High Chromium Cast Iron Overlay Welding Process Experimental Research

Literature Overview

The paper by Wang Yan and Dai Haijun, published in Hot Working Technology (2005, Vol. 34, No. 12, pp. 40-41), presents experimental research on the overlay welding process of D938, a high-chromium cast iron electrode, on Q235 carbon steel substrate. The authors are affiliated with Xihua University and Chengdu Construction Machinery Co., Ltd. This work addresses a practical challenge in the construction machinery industry: providing wear-resistant surfaces on structural components through overlay welding while maintaining weldability and crack resistance.

Core Technical Content

Background and Material Selection

High-chromium cast iron (typically containing 12-20% Cr) is widely used for its excellent abrasion resistance due to the formation of hard chromium carbides (Cr7C3, Cr23C6). However, these materials suffer from poor weldability due to high carbon and alloy content, which leads to:

Challenge	Mechanism	Consequence
Cracking susceptibility	Rapid solidification of high-carbon austenite + martensite	Cold cracking in weld metal and HAZ
High hardness	Formation of hard carbides and martensite	Poor machinability, brittleness
Thermal cracking	Low-ductility phases at grain boundaries	Hot cracking during solidification
Dilution effects	Mixing with low-alloy base metal	Reduced hardness and wear resistance

The D938 electrode was identified as a promising but underdeveloped high-chromium cast iron surfacing electrode requiring process optimization.

Experimental Design and Parameters

The experimental study was conducted on Q235 carbon steel plates. The key process parameters and their optimization are summarized below:

Parameter	Range Tested	Optimal Value	Rationale
Welding current	60-160 A	100-120 A	Sufficient penetration without excessive heat input
Arc length	3-8 mm	2-3 mm (short arc)	Stable arc, reduced spatter, better deposition quality
Interpass temperature	100-400°C	300-350°C	Critical window for crack resistance
Preheat temperature	100-300°C	200-250°C	Reduces cooling rate, minimizes HAZ hardness
Post-weld cooling	Air cooling, furnace cooling	Slow cooling (furnace)	Reduces residual stress and martensite formation
Layer thickness	2-6 mm	3-5 mm (multiple passes)	Ensures full transformation of weld metal

Microstructure and Hardness Analysis

The experimental results demonstrated that the optimal process window (interpass temperature 300-350°C, short arc, controlled cooling) produces overlay welds with the following characteristics:

Microstructure: Predominantly austenite matrix with dispersed Cr7C3 and Cr23C6 carbides. The controlled interpass temperature promotes the formation of a tougher austenitic structure rather than brittle martensite.
Hardness: 60-70 HRC in the overlay zone, significantly exceeding the base metal hardness of approximately 140 HB (Q235).
Crack resistance: No cracking observed in the overlay welds when the interpass temperature was maintained within the specified range. Cracking was observed when interpass temperature exceeded 400°C or fell below 200°C.

Engineering Practice Implications

Application to Construction Machinery Components

The research has direct applicability to wear-resistant surfacing of construction machinery components such as:

Bucket teeth and cutting edges on excavators
Wear plates on conveyor systems
Crusher hammers and jaw plates
Bulldozer blade edges

The key practical insight is that the interpass temperature window of 300-350°C is narrow but achievable with proper thermal management. In field conditions, this requires:

Thermocouple monitoring at the weld zone to track interpass temperature in real time.
Controlled preheating using induction heating or oxy-fuel torches, with temperature verification using infrared pyrometers.
Post-weld stress relief through furnace cooling or controlled air cooling to minimize residual stresses.

Quality Control Considerations

Using the FMEA approach, the following failure modes should be considered for high-chromium cast iron overlay welding:

Failure Mode	Severity	Occurrence	Detection	Risk Priority	Countermeasure
Cold cracking	High	Medium	Low	24	Control interpass temperature 300-350°C
Hot cracking	High	Medium	Medium	16	Use short arc, stable welding technique
Excessive dilution	Medium	Medium	High	12	Use multiple thin passes
Hardness variation	Medium	Medium	High	12	Control cooling rate, verify with hardness testing
Surface porosity	Low	Low	High	4	Clean surface, proper flux coverage

Study Insights

The experimental approach taken by the authors is methodical and practical. By systematically varying the welding current and interpass temperature while maintaining other parameters constant, they identified the critical process window for crack-free overlay welding. The finding that 300-350°C represents the optimal interpass temperature range is particularly valuable, as it provides a clear, actionable target for field welders.

From a metallurgical perspective, the success of the process can be attributed to the balance between cooling rate and interpass temperature. At interpass temperatures below 200°C, the cooling rate is too high, leading to the formation of hard, brittle martensite and high residual stresses that promote cracking. At temperatures above 400°C, excessive grain growth and potential over-tempering of carbides reduce the wear resistance of the overlay.

Summary

This paper provides practical, experimentally validated guidance for the overlay welding of high-chromium cast iron on carbon steel substrates. The identification of the critical interpass temperature window (300-350°C) and the demonstration of crack-free welds with 60-70 HRC hardness represent significant contributions to the field. For engineers in the construction machinery and related industries, this work provides a clear process recipe that can be readily implemented with proper thermal management and quality control procedures.