EP0528720B1 - Process for co-laminating high speed steel on mild steel - Google Patents

Abstract

Method for manufacturing, by means of co-laminating, bars of a steel forming a medium or high alloy with a mild steel. <??>It comprises bars (1) consisting of alloyed steels obtained by means of powder metallurgy and whose compacting gangue (matrix) (5) has been conserved. <IMAGE>

Description

The subject of the present invention is a process making it possible to carry out a co-rolling of a medium or high alloy steel on a mild steel, which has hitherto never been possible to carry out industrially.

Colaminating is a well-known process which makes it possible to press by forging at a temperature of about 1150 ° C. a setting of noble steel, therefore expensive, on a low alloy steel support, therefore inexpensive. By this process we obtain bimetallic bars, also called insert bars or composite steel bars or even steel bars.

This co-laminating technique is currently used mainly for the manufacture of wear plates, for example rolling mill slides, or for the manufacture of industrial blades and knives with added setting, for example paper cutter blades, unroller or wood slicer.

However, if the co-lamination gives excellent results with low alloy steel starts, it is not satisfactory for medium or high alloy steel starts.

Within the meaning of the present description, by low alloy steel is meant steel grades comprising a maximum percentage of 2% of alloying elements such as silicon (Si), molybdenum (Mo), tungsten (W), vanadium (V) and / or chromium (Cr) such as, for example, the grades 80WC20, 110WC10, 90MCW5, or 60WC20 (according to the AFNOR standard). Medium or highly alloyed steels will be understood to mean steel grades comprising more than 2% of alloying elements such as for example Z160CDV12 or so-called high-speed steels of the 18-0-1 or 6-5-2 type, which are a special case of high alloy steels.

The reason why the co-lamination of medium or high alloy steel with mild steel did not been hitherto industrially implemented is that the alloying elements (Si, Mo, W, V, Cr) cause an excessive appearance of oxides which make the bonding of the setting on its support very random, where too high a scrap rate.

This is why, currently the industrial blades comprising a rapid steel setting which are found on the market are manufactured by copper brazing, the copper interposed between the mild steel support and the rapid steel setting ensuring effective bonding after melting and cooling.

The object of the present invention is to enable industrial manufacture by co-rolling of expanded steel bars comprising medium or high alloy steel settings.

For this purpose, according to the invention, the stakes are constituted by alloy steels obtained by powder metallurgy in their raw state of compaction.

The invention consists in fact in the use of the mild steel gangue completely covering the sintered steel ingots after compaction as a bonding layer with the mild steel of the support and the counter-setting. The method according to the invention is defined in claim 1. Claims 2 to 5 relate to preferred embodiments of the method, and claim 6 to the tool obtained by this method.

The production of steels and alloys by powder metallurgy is known: it consists in spraying the liquid metal into tiny droplets which are cooled in the form of powder constituted by microscopic spherical balls. The alloy bars are obtained by compacting, at very high pressure, mild steel capsules containing alloy powder. The ingots obtained are constituted by a sintered steel core to which is intimately linked a mild steel surface gangue originating from the capsule containing the powder before compacting. The ingots are then rolled into bars and these bars are then machined to rid them of their mild steel gangue.

In the process according to the invention, on the contrary, this gangue is preserved which during co-lamination will not cause not the appearance of oxides in harmful proportions with the sticking of the setting on its support.

• Figure 1 une vue schématique en perspective d'un assemblage d'une barre en acier doux avec une mise en acier rapide fritté et une contre-mise en acier doux ;
• Figure 2 une vue schématique en perspective illustrant l'opération de colaminage.
• Figure 3 une vue schématique en coupe d'échelle agrandie selon la ligne III-III de la figure 1 ;
• Figure 4 une vue schématique en perspective montrant partiellement une lame de massicot obtenue par le procédé selon l'invention.

In order to facilitate understanding of the invention, the application of the method to the manufacture of a cutter blade will be described below by way of non-limiting example, with reference to the appended drawings in which there is shown:

• Figure 1 a schematic perspective view of an assembly of a mild steel bar with a sintered high-speed steel setting and a mild steel counter-setting;
• Figure 2 a schematic perspective view illustrating the co-laminating operation.
• Figure 3 is a schematic enlarged sectional view along line III-III of Figure 1;
• Figure 4 a schematic perspective view partially showing a cutter blade obtained by the method according to the invention.

Figure 1 illustrates the first phase of manufacturing the cutter blade. The setting 1 is made of sintered high-speed steel provided with its mild steel compaction gangue on its mild steel support 2, by means of a weld bead 3. The setting 1 is bordered by a mild steel counter-setting 6 which is also secured to the support 2 by a weld bead 3. This coarse assembly by welding has the function of holding the parts 1, 2, and 3 during the co-laminating operation and of avoiding as much as possible the oxidation of the surfaces in contact during reheating to approximately 1100-1150 ° C which immediately precedes the co-lamination, the weld beads 3 playing the role of sealing beads.

Next, the laminating operation is carried out, which is shown diagrammatically in FIG. 2. During this operation, the block produced in FIG. 1 and preheated is passed at least one, and preferably several times, through a rolling mill. obtain a wrought ratio of approximately 4 to 5.

As indicated above, the fact that bet 1 is made of a sintered steel bar having kept its gangue of mild steel, the quality of the forging obtained will ensure a very good physico-chemical bond between stake 1, counter stake 6 and support 2.

We see in section in Figure 3 the core 4 of sintered high-speed steel of the setting 1 perfectly surrounded by its gangue 5 in mild steel. Colaminating plated this bet 1 and its counter bet 6 on the support 2, creating an intimate connection between the three parts.

To obtain the finished product, in this case the cutter blade shown in FIG. 4, the bar is then heat treated and machined. By milling and rectification along the lines X-X and Y-Y the parts 5a and 5b of the gangue are removed; a sharpening of the sintered high-speed steel core thus released makes it possible to form the cutting edge of the blade. After hardening, the holes and / or notches for fixing the tool 1 are made by drilling and / or milling in the mild steel part, namely the counter-setting and the support, this part not taking the hardening.

The possibility provided by the invention of using co-lamination for medium or high-alloy steel makes it possible to maintain a competitive price for finished products with that of the products currently obtained by brazing, despite the additional cost resulting from the use of steel. sintered. On the other hand, the quality of the tools obtained through the use of sintered steel is significantly higher than that of the tools currently offered on the market.

It is understood that the invention is not limited to the manufacture of cutter blades such as that described above, but encompasses any steel bar / expanded alloy obtained by co-laminating a sintered alloy setting which has retained its gangue mild steel and any tool made from such a bar.

Claims (6)

1. Process for the manufacture by co-lamination of bars from a soft steel support (2) and a metallic layer (1) enclosed in a superficial casing also made of soft steel (5), the layer (1) being positioned directly on the support (2), characterised in that the layer (1) is comprised of a moderately or strongly alloyed steel obtained by powder metallurgy, is sintered prior to being placed on the support (2) and having retained its compaction casing comprising the said superficial casing (5) in that prior to lamination the layer (1) is welded roughly to the support (2) and in that the whole is then passed to the rolling mill to simultaneously undergo a process of lamination of the layer on its support and a finishing of the whole.
2. Process according to claim 1, characterised in that the steel of the layer (1) contains more than 2% of alloy elements such as silicon (Si), molybdenum (Mo), tungsten (W), vanadium (V) and/or chromium (Cr).
3. Process according to claim 2, characterised in that the steel is of a grade designated Z160CDV12 (AFNOR standard).
4. Process according to claim 2, characterised in that the steel is a high-speed steel of the 18-0-1 or 6-5-2 type.
5. Process according to any one of the preceding claims, characterised in that prior to co-lamination a counter-layer of soft steel (6) is juxtaposed to the layer (1) on the support (2) and also joined thereto as well as to the layer (1) by welding seams (3).
6. Tool constituted by a soft steel support (2) and a moderately or strongly alloyed steel cutting part (1), said tool being made from a flat sintered steel bar (4) co-laminated to the support (2) by the process according to any one of the preceding claims.

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