Failure Analysis Data
Tool and Die Failure Analysis and Prevention
A tool or die passes through design, grade selection, steelmaking, machining, heat treatment, grinding and service, and a fault at any one of those steps can end its life early. This page sets out the causes the source groups tool and die failures under, the examination steps that separate them, and the measured evidence from the case studies behind the article.
The chain that produces a tool or die The source groups the causes of tool and die failure into the factors below, and notes that the factors are interdependent. A step done badly limits the life of the tool no matter how well the other steps are done, which is why the analysis of a failure so often ends one step earlier than the obvious fault.
| Estágio | What it has to deliver | How it shows up when it fails |
|---|---|---|
| Mechanical design | Has to suit the grade, the way the tool is manufactured, and the way it is used. Sharp corners and extreme changes in section mass are the two simple design faults behind the largest share of tool and die failures. | Cracks that start at a corner or at a step in section size, sometimes during the quench, sometimes in service. |
| Grade selection | Has to suit the design, the machining, the heat treatment and the service conditions. Toughness and wear resistance are traded against each other, and most tools are better off wearing out than breaking early. | Breakage in a tool that was never given a chance to wear, or rapid wear in a tool chosen for toughness alone. |
| Steel quality | Has to be macrostructurally sound, free of harmful inclusions and free of harmful surface defects at the level the job needs. | Cracks that trace back to a seam, a lap, hydrogen flakes, an unconsolidated center or a band of carbides. |
| Usinagem | Has to leave the surface microstructure, the surface finish and the residual stress state fit for heat treatment. | Quench cracks located by rough tool marks, EDM recast layers that spall, machining stresses that add to the quench. |
| Tratamento térmico | Has to deliver the intended microstructure, hardness and toughness at the surface and in the core. Improper heat treatment is the single largest source of failures during treatment and afterwards. | Untempered parts, overaustenitized structures, decarburized or over-carburized skins, shallow cases, soft spots, burnt surfaces. |
| Grinding and finishing | Has to leave the surface integrity intact. Grinding damage is far more likely when the part was not tempered properly or was overaustenitized. | Grinding scorch, rehardened white spots over a back-tempered layer, cracks that appear after the final grind or after regrinding. |
| Tool and die setup | Has to align precisely so that the working stresses stay even across the tool. | Uneven wear on one side, cracking at one edge, fatigue that starts at a misaligned contact. |
| Tool and die operation | Has to stay inside the load, temperature and lubrication the tool was built for. | Overload, friction heat, heat checking, wash-out, erosion, early fatigue. |
Source: ASM Handbook, Vol. 11, Failure Analysis and Prevention (ASM International), article Failures of Tools and Dies. The hardness ranges quoted on this page come from the same article, 58 to 68 HRC for most tools and dies and 30 to 55 HRC for plastic molding and hot working dies.
- Tools and dies are used at higher hardness than almost any other steel product, which is why a small processing fault has a large effect. The same article puts the two most common design faults at sharp corners and extreme changes in section mass, and recommends the largest fillet the design allows. Air hardening grades tolerate a sharp corner better than liquid quenching grades.
- A part that fails early usually carries more than one problem. Several contributing factors in varying degrees is the normal finding, so the aim of the analysis is the full picture rather than the first defect found.
What the examination establishes The source sets out a sequence for working through a tool or die failure. Each step below settles one question.
| Etapa | What it settles |
|---|---|
| Compile the history | Manufacturing route, heat treatment record and service life. Where the record is skimpy the analyst has to work from experience and engineering judgment. |
| Examine, measure, photograph | Document the extent and location of the damage before anything is cut. Design faults and machining problems are usually visible at this stage. |
| Nondestructive examination | Ultrasonic, x-ray or magnetic particle inspection before sectioning, so the internal picture is on record before the part is opened. |
| Verify the composition | Tool and die failures occasionally come from the wrong grade of steel being used, so the analysis starts by confirming what the part is made of. |
| Open the cracks and read them | Quench cracking is a very common cause, so the fracture surfaces are checked for temper color. Scale on a crack wall means the crack was open at a temperature above the tempering temperature. |
| Hardness survey | Confirms the quality of the heat treatment and often exposes the problem on its own. Surface and interior readings are taken separately. |
| Macrostructural examination | Cold etching with 10 percent aqueous nitric acid, or hot etching, brings out chill depth, decarburization, carburized cases, grinding scorch and heat patterns from service. |
| Grain size and retained austenite | Prior austenite grain size is often read by the Shepherd fracture method, and retained austenite is measured by x-ray diffraction. Both separate an overaustenitized part from a correctly treated one. |
| Microstructure, at and away from the damage | Required at the origin and in the unaffected metal, which calls for edge retention preparation. A stereomicroscope settles most cases, and high magnification fractography is only needed in a small share of them. |
| Compare and simulate | Good parts are compared with failed parts, and a simulation or an experimental heat treatment can confirm whether a part was tempered or how a structure was produced. |
Source: ASM Handbook, Vol. 11, the analytical approach section of Failures of Tools and Dies. The order matters, because destructive work closes off the visual and nondestructive examination that has to come first.
Failures that start in heat treatment Improper heat treatment is the largest single source of tool and die failures, during treatment itself and in the steps after it. The rows below pair the condition with the measured evidence in the source and the practice that avoids it.
| Condição | What the examination found | How it is avoided |
|---|---|---|
| Tempering skipped | Two D2 dies at 2.25 x 2.375 x 1.125 in. cracked in finish grinding. The interior read 63 to 64 HRC, typical of as-quenched D2, and the scorched surface had been back tempered to 55 to 58 HRC. The heat treater had stopped after the as-quenched hardness matched the drawing. | Move the part to the tempering furnace as soon as it reaches about 150 °F (65 °C). Temper twice or three times on the highly alloyed grades. As-quenched hardness can also read low on a decarburized surface, and grinding a spot to test it can start a crack. |
| Overaustenitizing | An M2 roughing tool cracked during hardening with a heavy grain boundary carbide film, coarse plate martensite and unstable retained austenite, at a Snyder-Graff intercept grain size of 4.5, which is ASTM 7 and coarse for the grade. An O1 ring forging read 61 to 62 HRC with retained austenite present, and cooling a section in liquid nitrogen took it to 64 to 65 HRC. | Hold the austenitizing temperature range for the grade and do not batch grades of different recommended temperature in one furnace load. Undissolved carbides control grain growth, and a higher temperature puts more carbon into solution. |
| Decarburized surface | An A2 blanking die with a chromium plate cracked in service over a decarburized layer about 0.002 in. (0.05 mm) deep, which let the brittle plate flex. An O1 ring forging decarburized to about 0.020 in. (0.5 mm) cracked during quenching, with a skin at 55 to 57 HRC that stayed 55 to 57 even after the core was refrigerated. | Control the furnace atmosphere, take the standard machining allowance off mill products before heat treatment, and specify decarb free stock where the working surface will not be cleaned up afterwards. |
| Carburizing past the intended case | A P20 mold 8 x 8 x 1.375 in. came out of a carburize and reharden cycle with a dark etching case about 1/8 in. (3.2 mm) thick, cracks 0.070 and 0.113 in. deep, and 1.96 percent carbon in the outer 0.010 in. (0.25 mm). An S7 punch was taken to 2.94 percent carbon in the outer 0.005 in. and read 63 to 64 HRC at the surface falling to 55 HRC an inch in and 53 HRC at the center. | Control the cycle, use liquid carburizing where the case has to stay thin, and check whether the grade can be carburized lightly at all. S7 is difficult to carburize to a light case, and the punch would have been better made in another grade. |
| Quenching that missed the working surface | A W1 header die 1.5 in. in diameter and 2.5 in. long chipped at the striking face. Macroetching showed a shallow chill zone that could not support the edge, and the sharp corners of the striking face cavity concentrated the stress. A W1 wire forming die broke in service with a bore that had never hardened, at 35 to 38 HRC in the one corner region that took the quench and 29 to 30 HRC elsewhere. | Flush quenching through a bore is a poor way to harden a working surface. Use a procedure that produces the case at the surface the tool actually works with, and round or fillet the corners. |
| Soft spots from the quench | A W2 component at 1.05 percent carbon quench cracked, and cold etching revealed unhardened patches on the surface. Fixtures, tongs, inadequate agitation and vapor pockets all leave these soft spots. | Support the part so contact does not create a chill, agitate the quench, and keep the bath clean. Soft spots matter most on water and brine quenching grades. |
| Burning and melting | A D2 powder metallurgy die component melted and deformed through flame impingement during heat treatment. An M2 part came out of hardening with a rippled surface from a remelted layer, with carbon enriched to 1.28 percent in the outer 0.005 in., which lowered the melting point of the skin. | High speed steels are the most exposed because their austenitizing temperatures are far higher than the rest of the tool steel family. Keep the part out of direct flame paths and control the furnace atmosphere. |
| High speed steel rehardened without an anneal | A second hardening treatment without an intermediate anneal produces rapid grain growth at the high austenitizing temperature, and the fracture takes on a shiny, coarse, fish scale appearance from the coarse grain. | Always anneal a high speed steel part before rehardening it. The fine carbides that resist grain growth are produced by the anneal and are gone after the first hardening. |
| A heavy white nitride layer | A 4150 chuck jaw hardened and tempered before nitriding broke with a brittle white iron nitride layer at the surface, present also as a grain boundary film around the grains just below it. The crack followed that film. | Control the nitriding potential so the compound layer stays thin and continuous, and remember that a nitrided case is brittle where it is thick. The same layer builds on tool steel parts that are nitrided. |
Source: ASM Handbook, Vol. 11, Failures of Tools and Dies, cases illustrated in Figures 10 to 33 of the scan. Hardness values are as measured in the reported cases.
- Two failure patterns repeat across the cases. A tool that was not tempered usually fails in the next operation, whatever that operation is, and a tool that was overaustenitized usually fails where the retained austenite sits. Both leave a signature that a hardness survey and a micrograph can read.
- Retained austenite is worth measuring on any part that has to hold size or that cracked without an obvious overload. The amount each reaction moves a dimension, and the way to plan around it, is set out on the size change in heat treatment page.
- Where the failed part came out of a furnace cycle that is not yet solved, the heat treatment troubleshooting chart works the same problem from the symptom end.
Machining, EDM and grinding damage Machining problems are a common cause of tool and die failure. The defect usually looks minor on the shop floor and shows up as a crack at the quench or as spalling in service.
| Operation and defect | Measured evidence | Rule for the shop |
|---|---|---|
| EDM recast layer | Four 1/8 in. holes spark eroded in an A4 primer cup plate spalled during jig bore grinding. The layer stack read 35.5 HRC in the as-cast skin, 63.5 HRC in the as-quenched martensite below it, 56 HRC in the back tempered zone, and 59 to 61 HRC in the base metal. | Stone or grind the cavity surface after EDM, then temper it. Leaving the as-cast and as-quenched layers in place is a common cause of edge spalling before the tool ever runs. |
| EDM on a mold cavity | An S7 plastic mold die was found cracked before use, with a crack following a recessed gear tooth contour to an average depth of 1/16 in. (1.6 mm). Etching showed a light rim at the teeth, and the section carried an as-quenched martensite skin over a grossly overaustenitized core, so both the EDM layer and the heat treatment were wrong. | Remove the damaged layer and check the heat treatment of the same part. Where the two faults sit together the surface fix alone will not save the die. |
| Rachaduras de moagem | An S1 cutter die 1.25 x 6 x 15 in. that had been carburized to 62 to 64 HRC cracked and spalled during regrinding, with the scorch pattern visible beside the cracks. Two A6 parts properly hardened to 57 HRC shattered in finish grinding, with a surface hardness that wandered between 48 and 56 HRC, rehardened white spots about 0.003 in. (0.08 mm) deep and a back tempered zone about 0.015 in. (0.38 mm) deep. | Treat grinding as a heat treatment operation. Gentle passes, free cutting wheels, enough coolant and a part that was tempered properly is the whole of the recipe. |
| Rough machining marks | An S7 punch cracked during quenching at a 540 °C (1000 °F) oil quench followed by air cooling, with the cracks located by very coarse tool marks and temper color on the crack walls. A ground finish carries far less risk than a worked one. | Finish the stressed surfaces to a smooth geometry before hardening. Cutter marks are stress raisers with the same effect as a small radius. |
| Identification and stamp marks | An S7 air hardening die cracked during quenching from a deep sharp stamp mark, and the die had not been tempered, at 61.5 to 62 HRC with a slightly decarburized skin at 59 to 60 HRC. An S5 sledge hammer head cracked from a decarburized surface and a deep stamp mark together. | Keep stamps away from stressed sections and out of fillets, stamp shallow and round the edges, or mark on a face that is later removed. |
Source: ASM Handbook, Vol. 11, Failures of Tools and Dies, the machining and finish grinding section, Figures 4 to 12 of the scan.
- The EDM layer is the most repeatable of these numbers across the literature, and the fix is standard. Remove the recast and as-quenched layers, then temper the surface, because a spark eroded surface carries a hardness gradient over a very short distance.
- The white layer, its depth on different grades and how to handle it, is worked through on the EDM white layer article.
- Where the heat treatment itself is in doubt, the pattern of mistakes that produces a brittle as-quenched part is collected on the D2 heat treatment mistakes page.
Steel quality defects that reach the bench Faulty material causes a low share of tool and die failures, and it is the share a buyer can act on before the steel is cut. The defects below are all visible in the finished tool only if someone looks for them.
| Defect | What it looks like | Where it is caught |
|---|---|---|
| Seams and laps | An H12 coil spring cracked after heat treatment because a tight seam survived centerless grinding and opened during quenching. An A8 ring forging cracked after forging and annealing with scale on the crack walls to 1/2 in. (13 mm) below the surface, and alkaline chromate etching showed oxygen enrichment, proof the defect was open while hot. | Surface condition and a magnetic particle or penetrant check on bar stock that will be quenched hard. Seams that stay in the part do not stay quiet. |
| Hydrogen flakes | An O1 die cracked during heat treatment. Opened cracks showed coarse shiny facets, the cracks ran lengthwise and sat in the center of the section, and the shallow ones carried temper color while the deeper ones did not. | Vacuum degassing at the mill, and section sizes that let hydrogen diffuse out. This is a steelmaking defect, so the answer is on the purchase order rather than in the tool room. |
| Unconsolidated center | A W2 die insert cut from a 6 x 10 in. billet cracked during rehardening, and the origin sat at the center of the section. Hot acid etching brought out an unsound centerline condition. | Where a large section gets limited hot reduction, the center of the bar deserves an ultrasonic check. Three such failures turned up in one 20 year study of tool failures. |
| Carbide segregation and banding | The flange edge of a roll turned from 9 in. diameter D2 bar chipped in first use, with poor carbide distribution and morphology and a grain size of ASTM 6.75. A 2.75 in. scoring die in A2 spalled at the cutting edge where a band of carbides intersected the profile. | Ask for the carbide distribution to be controlled on high alloy bar, especially for edges and rolls. Where a band sits in the wrong place, the grade is the problem, not the heat treatment. |
| Overheating during hot working | An H12 forged liner came back with poor tensile ductility, a coarse tensile fracture and a grain size coarser than ASTM 1, from a forging temperature high enough to take most of the sulfides into solution. | Heavy hot reduction can repair most of this damage, limited reduction cannot. A coarse fracture test on a forging is a cheap check on the bar before the tool is cut from it. |
Source: ASM Handbook, Vol. 11, Failures of Tools and Dies, the influence of steel quality section, Figures 34 to 42 of the scan.
- The machining allowance on hot rolled bar exists partly for this reason. The cases above include a pin and a cam made from S5 whose mill bark was never removed, both heavily decarburized and fracturing early in service, where decarb free stock was the answer. The allowances are tabulated on the tabela de tolerância de usinagem.
- Certificate, test report and the checks that tie a delivered heat back to the mill are set out on the página de verificação de qualidade.
Service conditions that wear a good tool out A tool made from the right grade, well designed, correctly machined and properly heat treated can still fail early because of how it was set up and run. In these cases the shop floor carries the answer, and the examination only shows that nothing else was wrong.
| Service condition | Case evidence | What the answer usually is |
|---|---|---|
| Friction heat at the working edge | Two H13 shear knives used to grip hot rolled bar at 1500 to 1800 °F (815 to 980 °C) spalled on the gripping edge, and the tip carried freshly formed martensite at 59 to 60 HRC. A 5 in. wide S7 cutter blade showed dark etching bands along the working edge after resharpening, from frictional heat back tempering the steel. | Cooling between operations, and a grade that holds hardness at the working temperature. Friction heat can put the surface above the austenitizing temperature while the core stays cold. |
| Severe wear with inadequate clearance | An air hardening die 3.625 in. in outside diameter came out crazed and eroded with vertical scratch marks that pointed to a clearance problem, and the rubbing had reaustenitized part of the surface into brittle as-quenched martensite. | Check the clearance before blaming the steel. The die in this case was properly machined and heat treated, and the abuse was in the press. |
| Hot work service damage | ||
| Heat checking and wash-out | A runner block in a proprietary hot work steel produced more than 100,000 aluminum transmission case covers before the surface showed heat checking in one area and wash-out in another. Zinc die casting dies erode in preference to heat checking because the service temperature is lower, and an H13 zinc die casting nozzle carried a furrow about 3 in. long and 1/16 in. wide with zinc intruding into the crack. | Heat checking is a thermal fatigue network driven by alternate heating and cooling. Water cooling on susceptible grades makes it worse. Erosion is a flow and alloying question, and a misaligned bore worked against the nozzle in this case. |
| Fatigue that starts at heat checks | An H26 exhaust valve punch split lengthwise after 1,007 parts. The fracture faces showed progressive crack growth, the working face was heat checked, and the heat checks were the initiation sites. The surfaces had been nitrided after heat treatment. | Heat checks are cracks. Where the tool also sees a cyclic bending load, they become the origin of a fatigue failure and the tool needs a grade or a cooling change rather than a repair. |
| Decarburization during service | A 5.3125 in. H13 mandrel used to pierce and extrude brass cracked after 298 pushes, about 30 percent of its expected life. Macroetching showed a heavily decarburized surface, and the decarburization had taken place in service. | A reducing or protected atmosphere only helps in the furnace. Where the tool works in air at temperature, the surface chemistry moves anyway and the working life has to be planned for it. |
Source: ASM Handbook, Vol. 11, Failures of Tools and Dies, the influence of service conditions section, Figures 43 to 51 of the scan.
- Alignment problems are named in the source as a common cause of failure in shearing tools, and fatigue failures in tools most often start at a change in section size, a sharp corner or a stamp mark.
- Heat checking is covered from the selection end on the thermal fatigue resistance page, and the grades chosen to resist it are set out on the hot work family page.
When the crack appeared during the quench
A quench crack runs from the surface toward the center of mass, carries temper color on its walls once the part is tempered, and is always intergranular. The mechanisms, the risk factors and the way to read one are collected on the página de rachaduras de resfriamento.
When the tool broke before it wore
Breakage that comes early usually means the toughness side of the grade decision was set too low for the load, or the heat treatment left the part too brittle to use. The grades that buy toughness and what they give up for it are set out on the cracking resistance page e o chipping resistance page.
When the surface is damaged and the cause is not obvious
Damage that has to be classified before it can be fixed is a reading exercise. The six damage modes, what each one looks like at three scales of examination and the factors behind it are collected on the damage mode identification chart.
When the part cracked with no obvious overload
Some fractures come from a change in the steel rather than from a load, and the temperature window that caused it is often in the process record. The types of embrittlement, their trigger temperatures and their remedies are collected on the Página sobre tipos de fragilização do aço.
Confirme antes de fornecer um orçamento.
These cases and figures are for general reference only. Failure analysis conclusions rest on the actual part, its heat treatment record and its service history. Confirm the condition of your own tool against its certificate, its process record and a metallurgical examination before acting on a diagnosis.
Values quoted here are the measurements reported in the source for the specific parts in each case. They illustrate the size of the effect rather than a specification.
Páginas de referência relacionadas
Tool steel heat treatment guide · Tool steel processing characteristics · Hardness testing methods · H13 failure modes and limitations · Aços para ferramentas de trabalho a frio · Tool steel supply
Source: ASM Handbook, Volume 11, Failure Analysis and Prevention (ASM International), article Failures of Tools and Dies by George F. Vander Voort, pages 2505 to 2556 of the scanned volume. Reference data for comparison only. Confirm the grade, the heat treatment record and the failure analysis findings with your own metallurgist before changing a process. Aobo Steel supplies tool steel in the annealed condition.