Research on One-Step Weld Overlay Electrodes for Die Cutting Edges

Literature Overview

This paper presents research on the development of a "one-step" weld overlay electrode specifically designed for the hardening and wear resistance enhancement of die cutting edges. In metal forming and sheet metal processing, die cutting edges (punches and dies) are subjected to extreme contact stresses, abrasive wear, and adhesive wear during the shearing of sheet metal. The service life of these cutting edges is often limited by wear, which necessitates frequent regrinding and re-hardening, resulting in significant downtime and cost. The "one-step" weld overlay approach aims to deposit a wear-resistant alloy layer onto the cutting edge in a single welding pass, eliminating the need for multiple passes or post-weld grinding, thereby improving manufacturing efficiency and reducing production costs.

Core Technical Points

Requirements for Die Cutting Edge Overlay

The overlay layer on die cutting edges must satisfy a set of demanding requirements that are often in conflict:

Requirement	Specification	Challenge
Hardness	≥ 55 HRC (600–700 HV)	High carbon content promotes brittleness
Wear resistance	High resistance to abrasive and adhesive wear	Requires hard carbide phases
Toughness	Adequate fracture toughness to resist chipping	Competes with hardness
Red hardness	Maintain hardness at elevated temperatures	Requires alloying elements (W, Cr, V)
Weldability	Low cracking susceptibility	High carbon and alloy content reduce weldability
Surface finish	Smooth surface suitable for cutting	Requires self-leveling weld metal

The fundamental challenge in developing a one-step overlay electrode is achieving a balance between hardness and toughness while maintaining weldability in a single pass. Traditional multi-pass approaches allow for a softer transition layer followed by harder overlay passes, but the one-step approach must achieve this balance within a single weld deposit.

Electrode Composition Design

The electrode composition was optimized through a systematic approach based on the following design principles:

Design Principle	Element Selection	Role
Hardenability	C (1.0–1.5%), Cr (8–12%)	Form hard carbides, improve hardenability
Red hardness	W (2–4%), V (1–2%)	Form stable carbides at elevated temperatures
Toughness	Ni (2–5%)	Improve ductility, reduce cracking susceptibility
Weldability	Mn (1.0–1.5%), Si (0.3–0.5%)	Deoxidation, improve fluidity
Grain refinement	Ti (0.05–0.1%), Nb (0.02–0.05%)	Refine grain structure, improve toughness

The final optimized composition of the one-step overlay electrode is presented below:

Element	C	Cr	W	V	Ni	Mn	Si	Fe
wt%	1.20	10.0	3.0	1.5	3.5	1.20	0.40	Balance

This composition is designed to produce a martensitic matrix with a dispersion of M₆C, M₂₃C₆, and MC carbides, providing a combination of high hardness and adequate toughness.

Microstructural Analysis

Metallographic examination of the overlay weld metal revealed the following microstructural features:

Zone	Microstructure	Hardness (HV)
Weld center	Fine martensite + M₆C carbides	650–700
Weld edge	Coarser martensite + M₂₃C₆ carbides	580–620
HAZ	Tempered martensite + retained austenite	450–500
Base metal (transition)	Pearlitic-ferritic	250–300

The hardness distribution across the overlay cross-section shows a gradient from the base metal through the HAZ to the weld center, with the maximum hardness achieved in the weld center region. The presence of retained austenite in the HAZ contributes to the toughness of the transition region and helps to mitigate cracking susceptibility.

One-Step Welding Process

The one-step welding process was optimized using the following parameters:

Parameter	Value	Rationale
Welding method	SMAW (shielded metal arc welding)	Field applicability, equipment simplicity
Electrode diameter	3.2 mm	Adequate deposition rate, manageable arc
Welding current	120–160 A	Sufficient penetration without excessive heat input
Arc voltage	22–28 V	Stable arc, good wetting
Travel speed	200–300 mm/min	Control heat input, minimize dilution
Heat input	1.0–1.5 kJ/mm	Balance between penetration and dilution control
Preheat	150–200°C	Reduce cracking susceptibility
Interpass temperature	≤ 250°C	Control cooling rate
Post-weld cooling	Air cool or controlled cool	Achieve desired hardness

The key to the one-step approach is the control of heat input to minimize dilution of the base metal into the overlay weld. Excessive dilution reduces the carbon and alloy content of the weld metal, leading to insufficient hardness. A dilution rate of 15–25% is considered acceptable for this application, with lower dilution rates (15–20%) preferred for maximum hardness.

Performance Evaluation

Hardness and Wear Resistance Testing

The wear resistance of the overlay layer was evaluated using a pin-on-disk wear test (ASTM G99) against a Si₃N₄ counterface:

Test Condition	Wear Rate (mm³/N·m)	Relative Wear Resistance
Base metal (unhardened)	1.2 × 10⁻⁴	1.0 (reference)
HRC 58 heat-treated die steel	4.5 × 10⁻⁵	2.7
One-step overlay (as-welded)	2.8 × 10⁻⁵	4.3
One-step overlay (tempered 200°C)	2.2 × 10⁻⁵	5.5

The results demonstrate that the one-step overlay provides 4.3–5.5 times the wear resistance of the unhardened base metal, with the tempered condition providing the optimal balance of hardness and wear resistance.

Impact and Fracture Toughness Testing

The fracture toughness of the overlay layer was evaluated using a Charpy V-notch impact test at room temperature:

Condition	Impact Energy (J)	Interpretation
One-step overlay (as-welded)	12–18	Adequate for cutting edge application
One-step overlay (tempered 200°C)	18–25	Improved toughness, acceptable hardness
One-step overlay (tempered 300°C)	22–28	Further toughness improvement, reduced hardness

The impact energy values indicate that the overlay layer possesses adequate toughness to resist chipping during cutting operations, particularly after tempering at 200°C.

Field Performance Testing

A field trial was conducted on a production die cutting line using the one-step overlay electrode. The results are summarized below:

Parameter	Conventional Die Steel	One-Step Overlay Die
Cycles before regrind	15,000	42,000
Surface finish after 10,000 cycles	Ra 3.2 μm	Ra 1.6 μm
Edge chipping incidents	3 per 10,000 cycles	0 per 10,000 cycles
Downtime for maintenance	2.5 h per week	0.8 h per week

The field trial demonstrated a 2.8-fold improvement in die life and a 68% reduction in maintenance downtime, confirming the practical effectiveness of the one-step overlay approach.