SE1950064A1

SE1950064A1 - 3d printed high carbon content steel and method of preparing the same

Info

Publication number: SE1950064A1
Application number: SE1950064A
Authority: SE
Inventors: Ulrik Beste
Original assignee: Vbn Components Ab
Priority date: 2019-01-18
Filing date: 2019-01-18
Publication date: 2020-07-19
Also published as: SE543594C2

Abstract

The present invention relates to a 3D printed product of an iron based alloy having a narrow distribution of carbide areas and to a method of preparing the product where the HIP and hardening is combined.

Description

1 3D PRINTED HIGH CARBON CONTENT STEEL AND METHOD OF PREPARING THESAME FIELD OF THE INVENTION The present invention relates to 3D printed products of an iron based alloy With highhardness. The 3D printed products are hardened using a furnace in which theproduct obtained from 3D printing is treated during Hot Isostatic Pressure (HIP) and quenched.

BACKGROUND Today, when producing Powder Metallurgy materials, there exists a number ofdifferent techniques. One of the major methods is PM-HIP; Powder Metallurgy HotIsostatic Pressing. The technique is to atomise (granulate) a metal powder, putting thispowder into a container, sealing this container, and expose the sealed container forHIP, for example according to the standard process, at 1120-1150°C, at 100 MPa intypically 3 hours. The result is a consolidated material block which typically needs to be further processed.

The container can be of different shapes, highly dependent on the material and theshape needed for the final part. It can also be a standard cylinder shape, if the material is going to become a bar for further production.

In the latter case, for example for production of PM-HSS (powder metallurgy highspeed steels) the material block is then typically forged and rolled to final bardimensions. These bars are then typically soft annealed and then transported to astock. Later on, they are transported to a workshop where the soft machining is done,for shape of the wanted detail such as a gear hob. However, after the soft machining,the gear hob blanks are hardened in a vacuum furnace and then tempered in anotherfurnace. And finally, the hardened blanks could be ground to achieve the wanted tolerance of the surfaces.

Typically, after machining of a soft annealed steel bar, hardening of the material isperformed. One of the most common hardening process for PM-HSS is heating up to1 180°C, remain at that temperature for a hold time, and then quench down to 25- 50°C and assuring that the cooling rate minimum is 7°C / s between 1000°C and 2 800°C. The hardening is then followed by tempering, where the material is repeatedlyheated up to 560°C With >1h hold time, and then cooled to <25°C between the repetitions.

The temperatures are, of course, dependent of type of alloy and the goal for hardness.In addition, a stress revealing step (typically 600-700°C in 2h plus slow cooling to500°C and then cool down to 25°C) can be added if heavy soft machining has been done.

The result of the PM-HIP process is, beyond the powder quality, composition, forging and rolling, therefore an effect of temperature, pressure and time.

HIP process can also be utilized on 3D-printed (additive manufactured) metal alloys.The process can then act as a way to close eventual pores from the 3D-printingprocess. The process will then act to ensure a full density component. After a HIP process of a 3D-printed product, a traditional hardening process can then be used.

The result of 3D-printing, HIP and hardening process is then, in addition to powderquality, composition and 3D-printing parameters, also a result of temperature, pressure and time. Still this multiple step process is time consuming.

SUMMARY OF THE INVENTION The object of the present invention is to overcome the drawback of prior art. Thereforethe present invention provides a method where HIP and hardening are combined andunexpectedly the obtained material had improved mechanical properties incomparison with the traditionally HIP and hardened material. The present inventionalso aims at providing materials or products having a more homogenous carbide sizeor carbide area distribution. For example the hardness of the material was improved with up to 12% and the abrasion study revealed a 7.5% lower wear rate.

In a first aspect the present invention relates to a 3D printed product according to claim 1 .

In a second aspect the present invention relates to a method method of preparinga 3D-printed product comprisinga. providing a powder of an iron based alloy wherein the iron based alloy further comprises carbon and unavoidable amounts of impurities; 3 b. 3D printing a product from the iron based alloy in a free forming apparatushaving a chamber wherein the 3D printing is performed in vacuum; and c. treating the obtained product in step b byi. placing the product in a furnace; ii. heating the product to a first temperature of at least 850°C, increasingthe pressure in the furnace to a first pressure of at least 8OMPa andkeeping the product at the first temperature and pressure during a firsthold time; iii. heating the product to a second temperature of at least 950°C andkeeping the product at the second temperature and at a second pressureduring a second hold time; iv. quenching the product to a third temperature and reducing the pressurein the furnace to a third pressure, and keeping the product at the thirdtemperature and pressure for a third hold time; and v. performing a temperature cycle by heating the product to a fourthtemperature and increasing the pressure in the furnace to a fourthpressure and keeping the product at the fourth temperature andpressure for a fourth hold time, followed by lowering the temperature of the product to a fifth temperature.

All embodiments described herein are applicable to all aspects unless stated otherwise.BRIEF DESCRIPTION OF THE FIGURES Figure 1, Abrasion wear rates for Material 280 with different heat treatments. Thefigure shows the surprisingly low wear volume of Material 280-5 after combined HIPand hardening treatment in comparison with Material 280-4 after traditional HIP andheat treatment. Both using the hardening temperature of 1 180°C and a followingtempering of 3 x lh at 560°C. At the final sliding distance in the test (31 m), themeasured wear rate was 0.0055 mm3 for the 280-4 and 0.0051 mm3 for the 280-5 respectively. This corresponds to a reduction of wear rate of 7.5%.

Figure 2, SEM picture of Material 150 after a) traditional HIP and hardening (WD = 7.6mm, EHT =10.00kV, Magnification 10.00KX) and b) after combined HIP and hardeningaccording to the present invention (WD = 6.7mm, EHT =10.00kV, Magnification10.00KX). 4 Figure 3, SEM picture of Material 150 Where the edges of the carbides have beenmarked up after a) traditional HIP and hardening and b) after combined HIP and hardening according to the present invention.

Figure 4, SEM picture of Material 280 after a) traditional HIP and hardening (WD =7.5mm, EHT =10.00kV, Magnification 10.00KX ) and b) after combined HIP andhardening according to the present invention (WD = 5.9mm, EHT =10.00kV,Magnification 10.00KX).

Figure 5, SEM picture of Material 280 Where the edges of the carbides have beenmarked up after a) traditional HIP and hardening and b) after combined HIP and hardening according to the present invention.

Figure 6 SEM picture of Material 290 after a) traditional HIP and hardening (WD =6.3mm, EHT =10.00kV, Magnification 10.00KX ) and b) after combined HIP andhardening according to the present invention (WD = 4.5mm, EHT =10.00kV,Magnification 10.00KX).

Figure 7, SEM picture of Material 290 Where the edges of the carbides have beenmarked up after a) traditional HIP and hardening and b) after combined HIP and hardening according to the present invention.

Figure 8, SEM picture of Material 350 after a) traditional HIP and hardening (WD =4.6mm, EHT =10.00kV, Magnification 10.00KX ) and b) after combined HIP andhardening according to the present invention (WD = 4.5mm, EHT =10.00kV,Magnification 10.00KX).

Figure 9, SEM picture of Material 350 Where the edges of the carbides have beenmarked up after a) traditional HIP and hardening and b) after combined HIP and hardening according to the present invention.

Figure 10, a schematic illustration of the effect on the carbide area distribution of thepresent invention (dotted line) in comparison With traditional HIP and hardening (solid line).

Figure 11, a schematic illustration of the method according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION In the present application the term three-dimensional printing or 3D-printing or freeforming or additive manufacturing denotes the same thing and is used interchangeably.

In the present application the term “carbide size” denotes the vvidest part of a cross sectional area of a carbide or carbide Cluster.

In the present application the term “carbide area” denotes the cross sectional area of a carbide.

In the present application the term “carbide cluster area” denotes the cross sectionalarea of a carbide cluster. A carbide cluster are individual carbides arranged so close to each other that they act as one large carbide.

In the present application the term “average carbide area” denotes the average cross sectional area of carbides.

In the present application the term “average carbide cluster area” denotes the average cross sectional area of carbide clusters.

In the present application the term “maximum carbide area” denotes that a maximumof 10% of the carbides has this area or a larger are, preferably a maximum of 5%, more preferably a maximum of 1%.

In the present application the term “maximum carbide size” denotes that a maximumof 10% of the carbides has this size or a bigger size, preferably a maximum of 5%, more preferably a maximum of 1%.

The 3D-printed product The aim of the present invention is to present a three-dimensional (3D) printedproduct made of, or comprising, an iron-based alloy having high hardness and hasgood high temperature properties. The alloy comprises a metal matrix and grains ofcarbides embedded in the metal matrix. The alloy is based on iron (balance Fe) andcomprises carbon and chromium and may further comprise tungsten, cobalt,vanadium, molybdenum and carbon. Preferably the alloy has a very low oxygencontent, preferably an oxygen content equal to or less than 100 ppm by Weight, more preferably less than 50 ppm by Weight.

The chromium (Cr) content is equal to or greater than 2.0 and equal to or less than 22 Weight%. In one preferred embodiment the content is 3 to 10 Weight%, preferably 3.5 6 to 4.5 Weight%. In another preferred embodiment the chromium content is 18-22 Weight%, more preferably around 20Wegiht%.

The tungsten (W) content is equal to or greater than 2 and equal to or less than 13 Weight%. In one preferred embodiment the content is preferably 6 to 11Weight%.

The cobalt (Co) content is equal to or greater than 9 and equal to or less than 18 Weight%. In one embodiment the content is preferably 10 to 17 Weight%.

The vanadium (V) content is equal to or greater than 3 and equal to or less than 8 Weight%. In one embodiment the content is preferably 4 to 7 Weight%.

The molybdenum (Mo) content is equal to or greater than 1 and equal to or less than10 Weight%. In one embodiment the content is preferably 2 to 8 Weight%, more preferably 5 to 7 Weight%.

The carbon (C) content is equal to or greater than 1.0 and equal to or less than 5.0Weight%. In one embodiment the content is preferably equal to or greater than 1.4 and equal to or less than 3.0, more preferably 2.20 to 2.60 Weight%.

Besides unavoidable impurities the rest of the alloy is iron i.e. Fe balance. The amountof balanced iron depends on the amount of the other components. Typically theamount of iron is 50-70Weight%, preferably 60-65Weight%. The oxygen content in the3D printed product should be as low as possible. In the present invention the oxygen content is preferably 30ppm or less, or 20ppm or less.

The alloy may further comprise unavoidable amounts of impurities or traces ofimpurities of other elements. These elements may be but is not limited to niobium,nickel, manganese, silicon, boron, tantalum, or a combination thereof. The totalamount of said other elements or impurities is preferably less than 1 Weight%, or less than 0.5 Weight%, or less than 0.05 Weight%.

One advantage of the present invention is that it does not require the use of anyorganic binders or adhesives and therefore the 3D-printed product usually comprisesa combined content of iron, vanadium, molybdenum, carbon, tungsten, chromiumand cobalt Which is equal to or greater than 95 Weight%. In one embodiment of the invention the combined content of iron, vanadium, molybdenum, carbon, tungsten, 7 chromium and cobalt is equal to or greater than 97 Weight%. Preferably the combinedcontent of iron, vanadium, molybdenum, carbon, tungsten, chromium and cobalt isequal to or greater than 98 Weight%. More preferably the combined content of iron,vanadium, molybdenum, carbon, tungsten, chromium and cobalt is equal to or greaterthan 99 Weight%. Most preferably the combined content of iron, vanadium,molybdenum, carbon, tungsten, chromium and cobalt is equal to or greater than 99.9Weight%. In one embodiment of the invention the amount of organic compounds in the3D-printed product is equal to or less than O.1Weight%. Preferably, the amount oforganic compounds in the 3D-printed product is equal to or less than O.O5Weight%. Inone embodiment of the invention the product is essentially free from any organiccompounds. The carbon in the product is mainly in form of carbides such as tungstenand chromium carbides, but elemental carbon and elemental tungsten can also be present in the matrix.

The multiphase alloy comprises a matrix of mainly iron, carbon and chromium butmay also comprise cobalt, tungsten and/ or molybdenum. There are carbides ofchromium, vanadium, molybdenum and tungsten, CrC-types, VC and WC or W/ MoöC,present in the matrix. The carbides of the present invention are mainly W/ MoöC andVC and the total amount of said carbides is 20-30 volume% preferably 22-28volume%. The carbides of the 3D printed product are evenly distributed (Welldispersed) and the size distribution is narroW as seen in Table 3 and schematicallyillustrated in Figure 10. The maximum carbide size of the 3D printed hardenedproduct is 10um or less. In one embodiment the maximum carbide size is 5um or less,preferably 3um or less. The average carbide size is usually 5um or less, or Sum or lessor 1 um or less. The average carbide area is preferably 5um2 or less, more preferably 2um2 or less, even more preferably 1um2 or less but preferably O.25um2 or larger. Themaximum carbide area is preferably 1Oum2 or less, preferably 8um2 or less, or 5um2 orless, or 4 um2 or less. The small carbide size, carbide area and maximum carbide areaof the product according to the present invention is partly a result of the method according to the present invention.

Metal compounds that contain carbides sometimes suffer from that carbides formsclusters, stringers, dendritic or net structures Which makes the material more brittle.Typically in these types of alloys, especially With high chromium and carbon,chromium forms carbides (such as CrvCg, and CrgaCö but also other stoichiometrictypes). These carbides typically grow quickly in solidification stage Which results in large and long stringers With dimensions from lOO-lOOO um in size. These large 8 carbides reduce the macro fracture toughness and fatigue resistance in the material.Therefore, one of the advantages of the present invention is that the 3D-productcontains carbides or carbide grains that are in general smaller than those found in theprior art and are well-dispersed in the matrix. This is a result of the method according to the present invention.

One advantage of the present invention is the achievement of improved mechanicalproperties of the 3D-printed product. The hardness of the hardened product(austenitizing at 1180°C, followed by tempering three times at 560°C for 1h and thenair cooled, the temperature between the temperature stages was below 25°C) may beat least 1050 HV2kg (HV2), such as at least 1075 HV2kg, or at least 1100 HV2kg, orat least 1 125 HV2kg. In some embodiments the hardness is 1075-1 175 HV2kg or 1 100-1 150 HV2kg. The hardness was determined by using a 2kg Vickers indention(HV2).

Without being bound by theory, the mechanical properties of the present invention arebelieved to be a result of the fine microstructure of the product. The 3D-printedproduct is essentially free from dendritic structures of carbides. The carbides aresmall in size and they are evenly distributed within the matrix as seen in the figures.The alloy of the 3D-printed hardened product usually does not comprise any or onlyvery few carbides having a size equal to or larger than 15um. Instead the average size of the carbides is equal to or less than 10um, or equal to or less than 5um.

Not only does the present invention facilitate the preparation of products andcomponents that have improved mechanical properties, it also makes it possible toprepare products with advanced or complex three-dimensional shapes and forms. Theproduct may comprise cavities, channels or holes and the product may have curvedportions or spiral forms. These shapes or forms are prepared without any removal ofthe alloy besides any optional after treatments. The cavities, holes or channels may becurved, that is to say that their surfaces may be curved, helical or spiral or the like. Insome embodiments the product contains cavities where the cavities are sealed or havean opening wherein the diameter or width of the opening is less than the diameter orwidth of the underlying cavity. The product may be a cutting tool such as a millingcutter, shaper cutter, power skiving cutter, drill, milling tool etc., or a forming toolsuch as extrusion head, wire drawing die, a hot rolling roll, etc., or wear componentssuch as pumps or valve components, gliding or roll bearing rings, etc. The productaccording to the present invention also has good high temperature working properties such as wear resistance at high temperature.

The method The present method is schematically shown in Figure 1 1.

The present invention also relates to a method of preparing, from an alloy powder, a3D printed product comprising a combined HIP and hardening process. The alloy is aniron based alloy (Fe balance) further comprising carbon and unavoidable amounts ofimpurities. The ally may further comprise at least one of chromium, tungsten, cobalt,vanadium and molybdenum. In one preferred embodiment the iron based alloycomprises carbon, chromium, vanadium and molybdenum. In another preferredembodiment the iron based alloy comprises carbon, tungsten, chromium, cobalt,vanadium and molybdenum. In yet another preferred embodiment the iron based alloy comprises carbon, tungsten, chromium, vanadium and molybdenum.

In yet another preferred embodiment the alloy is as defined above. The alloy is basedon iron (balance Fe) and comprises carbon and chromium and may further comprisetungsten, cobalt, vanadium, molybdenum and carbon. Preferably the alloy has a verylow oxygen content, preferably an oxygen content equal to or less than 100 ppm by Weight, more preferably less than 50 ppm by Weight.

The chromium (Cr) content is equal to or greater than 2.0 and equal to or less than 22Weight%. In one preferred embodiment the content is 3 to 10 Weight%, preferably 3.5to 4.5 Weight%. In another preferred embodiment the chromium content is 18-22 Weight%, more preferably around 20Wegiht%.

The tungsten (W) content is equal to or greater than 2 and equal to or less than 13 Weight%. In one preferred embodiment the content is preferably 6 to 1 1Weight%.

The carbon content of the iron based alloy may be equal to or greater than 0.2 andequal to or less than 5Weight%. In one embodiment the carbon content is equal to orgreater than 2.20 and equal to or less than 2.60 Weight%. In one preferred embodiment the content is 2.30 to 2.50 Weigh%.

The chromium content may be equal to or greater than 2 and equal to or less than 30Weight%. In one preferred embodiment the content is 3.8 to 4.4 Weight%, preferably3.9 to 4.3 Weight%.

The tungsten (W) content may be equal to or greater than 2 and equal to or less than25 Weight%. In one preferred embodiment the content is equal to or greater than 5 andequal to or less than 13 Weight%. In a more preferred embodiment the content is 6 to 1 1Weight%.

The cobalt (Co) content may be equal to or greater than 5 and equal to or less than 25Weight%. In one embodiment the content is equal to or greater than 9 and equal to orless than 18 Weight%. In a more preferred embodiment the content is 10 to 17 Weigh%.

The vanadium (V) content may be equal to or greater than 2 and equal to or less than15 Weight%. In one preferred embodiment the content is equal to or greater than 5 andequal to or less than 8 Weight%. In a more preferred embodiment the content is 6 to 7 Weigh%.

The molybdenum (Mo) content may be equal to or greater than 2 and equal to or less than 20 Weight%. In a preferred embodiment the content is equal to or greater than 3 11 and equal to or less than 10 weight%. In a more preferred embodiment the content is 4 to 8 weigh%, more preferably 5 to 7 weight%.

The oxygen content in the 3D printed product should be as low as possible. Preferably the oxygen content is 30ppm or less, or 20ppm or less. 3D printing Referring now to figure 1 1. The method uses a free forming apparatus (a 3D-printer)having a chamber in which the powder is arranged. The method of free formingcomprises providing a powder of an iron based alloy (step 10) and 3D printing saidpowder step (step 12). This is done by forming a layer of a powder of an alloy in anoxygen-low environment in the chamber as defined below. The method of 3D printingmay be done as described in WO2018/ 169477 which is hereby incorporated byreference or based on the method described in WO2018/ 169477. One suitable freeforming apparatus is an electron beam apparatus (EBM) from Arcam such as theARCAM A2X. The alloy comprises carbon, tungsten, molybdenum, chromium,vanadium and cobalt in the amounts described above and the choice of alloy dependson the desired properties of the final product. The content of oxygen and otherimpurities in the reactor should be as low as possible, such as equal to or less than 10ppm (corresponding to a gas purity grade 5), or equal to or less than 1 ppm(corresponding to a gas purity grade 6) and the environment in the reactor maycomprise inert gases such as argon or helium. The vacuum pressure in the reactormay be 1-5X10-3mBar or lower, preferably 1-5X10-4 mBar or lower. In one embodimentthe initial pressure in the reactor is around 1-10X10-5mBar (1-10X10-3 Pa) and then aninert gas such as helium or argon is added to increase the pressure to 1-5x10-3mBaror lower, or preferably 1-5X10-4 mBar or lower. The powder is then melted locally byexposing the powder to an energf beam during a period of time sufficient to melt it.The energy beam may be a laser beam or an electron beam. The beam is swept acrossthe powder in a pattern. The duration of the sweep may range from milliseconds to minutes depending on the alloy and the size of the particles in the powder. The melted 12 powder is then allowed to at least partly solidify into a multiphase metal alloy. Anotherlayer of powder may then be applied on top of the solidified alloy.

In order to avoid crack formation in the product and for improving the properties ofthe same, the product is maintained at an elevated temperature (first elevatedtemperature) during the printing or the formation of the 3D-printed product. Crackformation may be due to a combination of increased internal stresses and increasedmaterial brittleness at lower temperatures. The increase in internal stresses is causedby the volume changes at the phase transformations and also ordinary thermalexpansion. The elevated temperature to avoid crack formation may be 300 °C orhigher, or 400 °C or higher, or 500 °C or higher, or 550 °C or higher, or 600 °C orhigher, or 700 °C or higher, or 800°C or higher, or 900°C or higher, but usually nothigher than 1 100°C. For example the base plate or the Working table that the productis built on may comprise a heater. The 3D-printed product may therefore exhibit atemperature gradient within during the building of the product. The heating of theproduct should be controlled so that the temperature of the built product during thebuilding process is preferably 600 °C or higher, or 700 °C or higher, or 750°C orhigher, but usually 900°C or lower or 850°C or lower, or 800°C or lower. In oneembodiment the temperature is 720°C-790°C such as 780°C. The temperature shouldof course be low enough for the melted powder to at least partly solidify before theapplication of a new powder layer. The present invention allows a lower temperaturewhich not only makes the method cheaper but may also have a positive influence on the microstructure.

In one embodiment the 3D printing comprises the steps ofA. forming a layer of a powder of the iron based alloy on a base plate in thechamber wherein the iron based alloy further comprises carbon andunavoidable amounts of impurities;wherein the powder comprises substantially spherical particles and/ orsubstantially spherical particles;B. melting the powder locally by exposing the powder to an energy beamduring a sufficient period of time to form a melt pool; andC. letting the melted powder in the melt pool solidify into a multiphasealloy;D. optionally preparing an additional layer of powder on top of the previouslayer by repeating the steps i-iii wherein step ii comprises placing the powder on top of the previous layer; 13 and wherein the product being built is kept heated at an elevated temperature during the method.

The advantage of using EBM in comparison with laser is that thicker powder layersmay be prepared and powders with larger particles may be used. The growth of thecarbides occurs during the solidification of the molten material and in order to limitthe size of the carbides the growth time should be limited. The solidification time ismainly inﬂuenced by the heat diffusion rate, the heat of solidification and the heatdiffusion distance. The solidification rate in traditional casting techniques may beenhanced by cooling down the melted material using any suitable technique, such ascasting in highly-cooled refractory molds or to cast smaller details. Also, in existingprior art cladding techniques the cooling speed is also high, but not high enough to prevent carbide growth or to receive a fully dense material.

New combined HIP and hardening . The obtained 3D printed product is the treated in a combined HIP and hardeningprocess. This may be done using a Quintus machine preferably equipped with UniformRapid Quenching (URQ®). In this combined process the 3D printed product is placedin a suitable oven or furnace (step 14). The printed product is heated to a firsttemperature of at least 850°C and the pressure is increased to a first pressure of atleast 8OMPa. The product is kept at this temperature and pressure for a first hold time(step 16) before the temperature is further increased to a second temperature of atleast 950°C. At the second temperature the product is kept for a second hold time(step 18) before rapidly quenched (cooled) to a third temperature and the pressure isalso reduced to a third pressure (step 20). The quenching may be done using anysuitable means for example gas such as inert gas. In order to obtain better mechanicalproperties and microstructure the quenching is rapid preferably done at a cooling rateof at least 10°C/s, more preferably 20°C/s, more preferably 30°C/s, more preferably atleast 40°C, more preferably up to 50°C / s. The product is kept at the third temperatureand pressure for a third hold time. After quenching and reduction of the pressure atemperature cycle (tempering) is performed where the temperature is increased to afourth temperature and where the pressure is increased to a fourth pressure. Theproduct may be kept at the fourth temperature and fourth pressure for a fourth holdtime before the temperature is lowered to a fifth temperature. The pressure may alsobe lowered to a fifth pressure. The temperature cycle may be repeated at least once, preferably twice. 14 In one embodiment the first temperature is at least 1000°C but preferably 1200°C orlower, preferably in the range of 1100°C to 1200°C, more preferably in the range of1120°C to 1150°C.

In one embodiment the second temperature is at least 1050°C preferably in the rangeof 1100°C to 1200°C, more preferably in the range of 1180°C to 1200°C. Second temperature is higher than the first temperature.

In one embodiment the third temperature is 75°C or lower. In the quenching step (step20) the temperature is in one embodiment rapidly quenched from the secondtemperature to the third temperature of 50°C or lower and wherein the third pressure is preferably 65MPa or lower.

In one embodiment the first pressure is less than 21OMPa preferably in the range of90- 12OMPa.

In one embodiment the second pressure is at least 8OMPa, preferably at least 9OMPa,or preferably at least lOOMPa, preferably less than 21OMPa, more preferably less than15OMPa. In one preferred embodiment the first and the second pressure is the same, i.e. the pressure is not changed in step 18.

In one embodiment the third pressure is in the range of 30-7OMPa, preferably 55-65MPa.

In one embodiment the fourth pressure is at least 7OMPa preferably in the range of 70-8OMPa more preferably around 75MPa.

In one embodiment the fourth temperature is in the range of 500-600°C preferably 550 to 580°C more preferably around 560°C.

In one embodiment the f1fth temperature is 50°C or lower preferably in the range of -25°C.

The hold times are dependent on the alloy composition and the thickness of theproduct. In one preferred embodiment each hold time is suff1cient so that the productobtains the set or aimed temperature or the temperature of the furnace. In onepreferred embodiment the first hold time is in the range of 1 to 4 hours preferably 3 hours. In one embodiment the second hold time is in the range of 10 minutes to 60 minutes preferably 30 minutes. In one embodiment the third hold time is in the rangeof 1 second to 1 hour or from 30 second to 30 minutes. In another embodiment the fourth hold time is in the range of 30 minutes to 3 hours preferably 1 hour.

As is seen in the examples the products according to the present invention or obtainedby the method according to the present invention has unexpectedly high hardness.This is unexpected in comparison with traditional hardening processes since thealloys treated according to traditional hardening already have been hardened to their“full hardening temperature” according to traditional knowledge. That this effect isachieved for different type steels is also evident when studying and comparing theresults from PM-HSS materials (Material 150, 280 and 290) and highly alloyed martensitic stainless steels (Material 350).

All the embodiments disclosed herein should be understood as a few illustrativeexamples of the present invention. It Will be understood by those skilled in the art thatvarious modifications, combinations and changes may be made to the embodimentsand aspects Without departing from the scope of the present invention. In particular,different part solutions in the different embodiments can be combined in other configurations, where technically possible.

EXAMPLES Example 1 The Quintus QIH 21 URQ machine has been used for comparing separate HIP andhardening and combined HIP and hardening for 3D-printed highly alloyed materials,with compositions as shown in Table 1. Four 3D-printed Fe alloys have beencompared, three high speed steel types and one martensitic stainless steel type. The3D printing was basically performed as described in WO2018/ 169477 which is herebyincorporated by reference. All four material types have first been conventionalconsolidated by HIP, hardened and tempering in conventionally manner. Then,samples from exactly the same 3D-printing batches have been treated by the newcombined HIP, hardening and tempering process with same hardening and annealing time and temperature settings as traditional. See table 1. 16 Table 1. Tested 3D-printed materials Constituting elements (weight%) Material C Cr W Co V Mo Fe Material 150 1.5 4.0 2.5 4.0 2.5 Bal Material280 2.3 4.2 6.5 10.5 6.5 7.0 Bal Material290 2.5 4.0 11.0 16.0 6.3 5.0 Bal Material350 1.9 20.0 4.0 1.0 Bal The conventional HIP parameters were heating up to 1 120-1 150°C, hold time 3h atHIP pressure 100 MPa, and then a cooling down to room temperature with following pfCSSUfC fClCaSC.

The conventional hardening was performed in a traditional vacuum furnace, heatingup the test details 1 180°C, with a hold time of approX. 30min, followed by a rapidquenching where the cooling speed in the interval 970°C -800°C is higher than 7°C/ s,and then followed by cooling in air to 25-50°C. Then, the test details were temperedthree (3) times, by heating up the details to 560°C, hold time 1h, then cooled down to °C between the three temperature cycles.

The conventional HIP parameters and hardening + tempering are all standards procedures done at large suppliers.

The new combined HIP, hardening and tempering process according to the presentinvention use the following parameters: First, the details were heated up to 1 120- 1 150°C during the same time as the pressure is increased up to 100 MPa. At thisstage, a hold time of 3h is maintained, followed by an increase in temperature up to 1 180°C is performed with a new hold time of 30 min. From this stage, a rapidtemperature quenching down to 20°C is done (where the pressure also drops down to60 MPa). Then, a temperature increase up to 560°C (followed by an increased pressureup to 75 MPa) is done three times, this is the tempering cycles. The hold time at 560°C is 1h each, and the temperature between the temperature cycles were 20°C.

The material samples have then been compared in hardness and in microstructure.The hardness measurements were done by using a 2kg Vickers indenter on grindedand polished samples by standard material analysis method with final grinding withSiC P4000, according to SS-EN ISO 6507. In this stage, the hardness was measured on several places from the pieces with the same result. 17 After cutting of samples from the treated material pieces the samples Were furthertreated to facilitate the carbide volume measurements. This preparation Was furtherpolishing by lum diamond in 5 minutes, followed by Struers OP-S solution (40um SiOg at pH 9.8), a Well-known method to facilitate carbide structure analysis.

Results The hardness of all samples is presented in Table 2. In general, the hardness after thecombined HIP, hardening and tempering process is surprisingly much higher than forthe conventional HIP and heat treatment process. For Material 150 it is 12% higher,for Material 280 it is 1 1.8% higher, for Material 290 it is 5% higher and for Material350 it is 12% higher.

Table 2. Hardness of all test samples (HV2kg)Material Hardness after Sample Hardness after Sampleconventional HIP combined HIP andand conventional heat treatmentheat treatment.Material 150 832 Mol 17 932 Mol 10Material 280 950 Mol 15 1058 Mol 11Material 290 1036 Mol 16 1088 Mol 3Material 350 675 Mol 14 757 Mol 9 The Wear resistance Was analyzed for a conventional HIP and heat treated Material 280 and the same grade With the new combined HIP and heat treatment.

The test for analyzing the abrasion resistance used is a commercial dimple grinder(Gatan), having a grinding Wheel rotating on a horizontal aXis pressed onto a samplerotating on a vertical aXis. A diamond slurry, average particle size of 2.5 um, Wasintroduced into the contact before each run. A fixed load of 20 g Was applied to thegrinding Wheel once it contacted the sample. Each test had a duration of 500 Wheelrotations Which adds up to a total sliding distance of approximately 31 m. For statistical purposes the test Was repeated three times per sample.

Cubes of the three test materials Were prepared With testing surfaces, approx. 6x6 mm, ground and polished to a surface roughness of Ra~3 um. The Wear rates Were 18 given by measuring the removed (abraded) material volume by white light optical profilometry.

The result was a 7.5% lower wear rate for the combined HIP and heat treated grade,despite that they have been hardened at the same max temperature, 1180°C, se Figure 1.Carbide calculations In the carbide size analysis, a comprehensive microstructural analysis has been performed and corresponding representative microstructures are shown here.

The most important microstructural change is the reduction of carbide (and / orcarbide cluster) area and the narrowing of the carbide area distribution, as shown inTable 3. A general trend of much smaller maximum carbides/clusters is revealed but alarger average carbide area. This suggests that the carbide area distribution is verynarrow. This indicates that the toughness of the alloys has been improved, since thetoughness of these types of hard and highly alloyed materials is set by the “largestimperfection” in the materials. These imperfections are typically some kind ofcontamination, oxide, large carbides or carbide clusters but can also be grindingerrors, white layers from too warm grinding. Also the material becomes more homogenous and isotropic with a more narrow carbide distribution.

The microstructure was analyzed in the Scanning Electron Microscope (SEM) asshown in the figures. The SEM was a Zeiss Ultra 55 FEG-SEM, using secondaryelectron image mode. The primary electron energf (EHT, extra high tension voltage))was 3, 5 and 10 keV and the aperture used was 30 (standard) or 60mm. Themicrostructure of the material showed both surprisingly high carbide content and very fine carbides, figure 2, 4, 6 and 8.

The carbides were calculated by taking the microstructure seen in for example figure 2and marking the borders of single carbides or clusters of carbides and using a suitable software.

The result could be seen in figure 3, 5, 7 and 9. The results of the calculations of the carbide areas and ratios are seen in Table 3.

Table 3. Carbide ratios, sizes and diameters based on calculations.

Material Sample Total carbide Average Carbide Maximum ratio (% area) area [um2] carbide/ carbide 19 Cluster area [pm2] Material 150 Mol 17* 13.67 0.021 2.22Mol 10 9.7 0.027 1.97Material 280 Mol 15* 25.33 0.15 4.49Mol 11 22.20 0.088 2.66Material 290 Mol 16* 30.6 0.15 11.16Mol 3 27.1 0.35 4.52Material 350 Mol 14* 21.62 0.48 8.16Mol 9 19.11 0.97 6.28 * Conventional HIP and conventional heat treatment

Claims

1. A 3D-printed product made of an iron based alloy comprising a metal matrixand grains of carbides embedded in the metal matrix; Wherein the alloy comprises Carbon: equal to or greater than 1.0 and equal to or less than 5.0 Weight%;Chromium: equal to or greater than 2.0 and equal to or less than 22.0 Weight%;Iron: balance; Wherein the alloy further comprises at least two of the elements: Tungsten: equal to or greater than 2 and equal to or less than 13 Weight%,Cobalt: equal to or greater than 9 and equal to or less than 18 Weight%,Molybdenum: equal to or greater than 1 and equal to or less than 10 Weight%,and Vanadium: equal to or greater than 3 and equal to or less than 8 Weight%; andWherein the alloy comprises unavoidable trace amount of impurities; Wherein the maximum carbide area is less than 5um2 and Wherein the average carbide area is larger than 0.25um2 but less than 2 um

2. . The 3D-printed product according to claim 1 Wherein the carbon content is equal to or greater than 1.4 and equal to or less than 3.0 Weight%. . The 3D-printed product according to claim 1 or 2 Wherein the alloy further comprises Tungsten: equal to or greater than 2 and equal to or less than 13 Weight%,Molybdenum: equal to or greater than 1 and equal to or less than 10 Weight%,Vanadium: equal to or greater than 3 and equal to or less than 8 Weight%; andoptionally Cobalt: equal to or greater than 9 and equal to or less than 18 Weight%. The 3D-printed product according to claim 1 or 2 Wherein the alloy comprisesCarbon: equal to or greater than 1.0 and equal to or less than 3.0 Weight%;Chromium: equal to or greater than 2.0 and equal to or less than 22.0 Weight%;Molybdenum: equal to or greater than 1 and equal to or less than 10 Weight%,and Vanadium: equal to or greater than 3 and equal to or less than 8 Weight%;Iron: balance; and Wherein the alloy comprises unavoidable trace amount of impurities. The 3D-printed product according to claim 1 or 2 Wherein the alloy comprisesCarbon: equal to or greater than 2.20 and equal to or less than 2.60 Weight%,Tungsten: equal to or greater than 5 and equal to or less than 13 Weight%, Chromium: equal to or greater than 3.5 and equal to or less than 4.5 Weight%, 10. 21 Cobalt: equal to or greater than 9 and equal to or less than 18 Weight%;Molybdenum: equal to or greater than 3 and equal to or less than 10 Weight%;Vanadium: equal to or greater than 5 and equal to or less than 8 Weight%;Iron: balance; and unavoidable trace amount of impurities. The 3D-printed product according to claim 1 Wherein the average carbide areais less than 1um2. The 3D-printed product according to claim 1 Wherein the iron based alloycomprises Carbon: equal to or greater than 2.25 and equal to or less than 2.40 Weight%,Tungsten: equal to or greater than 6 and equal to or less than 8 Weight%,Chromium: equal to or greater than 3.5 and equal to or less than 4.5 Weight%Cobalt: equal to or greater than 9 and equal to or less than 12 Weight%;Molybdenum: equal to or greater than 5 and equal to or less than 8 Weight%;Vanadium: equal to or greater than 5 and equal to or less than 8 Weight%;Iron: balance. The 3D-printed product according to any one of claims 1 to 7 Wherein themaximum carbide area is 4um2 or less preferably 3um2 or less. The 3D printed product according to any one of claims 1 to 8 Wherein theproduct has a hardness of at least 105OHR2kg, preferably at least 11OOHR2kg.A method of preparing a 3D-printed product comprising a. providing a powder of an iron based alloy Wherein the iron based alloy further comprises carbon and unavoidable amounts of impurities;b. 3D printing a product from the iron based alloy in a free forming apparatushaving a chamber Wherein the 3D printing is performed in vacuum; and c. treating the obtained product in step b by i. placing the product in a furnace; ii. heating the product to a first temperature of at least 850°C, increasingthe pressure in the furnace to a first pressure of at least 8OMPa andkeeping the product at the first temperature and pressure during a firsthold time; iii. heating the product to a second temperature of at least 950°C andkeeping the product at the second temperature and at a second pressureduring a second hold time; iv. quenching the product to a third temperature and reducing the pressurein the furnace to a third pressure, and keeping the product at the third temperature and pressure for a third hold time; and 11. 12. 1

3. 1

4. 1

5. 1

6. 1

7. 1

8. 1

9. 20. 21. 22 v. performing a temperature cycle by heating the product to a fourthtemperature and increasing the pressure in the furnace to a fourthpressure and keeping the product at the fourth temperature andpressure for a fourth hold time, followed by lowering the temperature ofthe product to a fifth temperature. The method according to claim 10 wherein the vacuum pressure is 1-5x10-3mBar or lower, preferably 1-5X10-4 mBar or lower and wherein the energfbeam preferably is an electron beam. The method according to claim 10 or 11 wherein the first temperature is at least1000°C but preferably 1400°C or lower, preferably in the range of 1100 to1200°C, more preferably in the range of 1120 to 1150°C; wherein the secondtemperature is higher than the first temperature. The method according to any one of claims 10 to 12 wherein the secondtemperature is at least 1050°C preferably in the range of 1100 to 1200°C, morepreferably in the range of 1180 to 1200°C; wherein the second temperature ishigher than the first temperature. The method according to any one of claims 10 to 13 wherein the thirdtemperature is 50°C or lower and wherein the third pressure is preferably65MPa or lower. The method according to any one of claims 10 to 14 wherein the first pressureis at least 90MPa, or preferably at least 100MPa, preferably less than 210MPa,more preferably less than 150MPa. The method according to any one of claims 10 to 15 wherein the fourthtemperature is in the range of 500-600°C preferably 550 to 580°C morepreferably around 560°C. The method according to claim 15 wherein the first pressure is in the range of90- 120MPa. The method according to any one of claims 10 to 17 wherein the third pressureis in the range of 55-65MPa. The method according to any one of claims 10 to 18 wherein the fourthpressure is at least 70MPa preferably in the range of 70-80MPa more preferablyaround 75MPa. The method according to any one of claims 10 to 19 wherein the fifthtemperature is 50°C or lower preferably in the range of 20-25°C. The method according to any one of claims 10 to 20 wherein the first hold time is in the range of 1 to 4 hours preferably 3 hours. 22. 23. 24. 25. 26. 23 The method according to any one of claims 10 to 21 wherein the second holdtime is in the range of 10 minutes to 60 minutes preferably 30 minutes. The method according to any one of claims 10 to 22 wherein the third hold timeis in the range of 1 second to 30 minutes. The method according to any one of claims 10 to 23 wherein the fourth holdtime is in the range of 30 minutes to 3 hours preferably 1 hour. The method according to any one of claims 10 to 24 wherein the alloy furthercomprises at least one of chromium, tungsten, cobalt, vanadium andmolybdenum. The method according to claim 20 wherein the alloy comprises Carbon: equal to or greater than 1.0 and equal to or less than 5.0 weight%;Chromium: equal to or greater than 2.0 and equal to or less than 22.0 weight%;Iron: balance; wherein the alloy further comprises at least two of the elements: Tungsten: equal to or greater than 2 and equal to or less than 13 weight%,Cobalt: equal to or greater than 9 and equal to or less than 18 weight%,Molybdenum: equal to or greater than 1 and equal to or less than 10 weight%,and Vanadium: equal to or greater than 3 and equal to or less than 8 weight%; and wherein the alloy comprises unavoidable trace amount of impurities. 27.The method according to any one of claims 10 to 27 wherein the step of 28. quenching the product is done at a cooling rate of at least 10°C/ s, preferably atleast 20°C/s, preferably at least 30°C/s, or at least 40°C/s.The method according to claim 10 wherein the 3D printing comprises the stepsofA. forming a layer of a powder of the iron based alloy on a base plate in thechamber wherein the iron based alloy further comprises carbon andunavoidable amounts of impurities;wherein the powder comprises substantially spherical particles and/ orsubstantially spherical particles;B. melting the powder locally by exposing the powder to an energy beamduring a sufficient period of time to form a melt pool; andC. letting the melted powder in the melt pool solidify into a multiphasealloy;D. optionally preparing an additional layer of powder on top of the previouslayer by repeating the steps i-iii wherein step ii comprises placing the powder on top of the previous layer; 24 and Wherein the product being built is kept heated at an e1evatedtemperature during the method.29. The method according to c1aim 10 Wherein step of performing a temperaturecycle, step v, is repeated at 1east one time, preferably two times.30. The method according to any one of c1aims 10 to 29 Wherein the secondpressure is at 1east SOMPa, preferably at 1east 9OMPa, or preferably at 1eastlOOMPa, preferably 1ess than 21OMPa, more preferably 1ess than 15OMPa.