FIELD OF THE INVENTION
The present invention relates to a low alloy steel grade with improved
abrasion resistance and impact toughness. The invention further relates to a
direct water quenching process for producing a low alloy steel grade with
improved abrasion resistance and impact toughness.
BACKGROUND OF THE INVENTION
The process of wear involves gradual and progressive loss of material from
the surface of a component due to relative motion between the active and
counter body species either by mechanical action or chemical reaction.
Depending upon the environment of application, the material interacts with
different kinds of abrasives and as a result wears out. Therefore, abrasive
wear resistant materials become highly desirable in the industrial applications
such as agriculture, earth moving, excavation, mining, mineral processing,
transportation etc.
The increasing cost of replacing worn parts in mining and earth moving
equipment confronts a continual challenge to materials development. As per
the report of a national survey in 1997, for UK industries who have wear
problem, the cost of wear was typically about 0.25% of their turnover. Out of
this, abrasive wear alone contributes to around 63% [1]. This undesirable
loss, particularly due to the process of wear, can be reduced to at least half
by replacing the currently used materials with new ones and/or by selecting a
better design of the components. However, a new design of a component is
often coupled with other associated risk, and also does not always make an
economically viable alternative. To the contrary, the use of new material can
be considered as a better option.

Components in wear resistant applications, particularly in mining and
earthmoving sectors, are essentially required to have adequate abrasion
resistance along with the ability to resist chemical attacks. As impact loading
is mostly unavoidable in such applications, the requirement for good impact
toughness also becomes one of the major concerns. Typically, the material
with high abrasion resistance is hard and brittle. Hence, these materials are
limited by low impact toughness, which leads to the generation of cracks
while experiencing sudden impact loading [2]. Thus, there is a need to
develop new grade of material which is highly resistant to abrasion together
with good impact toughness.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a low alloy steel
grade with improved abrasion resistance and impact toughness.
Another object of the invention is to propose a direct water quenching
process for producing a low alloy steel grade with improved abrasion
resistance and impact toughness.
SUMMARY OF THE INVENTION
Accordingly, there is provided Low alloy steel grade with improved abrasion
resistance and impact toughness produced through direct water quenching
process. As per the invention, two different alloys were designed and cast at
40 kg scale which were subsequently forged. In order to ensure the complete
homogenization, the forged steel plates were first austenitized at 1200°C for
30 mins. After that the plates were quenched in water to room temperature.

DETAILED DESCRIPTION OF THE INVENTION
The present inventions based on studies and experimentations noted that the
requirement of good impact toughness along with superior abrasion
resistance with martensite in the microstructure.
The next step was to design an alloy composition considering the following
factors:
1. Higher Ms temperature.
2. Low carbon equivalent to eliminate the problem of weldability and low
carbon content to improve impact toughness.
3. Higher hardenability to eliminate bainite or pearlite formation during
quenching below Ms temperature.
The chemical composition of the proposed alloys, their carbon equivalent (CE)
values and Ms temperature calculated empirically as well as through
dilatometry experiment are shown in Table 1.


In order to ensure the complete homogenization, the forged steel plates were
first austenitized at 1200°C for 30 mins. After that the plates were quenched
in water to room temperature. Mechanical properties (on ASTM standard
samples) for above mentioned experiments are shown in Table 2.

1. Eliminate the need for any extra facility to perform heat treatment, i.e.
to obtain steel product directly from the hot strip mill.
2. Improved abrasion resistance and impact toughness in a low alloy
composition, particularly at lower Si level as compared to conventional
steel grades currently used in abrasion resistant applications.

WE CLAIM:
1. A process for producing low alloy steel comprising the steps of:
casting a steel alloy with composition 0.10 to 0.25 - carbon, 1.0 –
1.8 Manganese, 0.40 – 0.6 Silicon, 0.15 – 0.25 Chromium, 0.10 – 0.15
Molybdenum, 0.40 – 0.65 Nickel, 0.34 – 0.69 Carbon equivalent, 0 –
0.01 Vanadium, 0 -0.08 Titanium, 0 – 0.01 Boron, balance being Iron
and residual impurities (in wt.%);
homogenizing the steel alloy by austenitizing at 1150-1200°C for 30-45
minutes; and
direct by water quenching to room temperature.
2. The process as claimed in claim 1, wherein the low alloy steel
comprises 100% martensite.
3. The process as claimed in claim 1, wherein abrasive wear volume loss
for low alloy steel is 262-307 mm3 on a dry sand rubber wheel test
machine.
4. The process as claimed in claim 1, wherein Charpy impact toughness
of low alloy steel at room temperature is 28-62 J/cm2.
5. The process as claimed in claim 1, wherein Charpy impact toughness
of low alloy steel at -40 deg. C is 21-35 J/cm2.
6. The process as claimed in claim 1, wherein Hardness (at 1 kg load) of
low alloy steel is 411 Hv-506 Hv.
7. The process as claimed in claim 1, wherein Yield Strength of low alloy
steel is 966-1190 MPa.

8. The process as claimed in claim 1, wherein Ultimate Tensile Strength
of low alloy steel is 1240-1565 MPa.
9. The process as claimed in claim 1, wherein Total elongation of low
alloy steel is 9-14 %.
10. The process as claimed in claim 1, wherein the low alloy steel
comprises 100% martensite.
11. The process as claimed in claim 1, wherein abrasive wear volume loss
for low alloy steel is 262-307 mm3 on a dry sand rubber wheel test
machine.
12. The process as claimed in claim 1, wherein Charpy impact toughness
of low alloy steel at room temperature is 28-62 J/cm2.
13. The process as claimed in claim 1, wherein Charpy impact toughness
of low alloy steel at -40 deg. C is 21-35 J/cm2.
14. The process as claimed in claim 1, wherein Hardness (at 1 kg load) of
low alloy steel is 411 Hv-506 Hv.
15. The process as claimed in claim 1, wherein Yield Strength of low alloy
steel is 966-1190 MPa.
16. The process as claimed in claim 1, wherein Ultimate Tensile Strength
of low alloy steel is 1240-1565 MPa.
17. The process as claimed in claim 1, wherein Total elongation of low
alloy steel is 9-14 %.

18. A low alloy steel comprising:
0.10 to 0.25 carbon, 1.0 to 1.8 Manganese, 0.40 to 0.6 Silicon, 0.15
to 0.25 Chromium, 0.10 to 0.15 Molybdenum, 0.4 to 0.65 Nickel, 0.34
to 0.69 Carbon equivalent, 0 to 0.01 Vanadium, 0 -0.08 Titanium, 0
to 0.01 Boron, balance being Iron and residual impurities (all in
wt.%)