Rock Drill Rod Material Comparison:RockHound's 23CrNiMo vs Sanbar64
Introduction
When sourcing top hammer drill rods(https://rhdrill.com/cat/rods/), one of the most frequent technical questions procurement engineers and drilling contractors ask is:
Article URL：https://rhdrill.com/rock-drill-rod-raw-material-23crnimo-vs-sanbar64/
“Why don’t Chinese manufacturers use the same steel as Sandvik?”
It’s a fair question — and one worth answering with precision.
Sandvik’s Sanbar 64 is the benchmark proprietary steel for extension rods and shank rods in top hammer drilling worldwide. RockHound uses 23CrNiMo (designated ZK23CrNi3Mo under Chinese national standards), a Nickel-Chromium-Molybdenum carburizing steel from Guiyang Special Steel (RockHound’s Supplier). Both belong to the same alloy family. Both are designed for high-frequency impact loading. But they are not interchangeable — and the differences matter.
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This article explains:
Why Chinese drill rod manufacturers cannot simply use Sanbar 64
The metallurgical difference between 23CrNiMo and Sanbar 64
How heat treatment hardness profiles compare
What real field test data from an iron mine says about 23CrNiMo rod performance
Material Comparison-23CrNiMo vs Sanbar64
Why Chinese Manufacturers Don't Use Sanbar 64
- Sanbar 64 Is a Proprietary Grade — Not a Standard Steel
Sanbar 64 is not a published ISO or GB standard steel grade. It is a proprietary alloy developed and produced exclusively by Sandvik Materials Technology (now marketed under the Alleima brand). The full chemical composition is not publicly disclosed, and the material is only available through Sandvik’s supply chain.
This means no third-party steel mill — in China or elsewhere — can legally reproduce Sanbar 64. A Chinese manufacturer claiming to “use Sanbar 64” would be making an unverifiable assertion.
- The Supply Chain Gap: Vertical Integration vs. Open Market Procurement
Sandvik operates a fully vertically integrated production chain: from electric arc furnace steelmaking through secondary metallurgy, bloom casting, billet rolling, hollow bar extrusion, and heat treatment — all under one roof. This gives Sandvik complete control over steel cleanliness, inclusion morphology, and microstructural consistency.
Chinese drill rod manufacturers procure raw steel from third-party steel mills. Even when sourcing from reputable suppliers such as Guiyang Special Steel (RockHound’s Supplier), the manufacturer relies on their steel mill’s internal quality system, which operates independently of the rod machining and heat treatment facility.
This separation of steelmaking and rod manufacturing is the fundamental structural difference — not simply a question of technical capability.
- The Honest Answer on Current Quality Gap
There is no point in concealing this: there is a gap, and it primarily comes down to three factors:
Factor Sandvik / Sanbar 64 RockHound / 23CrNiMo
Steelmaking cleanliness EAF + secondary refining + vacuum degassing + tight inclusion control Third-party mill; cleanliness depends on mill grade and heat
Chemical composition consistency Proprietary, batch-to-batch controlled Per GB/T standard, heat-to-heat variation within allowable range
Raw bar surface quality Max 0.20 mm outer defect depth, 0.15 mm inner Dependent on mill inspection and acceptance criteria
Supply chain accountability Fully integrated, single manufacturer Separate mill + rod manufacturer
This doesn’t mean 23CrNiMo rods underperform in all conditions. It means the performance ceiling of Sanbar 64, under identical manufacturing conditions, is higher — and the consistency is tighter. The question for buyers is always whether that performance premium justifies the price difference in their specific application.
Metallurgical Comparison: 23CrNiMo vs Sanbar 64
Alloy Family and Design Intent
Both steels belong to the Ni-Cr-Mo low-alloy carburizing steel family. The alloying strategy is fundamentally the same:
Nickel (Ni): Improves case-core toughness, impact resistance, and low-temperature fracture resistance
Chromium (Cr): Increases hardenability, surface hardness, and oxidation resistance
Molybdenum (Mo): Improves fatigue strength, creep resistance, and resistance to temper embrittlement
The difference lies in the refinement of that approach.
Drill Rod Material Comparison-23CrNiMo vs Sanbar64
23CrNiMo (ZK23CrNi3Mo) — RockHound Raw Material
23CrNiMo is a Chinese national standard carburizing steel, widely used across the rock drilling tool industry in China. Key characteristics:
Carbon (C): ~0.20–0.25% — low enough for deep carburizing, sufficient for core strength
Nickel (Ni): ~2.75–3.25% — high nickel content contributes to toughness and retained austenite control
Chromium (Cr): ~0.60–0.90%
Molybdenum (Mo): ~0.20–0.35%
Good hardenability — suitable for deep carburizing of hex bar sections up to H35mm and larger
Stable mechanical properties after carburizing and quenching when heat treatment is properly controlled
RockHound sources this steel from Guiyang Special Steel (as RockHound’s Supplier), one of China’s established specialty steel producers with dedicated production lines for rock drilling steel grades.
Sanbar 64 — Sandvik’s Proprietary Drill Steel
Sanbar 64 is described by Sandvik as an air-hardening, high-nickel alloy steel with excellent response to gas carburizing. Key published characteristics:
Alloy family: Ni-Cr-Mo, with higher nickel content and tighter trace element control than standard commercial grades
Air-hardening capability: The steel can harden without oil or water quenching, which reduces quench cracking risk and allows more controlled hardness gradients
Inclusion control: The manufacturing specification limits surface defect depth to ≤0.20 mm on the outer surface and ≤0.15 mm on the inner bore — critical for fatigue crack initiation resistance
Internal bore carburizing: Sandvik specifically requires internal carburizing of hollow rods to maximize fatigue life, particularly in corrosive underground environments
Straightness tolerance: ≤1 mm per 1,000 mm — ensuring consistent energy transmission along the rod
The key engineering advantage of Sanbar 64 is not primarily its alloy composition (which is broadly similar to other Ni-Cr-Mo grades) but rather the consistency of the microstructure achieved through Sandvik’s proprietary steelmaking process. Lower non-metallic inclusion levels mean fewer potential fatigue crack initiation sites — which translates directly to longer rod service life under repeated impact loading.
Heat Treatment and Hardness Profile Comparison
Material composition determines the potential of a drill rod. Heat treatment determines whether that potential is realized.
Rock drilling rods require a dual-zone hardness profile:
A hard, wear-resistant surface case to resist thread wear and abrasion
A tough, impact-absorbing core to handle repeated piston percussion without brittle fracture
The following table compares published heat treatment data for Sanbar 64 with RockHound’s target specification for 23CrNiMo rods:
Parameter Sanbar 64 (Sandvik Published Data) 23CrNiMo — RockHound Target
Heat Treatment Method Overall gas carburizing Deep carburizing + quenching
Carburizing Temperature 920–930°C 910–930°C
Recommended Surface Carbon 0.5–0.7% 0.5–0.8%
Case Depth 0.6–1.2 mm (thread-dependent) 0.8–1.5 mm
Cooling After Carburizing Forced air (air-hardening) Oil quench
Surface Hardness 57–62 HRC 58–62 HRC
Core Hardness 36–44 HRC 38–42 HRC
Tempering Temperature 180–230°C, 1 hour 180–220°C
Related Readings:20 Hour Heat Treatment In Rock Drilling Tools
Key observation: When properly heat-treated, RockHound’s 23CrNiMo rods achieve a surface hardness of 58–62 HRC and a core hardness of 38–42 HRC — values that fall within the Sanbar 64 recommended range. The hardness numbers are comparable. The difference lies in the consistency and repeatability of achieving that profile across production batches, which is directly tied to raw material cleanliness and furnace atmosphere control.
The carburized case protects the threaded sections — the highest-stress zone of the drill rod — against both abrasive wear and fatigue crack initiation. The tough core absorbs the axial percussion energy transmitted by the rock drill piston (in this application, 180 bar impact pressure from the Epiroc COP 1838HD+).
RockHound's 20-Hour Heat Treatment in Rock Drilling Tools
Manufacturing Process: Where RockHound Controls What It Can
RockHound cannot replicate Sandvik’s vertically integrated steelmaking. But within the rod manufacturing process, several critical quality control steps directly influence rod performance:
Precision Thread Machining
The thread is the most fatigue-critical section of any extension rod. Thread root geometry, surface finish, and case depth at the thread root determine whether the rod reaches its theoretical fatigue life or fails prematurely. RockHound machines threads to standard profiles (T38, R32, T45, T51) using CNC turning centers with controlled cutting parameters to minimize residual tensile stress at the thread root.
Straightening
A straight rod transfers percussion energy efficiently along its axis. Lateral deviation introduces bending stress components during rotation, accelerating fatigue at stress concentration points. RockHound uses a 6-meter automated straightening system targeting ≤1 mm deviation per 1,000 mm — matching Sandvik’s published tolerance.
Discover More: The Processing of Threaded & Tapered Drill Rod:https://rhdrill.com/the-processing-of-thread-rock-drilling-rods/
The Processing of Thread Rock Drilling Rods
Taper Drill Rod Manufacturing Process
Carburizing Atmosphere Control
Gas carburizing requires stable carbon potential control in the furnace atmosphere. RockHound’s heat treatment process targets a surface carbon content of 0.5–0.8% with case depth adjusted to thread dimension, consistent with Sandvik’s own published recommendations for Sanbar 64.
Quality Inspection
Each rod production batch undergoes Brinell/Rockwell hardness verification, dimensional inspection, and thread gauge checking before dispatch.
Field Performance: RockHound 23CrNiMo Rods at Iron Mine — Real Test Data
The most relevant evidence for any drilling contractor is not the spec sheet — it’s what happens underground.
Test Overview
Location: Iron Mine, Hebei Province, China (–540m underground level)
Test Period: July–August 2025
Rock Conditions: Protodyakonov hardness coefficient f = 13–15 (corresponding UCS: 130–150 MPa) — classified as hard to very hard rock
Drill Rig: Epiroc (Atlas Copco) Boomer 281
Rock Drill: COP 1838HD+
Drilling Parameters: Feed 75–80 bar | Impact 180 bar | Rotation 190 bar | Flush 10–12 bar
Rod Specification: ZK23CrNi3Mo, H35 × 4,305 mm, T38/R32
Drill Rod Service Life Results
Rod No. Service Life (metres) Failure Mode
1# 3,529 m Thread fracture at bit end
2# 3,753 m Thread fracture at bit end
3# 3,478 m Thread fracture at bit end
4# 3,389 m Thread fracture at bit end
5# 3,645 m Thread fracture at bit end
6# 3,725 m Thread fracture at bit end
7# 3,712 m Thread fracture at bit end
8# 3,549 m Thread fracture at bit end
Average 3,597.5 m Thread fracture at bit end (100%)
Detail: Field Test Report: MF T38-R32 Drill Rods & Bits at Iron Mine
What Do We Learn From This Data?
3,597.5 metres average footage in f13–f15 iron ore, operating at 180 bar impact pressure, is a meaningful performance benchmark. The consistent failure mode — thread fracture at the bit end (small end) — is the expected and normal fatigue failure location for a top hammer extension rod. This is where bending stress amplitude is highest due to the asymmetric loading condition at the bit connection point. There were no mid-body fractures or shank-end failures, indicating that the carburized case and core properties are performing as designed.
This data does not claim parity with Sandvik rods running the same conditions. It demonstrates that properly manufactured 23CrNiMo rods deliver commercially viable and consistent service life in hard rock conditions, making them a competitive option for operations where the cost-per-metre calculation matters.
Button Bit Performance (Same Test)
For reference, the R32 threaded button bits tested concurrently averaged 352.8 metres per bit under the same f13–f15 conditions, with all five bits recording normal wear as the failure mode.
More Project Test Report: R32 51mm Retrac Button Bit for Hard Rock At Copper Mine Proven In Chile
How to Choose: When 23CrNiMo Is the Right Call
Drilling Scenario Recommendation
Hard–very hard rock (f ≥ 12), high production mining, maximum service life priority Sandvik Sanbar 64-based rods are the established premium benchmark for longest footage and lowest cost per meter in extreme conditions
Medium–hard rock (f = 8–12), cost-sensitive operations, or trials/price benchmarking 23CrNiMo rods (properly heat treated) offer reliable, predictable performance and excellent value compared to premium brands
Hard rock (f = 13–15) underground mining with budget constraints RockHound 23CrNiMo field data suggests competitive service life — request trial batch to validate against site-specific conditions
New mine startup or Capex-constrained operations 23CrNiMo rods reduce initial tooling spend while maintaining acceptable footage and reliability during early-stage ramp-up
Conclusion: Honest Assessment, No Overselling
The gap between 23CrNiMo and Sanbar 64 is real, and it is rooted in structural differences in steelmaking technology and supply chain integration — not in a lack of engineering knowledge among Chinese manufacturers.
Sanbar 64 benefits from over a century of proprietary development, fully integrated production, and the tightest available inclusion control in drill steel manufacturing. These advantages are reflected in its cost.
RockHound’s position is straightforward: 23CrNiMo, when sourced from a reputable Chinese specialty mill and subjected to correctly controlled carburizing, thread machining, and straightening processes, delivers real-world service life that is competitive for a wide range of drilling conditions. The field data from the f13–f15 iron mine supports this.
We recommend that prospective customers in hard rock operations request a trial batch, instrument the footage per rod, and make the decision based on their own cost-per-metre results — not on brand name alone.