When Do You Need To Replace Your Chrome Carbide Plate?

Dec. 02, 2024

When Should You Consider Replacing Your Chrome Carbide Plate?

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CHROME CARBIDE OVERLAY PLATE

(UNDERSTANDING THE DIFFERENCE)

Bob Miller

Bob Miller serves as a metallurgist and wear consultant at Clad Technologies, based in Birmingham, Alabama, 205-978-XXXX.

Introduction

Thirty years ago, the Chrome Carbide Overlay Plate was produced by only a handful of companies. Due to its remarkable popularity and versatility for extreme abrasion applications, the number of manufacturers has surged. As in many evolving technologies, differences in production methods can significantly impact the final product. Consumers often mistakenly believe that all chrome carbide plates are essentially the same. This article clarifies this misconception by detailing the various methods of manufacturing overlay plates and their influence on quality, consistency, and wear properties.

The Basic Product

The Chrome Carbide Overlay Plate consists of a mild steel base layer upon which a highly abrasion-resistant welded overlay is applied using either an open arc or submerged arc process. Plate thickness typically ranges from 3/8” to 1-1/2”; widths vary from 4” to 8” and lengths from 8” to 20”. The overlay can have one or two layers, measuring 1/4” or 3/8” thick. The bead widths vary depending on the manufacturing process, generally measuring around 1-1/2” wide and are prone to random check cracking. This check cracking, a natural occurrence in welding, can be managed through the chemical makeup of the overlay or the cooling method used. Chemical compositions of the overlay range from 15% to 30% Chromium and 3.0% to 4.5% Carbon. Manganese and Silicon can fluctuate between 1% and 4% each, while Molybdenum can reach up to 3%. The hardness of the deposit ranges from 400 BHN to 600 BHN, typically falling between 550 BHN and 600 BHN. The finished plates can be formed and modified; holes can be created using either plasma or electrical discharge machining (EDM) techniques.

Hardness, Chemistry & Wear

While hardness has traditionally been used to judge wear resistance, it can be misleading. For example, comparing an alloy steel to a white iron, both with hardness values of 550 BHN, reveals that the white iron consistently outperforms in wear resistance.

Material

Hardness
(BHN)

G65
(Weight Loss)

Alloy Steel

550

0.50

3.50

0.50

1.40

White Iron

550

4.50

20.0

2.0

0.22

Mild Steel

0.25

0.00

2.51

C=Carbon, Cr=Chromium, Mo=Molybdenum

This significant difference in wear resistance, despite identical hardness values, stems from macro vs. micro hardness measurements. Standard hardness tests, including Brinnel and Rockwell, assess a material's overall hardness. Each metallurgical component has its microhardness, affecting the overall macrohardness. The alloy steel has a single component (Martensite), while white iron comprises both chrome carbide with a high microhardness embedded in austenite, which has a low microhardness. The resulting Brinell macrohardness (550 BHN) is an average of the two microhardness levels. Hardness values become meaningful only across similar families of steels, which can often mislead. Hence, it is better to focus on actual chemical compositions and their metallurgical structures. These factors reflect in wear testing, such as ASTM G65, rather than firmness testing.

Wear Testing – ASTM G65

Different wear types exist, but low-stress or scratching abrasion is common in mining operations. The Dry Sand Rubber Wheel Test, or ASTM G65, quantitatively measures a material's resistance to this type of abrasion under controlled lab conditions. While actual field conditions might be influenced by impact, corrosion, and galling, examining test results in context with the material's chemical composition and microstructure offers valuable insights regarding field performance. This criteria should guide all materials used in applications facing abrasive wear.

Methods of Manufacture

Since the inception of the Chrome Carbide overlay plate, various manufacturing methods have emerged. Presently, popular manufacturing techniques include:

Arc Welding Methods
1. Open Arc
2. Submerged Arc or Fusion Bond Welding
Base Plate Configuration
1. Flat Plate or Table Design
2. Cylindrical Drum

Choosing any of the above variables can significantly influence the plate's quality, consistency, integrity, and wear characteristics. Below is a closer look at each variable.

Arc Welding Process

Two principal welding techniques, open arc and submerged arc, are utilized for manufacturing cladded plates. The consumer should understand the welding process's relevance due to its direct link to wear resistance. Preliminary clarifications are necessary:

Arc welding deposits blend wire and base metal compositions, characterized by a dilution percentage. A 30% dilution factor means the weld has 30% base metal and 70% wire.
These deposits are thoroughly mixed, ensuring no visible division between the base metal and wire components, resulting in a homogeneous product.

Open Arc Welding:

This process uses a cored wire without additional gas or flux—ingredients are allocated within the tube's core. The wire consists of a low-carbon strip, with essential components included during manufacturing. The wire is packaged in 500 lb. containers. Since it is the singular welding consumable, managing inventory is straightforward. Process control is simple, focusing on standard arc voltages, currents, and wire feed rates. Although deposits are typically smooth, they can suffer from roughness and poor coherence between weld beads. A major limitation of the open arc method is its inability to achieve the chemical compositions ideal for maximum wear resistance in the first layer. This limitation relates to a combination of wire fabrication and process variables, with the woven tube accommodating a limited amount of alloy (approximately 30% Chromium and 5% Carbon, among others). Moreover, open arc typically results in around 40% dilution, yielding a deposit composition of roughly 18% Chromium and 3.0% Carbon. The ASTM G65 abrasion tests show that a minimum of 20% Chromium and 4% Carbon is necessary for satisfactory wear performance. Second layers are also influenced by dilution but to a lesser degree, typically showing 25.2% Cr and 4.2% Carbon—sufficient for acceptable wear.

From the evidence presented, submerged arc deposits outperform open arc deposits in wear resistance.

Submerged Arc / Fusion Bond Welding:

Submerged Arc welding utilizes either solid or cored wire along with added flux. The arc melts both the wire and the flux, producing a weld bead with an easily removable slag. Dilution factors generally range from 30-40%. Fusion Bond Welding, a variation of submerged arc, includes alloy powder, reducing dilution to about 10%. By over-allocating alloy powder, this dilution can be minimized. As a result, it is feasible to deposit a composition of 30% Chromium and upwards of 4.0% Carbon in the first layer, which is very acceptable for wear purposes.

Enhanced features associated with Fusion Bond Welding include smooth deposits with shallow peaks and valleys, improved process control, and consistent deposits. The main drawback lies in managing multiple welding consumables: wire, flux, and alloy powder. However, the flexibility of the arc welding process and control over deposit chemistry compensate for this shortcoming.

Condition

Dilution (%)

G65

(Weight Loss)

Open Arc Wire

5.00

30.0

Open Arc 1st Layer

40%

3.00

18.0

1.25

Open Arc 2nd Layer

40%

4.20

25.2

Sub Arc 1st Layer

10%

4.30

28.0

0.33

Sub Arc 2nd Layer

10%

4.55

0.19

Mild Steel

2.51

Base Plate Configuration

A36 or flat steel plates in various sizes are sourced for overlay. Manufacturers have two options for configuring these plates for the overlay process: (1) utilize the flat plate as purchased and simply place it on a designated flat table, or (2) roll the flat plate into a cylinder, seam weld it, and position it on a specialized horizontal turning device for the overlay process. Each choice comes with advantages and drawbacks that impact the final product's quality and integrity. Details of each method are outlined below.

Table Method:

This approach offers simplicity in plate management. Since the plate is acquired as flat stock, it is logical to lay it on the table and overlay with either an open arc or Fusion Bond welding method. After overlaying, the plate is straightened or flattened and then cut to size. This process is straightforward. However, significant complications can arise when welding base plates thinner than 3/4". Distortion creating large humps can occur, compromising deposit integrity. Whenever a hump interrupts the welding arc, it increases base plate penetration and dilution, potentially generating unacceptable wear properties in that area. While this method is economically beneficial from a manufacturing perspective, it poses challenges.

Drum Method:

The downside of this cylinder approach lies in handling and prepping the plates. Each plate must first be rolled and seam welded before being positioned for overlay on the turning device. Upon completion, it must be cut along the seam and unrolled for plasma trimming. Despite this drawback, this production method effectively eliminates distortion. No humps form during welding, and any dimensional variations can be easily addressed through adjustments in the turning fixture, optimizing process control. The composition and wear characteristics remain consistent throughout the plate.

Numerous options exist for manufacturing overlay plates, with final choices often influenced by raw material availability, manufacturing space, and economic factors. Clearly, these manufacturing processes affect the end product significantly, which may confuse consumers. The following chart provides guidance for buyers when choosing an overlay plate supplier, rating features on a scale of 1 to 10, with 10 being the most favorable.

Feature

Open Arc Weld

Sub Arc Fusion Bond

Flat Table

Drum

Distortion

Micro-Structure

Process Control

Inventory

N/A

Wear Properties

Cost-Effectiveness

Process Complexity

Total

Conclusion

A variety of methods for manufacturing overlay plates have been explored and assessed. Each method comes with distinct advantages and limitations. As technology progresses, new manufacturing procedures will likely be introduced, with their success depending on consumer acceptance. Existing methods will continue to evolve for improvement where necessary. Nevertheless, consumers must navigate the current landscape. Equipped with the information presented in this article, buyers can effectively differentiate among overlay plate suppliers. A simple checklist may prove beneficial.

1. 1. Welding Method
    - Sub Arc Bulk Welding
    - Open Arc
    - Other
  2. Plate Configuration
    - Flat Table
    - Cylindrical Drum
  3. In-House Wear Testing
    - ASTM G65
    - Outside Source
    - Other
  4. Quality Control Method
    - Wire Chemistry
    - Deposit Chemistry
    - Hardness
    - Wear Test
    - None
  5. Testing Frequency
    - Each Plate
    - Periodically
    - Upon Request
    - Not Available
  6. Certification
    - Specifications
    - Actual Test Results
  7. Sizes
    - Thickness, Lengths, Widths
    - Cladding Thickness
  8. Availability
    - Days
    - Weeks
    - Months

Reprinted Articles courtesy of cladtechnologies.com

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