Tool Steel Hardfacing Guide: Buildup, Wear Overlay & Electrode Selection

Hardfacing is the application of a wear-resistant alloy overlay to a surface that sees abrasion, impact, erosion, or metal-to-metal contact. On tool steel, hardfacing serves two purposes: restoring worn tooling to service dimensions and applying a wear layer that outperforms the original base metal. The right hardfacing alloy can push surface hardness above 60 HRC and multiply the service life of dies, punches, shear blades, and forming tools by 3-10 times.

The key distinction: hardfacing isn’t about joining two pieces. It’s about depositing a specialized alloy onto a surface to change its properties. The welding is the delivery mechanism. The metallurgy of the deposit is what provides the performance.

Hardfacing vs Buildup

These are two different operations that are often combined in a single repair.

Buildup restores the worn surface to its original geometry. The deposit should approximate the base metal’s properties (hardness, toughness, machinability). Buildup uses the matching filler for the tool steel grade (H13 rod on H13 base, for example) or a lower-alloy filler like ER80S-D2.

Hardfacing applies a different, harder alloy on top of the restored surface. The hardfacing deposit is selected for its wear resistance, not for matching the base metal. It’s typically much harder than the base and may be non-machinable (finished by grinding only).

Combined operation:

1. Grind the worn tool to clean, sound metal
2. Preheat per the base metal grade
3. Build up to within 1/16 to 1/8 inch of final dimension using matching filler
4. Apply buffer layer (if needed)
5. Apply hardfacing cap layer to final dimension plus grinding allowance
6. PWHT per base metal requirements
7. Grind to final dimension

Buffer Layer: When and Why

A buffer layer is a ductile intermediate deposit between the tool steel base (or buildup) and the hardfacing overlay. It’s critical for preventing two types of failure:

Dilution control: When hardfacing is applied directly to high-carbon tool steel, carbon from the base metal dilutes into the first layer of hardfacing deposit. This changes the hardfacing chemistry and can reduce its wear resistance. A buffer layer absorbs that dilution, allowing the hardfacing to achieve its designed composition in the second or third layer.

Stress absorption: The hard hardfacing overlay and the hard tool steel base metal both have limited ductility. Thermal stresses from welding and service temperature changes create stress at the interface. A ductile buffer layer deforms plastically to absorb that stress, preventing delamination or cracking at the base/overlay interface.

Common buffer materials:

• E309L stainless: Good all-around buffer for most tool steels
• E312 stainless: Higher ferrite content, better for high-carbon bases like D2
• ERNiCr-3 (Inconel 82): Nickel-based, used on the most difficult substrates
• ER80S-D2: For lower-alloy tool steels (P20, 4140) where austenitic buffer isn’t needed

Buffer layer thickness: 1-2 passes (approximately 1/16 to 1/8 inch). Enough to isolate the hardfacing from base metal dilution, but not so thick that it creates a weak zone.

Hardfacing Electrode Types

Hardfacing alloys are classified by their primary carbide-forming element and the resulting wear resistance.

Chromium Carbide

The most common hardfacing type for abrasion resistance. Available as stick electrodes, MIG wire, and flux-core wire.

Characteristics:

• Hardness: 55-65 HRC
• Primary carbide: Cr7C3 (chromium carbide)
• Best for: Low-stress abrasion (grinding, sliding contact)
• Deposit is non-machinable (grind only)
• Check cracking is normal and expected

Common products: Stoody 100HC, Lincoln Wearshield BU, ESAB Stoody Build-Up 2

Tungsten Carbide

The hardest common hardfacing deposit. Used where extreme abrasion resistance justifies the high cost.

Characteristics:

• Hardness: 60-70+ HRC (matrix + carbide particles)
• Primary carbide: WC (tungsten carbide) in a matrix
• Best for: Severe abrasion (earth-moving, mining, drilling)
• Applied as a tubular wire with embedded WC particles or as a rod with WC granules
• Very expensive but 5-10x longer service life than chromium carbide in severe applications

Complex Carbide (Multi-Element)

Advanced hardfacing alloys combining chromium, niobium, vanadium, tungsten, and boron carbides for specific wear environments.

Characteristics:

• Hardness: 55-68 HRC depending on formulation
• Tailored for specific combinations of abrasion, erosion, and impact
• Used in mining, oil and gas, and heavy industrial applications
• Higher cost but optimized performance for specific conditions

Cobalt-Based (Stellite Type)

Cobalt-chromium-tungsten alloys that maintain hardness at elevated temperatures.

Characteristics:

• Hardness: 38-55 HRC (lower than carbide types but maintains hardness at temperature)
• Excellent for metal-to-metal wear, erosion, and corrosion at high temperature
• Used on valve seats, hot forging dies, and cutting edges that operate at elevated temperature
• Machinable (unlike carbide types)

Common products: Stellite 6 (38-45 HRC), Stellite 1 (48-55 HRC), Stellite 21 (28-35 HRC)

Application Procedure

Step 1: Surface Preparation

Grind the tool surface to clean, sound metal. Remove all worn material, cracks, fatigue damage, and previous hardfacing that has failed. The substrate must be solid because hardfacing applied over defects will delaminate.

Step 2: Preheat

Follow the tool steel preheat requirements for the base metal grade. Preheat is still mandatory even though the final surface will be hardfacing.

Step 3: Apply Buffer Layer

If the base metal is high-carbon tool steel (A2, D2, O1, M2) or if the hardfacing alloy is prone to dilution cracking, apply a buffer layer.

Technique: Run stringer beads of E309L or E312 stainless across the surface. Overlap each bead by 30-50%. Build to 1/16 to 1/8 inch total thickness. Let interpass temperature stay within the base metal’s specified range.

Step 4: Apply Hardfacing

Bead pattern depends on the wear mechanism:

• Stringer beads (parallel): Standard for uniform wear surfaces. Overlap beads by 30-40%.
• Dot pattern: Individual dots of hardfacing deposited in a grid pattern. Used on surfaces that experience soil flow (plow points, tillage tools). The gaps between dots allow soil to pass without excessive friction.
• Crosshatch pattern: Two layers of parallel beads, second layer perpendicular to the first. Creates a multi-directional wear surface.
• Waffle pattern: Grid of beads with gaps, similar to dot pattern but with continuous lines. Used on earth-moving bucket lips.

Number of layers:

• First layer: Chemistry is diluted by the buffer or base metal. Hardness is typically 5-10 HRC below the maximum.
• Second layer: Near full hardness as dilution from previous layer is minimal.
• Third layer: Full design hardness. Rarely needed unless extremely thick overlay is required.

For most tool steel hardfacing, two layers over a buffer provide full wear resistance.

Step 5: PWHT

After hardfacing, PWHT follows the base metal requirements. The hardfacing deposit won’t be affected by the PWHT temperatures used for most tool steels (under 1100F), since carbide hardfacing alloys are stable well above those temperatures.

Step 6: Finish

Hardfacing deposits are ground, not machined (except cobalt-based types). Use aluminum oxide or silicon carbide grinding wheels. Diamond wheels cut fastest on very hard deposits.

Check Cracking: Normal vs Problem

Many hardfacing alloys develop a network of fine transverse cracks during cooling. These are stress-relief cracks (also called check cracks) that form because the hard deposit contracts more than the ductile substrate as it cools.

When check cracks are normal:

• Confined to the hardfacing layer only
• Fine, uniformly distributed across the surface
• Don’t extend into the buffer layer or base metal
• Present in chromium carbide, tungsten carbide, and complex carbide deposits
• These cracks actually help the deposit survive thermal cycling by relieving stress

When cracks are a problem:

• Cracks extend through the buffer layer into the base metal
• Large, irregular cracks that follow the fusion line
• Cracks that propagate from the overlay into the tool body
• Delamination where the hardfacing separates from the substrate

Problem cracks typically indicate insufficient buffer layer, excessive heat input, or welding over a defective substrate.

Hardfacing on Specific Tool Steels

H13 (hot-work dies): Stellite 6 or 21 on working surfaces for hot-wear resistance. Chromium carbide on non-contact wear surfaces. Buffer of E309L over the H13 base.

D2 (cold-work dies): D2’s high chromium causes extreme HAZ hardness. Always use E312 stainless buffer. Chromium carbide hardfacing for cutting edges. Two-layer minimum.

P20 (plastic molds): Typically needs buildup more than hardfacing. Use matching P20 or ER80S-D2 filler for dimension restoration. Hardfacing is used on gate areas and parting line wear surfaces.

O1 (cold-work): Similar approach to D2 but with lower preheat. E309L buffer, chromium carbide overlay. PWHT must match O1’s tempering temperature (350-500F), which is below most hardfacing stress-relief temperatures. Coordinate the PWHT carefully.

Hardfacing extends tool life dramatically when applied correctly. The investment in buffer layers, proper preheat, and correct electrode selection pays for itself many times over in reduced tool replacement costs and downtime.