Procurement teams ordering cemented carbide components for the first time often frame the decision as a simple hardness question. It is not. A mining operation in Western Australia switched to a higher-HRA insert hoping to extend wear life on their roadheader. Tool life dropped by over 30% in the first week — the grade was too brittle for the impact cycle, and chipping replaced abrasive wear as the dominant failure mode. The cost was not just replacement parts. It was unplanned downtime, delayed shift targets, and a root-cause investigation that took longer than the original ordering process.
To place this failure mode in the complete equipment context, review the tungsten carbide rod blanks for properties.
Cemented carbide grades are defined by three interdependent variables: hardness (HRA), cobalt content (%), and grain size (µm). Getting one wrong pulls the others out of balance. This guide covers how those variables interact, what the published spec numbers actually mean in service, and how to use Ruixin’s SR7X, SR8C, and SR10C grades as a decision framework for mining, tunneling, road milling, and wear part applications.
What Cemented Carbide Grades Actually Measure
Grade designations are not arbitrary product codes. Each one encodes a specific balance of hardness, toughness, and wear resistance engineered for a defined class of service conditions. The numbers are what you actually buy.
Cemented carbide (WC-Co) is a composite: tungsten carbide (WC) particles sintered in a cobalt (Co) binder. The WC provides hardness and wear resistance. The cobalt binder provides ductility and fracture toughness. Every grade is defined by how much cobalt is present and how coarse or fine the WC grain structure is.
Hardness (HRA)
HRA is measured on the Rockwell A scale and is the primary indicator of wear resistance. The harder the grade, the more it resists abrasion from rock or aggregate contact. The practical range for mining-grade cemented carbide runs from HRA 87 to HRA 93. Ruixin SR7X sits at HRA 91.0 ± 0.5, near the harder end. SR8C sits at HRA 89.0 ± 0.5. SR10C sits at HRA 88.0 ± 0.5.
Higher HRA is not always better. At HRA 91+, the grade becomes progressively more brittle. Any application with significant impact loading — interrupted cutting, hard inclusion encounters, variable formation — will cause fracture rather than wear. The tool fails faster, not slower.
Cobalt Content (%) and the Toughness Trade-off
The relationship between cobalt content and hardness is inverse. Increasing cobalt from approximately 6% to 12% drops HRA from ~92 to ~88, but raises flexural strength from ~2,000 MPa toward ~2,400 MPa. Flexural strength (MPa) is the metric that predicts how well a grade survives impact loading.
Ruixin SR7X, SR8C, and SR10C are positioned at different points on this hardness-toughness curve. SR7X delivers maximum wear resistance at the cost of toughness. SR10C delivers maximum toughness at a modest reduction in wear resistance. SR8C is the balanced midpoint used across the widest range of applications.
Grain Size (µm) and Its Effect on Edge Retention
Grain size controls the texture of the carbide microstructure. At 1.0–1.2 µm (fine grain), the WC particles are tightly packed, producing a hard, dense surface with excellent abrasion resistance and sharp edge retention. This is the grain structure of Ruixin SR7X. At 2.0–3.0 µm (medium grain), the structure is slightly coarser, which reduces hardness modestly but increases the material’s capacity to absorb and distribute impact energy. Both SR8C and SR10C operate in this range.
The practical implication: fine-grain grades maintain tighter dimensional tolerances and sharper cutting edges in low-impact abrasive service. Medium-grain grades perform better where repeated impact is part of the operational cycle. Grain size is as consequential a selection variable as HRA — a grade selected purely on hardness will underperform if the grain structure is mismatched to the load type.
The Three Ruixin Standard Grades: Full Specification Breakdown
Ruixin manufactures three standard mining and wear application grades — SR7X, SR8C, and SR10C — each with published specifications verified at the factory. The table below is Ruixin’s internal reference data, not marketing claims.
| Grade | Density (g/cm³) | Hardness (HRA) | Flexural Strength (MPa) | Grain Size (µm) | Primary Positioning |
|---|---|---|---|---|---|
| SR7X | 14.70 ± 0.05 | 91.0 ± 0.5 | ≥ 2,000 | 1.0–1.2 | Maximum wear resistance; low-impact abrasive service |
| SR8C | 14.65 ± 0.05 | 89.0 ± 0.5 | ≥ 2,200 | 2.0–3.0 | Balanced wear and toughness; roadheader, road milling |
| SR10C | 14.45 ± 0.05 | 88.0 ± 0.5 | ≥ 2,200 | 2.0–3.0 | Maximum toughness; high-impact mining and tunneling |
One distinction that competing grade tables typically omit: SR8C and SR10C share the same grain size range (2.0–3.0 µm) and the same minimum flexural strength (≥ 2,200 MPa), but SR10C carries a lower density (14.45 vs. 14.65 g/cm³). That density difference reflects a higher cobalt binder proportion in SR10C, which is what delivers its superior toughness under sustained impact loading. Selecting between SR8C and SR10C is a cobalt-ratio decision driven by the impact frequency and severity in your application, not a hardness decision.
SR7X — When Wear Resistance Is the Dominant Requirement
Ruixin SR7X at HRA 91.0 and 1.0–1.2 µm grain size is the correct choice when abrasion is the primary failure mode and impact loading is minimal. Typical applications include wear-resistant strips, carbide liners, and precision components in steady-state sliding contact with abrasive media. SR7X is also used in road milling inserts operating on consistent, homogeneous asphalt where formation hardness variation is low.
SR7X is not suitable for interrupted cutting, variable rock formations, or any application where the tool body experiences shock loads. At HRA 91.0, the grade has sufficient flexural strength for abrasive service (≥ 2,000 MPa) but sits near the brittleness threshold for impact applications. Running SR7X in a high-impact environment is the single most common source of premature chipping failure we see from new customers.
SR8C — The Balanced Grade for Most Mining Applications
Ruixin SR8C at HRA 89.0, 2.0–3.0 µm grain, and ≥ 2,200 MPa flexural strength is the starting point for roadheader picks, coal tooth inserts, and road milling carbide in mixed service conditions. It handles moderate impact and sustained abrasion without the brittleness risk of SR7X or the wear-rate penalty of SR10C.
The 2.0–3.0 µm grain range gives SR8C better impact energy absorption than SR7X while keeping HRA high enough to resist abrasive wear in medium-hard formations (Mohs 4–6). Coal seams and roadheader formations typically involve variable strata — alternating soft coal with harder sandstone or mudstone bands. SR8C’s balanced profile makes it the default recommendation for 70–80% of shearer and roadheader applications we supply.
SR10C — When Impact Is the Governing Failure Mode
Ruixin SR10C at HRA 88.0 and ≥ 2,200 MPa flexural strength is specified when impact loading is frequent, severe, or unpredictable. Applications include shield machine carbide tips in mixed-face tunneling, DTH button inserts in fractured rock formations, and longwall shearer picks operating in seams with hard rock inclusions above 80 MPa UCS.
The lower HRA (88.0 vs. 89.0 for SR8C) is the necessary trade-off for the additional cobalt content that provides toughness. In practice, the wear-rate difference between SR10C and SR8C only becomes material in highly abrasive formations. For most high-impact applications, SR10C’s extended tool life from fracture resistance more than compensates for the marginal reduction in abrasion performance.
Grade Selection by Application
The table below maps Ruixin’s three standard grades to specific working conditions. Use this as a first-pass selection filter, not a final specification. Complex formations or non-standard machine configurations should be verified with a grade consultation.
| Application Scenario | Recommended Grade | Key Parameters | Why This Grade |
|---|---|---|---|
| Longwall shearer picks, medium-hard coal, occasional hard inclusions | SR8C | HRA 89.0, ≥ 2,200 MPa, 2.0–3.0 µm | Balanced toughness and wear resistance handles variable seam conditions without fracture |
| Roadheader picks, complex strata with frequent hard rock bands | SR10C | HRA 88.0, ≥ 2,200 MPa, 2.0–3.0 µm | Higher cobalt content absorbs repeated impact from hard rock inclusions |
| Road milling inserts, homogeneous asphalt, sustained abrasion | SR7X or SR8C | HRA 91.0 or 89.0, 1.0–1.2 or 2.0–3.0 µm | SR7X for consistent low-impact pavement; SR8C when concrete or aggregate layers are present |
| Shield machine carbide tips, mixed-face tunneling | SR10C | HRA 88.0, ≥ 2,200 MPa | Mixed-face conditions create unpredictable impact; maximum toughness grade prevents catastrophic fracture |
| Carbide wear strips and liners, sliding abrasion service | SR7X | HRA 91.0, 1.0–1.2 µm, 14.70 g/cm³ | High density and fine grain maximise surface hardness for pure abrasion resistance |
| DTH spherical buttons, medium-hard rock (80–120 MPa UCS) | SR8C | HRA 89.0, ≥ 2,200 MPa | Balanced grade survives rotary impact of DTH percussion without fracture or excess wear |
What Happens When You Choose the Wrong Carbide Grade
The wrong cemented carbide grade does not just underperform — it fails in a predictable, quantifiable way that costs more than the original savings on unit price. Understanding the specific failure modes makes the selection logic concrete.
Consequence 1 — Grade Too Hard: Chipping and Fracture
Running a high-HRA grade (such as SR7X at HRA 91.0) in an impact-heavy application causes chipping and fracture rather than abrasive wear. The grade lacks the cobalt binder content to absorb repeated shock loads. Field data from roadheader applications shows that mismatched high-hardness grades fail by fracture 2–4x faster than a correctly specified balanced grade. The tool body is often damaged in the process, compounding replacement cost beyond the insert itself.
Consequence 2 — Grade Too Tough: Accelerated Abrasive Wear
Specifying SR10C when SR7X is appropriate — for example, in a pure sliding-abrasion wear part — wastes the toughness margin while paying a 15–20% wear-rate penalty. In abrasion-dominant applications, the higher cobalt content of SR10C means the binder phase erodes faster, exposing WC particles that then pull out prematurely. Replacement intervals shorten, and total cost per operating hour rises despite using a “tougher” grade.
Consequence 3 — Thermal Shock from Hardness Mismatch
High-hardness grades with lower cobalt content have reduced thermal conductivity tolerance. In applications with high cutting speeds and inadequate coolant flow — road milling at elevated ambient temperatures being a common example — a mismatched hard grade accumulates thermal stress at the carbide-steel braze joint. Cracking at this interface can propagate into the carbide body within a single shift, causing insert loss and tool holder damage.
Consequence 4 — Inconsistent Batch Performance and Rejection Risk
Ordering the wrong grade for an OEM application creates downstream quality risk. If a carbide tip is specified at HRA 89.0 ± 0.5 (SR8C range) and the supplier substitutes a higher-hardness grade without disclosure, the tip passes dimensional inspection but fails in field performance testing. OEM customers sourcing from Ruixin receive material test reports and batch QC data with every shipment — which makes grade substitution immediately detectable.
How to Read a Carbide Grade Spec Sheet: A Practical Checklist
Most published grade specifications look similar on the surface. Knowing which numbers to interrogate — and which tolerances signal quality control discipline — separates a reliable supply source from one that will deliver inconsistent batches.
Check 1 — Density Tolerance Band
Density (g/cm³) reflects the actual cobalt-to-WC ratio in the sintered part. A tight tolerance (±0.05 g/cm³, as Ruixin specifies for all three grades) indicates consistent raw material composition and sintering process control. A wide or unstated density tolerance is a warning sign.
Check 2 — HRA Tolerance and Test Method
HRA should be stated with a tolerance band (e.g., 91.0 ± 0.5). Any specification without a tolerance is an unverifiable claim. Confirm the test is performed on the Rockwell A scale — not converted from Vickers or estimated from vendor literature.
Check 3 — Flexural Strength as Minimum Value
Flexural strength should appear as a minimum guaranteed value (≥ 2,000 MPa), not a nominal or typical value. The minimum is what your application must survive. Ruixin publishes ≥ 2,000 MPa for SR7X and ≥ 2,200 MPa for both SR8C and SR10C — these are floor values, not averages.
Check 4 — Grain Size Range, Not Just Category
Grade sheets that describe grain size as “fine,” “medium,” or “coarse” without µm values are not providing usable data. For engineering decisions, you need the actual range: 1.0–1.2 µm for SR7X, 2.0–3.0 µm for SR8C and SR10C.
Check 5 — Certification and Batch Traceability
ISO 9001:2015 certification covers the quality management system, not individual grade specs. Request a material test report (MTR) for each batch. Ruixin provides MTR, batch QC report, and ISO certification documentation with every commercial shipment.
Matching Cemented Carbide Grades to Rock and Formation Conditions
Grade selection requires understanding the formation your tools will contact, not just the machine. Rock hardness, abrasiveness, and structural integrity all influence which grade variable governs the failure mode.
Soft to Medium Formations (Mohs 2–4): Coal, Mudstone, Soft Limestone
In soft-to-medium formations, impact from variable seam structure is typically the limiting factor, not pure abrasion. Ruixin SR8C at HRA 89.0 is the standard recommendation for shearer picks and roadheader inserts in this formation class. The 2.0–3.0 µm grain and ≥ 2,200 MPa flexural strength provide enough toughness for occasional hard band encounters while maintaining sufficient wear resistance to achieve acceptable tool life.
For continuous-contact wear parts operating in soft formation material — conveyor liners, chute liners — SR7X at HRA 91.0 delivers the best abrasion life because impact is absent from the loading cycle.
Medium-Hard Formations (Mohs 4–6): Sandstone, Limestone, Mixed Strata
Medium-hard formation work is where grade selection becomes most consequential. The abrasion component is high enough to wear SR10C faster than necessary, but the impact component rules out SR7X. Ruixin SR8C is the correct default for this formation class — it sits at the hardness-toughness crossover point where neither failure mode dominates.
If the formation contains hard rock bands above 80 MPa UCS at intervals exceeding 20% of the cutting cycle, move to SR10C. The impact frequency in this scenario exceeds what SR8C’s cobalt content can absorb over a full shift.
Hard Rock (Mohs 6+): Granite, Basalt, Hard Sandstone
Hard rock applications impose severe abrasion and significant impact simultaneously. This is the most demanding service class for cemented carbide, and no single standard grade optimally satisfies both conditions. Ruixin SR10C is the starting point because fracture prevention takes priority — a fractured insert causes tool holder damage and immediate production stoppage, whereas gradual abrasive wear allows planned replacement intervals.
For hard rock DTH drilling, Ruixin’s spherical carbide buttons are available in SR8C and SR10C to match specific rock abrasiveness (Cerchar index) and bit rotation speed. Send your ground condition report and bit model for a grade-specific recommendation.
Frequently Asked Questions
How do I choose the right cemented carbide grade for my application?
Grade selection starts with three variables: hardness (HRA), cobalt content (%), and grain size (µm). High-abrasion, low-impact applications need higher HRA and finer grain — Ruixin SR7X at HRA 91.0 is the starting point. High-impact applications need higher cobalt content for toughness — Ruixin SR8C at HRA 89.0 or SR10C at HRA 88.0 are the correct choices. Map your dominant failure mode (wear vs. fracture) to the grade that controls it, then verify with the formation hardness and machine impact cycle before placing an order.
What is the difference between SR7X and SR8C?
Ruixin SR7X has HRA 91.0, grain size 1.0–1.2 µm, density 14.70 g/cm³, and flexural strength ≥ 2,000 MPa — optimized for high wear resistance in abrasive, low-impact conditions. Ruixin SR8C has HRA 89.0, grain size 2.0–3.0 µm, density 14.65 g/cm³, and flexural strength ≥ 2,200 MPa — designed for balanced wear and toughness in roadheader and road milling applications where impact is a factor. The most consequential difference in practice: SR8C tolerates interrupted cutting and hard rock inclusions that would fracture SR7X within a single production shift.
Which grade performs best under high-impact conditions?
Ruixin SR10C performs best under high-impact conditions. At HRA 88.0 and flexural strength ≥ 2,200 MPa, SR10C carries the highest cobalt binder proportion in the standard Ruixin range — which is what drives toughness. The density of 14.45 g/cm³ (vs. 14.65 for SR8C) reflects this higher binder content. For extreme or unpredictable impact loads — shield machine mixed-face tunneling, longwall shearer picks in seams with frequent hard inclusions — SR10C is the standard starting grade. Custom grade formulation with higher cobalt content is available for applications outside the standard range.
How does cobalt content affect carbide performance?
Cobalt is the binder that holds WC particles together in a cemented carbide composite. Higher cobalt content raises flexural strength and impact toughness but lowers HRA and wear resistance. The relationship is inverse and measurable: moving from roughly 6% cobalt to 12% cobalt drops HRA from approximately 92 to 88, while raising flexural strength from around 2,000 MPa to above 2,200 MPa. Ruixin grades SR7X, SR8C, and SR10C are positioned at specific points on this curve. SR7X carries lower cobalt for maximum hardness; SR10C carries higher cobalt for maximum toughness; SR8C sits between them for balanced performance.
What causes premature carbide tip failure?
Premature carbide tip failure has three primary causes. First, grade mismatch: a grade too hard for the impact cycle fractures instead of wearing gradually — running Ruixin SR7X in a high-impact roadheader causes chipping that can fail the tip in under one shift. Second, thermal shock: inadequate cooling in high-speed cutting causes cracking at the carbide-steel interface, propagating into the insert body. Third, mechanical overload: impact forces exceeding the grade’s flexural strength threshold cause sudden fracture rather than deformation. All three failure modes are preventable through correct grade selection, confirmed with material test report documentation from a traceable batch.
What is the best carbide grade for longwall shearer picks in high-impact coal seams?
For longwall shearer picks in high-impact coal seams, Ruixin SR8C is the standard starting grade for medium-hard coal with occasional hard rock inclusions. Where hard inclusions are frequent — above 20% of the cutting cycle or where seam UCS exceeds 80 MPa — Ruixin SR10C is the correct specification. Both grades are available as coal tooth carbide tips in standard and custom dimensions compatible with major shearer pick holder designs. Send your seam geology report and current grade designation for a confirmed recommendation.
What cobalt content is best for high-impact versus high-abrasion carbide applications?
For high-abrasion, low-impact applications, lower cobalt content (approximately 6%) delivers HRA above 91 and maximum wear resistance — Ruixin SR7X sits in this range. For high-impact applications, cobalt content of 10% or above achieves flexural strength above 2,200 MPa needed to survive repeated shock loading — Ruixin SR8C and SR10C meet this requirement. Mixed conditions — where both abrasion and impact are significant — are served by SR8C’s balanced profile, which represents the optimal cobalt ratio for the majority of mining and tunneling applications Ruixin supplies globally.
Get a Custom Grade Recommendation
The three standard grades — SR7X, SR8C, and SR10C — cover the majority of mining, tunneling, road milling, and wear part applications. For conditions outside the standard range, Ruixin formulates custom grades to your performance specification, with grade formulation backed by collaboration with Central South University and verified by batch material test reports.
Send your application details to our engineering team: rock type or formation, machine model, current carbide grade designation, and your dominant failure mode (wear or fracture). We confirm grade selection and available dimensions within 24 hours.
Ruixin Tungsten Carbide manufactures cemented carbide components at our 14,200 m² ISO 9001:2015-certified facility in Jinan, Shandong — factory-direct, no trading company markup, with 500 tons annual capacity. OEM drawings accepted. Samples available before volume order.
For cemented carbide grades matched to your application, explore our full product range including coal tooth carbide tips, spherical DTH carbide buttons, and shield machine carbide tips. For background on how grade composition drives field performance, see our detailed technical reference: Cemented Carbide: What Nobody Ever Told You.
For procurement teams assessing total cost of ownership, our tungsten carbide wear parts for mining guide covers replacement interval calculation and grade-specific cost-per-hour analysis.
Email: info@ruixintungstencarbide.com
WhatsApp: +86-15253178777
Send your drawings. We’ll confirm the grade, dimensions, and lead time within one business day.
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