CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Microhardness of D227 and D237 Welding Rod Overlay Metals
Literature Overview
This study by Zhang Youyi, Yang Yue, and Qu Jinshan, published in Electric Welder in 2009, investigates the microstructure and microhardness distribution of overlay metals deposited using D227 and D237 welding rods. The research was conducted at Sichuan Engineering Vocational Technical College and Xihua University, representing a practical engineering-oriented investigation into commonly used hardfacing electrode systems. D227 and D237 are well-known high-chromium cast iron hardfacing electrodes widely used in industrial applications for protecting surfaces against abrasive wear and corrosion.
Electrode Composition and Application Scope
D227 and D237 welding rods belong to the high-chromium white cast iron family of hardfacing materials. Their nominal compositions and intended applications are as follows:
| Parameter | D227 | D237 |
|---|---|---|
| Carbon (C) | 2.5-3.5% | 3.0-4.0% |
| Chromium (Cr) | 15-20% | 20-25% |
| Hardness (HRC) | 58-66 | 62-70 |
| Primary Carbide | Cr7C3, Cr23C6 | Cr7C3, Cr23C6 |
| Matrix Structure | Ferrite/Martensite | Martensite |
| Typical Application | Moderate abrasion, corrosion | Severe abrasion, high temperature |
| Base Material Compatibility | Carbon steel, low-alloy steel | Carbon steel, low-alloy steel |
Both electrodes are designed for shielded metal arc welding (SMAW) and are applied in single or multiple layers to provide a wear-resistant surface. The high chromium content promotes the formation of hard chromium carbides, while the carbon content determines the amount and type of carbides formed in the microstructure.
Microstructural Analysis
The microstructure of D227 and D237 overlay deposits consists of two primary phases:
- Hard carbide phase: Chromium carbides (primarily Cr7C3 and Cr23C6) are distributed throughout the microstructure. These carbides are extremely hard (HV 1800-2200) and provide the primary wear resistance. The morphology and distribution of carbides depend on the cooling rate, carbon content, and chromium content.
- Matrix phase: The matrix can range from ferrite to martensite, depending on the cooling rate and alloy composition. In D227 deposits, the matrix tends to be more ferritic due to the slightly lower carbon content, while D237 deposits typically exhibit a more martensitic matrix due to the higher carbon and chromium levels.
The microhardness distribution within the overlay deposit is not uniform. Typical patterns include:
- Higher hardness in the surface region due to faster cooling and finer carbide distribution
- Lower hardness near the substrate interface due to dilution effects and slower cooling
- Possible hardness variation between passes in multi-layer deposits
The study likely demonstrates that D237 achieves higher overall hardness than D227 due to its higher carbon and chromium content, which promotes more extensive carbide formation and a harder martensitic matrix. However, this increased hardness comes at the cost of reduced toughness, making D237 more susceptible to cracking under impact loading.
Process Considerations and Defect Prevention
Successful application of D227 and D237 hardfacing electrodes requires careful process control:
| Process Parameter | Recommended Range | Effect of Deviation |
|---|---|---|
| Preheating Temperature | 200-300°C | Too low: cracking; Too high: grain coarsening |
| Interpass Temperature | 200-300°C | Too high: reduced hardness; Too low: cracking |
| Travel Speed | Moderate | Too fast: incomplete fusion; Too slow: excessive dilution |
| Layer Thickness | 2-4 mm per pass | Too thick: center cracking; Too thin: excessive dilution |
| Electrode Angle | 15-25° from vertical | Affects penetration and dilution |
Common defects in high-chromium cast iron hardfacing include:
- Cracking: Hot cracking due to low ductility of the cast iron deposit and cold cracking due to hydrogen embrittlement and martensitic transformation.
- Porosity: Gas porosity from inadequate shielding or surface contamination.
- Excessive dilution: Results in reduced hardness and loss of wear resistance.
- Spalling: Poor bond strength leading to delamination of the overlay.
Engineering Practice Applications
D227 and D237 electrodes are widely used in the following industrial applications:
- Mining equipment: Crusher jaws, bucket teeth, and conveyor components subject to severe abrasive wear.
- Cement industry: Mill liners, grinders, and kiln components exposed to abrasive materials at elevated temperatures.
- Power generation: Coal handling equipment, fans, and hoppers.
- Agricultural machinery: Plowshares, harrow teeth, and other soil-engaging components.
In pressure vessel and heat exchanger repair applications, these electrodes may be used for local repair of worn surfaces on piping and vessel components, provided that the thermal effects on the base material are properly managed.
Study Insights and Reflections
The systematic comparison of D227 and D237 provides valuable practical guidance for selecting the appropriate electrode based on service conditions. The key trade-off is between hardness (wear resistance) and toughness (crack resistance). In applications where the component is subjected to impact loading or thermal cycling, D227 may be the preferred choice despite its slightly lower hardness, as its more ferritic matrix provides better crack resistance.
The research underscores the importance of understanding the relationship between microstructure and properties in hardfacing materials. The hardness of these deposits is not solely determined by the electrode composition but is also strongly influenced by the cooling rate, which depends on the base material thickness, preheating temperature, and welding parameters. This insight is critical for process optimization in industrial settings where welders must balance productivity with quality requirements.