DE2006477A1 - Easily machinable steel mill stocks and methods of making the same - Google Patents

Description

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M /. _fV% , ^L. '"., -. Munich-Pullach, February 12th 19? O

INLiITD STIEL COMPANY, a company under the laws of the state, Delaware, 30 "West Monroe Street, Chicago, Illinois 60603"

Easily machinable steel workpieces and methods of making the same

The invention relates to hot rolled steel workpieces, soft have a tellurium and / or be narrow old which improves the machinability *

The invention is particularly directed to a method for producing such steel workpieces, in which the in a Mold poured molten steel from above tellurium, and / or selenium is added in such an amount that the machinability of the elongated workpieces hot-rolled from this after the solidification of the steel block is improved.

These hot-rolled steel workpieces can be bars, tubes or billets *

That. The starting product for these hot-rolled steel workpieces is always a steel block that is reduced in cross-section by hot rolling and becomes smaller in several rolling stages polygonal bodies are formed, for example initially into a Yor-rolled block, from which billets, bars or other rolled bodies are produced by further hot rolling *

Steels with a sufficient tellurium and / or selenium content to improve their machinability, which must be at least 0.03% and at most 0.20 % , in particular tellurium-containing steels with or without selenium gel, tend during hot rolling of both the steel block and the bloom or of the billet to the formation of surface defects, known as surface cracks, This is where

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there are numerous small hooves on the surface, especially on the edges of the steel workpieces A stronger surface or · Edge cracking of the workpieces leads to uselessness same.

This appears when the steels of the aforementioned type are hot-rolled Occurring surface cracks could hitherto only be avoided by removing the steel blocks, roughing blocks or billets be subjected to a very precisely regulated heat treatment prior to hot rolling, either by using a burner heater ten furnace, the burner flames are guided so that their tips do not brush the steel surface, as in the German patent specification 1 237 belonging to the applicant is described, or according to that in the German patent application P 15 084 07.8 (DiS 1 508 40?) Contained the proposal of the Applicant the oxidizing effect of the furnace atmosphere is closely monitored and regulated. In the former case, one is extreme precise adjustment of the fuel supply necessary during the heating of the steel workpieces according to the second proposal is dependent on carefully coordinated conditions, namely the heating of the workpieces in one Burner-heated oven from their special pre-drying and a precisely controlled oven atmosphere or from a special and very elaborate furnace construction

The object of the invention is to create a simpler method of avoiding surface cracking during hot rolling of steel workpieces that contain tellurium in particular, with no precise compliance with conditions during the heating of the Steel workpieces before hot rolling is required.

According to the invention this is achieved in that the tellurium and / or selenium only after filling at least the larger part the ingot mold with the steel melt that does not skim a plate or selenium and added to the molten steel after the formation of a solidified side and bottom edge zone and thus one after it complete solidification only in its interior, but not in

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its surface zones containing tellurium and / or selenium Steel block: created and then hot rolled

Due to the strong reduction in the Tellurium or selenium content in the edge or surface zones of the cast ingot and the hot-rolled steel workpieces their surface roughness is largely avoided

If in the following the argument is of a "substantial reduction" in surface cracking, this means that the surface cracking of the rolled workpieces, if it still occurs, is practically insignificant and is not associated with any deterioration in the value of the workpieces, and if it is said that the edge zones of the steel block or the surface ions of the hot-rolled workpieces have "no noteworthy contents" of tellurium and selenium, this means that these contents are so low that they do not result in surface cracks which would render the rolled workpieces unusable.

Normally, the solidified cast ingots are reheated to the warming orphan, usually in a deep oven those to prevent surface burns to avoid direct flames on the blocks as far as possible is · In addition, it appears to ensure the through However, given the success of the invention, it is also necessary: j

a) during the heating of the steel blocks prior to hot rolling in accordance with the proposal according to the aforementioned Patent application F 15 084 07.8-24 proceed and

b) the heating of the roughing blocks or billets prior to further hot rolling of the same either in the same way or in the sense of the aforementioned German patent specification 1 237 155 to be carried out »

Whichever of these heating methods may be used, it should be noted that those in connection with these proposed, precise monitoring and control measures

0098387 145.6

taking within the scope of the invention is not required «So can χ · Β · when the steel block manufactured according to the invention is re-machined, a slight flame impact at its ends must be accepted, and it is also not necessary when heating in a certain furnace atmosphere. To monitor and regulate ren water content in the same way as described in the patent application mentioned · The special and very complex furnace construction described therein is also not required, so that thus also in this respect essential advantages can be achieved by the invention *

The invention is intended primarily for such steels, whose Machinability primarily through the addition of tellurium, i.e. not clay selenium, should be improved appears more strongly than in cases in which the tellurium is completely or largely replaced by selenium

The effect of the fiction according to the method is based on The fact that during the hot rolling of the steel billet to roughing billets and billets and during the hot rolling of the same none Tellurium or selenium from the inside, this rolling stock penetrates its surface layer, so that the workpiece, which is hot-rolled to a smaller cross-section, is in its tuner contains tellurium and / or selenium throughout in such an amount that it improves its machinability, however does not contain any significant amounts of tellurium and selenium in its surface layer Surface cracking avoided or reduced to a practically defensible hatred.

The method according to the invention is suitable for both killed and unkilled steels.

The invention also relates to hot-rolled steel workpieces, the interior of which is continuously tellurium and / or selenium in

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an amount sufficient to improve the machinability and the surface layer does not contain any appreciable amount Contains tellurium and selenium and is free of surface cracks to a practically acceptable extent

The total content of tellurium and / or selenium in the interior of the hot-rolled workpiece so j disregarding its surface layer is preferably 0.03 to 0.20 wt, - # "At a content of O _t O3% is normally no improvement in the workability of the steel expected, while at a content above 0.30 % the associated further improvement in machinability is so small that it is not economically justifiable in view of the costs of tellurium and selenium.

tigt appears »

The invention is of particular importance for the production of hot-rolled workpieces from unkilled steel, that is, from a steel that is in the mold during solidification so much gas is evolved that the upper part of the The steel block remains in a molten state »The gas that develops during the solidification process causes it a circulation of the steel melt inside the block

A billet or other steel workpiece made from unsmoothed j

Steel is characterized by a particularly high plasticity with correspondingly improved Preßfließvermögen, which is very important for the press molding of billets or bars, so to that having so for steel workpieces eßvermö a high plasticity and in particular a high J ¹ Ii gene during pressing, unkilled steel is chosen *

May only allow the steel to agitate in the mold have a low manganese content of generally not more than 0.60% by weight. However, if the manganese content is kept low, so the sulfur content must also be low, since the steel is a probe becomes hot brittle, that is, during hot processing, i.e. also during

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Hot rolling bites forms “For this reason it has not been done so far managed to find a gufc machinable steel with a sufficiently high To produce sulfur content from unkilled steel.

These difficulties are overcome by the invention, through which the desired machining properties are obtained exclusively with the help of the tellurium and / or selenium content, without the hangan content having to be increased above 0.60% , which would prevent the steel from circulating in the mold So that the invention creates a non-killed steel with excellent machining properties, which at the same time is characterized by its high plasticity, known for its P and, dead all, by its high viscosity.

It may cause me to eat the billets made of this steel or bars

The invention is explained in more detail below with reference to the drawing.

a diagram showing the distribution of the tellurium content over the cross-section of a Te-containing gate rolling block gate it emerges from his eviction in a club;

Jig · 2 a vertical cut through a mold with just in this cast unkilled steel in the state of the hand zones formation;

ÜLg.3 a vertical cut through a mold in which a Killed steel melt begins to solidify;

FIG. 4 shows a cross section through a hot-rolled steel rod produced according to the invention and FIG

an enlarged part of the Hg 4 *

First consider Pig 2, which illustrates a mold 10 filled with unskilled steel of the following typical composition:

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0.03 to 0.15 (wt .-) Sl carbon ₉ 0.25 to 0.60% manganese, up to su 0 _f 025 % sulfur j up to 0.015 % phosphorus, best iron «

The mold 10 is of the usual size and design.

2
area is 69.5 cm, and it is slightly tapered towards the top. The pouring temperature of the steel melt is 1580 to 1593 ° C.

FIG. ₈ 2 shows the movement of molten steel in the molten column. Mold 10 and the formation of a solidified hand zone 11 on the inner wall and on the bottom of the mold.

After the formation of the hand zone 11, tellurium becomes in 5bim of pellets or shot the still liquid steel inside the block at f

Head 14 - the same clogged «The inner overturning movement indicated by the arrows 13 is characteristic of the unquenched steel and supports the even distribution of the tellurium within the molten steel 12 · The tellurium content inside the block according to its VertesM.gujsgmiä. The steel work piece rolled from this is generally 0.03 Ms 0.20

After the block has solidified completely, the mold is stripped from it, whereupon the block is heated to the rolling temperature of 1100 to 1150 ° G, in the above-described manner according to the German patent application P. 15 084 Ο7 «θ, *

but with somewhat less strict compliance with the procedural conditions

Once the whale temperature has been reached, the block becomes more normal Hot rolled in several rolling stages sum Vorwalsblock, club and finally to a pole with circular cross-section according to Üg «4» if intermediate heating z «B» of the roughing block between the individual rolling stages or the stick are required, these are carried out by means of one or the other of the two goal-mentioned procedures, but also never with less precise control measures.

009838/1 U 5 6

The rod 15 or any other steel workpiece of this type 1st Evenly interspersed with tellurium within you, like this is indicated somewhat exaggerated at 17, the tellurium content Is dimensioned so high that the machinability of the workpiece 15 is thereby improved. The edge layer 18 of the rod 15 has no tellurium content worth mentioning and is shown in FIG. 4 and 5 shown enlarged} although this is not intended to indicate that this edge layer is sharply defined from the Inside the rod 15 lifts

Fig. 1 illustrates the relative distribution of tellurium over the cross section of a steel manufactured according to the invention Workpiece, which in this case is a lead »- As the arrow along the ordinate in Fig. 1 shows, the tellurium content of the surface to the center of the workpiece indicated on the abscissa at 14 cm. Those indicated on the abscissa Length measurements are based on the workpiece surface »

Curves 20 and 21 give two examples of the relative distribution of tellurium between the surface and the center. The actual tellurium content at any point on the cross-sectional area depends on the total amount of tellurium added to the steel block. It is clear from both curves shows that in each case the tellurium content in the outer skin of the roughing block is practically zero

The relative tellurium content at a certain cross-sectional part lies between the curves 20 and 21, the position of these Curves to one another and the course of curve 21 depend on the level of the steel block from which the rolled cross-section originates Tellurium distribution a curve which lies between curves 20 and 21 of FIG. If, however, a whale cross-section from the bottom part of the steel block is involved, curve 21 can be further below curve 20 for this cross-section

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run as it is in SIg.1 of the case, the sharp rise 22 curve 21 can also be more or less continuous "

The practical freedom from tellurium of the surface zoae of the steel block and the work piece hot-rolled from this is decisive for ensuring that no surface cracks occur during hot rolling.

The tellurium must not be earlier than one minute after pouring the molten steel in the mold are added, preferably two to five minutes after pouring the Molten steel added · The greater the period between the Shedding the steel and adding the tellurium is the more The edge zone of the block, which does not contain tellurium, and the workpieces hot-rolled from it, become thicker. "

The minimum time between the killing of the mold and the addition of the tellurium is caused by the occurrence or light occurrence the surface cracking during hot rolling determined · If surface cracking occurs during hot rolling »so is this is a sign that the period between the shell of the mold and the addition of the tellurium was too short for that a tellurium-free, solid cast skin could have formed. This problem can be avoided by increasing this "period of time." can be solved easily.

If the rolled workpiece, ζ · Β · the bar 15 », is made of unkilled steel, it not only has improved machinability, but also good deformability, which is characteristic of workpieces made of unkilled steel · Due to the relatively low carbon content (0.03 to 0 , 15 %) the toughness of the steel rod is increased, while the relatively low sulfur content (up to 0.025%) improves its plasticity, so that overall the flexibility when pressing the rod is increased, as a result of the low sulfur content can also the manganese content (0.25 to 0.60 %) can be kept lower than is normally the case with higher sulfur contents, which are correspondingly higher

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Manganese content must be faced to that by the sulfur to counteract the brittleness of the steel caused · On the other hand, the low manganese content makes the steel restless Cast SEU, which in turn ensures that the cast skin of the steel block is essentially made of relatively pure. Si sen consists «This cast skin is more elastic than one that has significant contents of accompanying elements and is increased hence the fluidity of the steel rod when eating Impairment of the machinability of the steel caused by the low sulfur content is more than offset by its Tellurium content (0.03-0.2%), especially when you're using this goes up to the upper limit

A steel rod of the above composition is in view of their deformability by pressing and their machinability the preferred steel workpiece within the scope of the invention According to the invention, a drawable and machinable steel rod can also have the following composition:

0.03 to 0.18 (weight )% carbon, 0.25 to 0.90 % manganese, up to 0.13 % sulfur, up to 0.04 % phosphorus, 0.03 to 0.20%! Tellurium, Best Iron

HLg. 3 relates to the casting of a killed steel, and in this case the mold 30 is filled up to about 85 to 90% with the steel melt containing no tellurium.The killed steel can have the following composition that is typical for it:

0.07 to 0.09 (wt.)% Carbon, 0.95 to 1.05 % manganese, 0.28 to 0.32 % sulfur, 0.05 to 0.0? % Phosphorus, best iron.

The mold 30 is partially filled up to the level 33, and it forms, as can be seen from Ϊ1? # 3 su, at least at the Sides and on the bottom a frozen band zone 31 «As soon as this has formed, the initially empty upper part 34 is the Mold 30 is refilled with the molten steel and tellurium is added at the same time. If there is a firm crust before at 33

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should have formed "this is broken up before the mold is filled or" before the tellurium is introduced. Bas tellurium is expediently added to the molten steel jet entering the mold so that it is evenly distributed with it in the still liquid core 32 of the steel block . Due to the added tellurium, the average tellurium content of the workpieces O ₉ O3 rolled out of the steel block is up to 0.20%

Pas tellurium can also be introduced into the steel block in such a way that, as shown in Jig »2, the The mold is immediately completely filled with the melt of killed steel »whereupon after the formation of solidified strip zones At least along the inner wall of the mold, the tellurium is mechanically pressed down into the melt and the liquid blocker is stirred mechanically or by means of inert pressurized gas · If necessary, the 50 Mt mold can be equipped with a conventional heat hood «

In the case of a workpiece made of killed steel in the above-described Weis ©, the tellurium distribution is roughly as shown in ELg »1, and the cross-section is as illustrated in Figs. 4- and 3. Sa the hot-rolled The workpiece made of calmed steel is free of significant tellurium content in its surface zones, ea j shows at most a liinisum of surface cracks

The invention is not limited to unkilled or killed steels and also not to the steel compositions given above; instead, steels with different compositions can also be added in the molten state in accordance with the invention (0.03 to O ₉ 2% by weight) of tellurium , e.g. carbon steels with the usual Α 1000, 1100 and 120Q ropes of the following composition:

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Series

1000

1100

1200

Carbon, uew «-% 0.08 - 1.

Hangan,

Hiosphorus,

Sulfur,

Silicon,

Bisen

M. It M.

0.25-1.65 to below 0.12 to below 0.06 to below 0.30 Order

0.08 - 0.55 0.30 - 1.65 to below 0.04 to below 0.40 to below 0.30 Best

up to 0.13 0.60 - 1.00 0.07 - 0, 0.08 - 0,

Best

However, not only carbon steels but also alloy steels can be treated by the method according to the invention. It is important in every case that the tellurium, always 0.03r to O ₉ 20% by weight, is only added to the steel melt in the mold when a solidified strip zone of the steel has formed at least on the mold wall. This ensures that the steel workpieces obtained by hot rolling the completely solidified steel block and the intermediate products contain so much tellurium inside that their machinability is improved and that they have a surface layer free of significant tellurium content and therefore free of surface cracks are at least to the extent that the quality and usability of the workpieces are practically not impaired thereby.

If the steel is an alloyed, unkilled steel, the strip zone of the cast steel block and of the workpieces rolled from this essentially made of iron and the alloying elements "

If necessary, the tellurium can be added to the inflowing steel melt at a point above the mold, but It is then necessary to have a suitable device to collect the tellurium oxide vapors that form above the mold and to provide tellurium vapors, which must be of such a nature that the deoxidation of the Steel before "entry into the mold is insignificant

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Further elements can be added to the tellurium, which improve the machinability of the steel · This includes lead, which can be added in a known manner des tellurium CO, 03 to 0.20 %) is replaced by selenium. The selenium or selenium plus tellurium, if part of it is replaced by selenium, is added to the steel melt in the mold in the same way as has been described in detail above for tellurium, after it has at least one on the mold wall has formed a solidified edge zone,.

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Claims (1)

/ UUbA / 7 PATENT CLAIM 1. Process for the production of hot rolled elongated Steel workpieces, e.g. from billets or bars, from the mold cast steel blocks, which in the molten state in the mold have a tellurium that improves the machinability and / or selenium addition is added, characterized in that that the tellurium and / or selenium after! filling at least the larger part of the mold with tellurium and selenium-free molten steel only after formation of a tellurium-free and selenium-free solidified strip zone at least along the mold side walls the molten steel is added, whereupon from the steel block after its complete solidification by hot rolling only sufficient in their interior to improve their machinability, but none in their surface zone workpieces containing significant amounts of tellurium and / or selenium are produced 2 » Method according to claim 1, characterized in that when casting a non-killed steel, the tellurium and / or selenium is introduced and dispersed in the steel melt circulating in the mold. 3 _# Process according to claims 1 and 2, characterized in that initially a larger part of the mold is filled with the molten steel and, after its solidified edge zone has formed, the tellurium and / or selenium is added simultaneously with the additional molten steel to completely fill the mold and below the Effect of this refilled steel melt is dispersed in the molten interior of the entire steel block, 4. Process according to Claims 1 and 2, characterized in that that the tellurium and / or selenium is driven down into the steel melt and stirred with it. 009838 / U56 200647? 5 · Procedure according to. Claims 1 to 4, characterized in that net that the tellurium and / or selenium does not expire before at least one minute after filling the larger part of the mold with the molten steel 6 · Honor peat according to claim 5 »characterized in that the Tellurium and / or selenium after two to five minutes is brought in 7 · From a steel block produced according to claims 1 to .6, hot-rolled steel workpiece with one of its machinable * · performance-improving tellurium and / or selenium content, marked f net by no significant amounts of tellurium and selenium containing surface layer, which in one for practice Sufficiently free from surface cracks to a reasonable extent is· 8 · Steel workpiece according to claim 7 »tL & darch characterized in that it consists of 0.03 to 0.18 (weight» «.)% KoMenatoff, 0.25 to 0.90 % manganese, up to 0.15 % sulfur, up to su 0 .04% phosphorus, 0.03 to 2.0% tellurium, the remainder consists of iron / is compressible. 9 »Steel workpiece according to claim 8, characterized in that it consists of 0.03 to 0.15 (Ge * -)% carbon, 0.25 to 0.60 manganese, up to 0.025% sulfur, up to 0.015 % phosphorus, 0 , 03 to i 0.20 % tellurium, the remainder consists of iron 10 · Steel workpiece according to claim 8, characterized in that its surface layer consists essentially of pure iron, 11 · Steel workpiece according to claim 9 made of non-killed steel, characterized by a surface layer consisting essentially of pure iron · " 009838/1456 ^: 12 · Steel workpiece made of a steel according to claims 7 to 11 with one or more alloy metals, thereby characterized in that it has a surface layer consisting essentially of pure iron and alloy metals 13 · Cast steel block for the manufacture of hot rolled. Steel workpieces according to claims 7 to 12, characterized by one finely divided inside, the machinability of the workpieces improving OJellur and / or selenium fairy content and one Upper compartments with no significant tellurium or selenium content zone on its perimeter » 0 0-9 838/1456