and content of the matrix.

Now introduce austenite nominal diameter α to discuss the degree of refinement of primary austenite before and after modification. At the same time introduce the concept of carbide shape factor P/ A to investigate the extent of eutectic carbide shape. And also the size before and after modification. By quantitative microscopy electron probe and energy spectrum technology to study the effects of grain boundary metallurgical quality. And also the matrix structure and composition content on the comprehensive properties of high chromium white cast iron. The modifier used is not only a strong carbide forming element but also a strong graphitization element. SⅠ and SⅢ with strong purification capability during the modification process.

 

  1. A. the controlled chemical composition of high chromium white cast iron used in the research is shown in table 8.

Table 8 the controlled chemical composition in the research

C Si Mn Cr Mo Cu Ti V
1.8-3.0 0.6-2.3 0.5-2.5 14-16 < 3.0 0.5-0.58 0.08-0.2 0.2-0.4

Abrasion-Resistant White Cast Iron 17 -ASTM A532_A532M

Abrasion-Resistant White Cast Iron 17

-ASTM A532_A532M

  1. 4. Domestic and international standard for abrasion resistant white cast iron

The relevant domestic and international standards listed in table 6 and table 7 respectively.

Table 6  Chemical composition of GB8263-87 wear resistant white cast iron in China %

Material grade C Si Mn Cr Mo Ni Cu W S P
KmTBMn5W3 3.0~3.5 0.8~1.3 4.0~6.0 2.5~3.5 ≤0.10 ≤0.15
KmTBM5Cr4 2.5~3.5 0.5~1.0 0.5~1.0 3. 5~4.5 4.5~5.5 ≤0.10 ≤0.15
KmTBNi4Cr2 – DT 2.7~3.2 0.3~0.8 0.3~0.8 2.0~3.0 0~1.0 3.0~5.0 ≤0.10 ≤0.15
KmTBNi4Cr2 – GT 3.2~3.6 0.3~0.8 0.3~0.8 2.0~3.0 0~1.0 3.0~5.0 ≤0.10 ≤0.15
KmTBCr9Ni5Si2 2.5~3.6 1.5~2.2 0.3~0.8 8.0~10.0 0~1.0 4.5~6.5 ≤0.10 ≤0.15
KmTBCr2Mo1Cu1 2.4~3.6 ≤1.0 1.0~2.0 2.0~3.0 0.5~1.0 0.8~1.2 ≤0.10 ≤0.15
KmTBCr15Mo2 – DT 2.0~2.8 ≤1.0 0.5~1.0 13.0~18.0 0.5~2.5 0~1.0 0~1.2 ≤0.06 ≤0.10
KmTBCr15Mo2 – GT 2.8~3.5 ≤1.0 0.5~1.0 13.0~18.0 0.5~3.0 0~1.0 0~1.2 ≤0.06 ≤0.10
KmTBCr20Mo2Cul 2.0-3.0 ≤1.0 0.5~1.0 18.0~22.0 1.5~2.5 0~1.5 0.8~1.2 ≤0.06 ≤0.10
KmTBCr26  2.3-3.0 ≤1.0 0.5~1.0 23.0-28.0 0-1.0 0~1.5 0~2.0 ≤0.06 ≤0.10

 

Table 7 Chemical composition of ASTM A532/A532M-93a     %

Class Type Designation C Si Ni Cr Mo Cu P S
A Ni-Cr-Hc 2.8~3.6 ≤0.8 3.3~5.0 1.4~4.0 ≦1.0   ≦0.3 ≦0.15
B Ni-Cr-Lc 2.4~3.0 ≤0.8 3.3~5.0 1.4~4.0 ≦1.0   ≦0.3 ≦0.15
C Ni-Cr-GB 2.5~3.7 ≤0.8 ≦4.0 1.0~2.5 ≦1.0   ≦0.3 ≦0.15
D Ni – HiCr 2.5~3.6 ≤2.0 4.5~7.0 7.0~11.0 ≦1.5   ≦0.10 ≦0.15
A 12 %Cr 2.0~3.3 ≤     1.5 ≦2.5 11.0~14.0 ≦3.0 ≦1.2 ≦0.10 ≦0.06
B 15 %Cr -Mo 2.0~3.3 ≤     1.5 ≦2.5 14.0~18.0 ≦3.0 ≦1.2 ≦0.10 ≦0.06
D 20 %Cr -Mo 2.0~3.3 1.0~2.2 ≦2.5 18.0~23.0 ≦3.0 ≦1.2 ≦0.10 ≦0.06
A 25%Cr 2.0~3.3 ≤     1.5 ≦2.5 23.0~30.0 ≦3.0 ≦1.2 ≦0.10 ≦0.06

Abrasion-Resistant White Cast Iron 16 -ASTM A532_A532M

Abrasion-Resistant White Cast Iron 16

-Bimetal composite castings

 

  1. 3.Bimetal composite castings such as roll and so on

First of all most of the casting process use bimetal composite casting process. Because the casting process can get good abrasion resistance of high chromium white cast iron. That of course can effectively use of such materials. Furthermore can overcome the insuperable functional properties of the material itself. Such as for roll, hammer head and board hammer casting. Consequently which makes the castings composed of two kinds of metal materials as a whole. The working surface is mainly high chromium cast iron. And the non working surface is high toughness and low cost ast metal materials. Therefore it makes the bimetal composite castings safe, reliable and durable.

In conclusion the bimetal composite castings have the advantage of low economical cost.  Finally it also can meet the technical requirement and satisfactory performance. Table 5 shows the typical components of the composite casting roller and various composite bimetal castings with chromium abrasion resistant white cast iron.

 

Table 5 The main chemical composition of bimetal composite castings with chromium white cast iron

Material grade C Si Mn P S Ni Cr Mo Remark
1 2.9-3.5 0.3-0.6 0.2-0.5 0.05-0.1 0.05-0.06 2.0-4.0 0.6-1.0 0.2-0.3 Another material uses a high and tough cast metal. The composite roll uses mostly are the ductile iron. And meantime most of the other antiwear castings use carbon steel (medium and low carbon steel).
2 2.5-2.8 0.8-1.5 0.4-0.6 0.1-0.2 0.04-0.08 0.4-1.0
3 2.5-3.5 0.7-1.1 0.4-0.6 0.1-0.2 0.04-0.08 1.0-4.5 1.0-1.8 0.2-0.6
4 2.3-2.9 0.4-0.9 0.8-1.2 0.07 0.07 0.5-1.5 13-20 0.7-2.0
5 2.5-3.2 2.0-3.0 0.5-1.0 0.04 0.04 4.5-7.0 7-9 0.5-1.0

A