Alloy steel tire cord and its heat treatment process

KINGDOM OF BELGIUM

PATENT

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NUMBER OF

PUBLICATION

MINISTRY OF ECONOMIC AFFAIRS

NUMBER OF

Classif

DEPOSIT

09000930

Boarding school.

Date of issue on

C21D C22C

February 1995

The Minister of Economic Affairs

Having regard to the Paris Convention of March 20, 1883 for the Protection of Industrial Property;

Considering the law of March 28, 1984 on patents for invention, in particular article 22;

Considering the royal decree of December 2, 1986 relating to the request, the issue and the maintenance in force of patents of invention, in particular 1 article 28;

Having regard to the minutes drawn up on October 1, 1990 at 2 p.m. at the Industrial Property Office

STOPPED :

ARTICLE 1. “It is issued to: THE GOODYEAR TIRE &amp; RUBBER COMPANY East Market Street 1144, AKRON OHIO (UNITED STATES OF AMERICA) represented by: PLUCKER Guy, OFFICE KIRKPATRICK SA, Avenue Wolfers 32 - B 1310 LA HULPE.

a 20 year patent of invention, subject to the payment of annual fees, for: STEEL ROPE AND ITS HEAT TREATMENT.

PRIORITY (S) 02.10.89 US USA 415948

ARTICLE 2.- This patent is granted without prior examination of the patentability of the invention, without guarantee of the merit of the invention or of the accuracy of the description thereof and at the risk and peril of the applicant (s).

WUYTS L Director.

Brussels, February 21, 1995

BY SPECIAL DELEGATION:

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Alloy steel rope and its heat treatment.

Background of the invention.

It is frequently desirable to reinforce manufactured rubber products, for example tires, conveyor belts, transmission belts, timing belts, hoses and the like, by incorporating steel reinforcing elements into them. Vehicle tires are often reinforced with ropes made of brass coated steel filaments. These tire ropes are frequently made of high carbon steel or high carbon steel coated with a thin layer of brass. Such a tire cord can be a monofilament, but is normally made of several filaments gathered in strands. Most often, depending on the nature of the tire to be reinforced, the strands of filaments are, moreover, wired to form the cord.

It is important that the steel used for the filaments serving as reinforcing elements has a high strength and a high ductility, in addition to a high resistance to fatigue. However, many alloys which exhibit this delicate combination of required properties do not lend themselves to processing in a practical industrial process. More specifically, it is extremely difficult to patent many of these alloys which, moreover, have extremely good physical properties because they have a low isothermal transformation speed requiring a long stay in the equalization zone (transformation zone) . In other words, a long stay in the transformation zone is necessary during the patenting to modify the microstructure of the steel from the cubic state with faces centered to the cubic state centered.

In industrial operations, it is desirable that the transformation of the cubic microstructure with centered faces into a cubic microstructure

U9UUU93U centered is done as quickly as possible during the transformation phase of the patenting. For a given production speed, the equipment required is less bulky the higher the transformation speed. In other words, if it takes longer for processing to take place, the length of the processing area must be increased to maintain the same manufacturing speed. Obviously, it is also possible to decrease the manufacturing speed to take account of the low transformation speed by increasing the residence time in the transformation zone (equalization zone). For these reasons, it is very apparent that it would be desirable to develop an alloy steel having a high isothermal transformation speed during patenting and also having a high resistance, a high ductility and a good resistance to fatigue.

Patenting is a heat treatment applied to steel wire and wire rod with a carbon content of 0.25% or more. Typical steel for tire reinforcement usually contains about 0.65 to 0.75% carbon, 0.5 to 0.7% manganese and 0.15 to 0.3% silicon, the rest being obviously iron. The aim of patenting is to obtain a structure which combines high tensile strength with great ductility and therefore gives the yarn the ability to withstand a large reduction in section in order to achieve the desired finished dimensions by combining high resistance to traction with good toughness.

Patenting is normally performed in continuous operation and typically involves first heating the alloy to a temperature in the range of about 850 ° C to about 1150^eC to form austenite, then to cool it at a rapid rate to a lower temperature at which the transformation takes place and modifies the microstructure from cubic with centered faces to cubic centered having the desired mechanical properties. Often, although it is desired to form a single allotrope, it

0900G930 actually forms a mixture of allotropes comprising more than one microstructure.

Overview of 1¹ invention.

The subject of the invention is alloy steels which can be drawn into filaments having a high tensile strength, a high ductility and a remarkable resistance to fatigue. These alloy steels also have a very rapid transformation pace during patenting.

A more specific subject of the invention is an alloy steel which is particularly suitable for the manufacture of reinforcing wires for rubber products and which essentially consists of (a) approximately 96.5 to approximately 99.05% by weight of iron, ( b) about 0.6 to about 1.0% by weight of carbon, (c) about 0.1 to about 1.0% by weight of silicon, (d) about 0.1 to about 1.2% by weight manganese, (e) about 0.1 to about 0.8% by weight of chromium and (f) about 0.05 to about 0.5% by weight of cobalt.

The invention also relates to a method of manufacturing a steel filament having a remarkable combination of strength and ductility, which comprises the successive stages (1) of heating a steel wire, at a first stage patenting, up to a temperature in the range of about 900^eC at about 1100 ° C for a period of at least about 5 seconds, the steel wire consisting essentially of (a) about 95.0 to about 99.1% by weight of iron, (b) about 0.6 to about 1% by weight of carbon, (c) about 0.1 to about 1.2% by weight of manganese, (d) about 0.1 to about 2% by weight of silicon and (e) about 0.1 about 0.8% by weight of chromium; (2) rapidly cooling the steel wire to a temperature in the range of about 540 ° C to about 620 ° C in less than about 4 seconds; (3) maintaining the steel wire at a temperature in the range of about 540 ° C to about 620 ° C for a time sufficient for the microstructure of the steel of the wire to transform into a microstructure essentially

09000930 centered cubic; (4) cold drawing the steel wire to a reduction in section sufficient to reduce the diameter of the steel wire from about 40% to about 80%; (5) heating the steel wire in a second patenting stage to a temperature which is in the range of about 900 ° C to about 1100 ° C for a period of at least about 1 second; (6) rapidly cooling the steel wire to a temperature in the range of about 540 ° C to about 620 ° C in a time of less than about 4 seconds; (7) maintaining the steel wire at a temperature in the range of about 540 ° C to about 620 ° C for a time sufficient for the microstructure of the steel of the wire to transform into an essentially cubic centered microstructure , and (8) cold drawing the steel wire to a reduction in section sufficient to reduce the diameter of the steel wire from about 60% to about 98% to produce the steel filament.

Detailed description of the invention.

The alloyed steels of the invention have a high tensile strength, a high ductility and a high resistance to fatigue. In addition, they have an extremely high isothermal transformation speed. For example, the steels of the invention can be transformed virtually completely from a cubic microstructure with centered faces into a cubic microstructure centered during a patenting in about 20 seconds at most. In most cases, the steels of the invention can be transformed essentially completely into a centered cubic structure in less than about 10 seconds during patenting. This is very important because it is very difficult in industrial operations to have more than about 15 seconds for processing to take place. It is highly desirable that the transformation be completed in about 10 seconds if not less. Steels that require more than about 20 seconds for processing to take place

U900C930 are very inconvenient to use.

Eight alloys have been developed with a satisfactory combination of properties. One of these alloys has been found to have a combination of properties which is excellent for use in steel filaments for reinforcing rubber. It essentially consists of approximately 95.5% by weight to approximately 99.05% by weight of iron, approximately 0.6% by weight to approximately 1% by weight of carbon, approximately 0.1% by weight to approximately 1% by weight. weight of silicon, approximately 0.1% by weight to approximately 1.2% by weight of manganese, approximately 0.1% by weight to approximately 0.8% by weight of chromium and approximately 0.05% by weight to approximately 0 , 5% by weight of cobalt. This alloy preferably contains about 97.4% by weight to about 98.5% by weight of iron, about 0.7% by weight to about 0.8% by weight of carbon, about 0.1% by weight to about 0.3% by weight of silicon, approximately 0.4% by weight to approximately 0.8% by weight of manganese, approximately 0.2% by weight to approximately 0.5% by weight of chromium and approximately 0.1% by weight to about 0.2% by weight of cobalt.

An alloy which has a very good combination of properties consists essentially of about 95.8% by weight to about 99.3% by weight of iron, about 0.4% by weight to about 1% by weight of carbon, about 0, 1% by weight to approximately 1% by weight of silicon, approximately 0.1% by weight to approximately 1.2% by weight of manganese, approximately 0.05% by weight to approximately 0.5% by weight of molybdenum and from about 0.05% by weight to about 0.5% by weight of cobalt. More advantageously, this alloy essentially contains approximately 97.6% by weight to approximately 98.5% by weight of iron, approximately 0.6% by weight to approximately 0.7% by weight of carbon, approximately 0.1% by weight to about 0.3% by weight of silicon, about 0.6% by weight to about 1% by weight of manganese, about 0.1% by weight to about 0.2% by weight of molybdenum and about 0.1% by weight to about 0.2% by weight of cobalt.

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Another alloy which has been found to have a good combination of properties consists essentially of about 96% by weight to about 99.1% by weight of iron, about 0.6% by weight to about 1% by weight of carbon, about 0.1% by weight to approximately 1.2% by weight of manganese, approximately 0.1% by weight to approximately 1% by weight of silicon and approximately 0.1% by weight to approximately 0.8% by weight of chromium . This alloy preferably contains about 97.5% by weight to about 98.5% by weight of iron, about 0.8% by weight to about 0.9% by weight of carbon, about 0.2% by weight to about 0.5% by weight of manganese, approximately 0.3% by weight to approximately 0.7% by weight silicon and approximately 0.2% by weight to approximately 0.4% by weight of chromium.

Another alloy which has been found to have a good combination of properties consists essentially of about 95.74% by weight to about 99.09% by weight of iron, about 0.6% by weight to about 1% by weight of carbon , about 0.1% by weight to about 1% by weight of silicon, about 0.1% by weight to about 1.2% by weight of manganese, about 0.01% by weight to about 0.06% by weight niobium, about 0.05% by weight to about 0.5% by weight of molybdenum and about 0.05% by weight to about 0.5% by weight of cobalt. This alloy preferably preferably contains approximately 97.66% by weight to approximately 98.58% by weight of iron, approximately 0.7% by weight to approximately 0.8% by weight of carbon, approximately 0.1% by weight to about 0.3% by weight of silicon, about 0.4% by weight to about 0.8% by weight of manganese, about 0.02% by weight to about 0.04% by weight of niobium, about 0.1 % by weight to approximately 0.2% by weight of molybdenum and approximately 0.1% by weight to approximately 0.2% cobalt.

An alloy which exhibits a satisfactory combination of properties consists essentially of about 96.3% by weight to about 99.15% by weight of iron, about 0.6% by weight to about 1% by weight of carbon, about 0.1 % by weight to approximately 1% by weight of silicon, approximately 0.1% by weight to approximately 1.2% by weight of manganese

09000930 and from about 0.05% by weight to about 0.5% by weight of vanadium. This alloy preferably contains essentially about 97.9% by weight to about 98.7% by weight of iron, about 0.7% by weight to about 0.8% by weight of carbon, about 0.1% by weight at about 0.3% by weight of silicon, about 0.4% by weight to about 0.8% by weight of manganese and about 0.1% by weight to about 0.2% by weight of vanadium.

Another alloy which has been found to have a satisfactory combination of properties consists essentially of about 95.4% by weight to about 99.29% by weight of iron, about 0.4% by weight to about 1% by weight of carbon , about 0.1% by weight to about 1% by weight of silicon, about 0.1% by weight to about 1.2% by weight of manganese, about 0.1% by weight to about 0.8% by weight of chromium and about 0.01% by weight to about 0.06% by weight of niobium. This alloy preferably contains about 97.66% by weight to about 98.68% by weight of iron, about 0.6% by weight to about 0.7% by weight of carbon, about 0.1% by weight to about 0.3% by weight of silicon, approximately 0.4% by weight to approximately 0.8% by weight of manganese, approximately 0.2% by weight to approximately 0.5% by weight of chromium and approximately 0.02% by weight to about 0.04% by weight of niobium.

Another alloy which has been found to have a satisfactory combination of properties consists essentially of about 94.94% by weight to about 98.99% by weight of iron, about 0.6% by weight to about 1% by weight of carbon , about 0.1% by weight to about 1% by weight of silicon, about 0.1% by weight to about 1.2% by weight of manganese, about 0.1% by weight to about 0.8% by weight chromium, approximately 0.05% by weight to approximately 0.5% by weight of vanadium, about 0.01% by weight to about 0.06% by weight of niobium and about 0.05% by weight to about 0.5% by weight of cobalt. This alloy preferably preferably contains essentially about 97.16% by weight to about 98.38% by weight of iron, about 0.7% by weight to about 0.8% by weight.

0900C930 weight of carbon, approximately 0.1% by weight to approximately 0.3% by weight of silicon, approximately 0.4% by weight to approximately 0.8% by weight of manganese, approximately 0.2% by weight to approximately 0.5% by weight of chromium, approximately 0.1% by weight to approximately 0.2% by weight of vanadium, approximately 0.02% by weight to approximately 0.04% by weight of niobium and approximately 0.1% by weight to about 0.2% by weight of cobalt.

Another alloy which has been found to have a satisfactory combination of properties consists essentially of about 94% by weight to about 99.29% by weight of iron, about 0.4% by weight to about 1% by weight of carbon, about 0.1% by weight to approximately 1% by weight of silicon, approximately 0.1% by weight to approximately 1.2% by weight of manganese, approximately 0.05% by weight to approximately 0.5% by weight of vanadium , about 0.05% by weight to about 0.5% by weight of molybdenum and about 0.01% by weight to about 0.06 by weight of niobium. This alloy preferably preferably contains approximately 97.76% by weight to approximately 98.68% by weight of iron, approximately 0.6% by weight to approximately 0.7% by weight of carbon, approximately 0.1% by weight to about 0.3% by weight of silicon, about 0.4% by weight to about 0.8% by weight of manganese, about 0.1% by weight to about 0.2% by weight of vanadium, about 0.1 % by weight to approximately 0.2% by weight of molybdenum and approximately 0.02% by weight to approximately 0.04% by weight of niobium.

Another alloy which has been found to have a satisfactory combination of properties consists essentially of about 95.74% by weight to about 99.09% by weight of iron, about 0.6% by weight to about 1% by weight of carbon , about 0.1% by weight to about 1% by weight of silicon, about 0.1% by weight to about 1.2% by weight of manganese, about 0.01% by weight to about 0.06% by weight niobium, about 0.05% by weight to about 0.5% by weight of molybdenum and about 0.05% by weight to about 0.5% by weight of cobalt. This alloy preferably preferably contains essentially about 97.26% by weight to about 98.38% v / yy V / JU by weight of iron, about 0.7% by weight to about 0.8% by weight of carbon, about 0 0.3% by weight to about 0.7% by weight of silicon, about 0.4% by weight to about 0.8% by weight of manganese, about 0.02% by weight to about 0.04% by weight of niobium, about 0.1% by weight to about 0.2% by weight of molybdenum and about 0.1% by weight to about 0.2% by weight of cobalt.

Wire rods having a diameter of about 5 mm to about 6 mm which are formed from the alloy steels of the present invention can be formed into steel filaments which can be used as reinforcing elements for rubber products. These machine wires are typically cold drawn to a diameter in the range of about 2.8mm to about 3.5mm. For example, a wire rod having a diameter of about 5.5 mm can be cold drawn into a wire having a diameter of about 3.2 mm. This cold drawing increases the strength and hardness of the metal.

The cold drawn wire is then patented by heating the wire to a temperature in the range of about 900 ° C to about 1100 ° C for a period of at least about 5 seconds. In cases where electrical resistance heating is performed, a heating time of about 5 seconds to about 15 seconds is typical. An even more typical heating time is in the range of about 6 seconds to about 10 seconds when electric resistance heating is performed. It is obviously also possible to heat the wire in a fluidized bed oven. In such cases, the wire is heated in a fluidized bed of fine-grained sand. In fluid bed heating techniques, the heating time is generally in the range of about seconds to about 30 seconds. A more typical heating time in a fluidized bed oven is in the range of about 15 seconds to about 20 seconds.

is also possible to heat the wire for the

09000930 patenting in a convection oven. However, in the case where convection heating is carried out, longer heating times are required. For example, it is typically necessary to heat the wire by convection for a period of at least about 40 seconds. It is preferred that the wire is heated by convection for a period of time from about 45 seconds to about 2 minutes.

The exact duration of heating is not critical. However, it is important that the temperature is maintained for a sufficient time to austenitize the steel. In industrial operations, temperatures in the range of about 950 ° C to about 1050 ° C are maintained to austenitize the steel of the wire.

During patenting, after the formation of austenite, it is important to rapidly cool the steel wire to a temperature in the range of about 540 ° C to about 650 ° C in less than about 4 seconds. It is desirable that this cooling takes place in a period of 3 seconds if not less. This rapid cooling can be carried out by immersing the wire in molten lead which is maintained at a temperature of 580 ° C. Many other techniques for rapid wire cooling can also be applied.

After the wire has been rapidly cooled to a temperature in the range of about 540 ° C to about 620 ° C, it is necessary to maintain the wire at a temperature in this range for a time sufficient for the microstructure of the steel of the wire is transformed from a cubic microstructure centered of austenite into an essentially cubic microstructure with centered faces. As already indicated, for practical reasons, it is very important that this transformation takes place within approximately 15 seconds and it is highly preferable that the transformation takes place within 10 seconds if not less.

09000930

Patenting is considered complete after the transformation to an essentially cubic centered microstructure has been completed. At the end of the first patenting stage, the patented wire is again drawn using a cold drawing technique. At this stretching stage, the wire diameter is reduced from about 40% to about 80%. It is preferred that the wire diameter be reduced from 50% to 60% by drawing. After this stretching has been completed, the drawn wire typically has a diameter of from about 1 mm to about 2 mm. For example, a wire originally having a diameter of

3.2mm can be stretched to a diameter of about 1.4mm.

The cold drawn wire is then patented during a second stage of patenting. This second patenting operation is carried out essentially using the same technique as that applied in the first patenting stage. However, because the wire diameter is smaller, it takes less time to austenitize the steel of the wire. For example, if electric resistance heating is performed, heating in the second patenting stage can be done in as little as about 1 second. However, it may be necessary to expose the wire to electrical resistance heating for 2 seconds or more for the steel to be austenitized as it should be. If a fluidized bed oven is used for heating, a heating time of 4 seconds to 12 seconds is typical. In cases where convection heating is performed, a heating time in the range of about 15 seconds to about 60 seconds is typical.

After the wire has undergone the second complete patenting operation, it is again cold drawn. During this cold drawing, the diameter of the wire is reduced from about 60% to about 98% to give the steel filaments according to the invention. It is more typical for the wire diameter to be reduced from about 85% to about 90%. Thus, the filaments according to the invention typically have a diameter of the interval from approximately 0.15 mm to approximately

09000930

0.38mm. Filaments having a diameter of about 0.175 mm are typical.

Often it may be desirable to twist two or more filaments into a cord for use as a reinforcement for rubber products. For example, it is typical to twist two of these filaments into a cable for use in passenger car tires. Obviously, it is also possible to twist a larger number of the filaments into a cable for use in other applications. For example, it is typical to twist around 50 cable filaments that are ultimately used in tires for earth-moving machinery. Often it may be desirable to cover the steel with a layer of brass. Such an operation of coating steel reinforcing elements using a ternary brass is described in US Patent No. 4,446,198.

The present invention is described in more detail in the following examples. These are only intended to illustrate and are not to be considered as limiting the scope of the invention, nor the manner of putting it into practice. Unless stated otherwise, parts and percentages are always by weight.

EXAMPLES 1 TO 9. In the present experiment, nine alloys are prepared, the isothermal transformation times of which are determined by a hardening dilatometry test. The approximate quantities of the various metals of these nine alloys are detailed in Table I. The quantities in Table I are percentages by weight.

09000930

TABLE I

<td>Ex.</td><td>Fe</td><td>VS</td><td>Yes</td><td>Mn</td><td>Çr</td><td>V</td><td>Nb</td><td>Mo</td><td>CO</td>

<td> 1</td><td> 98,15</td><td> 0,65</td><td> 0,20</td><td> 0,80</td><td> -</td><td> -</td><td> -</td><td> 0,10</td><td> 0,10</td>

<td> 2</td><td> 98,05</td><td> 0,75</td><td> 0,20</td><td> 0,60</td><td> 0,30</td><td> -</td><td> -</td><td> -</td><td> 0,10</td>

<td> 3</td><td> 98,10</td><td> 0,80</td><td> 0,50</td><td> 0,30</td><td> 0,30</td><td></td><td> -</td><td> -</td><td> -</td>

<td> 4</td><td> 98,22</td><td> 0,75</td><td> 0,20</td><td> 0,60</td><td> -</td><td> -</td><td> 0,03</td><td> 0,10</td><td> 0,10</td>

<td> 5</td><td> 98,15</td><td> 0,75</td><td> 0,20</td><td> 0,80</td><td> -</td><td> 0,10</td><td> -</td><td> -</td><td> -</td>

<td> 6</td><td> 98,02</td><td> 0,65</td><td> 0,20</td><td> 0,80</td><td> 0,30</td><td> -</td><td> 0,03</td><td> -</td><td> -</td>

<td> 7</td><td> 97,17</td><td> 0,75</td><td> 0,75</td><td> 0,80</td><td> 0,30</td><td> 0,10</td><td> 0,03</td><td> -</td><td> 0,10</td>

<td> 8</td><td> 98,32</td><td> 0,65</td><td> 0,20</td><td> 0,60</td><td> -</td><td> 0,10</td><td> 0,03</td><td> 0,10</td><td> -</td>

<td> 9</td><td> 97,92</td><td> 0,75</td><td> 0,50</td><td> 0,60</td><td> -</td><td> -</td><td> 0,03</td><td> 0,10</td><td> 0,10</td>

The dilatometric test simulates the heat treatment cycle during a patenting operation. It consists of three stages. Each of the alloys is austenitized at 980 ° C for 64 seconds. After being austenitized, each of the alloys is rapidly cooled to 550 ° C in 4 seconds. Measurements are made to determine how long it takes for the microstructure of each of the steels to start to change from the face centered cubic microstructure to the centered cubic microstructure (start). This determination is made by monitoring the heat generation. It is also confirmed by a study of the expansion curve and of the real microstructures of the specimens thus cooled. The time required for the microstructure of the alloy to be converted in substance completely to a centered cubic microstructure is also measured (end). These times are shown in Table II for each of the alloys.

09000930

TABLE II

Processing speeds

Example

9

Start (dry

End (dry)

3.5

7 9

6.5 5

As can be seen, the total transformation time required for the alloy of Example 4 is only

3.5 seconds. All the alloys, with the exception of that of Example 3, have transformation times of 10 seconds if not less. The alloy of Example 3 has a relatively low transformation speed. However, the physical properties of the filaments made from the alloy of Example 3 are exceptionally good.

0.25 mm filaments are formed from machine wires formed from each of these nine alloys. The operation is carried out by cold drawing 5.5 mm machine wires from each of the alloys to 3.2 mm wires. Next, the threads are patented and they are cold drawn again to a diameter of approximately 1.4 mm. The strands are patented again during a second patenting stage, after which they are cold drawn again to the final diameter of 0.25 mm of the filaments. Next, the tensile strength, the percentage elongation at break and the necking at break are determined by testing the filaments. These physical parameters are detailed in Table III.

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TABLE III

Example Elongation Resistance Strict Tensile

<td> 1</td><td> 2690</td><td>MPa</td><td> 2,2%</td><td> 47%</td>

<td> 2</td><td> 3110</td><td>MPa</td><td> 2,4%</td><td> 38%</td>

<td> 3</td><td> 3100</td><td>MPa</td><td> -</td><td> 52%</td>

<td> 4</td><td> 3038</td><td>MPa</td><td> 2,3%</td><td> 39%</td>

<td> 5</td><td> 3034</td><td>MPa</td><td> 2,3%</td><td> 41%</td>

<td> 6</td><td> 2610</td><td>MPa</td><td> 2,1%</td><td> 34%</td>

<td> 7</td><td> 2971</td><td>MPa</td><td> 2,3%</td><td> 45%</td>

<td> 8</td><td> 2670</td><td>MPa</td><td> 2,2%</td><td> 42%</td>

<td> 9</td><td> 3076</td><td>MPa</td><td> 2,3%</td><td> 41%</td>

As can be seen, each of the alloys has an excellent combination of high tensile strength and high ductility. As is apparent, these alloys can also be patented in industrial practice because of their high processing speed.

COMPARISON EXAMPLES 10 TO 30 The nine alloys of the invention provide an unusual combination of high tensile strength, high ductility and high processing speed. The present series of comparison examples is given to show that many similar alloys have unsatisfactory transformation rates. During this comparison experiment, 21 alloys are produced which are subjected to the hardening dilatometry test as described in Examples 1 to 9. The approximate quantities of the different metals in the 21 alloys tested are detailed in the table. IV. The quantities given in Table IV are percentages by weight.

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TABLE IV

<td>Ex.</td><td>Fe</td><td>VS</td><td>if</td><td>Mn</td><td>Cr</td><td>V</td><td>Nb</td><td>Mo</td><td>co</td>

<td> 10</td><td> 97,85</td><td> 0,65</td><td> 0,50</td><td> 0,80</td><td> -</td><td> -</td><td> -</td><td> 0,10</td><td> 0,10</td>

<td> 11</td><td> 97,45</td><td> 0,65</td><td> 0,50</td><td> 0,80</td><td> 0,30</td><td> 0,10</td><td> -</td><td> 0,10</td><td> 0,10</td>

<td> 12</td><td> 97,75</td><td> 0,75</td><td> 0,50</td><td> 0,60</td><td> 0,30</td><td> -</td><td> -</td><td> -</td><td> 0,10</td>

<td> 13</td><td> 97,85</td><td> 0,75</td><td> 0,50</td><td> 0,80</td><td> -</td><td> 0,10</td><td> -</td><td> -</td><td> -</td>

<td> 14</td><td> 97,50</td><td> 0,75</td><td> 0,75</td><td> 0,80</td><td> -</td><td> 0,10</td><td> -</td><td> 0,10</td><td> -</td>

<td> 15</td><td> 97,72</td><td> 0,65</td><td> 0,50</td><td> 0,80</td><td> 0,30</td><td> -</td><td> 0,03</td><td> -</td><td> -</td>

<td> 16</td><td> 97,37</td><td> 0,75</td><td> 0,75</td><td> 0,80</td><td> 0,30</td><td> -</td><td> 0,03</td><td> -</td><td> -</td>

<td> 17</td><td> 97,95</td><td> 0,75</td><td> 0,20</td><td> 0,60</td><td> 0,30</td><td> 0,10</td><td> -</td><td> 0,10</td><td> -</td>

<td> 18</td><td> 97,65</td><td> 0,75</td><td> 0,50</td><td> 0,60</td><td> 0,30</td><td> 0,10</td><td> -</td><td> 0,10</td><td> -</td>

<td> 19</td><td> 97,37</td><td> 0,75</td><td> 0,75</td><td> 0,60</td><td> 0,30</td><td> 0,10</td><td> 0,03</td><td> 0,10</td><td> -</td>

<td> 20</td><td> 98,02</td><td> 0,75</td><td> 0,20</td><td> 0,80</td><td> -</td><td> 0,10</td><td> 0,03</td><td> -</td><td> 0,10</td>

<td> 21</td><td> 97,72</td><td> 0,75</td><td> 0,50</td><td> 0,80</td><td> -</td><td> 0,10</td><td> 0,03</td><td> -</td><td> 0,10</td>

<td> 22</td><td> 97,82</td><td> 0,75</td><td> 0,20</td><td> 0,80</td><td> 0,30</td><td> -</td><td> 0,03</td><td> 0,10</td><td> -</td>

<td> 23</td><td> 97,52</td><td> 0,75</td><td> 0,50</td><td> 0,80</td><td> 0,30</td><td> -</td><td> 0,03</td><td> 0,10</td><td> -</td>

<td> 24</td><td> 97,17</td><td> 0,75</td><td> 0,75</td><td> 0,80</td><td> 0,30</td><td> 0,10</td><td> 0,03</td><td> 0,10</td><td> -</td>

<td> 25</td><td> 98,02</td><td> 0,65</td><td> 0,20</td><td> 0,60</td><td> 0,30</td><td> 0,10</td><td> 0,03</td><td> -</td><td> 0,10</td>

<td> 26</td><td> 97,72</td><td> 0,65</td><td> 0,50</td><td> 0,60</td><td> 0,30</td><td> 0,10</td><td> 0,03</td><td> -</td><td> 0,10</td>

<td> 27</td><td> 97,72</td><td> 0,65</td><td> 0,75</td><td> 0,80</td><td> 0,30</td><td> 0,10</td><td> 0,03</td><td> -</td><td> 0,10</td>

<td> 28</td><td> 98,02</td><td> 0,65</td><td> 0,50</td><td> 0,60</td><td> -</td><td> 0,10</td><td> 0,03</td><td> 0,10</td><td> -</td>

<td> 29</td><td> 97,67</td><td> 0,75</td><td> 0,75</td><td> 0,60</td><td> -</td><td> 0,10</td><td> 0,03</td><td> 0,10</td><td> -</td>

<td> 30</td><td> 97,47</td><td> 0,75</td><td> 0,75</td><td> 0,80</td><td> -</td><td> -</td><td> 0,03</td><td> 0,10</td><td> 0,10</td>

The transformation rates for each of the 21 alloys are given in Table V.

0900093C

<td colspan="3">TABLE V</td>

<td>Example</td><td>Start (dry)</td><td>End (dry)</td>

<td> 10</td><td> 3</td><td> 11</td>

<td> 11</td><td> 20</td><td>NF</td>

<td> 12</td><td> 3</td><td> 11</td>

<td> 13</td><td> 2</td><td> 14</td>

<td> 14</td><td> 19</td><td> 49</td>

<td> 15</td><td> 14</td><td> 21</td>

<td> 16</td><td> 8</td><td> 45</td>

<td> 17</td><td> 13</td><td> 35</td>

<td> 18</td><td> 25</td><td>NF</td>

<td> 19</td><td> 30</td><td>NF</td>

<td> 20</td><td> 1,9</td><td> 14</td>

<td> 21</td><td> 1,5</td><td> 11</td>

<td> 22</td><td> 25</td><td> 48</td>

<td> 23</td><td> 35</td><td>NF</td>

<td> 24</td><td> 30</td><td>NF</td>

<td> 25</td><td> 2</td><td> 20</td>

<td> 26</td><td> 6</td><td> 31</td>

<td> 27</td><td> 15</td><td> 45</td>

<td> 28</td><td> 3</td><td> 19</td>

<td> 29</td><td> 9</td><td> 36</td>

<td> 30</td><td> 8</td><td> 25</td>

<td>not finished in</td><td>50 seconds</td><td>at 550 ° C.</td>

As can be seen, none of the comparison alloys tested complete the transformation (conversion to an essentially cubic centered microstructure) in less than 10 seconds. Consequently, none of the comparison alloys can be patented easily on an industrial scale. On the other hand, the alloys of Examples 1, 4 and 9 complete the transformation in 5 seconds if not less.

09000930

Although various embodiments and details have been given to illustrate the invention, it is obvious that it is susceptible of numerous variations and modifications without departing from its scope.

09000930