UDDEHOLM TOOL STEELS FOR FORGING APPLICATIONS
UDDEHOLM TOOL STEELS FORFORGINGAPPLICATIONSTOOLING APPLICATION HOT WORK TOOLING1
UDDEHOLMS ABNo part of this publication may be reproduced or transmitted for commercialpurposes without permission of the copyright holder.This information is based on our present state of knowledge and is intended to providegeneral notes on our products and their uses. It should not therefore be construed as awarranty of specific properties of the products described or a warranty for fitness for aparticular purpose.Classified according to EU Directive 1999/45/ECFor further information see our “Material Safety Data Sheets”.Edition 4, 10.20172TOOLING APPLICATION HOT WORK TOOLING
Selecting a tool steel supplier is a key decision for all parties, including the toolmaker, the tool user and the end user. Thanks to superior material properties,Uddeholm’s customers get reliable tools and components. Our products are alwaysstate-of-the-art. Consequently, we have built a reputation as the most innovativetool steel producer in the world.Uddeholm produce and deliver high quality Swedish tool steel to more than 100,000customers in over 100 countries.Wherever you are in the manufacturing chain, trust Uddeholm to be your number onepartner and tool steel provider for optimal tooling and production economy.CONTENTSHot forging of metals4Warm forging7Progressive forging8Effect of forging parameters on die life10Die design and die life11Requirements for die material14Manufacture and maintenance of forging die16Surface treatment17Tool steel product programme– general description– chemical composition– quality comparison192020Tool steel selection chart21Cover illustration: Connecting rod forging tool.Most of the photos are coming from Arvika Smide AB, Sweden and Fiskars Brands Finland Oy AbTOOLING APPLICATION HOT WORK TOOLING3
HOT FORGINGOF METALS4In hot forging a heated up billet is pressedbetween a die set to a nearly finished product.Large numbers of solid metal parts are produced in aluminium alloys, copper alloys, steelor super-alloys where irregular shapes need tobe combined with good mechanical properties.The main methods of drop forging are hammerforging and press forging.mean to say that wear resistance is not important, particularly in smaller dies, which in factnormally fail as a result of wear. In hammer forging, there is a lot to be said for using inserts ofa more wear-resistant die steel which are shrinkfitted into a tough holder material.For larger, high-production hammer dies,which may be resunk a number of times, it isimportant that the die steel used has sufficienthardenability that the later cavities are not sunkin softer material with inferior wear resistance.HAMMER FORGINGPRESS FORGINGHammer forging is characterized by a very shortcontact time and very rapid rate of increase offorce with time (impact loading). The cumulativecontact time for the bottom die can be fairly longif one includes the time between blows. However, since a lubricant with “blow-out” effect isnormally used with hammers, effective contactbetween the part and the die only occurs duringthe actual forging blow.These features imply that impact toughnessand ductility are important properties for diesteel to be used in hammer dies. This does notIn press forging, the contact time under pressure is much longer, and the impact load ismuch lower than in hammer forging. In generalterms, this means that the heat resistance andelevated temperature wear resistance of the diesteel are relatively more important than theability to withstand impact loading. However,one must optimize impact toughness andductility in relation to wear resistance; thisapplies particularly for large press dies whichare not supported from the sides. Since thesurface temperature of press dies will duringTOOLING APPLICATION HOT WORK TOOLING
service generally be higher than for hammerdies, it is important that the die surface is notexcessively chilled by lubrication. Otherwise,premature heat checking or even thermal shockcracking may result.bustion of oil-based lubricant in the confinedspace between forging and die can also giverise to a type of erosive wear.TYPICAL DIE FAILURESThe deterioration of forging dies is usuallyassociated with several processes which mayoperate simultaneously. However, one of thesenormally dominates and is the ultimate cause offailure. In general, four distinct damage mechanisms can be distinguished: wear mechanical fatigue and gross cracking plastic deformation thermal fatigue cracking (heat checking)Different damage mechanisms can dominate indifferent parts of the cavity.Thermal fatigue WearWearThermal Cracking WearfatiguePlasticWear.GROSS CRACKINGForging dies might fail as a result of some formof gross cracking. This may occur during a single cycle or, as is most common, over a numberof cycles; in the latter instance, the crack growthproceeds via a high-stress fatigue mechanism.Gross cracking is more frequent in hammerblocks than in press tooling, because of thegreater degree of impact.WEARIf all other damage mechanisms are suppressed, a forging die will ultimately wear out(parts out of tolerance). Wear occurs when thework material plus oxide scale glide at highvelocity relative to the cavity surface under theaction of high pressure. It is most pronouncedat convex radii and in the flash land. Wear isincreased drastically if the forging temperatureis reduced (higher flow stress for the workmaterial). The explosion which occurs via com-TOOLING APPLICATION HOT WORK TOOLING5
Gross cracking is a failure condition which canalmost always be rectified. Normally, cracking lies inone or more of the following: overloading, e.g. work material temperaturetoo low die design, e.g. too sharp radii or too thin wallthickness inadequate preheating of the die inadequate toughness of die steel (wrongselection) too high hardness of die material poor quality heat treatment/surface treatment inadequate die support/alignmentTHERMAL FATIGUE CRACKINGThis results if the surface of the cavities issubjected to excessive temperature changesduring the forging cycle. Such temperaturechanges create thermal stresses and strains atthe die surface which eventually lead to cracking viaa low-cycle fatigue mechanism (heat checking).Thermal fatigue cracking is increased by thefollowing factors: cavity surface at too high temperature(excessive billet temperature and/or longcontact time) excessive cooling of die surface betweenforgings inadequate preheating of die wrong selection of die steel and/or poor heattreatmentAll these factors will increase the differencebetween maximum and minimum temperature inthe die surface.Totally cracked die.PLASTIC DEFORMATIONThis occurs when the die is locally subjected tostresses in excess of the yield strength of thedie steel. Plastic deformation is quite commonat small convex radii, or when long thin toolingcomponents e.g. punches, are subjected to highbending stresses.The following can be the cause of plasticdeformation in forging dies: too low billet temperature (high flow stress ofwork material) inadequate hot strength of die steel die temperature too high die material too soft6TOOLING APPLICATION HOT WORK TOOLING
DIE MATERIAL PROPERTIESThe properties profile required for tool steel inforging dies depends to some extent on thetype of forging operation, on the work materialand on the size of the part, depth of cavity etc.However, a number of general characteristicswill always be required in all forging operations.The particular die damage mechanism are givenin parentheses. Sufficient hardness and ability to retain this atelevated temperatures—temper resistance(wear, plastic deformation, thermal fatiguecracking).FORWARD EXTRUSIONTubeRodPunchWorkmaterialDieBACKWARD EXTRUSIONCan Enhanced level of hot tensile strength and hothardness (wear, plastic deformation, thermalfatigue cracking). Good toughness and ductility at low andelevated temperatures (gross cracking,thermal shock cracking, thermal fatiguecracking). It is important that the die steelexhibits adequate toughness/ductility in alldirections.OPEN DIE EXTRUSIONReducing Adequate level of fatigue resistance (grosscracking). Sufficient hardenability (retention of wearresistance etc. if the die is resunk). Amenability to weld repair.LATERAL EXTRUSION Good machinability, especially prehardeneddie blocks.WARM FORGINGWarm forging is a precision forging operationcarried out at a temperature range between550–950 C (1020–1740 F). It is useful for forging of details with intricate shapes, with desirable grain flow, good surface finish and tighterdimensional tolerances than if hot forged.The weight of the forged piece is between0.1–50 kg (0.22–110 lbs) and the production rateabout 10–40 pieces per minute. The contact timeis about 200 ms and the mechanical loads at 600 C(1110 F) are 3 to 5 times higher than in hot forging.Automatic multistation presses with integratedcooling/lubricating systems are often used.IRONINGHEADINGUPSETTINGTypical processes in warm forging.TOOLING APPLICATION HOT WORK TOOLING7
TYPICAL FAILURESDuring the warm forging operation the tool partsare exposed to rather high temperature, highmechanical loads and intensive cooling.As a result of this alternate heating and coolingthe tool parts are subjected to high thermal fatigue.An additional factor is the degree of hot wearof the material, which depends on the surfacetemperatures and the mechanical stresses onthe tool.TOOL MATERIAL PROPERTIESThe tool parts are subjected to both highmechanical stresses and high thermal stresses.For these reasons a tool steel has to bechosen which has a good temper resistance,good wear resistance, high hot yield strength,good thermal conductivity and good thermalfatigue resistance. A warm forging steel mustexhibit a properties profile which is in betweenthe typical properties profiles for hot work andcold work steel.PROGRESSIVEFORGINGIn progressive forging a large number ofsymmetrical, precision-forged parts with forgedweights of up to about 5 kg (11 lbs) are produced. The fully automatic process involvessupplying hot rolled bars at one end of the line,heating them inductively, cutting them to therequired size, shaping them in 3–4 stages anddischarging finished forgings at the other end ofthe line.Depending on the weight of the forgings,production capacity is between 50 and 180 perminute.TYPICAL FAILURESTool parts used in the progressive forging,such as die, stem, stem holder, punch andcounter punch-ejector are subjected to veryhigh stresses.As the production speed is very high, thedie parts need to be water-cooled to protectthem against overheating. Nevertheless, despite intensive cooling, the tool surfaces can bestrongly heated, even by the brief contact, withthe hot metal being forged.As a result of this alternate heating and cooling the die parts are subjected to extremely highthermal fatigue. The degree of the thermal fatiguecracking constitutes a measure of the material life.An additional factor is the degree of hot wearof the material, which depends on the surfacetemperatures and the mechanical stresses onthe die.TOOL MATERIAL PROPERTIESThe required properties profile of the hotforming die and die parts are: high temperature strength and good temperresistance to withstand hot wear and thermalfatigue cracking good thermal conductivity to withstandthermal fatigue cracking good hot ductility and toughness to resistinitiation and rapid spread of thermal fatiguecracking8TOOLING APPLICATION HOT WORK TOOLING
FORGING IN A FULLY AUTOMATIC 11Two-part cutting bushWork metalStopperCutterBlankStem/PunchHollow punchBolsterCounter punch-ejectorDieWaste metalPiercerProductTOOLING APPLICATION HOT WORK TOOLING9
EFFECT OFFORGING PARAMETERSON DIE LIFEApart from the influence of the actual diematerial and its heat treatment/surface treatment, a number of parameters related to theforging operation affect die life: billet temperatureTYPICAL HOT FORGINGTEMPERATURESSTEEL1050–1250 C (1920–2100 F)CU-ALLOYS650–800 C(1200–1470 F)AL-ALLOYS350–500 C(660–930 F)TI-ALLOYS800–1000 C(1470–2010 F)BILLET SHAPE ANDSURFACE CONDITION billet shape and surface condition work material cavity stress level and contact time type of forging operation type of lubricantBILLET TEMPERATUREReduced billet temperature in forging is favourable from the viewpoint of mechanical properties in the forged part itself. This is particularly important if the components are not heattreated after forging. However, the higher flowstress of the work material, which is associatedwith a reduced forging temperature, results inboth increased wear and a higher risk for plasticdeformation. Further, since the forging loadsincrease, the probability for gross cracking isenhanced.The greater the difference between the shape ofthe billet and that of the final forging, the greateris the degree of wear because the relativemovement between work material and die mustincrease. Likewise, hard, adherent scale on thebillet surface will increase wear, especially if thegliding distance is large.WORK MATERIALThe higher the flow stress of the work material,the faster is die deterioration due to wear and/orplastic deformation, at the same time as the riskfor gross cracking is increased. Hence, stainlesssteel is more difficult to forge than carbon steelat the same sModerateNi- andCo- ACT ENERGY OR PRESS POWERForgeability of different types of material.10TOOLING APPLICATION HOT WORK TOOLING
CAVITY STRESS LEVELAND CONTACT TIMEAn increased stress level in the cavity, can befound, for example, in high precision forging,and has the following consequences: increased stress in the tool with higher risk fordeformation or gross cracking increased heat transfer from billet to die(heat checking) more pronounced wearProlonged contact between billet and die duringforging results in accelerated wear and a greaterrisk for heat checking. For very long contacttimes, the surface layer of the tool may becomeso hot that it transforms to austenite. Crackingproblems can then be experienced if this layerrehardens during the cooling part of the cycle.TYPE OF FORGING OPERATIONBecause of the much higher impact load,hammer dies tend to fail by cracking to anextent which is greater than in press forgingwhere the loading rate is lower. Thermal fatigue(heat checking) is more common in powderforging and other near-net-shape forgingprocesses involving long contact times.TYPE OF LUBRICANTOil-based lubricants can give rise to excessivewear/erosion due to the explosion-like combustion of the oil between billet and cavity. On theother hand, water base lubricants cool the diesurface to a greater extent which increases therisk of thermal fatigue cracking.DIE DESIGNAND DIE LIFEAssuming that the forging equipment is ingood condition (properly adjusted and withoutexcessive play in the ram guide system), thenadherence to the following “die design” principles will reduce the risk for catastrophic diefailure: proper die support dovetails, if used, should be properly dimen-sioned, have sufficiently large radii and beproperly finished (grinding marks should betangential and not axial), see figure below. sufficient wall thickness, and sufficientmaterial below the cavity and betweenindividual cavities adequate radii and fillets in the cavity proper dimensioning of flash land and gutter proper design of parting plane and, if used,die locks correct use and design of setting plugs,punches and knockout pins sufficiently large cushion-face area in hammerforging in relation both to die block thicknessand to the capacity of the hammer usedImproper die support, insufficient materialthickness in the die and too small radii are allvery common reasons for a die failing catastrophically by cracking, and will be furtherenlarged upon.Grinding of dove-tail radii.TOOLING APPLICATION HOT WORK TOOLING11
DIE SUPPORTIt is very important that the die is properlysupported underneath by a perfectly flat backing surface with sufficient hardness. Concavedepressions in the support surface immediatelyunder the die cavity are particularly deleteriousbecause they exaggerate the tensile stresses atradii.Proper backing is especially important inhammer forging because there is usually no sidesupport in this case. When dies of greatly different dimensions are used on the same press orhammer, it is essential to remove any cavities inthe backing block or plate when switching froma small to a large die.For press forging, side support of the die isdesirable but this is not always possible. Shrinkfitting of inserts into a massive holder providesthe best security against cracking in press dies.Hmin,inch mm16 40014 35012 30010 2508 2006 1504 10010 2550751000.4 1234hmax1255150 mm6 inchMinimum height (Hmin) of hammer dies with a maximumdepth of cavity (hmax).hmaxFILLET RADIIThe greatest tensile stresses in a forging dieoccur at the radii between the sides and bottomof the cavity. The smaller the radius, the higherthe stresses. In general, the forging should bedesigned so that die fillet radii less than 2 mm(0.08 inch) can be avoided. For deeper cavities, 50 mm ( 2 inch), this radius limit needs to beincreased to 5 mm (0.2 inch).It is especially important during die makingthat radii are ground and polished with grinding marks, if any, in the tangential direction. Inparticular, EDM residues, which may containcracks, must be removed completely at radii(and preferably from the rest of the die as well).If this is not possible, then the die should atleast be retempered at 25 C (50 F) below theprevious tempering temperature.DIE MATERIAL AND WALL THICKNESSA number of more or less empirical methods ordimensioning of forging dies are available,which range in complexity from simple “rule ofthumb” to fairly advanced nomograms with atheoretical base. However, there is no doubtthat the stresses imparted to the die by a givenforging machine increase profoundly as the diedimensions are decreased.12TOOLING APPLICATION HOT WORK TOOLINGHminAs a rule of thumb for solid die blocks in pressforging the thickness below the cavity should beat least 1.5 x cavity depth.As a minimum wall thickness in hammer forgingthe recommendations are according to the tablebelow.tDepth of cavity 4.96.3Distancecavity to outeredge of a die .35.16.3Mnimum wall thickness (t) recommended in hammerdies between cavity and outer edge.
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REQUIREMENTSFOR DIE MATERIALHARDENABILITYIn large press or hammer dies made frompre-hardened die steel, it is important that thehardness is uniform throughout the block. If thedie steel has too low hardenability, the block willbecome softer away from its outer surface anddie life for deep cavities or after progressiveresinking will be impaired.TOUGHNESS AND DUCTILITYThe surface of the cavity can during use easilydevelop small cracks or other blemishes whichmay propagate in an unstable manner under theaction of the high forging stresses, especially atradii etc. Notch toughness indicates the abilityof the die material to resist crack developmentfrom such defects.All products, in the Uddeholm tool steelprogramme for the forging industry, are characterized by the highest levels of toughness andductility in all directions in the bar or block.Hence, the forger can rest assured that theresistance to gross cracking is the highest possible in dies made from Uddeholm die steel.Proper die preheating will considerably reducethe risk for catastrophic failure via cracking.plotted against tempering temperature for giventempering time. Another method of presentingtemper resistance data is to plot room temperature hardness against time at a given temperingtem
Progressive forging 8 Effect of forging parameters on die life 10 Die design and die life 11 Requirements for die material 14 Manufacture and maintenance of forging die 16 Surface treatment 17 Tool steel product programme – general description 19 – chemical composition 20 – quality comparison 20 Tool steel selection chart 21 Cover illustration: Connecting rod forging tool. Most of the .
General Catalog of TOOL STEELS Hitachi Metals, Ltd. COLD WORKING TOOL STEELS COLD WORKING TOOL STEELS SLD MAGIC HOT WORKING TOOL STEELS DIE STEELS FOR DIE CASTING . Cold die steels, alloy tool steels and carbon tool steels Furnace type Salt bath Holding time (sec) Thickness X multiple 5 60
Drop forging Drop forging is carried out by impacting material with a hammer or by applying a great amount of pressure with a forging press or forging machine. When forging with a hammer the forging piece is o
Classification of tool steels 1. According to the method of quenching, such as water-hardening steels, oil-hardening steels and air-hardening steels. 2. According to alloys such as carbon tool steels and alloy tool steels. 3. According to applications such as shock-resisting steels, cold-working steels, hot-work
Uddeholm produce and deliver high quality Swedish tool steel to more than 100,000 customers in over 100 countries. Wherever you are in the manufacturing chain, trust Uddeholm to be your number one partner and tool steel provider for optimal tooling and production economy. CONTENTS. Introduction4 Tool steel fundamentals 5. Tool steel selection 12
:2016，Heat-treatable steels, alloy steels and free- cutting steels - Part 2: Alloy steels for quenching and tempering . ISO 683-3:2022，Heat-treatable steels, alloy steels and free-cutting steels - Part 3: Case-hardening steels . ISO 683-5
Relation of design to heat treatment 25 and chemical compositions of steels 26 9.1. Structural steels 26 9.2. Tool steels I 31 9.3. Stainless and heat resisting steels 32 Recommended heat treatments 34 10.1. Structural steels 34 10.2. Tool steels 35 Stainless and heat resisting steels 35 a. Group I—Hardenable chromium
Uddeholm Caldie or Uddeholm Vanadis 4 Extra. APPLICATIONS The properties profile of Uddeholm Sverker 21 combine to give a steel suitable for the manufacture of medium run tooling for applications where abrasive wear is dominant and the risk of chipping or cracking is not so high, e.g. for blanking and forming of thinner, harder work materials.
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