CA1159286A - Fabrication process of rolled steel having a good weldability and high elasticity and resiliency at low temperatures - Google Patents

Abstract

The invention relates to a method for manufacturing rolled steel, in particular concrete reinforcing bars. The process according to the invention is characterized in that a steel containing carbon (C), manganese (Mn), silicon (Si), aluminum (Al) and niobium (Nb) is used, that this steel is rolled, ensuring that the total reduction rate, achieved during the last three passes, is greater than 20% and that the temperatures for operations are adjusted before (T1), during (T2 ) and after (T3) the rolling of the product having a diameter (D), so as to ensure that the elastic limit (LE) and the resilience at -120.degree.C (KCV), expressed by LE = 1035 + 510 C + 192 Mn + 2270 Nb - 0.21 T1 -0.40 T2 - 0.48 T3 - 3.51 D and KCV = 2202 - 2066 C + 23.20 Mn - 2064 Nb - 0.77 T1 - 1 , 24 T2 - 0.23 T3 - 1.98 D reach the desired high values. The steel laminates obtained according to the process of the invention have good weldability, a high yield strength, as well as resilience at very low temperatures.

Description

28 ~

Method for the manufacture of laminates in acler having good soudabi.li.te ~, a high elastic limit ~ and a resilience to very low temperatures.

The present invention relates to a laminate manufacturing process made of steel, in particular of rounds with heteron, presenting a good weldability.
lity, a high elastic limit, as well as a resilience has very low temperatures.

It is well known that common concrete rods with a yield strength of the order of 400 N / mm2 presents only one very low toughness. So their translti.on temperature for the test. Charpy V resilience at 35 J / cln2 is around ~ 20C.
It follows that these products offer only a low resistance to rup ~ ure fragile at low temperatures.

In the past a Charpy V resllience at 35 J / cm2 and at temperatures ~
tures of the order of - 196C was not required for users common ntions of steel laminate com ~ e rounds b ~ ton.
However, recent developments in manufacturing technology and especially storage of liquefied gases has led to the need to have fairly large quantities of rolled steel in intense cold. So for example it is planned, for r.ai.sons security, to equip the liquefied gas storage tanks of a reinforced concrete envelope in analogy to security measures applied in the field of nuclear reactors.

To be usable for the constitution of the frame of such envelopes of liquefied gas tanks which. are exposed to ; ~ 30 temperatures from - 50C to - 196C the concrete bars must pre-feel in addition to adequate resilience at heart, weldability - satisfai.sante, which implies d. ~ s carbon contents lower than 0.2 ~. However, the known concrete rods, which have 0 ~ 16 - 0.2% C, are subjected to cold twisting, which has ~ n side for effect of give them a satisfactory elastic limit but what : on the other hand low tenacity, especially at low tem ~
peratures.

1,159 ~

We also tried for example to submit to the course even ~ e of the manufacturing rounds ~ concrete of a carbon tene ~ r all more than 0.20% at a treatment including an internal cooling tense on the surface at the exit of the black lami.
subsequent. This made it possible to obtain weldable b ~ ton rounds and tenancies without these rounds, however, showing temperaturLs of trans ~ i.on Charpy V-35 J1cm2 sense ~ much better ~ eu - 50C

Up to now only concrete rolls made from steel alll.é at 9% Ni? that underwent a double normalization followed by a revellu, or a hardening followed by an income, present the same Silence Charpy V-35 J / cm2 mi.nimum at -196C.

Thus, the object of the invention is to propose a method of fa-brication of laminates responding to the criteria.
alinea, this process being feasible ex hot rolling, pre-ference from a steel containing a ~ minimum of aluminum elements costly tying9 thus reducing the cost price of the laminates duits.
This object is achieved by the method according to the invention which is type in that a steel containing carbon is used bone (C) 9 manganese (MN), silicon (SI), aluminum (AL) and niobium (NB ~, that we roll this steel making sure that the total reduction rate achieved in the last three passes, that is greater than 20% and that the temperatures are adjusted for operations before (Tl) during (T2) and after (T3) the mining of the product having a diameter (D), so as to ensure that the elastic limit (LE) and the resilience -120 ~ C (KCV), ex-bonuses by , LE - lO35 + 51n C + 19 ~ MN + 2270 NB - 0.21 Tl - 0? 42 T2 - 0948 T3 - 3.51 D
and KCV = 2202 - 2066 C + 23.20 MN - 2064 NB - 0.77 Tl - 1.24 T2 - 0.23 T3 - 1.98 D
reach the desired high values.

.. ...;.,. ~
. .
- ~

) 1592 ~

It is understood that the concentrations of the various elements present or at all, while the temperatures of the different treatment phases, will only vary within certain limits.

So if the chemical composition of the steel used is chosen following vant the experiences recuei.llies during numerous tests which it is revealed that the oarbone content is less than 0.20 ~ will be all the lower when we aim for a temperature of eransltion lower For example, the preferred carbon is limited to I0 0.08% max. for a transition temperature Charpy V-35 J / cm2 a - 140C.

A manganese content of around 1.7% ~ improves resilience wanted to steel while improving its toughness, while a te-0.3% silicon neur is conducive to strengthening resistance.

Furthermore it is i.mpor ~ ant to calm the grain steel fi.na alu-mi.nium to improve weldability and considerably reduce the tendency to aging. The refining of the grain falls under ai.l-their elastic limit, as well as tenacity.

The Nb and possibly the V and / or the Mo will guarantee a limit of high elasticity, especially for large concrete rounds meters. ~

According to the invention the product is subjected to the particular thermomechanical cycle described during which the temperature of the product is controlled for all operations before, during and after the mining, the total reduction rate obtained during these passes must be significant, that is to say preferably greater than 20%.

It should be emphasized that the particular thermo-mechanical cycle, which is part of the process following the inventi.on, aims to obtain tention of a grai.n structure extre ~ ment at the heart of the product, since the resilience at very low temperatures must guaranteed at the heart of the laminated product.

.
.. -:: ~
~. ~. : '' .
~: `~ '. : ''' i To achieve this result we choose on one side the temperature of the oven Judicieuse ~ follow the rules of the art so as to avoid a magnification of the grain on the semi-prodult. On the other hand, rolling start temperature will be such that we obtain the beginning of rolling a considerable refinement with grain and that avoids too much recrystallization.

Before the last three ~ 17 rolling passes undergoing steel.
rapid cooling in a cooling ramp Up to one temperature close to the transformation point Ar3.

The cooling treatment at the exit of the rolling mill consists in another vigorous cooling of the product, to a tem ~
perature at heart enough ~ ent low, in order to avoid any recrystals-lisa ~ lon.

The idea which is the basis of the present invention therefore consi.ste combine the beneficial effects achievable separately thanks to judicious choice of chemical elements incorporated into contents determined in steel with the effects of a direct interaction between the evolution of the temperature of the product being fabricatlon and reduction water applied during rolling.

The result obtained is materialized in particular by a size of extremely fine grain of the finished product.

To more easily produce products with temperatures-transition tures lower than at least -140C, we can following inventi.on implement a steel which has contents in nickel of the order of 5%, but less than 10%. Such steel, laminate according to the proaede according to the invention, has a resili-Charpy V-35 J / cm2 at -196C.

The advantages of the procedure according to the invention stand out so clear of the six experiences described by the following:

l. Rolling - a naturally hard acler for concrete reinforcing bars :; . ,,,,.:
:
:. .:

1 1 ~ 92 ~
I

- s -(C - 0 ~ 35% approximately) ab) uti.t to a pr du.it having characteristics satisfactory traction ristiqlles, including in particular a limit elasticity exceeding 400 MPa.

However, the transition temperature for the Charpy V test at a energy level of 35 J / cm2 is only + 20C. This steel does not therefore exhibits no tenacity at low temperatures. His weld.lite is mediocre.

2. Vn steel with carbon content limited to 0 ~ 18% ~ 4ui undergoes treatment according to the invention before, during and after rolling, also offers characteristics of sati.æfai.santes tracti.on.
A clear improvement compared to example l is made up of lengthening point of view and in particular of the transition temperature ti ~ n, which descends to N60C. The steel turns out to be weldable.

3. The use of a steel with chemical composition defined in this application, but may not undergo trafficking ment according to the invention, leads to mechanical characteristics insuffi cient from the point of view of elasticity and resistance.
The elongation is high. The transition temperature, even without treatment, however, is already about the same level as that of Example 2, where the treatment according to the invention was applied before, during and after rolling.

4. Combination of chemical composition and treatments before, during and after rolling according to the invention allow to achieve the coveted double improvement, namely:

- satisfactory mechanical characteristics and elongation Student, - the transition temperature falling to a very at least -140C.

5. A 9% Ni steel, in the normal hot rolling state produced a transition temperature Charpy V - 35 Jlcm2 to - 50C.

:. -., ~, , ~

, 1,159,286

6. The same 9 ~ Ni steel, whose resilience a - 196C is not normally achievable only by means of an expensive heat treatment reux (double normalization ~ tempering or quenching ~ tempering), allows to reach a transition temperature of -196C when apply the recommended treatment before, during and after the mining.

The 6 examples are summarized succinctly in Table 1 attached.

For the process according to the invention the importance of the composition chemical of steel as well as that of temperature control during manufacturing operations and rapid cooling post-rolling mill is highlighted by the following six experiments:
l. A naturally hard material for concrete reinforcing bars (C = 0.35% in viron) treats' according to the inventi.on process is quenched to the core.
This steel has a high yield strength, but the properties : ductility states are very low.
~ 0 For the Charpy V test, even at room temperature, the level energy does not exceed 35 J / cm2.

2. The implementation of a steel accusing chemical compostition determines ~ e in this application ~ but without application of the scale-according to the invention leads to mechanical characteristics insufficient from the point of view of elastic limit and resistance.
The transition temperature of the Charpy V resi.lience is 60C.
^ ~
3. The ~ me aaier laminate without thermomechanical treatment, but with post-mill cooling has an elastic limit and a significantly higher resistance than for example 2. The : transition temperature (-75C) is also improved by compared to example 20 4. ~ n introducing into the sche ~ ma of implementation of Example 3 ::: ..
:::., ~:
.,:. . ~:.

~ 159,286 still a thermom ~ can ~ lamirlage that, but uniqi1emerlt for der ~
last passes the lim ~ e of Elast ~ clté and the reslstanc ~ are still improved. It is the same ~ - for: The temperature ~ lre of transi.tion (-100C) S. By carrying out a thermomechanical treatment for all the ope-lamination rations, but without ref ~ oidissement post-lam1nolr, la yield strength and 1 ~ resistance are lowered by rapp ~ rt in examples 3 and 4. The transition temperature is however still improved (-115C).
6. The best results concerning the mechanical properties of steel showing the chemical composition determined in the pre-this request is obtained by the processing according to the invention, before, during and after the lamir, age, namely:
- satisfactory mechanical characteristics and an elongation Student.
- a transition temperature of Charpy V resilience very low.
The above results are represented in a succi.nte form in the attached table 2.
The following speci ~ ic example illustrates the application of formulas according to the invention:
LE = 1035 + 510 C + 192 Mn ~ 2270 ~ b - 0.21 Tl - 0.42 T2 - 0.48 T3 - 3.51 D (MPa) KCV ~ - 120 C = 2202 - 2066 C + 23.20 Mn - 2064 ~ b - 0.77 Tl - 1.24 T2 ~ 0.23 ~ 3 - 1.98 D (Joules) Parameters: C = 0.08 Mn = 1.60% Nb = O
Tl = 1000 C T2 = 800C T3 = 650 C
0 = 16 mm LE = 469 MPa KCV = 130 Joules ~ -120C

_7_ AT

. -. `,. . , .

; , .. .., ~, ~,.

I 159 ~ 8 ~

Although this description focuses on the production of concrete bars, the process according to the invention can just as easily be applied to other steels merchants such as smooth xonds, plates, squares, angles, profiles and sheets, as long as desired combine weldability, high limit properties elasticity and resilience at very low temperatures in the same product.

-7a-... . . .. .... . ... . ..
,;, ~. -,; - :::

-. :, ::
; ~. . . :

1,159Z88 -8- 'J'l ~ J r r ~ ~ w ~ _ ~ ~ ~ ~ _ , 1 ) ~ D
3. r ~ OO
~ Cl ~ O r ~ -tr ~ ~ - ~
CJ ~ t,).
__ ~ ~. _ ~
Z` ~
~ i ooa ~
u ~
oa ~
U) a ~ c ~) ~: r- ~
. __ __ __ ____ _ ~
. ~ o ~ o \ a ~
~ O rl. ra ~ o --t 11 UO ~ U) r ~
. , _ _ __ _ _. , _ _____ ~ 0 ~ ' r ~;
~) O r ~ OOOC ~ JO
c ~ F ~ ~
_ ............. _....... _... _..... .__ _ _ __.
. '~ ~
r ~ td ~ ~ ~. OO U7 O
~ rl O ~ J 1 ~ C ~ l ~
. 11 ~.
t ~ U ~
- ~ e. . , _, __ _ ~ o ~ o O ~, O
~ -J. OI 0 ~. -t U ~ ~ ~ 1 . ~ r. t . ~ 0 ~
: _ _ _, ~ 1 _...._.__ ~ ~ _ ~

. ., ~ hr ~ OF u ~
~ rl ~ rl ~ J ~ d ~ t.) ~ il ~

Ei ~. ~ F ~ c ~ E3. al ~, ( a ~ ~. aa ~ ~, u ~ ~, _ X 1 ~ cd ~ u ~ ~ F. 6 ~. ~ c ~
~ 1 o ~, 1 F ~ r- ~. -1 ~ O ~ ~ ~ 1 ~ _ ~ ~ _ ~ = e ~ = ~. , ~ ~
.

~.

-; -.

-::. .:

.:: :::. ~

9 11S9286 r ~ r ~ u IL
I_ ~ _ ._ ~ _ ~ _ ~ ,, _. __ ~
~ ~ a ~ ~ a LO ~ -1 r- ~ r- /. \ a ~ a ~ o O ¢ ~ O ~ O ~ O r- OO 6 ~ O
O ~ a1 V ~ J r ~ V ~ r ~ J ~ Lr) ~; ~ 1 ~ ~. ~ o ~: oa ~
11 ~ oooo C ~, .0 ~. t ~ ~
. ~ 0 a ~ _ ~~ ~ _ al __ ~ _ .. ~ ~ _. __ ~
rr- ~ I a rl O
o ~ o ~ o. "~ oa . ~ ~ Sl) ~. ~ OIO Ll ~ 6 ~ U) U ~ 0 ~ 3 VVOV ~ CO ~ ~ rl ___. a ~~ `~ ___ __ ~ __. _ ~ _-_, __ ~

U) ~ OV rl rl O
. ~ o ~ al o ~ o ~ ~. ~ r <~ 0 O 0 6 ~ 0.

rl aooo ~ ~ r _ __. ..............__ ~ __ ___ ~ _ ~ _ ___ _ __ '~, 1 ~ V
~ rl C) r <O rl O
o ¢ o ~ ao ~. ~ LO ~ OO ~ Lt ~
. r ~ O ~ O o ~~ oa ~ L ~ J r ~
11 ~ ~ O ~. V
_ .. _ ~ ~ ~ 'aJ -'--., _. ~ _ _ _. _ ~.
C ~ ~ a). ~ o ~
. b "~ - ~ O ~ O ~ 0 Lr ~ ¢ OS ~ v 0 o ~ o ~ ~ ~: ~ OO 6 ~
c ~ ^ ~ 3 ~ o OOO lc ~ l L ~ OO
. O r ~ --IU ~ ~ a ~ ~ ~ ~
~ 5 0 ~
_ ... __ _ ... _ ~ ~ __ ~ __. _ _ ..... _ Ln ~ 1 ~ rl ~ Q ~ ~ O
C ~ t ~ ~ 0 ~ O. .1 ~ -1 ~ 6 ~
^ V ~ 1 ~ 1 ~ 1-1: ~ 1-1 C ~ l rl OIVL ~ O .IJ CV CO CO Ln ~ 5 ~ 5 5 C ~
I; cr ~ OOOO

C ~ U ~ VVV ~ A
_ _ ~ r1 ~ _ __ a ~ _ _ _ . ~, P ~ l ~ I ~ aJ ~ a ~ ~
h ~ 1 ~ t ~
. D- 1 ~. , ~ h r1 ~, ~
~: :) ~ ~ O 1 ~ o V ~ ~ ~ ~ ~
~ ~ 0 V ~ 1 V ~ S l ~ 4 ~ t ~ l ~) h o ~ a ~ 5-r ~ Q ~ 5- ~~ 1 ~ ~ U ~ 1 Ln tl ~
. ~ ~ ~) ~ ~ ~ JV a ~ ~ ~ _ ~
5_1 ~ E3 tO CI ~ ~ C_) Q ~ q ~ al Q ~ ~ a) ~ IJ q ~ ~ U a) r ~ V aJ ~~
a ~ ~ ~ 1 ~ ~ c) ~ l) Il) I ~ 1 ~ ~ t ~ J 5 ~ ~ J ~ ~ L ~ ~ ~ ~ ~ n ~~ a ~ - ~ 4 ~ aJ ~ o ~ ~
P ~ (-dvv ~ 1) rl ~ V 5r ~ 0 ~ .J cl) Sl ~ ~ ~ ~ 3 V ~~ 5 0 E ~ _ a) ~ t ~ ll ~ (1) ~ ~ rl ~ O ~ rl _ ~ t ~ (IJ tlJ al ~
O ~ hh ta ~ vh E ~ ~ h rl O aJ v ol: ~ 1 ~ 5 ~ rl ~
X ~ C) ~ (IJ C ~ O ~ ~ O ~ 5 ~ (1) 5 ~ JO ~ 1 Q ~ C ~ ~ ~ ~ ~ h ~ ri ~ rl 1 ~ 1 C) ~ ~ rl ~ r ~ ~ 1 O ~ r ~ n s: ~ EE 6 ~ E ~ ~ E o F Ei ~ n, ~ E vu ~ ~
O: ~ CJ ~ J n) C) 1 ~) ~ al O ~ 1 al 1- ~ ~ i ~ O rl (IJ ~ rl ~ O
æ E ~ E ~ ~ rl ~; ~: 1 ~ ~ ~ ~ ~ ~ rl ~ 1: 1 :; ¢ ~ ~ h _ _. _ _ ._ ~ -:.
`~:
.

Claims (7)

The embodiments of the invention, about which an exclusive right of property or privilege is claimed, are defined as follows: 1. Method for manufacturing rolled steel, in particular round concrete, with good weldability, high limit elasticity, as well as resilience at very low temperatures tures, characterized in that a steel containing carbon (C), manganese (MN), silicon (SI), aluminum (AL) and niobium (NB), that we roll this steel taking care that the total reduction rate achieved over the three last passes, that is more than 20% and that we adjust the temperatures for operations before (T1), during (T2) and after (T3) the rolling of the product having a diameter (D), so as to ensure that the elastic limit (LE) and the re-silence at - 120 ° C (KCV), expressed by LE - 1035 + 510 C + 192 MN + 2270 NB - 0.21 T1 - 0.40 T2 - 0.48 T3 - 3.51 D
and KCV = 2202 - 2066 C + 23.20 MN - 2064 NB - 0.77 T1 - 1.24 T2 - 0.23 T3 - 1.98 D
reach the desired high values. 2. Method according to claim 1, characterized in that one chooses a lower carbon content 0.20% all the more low that we are targeting a lower transition temperature. 3. Method according to claim 1, characterized in that one raises the elastic limit of steel by applying a calming fine grain aluminum at a content of at least 0.03%. 4. Method according to claim 1, characterized in that one chooses a nickel content of less than 10% all the more high that we are targeting a lower transition temperature. 5. Method according to claim 1, characterized in that one regulates the start of rolling temperature by creating in the oven a controlled temperature, lower than 1200 ° C. 6. Method according to claim 1, characterized in that that we proceed before the last three passes of rolling to rapid cooling of the steel up a temperature corresponding to the transformation point Ar3. 7. Method according to claims 1 or 6, characterized in that one proceeds to the end of rolling has a cooling energetic hardening of the steel up to a temperature of heart low enough to avoid recrystallization station.