LU82408A1 - PROCESS FOR MANUFACTURING STEEL LAMINES HAVING GOOD WELDABILITY, HIGH ELASTICITY LIMIT AND RESILIENCE AT VERY LOW TEMPERATURES - Google Patents

Description

N. A 610

Patent application for .............................................. .....

Designation of the Inventor

(1) The undersigned Ren ^ NEYEN, Central Administration of ARBED PO Box 1802, LUXEMBOURG

acting as ¥ 28ê $ 8ë96 & - as agent for the depositor - ^ ARBED S.A ·

Avenue ... de ... la Liberté LUXEMBOURG

(3) of the invention relating to: ........ Pr.Qc.édâ ... d & ... f.abr.ic.atjLQiL..cÎe .... l-amlnés .... ea..steel ... presenting a ...............

good weldability, high yield strength and ....................................... ......................................

designated as inventor (s): i Mnrr, ot nrinnmC SCHUMMER Arthur î. Last name and first names ............................................... .................................................. .................................................. .....................

Address ....................... 8..ruedelaTuil ...................... ..........................

0 .., J. de la HAMETTE

2. Surname and first names ............................................. .................................................. .................................................. .......................

Address ... He ^ „kI, r FRANTZ Armand 3. Last and first names ................................. .................................................. .................................................. ..................................

Address .rue des Aubépines, LUXEMBOURG

He affirms the sincerity of the above indications and declares to assume full responsibility for them.

........ Luxembou.rg ..........................., on ... 2.8 .... April. ............................ 19 ..... 8.Q.

René NEYEN (representative) (signature) A 680 26_ (1) Last name, first names, firm, address.

(2) Last name, first names and address of the depositor.

ß A 610

EU PATENT APPLICATION

Submitter: ARBED S. A.

Avenue de la Liberté Luxembourg

Process for the production of rolled steel having good weldability, a high yield strength and resilience at very low temperatures # ·

Process for manufacturing rolled steel having good weldability, high yield strength and resilience at very low temperatures.

The present invention relates to a method for manufacturing rolled steel, in particular concrete reinforcing bars, having good weldability, a high yield strength, as well as a resilience ‘at very low temperatures.

• 10

Concrete rods of current production with an elasticity limit of the order of 4oo N / mm have a very low toughness <Thus their transition temperature for the Charpy V impact test at 35 J / cm ^ is of the order of + 20 ° C. These products 15 therefore offer only a weak brittle breaking strength at low temperatures.

_ 2

The specification consisting of Charpy V resilience at 35 J / cm and at temperatures of the order of - 196 ° C was not required in the past, in connection with rolled steel such as concrete reinforcing bars. However, recent developments in manufacturing technology and especially in the storage of liquefied gases has led to the need for steel laminations resistant to intense cold. Thus, for safety reasons, provision is made to provide the liquefied gas storage tanks with a reinforced concrete envelope in analogy to the safety measures applied in the field of nuclear reactors.

The concrete reinforcing bars intended to constitute the reinforcement of casings 30 of liquefied gas tanks which are at temperatures of - 50 ° C to - 196 ° C must have in addition to an adequate resilience at the heart of the product, a satisfactory weldability, which implies carbon contents of less than 0.2%. Now, the known crenellated rounds which have o, 16 - o, 2% C, are produced by cold twisting, which gives them a satisfactory elastic limit, but cc which, on the other hand, results in low toughness, especially a low temperatures.

- 2 -

We have therefore tried, for example, to combine, during the production of concrete reinforcing bars, a limitation of the carbon content to 0.20% with a treatment comprising an intense cooling on the surface at the outlet of the rolling mill, as well as a self-income, which made it possible to obtain weldable and stubborn concrete rods.

Such crenellations can reach Cliarpy V-35 J / cm transition temperatures of the order of -5 °° C.

Furthermore, it has been found that a concrete rod manufactures from 10% Ni steel, having undergone a double normalization followed by tempering, or else a quenching followed by tempering, feels a resilience Charpy V-35 J / cm “minimum at -196 ° C.

The aim of the invention is to propose a process for the manufacture of laminates which meet the above-mentioned criteria while being feasible for hot rolling, preferably from a steel containing a minimum of expensive alloying elements, thus reducing the cost price of the laminates produced.

This object is achieved by the process according to the invention which is characterized in that a steel is used containing determined contents of carbon (C), manganese (MN), silicon (SI), aluminum (AL) and niobium (NB), that this steel is rolled while ensuring that the total reduction rate, achieved during the last three passes, is greater than 20% and that the temperatures are adjusted for the operations before (T1) during (T2) and after (T2), the rolling of the product, having a diameter (d), so as to ensure that the elastic limit (LE) and the resilience at -120 ° C. (KCV), expressed by 30 LE = 1035 + 510 C + 192 MN + 2.27 NB - 0.21T1 -0.42 T2 - 0.48T3 - 3.51D and

KCV = 2.2 - 2.07C + 23.20 MN - 2.07 NB - 0.77 Tl 35 - 1.24 T2 - 0.23 T3 - 1.98 D

reach sufficiently high values.

Μ

It is understood that the concentrations of the various elements added, as well as the temperatures established, will only vary within certain limits.

5 Thus, the chemical composition of the steel used is chosen according to the experiences collected during numerous tests which have revealed that the carbon content will be all the lower the lower the transition temperature.

10 For example, carbon is preferably limited to $ 0.08 max.

for a transition temperature Charpy V-35 J / cm ^ at -140 ° C.

A manganese content of around $ 1.7 gives 1? desired resistance to steel while improving its toughness, tan-15 say that $ 0.3 of silicon is added to reinforce the resistance.

Calm fine grain steel is aluminum to improve weldability and considerably reduce the tendency to aging. The refining of the grain also raises the elastic limit, as well as the toughness.

H b et évtl. the. V and / or Mo will guarantee a high limit, especially in the case of large diameters.

25

According to the invention, the product is subjected to a particular thermomechanical cycle during which it is ensured that the temperature is controlled for all the operations before, during and after rolling. In particular for the last 30 rolling passes, the total reduction rate obtained during these passes must be sufficiently high, preferably greater than $ 20.

It is important to emphasize that the particular thermo-mechanical cycle which is part of the process according to the invention, is aimed at obtaining an extremely fine grain structure at the heart of the product since the resilience at very low temperatures must be guaranteed at the heart of the laminated product.

= _ / ι_

Thus the temperature of the oven is judiciously chosen so as to avoid a grain enlargement on the semi-finished product.

The temperature at the start of rolling is situated so that a considerable refinement 5 of the grain is obtained from the start of rolling and, on the other hand, too great recrystallization is avoided.

Before the last three rolling passes, the steel undergoes rapid cooling in a cooling ramp to a temperature close to the transformation point Ar-.

The cooling treatment at the outlet of the rolling mill consists, according to the invention, of vigorous cooling of the product to a sufficiently low core temperature, again to avoid any recrystallization.

The idea which is the basis of the present invention therefore consists in combining the beneficial effects achievable separately according to the judicious choice of the chemical elements incorporated in determined contents in steel with the effects of a directed interaction between evolution. the temperature of the product during manufacture and the reduction rates applied during rolling.

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

’In order to arrive at transition temperatures below −ldld0 G, it is possible according to the invention to use a steel 30 which has nickel contents of between 5 and 10 $.

Such steel, rolled according to the process according to the invention, exhibits a Charpy V-35 d / cm ^ to -19 (3 ° C.

The advantages of the process according to the invention clearly result from the six experiments described below: "5 -" 1. A naturally hard steel for concrete reinforcing bars (C = about 0.35%) led to tensile characteristics satisfactory, including in particular an elastic limit exceeding Ù00 MPa.

5

However, the transition temperature for the Charpy V test at an energy level of 35 J / cm ^ was + 20 ° C. This ► steel exhibits no toughness at low temperature. Its weldability was poor.

. 2. A carbon content steel limited to 0.18%, which undergoes the treatment according to the invention before, during and after rolling, also offered satisfactory tensile characteristics. A clear improvement compared to exom-15 pie 1 was noted from the point of view of elongation and in particular of the transition temperature, which fell to -60 ° C. The steel turned out to be weldable.

3. The use of a steel exhibiting the chemical composition determined in the present application, but without applying the treatment according to the invention, led to mechanical properties which are insufficient from the point of view of elastic limit and resistance. . The aspect ratio was high. The transition temperature, even without treatment, is however already at the same level as the adhesive of Example 2, where the treatment according to the invention was applied before, during and after rolling.

ù. The combination of the chemical composition and the treatments 30 before, during and after the rolling according to the invention made it possible to achieve a double improvement, namely: - satisfactory mechanical characteristics and high elongation, - a transition temperature falling to a very low temperature (- 1Ù0 ° C).

5. A 9% Ni steel, in the hot rolling state, achieves a Charpy V transition temperature - 35 J / cm ^ at - 50 ° 0,

L

- 6 - 6. The same 9% Ni steel, whose resilience at -196 ° C is normally only achievable using an expensive heat treatment (double normalization + tempering or quenching + tempering), allows to reach a transition temperature of -196 ° C. when the treatment recommended is applied before, during and after rolling.

The 6 examples are given in table 1 in the appendix of maniera s'uccincte.

• 10

For the process according to the invention, the importance of the chemical composition of the steel as well as that of the temperature control during the manufacturing operations and of the rapid post-rolling cooling is demonstrated by the following six experiments: 1. A naturally hard steel for concrete bars (C = 0, about 35%) treated according to the process of the invention is hardened to the core. This steel has a high yield strength, but the ductility properties are very low.

1 For the Charpy V test, even at ambient temperature the 2 energy level does not exceed 35 J / cm 25 2. The use of a steel showing the chemical composition determined in the present application, but without application of the treatment according to the invention leads to insufficient mechanical characteristics from the point of view of elasticity and resistance limit. The transition temperature of the Charpy V resilience is - 6o ° C.

3. The same rolled steel without micromechanical treatment, but with a post-rolling cooling has a yield strength and a resistance significantly higher than 35 for example 2. The transition temperature (- 75 ° C) is also improved compared to Example 2.

ς - 7 - 4. By introducing into the implementation diagram of Example 3 still a thermomechanical rolling, but only for the last passes the elastic limit and the resistance are further improved. It is the same for the temperature • •, o 5 transition temperature (- loo C).

5. By carrying out a thermo-mechanical treatment. For all the "rolling operations, but without post-black lami cooling, the elastic limit and the resistance are lowered v 10 compared to examples 3 and 4. The transition temperature however, is further improved (-115 ° C).

6. The best results concerning the mechanical properties of the steel showing the chemical composition determined in the present application are obtained by the treatment according to the invention, before, during and after rolling, namely: - satisfactory mechanical characteristics and high elongation.

^ - a transition temperature of the Charpy V resilience

very low.

The G examples are shown in Table 2 in brief form.

Although the present description is focused on the production of concrete reinforcing bars, the process according to the invention can just as easily be applied to other nerobe steels such as smooth round: · :, studs, squares, angles, profiles and sheets, as long as you want to combine the properties of weldability, 3o high yield strength and resilience at very low temperatures in the same product.

Claims (13)

1. Method for manufacturing rolled steel, in particular · concrete reinforcing bars, having good weldability, a high yield strength, as well as resilience at very low temperatures, characterized in that a steel is used containing determined contents of carbon (U), manganese (WN), silicon (Si), aluminum (AL) and niobium (NB), that this steel is rolled while ensuring that the rate 10 total reduction, carried out during the last three passes, that is to say greater than 2070 and that the temperatures are adjusted for the operations before (ïl), 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 15 -120 ° C (KCV), expressed by LE = 1035 + 510 C + 192 MN + 2.27 NB - 0.21 Tl - 0.40 T2 - 0.48 T3 - 3.51 D and 20 KCV = 2.2 - 2.07 C + 23.20 MN - 2.07 NB - 0.77 Tl - 1.24 T2 - 0.23 T3 - 1.98 I) reach sufficiently high values. 2. Method according to claim 1 characterized in that one chooses a carbon content which is lower the more one aims for a lower transition temperature. 3. Method according to claim 1, characterized in that the o * raises the elastic limit of the steel by operating a calming. 30 fine grain aluminum with a content of at least 0.05 / ". 4. Method according to claim 1, characterized in that 1'oi chooses a nickel content all the higher that is aimed at a lower transition temperature. * 7 {- DD 5. Method according to claims 1-4, characterized in that one regulates the rolling start temperature by creating in the oven a controlled temperature, less than 1200 ° C. Μ _ ο _ 6. Method according to claims 1-5, characterized in that one proceeds before the last three rolling passes to rapid cooling of the steel to a temperature corresponding to the transformation point Ar3. 5 7. Method according to claims 1-6, characterized in that one proceeds to the end of rolling vigorous cooling of the steel to a sufficiently low core temperature to avoid recrystallization. 10 ♦ “5 TAU U ·: Λ U I * r-Ί“ 3 '3 vO G -H ο ο oo LO 6-S r-l 3 rH <1- ι-l rH nj o r ·· σι ON O | • H: s \ <u ß ° È'S rl 3 OO ON ^ (fl O ON tl ιΟ ON O 3 CO O | tH CO O \ 3 vfl · - 0 Ή OOO o O rl 3 ON O- CO, cfl Ο ' d 'm r-) It ü O> s co o \ o ·> B 0 I-H 3 O O (O) o ro cflo es o es co, Il O 3 CO LO o>? \ 3 G 00 rl r — I 3 “Ο · Η OO LO o cs ο I 3 r · 'r- vo- ho io η BI d) uw \ <u £ LO tH en o3 COO in Q r — I Λ Ü O LO f ^ CVl ο 1 ö sr vo • H -f * * NB <u OW va) a es ^ "40 oe Ö ^ -H · Η O 3. en ο Ό 4J> 3 MJ» H * HL * o '3!> Fi dd O - in d) 3 f11 in rH Oolo H 1/3 3 3 3 co 3 H 3, _ | 4J l-ι 3 3 · Η -u O -U CO \ 3 / ~ \ 3 3 4J · Η / 3 r-l 'O 3 * H CD 3 - tfl 0 o H Λ 3 · ^ t! VS . T3P-I 3 G <U-H> g - gr-l-i-H jr · cfl 3 Ό in 3 ’Ό 3330 3 ^ 4J r—-, W) ^ vu X fj> 30 4j in 3 3 m: ·”! a 3 3 Ή 3 33. I, H -H PL, o 'P, H P · f13 ^ £ nl G “S -4 0-3 O>. H-33 .μ 43 n ^ 30X1 5¾ H Hr-ip · ^ μ, ce; <fl HOO TABLE II δ '? 1) (U <u Q) O lO lO \ QJ \ QJ. O ΙΟ i — I 1 — I r — 1 i — I rH O <J (O <0 <0. CO OO t'î O • * 3 3 · 3 3 · 3 3 o \ 00 <r lO O 10 3 3 3 3 3 3 Healthy rH g B 3 osos co U i— 'OOOOI ta .ouu ü OO eo eu a) a) 1-1 lO lO lO U lO <£ rH rH i — 1 O o <a <o -h <o 3 * lO 3 3 3 3 o I oms-s LO mog33 0 3 G CQ CO rH Il 1-133 3 co or m rH 3 0 0 0 CO u ο ο ο υ i —— ——_ a ) '~' io t — id) 6-S <0 MU Q) CJ CJ 3 rH lO O - m r-ι o -u <0 i-ι 0 <! G -3 3 <o O <Τ-Οθ3 3 · 3 3 S-S O ο ίο a o o G 3 -o oo r-i s * g CN oo 3 m u ~ i rH u i — i i — i 3 u o or m co i 3. O a ü 3 • ———— —1 ——— '3 ’3 lO va) i-i 6v? ι-l (O 3 <0 3 13 CJ ΙΛ.-1 O 3 3. — i OO <! O 3 3 3 -3 (OOQ - 3oo3 3 co co m co ο ίο ο o 3 u ο 3 or m co r- »g O o 3 co Il i — i cvj 3 O 1 3 rH 3 OR CJ UO 3 d ....... - —............ —— ... ....... - .......- - _r had —...... 1 "\ qj \ q) O t — i *" —i HO (O (O <JUU CJ ιη o -u -uo O MU O 3 3 3 3 OO 60 CO-gCNoOOO I COCO ooi — iu 3 ü 3 co or 'or m 3 rH co Il O 3 3 I oo 0 3 3 6-2 MU 3 (U .3 <ug ICU MU MU Ό O LO i — I i — 1 r — I “-! T — IO CO 3 <0 (Ο · 3 <0 '3 (o 60“ 033 3 3 3 3-00 CO, —1 Ο I 3 3 O 3 O 3 OO CO lO r -3 GG 3 G CT) ΟΊ + 'Il g OO o O 3 0 0 UO / \ CJ in jr (U · 3 3 I ΊΟ Ο, I 31 HU 60 G 3> = 033333 3 rH - 3 3 -3 3 * 3 in CO -3 3> i 33 3UH 0 13 0 O * 3 3 3 CX 3jO 33 3 G 3 ÎX -3 3 33 O KU 3 · 3 o 3 · 3 O. 3 C3LT1 003 13 XJ 3 3 Ό 3g 33 CO λ '-' Ό ü, 3 3 g -3 g 3 3 3 CJ 0) 3 3 ΟΌ 03 0.3 OO, —ly — s 3 O .ro O · 3 3 3 CO Ό 3 fcO in I 3 g iO 3 3 3 3 O 3 CO rH O 3 3 co g 33 O) H 30 -P-. O 3 30 O g &, 3 3 30 -3 3 33 * 3 in 3 C / 3 3 3 g 3 ^ 30 g - 3 ee) fcO fl 'J 3 · 3 Ό O 3 in * 3' 3 O OG ' '- Ο Ί3 3 33 -3 4-1 3g -3 ex 3 -3 Q 3 3 W) 3 G -3> -jx KU lO 3 O 3 lO 3 OW fl G 3 in 3 MU O iH ο o a. cx-3 3 · 3 ex ^ η 3 0 (χ · 3 · 3 · 3 · 3 ο ex * 3 · 3 in ex g gg> 3 g iwfl gog g in rH g 3 in co ο ίο O 0 3 OOOO 0 -3 0 3 3 · 3 MU rH Ο · 3 \: l ieC HHHH pejT) H Ό CG CX H 3 HJ PG <H in 3/3