One of the biggest misunderstandings in industrial hardfacing is assuming that hardfacing behaves like conventional structural welding.

It does not.

Traditional welding mainly focuses on:

•  Strength
•  Ductility
•  Structural integrity

Hardfacing, however, focuses on:

•  High hardness
•  Wear resistance
•  Abrasion resistance
•  Erosion resistance
•  Corrosion protection

Typical hardfacing materials include:

Hardfacing Material	Typical Hardness
Stellite 6	HRC 38–45
Chromium Carbide	HRC 55–62
Tungsten Carbide	HRC 60–70+

The challenge is simple:

Higher hardness usually means lower ductility.

As the overlay cools after welding, both the base material and hardfacing layer begin to shrink. Since these materials often have different thermal expansion coefficients, enormous tensile stress develops between the overlay and substrate.

This is especially common in combinations such as:

•  Carbon steel + Stellite
•  Stainless steel + tungsten carbide
•  Thick-wall valves + nickel-based alloys

In many industrial cases, hardfacing cracks are not caused because “the weld was poor,” but because:

Residual welding stress could not be properly released.

 

Why Do Many Hardfacing Cracks Appear Hours Later?

This is one of the most misunderstood phenomena in weld overlay applications.

Many repair shops assume:

“If no crack appears immediately after welding, the job is successful.”

But experienced hardfacing engineers know:

The most dangerous cracks are often delayed cracks.

This is particularly common in:

•  High carbon steel
•  Thick-wall valve bodies
•  High-hardness overlays
•  PTA weld overlay systems

Even after welding is complete:

•  Residual stress continues developing
•  Metallurgical structures continue transforming
•  Hydrogen diffusion is still occurring

As a result, cracks may appear 2 to 24 hours later.

In one API valve hardfacing project, we encountered a situation where:

•  Stellite 6 overlay developed edge cracks 10 hours after welding
•  Cracks concentrated near the weld stop area
•  No visible issue appeared during welding

After investigation, the root cause was identified as:

Excessive fluctuation in interpass temperature.

By implementing:

•  250°C preheating
•  Better interpass temperature control
•  Improved weld stop trajectory
•  Slow cooling insulation

the weld overlay cracking rate was significantly reduced.

In many industrial hardfacing projects, the real issue is not the equipment itself, but:

Lack of control over post-weld stress evolution.

 

Which Hardfacing Cracks Are Actually Acceptable?

This is where many end users become confused.

In reality, certain surface cracks are intentionally tolerated in high-hardness wear-resistant overlays.

For example, in:

•  Chromium carbide overlay plates
•  Carbide hardfacing layers
•  High-hardness wear overlays

it is common to see fine network-like cracks across the surface.

These are commonly known as:

•  Check cracks
•  Stress relief cracks
•  Relief checking

Their purpose is to release residual welding stress within the hardfacing layer.

Because in ultra-hard overlays:

A completely crack-free surface may actually indicate dangerous internal stress accumulation.

If residual stress cannot be released gradually, the result may become far worse:

•  Large-scale delamination
•  Overlay spalling
•  Sudden coating failure

This is why experienced hardfacing engineers often say:

Controlled cracking is safer than uncontrolled delamination.

However, dangerous cracks usually have the following characteristics:

•  Cracks penetrate into the substrate
•  Cracks continue propagating
•  Overlay edges begin separating
•  Delamination or hollow zones appear

These symptoms typically indicate:

•  Excessive heat input
•  Incorrect material selection
•  High dilution rate
•  Improper welding parameters

and usually require process redesign.

 

The 5 Most Common Causes of Hardfacing Cracks

1. Insufficient Preheating

In large valve PTA hardfacing projects, many cracks do not occur during welding itself, but during cooling.

Especially with:

•  Thick-wall carbon steel valves
•  High carbon steel
•  High-hardness overlays

insufficient preheating can dramatically increase cooling speed.

This often leads to:

•  Martensite formation
•  Residual stress concentration
•  Delayed cold cracking

In many cases, weld overlay cracking is not caused by poor welding technique, but by:

Poor thermal management.

 

2. Excessive Overlay Thickness

Many workshops try to improve productivity by depositing thick hardfacing layers in a single pass.

But in reality:

Thicker overlays generate much higher shrinkage stress.

This is especially problematic for:

•  Tungsten carbide overlays
•  Chromium carbide hardfacing
•  High-hardness iron-based alloys

Professional hardfacing procedures usually involve:

•  Multi-layer welding
•  Controlled interpass temperature
•  Intermediate cooling stages

to gradually release stress.

 

3. Rapid Cooling

Many hardfacing cracks are not “welded in.”

They are cooled in.

This is especially common during winter repairs or large component rebuilding when:

•  Parts are exposed to cold air immediately
•  Forced air cooling is used
•  Components contact cold floors

Professional workshops typically use:

•  Thermal insulation blankets
•  Slow cooling
•  Furnace cooling

to minimize thermal shock.

 

4. Excessive Heat Input

Whether using PTA, MIG, or SAW hardfacing:

Excessive heat input increases cracking risk.

Higher heat input leads to:

•  Deeper penetration
•  Larger heat affected zones
•  Greater shrinkage stress

Traditional arc welding overlays are particularly susceptible to this issue.

Compared with conventional welding:

•  PTA offers lower dilution
•  Laser cladding provides smaller HAZ

which generally lowers cracking risk.

 

5. Incorrect Material Selection

Many customers assume:

“Higher hardness always means better wear resistance.”

But in real industrial environments:

Toughness is often more important than hardness.

Especially in:

•  Mining wear parts
•  Crusher components
•  High-impact valve applications

overly brittle materials may fail prematurely.

Many wear part failures occur not because the overlay was “too soft,” but because:

The material lacked sufficient toughness.

 

PTA vs Laser Cladding: Which Process Cracks Less?

This is one of the most common questions in industrial hardfacing.

PTA (Plasma Transferred Arc) hardfacing offers:

•  Low dilution
•  Strong metallurgical bonding
•  High deposition efficiency
•  Thick overlay capability

making it widely used in:

•  Valve hardfacing
•  Oil & gas valve repair
•  Mining wear parts rebuilding

Compared with traditional MIG or SAW overlay welding:

PTA weld cracking risk is generally lower.

However, poor thermal control can still lead to:

•  Edge cracking
•  Residual stress cracking
•  Delayed cold cracks

Laser cladding, on the other hand, offers:

•  Extremely low heat input
•  Minimal heat affected zone
•  Lower distortion

which makes it one of the most crack-resistant cladding technologies available today.

It is especially suitable for:

•  Precision valve repair
•  Nuclear valve applications
•  Aerospace components

However, laser cladding also requires:

•  Stable powder feeding
•  Precise energy control
•  Consistent process parameters

Otherwise, microcracking may still occur.

 

How We Help Customers Reduce Hardfacing Crack Risk

Over the years, we have worked extensively on:

•  API valve repair
•  PTA valve hardfacing
•  Tungsten carbide overlay
•  Mining wear parts rebuilding

and discovered that:

More than 70% of cracking problems are caused by process instability rather than material defects.

This is why our systems focus heavily on:

•  Stable heat input control
•  Precision powder feeding
•  Interpass temperature management
•  Torch oscillation consistency
•  Automated weld path control

helping customers reduce:

•  Weld overlay cracking
•  Rework rates
•  Scrap rates
•  Overlay delamination risks

Our solutions are widely used in:

•  Oil & Gas
•  Petrochemical
•  Mining
•  Power Generation
•  Cement
•  Marine Engineering

industries worldwide.

Whether for valve hardfacing, weld overlay automation, or heavy wear component rebuilding, we provide customized hardfacing solutions designed for long-term industrial reliability.

 

FAQ: Hardfacing Cracks

1.Are hardfacing cracks always a defect?

No. Certain shallow surface cracks are normal stress relief cracks and are acceptable in many high-hardness overlays.

2.Why do cracks appear hours after welding?

Because residual stress, metallurgical transformation, and hydrogen diffusion continue after welding is completed.

3.Why does PTA hardfacing often crack near the edges?

Edge areas cool faster and concentrate stress more easily, especially if preheating and interpass temperature are poorly controlled.

4.Which process has the lowest cracking risk?

Laser cladding generally offers the lowest cracking risk due to its extremely low heat input, while PTA provides better balance between wear resistance, repair thickness, and cost.

5.How can weld overlay cracking be reduced?

The key factors include:

•  Proper preheating
•  Controlled interpass temperature
•  Optimized heat input
•  Slow cooling
•  Correct material selection

 

Conclusion: Successful Hardfacing Is Not Just About Hardness

One of the biggest mistakes in industrial hardfacing is focusing only on hardness.

In reality, long-term overlay performance depends on balancing:

•  Wear resistance
•  Toughness
•  Metallurgical bonding
•  Thermal stability
•  Residual stress control

Hardfacing cracks themselves are not always the real problem.

The real danger is failing to understand why they occur.

For industrial companies, choosing an experienced hardfacing solution provider is often far more important than simply purchasing welding equipment.

If you are looking for:

•  PTA hardfacing systems
•  Laser cladding solutions
•  Automated valve hardfacing equipment
•  Weld overlay automation systems
•  Hardfacing process optimization

contact us today for professional technical support and customized industrial hardfacing solutions.