EP0136433A1 - Austenitic manganese steel of the Hadfield type, and process for the manufacture thereof - Google Patents

Abstract

An austenitic manganese high-carbon steel is described with the following alloy contents in% by weight: <IMAGE> where the ratio of the carbon content to the manganese content is 1 to 8 to 1 to 14 and the rest consists of iron, impurities and the following micro-alloy additives in% by weight: 0.005 to 0.05, preferably up to 0.03 V, 0.008 to 0.02 B, the upper limit of the vanadium content being given as an additional microalloying element both for the sum of V and B and as an upper limit for any titanium content. The steel described also preferably has an aluminum content of 0.02 to 0.09% by weight. The vanadium and in particular the boron content cause grain refinement over the entire cross-section, even of large castings made of manganese high-carbon steel, and guarantee its cold-forming ability and strengthening ability during cold-forming.

Description

• 0,8 bis 1,8 C
• 6,0 bis 18,0 Mn
• 0 bis 3,0 Cr
• 0 bis 2,0 Ni
• 0 bis 2,5 Mo
• 0 bis 1,0 Si,

wobei das Verhältnis des Kohlenstoffgehaltes zum Mangangehalt 1 zu 8 bis 1 zu 14 beträgt und der Rest aus Eisen, Verunreinigungen., Desoxidationszusätzen und Mikrolegierungszusätzen, z.B. Bor, besteht.The invention relates to an austenitic manganese steel with the following alloy contents in% by weight:

• 0.8 to 1.8 C.
• 6.0 to 18.0 Mn
• 0 to 3.0 cr
• 0 to 2.0 Ni
• 0 to 2.5 months
• 0 to 1.0 Si,

the ratio of the carbon content to the manganese content being 1 to 8 to 1 to 14 and the rest consisting of iron, impurities, deoxidation additives and microalloying additives, for example boron.

Such high manganese steel is characterized by a very high hardness and above all by its strengthening ability during cold forming; it can harden after use due to impact, impact, abrasive or pressure loads. The stress results in a martensitic structural transformation in a surface layer, whereby the hardness in this layer increases from 200 HB to over 500 HB. The hard surface layer is removed by abrasive stress, but at the same time it is constantly re-formed by the same stress. The material below the surface layer has very good toughness and deformability. Austenitic manganese steels can therefore withstand large impact loads. The area of application is therefore tools for mining, the processing of minerals, bulletproof dance plates or steel helmets etc.

However, a high degree of fine grain is necessary for the favorable mechanical properties, in particular for the deformability of the material located under the hard surface layer. This fine grain is difficult to achieve, especially inside larger castings. Such castings have very different grain sizes in cross section; a fine-grained edge zone is followed by a very coarse-grained columnar crystalline layer, followed by a coarse globular-crystalline inner zone. Even by forging the The grain differences can not be completely compensated for; compensation is particularly difficult with castings. The elongation and notched impact strength are not sufficient in all cases, even if the alloy composition is strictly observed.

It is known to subject the block casting or shaped casting for grain refinement to a heat treatment which consists of a first, long-lasting annealing at 500 to 600 ° C for the conversion of austenite to pearlite, and from a second annealing process for the conversion back to austenite at 970 to 1110 ° C consists. Despite the complexity of the procedure, the effect is uncertain.

It is also known to pour off the melt at a very low casting temperature close to the melting point. Due to the low casting temperature, a high bacterial count and a finer grain are achieved. This method of operation causes great difficulties in casting practice and only simple shapes are possible because the melt does not completely fill remote areas or edges of the casting mold in the liquid state.

Finally, it is known to add steel for grain refinement to carbide- or nitride-forming elements such as Ti, Zr, Nb, V, B and / or N, the amounts chosen in each case being at least between 0.1 and 0.2% by weight. These microalloy additives have caused grain refinement, but have led to a decrease in elongation at break and notched impact strength.

The invention is based on an austenitic manganese high-carbon steel, as described, for example, in the DIN with the material no. ^1st 3401 is described. According to this standard, the alloy contents are in% by weight: C approx. 1.25, Mn 11 to 14, Cr to 2.5, Ni to 2 to stabilize the austenite, Mo to 2.5 to prevent coarse carbide deposits, the ratio the carbon content to the manganese content must be between 1: 8 and 1:14; that is, the manganese must match the carbon content on the one hand are sufficient for an austenitic structure and, on the other hand, must not stabilize the austenite so strongly that the hardening capacity suffers from cold working.

The object of the invention is to provide an austenitic manganese steel which can be hardened by cold working and which is fine-grained and deformable as uniformly as possible over the entire cross section without the disadvantages of the known measures. The elongation at break should be at least 20% and the other mechanical properties should not deteriorate.

• 0,005 bis 0,05, vorzugsweise bis 0,03 V
• 0,008 bis 0,02 B,

wobei die angeführte Obergrenze des Vanadiumgehaltes sowohl für die Summe von V und B als auch als Obergrenze für einen allenfalls vorhandenen Gehalt an Titan als zusätzliches Mikrolegierungselement gilt und wobei vorzugsweise ein Aluminiumgehalt von 0,02 bis 0,09 Gew.-% (als nach der Desoxidation im Stahl verbleibender Gehalt) vorgesehen ist.In the case of steel of the type mentioned at the outset, this object is achieved by the following contents of microalloying elements in% by weight:

• 0.005 to 0.05, preferably up to 0.03 V
• 0.008 to 0.02 B,

the above-mentioned upper limit of the vanadium content applies both to the sum of V and B and as an upper limit for any titanium content as an additional microalloying element, and preferably an aluminum content of 0.02 to 0.09% by weight (as per the Deoxidation remaining in the steel) is provided.

The vanadium and boron content are essential to the invention, the latter surprisingly not causing any deterioration in the mechanical properties.

Carbide-forming microalloying elements such as Ti, Zr, Nb are only used selectively and have no influence on grain refinement. Titanium binds any nitrogen present and prevents the formation of unwanted aluminum nitrides.

The boron has a grain-refining effect and slows down the excretion of grain boundary carbides, which has a favorable influence on the mechanical properties and - due to the shorter diffusion paths - the times required for heat treatments are reduced.

The aluminum content of the steel mentioned is expedient to ensure the safety of complete deoxidation necessary before the addition of boron.

In the production of the austenitic high manganese steel according to the invention, the microalloy additives being added after the insert has melted in the electric furnace or in the ladle and the casting is subjected to a heat treatment after removal from the mold, the vanadium is preferably introduced into the melt in the electric furnace at the end of the refining period and feeding the boron to the melt in the ladle after deoxidation; but it is also possible to add both the boron and the vanadium only in the ladle; the heat treatment preferably includes annealing at a temperature of 1050 to 1150 ° C and rapid cooling.

Before deoxidation and setting the desired tapping temperature in the range 1450-1620 ° C, the melt is covered with a calcareous slag to keep a casting temperature in the tundish 1420-1520 ⁰ C. The heat treatment of the block castings or molded castings mentioned is expedient for balancing the mechanical properties over the entire cross section of the casting. A water bath and / or cooling by flowing air, if appropriate after a first slower cooling step, are suitable for the cooling of the castings mentioned.

The invention is explained in more detail on the basis of exemplary embodiments and comparative examples:

Example 1:

• 1,25 Gew.-% Kohlenstoff, 13 Gew.-% Mangan, 0,5 Gew.-% Chrom, 0,4Gew.-% Nickel, 0,4 Gew.-% Molybdän. Die Schmelze wurde mit einer Schlacke aus Kalkstein mit einem Zusatz von Kalziumfluorid abgedeckt und nach Einstellung einer Abstichtemperatur von 158C°C eine Desoxidation mit Aluminium vorgenommen. Die Schmelzenmenge wurde beim Abstion zu gieicnen reiψentaoy drei gleichartige Gießpfannen aufgeteilt. In den drei Gießpfannen, wo identische Verhältnisse herrschten, wurden verschiedene Mikrolegierungszusätze zugegeben.

3000 kg of high manganese steel with the following composition were melted in an electric arc furnace:

• 1.25% by weight carbon, 13% by weight manganese, 0.5% by weight chromium, 0.4% by weight nickel, 0.4% by weight molybdenum. The melt was covered with a limestone slag with the addition of calcium fluoride and, after setting a tapping temperature of 158 ° C., deoxidation with aluminum was carried out. The The amount of melt was divided into three identical ladles at the casting stage. Various micro-alloy additives were added in the three ladles, where conditions were identical.

Pan A received an alloy addition of 2 kg of an alloy containing zircon and vanadium in a ratio of 1: 1 (zirconium and vanadium content each 0.1% by weight),

Pan B an addition of this alloy in the amount of 4 kg (zirconium and vanadium content each 0.2 wt .-%) and

Pan C added 100 g of vanadium (in the form of ferrovanadium) and 100 g of boron (in the form of ferrobor). (Vanadium and boron content each 0.01% by weight).

Crushing jaws with a wall thickness of 120 mm were cast from the metal of pans A to C, which also had a casting temperature of 1480 ° C, as is required for crushers to process ores. The cooled castings were removed from the mold and annealed for two hours at a temperature of 1110 ° C. After removal from the oven, the crushing jaws were quickly cooled in a water bath.

Man sieht die Überlegenheit der Proben aus der Pfanne C mit der erfindungsgemäßen Zusammensetzung sowohl was die absolut höheren Werte der Zugfestigkeit und insbesondere der Bruchdehnung an allen Stellen der Stäbe, besonders jedoch in deren Mitte, als auch die größere Gleichmäßigkeit über den Querschnitt betrifft.Test pieces were taken from the castings of pans A to C at the edge and in the middle and their tensile strength and elongation at break were determined. The following values were obtained:

One can see the superiority of the samples from pan C with the composition according to the invention both in terms of the absolutely higher values of tensile strength and in particular the elongation at break at all points of the bars, but especially in the middle thereof, and also the greater uniformity over the cross section.

Example 2:

• 1,18 Gew.-% Kohlenstoff, 13,1 Gew.-% Mangan, 0,25 Gew.-% Chrom, 0,1 % Nickel, 0,05 % Molybdän, 0,52 Gew.-% Silizium, 0.033 Gew.-% Phosphor, 0,008 Gew.-% Vanadium und Spuren erschmelzungsbedingter Verunreinigungen. Der Vanadiumgehalt war durch Zusetzen von Ferrovanadium am Ende der Feinungsperiode eingestellt worden. Nach Abdecken der Schmelze mit einer Schlacke ähnlich Beispiel 1 wurde eine Abstichtemperatur von 1540°C eingestellt und eine Desoxidation mit Aluminium durchgeführt. Nach dem darauf folgenden Abstich in die Gießpfanne wurde dort durch Zugabe von Ferrobor ein Borgehalt von 0,015 Gew.-% eingestellt. Bei einer Gießtemperatur von 1470°C wurde daraufhin die Schmelze in eine Sandgußform eingegossen. Das Gußstück in Form eines Brechkegels wurde erkalten gelassen, aus dem Sand genommen und geputzt. Hierauf wurde es in einem Glühofen eingebracht, erhitzt und dort4 Stunden bei einer Temperatur von 1100°C geglüht. Nach dem Glühen folgte eine rasche Abkühlung im Wasser, unterbrochen durch mehrmaliges Herausziehen und kurzes Verweilen in der Umgebungsluft.

7 tons of high manganese steel with the following composition were melted in an electric arc furnace:

• 1.18% by weight carbon, 13.1% by weight manganese, 0.25% by weight chromium, 0.1% nickel, 0.05% molybdenum, 0.52% by weight silicon, 0.033% by weight .-% phosphorus, 0.008% by weight vanadium and traces of melting-related impurities. The vanadium content was adjusted by adding ferrovanadium at the end of the refining period. After covering the melt with a slag similar to Example 1, a tapping temperature of 1540 ° C. was set and deoxidation with aluminum was carried out. After the subsequent tapping into the ladle, a boron content of 0.015% by weight was set there by adding ferroboron. The melt was then poured into a sand mold at a casting temperature of 1470 ° C. The casting in the form of a crushing cone was allowed to cool, removed from the sand and cleaned. It was then placed in an annealing furnace, heated and annealed there for 4 hours at a temperature of 1100 ° C. After the glow, there was a rapid cooling in the water, interrupted by repeated pulling out and brief lingering in the ambient air.

After cooling, the appearance of the casting was flawless. Test pieces were taken from the inside and from the edge zone, which had an almost uniformly small grain, regardless of the location of the sampling. The elongation at break and the tensile strength of the sample material were determined, which were 53 t 1% and 810 ± 10 N / mm2 in all cases.

• Es wurde gleich wie in Beispiel 2 Manganhartstahl, jedoch ohne den Gehalt an Vanadium und Bor, hergestellt und in derselben Weise ein gleiches Gußstück in Form eines Brechkegels gegossen. Nach gleichem Abkühl- und Wärmebehandlungsvorgang wie in Beispiel 2 wurde das erhaltene Gußstück geprüft. Es zeigte Risse, die durch Reparaturschweißen geschlossen werden mußten. Die metallographische Untersuchung ergab eine sehr ungleichmäßige Verteilung von Korngröße und Kornform über den Querschnitt. Auf eine sehr dünne feinkristalline Außenschicht folgte eine sehr breite Zone sehr grober, stengelförmiger Kristalliten und eine ziemlich grobe, globularkristalline Innenzone. Die Bruchdehnung in der Zone stengelförmiger Kristalliten lag - je nach der Richtung der Zugbeanspruchung - zwischen 12 und 19 %. Die Zugfestigkeit betrug in dieser Zone zwischen 578 und 653 N/mm2.

Example 3 (comparative example):

• Manganese steel was produced in the same way as in Example 2, but without the content of vanadium and boron, and an identical casting was cast in the same way in the form of a crushing cone. After the same cooling and heat treatment process as in Example 2, the casting obtained was tested. It showed cracks that had to be closed by repair welding. The metallographic examination showed a very uneven distribution of grain size and shape over the cross section. A very thin, fine-crystalline outer layer was followed by a very wide zone of very coarse, stem-shaped crystallites and a fairly rough, globular-crystalline inner zone. The elongation at break in the zone of stem-shaped crystallites was - depending on the direction of the tensile stress - between 12 and 19%. The tensile strength in this zone was between 578 and 653 N / mm2.

Claims (2)

1. Austenitic high manganese steel with the following alloy contents in% by weight 0.8 to 1.8 C. 6.0 to 18.0 Mn 0 to 3.0 cr 0 to 2.0 Ni 0 to 2.5 months 0 to 1.0 Si
the ratio of the carbon content to the manganese content being 1 to 8 to 1 to 14 and the rest consisting of iron, impurities, deoxidation additives and microalloying additives, for example B, characterized by the following contents of microalloying elements in% by weight: 0.005 to 0.05, preferably up to 0.03 V, 0.008 to 0.02 B,
the above-mentioned upper limit of the vanadium content applies both to the sum of V and B and also as an upper limit for any titanium content present as an additional microalloying element, and preferably an aluminum content of 0.02 to 0.09% by weight is provided. 2. The method for producing the austenitic manganese steel according to claim 1, wherein the micro-alloy additives are added after the insert has melted in the electric furnace or in the ladle and the casting is subjected to a heat treatment after removal from the mold, characterized in that the vanadium is preferably in the melt in the electric furnace at the end of the refining period and the boron are fed to the melt in the ladle after their deoxidation and the heat treatment comprises annealing at a temperature of 1050 to 1150 ° C. and rapid cooling.