EP0739993B1 - Steel and process for manufacturing workpieces with high abrasion resistance - Google Patents

Abstract

An abrasion-resistant steel contains (by wt.%) 0.24-0.3 (pref. 0.24-0.27) C, 0-2 (pref. 0-1 Si) 0-2 (pref. 0-1) Al, 0-2 (pref. 0.3-1.6) Mn, 0-4 (pref. 0-2) Ni, 0-3 (pref. 0.5-1.8) Cr, 0-0.6 Mo and 0-1.2 W. The steel may also contain 0.005-0.005% B, at least one of Nb, V, Zr and Ti in amt. less than 0.3% and at least one of Se, Te, Ca, Bi and Pb in amt. below 0.1%, the rest being Fe. The following relationships also apply, 4.6C + 1.05Mn + 0.54Ni + 0.66(Mo + W/2) + 0.5Cr + k ≥ 1.6, where k = 0 if the steel contains less than 0.0005% B and k = 0.5 if the steel contains more than 0.005% B and 0.6% ≤ (Al+Si) ≤ 2%. To improve their abrasion resistance sheets of the steel are heated to above austenisation temp. (e.g. 900 degrees C) then cooled to 450 degrees C at more than 1 degrees C/s, further cooled to 200 degrees C over 50 s to 60 minutes (pref. 100 s to 30 minutes) and finally returned to ambient (below 250 degrees C) in less than 3 h. This gives the steel a martensitic or martensitic-bainitic structure contg. 5-15% austenite and a hardness of 400-500 HB.

Description

The present invention relates to steels for manufacturing of parts with high abrasion resistance.

In the mineral industry, equipment such as that, for example, chutes, screens, attack blades, submitted very severe abrasive wear. To manufacture this equipment, we uses parts, and in particular sheets, of high-strength steel to abrasion, hardened, of hardness between, approximately, 550HB and 600HB. These steels contain from 0.35% to 0.5% carbon, and from 0.5% to 3% at least one alloying element such as manganese, chromium, nickel or molybdenum. These steels have the disadvantage of being very difficult to cut and weld, they have a low forming capacity and are, in general, fragile.

The object of the present invention is to remedy this disadvantage by proposing a steel making it possible to manufacture parts, and in particular sheets, easily weldable and cutable, and having a abrasion resistance comparable to that of parts according to the prior art.

To this end, the subject of the invention is a steel whose chemical composition comprises, by weight: 0.24% ≤ C ≤ 0.3% 0% ≤ If ≤ 2% 0% ≤ Al ≤ 2% 0% ≤ Mn ≤ 2% 0% ≤ Ni ≤ 4% 0% ≤ Cr ≤ 3% 0% ≤ Mo ≤ 0.6% 0% ≤ W ≤ 1.2% optionally from 0.0005% to 0.005% of boron, optionally at least one element taken from Nb, V, Zr and Ti, in contents lower than 0.3%, optionally at least one element taken from Se, Te, Ca, Bi and Pb in contents of less than 0.1%, the rest being iron and impurities resulting from the production,
the chemical composition further satisfying the following relationships: 0.6% ≤ Al + Si ≤ 2% and 4.6xC + 1.05xMn + 0.54xNi + 0.66x (Mo + W / 2) + 0.5xCr + K ≥ 1.6 with
K = 0 if the steel contains less than 0.0005% boron
K = 0.5 if the steel contains more than 0.0005% boron

Preferably, the chemical composition of the steel comprises: 0.24% ≤ C ≤ 0.27% 0% ≤ If ≤ 1% 0% ≤ Al ≤ 1% 0.3% ≤ Mn ≤ 1.6% 0% ≤ Ni ≤ 2% 0.5% ≤ Cr ≤ 1.8% and satisfies relationships: 0.15% ≤ Mo + W / 2 ≤ 0.45% and 0.6% ≤ Si + Al ≤ 1%

Better still, the chemical composition can also satisfy the relationship: 4.6xC + 1.05xMn + 0.54xNi + 0.66x (Mo + W / 2) + 0.5xCr + K ≤ 3.7 with
K = 0 if the steel contains less than 0.0005% boron
K = 0.5 if the steel contains more than 0.0005% boron

• on approvisionne une pièce en acier conforme à l'invention,
• on austénitise la pièce par chauffage au dessus de Ac₃, puis on la refroidit jusqu'à la température ambiante de telle sorte que, en tout point de la pièce, la vitesse de refroidissement entre la température d'austénitisation et 450°C soit supérieure à 1°C/s, et le temps de passage de la température de 450°C à la température de 200°C soit comprise entre 50s et 60mn, et de préférence comprise entre 100s et 30mn,
• éventuellement, on effectue un revenu à une température inférieure à 250°C pendant un temps inférieur à 3 heures.

The invention also relates to a method of manufacturing a steel part with high abrasion resistance, according to which:

• a steel part according to the invention is supplied,
• the part is austenitized by heating above Ac ₃ , then cooled to room temperature so that, at any point in the part, the cooling rate between the austenitization temperature and 450 ° C. is greater at 1 ° C / s, and the time from the temperature of 450 ° C to the temperature of 200 ° C is between 50 s and 60 min, and preferably between 100 s and 30 min,
• optionally, tempering is carried out at a temperature below 250 ° C. for a time of less than 3 hours.

To cool the room down to room temperature, from the austenitization temperature, the part can be soaked in oil, this is particularly the case when the part is a sheet of thickness included between 10mm and 100mm.

To cool the room down to room temperature, from the austenitization temperature, the room to air. This is particularly the case when the part is a sheet between 2mm and 20mm thick.

Finally, the invention relates to an abrasion resistant part made of steel according to the invention having a martensitic structure or martensito-bainitic containing between 5% and 15% of austenite, and having a hardness between 400HB and 500HB.

Parts in accordance with the invention, or manufactured by the process according to the invention, can be used for manufacturing wearing parts for equipment intended, in particular, for the exploitation of quarries and mines, public works, cement plants, steel, tile, brick or agriculture.

The invention will now be described in more detail, but from without limitation.

• plus de 0,24% de carbone pour permettre d'obtenir une dureté suffisante, nécessaire à une bonne résistance à l'abrasion, mais moins de 0,3% et, de préférence, moins de 0,27% pour obtenir une bonne soudabilité, une bonne découpabilité, une bonne aptitude au pliage et une ténacité satisfaisante ;
• de 0% à 2% de silicium et de 0% à 2% d'aluminium, la somme des teneurs en aluminium et en silicium étant supérieure à 0,6% pour ralentir la précipitation des carbures au cours du traitement thermique, mais inférieure à 2%, et de préférence, inférieure à 1% afin de faciliter l'élaboration de l'acier et de ne pas détériorer sa ténacité ;
• de 0% à 2% et, de préférence de 0,3% à 1,6% de manganèse, de 0% à 4% et, de préférence de 0% à 2% de nickel, de 0% à 3% et, de préférence de 0,5% à 1,8% de chrome, de 0% à 0,6% de molybdène, de 0% à 1,2% de tungstène, la somme de la teneur en molybdène et de la moitié de la teneur en tungstène étant de préférence comprise entre 0,15% et 0,45%, de façon à obtenir une trempabilité suffisante, mais pas trop importante, pour permettre d'obtenir une structure principalement martensitique ou martensito-bainitique contenant une proportion notable d'austénite retenue ; le chrome, le molybdène et le tungstène ayant, de plus, l'avantage de permettre la formation de carbures favorables à la résistance à l'abrasion;
• éventuellement, de 0,0005% à 0,005% de bore pour ajuster la trempabilité;
• éventuellement, au moins un élément pris parmi Nb, V, Zr et Ti pour obtenir un durcissement par précipitation qui ne détériore pas la soudabilité ;
• éventuellement, au moins un élément pris parmi Se, Te, Ca, Bi et Pb pour améliorer l'aptitude à l'usinage;

le reste étant du fer et des impuretés résultant de l'élaboration.The steel according to the invention contains, by weight:

• more than 0.24% of carbon to allow obtaining a sufficient hardness, necessary for good abrasion resistance, but less than 0.3% and, preferably, less than 0.27% to obtain good weldability , good cutability, good folding ability and satisfactory toughness;
• from 0% to 2% of silicon and from 0% to 2% of aluminum, the sum of the aluminum and silicon contents being greater than 0.6% to slow the precipitation of carbides during the heat treatment, but less than 2%, and preferably less than 1% in order to facilitate the production of the steel and not to deteriorate its toughness;
• from 0% to 2% and, preferably from 0.3% to 1.6% of manganese, from 0% to 4% and, preferably from 0% to 2% of nickel, from 0% to 3% and, preferably 0.5% to 1.8% chromium, 0% to 0.6% molybdenum, 0% to 1.2% tungsten, the sum of the molybdenum content and half the tungsten content preferably being between 0.15% and 0.45%, so as to obtain sufficient quenchability, but not too great, to allow obtaining a predominantly martensitic or martensito-bainitic structure containing a significant proportion of retained austenite; chromium, molybdenum and tungsten having, in addition, the advantage of allowing the formation of carbides favorable to abrasion resistance;
• optionally, from 0.0005% to 0.005% boron to adjust the hardenability;
• optionally, at least one element chosen from Nb, V, Zr and Ti to obtain hardening by precipitation which does not deteriorate the weldability;
• optionally, at least one element selected from Se, Te, Ca, Bi and Pb to improve the machinability;

the remainder being iron and impurities resulting from processing.

For the hardenability to be sufficient, it is preferable that the chemical composition of the steel satisfies the relationship: A = 4.6xC + 1.05xMn + 0.54xNi + 0.66x (Mo + W / 2) + 0.5xCr + K ≥ 1.6 with,
K = 0 if the steel contains less than 0.0005% boron
K = 0.5 if the steel contains more than 0.0005% boron.

But, so that the hardenability is not too important so as not to deteriorate the suitability for use, in particular by welding or by thermal cutting, it is also preferable that A remains less than or equal to 3.7.

This steel, due to its relatively low carbon content, has good weldability and good cutting ability by thermal means, but its abrasion resistance depends on its micrographic structure and therefore of the heat treatment to which it is submitted.

The inventors have found that when this steel has a structure consisting mainly of martensite or a mixture of martensite and bainite (martensito-bainitic structure) and from 5% to 15% retained austenite enriched in carbon, so as to have a hardness between 450HB and 500HB, its abrasion resistance was very comparable to that of martensitic steels with a hardness greater than 550HB and its ability to cold form by plastic deformation was good better. Good abrasion resistance results from the fact that, under the action of abrasive particles, the retained austenite is transformed locally in very hard martensite while benefiting from the ability to significantly deform the stressed metal. In addition, the presence of a fine dispersion of chromium carbides and molybdenum in the martensitic constituent improves wear resistance.

The inventors have also found that, to obtain this structure, it was necessary to austenitize the steel by heating above Ac ₃ , then to cool it to ambient temperature so that the cooling rate between the austenitization temperature and 450 ° C is greater than 1 ° C / s, and the time for the passage from the temperature of 450 ° C to the temperature of 200 ° is between 50 s and 60 min, and preferably between 100 s and 30 min. This heat treatment can optionally be supplemented by tempering at a temperature below 250 ° C. for a time of less than 3 hours.

To manufacture an abrasion-resistant part, a steel is produced in accordance with the invention, it is cast in the form of a semi-finished product which is then shaped by hot plastic deformation, for example by rolling or forging. The part thus obtained is then austenitized by heating above Ac ₃ , then cooled to ambient temperature so that, at any point, the cooling rate between the austenitization temperature and 450 ° C. is greater than 1 ° C / s, and the passage time from the temperature of 450 ° C to the temperature of 200 ° is between 50s and 60mn, and preferably between 100s and 30mn. Optionally, the part is subjected to tempering at a temperature below 250 ° C for a time of less than 3 hours.

The slow speed crossing of the 450 ° C / 200 ° C range has to allow the retention of metastable austenite, while promoting the formation of fine chromium and molybdenum carbides, homogeneously distributed in the martensitic constituent or martensito-bainitic.

When the massiveness of the room is suitable, to cool the room to room temperature, from room temperature austenitization, the part can be soaked in oil. It is notably the case when the part is a sheet of thickness between 10mm and 100mm.

In the same way, when the massiveness of the piece lends itself to it, to cool the room to room temperature, from the austenitization temperature, the part can also be quenched with air. This is particularly the case when the part is a sheet of thickness included between 2mm and 20mm.

A part, and in particular a sheet, resistant, is thus obtained. abrasion, made of steel according to the invention having a structure martensitic or martensito-bainitic containing between 5% and 15% austenite, and having a hardness between 400HB and 500HB.

For example, we made sheets with A steels and B in accordance with the invention, and with steels C and D according to the art prior.

The compositions of these steels were, in thousandths of% by weight: VS Yes Al Mn Or Cr Mo B AT 247 817 63 1290 495 726 328 2.8 B 251 263 704 1305 439 715 342 2.6 VS 254 310 65 1329 445 702 351 2.6 D 415 307 62 1285 293 712 349 2.7

The characteristics of the sheets TA1, TA2, and TB, in accordance with the invention, and the sheets TA3, TC and TD, given for comparison, were: sheet metal steel thickness. mm austenitization ° C quenching income ° C hardness after HB treatment hardness in HB abraded layer abrasion resistance index TA1 AT 35 900 oil 200 463 525 97 TA2 AT 5 900 air 200 455 526 105 TB B 35 900 oil 200 466 529 102 TA3 AT 35 900 water 200 476 492 70 TC VS 35 900 oil 200 468 495 79 TD D 35 900 water 200 552 561 100

The TD sheet, in accordance with the prior art, has a structure fully martensitic, a hardness greater than 550HB and an index of abrasion resistance of 100; but because of the carbon content of steel, it is difficult to weld.

TA3 sheet, made of steel according to the invention, has been soaked in water, which gives it a different structure than that which is required by the invention, and it has a resistance index to abrasion of 70, significantly lower than that of sheets TA1, TA2 and TB according to the invention, which are comparable to that of the sheet TD of reference.

TA1 and TB sheets are also different from TD sheets by their folding ability; TA1 and TB sheets can be folded on a radius equal to 6 times the thickness, while the TD sheet cannot be folded on a radius less than 15 times the thickness.

Due to their properties, parts in general, and sheets in particular, in accordance with the invention, are particularly suitable for the manufacture of any type of wear part subject to severe abrasion and incorporated, in particular, in equipment for handling of bulk products in all types of industries. As example, these parts can be attack blades and skids of reinforcement under loader / transporter or shovel bucket blades, guide plates for excavators and draglines, racks, drive crowns, sprockets, shields sides of impact or jaw crushers, screen grids for use in public works, in the exploitation of quarries or gravel pits; chain conveyor bottoms and squeegees, shields for hoppers or corridors, descender scales helical, sludge combs, classifier blades, pieces of slaughter or transport equipment, cyclone skirts for the exploitation of mines or coal mines; hopper shields or skips, clamshell blades, coke car bottoms, vibrating extractors, blasting chamber shields, guide or shift plates for the steel industry; knives disintegrators, blades and blender bottoms, bottoms wheel extruders, molds, parts of turbo-disintegrators, dosing hoppers for tile or brick factories; tools and teeth unpacking or stump removal, wood tongs, knives, choppers, beaters, hammers, smoothing plates, parts of land clearers or cleansers, log beams, subsoiler tines, scourers of cultivators or tillage.

Claims (11)

1. Steel for the manufacture of components having high abrasion resistance, characterized in that its chemical composition comprises, by weight: 0.24% ≤ C ≤ 0.3% 0% ≤ Si ≤ 2% 0% ≤ Al ≤ 2% 0% ≤ Mn ≤ 2% 0% ≤ Ni ≤ 4% 0% ≤ Cr ≤ 3% 0% ≤ Mo ≤ 0.6% 0% ≤ W ≤ 1.2% optionally from 0.0005% to 0.005% of boron, optionally at least one element taken from Nb, V, Zr and Ti, in contents of less than 0.3%, optionally at least one element taken from Se, Te, Ca, Bi and Pb, in contents of less than 0.1%, the balance being iron and impurities resulting from the smelting,
   the chemical composition furthermore satisfying the following relationships: 0.6% ≤ Al+Si ≤ 2%    and 4.6HC+1.05HMn+0.54HNi+0.66H(Mo+W/2)+0.5HCr+K $ 1.6    where
      K = 0 if the steel contains less than 0.0005% of boron
      with
      K = 0.5 if the steel contains more than 0.0005% of boron.
2. Steel according to Claim 1, chararterized in that its chemical composition comprises, by weight: 0.24% ≤ C ≤ 0.27% 0% ≤ Si ≤ 1% 0% ≤ Al ≤ 1% 0.3% ≤ Mn ≤ 1.6% 0% ≤ Ni ≤ 2% 0.5% ≤ Cr ≤ 1.8% the chemical composition furthermore satisfying the relationships: 0.15% ≤ Mo+W/2 ≤ 0.45%    and 0.6% ≤ Si+Al ≤ 1%.
3. Steel according to Claim 1 or Claim 2, characterized in that its chemical composition furthermore satisfies the relationship: 4.6HC+1.05HMn+0.54HNi+0.66H(Mo+W/2)+0.5HCr+K # 3.7    where
      K = 0 if the steel contains less than 0.0005% of boron
      with
      K = 0.5 if the steel contains more than 0.0005% of boron.
4. Process for manufacturing a component made of steel having high abrasion resistance, characterized in that,

   a steel component according to any one of Claims 1 to 3 is provided,

   the component is austenized by heating above Ac₃ and then cooled down to room temperature in such a way that, at every point in the component, the cooling rate between the austenization temperature and 450EC is greater than 1EC/s and the time to go from the temperature of 450EC to the temperature of 200EC is between 50 s and 60 min and preferably between 100 s and 30 min,

   optionally, an anneal is carried out at a temperature of less than 250EC for a time of less than 3 hours.
5. Process according to Claim 4, characterized in that, in order to cool the component down to room temperature from the austenization temperature, the component is oil-quenched.
6. Process according to Claim 5, characterized in that the component is a sheet having a thickness of between 10 mm and 100 mm.
7. Process according to Claim 4, characterized in that, in order to cool the component down to room temperature from the austenization temperature, the component is air-quenched.
8. Process according to Claim 7, characterized in that the component is a sheet having a thickness of between 2 mm and 20 mm.
9. Abrasion-resistant component, characterized in that it consists of steel according to any one of Claims 1 to 3 and in that the steel of which the component is composed has a martensitic or martensitobainitic structure containing between 5% and 15% of austenite and a hardness of between 400 HB and 500 HB.
10. Use of a component according to Claim 9 for the manufacture of wearing components subjected to abrasion.
11. Use of a component manufactured by the process according to any one of Claims 4 to 8 for the manufacture of wearing components subjected to abrasion.