FR2818290A1 - Stainless steel for shaping by severe working and notably by cold striking or drawing into small diameter wires, with a controlled composition for selection of the type and dimensions of its inclusions - Google Patents

Abstract

Stainless steel comprises (by weight): 5 \* 10<-3> to 100 \* 10<-3> % carbon; 0.2 to 2 % manganese; 10 to 23 % chromium; 0 to 17 % nickel; 0.1 to 2 % silicon; less than 3 % molybdenum; less than 4% copper; and less than 30\*10<-3> % sulfur. It also has controlled contents of the following elements: 1\*10<-3> to 100\*10<-3> % titanium; 1\*10<-3> to 400\*10<-3> % nitrogen; less than 40\*10<-4> % aluminum; less than 20\*10<-4> % magnesium; 4\*10<-3> to 20\*10<-3> % oxygen; the remainder iron and residual production impurities, and incorporating globular inclusions mainly containing titanium oxide. The stainless steel has an austenitic microstructure after heat treatment.

Description

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Stainless steel for severe shaping and in particular for striking or drawing a wire.

The present invention relates to a stainless steel for severe shaping and in particular the striking or drawing of a wire. Steel has inclusions suitable for these uses.

Stainless steels have a specific composition. The structure, for example austenitic, is ensured, after transformation, by a heat treatment of the hyper quenching type.

From a metallurgical point of view, it is known that certain alloying elements entering into the composition of steel promote the appearance of the ferrite phase with a metallographic structure of the centered cubic type. These elements are called alpha-genes. Among these are chromium, molybdenum, silicon.

Other elements called gamma-genes promote the appearance of the austenite phase of metallographic structure of the face-centered cubic type. Among these elements are carbon, nitrogen, manganese, copper, nickel.

In the field of severe shaping of stainless steel, the significant deformations cause in so-called dirty areas surface defects in the form of straw, which generate tears of metal.

In the field, for example, of drawing a wire with a diameter of less than 0.3 mm, called fine, stainless steel must not contain certain inclusions which, due to their size, their shape or their composition, generate wire breakage during its development.

In the production of stainless steels, for example austenitic, as for all other steels produced with conventional means and economically suited to mass production, the presence of sulphide type inclusions or oxides of variable composition is systematic and irremediable. In fact, stainless steels can, in the liquid state, contain in solution, due to the production processes, oxygen and sulfur contents of 100. 10-3%. During the cooling of steel in the liquid or solid state, the solubility of the elements oxygen and sulfur decreases and the energy of formation of oxides or sulphides is reached. We then witness the appearance of inclusions formed, on the one hand, of oxide-type compounds containing alloying elements having a high affinity with oxygen, such as calcium,

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magnesium, aluminum, silicon, manganese, chromium, and on the other hand, sulphide-type compounds containing alloying elements having a high affinity with sulfur such as manganese, chromium, calcium, magnesium. Inclusions may also appear which are mixed compounds of the oxysulphide type.

It is possible to reduce the amount of oxygen contained in stainless steel by using strong reducing agents such as magnesium, aluminum, calcium, titanium or a combination of several of them but these reducing agents generally lead to the creation, in the 'steel, large inclusions rich in MgO, Athos, CaO, Ti203 in the form of crystallized, hard and undeformable refractories. The presence of these inclusions generates, for example, the incidents mentioned above in the field of wire drawing generating tears or breaks.

Patent application FR 95 04 782 is known which deals with an austenitic stainless steel for the production of wire which can be used in the field of wire drawing and in the field of the production of parts subject to fatigue.

It was found that the stainless steel described did not generally exhibit, depending on the different compositions, reliable performance both from the point of view of the number of breaks during drawing and from the point of view of resistance to heat. tired. In other words, the steel compositions described in the cited patent application are not entirely satisfactory, in particular because of the far too broad definition of the inclusion domain.

It has been demonstrated in patent FR 98 03 263 a closed zone in the inclusion domain, defined by intervals of specific residual element contents which ensure optimum and reliable performance in particular, in drawing and fatigue.

It can be seen that for the same composition of a stainless steel, the type, size, shape and number of inclusions modify the behavior of the steel in the form of a wire in its manufacture as well as in its use.

The object of the invention is to produce a stainless steel, in particular austenitic, comprising a type of inclusion selected in composition and size, which steel can be used in the form of wire with a diameter of less than 0.3 mm or even of wire intended for cold heading.

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- 1. 10-30/ 10-30/ - 1. 10-3% azote 400. 10-3% - aluminium < 40 10-4% -calcium < 2010-4%

10-4o/ - magnésium < 20. 10-4% 10-3o/ 0 0-30/ - 4. 10'% < oxygène total < 20. 10-3% pour l'obtention d'inclusions contenant principalement de l'oxyde de titane. The subject of the invention is a stainless steel of the following general and weight composition: - 5.10% carbon <100. 10-3%, - 0, 2% <manganese <2%, - 10% chromium <23%, - 0% <nickel 17%, - 0, 1% <silicon <2%, - molybdenum <3%, - copper <4%, - sulfur <30. 10-3%, iron and residual impurities inherent in the 'elaboration, which is characterized in that the following elements are controlled in its contents: - 1. 10-3% <titanium 100. 10-3%

- 1. 10-30 / 10-30 / - 1. 10-3% nitrogen 400. 10-3% - aluminum <40 10-4% -calcium <2010-4%

10-4o / - magnesium <20. 10-4% 10-3o / 0 0-30 / - 4. 10 '% <total oxygen <20. 10-3% to obtain inclusions mainly containing titanium oxide.

The other characteristics of the invention are: the composition of the steel comprises less than 15.10-3% sulfur.

- the composition of the steel comprises between 5.10-3% and 40. 10-3% titanium.

- the composition of the steel comprises between 6.10-3% and 12. 10-3% oxygen.

- During the production of a continuous casting bloom, after hot and cold treatment, the inclusions are dispersed and have an average diameter of less than 10 μm.

à 3 um et de préférence inférieure à 1 um. - les inclusions contiennent en outre dans leur composition de l'oxyde de chrome et de manganèse respectivement dans des proportions inférieures à
15% et 10% et de préférence dans des proportions inférieures à 10% et 5%. - inclusions mainly of titanium oxide Ti203, have a smaller size

at 3 µm and preferably less than 1 µm. - the inclusions also contain in their composition chromium and manganese oxide respectively in proportions of less than
15% and 10% and preferably in proportions of less than 10% and 5%.

- the inclusions may be surrounded, in small proportion, by a phase composed of Al2O3, SiO2, CaO.

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The following description and the single appended figure, all given by way of example, will make it easier to understand the invention.
The single figure shows a metallographic image of an example of inclusion according to the invention, in its dimensions and in its composition.

The steel according to the invention contains in its composition by weight, - 5. 10-3o / z carbon::; 100. 10-3%, - 0, 2% <manganese::; 2%, - 10%::; chromium <23%, - 0% <nickel <17%, - 0, 1% <silicon <2%, - molybdenum <3%, - copper <4%, - sulfur::; 30. 10-3%, - 1. 10-3% <titanium::; 100. 10-3% 1. 10-3o / 0 10-30 / nitrogen 400. 10-3%, - aluminum <40 10-4%, 10-40 / - calcium <20 10-4%, 0-4o / - magnesium <20. 10-4%, 10-3o / 0 10-3o / - 4. 10 '% <total oxygen::; 20. 10-3%, of iron and residual impurities inherent in the production, composition in which the elements titanium, nitrogen, aluminum, calcium, magnesium, total oxygen are controlled to generate in the steel inclusions mainly containing l titanium oxide.

Carbon, nitrogen, chromium, nickel, manganese, silicon are the usual elements making it possible to obtain a stainless steel, for example austenitic.

Molybdenum can be added to the composition of austenitic stainless steel to improve corrosion resistance, in a maximum content of 3%.

Copper can also be added to the composition of the steel according to the invention because it improves the cold deformation properties and therefore stabilizes the austenite. However, the copper content is limited to less than 4% to avoid hot processing difficulties because the copper lowers

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sensiblement la limite supérieure de température de réchauffage de l'acier avant transformation.

substantially the upper limit of the reheating temperature of the steel before transformation.

The values of the total oxygen contents are, according to the invention, between 4.10-3% and 20. 10-3% and preferably between 6.10-3% and 12. 10-3%.

It participates in the formation of titanium oxide and to a lesser extent in the formation of chromium and manganese oxide.

Titanium oxide is formed by the control of aluminum and oxygen associated with the addition of titanium during ladle metallurgy of steel.

For a total oxygen content of less than 4 10-3%, the oxygen fixes the elements magnesium, calcium, aluminum and does not form an inclusion of oxides rich in Ting.

composition des oxydes une forte proportion de Cr2Og, ce que l'on cherche à 1 éviter. For a total oxygen content greater than 10-3%, there is, in the

composition of the oxides a high proportion of Cr2Og, which one seeks to avoid.

In other words, to satisfy, according to the invention, the formation of Ti2O3 inclusions, it is necessary to control the oxygen and titanium contents, to control the nitrogen so as not to form titanium nitrides, to reduce to the extent as much as possible the contents of aluminum, calcium, magnesium, so that these so-called strong reducing elements do not promote the formation of spinels such as, for example, of the AO203MgO type. During its production, the steel is desulfurized.

The invention relates to a stainless steel containing inclusions of selected composition, obtained voluntarily, the composition being related to the overall composition of the steel, such that the inclusions are dispersed, with an average diameter of less than 10 μm, twist of the realization of the bloom.

According to the invention, the stainless steel which may be austenitic contains inclusions of determined composition of titanium oxide which are subdivided into inclusions with an average diameter of less than 3 μm and preferably less than 1 μm during hot and cold processing. bloom of steel, inclusions noticeably deformed and finely dispersed in the steel matrix.

The steel is produced with the classic and very productive means of elaboration of an electric steelworks such as electric furnace, AOD converter, ladle metallurgy and continuous casting.

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The oxide inclusions, according to the invention, are composed essentially of Ti2O3, and may contain in particular, to a lesser extent, Cr2O3 and / or MnO. In an example of inclusion, the weight proportions are as follows, after continuous casting: - 70% <TiO2 <90%, - 0% # Cr203 <20%, - 0% MnO 10%.

The inclusions obtained during the production of steel may contain, in proportion, less than 10% of bone.

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La figure unique présente sur une coupe polie, un exemple d'inclusion quasiment sphérique. Les inclusions sont peu déformées, dispersées, d'une taille d'environ 2 um. It is usual to characterize the concentration of inclusions by observing a polished section in the long direction of hot or cold rolling. The inclusionary property is the result of this characterization carried out according to different standards depending on the end use.

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The single figure presents on a polished section, an example of an almost spherical inclusion. The inclusions are little deformed, dispersed, about 2 µm in size.

In an application example, a steel was produced, the weight composition of which is as follows: carbon: 0.042%; nitrogen: 0.0213%; manganese: 1.020%; chromium: 18.22%; nickel: 8.6%; silicon: 0.404%; sulfur: 0.0032%; titanium: 0.019%; molybdenum: 0.267%; copper: 0.202%; phosphorus: 0.021%; aluminum: 0.0028%; calcium 0.0011%, total oxygen 0.0080%. iron and residual impurities inherent in the production.

During ladle production, titanium is introduced while controlling the oxygen content so that titanium oxide is the major component of the inclusions.

These latter inclusions do not present any harmfulness vis-à-vis fine drawing applications in wire with a diameter of less than 0.3 mm or parts subject to fatigue such as springs, tire reinforcements or even wire intended for cold heading.

Table 1 below shows an example of oxide inclusion compositions as a function of the stages in the production of the steel, ladle metallurgy before continuous casting and after casting.

TABLE 1

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<tb>
<tb> Size <SEP> Oxides <SEP>%
<tb> elaboration <SEP> inclusion
<tb> MgO <SEP> Al2O3 <SEP> SiO2 <SEP> CaO <SEP> TiO2 <SEP> Cr2O3 <SEP> MnO <SEP> FeO
<tb> (m)
<tb> Before <SEP> 1.54
<tb> casting
<tb> After <SEP> 8.6 <SEP> 0.45 <SEP> 3.87 <SEP> 0.57 <SEP> 0.22 <SEP> 79.1 <SEP> 9.44 <SEP> 4 , 9 <SEP> 1.44
<tb> casting
<tb>
It is noted that the inclusions comprise at the end of the metallurgical treatment in the ladle approximately 80% of titanium oxide, and the single-phase inclusions comprise, in the middle of the casting in a distributor, 77% of Ti 2 O 3, 8% of Cr 2 O 3 and 5% of MnO. They can be surrounded, in small proportion, by a phase composed of Al 2 O 3, SiO 2, CaO.

Claims (8)

1. Stainless steel for severe shaping and in particular for striking or drawing a wire, having the following weight composition: 10-30 / - 5. 10-3% carbon <100. 10-3%, - 0 , 2%::; manganese <2%, - 10%::; chromium s 23%, - 0% <nickel 17%, - 0, 1% <silicon::; 2%, - molybdenum <3%, - copper <4%, - sulfur # 30. 10-3% of iron and residual impurities inherent in the production, characterized in that the following elements are controlled in the contents:

- 1. 10-30 / 0 10-30 / - 1. 10 '% <titanium <100. 10-3%, - 1. 10-30 / 0 10-30 / nitrogen 400. 10-3%, 10- 40 / - aluminum <4010-4%, - calcium <20 10-4%, - magnesium <20. 10-4%, - 4. 10-3% <total oxygen <20. 10-3%, for obtaining inclusions mainly containing titanium oxide. 2. Steel according to claim 1, characterized in that the composition of the steel comprises less than 15. 10-3% sulfur. 3. Steel according to claim 1, characterized in that the composition of the steel comprises between 5. 10-3% and 40. 10-3% titanium. 4. Steel according to claim 1, characterized in that the composition of the steel comprises between 6.10-3% and 12. 10-3% oxygen. <Desc / Clms Page number 9> 5. Steel according to claim 1, characterized in that during the production of continuous casting bloom, after hot and cold treatment, the inclusions are dispersed and have an average diameter of less than 10 μm. 6. Steel according to claim 1, characterized in that the inclusions mainly of titanium oxide Ti203, have a size less than 3 µm and preferably less than 1 µm. 7. Steel according to claim 1, characterized in that the inclusions also contain in their composition chromium and manganese oxide respectively in proportions of less than 15% and 10% and preferably in proportions of less than 10% and 5%. 8. Steel according to claim 1, characterized in that the inclusions can be surrounded, in small proportion, by a phase composed of Athos, Si02, CaO.