Roadheader Picks Carbide Grade — SR8C vs SR10C | Ruixin



Why Mixed Ground Tunneling Destroys the Wrong Roadheader Picks Carbide Grade

A metro tunneling contractor running a roadheader through alternating layers of sandstone and clay marl switched to a harder carbide pick to reduce wear in the abrasive sections. Pick life dropped by 40% — the grade was too brittle for the impact cycle when the cutting head hit the embedded cobbles, and chipping replaced gradual abrasion as the dominant failure mode. The harder grade survived the sandstone but shattered in the mixed-face transitions.

This is the central problem in roadheader picks carbide grade selection for tunneling: no single formation machine, picks encounter sandstone, limestone, clay, gravel, and boulders, sometimes within the same meter of advance. The grade that optimizes for one ground type often fails prematurely in the next.

The failure isn’t random. It’s the predictable result of a mismatch between cobalt content and the impact-to-abrasion ratio at the cutting face. Quantify that ratio correctly, and you can extend pick life without changing the machine or the operator.

The Technical Variables That Determine Roadheader Pick Service Life

Grade selection for roadheader picks comes down to three interdependent specifications: hardness (HRA), cobalt binder content, and tungsten carbide grain size. Each maps to a specific failure mode at the cutting face.

Hardness (HRA) measures the carbide’s resistance to abrasive wear. At HRA 91.0, Ruixin SR7X can withstand continuous abrasion from high-silica sandstone longer than softer grades but sacrifices the flexural strength needed to absorb impact loads. The flexural strength of SR7X is ≥ 2,000 MPa, sufficient for pure abrasion environments but marginal when the cutting head encounters hard inclusions.

Cobalt content is the toughness lever. The relationship between cobalt percentage and hardness is inverse: increasing cobalt from 6% to 10% drops HRA from approximately 91.0 to 88.0, but flexural strength rises from 2,000 MPa to 2,200 MPa or higher. Cobalt acts as a ductile binder that arrests crack propagation. Ruixin SR8C at 8% cobalt delivers flexural strength ≥ 2,200 MPa, while SR10C at 10% cobalt provides the same flexural strength with additional margin for repeated shock loads.

For a broader overview of grade selection across all tunneling machine types, see our TBM carbide cutting tools guide.

Grain size governs the wear ceiling. Finer grains (1.0–1.2 µm in SR7X) create a denser WC-Co matrix that resists micro-abrasion but lacks the toughness for interrupted cutting. Coarser grains (2.0–3.0 µm in SR8C and SR10C) provide better toughness at a modest cost to hardness, a tradeoff that makes them the standard for roadheader picks in mixed ground.

For roadheader tunneling in mixed conditions, cobalt content and grain size are the limiting constraints. Grades optimized exclusively for hardness will fracture here. Grades optimized exclusively for toughness will wear too fast in the abrasive layers.

Roadheader Picks Carbide Grade Options and Performance Trade-offs

Three Ruixin grades cover the range of roadheader tunneling conditions from low-impact abrasive ground to high-impact mixed-face conditions. The table below maps each grade to its application window.

Application Scenario	Recommended Grade	Key Parameters	Why This Grade
Continuous abrasive sandstone or limestone (low impact)	SR7X	HRA 91.0, 6% cobalt, 1.0–1.2 µm grain, ≥ 2,000 MPa flexural strength	Maximum wear resistance in homogeneous abrasive formations. The fine grain structure resists silica abrasion over extended cutting cycles.
Mixed ground with clay, marl, gravel, and occasional cobbles (moderate impact)	SR8C	HRA 89.0, 8% cobalt, 2.0–3.0 µm grain, ≥ 2,200 MPa flexural strength	Balanced wear resistance and impact toughness. The 8% cobalt matrix handles intermittent impact from gravel layers while maintaining competitive abrasion life.
Hard-rock intrusions, boulders, fractured zones (high impact)	SR10C	HRA 88.0, 10% cobalt, 2.0–3.0 µm grain, ≥ 2,200 MPa flexural strength	Maximum impact toughness for the most demanding mixed-face conditions. Higher cobalt binder content absorbs shock from boulder encounters and prevents catastrophic tip fracture.

The choice is not “which grade is better” — it’s which failure mode your tunnel section punishes more. If your picks are wearing smooth and round before they reach change-out criteria, you need higher hardness (step up to SR8C or SR7X from a softer grade). If they are fracturing with sharp break surfaces, you need higher toughness (step up to SR10C from SR8C).

What Happens When You Choose the Wrong Grade

The cost of a grade mismatch in roadheader picks is measured in lost cutting time, not just pick price. Here are the quantified consequences:

Tip life drops by 30–50% when a grade optimized for pure abrasion is run in mixed-face conditions. The impact load from hard inclusions chips the carbide edge, and the effective cutting profile degrades long before abrasive wear would have ended the pick’s service life. In a metro tunneling project where pick change-out requires stopping the roadheader for 45–60 minutes per shift, this becomes a production bottleneck.

Replacement frequency doubles when picks fail by fracture instead of gradual wear. Instead of changing picks on a planned schedule (every 2–3 shifts based on wear measurements) the crew must stop mid-shift to replace fractured picks. The unscheduled downtime on a typical 70-ton roadheader costs €200–500 per hour, depending on the project.

Cost per excavated meter rises 20–35% when factoring in both pick consumption and the labor cost of unscheduled change-outs. A grade that costs 15% more per pick but delivers 50% longer service life reduces total cost per meter. A cheaper, mismatched grade increases it.

The wear pattern itself misleads troubleshooting. A chipped pick from a grade that is too hard looks similar to a chipped pick from a grade that is too soft applied in a different impact frequency. Without understanding the root cause, contractors often swap grades sideways instead of moving to the correct cobalt level.

Which Grade to Use — and Under What Conditions

The decision filter for roadheader pick grade selection follows ground conditions, not machine type.

If your tunnel face is predominantly abrasive sandstone or limestone with low fracture frequency, use Ruixin SR7X at HRA 91.0. The fine 1.0–1.2 µm grain structure and 6% cobalt deliver the highest wear resistance in this grade family. This grade will maintain its cutting profile longer than any alternative in continuous low-impact ground.

If your ground varies between soft clay, medium sandstone, and occasional gravel or cobble layers, use Ruixin SR8C at HRA 89.0 with 8% cobalt and 2.0–3.0 µm grain. This is the standard grade for most roadheader tunneling applications across metro, water diversion, and mountain tunnel projects. The 2,200 MPa flexural strength provides enough impact margin for intermittent hard inclusions without sacrificing heavy wear resistance in the abrasive sections.

If your tunnel face includes hard-rock boulders, highly fractured zones, or abrasive material mixed with large-diameter gravel, use Ruixin SR10C at HRA 88.0 with 10% cobalt. The higher cobalt content extends the grade’s tolerance for repeated shock loads. SR10C is the correct choice when pick fracture, not wear, is the primary failure mode.

For most roadheader tunneling setups, SR8C is the starting point. Ruixin manufactures SR8C as carbide tips for roadheader picks in standard and custom dimensions. Verify your ground conditions against the grade specs above before ordering.

How to Implement Grade Selection in Your Operation

Getting the right carbide pick grade into your roadheader requires three checks before you place the order.

1. Confirm the failure mode from actual wear patterns. Take photos of spent picks. A smooth, rounded wear surface indicates abrasive wear. Move to a harder grade (SR7X or SR8C). A jagged break surface with sharp edges indicates impact fracture. Move to a tougher grade (SR10C). Sharp-edged chips at the carbide tip point to a grade mismatch with the impact frequency.

2. Verify dimensional compatibility with your existing pick holders. Ruixin accepts OEM drawings for custom dimensions. Whether you are running Sandvik, Kennametal, or other tool-holder systems, provide the drawing or a sample pick for dimensional confirmation. We manufacture within standard carbide tolerances and can match existing pick body designs.

3. Request batch-level material test reports. Every shipment from Ruixin includes a material test report with density, HRA hardness, and flexural strength for the production batch. This is how you verify that the grade you ordered — SR8C at 14.65 g/cm³ density and HRA 89.0 — is what arrived. Batch consistency matters more in roadheader picks than in almost any other application because a single mixed-face section can expose dozens of picks to identical failure conditions. If one pick fails from a grade variance, the whole cutting head is compromised.

For tunneling applications where ground conditions vary significantly along the tunnel alignment, common in metro projects passing through different geological formations, Ruixin can supply mixed-grade batches. You can run SR8C picks in the cutting head positions that see the most impact and SR7X picks in the gauge positions that see the most abrasion. This hybrid approach optimizes service life across the entire cutting head.

If your roadheader picks are running HRA 90+ grades and fracturing, or running soft grades and wearing too fast, send us your application details. A custom grade formulation may be needed if your conditions fall outside the SR8C–SR10C window.

Frequently Asked Questions

How do I choose the right carbide grade for roadheader picks in mixed ground tunneling?

Start by identifying the dominant failure mode in your application. If picks are wearing down too fast in abrasive sandstone or hard rock, select a higher-hardness grade like Ruixin SR7X (HRA 91.0). If picks are chipping or fracturing under high-impact conditions from mixed strata with boulders, select a tougher grade like Ruixin SR8C (HRA 89.0, 8% cobalt) or SR10C (HRA 88.0, 10% cobalt). The correct grade is the one that balances your specific abrasion-to-impact ratio.

What is the difference between SR8C and SR10C for roadheader applications?

Ruixin SR8C has a hardness of HRA 89.0 with 8% cobalt content and 2.0–3.0 µm grain size, offering balanced wear resistance and toughness for standard mixed-ground roadheader work. Ruixin SR10C has a hardness of HRA 88.0 with 10% cobalt content and 2.0–3.0 µm grain size, trading some hardness for higher impact toughness. In applications with frequent hard-rock intrusions or boulder encounters, SR10C resists fracture better than SR8C, but it will wear faster in continuous abrasive ground.

Which carbide grade performs best under high-impact roadheader conditions?

For high-impact roadheader conditions such as mixed face tunneling with hard-rock boulders or heavily fractured zones, Ruixin SR10C is the recommended grade. Its 10% cobalt content at HRA 88.0 provides the highest impact toughness among our standard tunneling grades. The 2.0–3.0 µm grain size further reduces crack propagation risk. SR10C can absorb repeated shock loads that would chip a harder, lower-cobalt grade within a single shift.

How does cobalt content affect carbide pick performance in tunneling?

Cobalt acts as a binder in cemented carbide. Higher cobalt content (8% to 10%) increases toughness and impact resistance but reduces hardness (HRA) and wear resistance. Lower cobalt content (6%) increases hardness and wear resistance but reduces toughness. For roadheader picks in mixed ground tunneling, 8% cobalt (SR8C) offers the best balance for most conditions. Above 10% cobalt, wear resistance drops significantly and picks may need replacement sooner in abrasive formations.

What causes premature carbide tip failure on roadheader picks?

Premature failure on roadheader picks is typically caused by a grade mismatch with ground conditions. Three common failure modes exist: abrasive wear from high-silica-content rock wears down picks too fast if the grade is too soft; impact fracture from hard boulders or mixed strata chips and breaks picks if the grade is too hard; and thermal fatigue from excessive cutting speed causes micro-cracking at the carbide tip edge. Ruixin engineers can diagnose the failure mode from wear pattern photos and recommend a grade adjustment.

Can I use the same carbide grade for the entire tunnel length in a metro project?

Not if the geology changes significantly along the tunnel alignment. Metro tunnel projects frequently pass through multiple formation types: clay, sand, gravel, sandstone, and even hard rock, within a single kilometer. Ruixin recommends a ground-condition survey before grade selection and, where varied geology is confirmed, a mixed-grade batch supply. The gauge positions on the cutting head, which see higher abrasion, can run SR7X or SR8C, while the center and face positions, which see higher impact, can run SR10C. This is a standard approach we support for roadheader and shield machine carbide applications.

Get a Custom Grade Recommendation for Your Roadheader Picks

Send us your application details including rock type, roadheader model and power rating, current pick grade, and wear pattern photos. Our engineers will confirm the optimal Ruixin SR8C or SR10C grade selection, along with available dimensions, within 24 hours.

Email: info@ruixintungstencarbide.com
WhatsApp: +86-15253178777

OEM drawings accepted. Custom grade formulations available for specialized tunneling conditions. Batch material test reports included with every shipment.