EP2732061A1

EP2732061A1 - Chromium-molybdenum alloy

Info

Publication number: EP2732061A1
Application number: EP12710674.8A
Authority: EP
Inventors: Matthias Kuntz; Friedrich Muehleder
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2011-05-12
Filing date: 2012-03-13
Publication date: 2014-05-21
Anticipated expiration: 2032-03-13
Also published as: DE102011075697A1; WO2012152477A1; EP2732061B1

Abstract

The present invention relates to a chromium-molybdenum alloy, selected from the group consisting of 42CrMo4 and 18CrNiMo7-6, wherein the alloy comprises: manganese in an amount from ≥ 1.0% by weight to ≤ 1.3% by weight; aluminium in an amount from > 0% by weight to ≤ 0.05% by weight; niobium in an amount from > 0% by weight to ≤ 0.04% by weight and nitrogen in an amount from > 0% by weight to ≤ 0.015% by weight. The alloy according to the invention serves in particular for producing a component that has improved properties with respect to cyclic stress resistance in a rolling contact.

Description

description

title

Chrome alloy Molvbden

The present invention relates to a chromium-molybdenum alloy. More particularly, the present invention relates to an alloy based on 42CrMo4 or 18CrNiMo7-6 which comprises an alloy of manganese and a

Microalloying of aluminum, niobium and nitrogen has.

State of the art

For many applications, high-strength materials are needed. A significant limitation of the use of high-strength materials is given for example by their mechanical properties. Furthermore, the component manufacturing route may impose limitations. Especially for large-sized components, a high strength of importance, since often act large forces and a replacement of damaged parts is very expensive.

In the development of solid materials, it is possible to resort to alloys, since these are known to have a high hardness and tensile strength.

From DE 10 2007 021 101 A1 an alloyed steel is known, which in a

Motor vehicle and can be found here in particular in an internal combustion engine, such as a piston or as a piston component, use. This steel is based on an AFP steel and has the following composition, each in weight%: carbon: 0.35-0.50; Silicon: 0.15-0.80; Manganese: 1, 20-2, 00; Phosphorus: 0.00-0.0025; Nitrogen: 0.010-0.035; Chromium: 0.00-0.50; Molybdenum: 0.00-0.050; Nickel: 0.00-0.15; Copper: 0.00-0.40; Vanadium: 0.13-0.40; Titanium: 0.001-0.004; Aluminum: 0.00-0.04; Niobium: 0.00-0.05; in which at least two of the elements vanadium, aluminum and niobium are included. It is stated that a low titanium content of 0.001 wt.% To 0.004 wt.% Is a decisive factor in order to obtain mechanical properties comparable to the mechanical properties of tempered steels.

Disclosure of the invention

The invention relates to a chromium-molybdenum alloy selected from the group consisting of 42CrMo4 and 18CrNiMo7-6, the alloy comprising: manganese in an amount of> 1, 0 wt .-% to <1, 3 wt .-% ; Aluminum in an amount of> 0 wt .-% to <0.05 wt .-%; Niobium in an amount of> 0 wt .-% to <0.04 wt .-% and nitrogen in an amount of> 0 wt .-% to <0.015 wt .-%.

The alloy according to the invention has a defined composition of characteristic alloying elements. The basis for the

Alloy according to the invention form the tempering steel 42CrMo4 or the insert steel 18CrNiMo7-6. The composition of such alloys is known to those skilled in the art. According to the invention, a 42CrMo4 alloy and an 18CrNiMo7-6 alloy include in particular the following metallic ones

Compounds in the following concentrations, the concentrations being given in weight percent (wt.%) (Table 1):

Element 42CrMo4 18CrNiMo7-6

C> 0.38 to <0.45> 0.15 to <0.20

Si <0.40 <0.40

Mn> 0.60 to <0.90> 0.35 to <0.70

P <0.025

S <0.035

Cr> 0.90 to <1, 20> 1, 50 to <1, 80

Mo> 0.15 to <0.30> 0.25 to <0.35

Ni -> 1.40 to <1.70 The per se known alloys 42CrMo4 or the insert steel 18CrNiMo7-6 are modified according to the invention by an addition of manganese, whereby the amount of manganese according to the invention no longer corresponds to the amounts given in Table 1, but are higher, in particular in a range of> 1, 0 to <1, 3 wt .-%. Furthermore, the alloys according to the invention have a microalloy of niobium, aluminum and nitrogen.

In this case, aluminum is present in an amount of> 0 wt .-% to <0.05 wt .-%; Niobium in an amount of> 0 wt .-% to <0.04 wt .-% and nitrogen in an amount of> 0 wt .-% to <0.015 wt .-% before. Aluminum is particularly preferably present in an amount of> 0.01% by weight to <0.025% by weight; Niobium in an amount of> 0.01 wt .-% to <0.02 wt .-% and nitrogen in an amount of> 0.005 wt .-% to <0.010 wt .-% before. Further, in an alloy based on 18CrNiMo7-6, a niobium content of <0.03 wt% may be sufficient.

The specified concentrations always result in 100 wt .-%, wherein the unlisted rest is given in particular by iron (Fe).

By adding the aforementioned micro-alloying an initial state is generated in the alloy, which in further processing and / or

Heat treatment steps to a grain refining effect in the

Alloy structure leads. In particular, the micro-alloying elements prevent grain growth in a heat treatment. Therefore, according to the present invention, it is possible to obtain an ASTM grain size in a range of> 12 to <13 with a heat treatment route in a 42CrMo4-based alloy. Further, according to the present invention, in an alloy based on 18CrNiMo7-6, an ASTM grain size in a range of> 13 to <14 can be obtained. For the determination of the ASTM grain size (ASTM: American Society for Testing Materials), in particular the micrograph of the alloy with the ASTM straightening series of stylized grain boundary nets of sizes 1 (16 grains / mm ² ) to 8 (about 200 grains / mm ² ) hundred times magnification compared.

The aforementioned effect occurs in particular in that the microalloyed alloying partners can form aluminum and niobium according to the invention with the likewise added micro-alloyed nitrogen carbonitrides. These intermetallic compounds attach themselves to the grain boundaries and can thus prevent grain growth and thus lead to smaller particle sizes. The added manganese stabilizes especially the austenitic ones

Hochtenmperaturphase and delayed so, for example, at a

Heat treatment, the transformation of this phase in the martensitic low-temperature phase. This enhances the grain-refining effect. According to the invention it is therefore particularly possible to achieve alloys with a small grain size. In particular, a fine grain can ensure a more uniform distribution of the impurities, more perfect isotropy, greater strength, hardness, toughness and impact energy.

The alloy according to the invention makes it possible, in particular, to make it possible to increase the cyclic resistance and the resistance to rolling fatigue, whereby the component production route can essentially remain unchanged. This can improve the reliability of the components without significant additional costs or without

Additional costs are possible. Due to the improved mechanical

Properties can be improved, for example, the power density of large gearboxes.

Furthermore, it is possible to design components more compact, since correspondingly smaller or thinner components can be provided for comparable mechanical properties. As a result, material can be saved in the production of corresponding components, which can save considerable costs.

In particular for large transmission components, the load capacity and / or the behavior under rolling contact is of crucial importance.

According to the invention, existing component production routes based on the alloy according to the invention can remain unchanged. Changes to the processes are not or only insignificantly necessary in negligible effort. As a result, the alloy according to the invention can be produced in a simple and cost-effective manner without the need for

costly conversions and associated downtime in existing manufacturing processes are integrated. The alloy according to the invention can also be used without difficulty in existing processes in a wide range, which makes possible a wide range of application of the invention. This is particularly advantageous in the case of large transmission components, since here the component production route is severely limited due to the dimensioning of the components.

The alloy may further comprise phosphorus and / or sulfur and / or oxygen. These elements can occur as accompanying elements and can have a concentration in a conventional range known to the person skilled in the art. The presence of phosphorus, for example, can increase the strength, in particular the tensile strength, and the hardness, in particular at a carbon content of about 0.1% and at the same time

Improve corrosion resistance against atmospheric influences. The presence of sulfur can reduce ductility, allowing for greater component stability, particularly in rolling contact.

Within the scope of a further advantageous embodiment of the present invention

According to the invention, the manganese is present in an amount of> 1, 0 wt .-% to <1, 2 wt .-%, and / or the aluminum is in an amount of> 0.04 wt .-% to <0.05 Wt .-% before, and / or the nitrogen is present in an amount of <0.010 wt .-%. With such a composition could be particularly good

Properties with regard to hardness and stability can be found.

In a particularly preferred embodiment, the alloy according to the invention is a chromium-molybdenum alloy selected from the group consisting of 42CrMo4 and 18CrNiMo7-6, the alloy being used as further alloy components, ie as alloy constituents in addition to the

Base alloy constituents of the 42CrMo4 alloy or the 18CrNiMo7-6 alloy, exclusively comprising: aluminum, niobium, nitrogen and optionally phosphorus, sulfur and / or oxygen. In this case, the alloy constituents are present in particular in the above-described concentrations, the alloy components being present together with a remainder of iron and thus adding up to 100% by weight. In this context, the term "alloying component" refers in particular to substances which form mixed crystals with one another. The invention further relates to a method for producing a component, comprising the steps:

Providing an alloy according to the invention,

Forms of alloy,

Performing a heat treatment of the shaped alloy.

The inventive method can be produced in a particularly simple manner, a component which consists of the alloy according to the invention or is constructed essentially of this. In this case, an alloy according to the invention is first provided, which can be carried out by a conventional method known to the person skilled in the art. For example, the alloy may be provided in a conventional steelmaking process with the actual alloying adjustment in secondary metallurgy. Subsequently, the alloy is shaped, that is brought into a shape corresponding to the component to be produced. Subsequently, the molded alloy is subjected to a heat treatment. The heat treatment can have several functions. For example, the individual constituents of the alloy can be homogenized by a heat treatment. Furthermore, a heat treatment is used in particular to harden the alloy. This can be done, for example, in the case that the alloy according to the invention is based on an 18CrNiMo7-6 alloy, by a conventional multiple hardening. For this purpose, for example, the shaped alloy can be repeatedly heated to a temperature in a range of> 800 ° C to <1200 ° C and quenched after a short time of holding the temperature. This method is known to those skilled in the art.

In the case where the alloy according to the invention is based on a 42CrMo4 alloy, the heat treatment may in particular comprise the following steps:

Heating the alloy to a temperature in a range of> 1000 ° C to <1400 ° C, maintaining the temperature for a period in the range of> 3 minutes to <7 minutes, and quenching the alloy in a period of <1 minute Temperature in a range of <50 ° C; Heating the alloy to a temperature in a range of> 800 ° C to <1000 ° C, maintaining the temperature for a period in the range of> 20 minutes to <45 minutes, and cooling the alloy to a value of <1 minute Temperature in a range of> 550 ° C to <790 ° C, maintaining the temperature for a period in the range of> 60 minutes to <120 minutes and cooling the alloy in a period of <1 minute to a temperature in a range of <50 ° C;

Heating the alloy to a temperature in a range of> 750 ° C to <1000 ° C and maintaining the temperature for a period in the range of> 10 seconds to <45 seconds, and cooling the alloy to a temperature in a range of > 550 ° C to <745 ° C and holding the temperature for a period in the range of> 5 seconds to <10 seconds, and

then cooling the alloy for a period of <1 minute to a temperature in the range of <50 ° C,

Heating the alloy to a temperature in a range of> 750 ° C to <1000 ° C, maintaining the temperature for a period in the range of> 5 minutes to <15 minutes, and quenching the alloy in a period of <1 minute Temperature in a range of <50 ° C.

The heat treatment is thus a heat treatment comprising four steps. In principle, the four steps can also be carried out individually and independently of each other as a single heat treatment or in a suitable combination of the individual steps. Overall, heating ramps in a range of> 2 ° C / s to <4 ° C / s, in particular of 3.3 ° C / s are preferably used for each heating, whereas for each cooling quench ramps in a range of> 25 ° C / s to <75 ° C / s, in particular of 50 ° C / s used.

In a first step, a solution annealing is carried out, which serves in particular to homogenize the individual alloy components. This solution annealing is carried out in particular in a temperature range of> 1000 ° C to <1400 ° C, preferably at 1200 ° C for a period of> 3 minutes to <7 minutes, preferably 5 minutes. In a second step, the alloy becomes a two-stage

Subjected to heat treatment without intermediate quenching. This step is a so-called FP annealing (ferritic-perlitic) and serves

in particular to set a defined strength. This step is particularly described with reference to the first stage in a temperature range of> 800 ° C to <1000 ° C, preferably at 900 ° C for a period of> 20 minutes to <45 minutes, preferably for 30 minutes and then with reference to the second stage in a temperature range of> 550 ° C to <790 ° C, preferably at 680 ° C for a period of> 60 minutes to <120 minutes, preferably for 90 minutes performed.

In a third step, a so-called pendulum annealing takes place. In this step, the alloy is alternately heated to a temperature in a range of in particular> 750 ° C to <1000 ° C, preferably 850 ° C and subsequent to a temperature in a range of in particular> 550 ° C to <745 ° C, Preferably, the respective upper temperature is maintained for a period in a range of> 10 seconds to <45 seconds, preferably 30 seconds, and the respective lower temperature for a period in a range of> 5 seconds to <10 Seconds, preferably 7.5 seconds is held. By this pendulum annealing in particular the grain-refining effect is enhanced by a solution process takes place at each high temperature, whereas at the low temperature corresponding carbonitrides are released. This will be the

Grain formation increases, which is why a plurality of smaller nuclei is formed. By the pendulum annealing, so a variety of corresponding cycles, such as three cycles, this effect can be amplified.

In particular, the fourth step comprises heating the alloy to a temperature in a range of> 750 ° C to <1000 ° C, in particular

850 ° C, and maintaining the temperature for a period in the range of> 5 minutes to <15 minutes. This step is used in particular for curing the alloy. The invention further relates to a component comprising an alloy according to the invention. In this case, the invention includes in particular components that a Cyclic stress are exposed and in particular those experiencing a Wälzbeanspruchung. For example, components according to the invention include gearboxes and, in particular, large gearboxes or gearboxes whose components, such as toothed wheels or stationary components in the

General.

The invention further relates to the use of an alloy according to the invention for producing a component. This is a use

in particular for the production of such components advantageous, as described with respect to the component according to the invention.

Further advantages and advantageous embodiments of the objects according to the invention are illustrated by the drawing and explained in the following description. It should be noted that the

Drawing has only descriptive character and is not intended to limit the invention in any way. It shows

Fig. 1 is a schematic timing diagram for illustrating a

Production method according to the invention for a component comprising an alloy according to the invention.

FIG. 1 shows a time diagram of a method according to the invention for producing a component. The inventive method is based on the use of a chromium-molybdenum alloy according to the invention, selected from the group consisting of 42CrMo4 and 18CrNiMo7-6, wherein the alloy comprises: manganese in an amount of> 1, 0 wt .-% to <1.3 wt .-%; Aluminum in an amount of> 0 wt .-% to <0.05 wt .-%; Niobium in an amount of> 0 wt .-% to <0.04 wt .-% and nitrogen in an amount of> 0 wt .-% to <0.015 wt .-%. After the alloy has been shaped into the desired component, it is subjected to a heat treatment to set the desired mechanical properties.

The heat treatment comprises four steps and is shown schematically in FIG. 1 in a non-limiting embodiment in the form of a time diagram. In a first step, a solution annealing designated by a) is carried out, wherein the alloy is heated to a temperature range of 1200 ° C with a heating ramp of 3.3 ° C / s, where it remains for a period of 5 minutes and to a temperature of 0 ° C using a

Quench ramp of 50 ° C / s is cooled or quenched.

In a second step, an FP annealing designated by b) is carried out, wherein the alloy is heated to a temperature of 900 ° C. with a heating ramp of 3.3 ° C./s and remains at this temperature for a period of 30 minutes. Subsequently, the alloy is cooled to a temperature of 680 ° C using a quench ramp of 50 ° C / s and left at this temperature for a period of 90 minutes, after which the alloy is heated to a temperature using a quench ramp of 50 ° C / s is cooled or quenched from 0 ° C.

In a third step, there is a pendulum annealing called c). Here, the alloy is heated a total of three times with a heating ramp of 3.3 ° C / s to a temperature of 850 ° C and remains at that temperature for a period of 30 seconds. After the alloy has been maintained at a temperature of 850 ° C for the first and second time, each alloy is cooled to a temperature of 660 ° C using a quench ramp of 50 ° C / s and left there for 7.5 minutes each time is heated again to 850 ° C using the above-described Aufheizrampe. After leaving the alloy at a temperature of 850 ° C for the third time, it is cooled or quenched using a quench ramp of 50 ° C / s to a temperature of 0 ° C.

The fourth step is a hardening referred to as d), wherein the alloy is heated to a temperature range of 850 ° C with a heating ramp of 3.3 ° C / s, there for a period of 10 minutes and to a temperature of 0 ° C below Using a Abschreckrampe of 50 ° C / s is cooled or quenched.

Claims

claims

A chromium-molybdenum alloy selected from the group consisting of 42CrMo4 and 18CrNiMo7-6, the alloy comprising: manganese in an amount of> 1, 0% to <1, 3% by weight; Aluminum in an amount of> 0 wt .-% to <0.05 wt .-%; Niobium in an amount of> 0 wt .-% to <0.04 wt .-% and nitrogen in an amount of> 0 wt .-% to <0.015 wt .-%.

2. An alloy according to claim 1, characterized in that the manganese is present in an amount of> 1, 0 wt .-% to <1, 2 wt .-%, and / or the aluminum in an amount of> 0.04 wt % to <0.05% by weight, and / or the nitrogen is present in an amount of <0.010% by weight

3. Alloy according to claim 1 or 2, characterized in that the

Alloy is selected from a group consisting of 42CrMo4 and 18CrNiMo7-6, wherein the alloy contains as further alloying components exclusively: aluminum, niobium, nitrogen and optionally phosphorus, sulfur and / or oxygen.

4. A method of manufacturing a component, comprising the steps of:

Providing an alloy according to any one of claims 1 to 3, forming the alloy,

Performing a heat treatment of the shaped alloy.

5. The method according to claim 4, characterized in that

the alloy is based on a 42CrMo4 alloy; and

the heat treatment includes the following steps:

Heating the alloy to a temperature in the range of>

1000 ° C to <1400 ° C, keeping the temperature for a period in one

Range of> 3 minutes to <7 minutes and quenching the alloy in a period of <1 minute to a temperature in a range of <50 ° C;

Heating the alloy to a temperature in a range of> 800 ° C to <1000 ° C, maintaining the temperature for a period in the range of> 20 minutes to <45 minutes, and cooling the alloy to a value of <1 minute Temperature in a range of> 550 ° C to <790 ° C, maintaining the temperature for a period in the range of> 60 minutes to <120 minutes and cooling the alloy in a period of <1 minute to a temperature in a range of <50 ° C;

A component comprising an alloy according to any one of claims 1 to 3.

Use of an alloy according to any one of claims 1 to 3 for the manufacture of a component.