DE4040030A1 - Powder metallurgical cold work steel - useful for processing abrasive and corrosive plastics - Google Patents

Abstract

(A) a novel powder metallurgical cold work steel has the compsn. (by wt.) 2.2-2.5% C, 19.5-24.0% Cr, 0.9-3.0% Mo, 3.5-4.5% V, 1.6-3.0% Ta and/or Nb, 0.01-0.1% B, 0.05-0.09% S and balance Fe. (B) prodn. of the cold work steel involves preparing a melt of compsn. as in (A), atomising to powder of less than 1mm. particle size and then sintering or hot isostatically pressing to a body of more than 99.99% density. USE/ADVANTAGE - The cold work steel is useful for processing plastics esp. filled, highly abrasive and corrosive plastics. It has an extremely good combination of wear and corrosion resistance has optimal strength and toughness, is machinable in the soft condition and has a homogeneous, segregation-free, pore-free and very fine grain structure providing quasi-isotropic properties.

Description

The present invention relates to a powder metallurgical cold work steel and its production. This powder metallurgically produced cold work steel characterized by a high wear and Korro sion strength.

From DE-A-23 52 620 and US-A-42 49 945 are pul metallurgically produced steels, which are characterized by their fine, homogeneous texture and the resulting Characterize material properties, known.

The finely divided metal carbides give this Steel a very good hardness and wear resistance.

In US-A-42 49 945 is a powder metallurgi scher steel described by his finely divided Vanadium carbide special wear resistance and Zä ability.

However, the known alloys are the hay requirements for good wear resistance, simultaneous effectiveness against corrosion with additional sufficient strength is no longer adequate. A Another basic requirement is an economic bear beitungsmöglichkeit. For example, is out of the field Plastics processing known that although the Ver Abrasion resistance could be greatly improved, the However, more and more urgent corrosion problems were not solved.

It was therefore this invention Object of the proposal to propose a material, the ideally in an ideal manner to all requirements is fair.

This object is achieved by the in the patent claim 1 defined, powder metallurgical cold work steel ge  solves. The inventive powder metallurgical Kaltar Beitsstahl has a combination of very good Wear resistance and excellent corrosion resistance permanence. The invention thus provides a work fabric available for example for the art fabric processing, in particular for the area filled te, highly abrasive and corrosive art substances is suitable.

For the favorable wear and corrosion properties are responsible for several factors Lich. The underlying the analysis of the invention has been determined from the following considerations.

The right ratio of carbon to the Carbide-forming substances such as V, Ta, Nb, Cr gives a effective wear protection.

For steels produced by fusion metallurgy a share of <1.8% C is not possible because it is too coarse and irregular texture leads.

However, powder metallurgy can do this because there is a fast er during the atomization Steadiness on the smallest volume takes place and thereby rough excretions are prevented.

To get a high amount of carbides, Therefore, the carbon content was 2.2-2.5 wt .-% established.

The chromium content of 19.5-24.0 wt .-% was ge chooses to get high corrosion resistance, and additionally on the formation of chromium carbides one to achieve high wear resistance.

Molybdenum was added to the tensile strength and toughen the toughness values. Simultaneously ent stand molybdenum carbides, which in turn the Verschleißfe increase their strength. The temper brittleness is called Neben Effect also diminished.  

Vanadin is a strong carbide former and enhances essentially the wear and tear resistance. Because it But very expensive, it was based on the invention lying alloy with Ta and Nb (Cb) in the context of 1.6-3.0 wt .-% complements, in turn, very high levels of wear strength with high toughness and corrosion resistance obtained by their carbides.

The low proportion of boron improves over Aus Hardening the yield strength and strength. The Reduction of corrosion resistance is in Purchase, since the high Cr and V share this on lifts. In addition, by the boron content, the through hardening improves what with thick-walled components too lower voltages leads.

The advantages of this alloy composition lie in the balanced composition of the Elements to provide optimum strength and toughness highest wear and corrosion resistance to it hold.

Another advantage of this powder metallurgical Steel is the machining option in Soft To stood so that a comparatively economical Be work becomes possible. The cutting is done übli probably at Brinell hardness <290. Depending on austenitis level or starting level can be the optimal Kombina Wear resistance / toughness for the individual len use be selected.

The production of the steel is done using formation of globular nitrogen atomized powder in grain size ranges of 5-1000 microns. Through the atomization each powder grain already receives its finely divided, ho mogeneous microstructure. The powder is in steel capsules filled and sealed gas-tight. In the hot isosta Presses (HIP plant) sinter the powder grains in  the capsule under high gas pressure and high temperature a compact, homogeneous body together.

The steel produced in this way stands out by its homogeneous, segregation-free, pore-free and very fine-grained texture. As a result of this structure structure, this material has quasi-isotropic properties companies.

example

A melt of 4 tons was atomized. After that was determined the following particle size distribution:

97.1% <710 μm
80.0% <355 μm
64.0% <212 μm
28.3% <106 μm
0.6% <45 μm

The analysis of the powder was

C = 2.34% by weight P = 0.02% by weight S = 0.074% by weight Cr = 19.9% by weight Mo = 1.06% by weight Nb = 1.87% by weight V = 4.15% by weight B = 0.02% by weight

Such produced powder was in a Steel capsule with the dimensions 100/96 × 1200 mm filled and shaken until a filling density of about 69% is reached  has been. Subsequently, the capsule was replaced by the filling evacuated tube and during evacuation of the filling heated and sealed gas-tight. This with the Powder filled steel capsule was placed in a hot isostati cal press and at 1140 ° C for 3 h at Sintered 1000 bar dense.

Subsequently, the body was at 900 ° C during Annealed for 2 h and with max. 15 ° C / h to a temperature brought from 600 ° C. Thereafter, a cooling took place calm air. Afterwards the processing of the raw took place lings to a screw for a plastic extruder with subsequent curing at 1100 ° C and subsequent on leave at 190 ° C. The practical use of this snail resulted in a substantial service life improvement in abrasi ven and corrosive use compared to a normal ge common steel.

Claims (2)

1. powder metallurgical cold work tool, characterized by the following composition: 2.2-2.5% by weight carbon 19.5-24.0% by weight chrome 0.9-3.0% by weight molybdenum 3.5-4.5% by weight vanadium 1.6-3.0% by weight Ta / Nb (Cb) 0.01-0.1% by weight boron 0.05-0.09% by weight sulfur rest iron 2. A method for producing a powder metallurgi rule cold work tool according to claim 1, characterized in that a powder is prepared by a melt having the following composition 2.2-2.5% by weight carbon 19.5-24.0% by weight chrome 0.9-3.0% by weight molybdenum 3.5-4.5% by weight vanadium 1.6-3.0% by weight Ta / Nb (Cb) 0.01-0.1% by weight boron 0.05-0.09% by weight sulfur rest iron is prepared and this is atomized into powders with a particle size of <1 mm and the resulting powder is processed by sintering or direct hot isostatic pressing to a body whose density is <99.99%.