Title of Invention	A METHOD OF HEAT TREATMENT FOR PRODUCING A SHAFT FOR COMPRESSORS FROM A SHAFT MATERIAL
Abstract	The invention relates to a method of heat treatment for producing a shaft for compressors from a shaft material comprising the steps of a first hardening at a temperature between 920° C. and 960° C; a second hardening at a temperature between 820° C. and 860° C; and tempering at a tempering temperature between 620° C. and 660° C, wherein the heat treatment is carried out on a martensitic steel, wherein the martensitic steel is 26NiCrMoV14-5.

Title of Invention

A METHOD OF HEAT TREATMENT FOR PRODUCING A SHAFT FOR COMPRESSORS FROM A SHAFT MATERIAL

Abstract

The invention relates to a method of heat treatment for producing a shaft for compressors from a shaft material comprising the steps of a first hardening at a temperature between 920° C. and 960° C; a second hardening at a temperature between 820° C. and 860° C; and tempering at a tempering temperature between 620° C. and 660° C, wherein the heat treatment is carried out on a martensitic steel, wherein the martensitic steel is 26NiCrMoV14-5.

Full Text	Description The invention relates to a method for producing a shaft for compressors. In present-day mechanical engineering, it is routine for steel to be used at temperatures lower than minus 100°C, for example in compressors. Most grades of steel have a ferritic/ martensitic crystal structure and become very brittle at these low temperatures. Accordingly, these grades of steel cannot be used for many applications at minus 100°C. This could be remedied by using other steels, namely tough-at-subzero steels, instead of grades of steel with a ferritic/martensitic crystal structure. Tough-at-subzero steels are characterized by their austeniiic structure and are comparatively soft. In addition, these tough-at-subzero steels have low strength. In the case of solid bodies, toughness is to be understood as meaning the property of being able to undergo macroscopically measurable plastic deformation under mechanical stress. Toughness may also refer to the degree of resistance with which a body opposes a plastic change of shape, i.e. the level of mechanical stress and/or energy that has to be exerted to produce deformation. Brittleness may be considered to be the converse property. In order for steels to be used nevertheless in demanding mechanical engineering applications at lower than minus 100°C, steels of higher strength, with 10% to 20% of their structure made up by austenite, are used. These steels additionally also still exhibit good low-temperature properties. The proportion of 10% to 20% austenite is obtained by specific heat treatment . and an alloy content of 9% nickel. This steel is also known by the standard designation X8Ni9. However, one disadvantage of 9% nickel steel is that it begins to flow comparatively early under mechanical stress. In addition, it is possible that, for example, shafts of compressors deform when they are exposed to different temperatures. This occurs in particular whenever the austenite is unevenly distributed in the shaft. A martensitic material of the type 26 NiCrMoV14-5 is already known from the Stahlschliissel [key to steel] from the year 2004 (C.WEGST, M.WEGST, Verlag Stahlschliissel WEGST GmbH) . The production of steel plates in a continuous casting process with subsequent heat treatment in two hardening steps and a tempering step is already known from JP 10 26 58 46 A. Heat treatment for the production of high-strength steels with good low-temperature properties from a non-martensitic starting product, with two hardenings at different temperatures and subsequent tempering, is already known from the document JP 02133518 A. This is where the invention comes in, the object being to provide a method for producing a steel whereby the toughness at subzero temperatures of a steel is increased and the method can be easily implemented. The object is achieved by a method for producing steels in which a heat treatment is carried out on a martensitic steel, a heat treatment comprising hardening and tempering and characterized by the following steps being carried out: a) hardening at a temperature between 920°C and 960°C, b) carrying out a second hardening at a temperature between 820°C and 860°C, c) tempering at a temperature between 620°C and 660°C. To be regarded as one of the advantages is that the method offers a comparatively simple possible way of improving a steel in the sense that it has great toughness at subzero temperatures. The invention is based here on the aspect that a standard heat treatment, which provides a first and only hardening operation at about 850°C with a tempering operation at about 630°C under air cooling, does not produce satisfactory properties of the steel. The heat treatment according to the invention, in which first hardening at a first temperature and second hardening at a second temperature take place with quenching in water and then tempering takes place at a temperature in the specified temperature range surprisingly produces a steel of comparatively great toughness at subzero temperatures. This steel can be used down to at least minus 170°C, for example as a material for compressor shafts. In an advantageous development, martensitic steel of the type 3.5% Ni and 1.5% Cr, in particular the steel 26NiCrMoV14-5 according to Stahl-Eisen-Werkstoffblatt (SEW) [steel-iron material sheet] 555, is used in the method. It has been found that a martensitic steel is specifically suitable in particular for this method. In addition, martensitic steel can be produced particularly easily and therefore at lower cost. Particularly the steel 26NiCrMoV14-5 is a steel that can be provided with comparatively great toughness at subzero temperatures by the heat treatment according to the invention. In particular, the steel can be used as a material for compressor shafts. In addition, the steel 26NiCrMoV14-5 is, as it were, a standard shaft material for turbines and generators and is therefore more readily available than, for example, the steel with the designation X8Ni9. For example, the steel X8Ni9 has to be produced in special melts. Furthermore, the steel 26NiCrMoV14-5 is less expensive than X8Ni9 because of its lower content of alloying elements. A further advantage is that the martensitic crystal structure leads to more favorable behavior under mechanical stress. A further advantage is that a uniform crystal structure avoids peculiarities in the thermal expansion behavior. In a further advantageous development, the quenching in the hardening operations in steps a) and b) takes place in water. This provides a possible way of making the hardening operation particularly inexpensive. A further aspect here is that the quenching with water leads to good results. In a further advantageous development, the tempering operation is carried out with air cooling. Here, too, the particular advantage can be seen in the fact that air cooling provides a simple method by which very good results are achieved. The steel produced by this method exhibits very great toughness at subzero temperatures. Exemplary embodiments of the invention are described in more detail below. Instead of a 9% nickel steel, the steel 26NiCrMoV14-5 is used. A method for increasing the toughness of steels at subzero temperatures is used, involving carrying out a heat treatment that is distinguished by the following steps: 1) hardening at a temperature between 920°C and 960°C, 2) carrying out a second hardening at a temperature between 820°C and 860°C and 3) tempering at a temperature between 620°C and 660°C. It has been found that the temperature in the first hardening operation should be, in particular, around 950°C. Ideally, the temperature in the second hardening should be at a value of about 850°C. It has similarly been found that the temperature during the tempering operation should ideally be around 630°C. By this particular heat treatment, it is possible to provide the martensitic steel 26NiCrMoV14-5 with such great toughness at subzero temperatures that it can be used down to at least minus 170°C as a material for compressor shafts. There are, however, other possible uses for this heat-treated steel. It has been found that it is not out of the question for good batches of the steel 26NiCrMoV14-5 even to have adequate toughness at subzero temperatures after the standard heat treatment, i.e., using the standard heat treatment, first hardening is performed at about 850°C with quenching under water and then tempering is performed at a temperature of 630°C with air cooling. However, to ensure very good values with respect to toughness at subzero temperatures, as required in cryogenic compressors, the heat treatment according to the invention is required. WE CLAIM 1. A method of heat treatment for producing a shaft for compressors from a shaft material comprising the steps of: a first hardening at a temperature between 920° C. and 960° C; a second hardening at a temperature between 820° C. and 860° C; and tempering at a tempering temperature between 620° C. and 660° C, wherein the heat treatment is carried out on a martensitic steel, wherein the martensitic steel is 26NiCrMoV14-5. 2. The method as claimed in claim 1, wherein a quenching in the first hardening and the second hardening occur in water. 3. The method as claimed in claim 1, wherein air cooling occurs in the tempering operation. 4. The method as claimed in claim 1, wherein the temperature in the first hardening is 950° C. 5. The method as claimed in claim 1, wherein the temperature in the second hardening is 850° C. 6. The method as claimed in claim 1, wherein the temperature during the tempering operation is 630° C. ABSTRACT TITLE : "A METHOD OF HEAT TREATMENT FOR PRODUCING A SHAFT FOR COMPRESSORS FROM A SHAFT MATERIAL" The invention relates to a method of heat treatment for producing a shaft for compressors from a shaft material comprising the steps of a first hardening at a temperature between 920° C. and 960° C; a second hardening at a temperature between 820° C. and 860° C; and tempering at a tempering temperature between 620° C. and 660° C, wherein the heat treatment is carried out on a martensitic steel, wherein the martensitic steel is 26NiCrMoV14-5.

Full Text

Description

The invention relates to a method for producing a shaft for
compressors.
In present-day mechanical engineering, it is routine for steel
to be used at temperatures lower than minus 100°C, for example
in compressors. Most grades of steel have a ferritic/
martensitic crystal structure and become very brittle at these
low temperatures. Accordingly, these grades of steel cannot be
used for many applications at minus 100°C. This could be
remedied by using other steels, namely tough-at-subzero steels,
instead of grades of steel with a ferritic/martensitic crystal
structure. Tough-at-subzero steels are characterized by their
austeniiic structure and are comparatively soft. In addition,
these tough-at-subzero steels have low strength.
In the case of solid bodies, toughness is to be understood as
meaning the property of being able to undergo macroscopically
measurable plastic deformation under mechanical stress.
Toughness may also refer to the degree of resistance with which
a body opposes a plastic change of shape, i.e. the level of
mechanical stress and/or energy that has to be exerted to
produce deformation. Brittleness may be considered to be the
converse property.
In order for steels to be used nevertheless in demanding
mechanical engineering applications at lower than minus 100°C,
steels of higher strength, with 10% to 20% of their structure
made up by austenite, are used. These steels additionally also
still

exhibit good low-temperature properties. The proportion of 10%
to 20% austenite is obtained by specific heat treatment .

and an alloy content of 9% nickel. This steel is also known by
the standard designation X8Ni9.
However, one disadvantage of 9% nickel steel is that it begins
to flow comparatively early under mechanical stress. In
addition, it is possible that, for example, shafts of
compressors deform when they are exposed to different
temperatures. This occurs in particular whenever the austenite
is unevenly distributed in the shaft.
A martensitic material of the type 26 NiCrMoV14-5 is already
known from the Stahlschliissel [key to steel] from the year 2004
(C.WEGST, M.WEGST, Verlag Stahlschliissel WEGST GmbH) . The
production of steel plates in a continuous casting process with
subsequent heat treatment in two hardening steps and a
tempering step is already known from JP 10 26 58 46 A. Heat
treatment for the production of high-strength steels with good
low-temperature properties from a non-martensitic starting
product, with two hardenings at different temperatures and
subsequent tempering, is already known from the document JP
02133518 A.
This is where the invention comes in, the object being to
provide a method for producing a steel whereby the toughness at
subzero temperatures of a steel is increased and the method can
be easily implemented.
The object is achieved by a method for producing steels in
which a heat treatment is carried out on a martensitic steel, a
heat treatment comprising hardening and tempering and
characterized by the following steps being carried out:
a) hardening at a temperature between 920°C and 960°C,
b) carrying out a second hardening at a temperature between
820°C and 860°C,

c) tempering at a temperature between 620°C and 660°C.
To be regarded as one of the advantages is that the method
offers a comparatively simple possible way of improving a steel
in the sense that it has great toughness at subzero
temperatures. The invention is based here on the aspect that a
standard heat treatment, which provides a first and only
hardening operation at about 850°C with a tempering operation
at about 630°C under air cooling, does not produce satisfactory
properties of the steel. The heat treatment according to the
invention, in which first hardening at a first temperature and
second hardening at a second temperature take place with
quenching in water and then tempering takes place at a
temperature in the specified temperature range surprisingly
produces a steel

of comparatively great toughness at subzero temperatures. This
steel can be used down to at least minus 170°C, for example as
a material for compressor shafts.
In an advantageous development, martensitic steel of the type
3.5% Ni and 1.5% Cr, in particular the steel 26NiCrMoV14-5
according to Stahl-Eisen-Werkstoffblatt (SEW) [steel-iron
material sheet] 555, is used in the method.
It has been found that a martensitic steel is specifically
suitable in particular for this method. In addition,
martensitic steel can be produced particularly easily and
therefore at lower cost.
Particularly the steel 26NiCrMoV14-5 is a steel that can be
provided with comparatively great toughness at subzero
temperatures by the heat treatment according to the invention.
In particular, the steel can be used as a material for
compressor shafts. In addition, the steel 26NiCrMoV14-5 is, as
it were, a standard shaft material for turbines and generators
and is therefore more readily available than, for example, the
steel with the designation X8Ni9. For example, the steel X8Ni9
has to be produced in special melts. Furthermore, the steel
26NiCrMoV14-5 is less expensive than X8Ni9 because of its lower
content of alloying elements.
A further advantage is that the martensitic crystal structure
leads to more favorable behavior under mechanical stress.
A further advantage is that a uniform crystal structure avoids
peculiarities in the thermal expansion behavior.
In a further advantageous development, the quenching in the
hardening operations in steps a) and b) takes place in water.

This provides a possible way of making the hardening operation
particularly inexpensive. A further aspect here is that the
quenching with water leads to good results.
In a further advantageous development, the tempering operation
is carried out with air cooling.
Here, too, the particular advantage can be seen in the fact
that air cooling provides a simple method by which very good
results are achieved. The steel produced by this method
exhibits very great toughness at subzero temperatures.
Exemplary embodiments of the invention are described in more
detail below.
Instead of a 9% nickel steel, the steel 26NiCrMoV14-5 is used.
A method for increasing the toughness of steels at subzero
temperatures is used, involving carrying out a heat treatment
that is distinguished by the following steps:
1) hardening at a temperature between 920°C and 960°C,
2) carrying out a second hardening at a temperature between
820°C and 860°C and
3) tempering at a temperature between 620°C and 660°C.
It has been found that the temperature in the first hardening
operation should be, in particular, around 950°C. Ideally, the
temperature in the second hardening should be at a value of
about 850°C.
It has similarly been found that the temperature during the
tempering operation should ideally be around 630°C.

By this particular heat treatment, it is possible to provide
the martensitic steel 26NiCrMoV14-5 with such great toughness
at subzero temperatures that it can be used down to at least
minus 170°C as a material for compressor shafts. There are,
however, other possible uses for this heat-treated steel. It
has been found that it is not out of the question for good
batches of the steel 26NiCrMoV14-5 even to have adequate
toughness at subzero temperatures after the standard heat
treatment, i.e., using the standard heat treatment, first
hardening is performed at about 850°C with quenching under
water and then tempering is performed at a temperature of 630°C
with air cooling. However, to ensure very good values with
respect to toughness at subzero temperatures, as required in
cryogenic compressors, the heat treatment according to the
invention is required.

WE CLAIM
1. A method of heat treatment for producing a shaft for compressors from a
shaft material comprising the steps of:
a first hardening at a temperature between 920° C. and 960° C;
a second hardening at a temperature between 820° C. and 860° C; and
tempering at a tempering temperature between 620° C. and 660° C,
wherein the heat treatment is carried out on a martensitic steel, wherein
the martensitic steel is 26NiCrMoV14-5.
2. The method as claimed in claim 1, wherein a quenching in the first
hardening and the second hardening occur in water.
3. The method as claimed in claim 1, wherein air cooling occurs in the
tempering operation.
4. The method as claimed in claim 1, wherein the temperature in the first
hardening is 950° C.
5. The method as claimed in claim 1, wherein the temperature in the second
hardening is 850° C.
6. The method as claimed in claim 1, wherein the temperature during the
tempering operation is 630° C.

ABSTRACT

TITLE : "A METHOD OF HEAT TREATMENT FOR PRODUCING A SHAFT
FOR COMPRESSORS FROM A SHAFT MATERIAL"

The invention relates to a method of heat treatment for producing a shaft for
compressors from a shaft material comprising the steps of a first hardening at a
temperature between 920° C. and 960° C; a second hardening at a temperature
between 820° C. and 860° C; and tempering at a tempering temperature
between 620° C. and 660° C, wherein the heat treatment is carried out on a
martensitic steel, wherein the martensitic steel is 26NiCrMoV14-5.

Documents:

788-KOLNP-2009-(23-07-2012)-ABSTRACT.pdf

788-KOLNP-2009-(23-07-2012)-AMANDED CLAIMS.pdf

788-KOLNP-2009-(23-07-2012)-ANNEXURE TO FORM 3.pdf

788-KOLNP-2009-(23-07-2012)-DESCRIPTION (COMPLETE).pdf

788-KOLNP-2009-(23-07-2012)-EXAMINATION REPORT REPLY RECEIVED.pdf

788-KOLNP-2009-(23-07-2012)-FORM-1.pdf

788-KOLNP-2009-(23-07-2012)-FORM-2.pdf

788-KOLNP-2009-(23-07-2012)-OTHERS.pdf

788-KOLNP-2009-(23-07-2012)-PETITION UNDER RULE 137.pdf

788-KOLNP-2009-(25-04-2013)-CORRESPONDENCE.pdf

788-KOLNP-2009-(25-04-2013)-OTHERS.pdf

788-kolnp-2009-abstract.pdf

788-kolnp-2009-claims.pdf

788-kolnp-2009-correspondence.pdf

788-kolnp-2009-description (complete).pdf

788-KOLNP-2009-EXAMINATION REPORT.pdf

788-kolnp-2009-form 1.pdf

788-KOLNP-2009-FORM 18.pdf

788-kolnp-2009-form 2.pdf

788-kolnp-2009-form 3.pdf

788-kolnp-2009-form 5.pdf

788-kolnp-2009-gpa.pdf

788-KOLNP-2009-GRANTED-ABSTRACT.pdf

788-KOLNP-2009-GRANTED-CLAIMS.pdf

788-KOLNP-2009-GRANTED-DESCRIPTION (COMPLETE).pdf

788-KOLNP-2009-GRANTED-FORM 1.pdf

788-KOLNP-2009-GRANTED-FORM 2.pdf

788-KOLNP-2009-GRANTED-FORM 3.pdf

788-KOLNP-2009-GRANTED-FORM 5.pdf

788-KOLNP-2009-GRANTED-SPECIFICATION-COMPLETE.pdf

788-kolnp-2009-international preliminary examination report.pdf

788-kolnp-2009-international publication.pdf

788-kolnp-2009-international search report.pdf

788-kolnp-2009-others.pdf

788-kolnp-2009-pct request form.pdf

788-KOLNP-2009-PETITION UNDER RULE 137.pdf

788-KOLNP-2009-REPLY TO EXAMINATION REPORT.pdf

788-kolnp-2009-specification.pdf

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Patent Number

256477

Indian Patent Application Number

788/KOLNP/2009

PG Journal Number

26/2013

Publication Date

28-Jun-2013

Grant Date

21-Jun-2013

Date of Filing

02-Mar-2009

Name of Patentee

SIEMENS AKTIENGESELLSCHAFT

Applicant Address

WITTELSBACHERPLATZ 2, 80333 MUNCHEN

Inventors:

#	Inventor's Name	Inventor's Address
1	BEATE LANGENHAN	AHORNWEG 12, 41372 NIEDERKRÜCHTEN
2	RALF BODE	JULIUS-LEBER-STR.9 47441 MOERS

PCT International Classification Number

C21D 1/18,C21D 1/78

PCT International Application Number

PCT/EP2006/066319

PCT International Filing date

2006-09-13

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA