Overlay Welding Materials and Processes for Cold Stamping Dies

Literature Overview

Published in Welding (1999, No. 12) by Liu Renpei, Zhao Kun, Dong Zuyue, and Li Cuiyun from the Harbin Welding Research Institute, this paper addresses the development of overlay welding materials and processes specifically tailored for cold stamping die applications. The study develops a CrMoWVTi alloy system overlay metal and fabricates it into both GTAW flux-cored wire and covered electrode forms, providing a comprehensive solution for both die manufacturing and repair.

Failure Analysis of Cold Stamping Dies

Cold stamping dies experience a unique combination of severe service conditions:

Failure Mode	Mechanism	Critical Location
Wear	Adhesive and abrasive contact with sheet metal	Punch faces, die surfaces
Galling	Cold welding of die material to workpiece	Punch edges, trimming dies
Fracture	Cyclic plastic deformation leading to fatigue	High-stress zones
Erosion	Material loss from repeated impact loading	Punch tips, die corners

The performance requirements for cold stamping die overlay materials are demanding:

Hardness: HRC ≥ 60 for adequate wear resistance
Wear resistance: Comparable to or exceeding GCr15 bearing steel
Crack resistance: Approaching that of hot work die steels (to withstand cyclic loading)
Compatibility: Good weldability with common die base steels (Cr12MoV, Cr12, 5CrMnMo)

Material Development

The authors developed a CrMoWVTi alloy system overlay metal with the following design philosophy:

Alloy Design Principles

Chromium (Cr): Provides solid solution strengthening, improves hardenability, and forms stable carbides
Molybdenum (Mo): Enhances secondary hardening, increases red hardness, and improves wear resistance
Tungsten (W): Forms hard WC carbides, increases temper stability
Vanadium (V): Forms extremely hard VC and V₂C₃ carbides, refines grain structure
Titanium (Ti): Forms TiC carbides, improves wear resistance, and modifies grain boundaries

Performance Results

Property	Developed Material	GCr15 (Reference)	Hot Work Die Steel (Reference)
Hardness	HRC ≥ 60	HRC 60-65	HRC 45-50
Wear resistance	Comparable to GCr15	Baseline	Lower
Crack resistance	Approaching hot work die steel	Poor	Baseline
Toughness	Moderate	Low	High

The material was fabricated into two consumable forms:

GTAW flux-cored wire: For automated or semi-automated overlay welding with good surface finish
Covered electrode (SMAW): For field repair and manual overlay applications

Process Development

The authors developed a complete cold stamping die overlay welding process:

Process Parameters

Parameter	GTAW Flux-Cored Wire	SMAW Electrode
Current	150-250 A (DC)	100-180 A (DCRP)
Arc voltage	18-24 V	22-30 V
Travel speed	30-60 mm/min	20-40 mm/min
Shielding gas	Ar or Ar+2%O₂	Electrode flux
Preheat	150-200°C	200-300°C
Interpass temp	< 250°C	< 300°C
Post-weld treatment	Stress relief at 550-600°C	Stress relief at 550-600°C

Process Considerations

Preheating: Essential to prevent cracking in high-carbon die steels. The preheat temperature balances crack prevention against excessive grain growth.
Interpass temperature control: Must be maintained below 250-300°C to prevent temper softening of the overlay while avoiding cold cracking.
Post-weld stress relief: Critical for relieving residual stresses that could cause die failure during stamping operations.
Multi-pass strategy: For thick overlays, multiple thin passes are preferred over a single thick deposit to reduce cracking tendency and improve hardness uniformity.

Engineering Practice Validation

The paper reports successful application of the developed materials and processes for both:

Die manufacturing: Building up the wear surface of new dies by overlay welding onto a base die blank, followed by machining to final dimensions
Die repair: Restoring worn die surfaces by grinding away damaged material and re-overlaying with the developed consumable

Field trials demonstrated good performance, with improved service life compared to conventional die materials. The overlay approach offers economic advantages over full die replacement, particularly for expensive large dies where only the surface has been damaged.

Critical Insights

The dual consumable approach (flux-cored wire and covered electrode) represents a practical engineering decision that addresses different application scenarios:

Flux-cored wire for production environments requiring consistent quality and higher deposition rates
Covered electrode for field repair where equipment flexibility is needed

One significant advantage of the overlay approach for die manufacturing is the ability to use a lower-cost base steel (such as 45 steel or 50Cr) with a high-performance overlay surface, reducing material costs while achieving equivalent or superior surface properties. This cost-effective strategy is particularly valuable for high-volume die production.

The hardness of HRC ≥ 60 places this material in the category of ultra-hard overlay metals. However, materials at this hardness level are inherently brittle, and the paper's claim of crack resistance approaching hot work die steels suggests a carefully balanced composition. In practice, the transition zone between the hard overlay and the tougher base metal is often the critical location for failure initiation, and the quality of this transition is highly dependent on process control.

Summary

This study provides a comprehensive solution for cold stamping die overlay welding, combining material development with process optimization and practical validation. The CrMoWVTi alloy system achieves the challenging combination of high hardness (HRC ≥ 60), good wear resistance, and acceptable crack resistance. The availability of both flux-cored wire and covered electrode consumables ensures applicability across different manufacturing and repair scenarios. The work demonstrates that overlay welding is a viable and economical approach for both die manufacturing and repair, extending die life and reducing production costs in stamping operations.