DE1758703B1 - ROLLER FOR HOT ROLLING MILLS - Google Patents

Description

Carbon 0.03 to 0.2%

³⁵ chromium 3 to 8%

Molybdenum ......... 0 to 2%

Tungsten 0 to 7%

Vanadium 0 to 1%

The remainder is iron and manganese caused by the melting process. 0.3 to 3%

cleaning exists. Silicon. 0.2 to 2%

3. Roller according to claim 1 or 2, characterized overall A indicates that the working surface of a the sum of the percentages of chromium, molybdenum ™ welding job consists. ■ 45 Danish, tungsten and vanadium between about 4 and

about 9 lies and the remainder of iron with melting-related Impurities. _______ Opposite that from the British patent specification

776 482, the roller according to the invention differs in several respects:

So, according to the invention, is the maximum limit

The invention relates to a roll for hot rolling of 0.2% carbon critical, while according to the works that alloy a work surface from a British patent 776,482 the amount of carbon Has chrome steel, which can be up to 0.5% compared to thermal erosion.

fatigue and wear at the temperatures at 55 are further described in the British patent which is hot-rolled is stable. 776 482 high chromium contents, namely preferably above

Rolls used in hot rolling mills are suggested to be half 13%, while the chromium contents, sometimes have to be taken out of service, because according to the invention, are limited to a maximum of 8%. (1) excessive wear and (2) excessive wear and tear surface cracking or a superficial depiction of the sum of the elements chromium, scroll, which is due to a thermal molybdenum, tungsten and vanadium in the area between fatigue have to enter. The manufacturers should see 4 and 9. Likewise here are the comers Rolling it is common practice, steels with a component manganese and silicon not mentioned, high carbon content and a comparatively finally no

to use a low alloy content in order to obtain the best possible 65 statements about the exact composition of the markings Combination of mechanical properties weld made.

and to achieve profitability. In general, therefore, it appears that a number of confluences Rolls in the soft ^ strongly tempered condition Settlements which meet the conditions of the British patent

0.05 until 0.2% Carbon, 4.5 until 6% Chrome, 0.5 until 1.5% Molybdenum, 0.5 until 4% Tungsten, 0 until 0.5% Vanadium, 0.3 until 2.6% Manganese, 0.2 until 2% Silicon,

font 776 482 are sufficient, but which are outside of the areas to be evaluated as according to the invention, the Compositions according to the invention are inferior.

From "material Manual Steel and Iron", 1965 (sheet P 60-2, Table 1), it is further known that Mn contents by 0.3 / 1.1 ° / ₀ and Si contents of 0.3 / 0 , 4% are common for hot rolling.

This document has little in common with the subject matter of the present invention, since there the two to four times the amount of the maximum amount of carbon according to the invention and only a small amount Chromium amount is described, whereby the lower limits are not specified.

The working surface of the roller according to the invention has the following composition:

element Wide range,% Narrow area,% Preferred amount,% carbon
chrome
molybdenum
tungsten
Vanadium
manganese
Silicon 0.03 to 0.2
3 to 8
0 to 2
0 to 7
0 to 1
0.3 to 3
0.2 to 2 0.05 to 0.2
4.5 to 6
0.5 to 1.5
0.5 to 4
0 to 0.5
0.3 to 2.5
0.2 to 2 about 0.15
about 5
about 1
about 1.5
about 0
about 2
about 1

where the sum of the percentages of chromium, molybdenum, tungsten and vanadium between about 4 and about 9 and the remainder of iron with impurities caused by the melting.

According to a further preferred embodiment, the work surface consists of a weld job.

Based on the known principles for influencing high temperature hardness and resistance to softening, a number of weld cladding compositions have been prepared and tested for their thermal fatigue resistance. This property was measured by alternately directing an oxygen-acetylene flame onto the welded surface and quenching the heated surface by spraying water on it. These alternating temperature cycles were continued until cracking due to thermal fatigue occurred. The number of heating and quenching cycles required for visible cracking to begin was taken as a measure of relative thermal fatigue resistance. The test conditions were severe enough to cause all of the standard hot work tool steel rolls to crack within 500 cycles.
The resistance to softening and the hot hardness were also determined for many welding jobs. In Table I the compositions and the results of thermal fatigue are given, while in Table II the results of the hot hardness tests and the hardness after heating to elevated temperatures are given. Alloy steel No. 13 was included in the tests as the minimum alloy steel. Its low hot hardness made it uninteresting as an alloy steel; its softening tendency and thermal fatigue resistance were not determined. The figures in Table II confirm that the various alloying elements generally impart properties to weld deposits similar to those imparted by them to forged tool steels.

Table I.

stole C. Mn Si 7th Cr Ni Mon W. γ number of No. 0.28 1.87 0.65 5.74 0 1.52 0.97 0 Test cycles 1 0.185 1.85 0.62 5.64 0 1.42 1.07 0 16 * 2 0.16 7.00 0.61 5.79 0 1.36 1.25 0 1000 3 0.08 1.80 0.61 5.69 0 1.51 1.02 0 1000 4th 0.297 1.26 0.75 9.66 0 1.00 0 0 508 5 0.15 2.41 0.86 7.47 0 1.04 0 0 74 * 6th 0.39 1.18 0.51 2.11 0 0 7.41 0 1000 7th 0.19 0.90 0.57 1.73 0 0 7.26 0 10 * 8th 0.22 1.99 0.64 6.75 0 1.62 0 0 1000 9 0.09 1.83 0.70 0 7.27 4.36 0 0 110 * 10 0.16 2.60 0.54 2.0 0 0.68 0 0.3 278 * 11th 0.21 2.20 0.60 3.6 0 0 0 0 508 12th 0.15 0.96 0.40 2.0 0 0 0 0 20 * 13th

* Unusable.

Tabel!!

stole Softening tendency Rc after the Room temperature Hot hardness j? C 538 C ° 649 ° G No. . Rc before the warming 49 41 30th warming 42 42 427 ° C 42 30th 1 49 34 42 47 37 28 2 42 35 45 42 36 19th 3 42 25th 44 34 38 31 6th 45 40 52 39 44 33 8th 44 37 43 44 34 18th 9 52 - 44 43 36 25th 10 43 36 47 35 22nd 12th 11th 44 35 22nd 35 ZIRb 65 Rb 12th 47 - 37 13th - 82R _B

Rc - hardness as measured on the Rockwell C scale. All hardness measurements are on the Rockwell C scale, with the exception of the last three measurements for Alloy No. 13, which are on the Rockwell B scale (R _B ) .

In a single welding job it was thus shown that crack formation in the grains a resistance to thermal interfaces in a high-alloy intermetallic Fatigue as well as a resistance phase began and then continued in the usual way - wear and tear achieved at elevated temperatures. Reference-planted. As a result, the combination is legitimate The thermal fatigue was in surprise elements and the concentration of each of the We have found that carbon has this property as well as the carbon content of the determinant influenced. It has been found through tests that mung the resistance to thermal With any content of alloy components, all fatigue is important.

Compositions with an exceptional cons- The figures in Table II confirm that those in the

Stand ability to thermal fatigue of an existing literature available information be-carbon content of less than 0.2 ° / ₀ owned. At 30 plus the effects of chromium, molybdenum, Wolf carbon contents above 0.2 ° / ₀ , the test ram and vanadium on the hot hardness and the

Softening resistance of forged steels are generally applicable to welding jobs provided that the amounts of alloying elements are kept low enough to prevent the formation of second phases. The presence of chromium is desired because of the oxidation resistance, and the figures show that a steel with 2 ° / ₀ chrome, steel no. 13, insufficient curability and insufficient hot hardness has, except that it could be used in rolls for hot rolling mills. One . Increasing the chromium content to about 3.5% without the addition of other alloying components, Steel Nos. 12, gave a sufficient hardness at room temperature and at 427 ⁰ C, but the hardness at 538 ° C and the softening und.469 were too low. At about 8% chromium, and about 1 ° / ₀ molybdenum, steel no. 6, were the softening resistance and hardness at 649 ° C on the border.

50 The steel no. 11 shows the beneficial effect of low by the use of concentrations of vanadium in amounts up to 1 ° / ₀ in a composition that can be obtained otherwise, with respect to the hardness and the softening unsatisfactory WAE 55 re. While the addition of about 0.7% molybdenum and 0.3% vanadium increased hardenability, hot hardness and resistance to softening in the presence of only 2% chromium to an acceptable level in the case of steel No. 11, it was essential is forged tool steels because 60 seems 3 ° / ₀ to take reasonable chromium as minimal verwendder hot working during forging the slabs at face amount.

does not exist and thus gives only a limitation. Steel No. 9, an alloy of about 7%

in the case of welding jobs. Such an alloy is chromium and about 1.5 ° / ₀ molybdenum, has a Zuin Table I as steel no. Indicated 10th Thereupon it becomes satisfactory hot hardness, whereby the softening indicates that, although the carbon content is far 65, resistance is at the limit. Below the threshold value of 0.2 ° / ₀ Hegt, the proof is shown that molybdenum above about 4% was unusable due to thermal fatigue after only premature unusability of the test sample through 278 cycles. A microscopic thermal fatigue due to a grain boundary

pieces due to thermal fatigue always within 500 test cycles (within 278 cycles in fact) were unusable, and in some cases they were already unusable after ten cycles.

It was found that the lower practical Limit value for the carbon content at approximately 0.03 percent by weight. Alloys below This carbon content can provide excellent resistance to thermal fatigue but they are soft and their wear resistance is so poor that they are suitable for intended uses such as e.g. B. Restoration of rolls for rolling mills are unsuitable.

The figures in Table I also show that in the development of alloys which under the conditions strong cyclical temperature changes are used, care must be taken that Formation of either low-melting eutectic phases or hard, brittle intermetallic phases To prevent grain interface phases. These cause early unusability thermal fatigue due to a mechanism analogous to that used in the above high carbon steels described occurs. These phases are of the kind found in welding jobs when high concentrations of alloy elements, such as B. molybdenum and nickel, are present in the alloy steel. This loading

7 8

area phase resulted. In order to safeguard against possible thermal fatigue properties and an excellent, harmful formation of grain boundaries, the high-temperature behavior was used. There is, however, the upper limit for molybdenum set at 2%. All the danger of the formation of intergranular phases in chromium alloys, which contained tungsten in amounts of unsupported amounts with an excessively high alloy content from about l% to over 7%, have one constituent part, as is the case with steel no. 10 satisfactory hot hardness and a satisfactory visual hardness. Therefore a value of 9% is the resistance to softening. This has been set as the maximum without lowering total amounts of chromium, molybdenum, tungsten and reducing thermal fatigue resistance by vanadium.
Formation of grain boundary phases achieved. The upper limit value for tungsten with approximately 10 welding jobs was therefore set for good high-temperature properties through the addition of chromium, 8%, although the alloy is used in the expensive molybdenum, tungsten and vanadium as a result. Scored addition levels, the alloys having the lower tungsten, without thereby any concentrations were / forms at about 1.5 ° ₀ molybdenum ingredient which improves the fatigue-resistant material. speed of the alloy has a detrimental effect.

The figures in Table II show that Schweißaufträ- 15 Good high temperature properties can be obtained applying the chromium in amounts from about 3 to un- containing the above ferry 8 ° / _0, in Schweißge, for use in rolling elements in higher percentages as the ones for hot rolling mills were improved, included in the given. However, the properties which tungsten, vanadium and molybdenum or combinations give these elements are within the specified range of the three metals added. In each ao limit values very pronounced, and the use trap was however a total amount of chromium, of higher concentrations usually molybdenum, tungsten and vanadium of 4 ° / ₀ the mini- just a waste. In addition, the hazard is the useful concentration required for counteracting the deterioration in the thermal fatigue resistance to high temperature wear and durability of the welds due to the use of thermal fatigue. 25 higher percentages of alloying elements

As a minimum amount of 3% chromium for pregnant.

an oxidation resistance and hardenability required

is sary, it is at least l ° / ₀ of an additional hard surface are usual, may also Toggle

Alloy constituent or, in other words, be an essential part. The range for silicon is normal-

Total amount of 4 ° / ₀ required, corresponding to 30 wise between 0.2 and 2% and that for manganese

To achieve high temperature properties. from 0.2 to 3 ° / ". Phosphorus and sulfur can be in the

The steel no. 8, which has a total amount of chromium in commercial quantities. The rest

and tungsten containing from about 9 ° / _0, showed good consists essentially of iron.

Claims (2)

0.03 to 0.2% carbon, 3 to 8% chromium, 0 to 2% molybdenum, 0 to 7% tungsten, 0 to 1% vanadium, 0.3 to 3% manganese, 0.2 to 2% silicon, are used to be able to machine them and in order to achieve the r> "+ Q" + ",, r.,"., ",, i ^. the highest possible ductility, which meets the requirements of the patent claims:, ..... , ... ,,, ·,. ^ 1 gives low-alloy steels the best thermal fatigue resistance 1. Roll for hot rolling mills that have a work- 5 hardness and resistance then depend on the surface of an alloyed chrome steel volume of hard carbides that are present in the material and that are resistant to thermal fatigue. Hard carbides, which in the grain boundaries to wear at the temperatures at which are warm, promote the wear-resistant rolling, is resistant, but they reduce the resistance characterize that the working surface from ¹⁰ against thermal Fatigue. Materials with a high carbon content, which have shells made of free carbide at the grain boundaries of their microstructure, have a very low resistance to thermal fatigue, since during thermal 15 mixing treatment, microcracks occur in the brittle carbides and propagate rapidly. The alloy steel then cracks and flakes off and is no longer usable long before it becomes difficult to wear.
From the British patent specification 776 482 it is already apparent that rolls for hot rolling mills can be provided with surfaces by welding, which are made from M where the sum of the percentages from chromium, a steel, from not more than 0.5% carbon, Molybdenum, tungsten and vanadium between a little more than 6% chromium, not more than a total of 6% about 4 and about 9, the remainder being iron and molybdenum, tungsten and vanadium, there is contamination caused by the application. In this known roller, however, comes the 2. Roller according to claim 1, characterized in that the surface layer is not directly on the roller body indicates that the work surface is ready for deposition. In contrast, a roller is proposed according to the invention, which is characterized is that the work surface has the following composition: