Abrasion-Resistant White Cast Iron 5-ASTM A532_A532M

Abrasion-Resistant White Cast Iron 5

-ASTM A532_A532M

 

  1. B. High chromium white cast iron

The eutectic structure of high chromium cast iron (Cr > 13%) is different from that of ordinary pearlite white cast iron. And its eutectic carbide is M7C3 type of hexagonal system. The hardness of the carbide is up to HV1600 ~ 2100. At the same time the carburizing hardness of common white cast iron is HV1100. When Cr/ C is greater than 4 it forms M7C3 eutectic carbide. With the increase of Cr / C the solidification characteristics of the cast iron also change greatly.

When common white cast iron solidified eutectic carbide M3 C type is continuous. Meanwhile A body express isolated phase. On the contrary, the eutectic carbide M7C3 formed by the high chromium white cast iron express isolated. And the A body is a continuous phase. Which greatly reduces the separation or embrittlement of the high hardened abrasion-resistant relative to the matrix.

After heat treatment the matrix appears as martensite with high hardness. So that the cast iron shows good comprehensive properties. Grinding ball in cement industry we use Cr13% high chromium cast iron. And in the production of ball mill liners in cement industry we use high chromium steel with Cr1.0% to 1.5%.

In 1958,L.Limex molybdenum company T.E.Norman invented Cr15 – Mo3 (Cr15 % ~ 18 %). Which was recognized by its good anti-wear and comprehensive mechanical properties.There are two types of the cast iron. One is medium carbon (below 2.8%) and the other is high carbon (C2.8% to 3.6%). Due to the high cost of Mo the applications are limited. So by replacing part Mo with Ni, Cu and Mn developed many 15Cr type Abrasion-Resistant White Cast Iron. For example, type 15-2 – 1 and so on. In the following-up articles we’ll list the typical brands and related properties of high chromium white cast iron.

Abrasion-Resistant White Cast Iron Ni-Hard ASTM A532_A532M

Abrasion-Resistant White Cast Iron 4-ASTM A532_A532M Ni-Hard

 

Table 2 Wear-resistant white cast iron chemical composition and mechanical properties of Ni-Hard

ASTM A532 Ni-Hard iron pipe
ASTM A532 Ni-Hard iron pipe

 

Type chemical composition % mechanical properties(sand cast)after heat treatment
      C       Si       Mn       Ni       Cr       Mo       HRC             σb

/ kg·mm – 2

            αk

/ kg·..m·cm – 2

Ni-Hard
1
  3.0-3.6   0.3-0.5   0.3-0.7   3.3-4.8   1.5-2.0     0-0.4       53-61         25-35         2.0-4.0
Ni-Hard

2

  ≤    2.9   0.3-0.5   0.3-0.7   3.3-5.0   1.4-2.4     0-0.4       52-59         32-39         3.5-5.0
Ni-Hard

3

 

  2.6-3.2   1.5-2.0   0.4-0.6   5.0-6.0   8.0-9.0       53-63         50-60         3.5-6.0

Abrasion-Resistant White Cast Iron-Resistant White Cast Iron 3–ASTM A532_A532M

Abrasion-Resistant White Cast Iron 3

-ASTM A532_A532M

 

Table 1 typical examples of abrasion-resistant materials used in different abrasive wear conditions

Wear category Typical quick-wear parts performance requirement Wear resistant materials
High impact chiseling wear Cone crusher parts,

Large bucket teeth,

Caterpillar board for tanks and tractors and also

Jaw crusher jaw plate

High toughness αk ≥ 150J / cm2,

High strength σb ≥ 700 MPa,

High elongation  δ≥   30 %

High  manganese steel , Mn13, Mn18,

12Mn2Mo, 6Mn1Mo and

High chromium white cast iron- bimetal composite cast steel

Medium impact chiseling wear Impact Hammer Crusher,

Hammer head of medium and small hammer crusher,

ball mill lining and also

Blast furnace bell, strike plate

High strength σb ≥ 700 MPa,

High  hardness  HRC ≥ 50,

A certain toughness

αk ≥ 10 J / cm2

6Cr1Mo ,12Mn2Mo,

Cr15Mo3 white cast iron,

Cr – Ni – Mo white cast iron and also

Cr27 white cast iron

Low impact chiseling wear Hammer head of a crusher,

Ball mill liner, grinding ball,

Excavator crawler board

High  hardness  HRC ≥ 55,

αk ≥ 5  J / cm2

Ni – Hard4# ,Cr15 – Mo3 white cast iron,

Chromium white cast iron in high Si/ C and also

Cr20 – Mo2 – Cu1 white cast iron

High stress wear Limestone roller,

Pulverized coal grinding roll and grinding ball, hammer head,

Cement grinder,

Roller and bottom (scraping) plate for sanding machine

σb = (500~600) MPa,

High  hardness  HRC ≥ 55

Cr15Mo3 (low C type) white cast iron,

Hard nickel white cast iron(Ni – Hard4#),

Cr20 white cast iron,

Cr20 – Mo2 – Cu1 white cast iron

Low stress wear Shot blasting machine blade, guard board,

Sand nozzle,

Excavator bucket teeth (small sized),

Ploughshare,

Griddler, Screen roller,

Impurity pump overflow component

Turbine blade

High  hardness  HRC ≥ 55,

σb = (300~500) MPa

 

Pearlitic multivariate low alloy white cast iron,

Cr15Mo3 white cast iron,

Cr15Mo3 white cast iron containing CuTiV,

Chromium white cast iron in high Si/ C,

Duplex stainless steel

 

Abrasion-Resistant White Casting Iron-Resistant White Cast Iron 2–ASTM A532_A532M

There are currently two valuable chromium based Abrasion-Resistant White Cast Iron-resistant white cast iron. One is Ni Hard, another is high chromium white cast iron.

 

  1. A. Ni- Hard cast iron (nickel hard cast iron)

    wear-resistant white cast iron
    Wear-resistant ball

INCO created Ni – Hard (4.5%Ni, 1.6% ~ 2.0%Cr) martensitic white cast iron in 1932. The United States used it as a liner and an impurity pump overflow parts. Furthermore Japan and Europe countries have the application successively. However, due to the eutectic cementite in the white iron distributes along the A grain boundaries. As a result it seriously affects the mechanical properties of the cast iron (σb20 ~ 25kg/mm2).

In 1963 INCO created an improved Ni – Hard 4 , the content of Cr increased to 9%.  And the content of Si is 1.7%, Ni is 6%. The crystal of eutectic carbide changed from the original M3C to M7C3 type [(CrFe) 7C3]. Consequently which greatly improved the mechanical properties (σb 50kg/mm2).  Also HV reaches 600~800. It is just less than Cr15- Mo3 high chromium white cast iron. Hence in the production of grinding ring, roller, lining plate of ball mill  liner and other castings they have wide application.

The role of alloying elements in CA6NM martensitic stainless steel 8

The role of——micro alloy elements in CA6NM martensitic stainless steel tube

 

Adding micro alloy elements Ti, Nb and V in martensitic stainless steel tube is usually expected to form a nitrogen compound with C and N. As a result increasing the strength of the steel. Ti is a stabilizing element. At the same time it is a fine crystalline element. Ti can form a variety of stable carbon nitrogen compounds. Finally Ti (C, N) can effectively increase the toughness without sacrificing strength. The addition of 0.1% Nb in CA6NM martensitic stainless steel can effectively reduce the precipitation of the rich Cr ions. Because Nb can preferentially combine with C and N atoms to form nanometer grade Nb rich precipitates (5-15nm). The homogeneous distribution of rich Nb precipitates can significantly increase the strength of the steel and hence optimize its plasticity and toughness.

 

CA6NM tube chemical composition
CA6NM tube chemical composition
mechanical property of CA6NM martensitic stainless steel
CA6NM martensitic stainless steel

The role of alloying elements in CA6NM martensitic stainless steel 7

The role of——Si in CA6NM martensitic stainless steel

 

Si is a strong ferrite stabilizing element in martensitic stainless steel . It can suppress temper embrittlement and the decomposition of retained austenite during tempering. At high temperature or in a strong oxidizing medium adding a certain amount of Si to the surface to form a layer of Si02 oxide layer. As a result it significantly improves the oxidation resistance or corrosion resistance of steel. At the same time adding Si may inhibit the pitting corrosion of stainless steel in Cl. However, if the content of Si exceeds 4% there will greatly improv the brittleness of steel .

 

CA6NM martensitic stainless steel tube
CA6NM martensitic stainless steel tube

The role of alloying elements in CA6NM martensitic stainless steel 6

The role of——Al in CA6NM martensitic stainless steel

 

First of all as a deoxidizer we often add Al element into steel. At the same time Al is also a ferrite forming element. As a result its promoting effect on ferrite formation is about 2.5~3 times of that of Cr.

 

Al element can form a dense Al2O3 film on the surface of steel.As a result it can Improve  the antioxidant capacity of stainless steel.

 

CA6NM martensitic stainless steel tube
CA6NM martensitic stainless steel tube

 

 

The role of alloying elements in CA6NM martensitic stainless steel 5

The role of——Mn in CA6NM martensitic stainless steel

 

Mn is a kind of element that expands austenite phase zone in phase diagram. In steel, the stability of Mn to austenite is only below Ni, which can greatly improve hardenability of steel. Thus, in super martensitic stainless steel Mn can partially replace Ni. However, the corrosion resistance of stainless steel with low Cr content will decrease slightly due to the addition of Mn. When the content of Cr in stainless steel is high enough (17%), this effect is no longer obvious.

CA6NM martensitic stainless steel tube
CA6NM martensitic stainless steel tube

The role of alloying elements in CA6NM martensitic stainless steel 4

The role of alloying elements in CA6NM martensitic stainless steel——Cu

 

Cu has a weaker effect on the formation of austenite. A small amount of Cu addition can not optimize the martensitic microstructure of martensite. In the corrosive medium, Cu can form an enrichment layer under the oxide layer of the steel, thereby preventing the FeO from continuing to penetrate into the interior of the metal. Therefore, the addition of Cu into super martensitic steel can improve the corrosion resistance of steel in hydrochloric acid and sulfuric acid. And also improve the stress corrosion resistance. However, excessive Cu content can cause embrittlement of copper during hot working.

To be continued…

 

CA6NM chemical composition
CA6NM chemical composition
mechanical property of CA6NM martensitic stainless steel
CA6NM martensitic stainless steel

The role of alloying elements in CA6NM martensitic stainless steel 3

  1. The role of alloying elements in CA6NM martensitic stainless steel 3
  1. CA6NM martensitic stainless steel alloying elements——Mo

Mo——the addition of alloying element Mo in martensitic stainless steels is beneficial to the strength. And also to toughness and corrosion resistance. Mo is a ferrite forming element. It can reduce the Ms temperature. The addition of Mo in super martensitic steel can significantly reduce the martensite unidirectional zone. Meanwhile Mo can promote the passivation of Cr in some reducing corrosive media. Therefore, Mo can improve the corrosion resistance of Cr-Ni stainless steel in reducing acid. And effectively inhibit the pitting corrosion of Cl and improve intergranular corrosion resistance of steel.

 

However, Mo is a kind of austenite stabilization element, like Ni. Excessive addition can lead to the formation of retained austenite. In martensitic stainless steels Mo content is generally controlled below 5%.

CA6NM chemical composition
CA6NM chemical composition
mechanical property of CA6NM martensitic stainless steel
CA6NM martensitic stainless steel