Notes · 33 articles
Hard steel, written down
Short pieces for the person writing the drawing. No company news, only the things that change what a hardened steel part costs and how long it takes.
Process selection
Which finishing route the part wants: mill, grind, turn or burn.
Jig grinding hardened die plates: when hole position needs it
Jig grinding finishes holes in hardened steel to a few microns of position. When the tolerance justifies it, when wire EDM or hard milling will do, and what to specify.
Case hardening vs through hardening: 8620, 9310 and 4140 compared
Case hardened 8620 or 9310 gives a hard shell on a tough core. Through hardened 4140 is hard throughout. Distortion, grinding stock, cost and failure compared.
52100 bearing steel: hard turning races, rollers and sleeves
52100 bearing steel at 58 to 64 HRC can be hard turned with CBN instead of ground. What tolerance and finish hard turning holds and where grinding still wins.
Machining hardened steel after heat treatment: what actually changes
Hard milling at 55-62 HRC is not soft machining with a slower feed. What changes in tooling, fixturing, stock allowance and quoting when the part is cut after heat treat.
Hybrid routing: hard mill the shape, grind only what has to be perfect
The cheapest way to finish a hardened part is rarely one process. How to split a drawing between milling and grinding, and how to mark it so shops quote the same plan.
Pre-hardened or through-hardened: choosing the supply condition for tool steel
Buying steel already at 30-40 HRC skips heat treatment entirely. When that is the right call for a die or mould, and when it costs you the wear life you needed.
When wire EDM is the only answer: sharp corners in hardened dies
No milling cutter produces a truly sharp internal corner. Where that forces wire EDM into a hardened die, what it costs in time, and how to design around it when you can.
Hard turning vs cylindrical grinding: when the lathe replaces the grinder
Hard turning finishes hardened shafts and bores on a lathe instead of a grinder. What it holds, where it fails, and the four conditions that make it the cheaper route.
Hard milling, grinding or wire EDM: picking the finishing route at 55-62 HRC
Three ways to finish a hardened steel part, and the geometry, tolerance and volume rules that decide which one belongs on your drawing. With a side-by-side comparison.
Grades
What each tool steel is for, and what it costs to machine.
H11 vs H13: hot work steels for die casting and forging dies
H11 and H13 differ mainly in vanadium. How they compare for die casting and forging dies in toughness, wear, heat treat and machinability, and when each is better.
420 stainless mold steel: polishability, corrosion and hardness range
420 stainless mold steel suits clear plastic and corrosive resin molds. Its hardness range, polish quality, corrosion limits and the heat treat steps that decide them.
Tool steel grade equivalents: AISI, JIS, DIN and GB cross-reference
D2, SKD11 and 1.2379 are the same steel under three standards. A cross-reference table for tool steel grades, and why naming the equivalent shortens your lead time.
4140 and P20 pre-hardened: the workhorse grades nobody writes about
Most hardened steel parts are not 60 HRC exotics. They are 30-35 HRC 4140 and P20. What those grades hold, how they machine, and where they stop being enough.
D2 vs H13: which one is harder to machine, and why it matters to your quote
D2 and H13 sit at similar hardness but behave differently on the machine. A practical comparison of carbide content, abrasion, thermal behaviour and what each does to lead time.
O1 vs A2: what an oil quench really costs you in distortion
O1 is cheaper and machines easier. A2 moves less in heat treatment. A look at what that difference is worth once you price the finishing operation it forces.
S7 tool steel: the shock grade for punches, chisels and shear blades
S7 trades wear resistance for toughness that no cold work grade can match. Where it belongs, how it machines, and the heat treat detail that ruins parts when missed.
A2 vs D2: trading wear resistance for toughness, and what it does to the quote
A2 and D2 are both air-hardening cold work steels, but they fail differently and machine differently. Which to specify for punches, dies and forming tools.
Technique
What happens at the cutting edge above 45 HRC.
Hard milling troubleshooting: chatter, edge chipping and size drift
Three failure modes cover most hard milling problems. How to tell them apart from the part and the tool, and the fix order that solves each without guessing.
Rigidity in hard milling: runout, stickout and workholding
Hard milling fails on vibration, not on power. The four rigidity variables that decide whether a 60 HRC surface comes out at Ra 0.4 or covered in chatter marks.
Trochoidal and dynamic toolpaths in hardened steel: constant engagement wins
Hard milling fails at the corners, where engagement spikes. How trochoidal and dynamic toolpaths keep the load constant, and the parameters that actually matter.
Why hard milling runs dry: flood coolant, air blast and thermal cracking
Flood coolant on an interrupted hard milling cut destroys CBN edges. Why heat is a tool in hard machining rather than a problem, and when MQL earns its place.
CBN, coated carbide or ceramic: picking the cutting material for 45-65 HRC
Three cutting materials cover hardened steel, and the crossover points between them are narrower than most shops assume. Where each one wins and where each one shatters.
Quality
Heat treatment, surface integrity, and proving a part is right.
Hardness testing tool steel parts: Rockwell, Vickers and where to test
Rockwell C, Vickers and portable testers read tool steel differently. How to pick the method, where to put the indent and what to write on the drawing.
Gauges and fixtures in hardened steel: stability and stress relief
Hardened gauges and fixtures must hold size for years. How steel choice, stress relief, ageing and grinding sequence decide stability, and what to specify.
Cryogenic treatment for D2 and M2: what it changes and what it does not
Cryogenic treatment of D2 and M2 converts retained austenite and may extend tool life, but results vary. What it does, where it fits in the cycle and how to specify it.
The seven lines that make a hard steel RFQ quotable
Why hardened steel quotes come back wildly different, and the seven pieces of information that make shops price the same job. A checklist to run before you send the drawing.
Inspecting hardened parts: what to ask for and what it proves
CMM reports, hardness tests and finish traces each prove something different, and a standard proof package misses the failures that matter most on hardened steel.
Heat treat distortion: stress relief, stock allowance and datum strategy
Parts move in the furnace. How much, why, and the three drawing decisions — allowance, stress relief and datums — that decide whether you can machine it back.
White layer: the surface damage that passes inspection and fails in service
A dimensionally perfect hardened part can carry a re-hardened surface layer with tensile stress underneath. What causes it, why CMMs miss it, and how to specify against it.
Sourcing
Finding and judging a shop that can actually do this work.
Hardened injection mold inserts: cores, cavities and slides
How hardened mold inserts, cores, cavities and slides are made and specified: steel and hardness by function, fits, vents and the details that prevent flash.
Forming rolls for roll forming lines: grade, hardness and profile grinding
Roll forming tooling decides profile accuracy and tool life. Which tool steel and hardness suit the strip, how profiles are finished and what the drawing needs.
Why tooling work is moving to Vietnam — and what the supply base still cannot do
Vietnam has a real tool and die base built by mould and electronics manufacturing. An honest look at where it is competitive on hardened steel and where it is not.
Vetting a hard steel machine shop: questions a machine list cannot answer
Every shop shows the same photos of the same machines. Eight questions that separate shops which actually machine at 60 HRC from shops that own capable equipment.