The present invention relates to an improved process
for producing cold shear blades for side trimming and crop
chopping of hot rolled pickled coils.
The existing process for producing cold shear blades
for side trimming and crop chopping of hot rolled pickled coils
comprises preparing an alloy tool steel blades with reduced
addition of Cr and V, and without addition of Mo in EAF-VAD-
Ingot Casting-Hot Forging-Annealing-Rough Machining route,
hardening treatment of the blades by Austenitising in Electric
Resistance Heating Furnaces, oil quenching and tempering.
The chemical composition of the steel produced in the
existing process including range and preferred values of the
content of different ingredients is presented in Table I. In
the existing process the ingredients are melted in an electric
arc furnace, cast into ingets and rolled into blooms. The
blooms are forged into shear blades. The shear blades are first
machined to be of required size and shape, and then subjected to
the heat treatment for hardening the blades, comprising
(i) charging into an electric Heat Treatment furnace at a
charging temperature of 250°C max, (ii) heating in the furnace
at a rate of 60°C/hour, (iii) Austenitising at 980°C and soaking
for 1 hour, (iv) oil quenching to a temperature of 300°C, and
(v) air cooling to room temperature.
The hardened blades are tempered by heating upto
560°C at the rate of 6o°C/hour, soaking for 3 hours at 560°C,
and cooling to room temperature in air.
The main drawbacks of the existing process are :
(a) the chemical composition of the blades is not suitable
for making the same of fine microstructure and hence increased
hardness and (b) the hardening treatment by heating in an
Electric Heat Treatment Furnace and oil quenching causes non-
uniform surface hardness and decarburisation of the blades
leading to their reduced wear resistance and fracture toughness.
The object of the invention is to provide a process
for producing cold shear blades of increased hardness, wear
resistance and fracture toughness with a view to extending the
working life of the blades.
The invented process comprises (i) preparing alloy-
tool steel blades v/ith increased addition of Cr and V, and
inclusion of Mo in the chemical composition thereof in the EAF-
VAD-Ingot Casting-Hot Forging-Annealing-Rough Machining route;
(ii) stress relieving treatment; (iii) hardening treatment
of the blades by Austenitising in Vacuum H-T. Furnace; (iv)
quenching treatment with high pressure gas; and {v) double
tempering of the blades.
The chemical composition of the alloy tool steel blades
produced in the invented process has been optimised by carrying
out extensive investigations in the laboratory and pilot mill
with evaluation of hardness, wear resistance and fracture
toughness thereof.
The chemical composition of the alloy tool steel
blades optimised in the invented process is given in Table I
which also includes the chemical composition of the alloy tool
steel blades produced in the conventional process. It is noted
from Table I that in addition to increasing the content of Cr,
Mn and Vo, the content of C, Mn and Si is also increased in the
chemical composition of the blades produced in the invented
process, compared with the blades produced in the conventional
process.
:. .V.. ¦
The steel produced in the invented process is of
surface hardness 53-55 HRC, impact fracture toughness 8-10 KgM
(Unnotched Izod) and fine tempered Martensite microstructure
with 5-8% alloy carbides, which properties are considered
appropriate for obtaining an extended working life of the
blades.
The stress relieving treatment of blades followed in
the invented process comprises the following steps in sequence :
(i) the blades are charged into a furnace at an initial
temperature of 50°C max, (ii) heated at a rate of 5-8°C per
minute to a temperature of 650°C and soaked at this temperature
for A hours, and (iii) cooled «± 50 C^/inax in the furnace.
The hardening treatment of stress relieved blades
followed in the invented process comprises the following steps
in sequence : (i) the blades are charged into a vacuum H.T.
Furnace at an initial temperature of 50 C max, (ii) heated at
a rate of 5-8°C per minute to a preheating temperature of
540°C and soaked at this temperature for 30 minutes, (iii)
heated at a rate of 5-8°C per minute to a preheating temperature
of 800°C and soaked at this temperature for 25 minutes, (iv)
austenitised at a temperature of 103Q°C for 40 minutes and (v)
quenched by blowing Nitrogen gas into the furnace (a) at a
pressure of 5.0 bar for cooling the blades from 1030°C to 600°C
at a rate of at least 100°C per minute, (b) at a pressure of
3.5 bar for cooling the blades from 600°C to 100°C at a rate
of at least 50°C per minute and (c) at a pressure of 1.5 bar
for cooling the blades from 100°C to room temperature at a rate
of 2-5°C per minute.
The hardened blades are double-tempered in the following
steps in sequence : (a) in the first tempering treatment (i)
the blades are charged into a furnace at an initial temperature
of 50°C max, {ii) heated at a rate of 5°C per minute to a
temperature of A80-500°C, and soaked at this temperature for
3 hours and (iii) cooled to 50°C max at a rate of 5-10°C per
minute; and (b) in the second tempering treatment (i) the blades
are charged into a furnace at an initial temperature of 50° C
max, (ii) heated at a rate of 5°C per minute to a temperature
of 500 - 530°C, and soaked at this temperature for 3 hours and
(iii) cooled to room temperature at a rate of 5-10oC per
minute.
The shearing performance of the blades produced in
the invented process has been compared with the blades produced
in the conventional process. It has been found that the blades
produced in the invented process are capable of side trimming of
25,000-30,000 Tons, and crop chopping of 27,000-32,000 Tons of
hot rolled pickled coils, whereas the blades produced in the
conventional process are capable of side trimming of 5000-
6000 Tons and crop chopping of 5000 - 6000 Tons of the said
coils. Thus the working life of the blades produced in the
invented process is expected to be 5 to 6 times mere than that
of the blades produced in the conventional process.
Although the cost of manufacture of the blades in the
invented process:"-js higher by about 15-20% compared with the
conventional process, the extended service life of the blades
produced in the invented process makes the process appreciably-
cost-effective considering the increased tonnage of the coils
side-trimmed and crop chopped and reduced down time of the plant
required for replacement of woro out blades. It has been
estimated that the shearing cost is reduced by about 75% by
using the blades produced in the invented process.
The distinguishing features of physical properties
and performance of shear blades produced in the invented and
existing processes are presented in Table II.
The distinguishing features of the invented process
from the existing process are summarised in Table III,
We Claim :-
1. An improved process for producing cold shear blades
for side triaming and crop chopping of hot rolled pickled coils,
characterised in that the process comprises the following steps
in sequence : (a) preparing blades from alloy tool steel of
chemical composition (by weight %): C-0.60 to 0.65, Mn-0.30 to
0.70, Si-0.60 to 1.00, Cr-4.00 to 5.50, Mo-1.00 to 1.50, V-0.80 to
1.20 and Fe- the balance, suitable for increasing the fineness of
microstructure, surface hardness, wear resistance and fracture
toughness thereof in the steel making route of: Electric arc
furnace-wacuum decarburisation**Ingot Casting-*-Hot Forging-*-Rough
Machining ~&xKriat; (b) applying stress relieving treatment on the
blades in the manner, comprising charging the blades into a furnace
at an initial temperature of 50°C max, heating at a rate of 5-8°C
per minute to a temperature of 650°C and soaking at this temperature
for A hours, and cooling in the furnace to a temperature of 50°C
max; (c) finish machining and grinding of stress relieved blades;
(d) applying hardening treatment on the plates in the manner,
comprising charging the blades into a vacuum H.T. Furnace at an
initial temperature of 50°C max, heating to a preheating temperature
of 540°C at a rate of 5-8°C per minute and soaking at this
temperature for 30 minutes, heating to preheating temperature of
800°C at a rate of 5-8°C per minute and soaking at this temperature
for 25 minutes, austenitising at a temperature of 1030°C for 40
minutes and quenching by blov/ing Nitrogen gas into the furnace;
and (e) applying tempering treatment on the blades in the manner,
comprising the first step in which the blades are charged
into a furnace at an initial temperature of 50°C max, _____________
heated to a temperature of 480-500°C at a rate of 5°C per minute
and soaked at this temperature for 3 hours, and cooled to 50°C
max at a rate of 5-10°C per minute; and the second step in which
the blades are charged into a furnace at an initial temperature
of 50°C max, heated to a temperature of 500-530°C at a rate of
5°C per minute and soaked at this temperature for 3 hours, and
cooled to room temperature at a rate of 5-10°C per minute.
2. The process as claimed in claim 1, wherein the chemical
composition of the blades is (by weight %) : C-0.65, Mn-0.50,
Si-0.70, Cr-4.90, Mo-1.30, V-0.80 and Fe- the balance.
3. The process as claimed in 1 or 2, wherein the blades
are quenched by blowing Nitrogen gas into the furnace at a
pressure of 5.0 bar for cooling the blades from 1030°C to 600°C
at a rate of at least 100°C per minute, at a pressure of 3.5 bar
for cooling the blades from 600°C to 100°C at a rate of at least
50°C per minute and at a pressure of 1.5 bar for cooling the
blades from 100°C to room temperature at a rate of 2-5°C per
minute.

An improved process for producing cold shear blades for
side triaming and crop chopping of hot rolled pickled coils,
characterised in that the process comprises the following steps
in sequence: (a) preparing blades from alloy tool steel of
chemical composition (by weight %): C-0.60 to 0.65, Mn-0.30 to
0.70, Si-0.60 to 1.00, Cr-4.00 to 5.50, Mo-1.00 to 1.50, V-0.80 to
1.20 and Fe- the balance, suitable for increasing the fineness of
microstructure, surface hardness, wear resistance and fracture
toughness thereof in the steel making route of; Electric arc
furnace→ vacuum decarburisation→ Ingot Casting→ Hot Forging→ Rough
Machining; (b) applying stress relieving treatment on the blades
in the manner, comprising charging the blades into a furnace at an
initial temperature of 50°C max, heating at a rate of 5-8°C per
minute to a temperature of 650°C and soaking at this temperature
for 4 hours, and cooling in the furnace to a temperature of 50°C
max; (c) finish machining and grinding of stress relieved blades;
(d) applying hardening treatment on the plates in the manner,
comprising charging the blades into a vacuum H.T. Furnace at an
initial temperature of 50°C max, heating to a preheating temperatur
of 540°C at a rate of 5-8°C per minute and soaking at this
temperature for 30 minutes, heating to preheating temperature of
800° C at a rate of 5-8° C per minute and soaking at this temperature
for 25 minutes, austenitislng at a temperature of 1030°C for 40
minutes and quenching by blowing Nitrogen gas into the furnace;
and (e) applying tempering treatment on the blades in the manner,
comprising the first step in which the blades are charged into a
furnace at an initial temperature of 50°C max, heated to a
temperature of 430-500°C at a rate of 5°C per minute and soaked
at this temperature for 3 hours, and cooled to 50°C max at a rate
of 5-10°C per minute; and the second step in which the blades are
charged into a furnace at an initial temperature of 50°C max, heate
to a temperature of 500-530°C at a rate of 5°C per minute and soake
at this temperature for 3 hours, and cooled to room temperature at
a rate of 5-10° C per minute.