High Chromium Iron Surfacing Process Experimental Research

Literature Overview

This paper by Wang Yan from Xihua University and Dai Haijun from Chenggong Construction Machinery Co., Ltd., published in Hot Working Technology (2005, Vol. 34, No. 12, pp. 40-41), presents experimental research on the surfacing process of D938, an enhanced high chromium iron surfacing electrode. The study focuses on optimizing welding parameters to achieve crack-free, wear-resistant surfacing layers on Q235 steel substrates for abrasive wear applications.

Core Technical Content

Background and Challenge

D938 represents a next-generation high chromium iron surfacing electrode designed to provide superior abrasion resistance through its high volume fraction of primary carbides (Cr7C3 and Cr23C6) in a martensitic matrix. However, the paper identifies a critical challenge: D938 exhibits poor weldability characterized by a high susceptibility to hot cracking during deposition. This limitation has historically restricted its application to specific process conditions and substrate geometries.

High chromium irons (typically containing 20-30% Cr and 2-4% C) are widely used in mining, cement, and construction equipment where severe abrasive wear is the dominant failure mechanism. Their excellent wear resistance stems from the hard carbide phase, but this same microstructure creates significant hot cracking susceptibility due to:

High solidification temperature range
Large thermal expansion coefficient mismatch between carbides and matrix
Sulfur and phosphorus segregation at grain boundaries
Low ductility of the solidifying shell

Experimental Approach and Key Findings

The experimental study investigated surfacing of D938 on Q235 carbon steel substrates, systematically varying welding parameters to identify optimal process conditions. The critical findings include:

Process Parameter	Critical Range	Effect on Cracking
Welding current	Controlled selection (specific value optimized)	Lower current reduces heat input and cracking tendency
Interpass temperature	300-350°C (strictly controlled)	Too low increases stress; too high promotes grain growth and carbide coarsening
Arc length	Short arc welding	Ensures stable arc, reduces spatter, improves heat concentration
Preheating	Required	Reduces thermal gradient and residual stress
Post-weld cooling	Slow cooling (furnace cool or insulated)	Minimizes thermal shock and martensitic transformation stress

The interpass temperature control of 300-350°C represents the single most critical process parameter identified in this study. This temperature range serves a dual purpose: it is high enough to reduce thermal gradients and residual stresses that promote cracking, yet low enough to prevent excessive grain growth and carbide coarsening that would degrade the wear resistance properties of the surfacing layer.

Microstructure and Property Analysis

The successful surfacing layers achieved with the optimized parameters exhibited:

A martensitic matrix with retained austenite content controlled within acceptable limits
Uniformly distributed primary carbides without excessive coalescence
Surface hardness in the range of 58-62 HRC, appropriate for abrasive wear service
Crack-free surface and subsurface regions
Adequate bonding strength to the Q235 substrate

The importance of slow cooling cannot be overstated. Rapid cooling of high chromium iron surfacing layers promotes high retained austenite content, which while reducing cracking during welding, leads to phase instability during service. The retained austenite transforms during wear or thermal cycling, creating volume expansion and potentially causing spalling of the surfacing layer. Controlled cooling through furnace cooling or insulated holding allows transformation to proceed at a controlled rate, producing a more stable microstructure.

Engineering Practice Integration

In my experience with high chromium iron surfacing applications in construction equipment, particularly for bucket teeth, wear plates, and hydraulic cylinder liners, the following practical considerations emerge from this research:

Substrate preparation is critical: The Q235 substrate used in this study is relatively straightforward, but in practice, surfacing is often applied to pre-existing worn surfaces or over previously failed surfacing layers. Surface cleaning, removal of contaminated layers, and proper bevel preparation are essential prerequisites.
Multi-pass strategy: For thick surfacing layers (>6 mm), a build-up strategy using multiple passes with interpass temperature monitoring is essential. Each pass should be individually monitored for temperature to maintain the 300-350°C window.
Post-weld heat treatment consideration: While the paper focuses on achieving crack-free deposition, many industrial applications benefit from a post-weld stress relief treatment at 500-600°C to further reduce residual stresses without significantly affecting hardness.
Application-specific parameter adjustment: The optimized parameters for Q235 substrates may need adjustment when applied to higher-alloy substrates such as low-alloy steels or previously hardened surfaces, where the carbon and alloy content affects the local carbon activity and cracking susceptibility.

Key Reflections and Study Insights

This paper, while relatively concise, addresses a fundamental challenge in surfacing technology: balancing wear resistance with weldability. The D938 electrode represents a material that pushes the boundary of what is achievable in high chromium iron surfacing, and the identified process window provides practical guidance for its implementation.

The strict interpass temperature control requirement (300-350°C) highlights an important principle in high-alloy surfacing: the process must be carefully managed to control both thermal stresses and metallurgical evolution simultaneously. In industrial settings, this often requires investment in temperature monitoring equipment and operator training to maintain consistent process discipline.

The 2005 publication date of this paper is worth noting—many of the process principles identified remain valid today, though modern equipment and monitoring capabilities have made parameter control more achievable. The fundamental metallurgical challenges of high chromium iron surfacing remain unchanged, and the solutions proposed here continue to provide valuable guidance for current practice.

The research demonstrates that even materials with inherently poor weldability can be successfully applied through careful process engineering, which is an encouraging perspective for engineers facing similar challenges with other difficult-to-weld overlay materials.