EP1288323A1 - Corrosion resistant and cold formable chromium steel - Google Patents

Abstract

Chromium steel contains (in wt.%): 0.005-0.1 carbon (C), 0.2-1.2 silicon (Si), 0.4-2.0 manganese (Mn), 0.05-1.2 molybdenum (Mo), 0.01-0.5 nickel (Ni), 0.5-2.0 copper (Cu), 0.001-0.6 bismuth (Bi), 0.002-0.10 vanadium (V), 0.002-0.10 titanium (Ti), 0.002-0.10 niobium (Nb), 0.15-0.80 sulphur (S), up to 0.05 aluminium (Al), up to 0.08 nitrogen (N) and a balance of iron (Fe). Preferably the steel contains (in wt.%): 0.002-0.06 C, 0.3-0.8 Si, 0.5-1.6 Mn, 0.05-0.8 Mo, 0.01-0.1 Ni, 0.55-1.6 Cu, 0.002-0.22 Bi, 0.005-0.08 V, 0.005-0.08 Ti, 0.005-0.08 Nb, 0.15-0.65 S, and a balance of Fe

Description

The invention relates to a cold-deformable, corrosion-resistant Chromium steel in particular with a ferritic structure and takes priority German patent application 101 43 390.5 to which reference is made to the content.

Such steels are known. They have good magnetizability, such as the soft magnetic described in U.S. Patent 4,714,502 Steel with up to 0.03% carbon, 0.40 to 1.10% silicon, up to 0.50% manganese, 9.0 to 19% chromium, up to 2.5% molybdenum, up to 0.5% nickel, up to 0.5% copper, 0.02 to 0.25% titanium, 0.010 to 0.030% sulfur, to 0.03% nitrogen, 0.31 to 0.60% aluminum, 0.10 to 0.30% lead and 0.02 to 0.10% zirconium. The steel is rustproof and cold formable; it is suitable as a material for Manufacture of cores for solenoid valves, electromagnetic clutches or housing of electronic injection systems for internal combustion engines.

Another soft magnetic stainless chrome steel with up to 0.05% carbon, up to 6% silicon, 11 to 20% chromium, up to 5% aluminum, 0.03 to 0.40% Lead, 0.001 to 0.009% calcium and 0.01 to 0.30% tellurium is from the U.S. patent 3 925 063 known and owns due to its contents Lead, calcium and tellurium have good machinability. A disadvantage of this However, steel is the use of toxic, machinability improving elements lead and tellurium.

The relatively high levels of silicon, aluminum and titanium lead in this steel, however, due to the formation of hard oxide inclusions high wear during mechanical finishing. That should counteract the relatively high lead content of 0.03 to 0.40%. However, this is bought with a not inconsiderable environmental and health hazard through the toxic lead.

Finally, from US Pat. No. 5,190,722 is another cold formable stainless steel with up to 0.02% carbon, up to 0.5% silicon, up to 0.5% Manganese, 10 to 18% chromium, 0.3 to 1.50% molybdenum, up to 1.0% vanadium, 0.05 to 0.5% titanium, up to 1.0% niobium, 0.01 to 0.2% sulfur, up to 0.05% Nitrogen, 0.30 to 2.0% aluminum and 0.0005 to 0.05% boron are known. This Steel is suitable electronically as a material for valve housings and valve cores controlled fuel injection systems. The high levels of aluminum and titanium also lead to hard, uneven structures in this steel distributed oxidic secretions with the consequence of an impairment mechanical, in particular machinability.

Common characteristic of many cold-formable and corrosion-resistant Ferritic chrome steels are their poor cutting behavior due to gluing in the cutting edge area. Such bonds consist of mostly oxidic welds or deposits, the one on the sharp cutting edges of the cutting tools high wear and tear leading to edge chipping. That danger is especially large for miniaturized precision parts and their micro-machining. For example, in micro drilling in the diameter range of 0.2 to 1 mm on the particularly sharp-edged drill bits a strong one Tool wear on. With decreasing drill or bore diameter there is also an increased risk of the hole running sideways or a loss of straightness of the bore. It also arises usually a ridge on the edges of the hole, the more pronounced the worse the machinability. There are similar problems in the machining of grooves, recesses, blind holes and slits.

The cause of the mentioned run is inhomogeneity in the structure, in particular hard excretions in the form of nests and islands Titanium carbides, carbonitrides, nitrides, manganese sulfide and heterogeneous silicon aluminum oxides. These excrements are replaced by thin micro-drills for example with diameters under 0.5 mm and slim Micro tools towards softer material zones. Such one Evasion naturally does not take place when the excretions finely dispersed or fine-grained homogeneous and distributed in the structure.

So far, efforts have been made with the usual ferritic steels Forming behavior or cold formability with the help of alloying elements to improve. Which have a favorable effect on the forming behavior However, alloying elements often cause deterioration the machinability with it, resulting in the poor machining behavior ferritic steels with good cold formability explained. A characteristic for bad machinability is the wear on the tool cutting edge. This wear occurs as abrasion, open space closure, lime wear, Diffusion wear, oxidation wear, or it is formed Construction cutting and gluing especially when machining ferritic Low carbon steels.

Starting from this prior art, the invention aims a cold-formable corrosion-resistant chrome steel with improved Machinability, especially with a low tendency to build-up edges and / or to create bonds, in particular a Directional drilling, embossing and punching also possible when Tools with a small cross-section and low rigidity, for example Micro drills are used.

In order to achieve this goal, the invention proposes a steel with at least 8% chromium and at most 0.1% carbon and certain contents of manganese and / or bismuth, titanium and / or vanadium and / or niobium, as well as sulfur and copper, which in the melt lead to primary precipitates in the form of sulfocarbides of the metals titanium, vanadium and niobium of the type Me ₄ C ₂ S ₂ , for example Ti ₄ C ₂ S ₂ . The sulfocarbides are in a fine distribution in the melt and serve as nuclei for manganese sulfide precipitates, which are then distributed evenly and finely in the melt. The presence of bismuth promotes the finely dispersed and homogeneous distribution of the manganese sulfide in the steel.

Copper works in the same direction, which is probably the wettability of the Manganese sulfide improved and in particular its wetting angle Iron / chrome matrix changed so that finely dispersed, spherical, cigar-shaped and constricted manganese sulfide excretions arise.

Bismuth promotes the elimination of the titanium sulfocarbides and causes this way a finely dispersed excretion of the manganese sulfide low supersaturation of the melt.

The effect of the alloying elements promoting machining, for example bismuth and copper is synergistic.

To suppress the formation of titanium carbide and the formation of finely dispersed To promote sulfocarbides, the levels of machining should promote Elements titanium, vanadium, niobium on the one hand and the one for the creation carbon and sulfur responsible for sulfocarbides be coordinated in a certain way. Higher levels of manganese and sulfur to improve micro-machinability are then no longer necessary because the manganese sulfide is in larger connected agglomerates is present. At the same time, the emergence of intermetallic titanium / aluminum precipitations that impair machinability suppresses and prevents titanium and Aluminum goes into solution and so the tendency to form bonds and reinforce construction edges.

The nitrogen content of the steel should be as low as possible to avoid formation of primary germs from titanium carbosulfides by setting the To affect Titan as TiN.

The chrome steel according to the invention contains in detail 0.005 to 0.1% carbon 0.2 to 1.2% silicon 0.4 to 2.0% manganese 8 to 20% chrome 0.05 to 1.2% molybdenum 0.01 to 0.5% nickel as well as in detail side by side 0.5 to 2.0% copper 0.001 to 0.6% bismuth 0.002 to 0.10% vanadium 0.002 to 0.10% titanium 0.002 to 0.10% niobium 0.15 to 0.80% sulfur up to 0.05% aluminum up to 0.08% Nitrogen, Rest of iron.

Preferably, the present invention contains chromium steel each within the above content limits 0.002 to 0.06% carbon 0.3 to 0.8% silicon 0.5 to 1.6% manganese 11 to 18% chrome 0.05 to 0.8% molybdenum 0.01 to 0.1% nickel 0.55 to 1.60% copper 0.002 to 0.22% bismuth 0.005 to 0.08% vanadium 0.005 to 0.08% titanium 0.005 to 0.08% niobium 0.15 to 0.65% Sulfur, Rest of iron.

In order to promote the formation of sulfocarbides in finely dispersed and homogeneous distribution, the alloying elements titanium, vanadium and niobium or sulfur, carbon and nitrogen or copper and manganese should be coordinated as follows: K1 =% Ti +% V +% Nb K1 = 0.005 to 0.15 K2 = % S 10 * (% C +% N ) K2 = 0.8 to 3.8 K3 = % Cu % Cu + Mn K3 = 0.25 to 0.85.

The chrome steel according to the invention is suitable due to its good machinability as a material for the manufacture of precision devices and highly precise Micro components with low tool wear with micro bores and recesses, for example in the tenth or hundredth range of a millimeter, high surface quality and directional accuracy. For example, you can drill holes with a diameter Produce less than 1 mm in one step without running. Furthermore The steel has excellent polishability, especially when Electropolishing.

It is of particular advantage that the better machinability without higher Contents of toxic alloy components such as lead, selenium and / or tellurium, which are missing entirely or whose total content is below Is 0.05%.

The chrome steel according to the invention is suitable, for example, as a material for writing tips on ballpoint pens. Such nibs and the associated printheads require high corrosion resistance, Fine workability and uniformity of ink supply. So there is the writing head of a ballpoint pen in the front part from a holder for the writing ball, for example made of corundum and from several channels and holes for supplying the writing ink or paste. Rear Part of the print head usually consists of a connection to a storage container, for example a metal or plastic cylinder for the writing paste or ink, which can also be under pressure. The The ink or paste is supplied to the ball using a pen centric fine bore channel with a diameter of less than 0.5 mm and several laterally symmetrically arranged recesses. The centric Fine bore channel must be positioned so that the writing ball and the recesses arranged symmetrically to it exactly in the middle of the ball will be hit because the writing ball will only rotate is evenly wetted on all sides with ink or writing paste.

If these requirements are not met, for example because of a hole has run laterally, the writing ball is only corresponding on one side Ink or paste loaded. This leads to a when writing uneven line width and poor typeface.

Another requirement for an even supply of ink or Writing paste to the writing ball is high corrosion resistance and Surface quality, which is reflected in a corresponding gloss and reflectivity shows, as well as good wettability.

example 1

A wire with a diameter of 3 mm and the composition according to V1 in Table 1 with the following K values was used to produce spray nozzles for a monofilament made of plastic: K1 = 0.08 K2 = 1.94 K3 = 0.59 and a length of 4.4 mm initially aimed. The wire was then cut into slices and the slices were formed in a molding press at room temperature with a degree of deformation of ϕ = 0.45 into die blanks with a slice thickness of 2.8 mm. The nozzle blanks were then drilled centrally in an automatic drill using a hard metal drill with a diameter of 0.4 mm. When drilling, only a very small burr was created, which could be easily removed by electropolishing for twenty seconds while simultaneously rounding the edge of the hole, leaving a shiny surface.

After cleaning and drying, the nozzles were readily usable.

The excellent quality of the nozzle surface due to the good machinability results in low wall friction and allows spinning with relatively low pressure, even with melt plastics high viscosity.

Example 2

In a manner similar to that of Example 1, a wire made of chromium steel with the composition according to V6 in Table I and the following K values was: K1 = 0.13 K2 = 1.26 K3 = 0.47 cold formed into a nozzle blank with a disc thickness of 5.5 mm and a press seal seat. The blank was provided with six blind holes each with a diameter of 0.8 mm and a depth of 4.9 mm in order to produce a nozzle opening with a diameter of 85 μm in an automatic drilling machine. After cleaning in an ultrasonic bath and drying with hot air, melt holes with the specified diameter of 85 μm were made in the bottom of the blind holes using an Nd YAG laser. Such laser drilling leads to problems if the blind hole is not straight. No such problems were encountered when trying. In addition, there was no toxic metal fumes due to the absence of lead, selenium and tellurium in the test steel. The accuracy of the bore produced in this way allows further processing to straight, curved or star-shaped slots.

Example 3

To the machinability of the chrome steel according to the invention and the Drill tests were used to assess the straightness of microbores Carbide drills in the diameter range from 0.2 to 1.5 mm, in particular with a drill diameter of 0.8 mm and a speed of 37,000 rpm and a hole depth L of 5 mm.

The straightness of the bores was determined for each bore diameter using a test wire whose diameter was approximately 10 μm smaller than the bore diameter and whose immersion depth E was determined as shown in FIG. 1. The immersion depth E and the hole depth L became according to the formula KR = 1 - E / L in each case a curvature factor is calculated which indicates an absolutely straight or smooth bore at KR = 0.

The analyzes of the test steels V1 to V6 according to the invention and of comparison steels V7 to V12 and the measurement results are summarized in Tables I and II below.

Example 3

When producing micro bores with diameters less than 1 mm, the Training of the chip for the drill wear and for the quality of the Drilling of particular importance. Inadequate chip formation and the suitability of a material for the production of microbores can be derive in a simple manner from the height or width of a burr. On wide burr is a sign of poor machinability because of it then squeezing the material out of the hole and A burr arises at the edge or edge of the hole.

In a series of tests, the width of the ridges was determined with the help of a microscope at an angle of 20 to 30 degrees. In In Table II above, the ridge width GB is dependent on the K factors compiled, while FIGS. 2 and 3 electron microscopic Microbores with differently wide burrs Play BG. Fig. 2 clearly shows the sudden improvement the susceptibility to burrs when testing with the steel according to the invention a ridge width of only 0.060 mm compared to a ridge width of 0.187 mm for the comparative steel according to FIG. 3.

Claims (6)

Chrome steel with 0.005 to 0.1% carbon 0.2 to 1.2% silicon 0.4 to 2.0% manganese 0.05 to 1.2% molybdenum 0.01 to 0.5% nickel as well as individually or side by side 0.5 to 2.0% copper 0.001 to 0.6% bismuth 0.002 to 0.10% vanadium 0.002 to 0.10% titanium 0.002 to 0.10% niobium 0.15 to 0.80% sulfur up to 0.05% aluminum up to 0.08% Nitrogen, Rest of iron. Chrome steel according to claim 1 with 0.002 to 0.06% carbon 0.3 to 0.8% silicon 0.5 to 1.6% manganese 11 to 18% chrome 0.05 to 0.8% molybdenum 0.01 to 0.1% nickel as well as individually or side by side 0.55 to 1.60% copper 0.002 to 0.22% bismuth 0.005 to 0.08% vanadium 0.005 to 0.08% titanium 0.005 to 0.08% niobium 0.15 to 0.65% Sulfur, Rest of iron. Chrome steel according to claim 1 or 2, characterized in that it satisfies at least one of the following three conditions: K1 =% Ti +% V +% Nb K1 = 0.005 to 0.15 K2 = % S 10 * (% C +% N ) K2 = 0.8 to 3.8 K3 = % Cu % Cu + Mn K3 = 0.25 to 0.85. Use of a steel according to one of claims 1 to 3 for manufacturing of objects by machining. Use of a steel according to one of claims 1 to 3 for manufacturing objects by micro-machining. Use of a steel according to one of claims 1 to 3 as a material for the manufacture of precision devices, micro components, Stylus tips and heads, printer nozzles, dosing devices and electronic components with openings and recesses smallest dimensions.

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