Drilling hardened steel has always been a significant challenge for CNC engineers due to the material’s high hardness, strength, and poor thermal conductivity. Ordinary drill bits often fail to handle these demands, causing issues such as tool burning, edge chipping, and hole positional errors during machining. Choosing the right drill bit designed specifically for hardened steel is crucial for achieving consistent, high-quality results.

This article provides a practical overview of common drill bit types used in machining hardened steel, including cobalt drill bits, carbide drill bits for hardened steel, and solid carbide drill bits. We analyze their advantages and drawbacks in terms of performance, tool life, and cost-effectiveness, supported by real-world application scenarios.

If you’re searching for the best drill bits for hardened steel or wondering what the best drill bit for hardened steel is, this guide offers expert advice to help you improve machining efficiency and precision when working with high-hardness materials.

Why Drilling Hardened Steel Requires Specialized Drill Bits

In CNC machining, hardened steel typically exhibits surface hardness exceeding HRC55 and can reach as high as HRC65. This creates a demanding metal matrix that quickly wears down ordinary drill bits and risks tool cracking or heat-related damage due to cutting heat buildup. Therefore, drill bits for hardened steel must have superior thermal hardness, compressive strength, and wear resistance to ensure efficient and stable drilling.

Material Properties and Machining Challenges of Hardened Steel

Hardened steel is heat-treated steel containing abundant martensitic or bainitic microstructures, which contribute to its high hardness and toughness. Machining this material presents several challenges compared to conventional carbon or low-alloy steels:

• Extremely high cutting resistance requiring a robust cutting edge

• Poor thermal conductivity, causing rapid temperature rise in the cutting zone

• Hard surface leading to premature tool wear or chipping

• Difficulty controlling drilling accuracy, resulting in skewed holes or burned hole walls

Given these factors, standard HSS or low-end alloy drill bits are inadequate for hardened steel. Instead, carbide drill bits or solid carbide drill bits specifically designed for high-hardness materials are necessary.

Why Ordinary Drill Bits Can’t Handle Hardened Steel

Many beginners mistakenly assume all drill bits are interchangeable. While HSS drill bits work well for softer metals like aluminum and mild steel, they fail rapidly when machining hardened steel due to plastic deformation, thermal softening, and edge deterioration.

Common shortcomings of ordinary drill bits include:

• Insufficient cutting edge hardness for continuous penetration of hardened material

• Poor heat resistance leading to premature failure under high temperatures

• Lack of optimized geometry for chip evacuation and cooling

• Short tool life, resulting in higher costs and lower efficiency

Thus, in industrial settings, high-performance carbide drill bits with advanced coatings like TiAlN or DLC are strongly recommended for hardened steel machining.

Basic Requirements for Drill Bits for Hardened Steel

To drill steels above HRC55 efficiently and stably, drill bits must meet several critical technical criteria:

• High-hardness substrate: Typically ultra-fine-grained solid carbide with excellent wear resistance and toughness

• Heat resistance: Maintain cutting performance at temperatures above 600°C

• Optimized blade geometry: Features like adjusted cutting angles, reinforced core thickness, and specialized point angles to enhance feed force and chip evacuation

• Advanced coatings: TiAlN, AlCrN, or DLC coatings improve surface hardness, reduce friction, and extend tool life

• Suitability for high-speed CNC machining: Able to withstand high temperatures and loads during high-speed operations

Only tools meeting these requirements can truly be considered the best drill bits for hardened steel.

Comparison of Common Drill Bits for Hardened Steel

Machining hardened steel demands tools with exceptional wear resistance and thermal stability. The market offers various drill bit types with significant differences in performance, cost, and application scope. Below is a comparison of common types to guide engineers in selecting the best drill bit for hardened steel.

HSS Drill Bits: Low Cost but Limited Lifespan

High-speed steel (HSS) drill bits are traditional, widely used tools with advantages including low cost and versatility for soft metals. However, they underperform on steel harder than HRC45, suffering from edge deformation and rapid wear.

• Ideal for: Carbon steel, low-alloy steel, plastics, aluminum alloys

• Not recommended for: Hardened steel and heat-treated steels

• Typical issues: Edge softening, tool annealing, hole diameter inconsistencies

While basic, HSS drills do not meet modern CNC demands for high-hardness materials.

Cobalt Alloy Drill Bits: Suitable for Medium Hardness Steel

Cobalt drill bits (made from M35 or M42 high-speed steel containing 5-8% cobalt) offer better red hardness and wear resistance than regular HSS. They handle steels with hardness between HRC35 and 50 and are cost-effective for limited budgets.

• Advantages: Higher heat resistance, suitable for dry or low-coolant cutting; improved resistance to chipping; good for intermittent drilling

• Limitations: Wear rapidly above HRC55; require rigid machine setup and optimized feed rates

For medium-hard or tempered steels, cobalt drill bits provide a balanced option.

Carbide Drill Bits for Hardened Steel

Carbide drill bits, usually tungsten-cobalt based, possess very high hardness (often above HRA89) and excellent heat resistance. They are mainstream tools for high-hardness materials, offering sharp edges ideal for high-speed, precise drilling.

• Applications: Steel parts above HRC50, alloy tool steels, die steels, quenched components

• Advantages: Outstanding wear and heat resistance; compatible with advanced coatings (TiAlN, AlCrN); suitable for dry or high-speed machining

• Considerations: Lower toughness than HSS/cobalt, less suitable for manual drilling or unstable setups; higher upfront cost but lower long-term expense

Carbide drill bits are the first choice for many CNC shops machining hardened steel.

Solid Carbide Drill Bits for Hardened Steel: Ideal for Strength and Wear Resistance

Solid carbide drill bits differ structurally from welded carbide tools, being sintered as one piece with high hardness and toughness. They offer exceptional cutting strength, heat resistance, and chip resistance, making them top-tier solutions for hardened steel.

• Technical benefits: No welds (structural integrity); capable of extremely high speeds (>10,000 rpm) and micro-lubrication (MQL)

• Lifespan: Significantly longer than HSS or cobalt; ideal for batch and high-precision production

• Industries: Aerospace, automotive molds, high-hardness stamping dies, powder metallurgy

• Best used with: High-rigidity CNC machines; coatings like TiSiN and DLC; optimized cutting geometry

If you want the real best drill bit for hardened steel, solid carbide drill bits are the definitive high-end choice.

Which Type Is the Best Drill Bit for Hardened Steel?

In summary, choosing the appropriate type of drill bit should be based on a comprehensive evaluation of workpiece hardness, machining equipment capability, drilling quantity, and quality requirements:

If your machining involves high-hardness hardened steel (above HRC55) and you require high drilling accuracy and efficiency, the first choice is solid carbide drill bits for hardened steel. When paired with high-performance coatings and optimized CNC processes, they offer the best balance of machining stability and tool life.

How to Choose the Best Drill Bit for Hardened Steel

Selecting the right drill bit for hardened steel (above HRC55) is vital not only for machining efficiency and hole accuracy but also for tool longevity and overall cost control. Because working conditions vary widely, determining the best drill bit involves considering material hardness, hole size, tool geometry, and coating. Below is a systematic approach.

Selection Based on Material Hardness (HRC)

Cutting resistance and thermal load vary greatly with material hardness:

• HRC < 50: Cobalt drill bits offer cost-effective solutions for medium-hard steels.

• HRC 50–60: Carbide drill bits for hardened steel with sharp edges and strong wear resistance are recommended.

• HRC > 60: Solid carbide drill bits with high-performance coatings and stable cooling are essential.

Hot hardness, compressive strength, and microstructure stability of the tool material are key to tool life and hole quality. Harder materials require higher-grade, more precise tools.

Selection Based on Drilling Depth and Hole Diameter

Deep-hole and micro-hole drilling introduce complexities involving chip evacuation, cooling, and rigidity:

• Deep holes (>3×D): Use solid carbide drill bits with internal coolant channels to prevent overheating.

• Micro holes (<3mm): Require ultra-hard micro drills with excellent coaxiality and minimal runout, paired with precision spindles.

• Medium to large holes (>10mm): Carbide drills with reinforced cores improve bending resistance and cutting stability.

Also consider tool coating wear resistance, drill tip angle effects on feed stability, and smooth chip flute design for effective chip removal.

Impact of Coating Types (such as TiAlN, DLC) on Heat Resistance and Tool Life

PVD and CVD coating technologies on tool surfaces have become essential for enhancing drill bit performance, especially under the high-temperature and high-pressure cutting conditions of hardened steel machining. The role of coatings is particularly critical in these environments.

Common coating types compared below:

Selecting the right coating type can significantly extend tool life and reduce unit costs. For machining high-hardness steel, prioritize advanced coatings that offer heat oxidation resistance, low friction, and edge chipping resistance.

Comparison of Selection Criteria Between Standard and Customized Drill Bits

In specific batch sizes or complex machining conditions, standard drill bits may not fulfill all requirements, making customized tooling a viable option. However, standard and customized drill bits have different pros and cons:

Therefore, if you are machining standard parts or small batches, high-performance standard solid carbide drill bits for hardened steel should be prioritized. For large-volume customized products or high-precision mold hole machining, collaborating with professional tool manufacturers to develop custom drill bits is advisable.

CNC Machining Experience Sharing: Practical Skills for Drilling Hardened Steel

When machining high-hardness hardened steel (HRC55 and above), even using high-performance solid carbide drill bits specifically designed for hardened steel, improper cutting parameters, poor machine-tool system coordination, or operational negligence can still reduce tool life and hole position accuracy. Based on years of CNC practical experience, the following shares effective, safe, and low-wear drilling techniques essential for hardened steel processing.

Optimization of Speed, Feed Rate, and Cooling Strategy

During hardened steel drilling, the cutting zone rapidly accumulates heat and bears heavy edge loads. Proper cutting parameter settings are critical to extending tool life and maintaining processing efficiency.

• Spindle Speed (RPM): Set according to drill diameter, material hardness, and tool manufacturer recommendations. For materials above HRC60, avoid excessive speeds to prevent heat buildup and premature tool annealing.

• Feed Rate: Maintain a stable, continuous feed to prevent intermittent cutting that causes edge fatigue. Too low a feed rate accelerates edge wear.

• Cooling Methods:

  • Through-Spindle Coolant: The preferred method for high-hardness materials, providing direct cooling to the cutting zone and efficient chip evacuation.

  • Minimum Quantity Lubrication (MQL): Suitable for high-speed dry cutting, especially when machining titanium alloys and powder metallurgy steels.

  • Avoid intermittent external spray cooling to prevent thermal shock and tool chipping.

Correctly matching speed, feed, and cooling strategies significantly improves the service life and hole diameter consistency of drill bits for hardened steel.

Key Points to Avoid Chipping and Premature Tool Failure

Hardened steel drilling often causes micro-chipping, passivation, and burning at the tool edge due to load concentration and thermal fatigue, directly affecting hole accuracy and surface finish. Key operational practices include:

• Minimize Overhang Length: Use the shortest possible tool extension to reduce deflection and vibration.

• Pre-Drill Center Holes: For high positional accuracy, use a center drill to guide the main drill and reduce chipping risks.

• Timely Tool Replacement: Replace or resharpen drill bits immediately upon noticing slight dullness to avoid rapid chipping.

• Avoid Excessive Tool Withdrawal: Frequent retracting causes alternating thermal stress, leading to edge fracture.

This is especially critical when using solid carbide drills for hardened steel, whose edges are sharp but brittle, requiring precise operational control to maximize tool life.

Matching the Tool Holder and Machine Tool System to Improve Drilling Stability

Toolholder and spindle system stability are often overlooked but are crucial for drilling quality. The drill bit is only one part of a complex power transmission system.

• Toolholder Selection:

  • Use hydraulic or shrink-fit toolholders to significantly improve radial runout accuracy.

  • Avoid spring chucks (ER collets) for micro-hole or fine hole drilling.

• Spindle Rigidity Requirements:

  • Ensure spindle taper accuracy with high-precision standards (e.g., HSK63, BT40, BT50).

  • The machining center should have robust structural vibration resistance.

• Machine Tool Parameter Settings:

  • Activate constant torque control and acceleration buffer functions to reduce start-up shock.

  • For long drills, enable “retract deceleration” or “bottom-of-hole deceleration” to lower edge load.

A precise clamping system combined with a stable machine tool platform is key to maximizing tool life and stabilizing hole position accuracy when machining hardened steel.

Common Misuses and Troubleshooting of Solid Carbide Drill Bits

Even when using high-quality solid carbide drill bits, improper usage can still lead to the following common issues:

Recommended Best Drill Bits for Hardened Steel in 2025 (Engineer Picks)

With hardened steel increasingly used in molds, automotive, powder metallurgy, and tooling, demands for drill performance rise. For materials above HRC55–65, selecting drills that balance stability, durability, and cost-effectiveness is vital. Based on Samho Tool’s 2025 product line and real customer feedback, here are recommended options tailored by batch size and process.

High Cost-Effective Recommendation: Suitable for Small and Medium Batch Processing

• Samho Ultra-Fine Carbide Cobalt Drill (M35 cobalt drill):
  Suitable for steel parts with hardness HRC48–52. Cost-effective for intermittent or semi-automatic machining.

• TiAlN Coated Carbide Drill:
  Ideal for mold steel around HRC55 and small batch drilling tasks.

Advantages:

• Controllable cost for diverse small batch orders.

• Basic heat and wear resistance.

• Compatible with conventional vertical machining centers without advanced cooling.

Typical Long-Tail Keywords:
“High cost-effective hardened steel drill recommendation”
“Carbide drill suitable for HRC55 steel drilling”

This category suits small- to medium-sized manufacturers and users adopting “replace and grind” tool management strategies.

High-Performance Recommendation: Suitable for Mass Production and High-Precision Processing

• Samho Solid Carbide Drill Bits for Hardened Steel:
  Featuring full sintered carbide construction with excellent rigidity and vibration resistance.

• Advanced TiSiN/DLC Nano Coatings:
  Provide superior heat and wear resistance.

• Supports High-Speed Dry Cutting or Minimal Quantity Lubrication (MQL):
  Ideal for modern CNC machining centers.

• Long Tool Life and Stable Dimensional Control:
  Suitable for repeated multi-batch drilling in HRC60–65 mold steel, hot work tool steel, etc.

Tool Configuration Recommendations for Different Application Scenarios (Through-Hole, Counterbore, Deep-Hole Drilling)

Selecting the right drill bit structure and parameters according to the hole type is key to improving machining outcomes. Based on Samho Tool’s product line and typical customer applications, the recommendations are as follows:

For multi-step holes or complex hole structures, Samho also offers customized non-standard drill bits to ensure consistent processing quality.

Common Long-Tail Keywords:

• “Recommended solid carbide drill bits for deep hole drilling”

• “Carbide drills for mold counterboring”

• “Are internal coolant drills suitable for hardened steel?”

Product Recommendation Appendix: Comparison Between Carbide Drill Bits for Hardened Steel and Solid Carbide Drill Bits

To assist users in better understanding and selecting drill bits, here is a comparison table of the two typical types:

Conclusion:
If you prioritize cost-effectiveness, choose high-grade coated carbide drill bits. For one-shot machining, high efficiency, and long tool life, Samho’s solid carbide drill bits for hardened steel are the best choice.

Conclusion: Efficiency Starts with the Right Drill Bit

Drilling high-hardness hardened steel is technically demanding. Selecting the right drill bit is foundational to efficient, quality machining. This article analyzed the material properties, drilling challenges, and compared HSS, cobalt alloy, carbide, and solid carbide drill bits in detail.

In practice, ensuring drilling stability and accuracy requires selecting tools based on hardness, hole depth, and diameter, and enhancing tool heat resistance with advanced coatings like TiAlN and DLC. Additionally, optimized cutting parameters, cooling strategies, and rigid tool holder and machine tool setups directly affect productivity and tool life.

In 2025, cobalt alloy and carbide drills with favorable cost-performance suit small to medium batches, while solid carbide drills meet high-strength, high-precision mass production demands. Tailored tool configurations for various hole types (piercing, countersinking, deep holes) further boost efficiency.

Choosing the right drill bit not only reduces tool change frequency and processing cost but also ensures workpiece quality and delivery schedules. CNC engineers and manufacturing leaders must prioritize adopting high-performance hardened steel drills to maintain competitiveness.

FAQ

Q1: Can ordinary drills drill hardened steel?
Ordinary HSS drills perform well on low-hardness steel but struggle with hardened steel (above HRC55), suffering edge wear, thermal softening, and chipping. Carbide or solid carbide drills designed for hardened materials are recommended for quality and tool life.

Q2: Which brand of carbide drills is more durable?
Samho Tool is renowned for ultra-fine carbide grains, advanced coatings, and strict manufacturing, especially in hardened steel processing. Their solid carbide drills offer toughness and wear resistance, extending tool life significantly.

Q3: How to judge if a drill is suitable for HRC60 steel?
Key criteria include:

• Solid carbide material with high wear and hot hardness.

• High-temperature oxidation-resistant coatings like TiAlN or DLC.

• Optimized tool geometry (cutting edge angle, core thickness, chip grooves).

• Manufacturer certification for HRC60+ materials.

• Verified tool life and hole quality through field trials or customer feedback.