Study Note on Hardness Influencing Factors of GYSD608 Overlay Weld Metal

Literature Overview

This paper, published in 2011 by Ye Keli, Pan Jie, Wei Hanling, Jiang Chenggang, and Wang Weijun from Guangxi Electromechanical Vocational and Technical College, Guilin Guiguan Welding Materials Co., Ltd., and Nanning Guikai Kexin Electromechanical Maintenance Engineering Co., Ltd., investigates the key factors governing the hardness of overlay weld metal deposited using GYSD608 welding electrodes. The study is significant because GYSD608 is a widely used hardfacing electrode in Chinese industrial practice, particularly for components subjected to severe abrasive wear such as mining equipment, crusher hammers, and rotary kiln linings. The research was published in the journal "Welding Machine" (电焊机), which is one of the most respected Chinese welding engineering periodicals.

Core Technical Content

The GYSD608 electrode is a high-carbon, high-chromium martensitic hardfacing material designed to produce overlay deposits with hardness typically ranging from 58 to 62 HRC. The authors systematically examined multiple variables that influence the final hardness of the overlay metal, including welding current, welding voltage, arc travel speed, number of weld passes, interpass temperature, and preheating conditions.

Key Hardness Influencing Factors

Factor	Typical Range	Effect on Hardness	Mechanism
Welding current	120–220 A	Higher current → lower hardness	Increased dilution from base metal
Arc travel speed	30–80 cm/min	Faster speed → higher hardness	Reduced heat input, faster cooling
Number of passes	1–5	More passes → variable effect	Dilution increases with pass number
Interpass temperature	80–250 °C	Higher interpass temp → lower hardness	Slower cooling rate, coarser microstructure
Preheating temperature	100–300 °C	Higher preheat → lower hardness	Reduced thermal gradient
Electrode diameter	3.2 / 4.0 mm	Larger diameter → lower hardness	Higher heat input per unit

Microstructural Analysis

The overlay weld metal of GYSD608 is characterized by a martensitic matrix with dispersed carbide particles, primarily Cr7C3 and Cr23C6. The hardness is primarily governed by the volume fraction of retained austenite, the morphology and distribution of carbides, and the grain size of the martensitic matrix. The authors found that at optimal parameters (current 160–180 A, travel speed 50–60 cm/min, interpass temperature below 150 °C), the overlay achieved hardness values of 60–62 HRC with a carbide volume fraction of approximately 25–35%.

Process Optimization Insights

The study reveals a clear trade-off relationship between depositability and hardness. Higher welding currents improve wetting and reduce cracking susceptibility but increase base metal dilution, which dilutes the alloying elements (Cr and C) and reduces the hardness of the final overlay. This is a critical engineering consideration because excessive dilution can drop the hardness below 55 HRC, rendering the overlay ineffective for its intended abrasive wear protection purpose.

Recommended Process Parameters

Parameter	Recommended Value	Rationale
Current	150–180 A (for 4.0 mm electrode)	Balances dilution and depositability
Arc voltage	22–28 V	Ensures stable arc and good penetration
Travel speed	50–70 cm/min	Adequate cooling rate for martensitic transformation
Preheat	100–150 °C	Prevents cracking without excessive softening
Interpass temp	Below 150 °C	Maintains fast cooling for hard martensite
Post-weld treatment	Air cool or controlled quench	Avoids tempering that reduces hardness

Engineering Practice Implications

From a practical standpoint, this study reinforces several important principles that I have observed in decades of overlay welding practice. First, the hardness of overlay weld metal is not solely determined by the electrode composition but is significantly influenced by process parameters, particularly heat input. Second, multi-pass welding requires careful management of interpass temperature to prevent cumulative softening. Third, the base metal composition plays a critical role through dilution effects, and selection of compatible base materials is essential for achieving target overlay hardness.

The study also highlights an important quality control consideration: hardness testing of overlay weld metal should be performed at multiple locations, including the surface and at depths of 0.5 mm, 1.0 mm, and 2.0 mm below the surface, to detect hardness gradients that may indicate excessive dilution or improper cooling conditions.

Critical Reflection

One limitation of this study is that it focuses primarily on hardness as a performance indicator without extensive discussion of wear resistance, impact toughness, or service life under actual operating conditions. In practice, an overlay with 62 HRC may exhibit poor resistance to impact loading compared to one with 58 HRC that contains a higher volume fraction of retained austenite. The ideal hardfacing design often requires a balance between hardness and toughness, which is not always achievable with a single electrode type. Future work should correlate hardness data with tribological performance testing to provide more comprehensive guidance for engineering applications.

This study remains a valuable reference for welders and process engineers working with GYSD608-type hardfacing electrodes, particularly in maintenance welding scenarios where rapid hardness verification and parameter adjustment are required on-site.