METHODE ET DISPOSITIF DE TRAITEMENT THERMIQUE PONCTUEL DE PIECES EN MATERIAU FERREUX

METHOD AND APPARATUS FOR SECTIONWISE HEAT TREATMENT OF COMPONENT PARTS OF FERROUS MATERIALS

Abrégé anglais

A b s t r a c t
By means of partial hardening of component part at the
bainite stage, combinations of high-tensile skin layer
properties with the basic properties of the cast material
are made possible. The part processed this way has a low
heat distortion and is easy to machine when hardened.
Component sections are being heated up to austenitizing
temperatures and subsequently quenched in a hot bath, in
which the material is being transformed according to the
time-temperature-transformation of the material.
(Fig. 2)

Revendications

- 5 -
The embodiments of the invention in which an
exclusive property or privilege is claimed are defined
as follows:
1. Method for partial heat treatment of com-
ponents of ferrous metals, characterized in that the
sections to be treated are being austenitized and
subsequently left in a quenching medium until the
desired transformation has taken place, so that a
partial bainite structure results.
2. Method according to claim 1, characterized
in that the sections to be treated are heated to a
temperature of 850 to 1000 centigrades.
3. Method according to claim 1, characterized
in that the quenching bath is a hot bath, the tempera-
ture of which is being held at 180 to 450 centigrades.
4. Method according to claim 3, characterized
in that as quenching medium a salt bath is being used.
5. Method according to claim 3, characterized
in that as quenching medium oil is being used.
6. Method according to claim 3, characterized
in that a metal bath is being used as quenching medium.
7. Apparatus for partial heat treatment of com-
ponents of ferrous metals, wherein the components to be
treated are austenitized and then quenched, and is
characterized in that a quenching bath is placed below
the heating place, into which bath the component falls
immediately after heating.

Description

The present application refers to a method and an apparatus
Eor partial heat treatrnent of component parts of ferrous
metals.
In order to obtain hig-tensile structural properties it is
known to submit component parts, as axles, toothed rims,
spur wheels, shift forks, to an isothermal heat treatment
at the bainitic stage. Thereby, the component parts are
being completel~ austenitized and consequently transformed
in a maintaining bath.
Ihe existing known method has the following disadvantages:
The high-tensile structural properties of bainite are
being transferred to sections of the component parts,
in which sections no such properties are not desired.
- The special treatment processes required after hardening
and the measurement changes over the entire component
parts.
Ihe object of the present invention is to develop an econo-
mical method and an apparatus enabling a partial formation
of bainite on the component.
Further objects are the elimination of problems in connec-
tiOII with the distortion, sequential processing of spots
not hardened and to achieve extended property combinations.
A method in accordance with the present invention, partial
heat treatment of components of ferrous metals includes
the steps that the sections to be treated are austenitized
and subsequentl~ left in a quenching medium till the desired
transformation has taken place so that a partial bainite
structure results~
~.
.~ ~....

~Ifd`;~ f~
- 2A -
An apparatus in accordance with the present invention for
the partial heat treatment of components of ferrous
metals wherein the components to be treated are austenitized
and then quenched, wherein a quenching bath is placed below
the heating station into which bath the component falls
immediately after heating.

In the following the invention is being described with
reference to ~he drawings, in which
Fig. 1 shows a schematic view of a plant for isother-
mal processing of ferrous parts in the bainite
stage, and
Fig. 2 shows the temperature curves of a random com
ponent part as well as the expected form of
the structure~
Test bodies with dimensions of 16 x 20 mm with predominantly
pearlitic structures were provided with bainitic outer
zones.
Test bodies of a raw material of the composition:
3,65 weight percent C, 2~38 weight percent Si, 0,46 weight
percent Mn, remnant Fe and with a structure of 75 percent
pearlite and 25 percent ferrite were partially heat treated.
At first the sections to be treated were inductively he~ted
to a temperature between 850 and 1000 centigrades.
The height of fall between the heating coil and the harde-
ning bath was set at approx. 90 mm. Subsequen~ly, the test
body was held in the salt bath at 275 centigrades for 120
minutes r
The test of the method was carr7ed out on a gear wheel
modulus 3, The raw material was GGG (spheroidal graphite
cast iron) with a pearlitic basic structure.
The heating was carried out, as with the test samples, up
to a temperature of 900 centigradQs. The heating time was

13 ~
32 seconds. Subsequently, the test wheel was held in a
salt bath at 280 centigrades for 120 minutesO
Furthermore, gear wheels, module 3, were so processed,
that a bainitic structure was created down to approx. 4 mm
below the dedendum.
In the modified inductive heating plant shown in Fig/ 1
the quenching bath 1 is placed immediately below the induc-
tive coil 2, so that the component 3 drops directly into
the bath, without the usual arrangement whereby the compo-
nent 3 is being sprayed by means of a sprinkler located
between the induction coil and the bath l. The quenching
medium can be a tempered salt bath or oil. It is, however,
also possible to use a metal bath.
In Fig. 2 a component A is shown, while the expected struc-
ture form together with the temperature to be expected are
shown in the corresponding TTT-curvesO
It is shown that the bainitic structure has excellent wear
properties at high tensile strengthsO
By usiny the described method excellent results were
achieved~ At a bainite content of approx. 90 percent, hard-
ness values in the range of 46 to 48 HRC were measured on
the test body or sample~ On sample gear wheels the hardness
values from the highest to the lowert point of the cog
measured were in the range from 39 to 41 HRC.