DE2147792B2 - Process for the production of forged or rolled steel bars from ledeburitic tool steels - Google Patents

Description

The invention is concerned with the production of semi-finished or finished products from ledeburitic Tool steels.

An improvement in the block structure in the manufacture of steels compared to the conventional one Ingot casting is achieved by remelting. By means of this procedure, in addition to a Better yield in the steelworks, an improved crystal arrangement that extends over the entire block area achieved. For ledeburitic steels, especially high-speed steels, one is sufficient not due to the type of melting - albeit improved - structural arrangement, as the requirements require much higher quality properties for these steels in operational use. Be like that For example, the consumer makes demands on the carbide distribution and the carbide grain size. The steel-iron guidelines are generally used as the basis for this assessment. For the highest operational requirements, the smallest possible carbide content is required for these steels. and austenite grain size and a uniform carbide distribution are required. However, these demands are only to be fulfilled if it is possible to give these steels a minimum deformation undergo. Depending on the thickness and the desired dimensions, a degree of deformation is necessary, the causes the primary Ledeburit network of the cast block or the remelted block Is smashed as completely as possible. For bettimmte A minimum of | 6-fold deformation is required to meet the highest requirements. However, this requires 4ass these steels only in relatively small dimensions Can be delivered. Less than 8 times the degree of insulation In most cases it is not sufficient to shatter the primary structure of the steel in such a way that 4ßß a still tolerable carbide distribution with corresponding small carbide grains is achieved. By methods such. B. the electroslag smelting process, the process with a self-consuming electrode in a vacuum arc furnace, melting in an electron beam furnace or plasma furnace, a relatively even carbide distribution is achieved due to the controlled solidification, but the carbides are still so coarse-grained that at least an 8-fold deformation is necessary will. When producing large final dimensions, however, at least one can also be used A sufficiently fine carbide distribution cannot be achieved with a multiple degree of deformation, since the necessary cross-section of the ingot due to the slow solidification of these large blocks has a relatively coarse primary structure.

If, on the other hand, an attempt is made to produce large final dimensions with at least 8-fold deformation by first compressing smaller raw blocks and then experiencing stretch deformation, this has the disadvantage that when the block is compressed in the direction of the block axis A at the block head and at the block base, a practically unformed zoneB remains (Fig. 1). This undeformed zone is created by the fact that the block base and the block head rest directly on the forge saddles and

by no flowing deformation like the other block parts can experience. If such a compressed raw block is then stretch-deformed again in the direction of the block axis, there is a risk that insufficiently deformed zones of the block will be arranged in the block axis A (Fig. 2) and thus lead to impermissible inhomogeneities in terms of carbide grain size and carbide distribution in the finished forged bar.

The upset block is made by cross forging

If further deformed, this circumstance is also noticeable in an unpleasant manner, since in the middle of the bar produced over about a third of the entire length there is an insufficiently deformed zone B on the surface, which can extend into the core zone and, in a metallurgical sense, practically still the cast structure has (FIG. 3), ie. this part of the rod must either be devalued to a lower quality or, in the case of a particularly poor structure, must be declared scrap. The removal of this undeformed or only slightly deformed zone requires the rod to be divided. As a result, there are of course limits to the production length, which can be uncomfortably noticeable in the end product due to short lengths or remnants and can lead to considerable material losses.

The requirement for at least an 8-fold degree of deformation has proven to be particularly disadvantageous. if large final dimensions, such as 250 mm diameter, have to be produced, there Here, starting block cross-sections must be used, even when using remelting processes no longer have a satisfactory primary structure. With these cross-sections it is no longer possible to meet the quality requirements in relation to the previously usual procedures in terms of carbide grain size and carbide distribution even approximately.

The purpose of the method according to the invention is to overcome the disadvantages described above, such as uneven Structure distribution over rod length and cross-section, insufficient carbide size and carbide distribution in individual rod zones, poor application

and increased risk of rejects.

For the production of tool steels in the form of square, round, flat or profile cross-sections or forgings are usually a round, square or menigned block as the starting form used. For erection of thin dimensions, such as. B. sheets or strips, is called Starting block used the so-called slab.

Surprisingly, after extensive trials and trials, the above was successful cited difficulties in the production of steel bars from ledeburitic tool steels, especially in large final dimensions, to be avoided when producing steel bars a slab-shaped remelting block is used as the starting block.

By means of the Elektroschiacke remelting process, a dense slab free of voids and block enlargement with the dimensions 450-150-375 mm was produced from a high-speed steel with the composition of S4-3-10 (Fig. 4). This slab was gradually upset on a 1200 t press to φ 190 mm in the direction of the block axis A (Fig. 5) and then by forging the upset forged blank transversely to the original block axis A (Fig. 6) to a final cross-section of 100 mm diameter and brought 1950 mm length. The metallographic examination of test disks from this forged bar revealed an extremely even, fine carbide distribution both from the edge to the core and over the entire longitudinal axis of the bar produced. According to steel-iron guidelines, the carbide distribution 15 mm from the edge of the disc was rated 1 to 1.51, but the worst zones of the rod were not rated worse than 21. In comparison, ratings are given in the core zone of a rod of comparable dimensions produced according to the conventional production process not infrequently found up to 4d.

Another test was carried out with a remelted slab block made of S 6-5-2 with the dimensions 1100 x 250 x 750 mm. This starting block was pre-deformed to a diameter of 3M) mm by step-by-step upset forging in the direction of the block axis A and then stretched transversely to the original block axis A to a final dimension of 2 ^ 0 mm in diameter. After removing the ends of the forging billet, a total length of good material "of 4500 mm" remained, which corresponds to an output of 9 ">» / o. Even with this relatively large final dimension, an extremely even carbide distribution over the rod and cross-section was achieved, which, according to the steel-iron test standard, was found to be 1.5 1 in the round areas and 2 to 3 1 in the core zones and 2d in individual outliers

became. . . ,

The invention thus relates to a process for the production of forged or rolled steel bars from ledeburitic tool steels with a largely homogeneous carbide distribution over the entire cross section and the entire length of the bar, which is characterized in that a consumable electrode suitable for a remelting process is produced from this steel This is remelted and the melt is brought to solidification in a water-cooled slab mold according to the principle of the growing ingot, the resulting slab is deformed by stepwise upset forging in the direction of the ingot axis A to an approximately square or round cross-section and the semi-finished product obtained in this way by further stretch deformation Forging or rolling the upset forged blank transversely to the original block axis A to the desired end cross section with at least 2-fold deformation, based on the upset forged starting cross section, is completed.

Further improvements to the block structure can be made in the context of this process by mechanical Shaking the mold or the block can be achieved during the remelting process. It is the same possible, the block structure by magnetic stirring "the To influence the melt during the solidification process in an advantageous manner. Further improvements are in a metallurgical way by inoculating the steel melt during the remelting process possible.

1 sheet of drawings

Claims (1)

Claim: Process for the production of forged or rolled steel bars from ledeburitic tool steels with largely homogeneous carbide distribution over the entire cross-section and the entire rod length, characterized in that a consumable electrode suitable for the remelting process is first produced from these steels, remelted and the melt in a water-cooled slab mold solidified according to the principle of the growing ingot, the resulting slab is deformed by step-wise upset forging in the direction of the longitudinal axis A of the ingot to an approximately square or round cross-section, and the semi-finished product obtained in this way is further stretched by forging or rolling the upset forged blank transversely to the original longitudinal axis of the ingot A. the desired final cross-section is completed with at least a double deformation, based on the upset-forged starting cross-section.