If you’ve ever watched a construction crew boring through solid granite, a well driller navigating layers of compacted shale, or a mining team tunneling through abrasive iron ore, you’ve probably glanced at the tool at the business end of the drill string: the button bit. These unassuming, studded tools don’t get nearly enough credit for how they turn rotational force into penetration, but every driller knows one thing works: a button bit that fails mid-job is a project that blows deadlines and budgets. As someone who’s spent the last 18 years supplying button bits to drillers across North America, I’ve lost count of how many times a customer has called me at 2 a.m. saying, “The buttons just sheared off—what do I do now?” Nine times out of ten, the answer ties back to something most folks don’t think about at first: material hardness. Hardness isn’t just a number on a spec sheet—it’s the backbone of how a button bit performs, and picking the wrong hardness is a fast track to downtime. Button Bit
Let’s start with the basics, because a lot of new drillers mix up hardness with toughness, and that’s where mistakes happen. Hardness is a material’s resistance to indentation or scratching—you measure it with scales like Rockwell C (HRC) or Vickers, so for button bits, we’re almost always talking HRC. Toughness, by contrast, is a material’s ability to absorb impact without breaking. Think of a diamond: it’s extremely hard, but if you drop it on concrete, it chips, right? That’s low toughness. A rubber eraser is low hardness, but it’s super tough—it stretches and deforms instead of breaking. Button bits need both, but hardness is the first line of defense against the forces that wear them out, specifically two big ones: abrasive wear and impact fatigue. Abrasive wear is when hard, sharp mineral particles grind against the button, like sandpaper on wood, slowly scraping away material. Impact fatigue is the repeated hammering of the bit’s buttons against rock as the drill spins, which creates tiny cracks that spread until the button breaks or falls off. Hardness directly impacts both, but only if you get it matched to the job at hand.
Let’s break down real-world examples, because this isn’t theory I learned in a lab—this is stuff I’ve seen play out on job sites. A few years back, we had a driller out in West Virginia who was boring through soft, sandy shale for a water well. He’d been using our standard bit with buttons at 52 HRC, and he was getting about 120 feet per bit run, which is solid for that rock type. But then he switched to a job that involved a layer of compacted sandstone mixed with small, embedded quartz crystals—quartz is a 7 on the Mohs scale, and that’s way harder than shale. He kept using the same 52 HRC bit, and within 30 feet, the buttons were so worn down they were half their original size. The bit was sliding instead of cutting, so he had to pull it out early, costing him time and money on trips to the tool crib.
That’s where the right hardness comes in. For abrasive, hard rock like quartz-laden sandstone, granite, or iron ore, we recommend buttons at 58 to 62 HRC. The extra hardness means the button resists that grinding, sandpaper-like wear far better than a softer bit. But here’s the catch: if you take that same 60 HRC bit and stick it in soft, low-compression shale, it’s going to fail in a different way. Soft rock doesn’t require that much hardness to cut, so the buttons don’t get much abrasive wear. Instead, because hard materials are brittle, the high HRC buttons will crack or chip from the repeated impact of drilling into soft rock. Soft rock means more bounce and more sudden, jarring hits on the bit, and a hard button can’t flex or absorb that impact. We had a driller in Ohio test that exact scenario last year—he used a 60 HRC bit on soft limestone and the buttons started cracking after just 80 feet, whereas a 52 HRC bit would have run over 200 feet. He switched, and his downtime dropped by 40% on that job.
It’s not just about rock hardness, either—other factors on the job site change what you need, and that’s something a lot of new drillers don’t account for. For example, rotary drilling vs. percussion drilling? Rotary drilling is more rotational force, so abrasive wear is the main enemy, meaning you lean toward higher HRC. Percussion drilling is a lot more impactful, so you need a balance—maybe 55 to 58 HRC, not too soft that it wears fast, not so hard it breaks. Another big one is drill speed and weight on bit (WOB). If a driller is cranking up the WOB to push harder into hard rock, the impact on each button is higher, so we’ll often suggest a slightly lower HRC (57 instead of 60) to add a little toughness, rather than risk chipping. Conversely, if they’re drilling at high RPM in super abrasive rock, upping the HRC a touch makes sense to slow wear. We have a saying here: “Hardness is your friend, but only when it’s matched to the force.”
Now, let’s talk about what’s inside the button bit itself, because not all button materials with the same HRC perform the same. When we manufacture our button bits, we use tungsten carbide for the buttons—this is the standard because it’s extremely hard and wear-resistant—but we can tweak the grain size of the carbide to adjust both hardness and toughness. Fine-grain tungsten carbide is higher hardness, up to 62 HRC, because the tiny, tightly packed grains resist indentation better. But fine grain is also more brittle, so it’s prone to chipping under impact. Coarse-grain tungsten carbide is a little lower on the HRC scale, around 55 to 58, but the larger grains are bonded together more tightly, so they absorb impact better without breaking. That’s why matching grain size to rock type is just as important as hardness. For example, for high-impact applications like tunneling through fractured rock, coarse-grain 56 HRC is better than fine-grain 60 HRC, even though it’s slightly less hard. I’ve seen too many drillers grab the highest HRC bit they see because they think it’s “better,” only to have it crack halfway through a job because they missed the grain size part.
Wear resistance is where hardness really shines, and it’s the metric that most drillers use to measure bit performance. We track wear rate in our shop, and for every 2 HRC increase in hardness above 52, abrasive wear drops by roughly 15 to 20% in rock with a Mohs hardness of 6 or higher. That means a 60 HRC bit will last almost twice as long as a 52 HRC bit drilling through granite. But again, this only holds if the application is right. If you run that 60 HRC bit in rock softer than Mohs 4, like shale or soft limestone, the wear rate plummets, but the impact failure rate jumps by a factor of three—because the hardness doesn’t help with the impact, and the brittleness becomes a liability. We had a customer in Texas last year who tried to use a 61 HRC bit for a water well through soft clay, and the buttons cracked so bad that he had to replace the bit three times in one day. He called me frustrated, and when I explained that clay doesn’t require high hardness, he switched to a 53 HRC bit, and that same job only took one bit, half the time.
There’s also the long-term cost angle, which is what most project managers care about, not just the bit’s initial price. A lot of drillers look at a cheaper, lower HRC bit and think they’re saving money, but they don’t account for the cost of downtime, bit changes, and labor. Let’s do a quick math example: a 52 HRC bit costs $150, runs 100 feet on hard rock, and needs to be changed every 100 feet. A 60 HRC bit costs $220, runs 180 feet on the same rock. On a 900-foot job, the 52 HRC bit would need 9 bits, totaling $1,350, plus 8 hours of downtime changing bits at $100 an hour, for a total of $2,150. The 60 HRC bit would need 5 bits, totaling $1,100, plus 2 hours of downtime, for a total of $1,300. That’s almost $800 in savings, all because of matching hardness to the job. I see this all the time—drillers chasing the lowest upfront cost end up spending way more in the long run, just because they didn’t understand how hardness affects performance.
Now, I want to be clear: this isn’t a one-size-fits-all rule. There are edge cases where even the best hardness match won’t work. For example, highly fractured rock, whether it’s hard granite that’s been crushed by tectonic activity or soft limestone full of cracks, needs a balance of hardness and toughness. In fractured rock, the buttons hit sharp edges of rock as the drill spins, so impact is higher, and a super hard button will chip on those sharp edges. For that, we’ll go with a 55 to 57 HRC coarse-grain carbide—enough hardness to resist general wear, enough toughness to handle the impact of hitting fractured edges. Another edge case is directional drilling, where the bit has to flex slightly to follow a path. The extra hardness of a high HRC bit makes it less flexible, so it’s prone to breaking if you need that flexibility, so we go with a slightly lower HRC there too.
After 18 years in this business, the biggest mistake I see is drillers treating hardness as a generic number instead of a tailored specification. When a driller comes to me with a job, the first thing I ask isn’t “What hardness bit do you want?” It’s: what type of rock, what’s its compressive strength, what’s the drilling method, what’s the expected WOB and RPM, and is there any fracturing in the rock? Those details tell us exactly what hardness and grain size to recommend, and that’s how we avoid the frustration of bits failing mid-job. Last month, a driller in Colorado called me panicking because his 59 HRC bits were cracking on a tunneling job through fractured gneiss. We sent him a shipment of 56 HRC coarse-grain bits, and he called back two days later saying he’d gone 400 feet with the same bit, no issues. That’s the kind of win that makes this job worth it.
If you’re a driller, project manager, or anyone who relies on button bit performance, the next time you’re picking a bit, don’t just look at the highest HRC number you can find. Ask yourself: is this rock abrasive enough to need extra hardness? Is the drilling method going to put extra impact on the buttons? Are you dealing with fractured rock that needs a little toughness over maximum hardness? Getting that right will cut downtime, lower costs, and make your job way less stressful.
At the end of the day, a button bit is a tool, just like a wrench or a hammer. You wouldn’t use a screwdriver to knock in a nail, and you shouldn’t use a soft bit for hard rock, or a hard bit for soft rock. Hardness is the core of how these tools perform, but it’s only effective when it’s matched to the job. If you’re working on a project, big or small, and you want to make sure you’re using the right button bit—no more mid-job surprises, no more wasted money on bits that don’t work—reach out to us to discuss your specific application. We’ve worked with drillers on everything from small residential well jobs to large-scale mining and tunneling projects, and we’ll help you pick the right hardness to get the job done right.
DTH Drill Pipe References
- Tabor, D. (1951). The Hardness of Metals. Oxford University Press.
- Sundin, K. G., & Sundqvist, B. (2004). Wear mechanisms of tungsten carbide tools in rock drilling. International Journal of Refractory Metals and Hard Materials, 22(4-5), 215-222.
- Ozsahin, S., & Nuhoglu, C. (2007). Effect of rock hardness on button bit performance in rotary drilling. Journal of Materials Processing Technology, 190(1-3), 352-358.
- Bell, R. (2012). Rock Drilling: Principles and Practice. CRC Press.
- Li, W., et al. (2018). Influence of carbide grain size on impact fatigue performance of button bits. International Journal of Rock Mechanics and Mining Sciences, 105, 1-8.
Super Rock Machinery Equipment (Qingdao) Co., Ltd.
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