EP0348380B2 - Use of an iron-base alloy in the manufacture of sintered parts with a high corrosion resistance, a high wear resistance as well as a high toughness and compression strength, especially for use in the processing of synthetic materials - Google Patents

Abstract

Use of an iron-based alloy for the production of sintered parts of high corrosion resistance, high wear resistance, high toughness and high compressive strength, in particular for processing plastics, having a composition, in % by weight, chromium 16.0-29.0, molybdenum 0.4-2.5, tungsten 0.3-2.0, vanadium 3.0-10.0, titanium up to 5.0, aluminium up to 1.0, boron up to 0.05, nitrogen 0.01-0.18, niobium up to 5.0, iron and preparation-related impurities as the remainder, the value formed from (% of Cr - 13) + 4.4 x (% of V - 3) + 2 x (% of Nb) + 4.2 x (% of Ti) being greater than 8.8, and the minimum carbon content of the alloy corresponding to the correlation Cmin = 0.3 + [(% of Cr - 13) x 0.06] + [(2 x % of Mo + W) x 0.03] + (% of V x 0.24) + (% of Nb x 0.13) + (% of Ti x 0.25) and the maximum carbon content of the alloy corresponds to the correlation Cmax = 0.7 + [(% of Cr - 13) x 0.06] + [(2 x % of Mo + W) x 0.03] + (% of V x 0.24) + (% of Nb x 0.13) + (% of Ti x 0.25), with the proviso that the matrix has a chromium content of at least 13% after hardening and annealing, and the carbide content is at least 25% by volume, the carbide grain size being less than 14 mu m and at least 5 % by volume of the carbides being in the form of MC carbides.

Description

The invention relates to the use of an iron-based alloy with a special composition as a material for the powder metallurgical production of parts with high corrosion resistance, high wear resistance and high toughness and pressure resistance, preferably for plastic molds, machine parts and tools for non-cutting shaping. In the plastics industry in particular, shaping parts are exposed to chemical and abrasive stresses at the same time, whereby these parts must have high material toughness, high pressure resistance and special material homogeneity due to the mechanical stresses. Such requirements are placed, for example, on materials that are used in devices for pressing fiber-reinforced or filler-containing plastics.
Austenitic steels or chromium steels with a chromium content of approx. 18%, for example alloys according to DIN material no., Are used for mechanical components such as screws etc. and also for forming and pressing tools, which are particularly exposed to corrosive stresses. 1.4528. Although such materials have sufficient corrosion resistance, the wear behavior is usually unsatisfactory in practical operation.
In order to improve or increase the wear resistance and the hardness of the steel, attempts have also been made to increase the carbide content of the alloy by means of higher carbon contents. These steels, for example alloys according to DIN material no. 1.2080 and material no. 1.2379, with a carbon content of approx. 2% and a chromium content of approx. 12%, have an improved wear resistance, but are less suitable for corrosive loads, whereby the parts behave anisotropically due to a possibly unfavorable carbide structure, are brittle or have a high tendency to break have, whereby usually there is not sufficient dimensional stability in the heat treatment.

It has also been proposed to use steels which have extremely wide range limits in their chemical composition, in particular for the carbon content, the chromium content and the vanadium content, although no indications have been given, such as an alloy which has high corrosion resistance and high wear resistance has sufficient toughness properties and high compressive strength, must be composed. Even the person skilled in the art could not learn from this how and how a combination of the required material properties can be achieved.

On the basis of this prior art, the object of the invention is to avoid the above disadvantages and, in particular, to create materials which can be used advantageously for the plastics processing industry and which, due to a special composition when using certain manufacturing processes, provide high corrosion resistance, high wear resistance and high pressure resistance have good toughness properties.

Silizium

max. 0,6

Mangan

max. 0,6

Schwefel

max. 0,015

Phosphor

max. 0,02

Chrom

18,0 - 25,0

Molybdän

0,6 - 1,7

Wolfram

0,5 - 1,5

Vanadin

3,5 - 5,6

Titan

bis 5,0

Aluminium

bis 1,0

Nickel

max. 0,5

Kobalt

max. 0,5

Kupfer

max. 0,4

Bor

bis 0,03

Stickstoff

0,03 - 0,1

Niob

bis 5,0

   Eisen und herstellungsbedingte Verunreinigungen als Rest,
wobei der Wert, gebildet aus $$\text{(\%Cr - 13) + 4,4x (\%V - 3) + 2x (\%Nb) + 4,2x (\%Ti)}$$

größer als 8,8 ist und der minimale Kohlenstoffgehalt der Legierung entsprechend dem Zusammenhang $$\begin{gathered} {\text{C}}_{\text{min}}\text{= 0,3 + [(\%Cr - 13) x 0,06] + [(2x \%Mo + W)} \\ \text{x 0,03] + (\%V x 0,24) + (\%Nb x 0,13)} \\ \text{+ (\%Ti x 0,25)} \end{gathered}$$

und der maximale Kohlenstoffgehalt der Legierung entsprechend dem Zusammenhang $$\begin{gathered} {\text{C}}_{\text{max}}\text{= 0,7 + [( \%Cr - 13)x 0,06] + [( 2x\%Mo + W)} \\ \text{x 0,03] + (\%V x 0,24) + (\% Nb x 0,13)} \\ \text{+ ( \% Ti x 0,25)} \end{gathered}$$

beträgt, zur pulvermetallurgischen Herstellung von Teilen mit hoher Korrosionsbeständigkeit, hoher Verschleißfestigkeit sowie hoher Zähigkeit und hoher Druckfestigkeit, insbesondere für Kunststofformen, Maschinenteile und Werkzeuge zur spanlosen Formgebung mit der Maßgabe, daß die Matrix nach dem Härten und Anlassen einen Chromgehalt von mindestens 13 % aufweist und der Karbidgehalt mindestens 25 Vol.-%, von welchem mindestens 5 Vol.-% der Karbide als MC-Karbide ausgebildet sind, beträgt, wobei die Karbidkorngröße kleiner als 14 µm ist.This object is achieved by the invention. The invention therefore relates to the use of an iron-based alloy with a composition in% by weight.

silicon

Max. 0.6

manganese

Max. 0.6

sulfur

Max. 0.015

phosphorus

Max. 0.02

chrome

18.0 - 25.0

molybdenum

0.6 - 1.7

tungsten

0.5 - 1.5

Vanadium

3.5 - 5.6

titanium

up to 5.0

aluminum

to 1.0

nickel

Max. 0.5

cobalt

Max. 0.5

copper

Max. 0.4

boron

to 0.03

nitrogen

0.03-0.1

niobium

up to 5.0

Iron and manufacturing-related impurities as the rest,
being the value formed from $$\text{(\% Cr - 13) + 4.4x (\% V - 3) + 2x (\% Nb) + 4.2x (\% Ti)}$$

is greater than 8.8 and the minimum carbon content of the alloy according to the context $$\begin{gathered} {\text{C.}}_{\text{min}}\text{= 0.3 + [(\% Cr - 13) x 0.06] + [(2x\% Mo + W)} \\ \text{x 0.03] + (\% V x 0.24) + (\% Nb x 0.13)} \\ \text{+ (\% Ti x 0.25)} \end{gathered}$$

and the maximum carbon content of the alloy according to the relationship $$\begin{gathered} {\text{C.}}_{\text{Max}}\text{= 0.7 + [(\% Cr - 13) x 0.06] + [(2x\% Mo + W)} \\ \text{x 0.03] + (\% V x 0.24) + (\% Nb x 0.13)} \\ \text{+ (\% Ti x 0.25)} \end{gathered}$$

is for powder metallurgical production of parts with high corrosion resistance, high wear resistance as well as high toughness and high pressure resistance, especially for plastic molds, machine parts and tools for non-cutting shaping, with the proviso that the matrix has a chromium content of at least 13% after hardening and tempering and the carbide content is at least 25 vol.%, of which at least 5 vol.% of the carbides are MC carbides, the carbide grain size being less than 14 μm.

mindestens 10,0 beträgt. Die Teile, die aus der erfindungsgemäß verwendeten Legierung nach einem pulvermetellurgischen Herstellungsverfahren gefertigt sind, müssen dabei nach dem Härten und Anlassen eine Chromkonzentration in allen Teilen der Matrix von mindestens 13 % aufweisen.It is preferred if the material has a niobium content of 0.2 to 3.0 and / or a titanium content of 0.2 to 3.5 and / or a boron content of 0.001 to 0.002. It is particularly preferred if the value is formed from $$\text{(\% Cr - 13) + 4.4x (\% V - 3) + 2x (\% Nb) + 4.2x (Ti)}$$

is at least 10.0. The parts which are produced from the alloy used according to the invention by a powder metallurgy manufacturing process must have a chromium concentration in all parts of the matrix of at least 13% after hardening and tempering.

Surprisingly, it has been shown that the alloy according to the invention from a minimum value, which takes into account the concentrations and the respective effect with the mutual influence of the carbide-forming elements chromium, vanadium, niobium and titanium, and which determines the wear resistance of the material in particular, in certain cases Limits set carbon contents and when using powder metallurgical manufacturing processes, materials that have high corrosion resistance, high wear resistance, high pressure resistance and high toughness at the same time and are advantageous, especially for the construction of plastic molds, can be used, the hardened and tempered state of the Chromium content in all areas of the matrix and the proportion as well as the composition and the grain size of the carbides can be adjusted according to the invention.

Description of the alloy or the effect of the alloying elements:

Silicon as a deoxidizing agent influences the composition of the oxides and, in low concentrations, can be advantageous for good polishability of the parts made from the alloy. Levels above 1% by weight, however, have an adverse effect on the solidification behavior and, if appropriate, on the conversion processes during the heat treatment. Manganese contents of up to 1% by weight may be important for sulfur contents of up to 0.03% by weight in order to bind the sulfur as sulfide and thereby improve the toughness of the material. Phosphorus has an embrittling effect and should be present in the steel as low as possible, but below 0.03% by weight. Chromium acts as an alloying element which, from a content of approx. 13% by weight in the matrix, makes the material resistant to corrosion. At the same time, chromium is a carbide former that can form M₂₃C₆ carbides with carbon in certain carbon activities and in the presence of molybdenum and vanadium in addition to M₇C₃ carbides. It is therefore important that the steel contains at least 16% by weight of chromium, but at most contains 29% by weight of chromium, because higher chromium concentrations lead to embrittlement of the material. Molybdenum in contents of 0.4 to 2.5% by weight and tungsten in Levels of 0.3 to 2.0% by weight cause an increase in secondary hardness in the heat treatment due to the formation of fine carbides and are important for adjusting the carbon activity of the alloy. Vanadium, as a strong carbide former, causes the formation of MC carbides, especially at levels above 0.7 to 3% by weight. Higher contents, in particular over 10%, lead to an improvement in wear resistance, but the toughness of the parts deteriorates considerably . Titanium up to 5% by weight improves the wear resistance of the material, in particular through the formation of MC carbide. Due to nitride formation, nitrogen contents from 0.01% have a grain-refining effect or prevent grain growth during annealing at high temperatures, thereby avoiding a drop in the toughness of the alloy. Furthermore, the wear resistance can be improved by nitrogen concentrations up to 0.18%. Aluminum can be alloyed as an element with a high affinity for oxygen and a high affinity for nitrogen in concentrations of up to 1% by weight to adjust the low oxygen content of the steel and to avoid grain growth, whereby advantageous effects on the conversion behavior and the toughness of the material can also be achieved. It was also found that a minimum value of the alloy, formed from the concentrations of the carbide- and nitride-forming elements chromium, tungsten, niobium, titanium and certain action factors of these elements is required for the setting of the desired mechanical properties of the part, by increasing this Worth an improvement in wear resistance and compressive strength with a slight decrease in toughness. Furthermore, it is important that the carbon content is set within narrow limits depending on the contents and on certain operating parameters of the carbide-forming elements in the steel in order to obtain the desired properties of the parts. This forms on the one hand for matrix hardening and to obtain high compressive strength M₇C₃, M₂₃C₆ and M₆C carbides and for setting high wear resistance MC carbides, but on the other hand there is a chromium content of more than 13% required for corrosion resistance in all areas of the matrix.
Powder-metallurgical production of the parts is essential because this significantly improves their isotropic properties of the material and the grain size of the precipitates or intermetallic phases can be kept small. Carbides with grain sizes over 14 µm significantly impair the mechanical properties, in particular the bending strength of the parts. The powder can be produced using all suitable processes, in particular using gas atomization processes, after which, if appropriate, compacting is carried out by hot isostatic pressing and / or by hot-working the powder in suitable casings.

Chrom

20,0

Molybdän

1,0

Wolfram

0,6

Vanadin

4,0

Stickstoff

0,04

The invention is described below for the purpose of further clarification using an example. From a melt with the following contents in% by weight

chrome

20.0

molybdenum

1.0

tungsten

0.6

Vanadium

4.0

nitrogen

0.04

Silizium

0,3

Mangan

0,35

Phosphor

0,012

Schwefel

0,011

Aluminium

0,001

Nickel

0,2

Kobalt

0,1

Kupfer

0,12

and a correspondingly set carbon concentration of 1.9 and

silicon

0.3

manganese

0.35

phosphorus

0.012

sulfur

0.011

aluminum

0.001

nickel

0.2

cobalt

0.1

copper

0.12

Iron and manufacturing-related impurities as the rest
an alloy powder was produced in the gas atomization process. After the powder had been poured into a capsule with a diameter of 250 mm and the capsule had been evacuated and sealed gas-tight, it was thermoformed at 1110 ° C. using a 6-fold degree of deformation. After soft annealing at 880 to 900 ° C and slow cooling, plastic molds were made from the forging rod. The hardness of the material was around 280 HB. The parts were hardened after heating to a temperature of 1140 ° C. by cooling in a warm bath, whereupon a hardness value of 61 HRC was measured. After tempering at 540 ° C the material hardness was 59 HRC. The mean bending strength, transverse to the direction of deformation, was 3.5 kilo N / mm and was therefore significantly higher than the values measured on conventionally manufactured parts with comparable hardness. The 0.2% compression limit was used to determine the compressive strength, the value being 2015 N / mm. The wear behavior of the part was tested in the grinding wheel test, in which a steel disc rotates in a corundum-water mixture, against which the sample is pressed.

Anpreßkraft der Probe

30 N

Schleifradwerkstoff

C 15

Härte des Schleifrades

126 (HV10)

Breite des Schleifrades

15 mm

Durchmesser des Schleifrades

168 mm

Drehzahl des Schleifrades

50 U/min

Probengröße

20 x 20 x 8

Al₂O₃-Schlämme:

(Feststoffanteil/H₂O) = 1

Al₂O₃-Korngröße

0,7 µm.

The following wear conditions were applied:

Contact pressure of the sample

30 N

Grinding wheel material

C 15

Hardness of the grinding wheel

126 (HV10)

Width of the grinding wheel

15 mm

Diameter of the grinding wheel

168 mm

Speed of grinding wheel

50 rpm

Sample size

20 x 20 x 8

Al₂O₃ sludges:

(Solids content / H₂O) = 1

Al₂O₃ grain size

0.7 µm.

During the test, specific wear (relative to the highly wear-resistant but less corrosion-resistant material with a composition of 2.3% C, 12.5% Cr, 1.1% Mo, 4.0%) was found after a period of 100 seconds. V) of 200%, 128% after 1000 h and 120% after 10,000 h. The corrosion behavior of the material was determined in the salt spray test, the corroded surface in% after 480 min. gave a value of 50. A further test of the corrosion behavior in 20% acetic acid over a period of 24 h yielded a value of 6.98 g / m h. The metallographic, electron microscopic and X-ray analyzes showed that the carbide content was approximately 39% by volume, of which approximately 10% by volume was present as MC carbides, the maximum carbide grain size being 10 μm.

Claims (6)

1. Use of an iron-based alloy with a composition in percent by weight of

   silicon   max. 0·6

   manganese   max. 0·6

   sulphur   max. 0·015

   phosphorus   max. 0·2

   chromium   18·0 - 25·0

   molybdenum   0·6 - 1·7

   tungsten   0·5 - 1·5

   vanadium   3·5 - 5·6

   titanium   up to 5·0

   aluminium   up to 1·0

   nickel   max. 0·5

   cobalt   max. 0·5

   copper   max. 0.4

   boron   up to 0·03

   nitrogen   0·03 to 0·1

   niobium   up to 5·0

   iron and impurities caused by the preparation as the rest, the value formed from $$\text{(\%Cr - 13) + 4.4x (\%V - 3) + 2x (\%Nb) + 4.2x (\%Ti)}$$

   

   being greater than 8.8 and the minimum carbon content of the alloy in accordance with the relationship amounting to $$\begin{gathered} {\text{C}}_{\text{min}}\text{= 0·3 + [(\%Cr - 13) x 0·06] + [(2x \%Mo + W)} \\ \text{x 0·03] + (\%V x 0·24) + (\%Nb x 0·13)} \\ \text{+ (\%Ti x 0·25)} \end{gathered}$$

   

   and the maximum carbon content of the alloy in accordance with the relationship amounting to $$\begin{gathered} {\text{C}}_{\text{max}}\text{= 0·7 + [(\%Cr - 13)x 0·06] + [(2x \%Mo + W)} \\ \text{x 0·03] + (\%V x 0·24) + (\%Nb x 0·13)} \\ \text{+ (\%Ti x 0·25)} \end{gathered}$$

   

   for the powder-metallurgical production of parts with high corrosion resistance and high wear-resistance and a high degree of toughness and a high degree of compressive strength, in particular for plastic moulds, machine parts and tools for non-cutting shaping, provided that the matrix after hardening and tempering has a chromium content of at least 13% and the carbide content amounts to at least 25% by volumes, of which at least 5% by volume of the carbides are formed as MC carbides, the carbides grain size being less than 14 µm.
2. Use of an iron-based alloy according to Claim 1 , characterized in that the value formed from $$\text{(\% Cr - 13) + 4·4(\%V - 3) + 2x(\%Nb) + 4·2x(\%Ti)}$$

   

   is greater than 10·0.
3. Use of an iron-based alloy according to Claim 1 or 2, with a niobium content in percentage by weight of from 0·2 to 3·0.
4. Use of an iron-based alloy according to one of Claims 1 to 3, with a titanium content in percentage by weight of from 0·2 to 3·5.
5. Use of an iron-based according to one of Claims 1 to 4, with a boron content in percentage by weight of from 0·001 to 0·002.
6. Use of an iron-based according to one of Claims 1 to 5, with a carbon content in percentage by weight of at least 1·8, but at most 6·2.