Effect of Overlay Welding Time Interval on Microstructure of Overlay Components

Literature Overview

This study published in Hot Working Technology (2017, Vol. 46, No. 13) by researchers from Xinjiang University and Xinjiang Weiao Technology Co., Ltd. investigates the effect of welding time interval on the microstructure of multi-layer overlay welds deposited on Q235B substrate using GMAW (Gas Metal Arc Welding) with ER50-6 wire. The research addresses a practical production issue in overlay welding where the time between successive passes significantly affects the final microstructure and properties.

Experimental Configuration

Test Parameters

Parameter	Value
Base material	Q235B carbon steel
Welding process	GMAW (Gas Metal Arc Welding)
Consumable	ER50-6 solid wire
Test configuration	Single pass, multi-layer overlay
Time intervals tested	30 s, 1 min, 2 min
Inspection method	Metallographic observation

Test Matrix

The study systematically varied the time interval between successive welding passes to investigate the effect of interpass cooling time on:

Cooling rate of subsequent passes
Grain size and morphology
Microstructural uniformity
Phase composition distribution

Key Technical Findings

Cooling Rate Behavior

Time Interval	Cooling Rate Effect	Microstructural Consequence
30 s	Very slow cooling	Coarse grains, non-uniform structure
1 min	Slow cooling	Coarse grains, non-uniform structure
2 min	Moderate cooling	Uniform structure, fine grains

When the time interval is short (30 s, 1 min), the previous weld pass retains significant heat, resulting in a lower cooling rate for the subsequent pass. This slow cooling allows sufficient time for grain growth and coarsening, leading to coarse and non-uniform microstructure.

When the time interval is longer (2 min), the previous weld pass cools sufficiently before the next pass is deposited, resulting in a more moderate cooling rate that produces fine and uniform grain structure.

Microstructural Characteristics

At 2 min interval:

Relatively uniform microstructure throughout the overlay
Fine grain size
Good phase distribution
Acceptable hardness profile

At 1 min and 30 s intervals:

Coarse grain structure
Non-uniform phase distribution
Potential for localized soft spots
Reduced mechanical property consistency

Engineering Practice Implications

Process Control Guidelines

For multi-layer overlay welding with GMAW process:

Minimum recommended time interval: 2 minutes between passes for Q235B substrate with ER50-6 wire
Maximum recommended time interval: 10-15 minutes to avoid excessive cooling and potential cracking
Temperature monitoring: Use infrared thermometry to verify interpass temperature remains within 150-250°C range
Layer thickness control: Maintain consistent layer thickness to ensure uniform cooling behavior

Quality Impact

Aspect	Short Interval (30 s - 1 min)	Optimal Interval (2 min)
Grain size	Coarse	Fine
Hardness uniformity	Poor	Good
Crack resistance	Reduced	Improved
Wear resistance	Inconsistent	Consistent
Fatigue performance	Degraded	Acceptable

Production Considerations

Production efficiency decreases with longer time intervals
Quality consistency improves with longer time intervals
Energy consumption increases with longer intervals (reheating may be required)
Operator fatigue may increase with longer intervals

Process Optimization

The optimal time interval represents a balance between:

Production efficiency (shorter is better)
Quality consistency (longer is better)
Energy consumption (shorter is better)
Equipment utilization (shorter is better)

For critical applications, the 2-minute interval should be maintained regardless of production pressure. For less critical applications, a 1-minute interval may be acceptable if quality verification confirms acceptable microstructure.

Study Insights and Reflections

This research highlights a fundamental aspect of multi-pass welding that is often overlooked in production environments: the time interval between passes is a critical process parameter that directly affects final microstructure and properties. The cooling rate behavior identified in this study is consistent with fundamental metallurgical principles, where slower cooling rates promote grain growth and coarsening. The practical implication is that production schedules must account for adequate cooling time between passes, particularly for overlay welding where consistent microstructure is essential for predictable service performance. Engineers and production managers should establish and enforce minimum time interval requirements in welding procedures, with clear documentation and operator training. The use of infrared thermometry for interpass temperature monitoring provides a practical solution for ensuring compliance with time interval requirements. This study reinforces the importance of process discipline in welding operations, where adherence to specified parameters directly determines the quality and reliability of the final product.