MATERIAU D'ACIER A HAUTE RESISTANCE THERMIQUE UTILE POUR PRODUIRE LES PARTIES SUPERIEURES DE PISTONS DE MOTEURS

STEEL MATERIAL WITH HIGH THERMAL RESISTANCE FOR PRODUCING ENGINE PISTON UPPER PARTS

Abrégé français

Ce matériau d'acier est utile pour produire les parties supérieures de pistons de moteurs présentant une haute résistance à l'usure, à la corrosion et à la chaleur. Cet acier a la composition suivante, en pourcentages en poids: 1,20 à 1,50 de Mn; 0,50 à 0,80 de Si; 0,35 à 0,40 de C; 0,10 à 0,50 de Mo; 0,08 à 0,13 de V; 0,010 à 0,065 de S; 0,015 à 0,050 d'Al; </= 0,035 de P; le pourcentage restant étant constitué de fer et d'impuretés découlant de la production.

Abrégé anglais

A steel material is useful for producing the upper part of engine pistons with
high wear, corrosion and heat resistance. This steel has
the following composition (in % by weight): 1.20 to 1.50 Mn; 0.50 to 0.80 Si;
0.35 to 0.40 C; 0.10 to 0.50 Mn; 0.08 to 0.13 V; 0.010 to
0.065 S; 0.015 to 0.050 Al; <= 0.035 P, the remainder being iron and
production impurities.

Revendications

5

Claims:

1. Steel material with the following composition (% by
weight):

Mn: 1.20 to 1.50
Si: 0.50 to 0.80
C: 0.35 to 0.40
Mo: 0.10 to 0.50
V: 0.08 t0 0.13
S: 0.010 to 0.065
Al: 0.015 to 0.050
P: <= 0.035
the remainder being iron and production impurities.

2. Use of a steel material according to claim 1 for
producing motor piston upper parts.

Description

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Steel Material With High Thermal Resistance For Producing
Engine PistowUpper Parts
Description
The invention relates to a steel material for producing
engine piston upper parts.
In diesel motors, extx'emely high compressions with good fuel
utilization, low emissions and high km life expectancy can
be obtained with steel forged piston upper parts. In this
connection, the piston upper parts are generally quenched
and tempered from.the material 42CrMo4 in a range from a00
to 1200 N/mm2, i.e. hardened by heating from room temperature
to 860°C and subsequently quenching in heavy-duty oil and
tempered by renewed heating to ca. 480 to 660°C with fiilal
cooling in a container_ The temperatures in the hardening
and/or tempering furnace are adjusted according to the
respective steel analysis and the customer instructions with
respect to strength.
The wear, corrosion and thezmal resistance properties of the
piston upper parts which are required by the consumer can
only be obtained with the above mentioned steel and the
forging method. However, the construction principle of the
pendulum shaft piston with a steel forged upper part and
aluminum skirt has the disadvantage that the motor is
expensive in comparison to the one-piece pistons produced
from aluminum which is also caused by the quenching and
tempering (heat treatment) of the steel piston upper part.
The object of the present invention is to provide a material
with which steel forged piston upper parts can be produced
without quenching and tempering, and hence more
economically, without negatively influencing the wear,
corrosion and heat resistaTice properties.


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This problem is solved according to the invention by a steel
material which has the following composition (: by weight):
Mn: 1.20 to 1.50
Si: 0.50 t0 0.80
C: 0.35 to 0.40
Mo: 0.10 to O.SO
v: 0.0$ to 0.13
S: 0.010 to 0.065
Al: 0.015 to 0_050
P: S 0.035
the remainder being iron and production impurities.
In this connection, the production impurities can especially
include the elements Ni and Cr which can each generally be
present in the steel material in an amount of _< 0.20 % by
weight.
In this connection, the steels according to the invention
can be produced in a customary manger in an electric oven,
whereby scrap is employed as a starting material. This
scrap is melted down in the electric oven and the melt is
subsequently refined for reduction of the phosphorous
contest. The steel is run off in a ladle for secondary
metallurgical treatment. This means that loading agents
such as FeSi, FeCr, MnCr or FeMo are added as a function of
the analysis of the steel obtained from the electric oven in
order to adjust the ranges of the individual elements in the
steel according to the invention. In this connection,
aluminu~tc is also added for steadying. The homflgenization of
the melt and its adjustment to the respectively desired
temperature then occurs in a pan furnace. Subsequently, the
fine adjustment of the weight amounts of the individual
elements in the claimed steel occurs through the addition of
the loading agents already mentioned above. Gases such as


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hydrogen dissolved in the melt are then removed by de-
gassing. If necessary, corrections are carried out here
with respect to the contest of aluminum which is normally
spooled in in wire form. Following the vacuum treatment,
the melt is then cast into a billet or block.
Piston upper parts which mast no longer be quenched and
tempered can be steel forged with the steel according to the
invention in order to obtain the desired high thermal
resistance properties. The piston upper parts are cooled in
a controlled manner from the forming heat (BY-treatment
BEST YIBLD).
8xampie
According to the process presented above, a steel material
according to the invention was produced which has the
following composition:
Mn: I.31
Si: 0.57
C. 0.38
Mo: 0.43
v: o.ix
S: 0.046
Al: 0.024
P: 0.011
Cr: O.I7
Ni: 0.03
reroaiader is iron.
The steel of the above composition was compared with respect
to its mechanical properties with the steel 42CrMo4
(standard analysis according to the norm 13~T 10083). The
results are presented is the following table:

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Table:
Comparison of hot-drawn samples


42CrMo4 r~~e _~P_~~~_L~ ono"C


tensile strength ' 930 630


Rm (N/mm2)


yield stxength 480


Rp 0 . 2 (N/mm2)


constriction Z (%) ~5


strain AS (%) 25


steel according to example room temperature ~C


tensile strength 1020 810


Rm ( N/mmZ )


yield strength 605


Rp 0 . 2 ( N /m~ttZ )


constriction Z (%) 58


strain A5 (%) 14.5


The values o~ the abvve~tabledemonstrate the advantageous


mechanical propert~.es of steel according to the
the


invention.