LU82987A1 - PROCESS FOR THE MANUFACTURE OF STEEL LAMINES HAVING GOOD WELDING, A HIGH ELASTICITY LIMIT AND RESILIENCE AT VERY LOW TEMPERATURES - Google Patents

Description

ψ A 630

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

Designation of the Inventor

(1) The undersigned Een® NE YEN, Central Administration of 1 ’ARBED

PO Box 1802, LUXEMBOURG

acting as çteüîispQSacÂX— as agent for the depositor - (2) ..................................... ..ARBED SA .............................................. ....

Avenue de la Liberté LUXEMBOURG

(3) of the invention relating to:

Process for the manufacture of rolled steel having good weldability, a high yield strength and resilience to ......... very low temperatures ".............. .................................................. .................................................. .......................

designated as inventor (s): 1. Surname and first names ...... S.ÇHUMMER Arthur ............................ .................................................. .........................................

Address 8 rue de la Tuillerie »ESCH / ALZETTE

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

. , 16 rue Henri Tudor, BELVAUX

Address ................................................. .................................................. .................................................. ...................................- 3. Name and forenames ....... ^ s ? Ek.Ç.uy ............................................ .................................................. ...................................

. , 31 rue Wurth Paquet, ESCH / ALZETTE

Address ................................................. .................................................. .................................................. ......................-..........

he affirms the sincerity of the abovementioned indications and declares to assume full responsibility for them.

4. BECK Jean-Paul, 82 Bd. Kennedy, ESCH / ALZETTE

5. FRANTZ Armand, 84 rue des Aubépines, LUXEMBOURG

............... Luxembourg ......................... i | e S December .... . 19 80 ....

(signature) A 68026_ (1) Last name, first names, company, address.

A 630

Applicant's patent application: 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._ - 1 -

The present invention relates to a process for the production of rolled steel, in particular S concrete rounds, having a good weldability, a high yield strength and a resilience at very low temperatures. weldability, high yield strength, as well as resilience at very low temperatures.

10 It is well known that concrete rods of current manufacture with an elastic limit of the order of 400 N / mm2 have only very low toughness. Thus their transition temperature for the Charpy V resilience test at 35 J / cm2 is of the order of + 20 ° C. It follows that these products offer only a low brittle fracture strength at low temperatures.

In the past, Charpy V resilience at 35 J / cm2 and at temperatures of the order of - 196 ° C was not required for common uses made of rolled steel such as concrete reinforcing bars. 20 However, recent developments in the technology for manufacturing and especially for the storage of liquefied gases have led to the need for fairly large quantities of rolled steel resistant to intense cold. For example, it is planned, for safety reasons, to provide the liquefied gas storage tanks 25 with a reinforced concrete envelope in analogy to the safety measures applied in the field of nuclear reactors.

To be usable for the construction of the reinforcement of such envelopes of liquefied gas tanks which are exposed to temperatures of - 50 ° C to - 196 ° C, the concrete reinforcing bars must present in addition to an adequate resilience to core, satisfactory weldability, which implies carbon contents of less than 0.2%. However, the known concrete rods, which have 0.16 - 0.2% C, are subjected to cold twisting, which on the one hand has the effect of giving them a satisfactory elastic limit but which on the other hand results in low toughness, especially at low temperatures.

- 2 -

An attempt has also been made, for example, to subject concrete rods with a carbon content of at most 0.20% during the course of manufacture to a treatment comprising intense cooling on the surface at the outlet of the rolling mill, as well as a subsequent autorlvenu 5. This made it possible to obtain weldable concrete rounds and strengths without these rounds having Charpy V-35 J / cm2 transition temperatures significantly better than - 50 ° C.

So far only the concrete rods made from a 10% alloy steel 9% Ni, which have undergone a double normalization followed by tempering, or else a quenching followed by tempering, have a Charpy V resilience -35 J / cm2 minimum at -196 ° C.

Thus, the object of the invention is to propose a process for the manufacture of laminates meeting the criteria mentioned in the first paragraph, this process being possible ex hot rolling, preferably from a steel containing a minimum of expensive alloying elements, thereby reducing the cost price of the laminates produced.

20

This object is achieved by the process according to the invention which is characterized in that a steel containing carbon (C), manganese (MN), silicon (SI), aluminum (AL) is used. ) 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 for the operations before (Tl) 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 -120 ° C (KCV), ex -30 awarded with LE = 1035 + 510 C + 192 MN + 2270 NB - 0.21 Tl - 0.42 T2 - 0.48 T3 - 3.51 D and 35 KCV = 2202 - 2066 C + 23.20 MN - 2064 NB - 0.77 T1 - 1.24 T2 - 0.23 T2 - 1.98 D reach the desired high values.

- 3 -

It is understood that the concentrations of the various elements present or added, as well as the temperatures of the various treatment phases, 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 of less than 0.20% will be all the lower the higher the transition temperatures. lower For example, carbon is preferably limited to 10 0.08% max. for a Charpy V-35 J / cm2 transition temperature at - 140 ° C.

* - A manganese content of around 1.7% gives the desired resilience to steel while improving its toughness, while a silicon te-15 neur of around 0.3% is favorable to build resistance.

Furthermore, it is important to calm the fine grain steel to the aluminum in order to improve the weldability and considerably reduce the tendency to age. The refining of the grain also raises the elastic limit, as well as the toughness.

The Nb and possibly the V and / or the Mo will guarantee a high elastic limit, especially for concrete rods of large dia-25 bolts.

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 the operations before, during and after mining, the total reduction rate obtained during these passes must be important, that is to say preferably greater than 20%. 1 should be emphasized that the particular thermo-mechanical cycle, which is part of the method according to the invention, aims to obtain a structure with an extremely fine grain at the heart of the product, since the resilience to very low temperatures must be guaranteed at the heart of the laminated product.

- 4 -

To achieve this result, the temperature of the oven is carefully chosen on one side according to the rules of the art so as to avoid a grain enlargement on the semi-finished product. On the other hand, the temperature at the start of rolling will be such that a considerable grain refinement is obtained from the start of rolling and that 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 Ar3.

- The cooling treatment at the outlet of the rolling mill consists of another vigorous cooling of the product, to a sufficiently low core temperature, in order to avoid any recrystallization.

The idea which is the basis of the present invention therefore consists in combining the beneficial effects achievable separately thanks 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 materialized in particular by an extremely fine grain size of the finished product.

In order to more easily produce products having transition temperatures below at least −140 ° C., it is possible according to the invention to use a steel which has nickel contents of the order of 5%, but less than 10 %. Such a steel, rolled according to the process according to the invention, exhibits a Charpy V-35 J / cm 2 resilience at -196 ° C.

The advantages of the process according to the invention emerge clearly from the six experiments described below: 1. The rolling of a naturally hard steel for concrete I - 5 - (C = 0.35% approximately) results in a product with satisfactory traction characteristics, including in particular an elastic limit exceeding 400 MPa.

However, the transition temperature for the Charpy V test at an energy level of 35 J / cm2 is only + 20 ° C. This steel therefore has no toughness at low temperatures. Its weldability is poor.

2. Carbon steel limited to 0.18%, which undergoes the treatment according to the invention before, during and after rolling, also offers satisfactory tensile characteristics.

A clear improvement compared to Example 1 is made from the point of view of elongation and in particular of the transition temperature, which drops to -60 ° C. The steel turns out to be weldable.

3. The use of a steel having the chemical composition defined in the present application, but not undergoing treatment according to the invention, leads to mechanical characteristics which are insufficient from the point of view of elasticity and resistance limit. The elongation is high. The transition temperature, even without treatment, however, is already approximately at the same level as that of Example 2, where the treatment according to the invention has been applied before, during and after rolling.

4. The combination of the chemical composition and the treatments before, during and after the rolling according to the invention make it possible to achieve the desired double improvement, namely: - the satisfactory mechanical characteristics and the high elongation, - the temperature transition down to a very low temperature of at least -140 ° C.

5. A 9% Ni steel, in the normal hot rolling state, achieves a Charpy V transition temperature - 35 J / cm2 at - 50 ° C.

- 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 briefly summarized in table 1 in the appendix.

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: A naturally hard steel for concrete reinforcing bars (C = 0.35% approximately) 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.

20

For the Charpy V test, even at room temperature, the energy level does not exceed 35 J / cm2.

2. The use of a steel exhibiting the chemical composition determined in the present application, but without application of the treatment according to the invention leads to mechanical characteristics which are insufficient from the point of view of elasticity and resistance limit.

The transition temperature for Charpy V resilience is 60 ° C.

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

4. By introducing in the diagram of implementation of example 3 - 7 - still a thermomechanical rolling, but only for the last passes the elastic limit and the resistance are further improved. The same is true for the transition temperature (-100 ° C).

5 5. By carrying out a thermomechanical treatment for all the rolling operations, but without post-rolling cooling, the elastic limit and the resistance are lowered compared with examples 3 and 4. The transition temperature however is further improved (~ 115 ° C).

10 6. The best results concerning the mechanical properties of the steel exhibiting the chemical composition determined in the present application are obtained by the treatment according to the invention, before, during and after rolling, namely: 15 - satisfactory mechanical characteristics and high elongation.

- a very low Charpy V resilience transition temperature.

20

The above results are shown in brief form in the attached Table 2.

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 merchant steels such as smooth, flat, square, angle bars, to sections and to sheets. , as long as it is desired to combine the properties of weldability, high yield strength and resilience at very low temperatures in the same product.

\

Claims (7)

1. Process for the production of rolled steel, in particular concrete rods, having good weldability, a high yield strength, as well as resilience at very low temperatures, characterized in that a steel containing carbon (C), manganese (MN), silicon (SI), aluminum (AL) and niobium (NB), that this steel is rolled while ensuring that the reduction rate total, produced during the last three passes, that is to say more than 20% and that the 10 temperatures are adjusted for the operations before (Tl), 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 I - 120 ° C (KCV), expressed by 15 LE = 1035 + 510 C + 192 MN + 2270 NB - 0.21 Tl - 0.40 T2 - 0.48 T3 - 3.51 D and KCV = 2202 - 2066 C + 23.20 MN - 2064 NB - 0 , 77 Tl 20 - 1.24 T2 - 0.23 T3 - 1.98 D reach the coveted high values. 2. Method according to claim 1, characterized in that a lower carbon content of 0.20% is chosen, the lower the higher the target of a lower transition temperature. 3. Method according to claim 1, characterized in that the elastic limit of the steel is raised by operating a fine grain calming with aluminum at a content of at least 0.03%. 30 4. Method according to claim 1, characterized in that a nickel content of less than 10% is chosen, the higher the lower the transition temperature. 5. Method according to claim 1, characterized in that the temperature of the start of rolling is adjusted by creating in the oven a controlled temperature, less than 1200 ° C. k η - 2 - 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. , 'ΊΑΙ'.Ι, ΚΑϋ I • in Hirni ιι mirr ι — rl -> ·· ιΠιτι · μ · ιι uhwhi “ο n“ la ^ fcnumw-ww ^ jn -> - um · * ικ ”ιιιιιιιιι - η iiwi "Wi / w> im ^ ni" i "miiMi>" i "" "iii> 11 --.- 11 im ï # '-S'H Ή \ <D vO Ë' HOO CO ΟΛ Vû I — ι 3 ' 1-i rH ^ cd OQ \ 0 \ U | • H: ¾ \ a) ß ° È'S rH C O O CTl IT) Cd Ο ΟΊ rH m cre ü P oo ο I rH fc'S! 00 O \ P Sf r Ö * rl OOOOO IH 3 <J \ rs CO cd o in Il ü cj 6vâ 00 ο \ p «BO rH POO 0-1 Q CO cd O Cd O CS vO Il UP CO iP O 6 ^ \ p Ë CO rH rH p ·> CJ · | Η OO * 0 o CS o IP Γ '· CS so • rl o Si · lO Il B l P CJ W 6 ^ MU k BU ~) rH ro PPOO co o ι —Ι “v ο o sr ό ι i cs Ο IP sf CO • H + Il B eu Cj en \ pp es' w * w OS P ^ * rH .H 5 PPW CJ X) 4J. > P -H Ή y-) · - <u o. in p U) rH po LO P w 05 PPP co P PO rH CJ mp P · Η -UO 4J M) \ p P p 4J <rC / P γ-η 'ü P-ripp - cP UP rH P. PP, PC <U -rl> a - λ pp xi en ρ · X) PPPG pv ^ -Ur- ^ 00 r-> \ p Jr, χ '4J> PP 4J pp p te * fi, ex PP -H px) 1 -H> lH .rC Ο, o SH Q, MP, E «S rH ßrp o inrpp \ p s_ / PCJjS 2 'Eh E-crHp, rH μ) cd <HO CJ i λ nj, i / u. i. j. ê'S q) g; <u eu o \ <D \ <D \ QJ \ 0J O LO rW i — I r — I p — IT— (o <J <o <o (O <0 OOKO s_i f_i ..- i μ * · ~ ι μ σ \ oo <τ vX) OWJ4-) iJ 3 3 -μ VJ-LOCN ι-Η β β ß Ο ß 0 ß CO II r — I 0 0 Ο Ο I β, -Ο ο ο ο υ υ Βν ° α> α) tu ι- (\ φ \ φ '3 υ IT! R-4 r-Ι ι- <ο Ο <ο <0 · η <0 β * \ φ μ μ 3 μ ο I ο ό en ·? Co ιο'οβμμομβ sew μ II ρη β β ß co -ο- μ π) ο ο ο η ο ϋ ϋ α ο ι —— 'φ ——— ———. —— ——- —————— seen pW Qj 6-¾ <0 seen q) υ ο μ γη \ φ ο ιο η ο μ <ο <μ ο <ί β · μ μ <ο ο <ί » .οο3μ> μμ 6-¾ ο ο vu ο ϋ ο ß 3 μ οο <- * β C-4 ο Ο 3 ιΟ (—ι il rt rt (3 ο ο <rmcoi cd ο α ο ο β φ ~ 3 \ φ '\ φ ι-Ι 6-¾ pHI <0 φ <0 μ' 3 ο ο ι-ι ο μ μ -μ ο o <co μ cc ή <ο ο ο 6-¾ Ρ β Ο Ο 3 μ CO CO ιο co ο vu ο ο β ο ο μ <fiocN r- * Β ο ο β co II ι-Η CN β Ο I cd ι — ι β ο ο ο α ο β ---- É ----- ----- eu ω ---- 1 * '5Φ 5Φ Ο pH rH 6-¾ ρμ ο <ο <ο <; μ μ u ιο ο μ μ ο Ο \ Φ Ο ß ß ß ß 0 0 6¾ CMpBCNO ο Ο Ο I CNC0 0 ο ι — ι ϋ ß υ ß co ο- '<r co Cd rH ro II υ ß ß I ο ο Ο β β 6-¾ \ cu <u αι φ φ - g \ φ \ ω \ φ 5Φ υ ΙΟ ι — I r — I ι — I ι — I 1 — I Ο CO β <ο <ο · μ <ο · Η (Ο 6-¾ -ομμ 3 μ 3 μ-ΟΟ οι i-η ο ι μ μ ο μ ο μ cocqco • μββ ß ß σ-ι οί + ιι Β ο ο ο ο φ ο υ u υ Λ ο Μ. 1 d Φ -μ Φ I Ό D- I μι 'Φ 6¾ ß β > cdßcdμμμ cdrH = μ μ · μ μ · μ φ w · η ^^ μ μ3 φίμ Ο / ΦΟ α / -n Ό μ μ ci. 3χι μμ μ β μ β, · η cd 3 μ Ο'Φ β · π φ β.μ α. μ ρμιΟ Φ ο ß UH Ό Φ cd Ό ΦΒ 3 μ 05 cu xd μ Β · η Β cd ß ß 'ή υ Φ Φ Φ φ-3 ΦΦ Φ, - <ΦΦ ru ^ μ Φ ^ Φ · η μ μ ω \ α μ μ μι μβ vu β φ ß μ ο φ cm ι — ι α 3 3 ω ε 3 β φμ 3 φ ~ eu y φ 3θοΕ Cu β μ μφ · μμ μβ · μ μ μ οι μ τι £ β Β μ ^ βα Β * - β cd Μ Ό Φ cd -μ ΌΟ υ “Ή ρ-ρ Cd Φ β φ -” φ ό μ μα · μ μ μβ · μ eu μ-μ ο φ μ οο μ β · μ τ> χ \ φ »φ β ο ß 'Φ ß ο' Φ ό ß μ w ß seen ο -μ φ φ eu eu- μ μ · μ eu-μ μ φ eu-μ · μ · μ · μ ο cu-μ · μ ιο eu Β Ê Ε μ Β μ φ β ο G Β φ μ £ μ μ ro Ο φ Φ ß Φ Φ Φ Φ Φ · μ Φ μ α · μ \ φ τ-η φ -μ νι Î5 Η Η Η μ pd ό Η ό od eu Η μ ρ-ι μ od <| Η in μ / β