XRF vs OES for Cast Steel: Why Carbon Matters Alongside Chromium, Nickel and Molybdenum

A replacement mill liner arrives with a material certificate. A handheld analyzer identifies chromium and molybdenum, and its screen displays a familiar alloy family. The casting appears to match the purchase order.

Is that enough to release it for installation?

Not necessarily. If the instrument is a conventional handheld X-ray fluorescence analyzer, it has not directly measured carbon. Carbon can be one of the most important elements controlling the hardness, heat-treatment response and fracture behavior of a cast-steel wear component.

This distinction matters for mining, cement and aggregate equipment. A liner, crusher component, liner bolt or other alloy part may contain the expected chromium and molybdenum while having an unsuitable carbon content, incorrect heat treatment or inadequate mechanical properties.

Positive material identification, commonly called PMI, is valuable. However, an alloy-identification result must be interpreted within the capabilities of the instrument and the requirements of the material specification.

This guide compares handheld XRF, spark optical emission spectrometry and combustion analysis. It explains what each method can establish, what it cannot establish, and how purchasers can specify a practical chemical-verification plan for cast-steel components.

Why Carbon Is Critical in Cast Steel

Carbon is a nonmetallic element, but its influence on steel can be greater than that of several deliberately added metals.

In suitable alloy systems, carbon affects:

• Potential hardness after quenching
• Strength and ductility
• Carbide formation
• Transformation behavior
• Tempering response
• Weldability
• Susceptibility to cracking
• The balance between abrasion resistance and impact resistance

The correct carbon content depends on the complete alloy and its intended microstructure. A higher carbon result is not automatically better for a wear component.

A heavily impacted liner may require a different balance of hardness and toughness from a component exposed mainly to sliding abrasion. The carbon requirement must therefore be evaluated together with chromium, molybdenum, manganese, nickel, heat treatment and service conditions.

A chemical certificate showing chromium and molybdenum alone cannot establish this balance.

Carbon Is Not a Substitute for Mechanical Testing

Even when carbon is within specification, a casting may have unsuitable properties because of:

• Incorrect austenitizing conditions
• Inadequate cooling through a heavy section
• An unsuitable tempering cycle
• Local segregation
• Coarse grains
• Shrinkage porosity
• Nonmetallic inclusions
• Residual stress
• Quench cracking

Chemical verification confirms composition at the sampled location. It does not independently confirm casting soundness, heat-treatment quality or fitness for service.

What Handheld XRF Measures

X-ray fluorescence uses an X-ray source to excite the material. The instrument measures characteristic fluorescence emitted by detectable elements and uses the resulting spectrum to estimate composition.

Conventional handheld XRF instruments are useful for identifying many alloying elements, including chromium, nickel and molybdenum. Depending on the instrument, calibration and operating conditions, they may also measure elements such as manganese, copper, cobalt, tungsten and certain lighter elements.

Their portability makes them useful for incoming inspection, material sorting and checking individual components against alloy-family expectations.

However, conventional handheld XRF does not directly measure carbon.

If a material grade is distinguished primarily by carbon content, an XRF grade match cannot confirm that distinction. The displayed grade name is an interpretation based on measured elements and the instrument’s grade library.

A Grade Name on the Screen Is Not a Complete Certificate

A grade-identification function typically compares measured composition with stored limits or reference patterns.

Its reliability depends on:

• Which elements the instrument measures
• The selected calibration
• The contents of the grade library
• Measurement time
• Surface preparation
• Sample geometry
• Coatings or contamination
• Instrument verification
• The similarity of competing grades

Two steels may have similar chromium, nickel and molybdenum contents but different carbon requirements. The instrument may identify their common family without resolving the carbon-based difference.

The inspector should therefore review the elemental results and method limitations, not just the suggested grade name.

What Spark OES Measures

Spark optical emission spectrometry, or spark OES, uses an electrical discharge to excite a small area of the metal surface. The emitted light is separated and analyzed to determine elemental composition.

With appropriate instrument configuration, calibration, sample preparation and operating conditions, spark OES can measure carbon and other elements important to steel specifications.

ASTM E415 provides a method for analyzing carbon and low-alloy steel by spark atomic emission spectrometry. Its scope includes defined ranges for alloying and residual elements.

The existence of a standard does not mean every instrument can analyze every casting grade under that standard. The laboratory must confirm that the specimen and required composition ranges fall within the method’s validated scope.

Bench OES and Mobile OES Are Not Identical Inspection Arrangements

Bench instruments normally analyze prepared samples under controlled laboratory conditions. Mobile spark OES can support testing of suitable components at other locations, but it still requires the correct instrument configuration and a suitable prepared surface.

Practical considerations include:

• Access to the test location
• Surface flatness
• Removal of scale and coatings
• Argon supply where required
• Instrument calibration
• Reference-material checks
• The size of the spark stand or probe
• The effect of surface decarburization
• Permission to leave a small test mark

A specification should identify the required result and accepted method. It should not assume that all equipment described as a “spectrometer" has the same capabilities.

What Combustion Analysis Adds

Combustion analysis is another established approach for determining carbon and sulfur.

A prepared sample is combusted under controlled conditions, and the resulting gases are analyzed. The procedure requires suitable sampling, sample mass, calibration and quality-control practices.

ASTM E1019 covers methods for determining carbon, sulfur, nitrogen and oxygen in specified metallic materials using combustion and inert-gas-fusion techniques. The applicable procedure must be selected for the element and material being tested.

Combustion analysis is particularly useful when carbon or sulfur needs an agreed laboratory confirmation. It does not provide a complete chromium–nickel–molybdenum analysis from the same carbon/sulfur measurement.

For some orders, spark OES provides routine composition verification while combustion analysis supplies an agreed confirmation of carbon or sulfur. Whether both are necessary depends on the specification, risk and analytical requirements.

XRF, OES and Combustion Analysis Compared

These methods answer different questions. A reliable inspection plan combines the methods needed for the actual purchase specification instead of treating one test as a universal substitute.

How Carbon, Chromium, Nickel and Molybdenum Work Together

The table below summarizes general metallurgical roles. It is not a grade specification or a recommendation to change an existing alloy.

The appropriate carbon range must come from the specified grade or an approved custom composition. It should never be inferred from a handheld analyzer’s chromium and molybdenum results.

Common Situations Where XRF Alone Is Insufficient

Cr-Mo Mill Liners

A handheld XRF result can support identification of the chromium–molybdenum alloy family. It cannot establish carbon content or confirm that the liner received the required heat treatment.

For a Cr-Mo liner, a practical verification package may include:

• Heat chemical analysis
• Carbon verification by an appropriate method
• Product marking and heat traceability
• Hardness at agreed locations
• Impact testing where required
• Heat-treatment documentation
• Surface or internal inspection where specified

For product context, see our Cr-Mo alloy-steel SAG mill liner page.

Carbon-Based Variants Within an Alloy Family

Some grade distinctions depend on carbon limits even when the major alloying elements are similar.

If the acceptance requirement depends on carbon, use a carbon-capable method. Do not accept a grade-library identification as proof of an element that was not measured.

Also avoid substituting a wrought-grade designation for a casting-grade designation simply because their names or major alloying elements appear similar.

High-Chromium White Iron

High-chromium white iron requires verification of carbon as well as chromium and other specified elements.

However, ASTM E415 is a carbon- and low-alloy-steel method. It should not automatically be applied to high-chromium white iron merely because both are iron-based materials.

The laboratory should select and validate an analytical procedure appropriate to the material, its composition and its metallurgical condition.

Repaired or Coated Surfaces

A reading on weld metal, hardfacing, plating or a contaminated surface may not represent the underlying casting.

Before testing, determine whether the measurement location is:

• Original parent metal
• Weld-repair metal
• A deposited wear layer
• A machined surface
• A coated surface
• A decarburized surface
• A region affected by previous cutting or heating

The test location must match the question being asked.

Surface Preparation Can Determine Whether a Result Is Useful

A technically capable instrument can still produce an unrepresentative result on an unsuitable surface.

Paint, rust, scale, oil, plating and embedded abrasive material can interfere with testing. Rough surfaces can also prevent correct probe contact or sealing.

For spark OES, sample preparation should follow the qualified procedure. Important considerations include:

• Removing the required surface layer
• Avoiding contamination from grinding tools
• Preparing sufficient flat area
• Controlling heat generated during preparation
• Avoiding regions altered by welding or cutting
• Identifying possible surface decarburization
• Using reference materials appropriate to the specimen

ASTM E415 notes that improved performance is expected when reference materials and specimens have similar composition and metallurgical condition. Analytical preparation therefore deserves the same attention as instrument selection. See the ASTM E415 method scope.

Do not specify an arbitrary grinding depth for every casting. The required preparation depends on surface condition, manufacturing history and the accepted procedure.

Sampling: A Correct Measurement Can Still Be Unrepresentative

A result can be analytically correct for the tested sample while being insufficient to characterize the whole component or shipment.

This distinction is particularly important for large castings.

Heat Analysis

A heat-analysis sample supports verification of the melt associated with production. It should be linked to the casting through a traceable heat identification.

A certificate without a reliable relationship to the delivered component provides limited assurance.

Product Analysis

Product analysis is performed on material taken from a casting or another agreed product location.

The purchase specification should define:

• Whether product analysis is required
• Where the sample is taken
• Who prepares it
• Which method is used
• Which tolerances apply
• How disagreements are resolved

Local Segregation

Castings can contain composition variation associated with solidification. One measurement does not map the entire casting.

Where local variation is a concern, the engineer and laboratory should agree on a sampling plan. Taking many readings without a defined plan does not necessarily produce a more representative conclusion.

ISO 4990 addresses general technical delivery requirements for steel, nickel and cobalt alloy castings, including sample and test-piece selection. The applicable material or product specification remains important when defining acceptance.

What a Useful PMI Report Should Contain

A report stating only “PMI passed" leaves important questions unanswered.

A value that was not measured should be identified as unmeasured. It should not be displayed as zero, assumed compliant or silently omitted where the element is necessary for acceptance.

A Practical Incoming-Inspection Workflow

Step 1: Review the Purchase Requirements

Confirm the drawing revision, material grade, required chemistry, heat-treatment condition and inspection requirements.

Identify which elements are essential to distinguish the specified material from plausible alternatives.

Step 2: Check Traceability

Compare the casting markings with the packing list, material certificate and heat-treatment records.

If identification is missing or inconsistent, resolve it before relying on analytical results.

Step 3: Use XRF for the Questions It Can Answer

Where appropriate, use handheld XRF to check detectable alloying elements and identify obvious material mix-ups.

Record the elemental results and any unresolved grade ambiguity.

Step 4: Verify Carbon When Required

If carbon is needed for grade confirmation or acceptance, obtain a result from an appropriate carbon-capable method.

Do not infer carbon from hardness, appearance or a grade-library match.

Step 5: Review Other Required Elements

Determine whether sulfur, phosphorus, silicon or other specified elements have been adequately measured by the accepted procedure.

Instrument capability must be confirmed for the required material and concentration range.

Step 6: Review Heat Treatment and Properties

Check hardness, impact, tensile or other required results. Confirm that test pieces and production castings have the agreed relationship.

Step 7: Resolve Deviations Before Release

If a result falls outside the acceptance criteria, follow the agreed procedure for retesting, investigation or disposition.

Do not average unrelated readings to make a nonconforming result appear acceptable.

Why Hardness Cannot Identify Carbon Content

Hardness is affected by composition, microstructure and processing.

The same steel can have very different hardness values in annealed, normalized, quenched or tempered conditions. Different alloys can also exhibit similar hardness.

Therefore, hardness cannot uniquely establish:

• Carbon content
• Alloy grade
• Chromium content
• Molybdenum content
• Impact toughness
• Internal soundness

Hardness remains valuable when used for its intended purpose. A hardness map can reveal variation across a casting and help investigate heat-treatment consistency.

For background on how liner geometry and material interact in service, see What Is a SAG Mill Liner and How Does It Work?.

Common Inspection Errors

Treating Every “Spectrometer" as Equivalent

XRF and spark OES use different physical principles and have different capabilities. Identify the actual method in the inspection plan.

Accepting a Grade Name Without Elemental Results

A library match is useful supporting information. It should not replace comparison of measured values with specified limits.

Measuring the Wrong Surface

A reading from a weld repair, coating or contaminated region may answer a different question from the one intended.

Applying a Standard Outside Its Scope

A method intended for carbon and low-alloy steel should not be assumed suitable for every high-alloy steel, white iron or nonferrous casting.

Confusing Chemical Compliance with Service Suitability

Correct chemistry does not establish that the component has the right shape, heat treatment, toughness or defect acceptance level.

Omitting Unmeasured Elements

If carbon is required but not measured, the report should make that gap visible.

RFQ Checklist for Chemical Verification

When requesting cast-steel components, include the following information.

Product and Material

• Drawing and revision
• Part number
• Quantity
• Material grade and standard
• Approved custom chemistry, if applicable
• Required heat-treatment condition
• Normal operating temperature
• Impact, abrasion and corrosion conditions

Chemical Testing

• Required elements
• Acceptance ranges and maximum limits
• Heat-analysis requirements
• Product-analysis requirements
• Carbon-capable method where needed
• Sulfur confirmation method where required
• Sampling locations
• Heat or lot definition
• Test frequency
• Reporting precision
• Retest and dispute procedures

Supporting Inspection

• Hardness range and locations
• Impact-test requirements
• Tensile-test requirements
• Metallographic requirements
• NDT methods and acceptance criteria
• Dimensional inspection
• Weld-repair restrictions
• Required certificates
• Customer or third-party witness points

Discuss these requirements before production. Adding an inspection requirement after casting and heat treatment can create sampling difficulties or make the original qualification plan unsuitable.

Safety and Engineering Responsibility

Handheld XRF equipment produces ionizing radiation and must be operated by trained personnel under applicable radiation-safety requirements and manufacturer instructions.

Spark OES creates an electrical discharge and leaves a small surface mark. Its use requires suitable equipment, surface preparation and site controls. It should not be used in a potentially flammable atmosphere without the necessary assessment and authorization.

Sampling, grinding and cutting introduce additional hazards. Never prepare or test a component while it is moving, inadequately supported or connected to uncontrolled equipment.

The inspection plan should be approved by personnel responsible for material acceptance. This article does not replace the governing material standard, a qualified laboratory procedure or equipment-specific engineering review.

Frequently Asked Questions

Can a Conventional Handheld XRF Analyzer Measure Carbon in Steel?

No. A conventional handheld XRF analyzer does not directly measure carbon. Use a suitable carbon-capable analytical method when carbon is required for acceptance.

Does an XRF Grade Match Prove the Casting Meets the Entire Material Specification?

No. It supports identification based on the measured elements. Unmeasured elements, heat treatment, mechanical properties and casting soundness require separate consideration.

Is Spark OES Always the Best Choice?

Not automatically. Its suitability depends on the alloy, analytical range, instrument, sample geometry, preparation and required accuracy. The laboratory should select a validated method.

Can Combustion Analysis Confirm Chromium and Molybdenum?

A carbon/sulfur combustion result does not provide a complete chromium–molybdenum analysis. Additional elemental analysis is required.

Can I Use a Wrought-Steel Grade as a Casting Grade?

Not without engineering and specification review. Similar major alloying elements do not make product standards or processing requirements interchangeable.

Must Every Casting Receive Every Test?

Not necessarily. Inspection frequency should follow the purchase specification, applicable standard and risk-based acceptance plan. Define the requirements before manufacture.

Conclusion

Handheld XRF is useful for alloy identification and checking detectable alloying elements. Its carbon limitation becomes important when accepting cast-steel mill liners and other components whose properties depend strongly on carbon.

A complete verification plan should connect:

• The specified material grade
• Traceable heat and product identification
• An analytical method capable of measuring required elements
• Representative sampling
• Heat-treatment documentation
• Mechanical and nondestructive testing where required

For Cr-Mo cast steel, confirming chromium and molybdenum is only part of the material-verification process. Carbon, residual elements, microstructure and processing must also match the agreed requirements.

Send EB China the component drawing, operating conditions and inspection specification for review. Manufacturing scope, analytical methods and acceptance criteria should be confirmed before quotation and production.

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Email: cast@ebcastings.com