Broaching is the quiet hero of part making. It creates precise internal splines, keyways, hexes, and complex forms with speed and repeatability. Using the common broaching materials ensures the tool glides, chips clear, and surfaces come out clean. Pick the wrong stock and you fight chatter, torn edges, and tool wear.
This guide walks through common broaching materials, what makes them work, and what to avoid so you get strong parts and stable production. If your part also needs turning, milling, grinding, or gear work, folding broaching into an integrated precision machining plan keeps tolerances and timelines on track.
What Makes a Material “Broachable”
Successful broaching comes down to a few traits. Hardness needs to be in a sweet spot so the tool cuts instead of rubs. The microstructure should be uniform so the teeth see consistent resistance through the stroke.
Chip behavior matters a lot. Short, well-broken chips clear the gullets and move out with the coolant. Gummy, stringy chips pack the tool and tear the surface.
Lubricity at the cut face helps the tooth shear cleanly and protects the cutting edge.
Finally, stability in fixturing matters so the part does not spring or distort as the tool enters, cuts, and exits.
The heat treat sequence is part of this picture. Many teams rough or finish broach before hardening and then use grind or hard turn to hit the final size. If broaching after heat treatment is required, the tool material and geometry need to match the higher hardness.
Common Broaching Materials That Run Well
Below are common broaching materials that run well:
Low and Medium-Carbon Steels
Plain steels like 1018, 1020, and 1045 are frequently broached for keyways and internal forms. They cut predictably and hold finish with the right coolant and feeds. Low carbon grades can smear and raise burrs if the feeds are too light or the tools are dull. Medium carbon grades, especially 1045, give a cleaner shear and better dimensional stability. For high volumes, free-machining variants with sulfur or lead improve chip control and tool life.
Alloy Steels
Alloy steels such as 4130, 4140, and 4340 are go-to choices for strength and fatigue resistance. In a broaching context, they perform best in the pre-hardened state. You get crisp edges and straight walls, then follow with induction hardening, nitriding, or through hardening as the print requires. If final broaching after heat treat is unavoidable, tool material moves from HSS to more wear-resistant options, feeds increase to stay above the work hardening zone, and coolant delivery becomes critical.
Stainless Steels
Stainless brings corrosion resistance but asks for careful process control. 303 is the friendliest grade for broaching because sulfur improves chip breakage. 304 and 316 can work harden and produce long, sticky chips. Sharp tools, assertive feeds, and high-performance cutting oils protect the edge and the finish. Pre-broach stress relief can also stabilize dimensions if the part started as cold-worked stock. When the environment is aggressive and strength matters, 17-4 PH in the solution-annealed state broaches well and can be aged afterward for high hardness.
Cast Irons
Gray and ductile iron are often excellent choices. Graphite in gray iron acts like a built-in lubricant, so broaches cut freely and leave a good surface. Ductile iron is tougher but still runs well with proper coolant flow. The main watchout is abrasive wear from hard inclusions or skin. Removing scale or adding a light pre-machine pass before broaching extends tool life and protects accuracy.
Aluminum Alloys
Aluminum is very broachable when the alloy is chosen wisely. 6061-T6 runs smoothly and finishes well with good chip evacuation. 2024 and 7075 also broach cleanly and bring higher strength for structural parts. Soft, commercially pure aluminum grades can smear and clog the teeth. Proper entry chamfers, keen edges, and a cutting fluid that controls built-up edge keep surfaces bright and dimensional, spread tight.
Copper Alloys
Free-cutting brass, especially C360, is one of the best metals for broaching. Chips break, finishes look great, and cycle times are short. Many bronzes also run well, provided you match the tool to the alloy. Aluminum bronze and some silicon bronzes are harder on tools because they are tough and abrasive. With the right coating and coolant, they still produce high-quality splines and keyways, but expect more attention to tool wear and inspection intervals.
Powder Metal Components
Sintered metals can be broached to create final forms without long milling cycles. Porosity affects chip formation and edge support, so tool geometry and coating selection matter. A stable fixture that supports the bore prevents chipping at the exit. When done right, PM parts accept broached features with consistent torque transmission and clean profiles.
Nickel Alloys and Titanium
These families sit in the “possible with care” bucket. Nickel superalloys and Ti-6Al-4V bring strength and heat resistance that challenge tools. If the print needs a broached internal spline or form, carbide or powder-metal HSS tools, positive rake, and rich coolant delivery are the starting points. Stroke speeds stay modest, and inspection frequency increases. Many programs choose to broach before final hardening or aging to hold cost and protect edges.
Engineering Plastics
Certain plastics broach well for light-duty features. Acetal (POM) and nylon cut cleanly and hold shape with generous relief angles and sharp edges. PEEK can also be broached in controlled setups. Heat builds fast in polymers, so chip clearance and gentle entry and exit are important. Thin walls and deep profiles are better molded or machined by other means.
What to Avoid or Approach With Caution
Avoid very hard stock when using HSS broaches. Once hardness creeps into the high forties on the Rockwell C scale, tool life drops fast, and finish degrades. If the part must be that hard, move broaching earlier in the sequence or step up to tool materials designed for the job.
Be careful with gummy materials that smear. Pure aluminum, oxygen-free copper, and low-carbon steels without free-machining additives can produce built-up edge and torn surfaces. The fix is sharp tools, adequate feed, and cutting fluids that prevent welding at the edge. If finish still suffers, a different alloy is the smarter move.
Watch for grades that work harden aggressively. Austenitic stainless steels like 304 and 316 can form a hardened skin if the cut is too light or the edge is dull. Keep the tool sharp, feed decisively, and avoid pecking behavior that rubs instead of shears. Stress-relieved stock often helps.
Do not broach through heavy scale, case, or plating. Mill or turn away the skin before the broach enters. If the part is carburized, leave stock and broach before heat treat, or use a finishing method suited for hard surfaces. Plating and anodizing go on after the broach, not before.
Avoid very thin-walled hubs and long, unsupported bores for deep internal forms. Broaching exerts a steady cutting force through the stroke. Without support, bores can bellmouth and walls can collapse. Smart fixturing, pilot features, and realistic depth-to-diameter ratios keep features true.
Finally, do not starve the cut of coolant. Broaching concentrates cutting along many teeth at once. A sulfurized or extreme-pressure oil improves shear and helps chips move out of the gullets. Filtration keeps fines from recirculating and dulling the edge. Stable coolant delivery is a simple way to protect the finish and extend tool life.
Design Moves That Make Broaching Easier
Small design choices give you better parts at a better cost. Add lead-ins and chamfers to help the broach start straight and exit clean. Specify clear tolerances for the profile and for any functional surfaces so the process can target what matters most. Leave honest stock for any post-broach heat treat or coat so dimensions land where you need them. If the feature is a spline, call out the standard that defines tooth form and fit so gauging is unambiguous.
Sequence planning matters too. Many programs rough machine, broach the internal form, heat treat, and then finish grind or hard turn the critical diameters. Others broach as the final step when heat treatment happens earlier in the routing. The best choice depends on part geometry, production volumes, and how the feature fits with the rest of the tolerance stack.
Choosing the best metals for broaching by application
If you need clean internal forms at scale and a friendly cutting response, free-cutting brass and 1045 steel are reliable picks. For higher strength with solid machinability, 4140 in the pre-hardened state is a frequent winner. For corrosion resistance with good cutting behavior, 17-4 PH before aging balances performance and process. For lightweight structures, 6061-T6 and 7075 give smooth broach cycles and crisp profiles. Cast irons provide stable bores and good finishes for housings and hubs.
Every choice should reflect how the part will live. Torque transmission calls for a tough, stable material with a finish that mates without fretting. Corrosive environments push you toward stainless, plated steel, or coated aluminum. High temperature service narrows the field to nickel alloys or heat-resistant steels, with process changes to match. When you weigh these needs against tool life, cycle time, and inspection plans, you land on the true best metals for broaching for your part.
Why Pair Broaching With A Full Precision Machining Workflow
Broaching does its best work inside a coordinated process. When turning, milling, centerless grinding, and gear work share the same floor as broaching, setups align, and datums stay consistent. Features can be sequenced so each step sets up the next with minimal handling. Gauging lives close to the machines that create the feature. That is how you hit tight timelines and repeat tolerances across lots and years. It is also how you keep costs in line without sacrificing performance
Talk With C. Thorrez Industries Inc.
If you are evaluating common broaching materials for a new spline, keyway, or internal profile, bring your print and a quick note on loads, environment, and volumes. C. Thorrez Industries Inc. can help you select the material, plan the sequence, and prove out a stable, scalable process.