EP1274872B1 - Method for the production of nitrogen alloyed steel, spray compacted steel - Google Patents

Abstract

Nitrogen alloyed steel produced by spray compacting contains (in wt.%): 0.8-2.5 C, 0.03-0.75 N, 0.15-1.8 Mn, not more than 1.0 P, not more than 0.03 S, not more than 0.05 S, 5.0-11.5 Cr, 0.5-6.0 Mo, not more than 4.0 V, not more than 4.0 Nb, not more than 3.5 W, not more than 0.005 O2, and optionally further alloying components and a balance of iron and the usual impurities. Independent claims are also included for: (a) a process for the production of the steel comprising spray compacting the steel using nitrogen as the spray gas; heat treating at up to 1150[deg] C; cooling; heating to the austenitic temperature of 1075-1225[deg] C; quenching; and annealing at 150-625[deg] C; and (b) a composite material containing the steel.

Description

The invention relates to a method for manufacturing of a nitrogen alloyed, ledeburitic steel with high wear resistance.

For tools and components that have a high Wear resistance will be common ledeburitic chrome steels are used. Such steels are for example in the steel-iron list among the Material numbers 1.2080 (X210Cr12), 1.2201 (X165CrV12), 1.2376 (X96CrMoV12), 1.2378 (X220CrVMo12-2), 1.2379 (X155CrVMo12-1), 1.2380 (X220CrVMo13-4), 1.2436 (X210CrW12), 1.2601 (X165CrMoV12), 1.2880 (X165CrCoMo12) as well as 1.2884 (X210CrCoW12). The concerned Steels each have a carbon content of more than 0.9% by mass, chromium contents of more than 10% by mass and various additives of the elements molybdenum, vanadium and Tungsten on. They are mainly used to manufacture Tools and components used for the Cutting or cold forming of metals or the Processing of plastics are used.

The known steels of the type explained above are placed in an electric arc furnace Ambient pressure melted. After tapping the melt is this with ladle metallurgical processes, for example with a pan oven or Degassing plant, further treated to be dissolved in the steel Gases, such as those contained in the respective steel Hydrogen, oxygen and nitrogen shares too reduce. For deoxidation in particular Element silicon in mass contents between 0.1 and 0.4% used to dissolve in the liquid melt Bind oxygen to oxides. These are then with the refining slag deposited.

The nitrogen solubility in manufacturing in Electric slag furnace under ambient pressure is natural very low. For example, H. Berns and J. Lueg in "Nitrogen Alloyed Tool Steels", Neue Hütte 36 (1991) 1, pp. 13 -18 that in pure Melting iron at a temperature of 1600 ° C only Dissolve 0.04% nitrogen. Because these levels also in the course of the ladle metallurgical treatments mentioned be further reduced in this way experience shows that steels only Nitrogen contents between 0.005 and 0.025 mass% lie.

If there are special requirements for their purity and the degree of segregation are discussed standing steel in addition according to an electric slag or Arc vacuum remelting process remelted. After pouring the melt into blocks or as a strand or after the additional remelting the blocks or the continuously cast bars by one Hot forming, such as forging or rolling, in the brought different delivery dimensions.

Because of their different carbon or The known ledeburitic have carbide contents Chrome steels in hardened and tempered condition different levels of wear resistance. there are the carbides because of those in block or continuous casting unavoidable segregations in rows and distributed unevenly in the material structure. this applies even if the steels after the block or Continuous casting have been remelted.

For example, the carbide distribution always leads to Problems if from one of the well-known chrome steels Component, for example a tool, are manufactured should have good cutting edge stability Has. Problems have also been identified in practice if finely contoured tool areas, such as for example threads in thread rolling jaws should be. The existing structure of the Carbide brings that in such applications Risk of crumbling and flaking, which results in the service life of the respective tools reduce considerably.

In addition to the prior art explained above from JP (A) 09078199 a conventionally produced steel known, the (in wt .-%) 0.7 - 1.5% C, max. 1.6% Si, max 1.0% Mn, 6.0 - 13.0% Cr, Mo and / or W in Held the condition (Mo + 1 / 2W) = 0.7 - 3.0%, 0.15-1.5% V, 0.025-0.15% N and the balance iron and contains unavoidable impurities. With C contents, this steel can also exceed 0.9% 0.15-1.5% Nb. The so composed Tool steel is said to have high wear resistance possess that is combined with great toughness. A high hardness of the known steel can conventional curing can be achieved.

The object of the invention was a method for the manufacture of a steel material that specify a further improved wear resistance and Has dimensional stability.

C: 0,8 - 2,5 %

N: 0,03 - 0,75 %

Si: 0,15 - 1,8 %

Mn: ≤ 1,0 %

P: ≤ 0, 03 %

S: ≤ 0,05 %

Cr: 5,0 -11,5 %

Mo: 0,5 - 6,0 %

V: ≤ 4,0 %

Nb: ≤ 4,0 %

W: ≤ 3,5 %

O₂: ≤ 0,005 %

   und als Rest Eisen und übliche Verunreinigungen,
   wobei ein der Summe seiner gewichteten Gehalte an Cr, Mo, V, Nb und W entsprechender Verschleißfaktor S_V folgende Bedingung erfüllt:
   0,55 < S_V < 3,42 mit: SV = (ACr/9,33) + (AMo/17,22) + (AV/3,92) + (ANb/7,15) + (AW/14,14),

A_Cr : Cr-Gehalt in Masse-%,

A_Mo : Mo-Gehalt in Masse-%,

A_V : V-Gehalt in Masse-%,

A_Nb : Nb-Gehalt in Masse-%,

A_W : W-Gehalt in Masse-%,

   und wobei das Silicium-Stickstoff-Verhältnis V_SiN folgende Bedingung erfüllt:
   0,21 ≤ V_SiN < 3,31 mit:

V_SiN = A_Si + 2 A_N

A_Si : Si-Gehalt in Masse-%,

A_N : N-Gehalt in Masse-%,

   umfassend folgende Arbeitsschritte:

• Sprühkompaktieren des Stahls unter Verwendung von Stickstoff als Sprühgas ,
• Warmumformen des Stahls nach dem Sprühkompaktieren bei Anfangstemperaturen von bis zu 1150 °C,
• Abkühlen des warmumgeformten Stahls,
• Wiedererwärmen des abgekühlten Stahls auf eine Austenitisierungstemperatur von 1075°C bis 1225 °C,
• Abschrecken des wiedererwärmten Stahls und
• Anlassen des abgeschreckten Stahls bei Temperaturen von 150 °C - 625 °C.

This object is achieved by a method according to claim 1 for the production of a nitrogen-alloy steel of high wear resistance with the following composition (in mass%):

C: 0.8 - 2.5%

N: 0.03 - 0.75%

Si: 0.15 - 1.8%

Mn: ≤ 1.0%

P: ≤ 0.03%

S: ≤ 0.05%

Cr: 5.0 -11.5%

Mo: 0.5 - 6.0%

V: ≤ 4.0%

Nb: ≤ 4.0%

W: ≤ 3.5%

O ₂ : ≤ 0.005%

and the balance iron and usual impurities,
a wear factor S _V corresponding to the sum of its weighted contents of Cr, Mo, V, Nb and W fulfills the following condition:
0.55 <S _V <3.42 with: S V = (A Cr / 9.33) + (A Mo / 17.22) + (A V / 3.92) + (A Nb / 7.15) + (A W / 14.14)

A _Cr : Cr content in% by mass,

A _Mo : Mo content in% by mass,

A _V : V content in mass%,

A _Nb : Nb content in% by mass,

A _W : W content in mass%,

and the silicon-nitrogen ratio V _SiN fulfills the following condition:
0.21 ≤ V _SiN <3.31 with:

V _SiN = A _Si + 2 A _N

A _Si : Si content in% by mass,

A _N : N content in mass%,

comprehensively the following steps:

• Spray compacting the steel using nitrogen as the spray gas,
• Hot forming of the steel after spray compacting at initial temperatures of up to 1150 ° C,
• Cooling the hot-formed steel,
• Reheating the cooled steel to an austenitizing temperature of 1075 ° C to 1225 ° C,
• Quenching the reheated steel and
• Tempering the quenched steel at temperatures from 150 ° C - 625 ° C.

An alloy steel produced according to the invention by spray compacting is distinguished, in contrast to steels produced by melt metallurgy, by a high carbon and an increased nitrogen content with a high content of special carbide-forming and nitride-forming elements, as a result of which a high wear resistance is achieved. The hard phases contained are predominantly in the form of carbide precipitates of the type MC (with M = V, Nb, W) and M ₇ C ₃ (with M = Cr, Mo) and in the form of carbonitride precipitates in the form of the phases M (C, N) (with M = V, Nb, W) and M ₇ (C, N) ₃ (with M = Cr, Mo) are present, because of the addition of nitrogen and the manufacturing process used, their size is optimized and homogeneously distributed in the microstructure , On the one hand, this leads to the fact that workpieces produced from steel produced according to the invention have increased durability even under abrasive loads. On the other hand, steel produced according to the invention can be hot worked well due to the homogeneity of its structure, despite the high alloy and hard phase contents. These properties make steel produced according to the invention particularly suitable for the production of tools or components which are subject to high wear stresses, such as are generally given, for example, when cutting materials or in the plastics processing industry because of the filler contents of modern plastics.

It has been found that according to the invention generated, produced by spray compacting nitrogen alloyed steels compared to ledeburitic Steels of the type discussed at the beginning in relation to the a particular application Wear resistance and / or an improved Possess tenacity. As a result, the improved Properties of steels produced according to the invention into one Increasing the service life of these steels manufactured tools or components. So point Cutting tools that are produced from an inventive Steel are made an improved Cutting edge stability and an improved Cutting edge stability. They also own out Steels produced according to the invention Components have improved resistance to Cracking. Furthermore, one according to the invention steel produced using an appropriate Heat treatment process to a hardness of up to 68 Harden HRC.

The advantages of a steel produced according to the invention are, as mentioned, by its alloy components in combination with a special production method, the spray compacting known per se. At the Spray compacting steel is done in a gas atomizer a molten steel in an inert gas flow in spherical drops atomized. Through the gas, the Metal drops quickly cooled to a temperature that between liquidus and solidus, often even below Solidus. The so cooled down, with high Moving speed and a firm or pasty Drops with a consistency compact due to the their own kinetic energy on a substrate a dense material composite. About the quick Solidification from the liquid phase can build up directly affects the structure of the sprayed block become. In detail, the spray compacting is in the Essays "Near net-shape casting through metal spray deposition - The Osprey process ", Otto H. Metelmann et al., Iron and Steel Engineer, November 1988, pp. 25-29, or "The Osprey Process: Principles and Applications", A.G. Leatham et al., The International Journal of Powder Metallurgy, Vol. 29, No. 4, pp. 321-329.

In particular, spray compacting has proven to be proven effective method to get the one you want Nitrogen content in the mentioned ledeburitic steels contribute. Unlike with the usual for Embroidery of steels used, expensive Processes such as the pressure electroslag remelting process under nitrogen partial pressures of up to 42 bar or that powder metallurgical embroidery of metal powder Ammonia, spray compacting excels both through its effectiveness as well as through its Economy. When testing the The method according to the invention was achieved by spraying with a nitrogen gas in the solidified block adjust up to 0.85 mass% nitrogen. About that With this procedure there is also the possibility the melt before spraying with feedstocks such as Chromium nitrogen or nitrided ferrochrome with one Pre-alloy the basic amount of dissolved nitrogen and the Continue embroidering metal droplets in the gas stream.

In contrast to casting, this enables Spray compact the production and segregation pore-free products that have a homogeneous structure and a have high density. At higher Flexibility in terms of shape and less Process steps similar product properties as in the powder metallurgical manufacture of such products be achieved.

Steels produced according to the invention with particularly excellent Properties show next to the rest Alloy components have a C content of 1.0 - 1.9 % By mass, an N content of 0.05-0.5% by mass, an Si content 0.15 - 1.5 mass%, a Cr content of 5.0 - 10.0% by mass, an Mo content of 0.5-5.5% by mass, a V content ≤ 3.5% by mass, an Nb content ≤ 3.5 Mass% and a W content ≤ 3.0%. so composite steels are particularly high Wear resistance.

A carbon content of more than 1 mass% and a Nitrogen content is more than 0.05 mass% advantageous to have a hardness of more than 60 HRC achieve. At the same time, the presence of the Carbon and nitrogen also the amount of contained hard phases and thus the wear behavior favorably influenced.

Especially by alloying with nitrogen a homogenizing effect when spray compacting the microstructure and a limitation of the hard phase size. This has a positive impact on the Toughness properties of steels produced according to the invention. contents of the element nitrogen, which has a value of 0.75 Mass% exceed, however, cause a Deterioration of wear behavior due to high Residual austenite content and greatly reduced Hard phase sizes.

Usually in steels for reasons of deoxidation only a small amount of silicon is in one steel according to the invention with a mass content of 0.1% up to preferably 1.5% by mass, since it is in the Basic matrix remains solved and the secondary hardness increases. In addition, it has been found that with increasing Silicon content a decrease due to increasing Nitrogen levels caused residual austenite levels is achieved. This diminishes as "softer" Structural component the wear resistance. So complement and influence each other in the specified Limits contained in steel according to the invention Nitrogen and silicon in their effect on hardness and Wear resistance in an optimal way. The mutual impact of nitrogen and Silicon contents on the residual austenite content go out Fig. 1 shows in which the X-ray measured austenite levels in ledeburitic Chrome steels of the type according to the invention depending on Silicon and nitrogen content are given (Heat treatment: 1075 ° C / 15 min in a warm bath and 560 ° C / 1h in air).

The presence of Tungsten for achieving hardness in one Steel produced according to the invention is not absolutely necessary is because the minimum contained special carbide formers sufficient for the formation of the required hard phases. To avoid increased manufacturing costs, therefore an addition of tungsten to the invention used steel can be dispensed with.

Cobalt is in a composition according to the invention Steel not included as this item is negative Can affect toughness and become a Would increase the cost of materials.

The chromium content is limited to values ≤ 11.5 mass% and is preferably in the lower specified Salary range to also increase the toughness of the to influence steel produced according to the invention positively.

Depending on the application, it can also be beneficial if Steel produced according to the invention further precipitation hardening Elements such as up to 0.75 mass% Nitrogen, up to 0.05 mass% boron, up to 0.5 mass% Titanium, up to 0.5% by mass of zirconium and / or up to 0.25 % By mass aluminum. Through these additional Alloy components can be hardness and thus Wear resistance of a steel produced according to the invention can be further increased.

It has been found that a steel produced according to the invention has an optimized wear resistance if the wear factor S _V corresponding to the sum of its weighted contents of the carbide-forming elements Cr, Mo, V, Nb and W is between 0.55 and 3.42.

At the same time, an optimized silicon-nitrogen ratio V _{SiN must be} set in order to influence the effect of the austenite-stabilizing element nitrogen by the ferrite-stabilizing effect of the element silicon and to further optimize the wear resistance in the steels according to the invention. It has been shown that if the range of 0.21 to 3.31 provided for the nitrogen-silicon ratio according to the invention is observed, the residual austenite components which are harmful to the wear resistance can be reduced to values ≤ 25% after a single tempering process.

According to a further advantageous embodiment of the Invention contains nitrogen alloys produced according to the invention Steel additional hard materials, such as titanium carbide (TiC), Silicon carbide (SiC), niobium carbide (NbC), chromium carbide (CrC), titanium nitride (TiN) tungsten carbide (WC), in its Matrix, which in the course of spray compacting as a solid Particles have been injected into the spray. This Measure causes a further increase in Resistance to wear, being the good Toughness properties of the nitrogen alloy matrix remain.

The tempering is preferably carried out at temperatures between 150 ° C and 300 ° C or between 500 ° C and 625 ° C. In contrast to pressure-embroidered steels when carrying out the method according to the invention due to the optimal setting of the silicon-nitrogen ratio a freeze for Austenite transformation is not required. If adhered to the process parameter according to the invention can be a hardness up to 68 HRC can be achieved even when on the move additional processing steps for further processing required are. The hot forming can be done by Forging or rolling take place.

Finally, a steel produced according to the invention can be special can be used well to produce a composite material, the at least one produced by a first steel first layer and at least a second, by one spray-compacted steel according to the invention formed has second layer, the steel of the first Layer has a different composition than that spray compacted steel. With such a Composite material can be the different Properties of the individual layers in an optimal way can be combined with each other. So he can steel according to the invention for example on a tough first layer a wear-resistant top layer form.

The invention is described below with reference to Embodiments explained in more detail.

Table 1 shows the chemical compositions of seven steels A - G in mass%. In addition, the wear factor S _V , the silicon-nitrogen _ratio V _SiN and the abrasion determined in a wear test in grams are recorded for each of the steels.

Steels A - D are those produced according to the invention Steels, while steels E - G are given for comparison are.

For the production of spray-compacted, nitrogen-alloyed Steels are made of scrap and / or pure metals, respectively with the addition of the necessary alloy components a melt has been created. Then the Melt in a protective gas stream containing nitrogen spherical droplets have been atomized.

In the course of atomization in the nitrogenous Gas flow was nitricked and cooled quickly the metal droplets to a temperature between the liquidus and Solidus, so that the droplets after cooling in Gas flow had a solid to pasty consistency. They were so designed, with a high Speed of droplets moving from 40 to 80 m / s aimed at a base plate on which the droplets due to their high kinetic energy compacted a dense material composite. The on block thus produced by spray compacting due to the rapid solidification occurring in the gas flow the metal droplets from the liquid phase and due to the introduced nitrogen content an even Distribution of hard phases and carbide or Carbonitride sizes compared to steels produced by melting metallurgy are reduced.

Figures 2 and 3 each show the micrograph of a by spray compacting in the manner according to the invention produced, nitrogen alloy steel in the annealed State, with the respective microstructure in FIG an enlargement of 100: 1 and in Fig. 3 with a Magnification of 500: 1 is shown.

Figures 4 and 5 show a comparison corresponding representation of the microstructure of the same Steel without added nitrogen if it is in is conventionally produced by melt metallurgy.

The one that is readily apparent from FIGS. 2 and 3 high structural homogeneity enables problem-free Forming the spray-compacted block by forging or rollers. Prior to the forming, a block or diffusion annealing.

The improved formability produced according to the invention Steels makes it possible to thermoform compared to the conventional approach to lower temperatures perform. The hardness required in each case the components produced according to the invention or tools can be shaped by Hardening from an austenitizing temperature between 1075 ° C and 1225 ° C with subsequent tempering between Set 150 ° C and 625 ° C, with hardnesses of up to 68 HRC can be achieved.

Steels according to the invention have a balanced ratio between the carbide- or carbonitride-forming elements, which is characterized by the wear factor S _V , which lies between 0.55 and 3.42 and is determined in the manner explained above. This balanced ratio of carbide / carbonitride formers leads to a superior wear resistance of steels produced according to the invention, which was confirmed in wear tests (FIG. 6).

In these tests, the wear behavior of steels A - G with rolling friction at a work of 8.0 Nm x 10 ^{-6 was} checked, whereby the counter roller was made of high-speed steel with the material number 1.3207 according to the steel-iron list and a hardness of 67 HRC.

To check the wear and shape retention of a Steel produced according to the invention in practice was in a first examination by spray compacting a raw block with a diameter of 400 mm from the nitrogen alloy steel C, whose Composition is given in Table 1. With a Long forging machine was this block in one double-hot forging to a diameter of 115 mm deformed, the forging start temperature at 980 ° C and the forging end temperature was 969 ° C.

The forged ingot was then soft annealed. The soft annealed material then became Threaded roller jaws manufactured, the dimensions of which are 85 mm x 50 mm x 24 mm and 95 mm x 50 mm x 24 mm. This Tools were subsequently turned on by heat treatment brought a hardness of 62 HRC.

With the thread roller jaws, screws were made from one stainless steel with material number 1.4401 manufactured according to the steel-iron list. The Work results and the state of wear from the Tools produced according to the invention were produced with the work results and the state of wear of Threaded roller jaws compared that from a steel produced by melting metallurgy more identical chemical composition, but without the addition of nitrogen, had been produced. It turned out that the Service life of the steel produced from the invention Threaded roller jaws were twice as long as the service life of the thread rolling jaws, which from the conventional produced steel of identical composition had been. So they got out with them Tools produced according to the invention 140,000 Manufacture screws, while those from conventionally produced Steel-made tools after the manufacture of 70,000 screws were worn out. Especially The excellent is to be emphasized in this context Dimensional stability of the steel produced according to the invention manufactured tools in the area of the thread tips.

In a second investigation, the was Spray compacted, nitrogen alloy steel C of Table 1 to a dimension of 160 mm x 160 mm forged and annealed. From the forged Steel were stamping tools for out of a micro alloy Steel existing chain links made from Sheets were punched with a thickness of 4 mm.

The results of the work and the wear behavior of the stamping tools produced from the steel produced according to the invention were again compared with a stamping tool which had been produced from a melt-metallurgically produced steel of the same composition, but without nitrogen. In this case, too, it was found that the tool produced from steel produced according to the invention had a significantly improved service life than the comparison tool. Thus, the stamping tool made from steel produced according to the invention was still ready for use after the production of 290,000 chain links, while the comparison tool was already worn out after the stamping of 200,000 chain links. In this context, the very good cutting edge stability of the punching tool produced from the steel produced according to the invention is still present, even after the production of 290,000 chain links.

Claims (9)

1. Method for the production of a nitrogen alloyed steel with high wear resistance having the following composition (in mass %):

   C: 0.8 - 2.5 %

   N: 0.03 - 0.75 %

   Si: 0.15 - 1.8 %

   Mn: ≤ 1.0 %

   P: ≤ 0.03 %

   S: ≤ 0.05 %

   Cr: 5.0 - 11.5 %

   Mo: 0.5 - 6.0 %

   V; ≤ 4.0 %

   Nb: ≤ 4.0 %

   W: ≤ 3.5 %

   O₂: ≤ 0.005 %

   with up to 0.05 % B, up to 0.5 % Ti, up to 0.5 % Zr, up to 0.25 % Al as facultative alloying constituents
   and iron and typical impurities as the remainder,
   wherein a wear factor S_v corresponding to the sum of its weighted contents of Cr, Mo, V, Nb and W satisfies the following condition:
   0.55 < S_v < 3.42 where: Sv = (ACr/9.33) + (AMo/17.22) + (AV/3.92) + (ANb/7.15) + (AW/14.14),

   A_Cr : Cr content in mass %,

   A_Mo : Mo content in mass %,

   A_V : V content in mass %,

   A_Nb : Nb content in mass %,

   A_W : W content in mass %,

   and wherein the ratio of silicon to nitrogen V_SiN satisfies the following condition:
   0.21 ≤ V_SiN < 3.31 where:

   V_SiN = A_Si + 2 A_N

   A_Si : Si content in mass %,

   A_N : N content in mass %,

   comprising the following steps:

   spray forming of the steel using nitrogen as the spraying gas,

   hot forming of the steel following spray forming at initial temperatures of up to 1150 °C,

   cooling down of the hot formed steel,

   reheating of the cooled steel to an austenitising temperature of 1075 °C to 1225 °C,

   quenching of the reheated steel and

   tempering of the quenched steel at temperatures of 150 °C - 625 °C.
2. Method in accordance with Claim 1, characterised in that tempering takes place at temperatures between 150 °C and 300 °C.
3. Method in accordance with Claim 1, characterised in that tempering takes place at temperatures between 500 °C and 625 °C.
4. Method in accordance with one of the previous claims, characterised in that the steel has a C content of 1.0 - 1.9 mass %, an N content of 0.05 - 0.5 mass %, an Si content of 0.15 - 1.5 mass %, a Cr content of 5.0 - 10.0 mass %, an Mo content of 0.5 - 5.5 mass %, a V content ≤ 3.5 mass %, an Nb content ≤ 3.5 mass % and a W content ≤ 3.0 mass %.
5. Method in accordance with one of the previous claims, characterised in that the steel contains up to 0.05 mass % of boron.
6. Method in accordance with one of the previous claims, characterised in that the steel contains up to 0.5 mass % of titanium.
7. Method in accordance with one of the previous claims, characterised in that the steel contains up to 0.5 mass % of zirconium.
8. Method in accordance with one of the previous claims, characterised in that the steel contains up to 0.25 mass % of aluminium.
9. Method in accordance with one of the previous claims, characterised in that the steel contains additional hard materials in its matrix such as titanium carbide, silicon carbide, niobium carbide, chromium carbide, titanium nitride, tungsten nitride, which have been injected into the spraying jet as solid particles in the course of spray forming.

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