DE2157305B2 - Use of a low-alloy steel for hot-rolled objects - Google Patents

Description

for hot-rolled objects with a thickness of more than 4 mm, measured in the transverse direction, a tensile strength of at least 78 kg / mm ² and a notch elongation of at least 6.6% and a notched impact strength of at least 6.0 kg m / cm ² must show at room temperature.

2. Use of a low-alloy steel according to claim 1 with the proviso that the objects require a hot-rolled steel which has a tensile strength of 81.0 kg / mm ² at a final thickness of 12 mm and an impact energy of 5 at 0 ^{0 C,} 2 kg · m absorbed.

3. Use of a low-alloy steel according to claim 2 with the proviso that the steel ^{is heat-treated for 30 minutes at 600 to 650 0} C after hot rolling, for objects which have a tensile strength of at least 743 kg / mm ² and at 0 ⁰ C must absorb an impact energy of at least -6.5 kg · m.

4. Use ^ ines r ^; Highly alloyed steel according to claim I with the proviso that the chemical composition of the steel contains one or more of the elements molybdenum, vanadium, titanium and zirconium in proportions between 0.1 and 0.5% molybdenum, 0.01 to 0.15 % Vanadium, 0.01 to 0.15% titanium and 0.01 to 0.10% zirconium are added, for warning rolled articles measured in the transverse direction, a tensile strength of at least 80.1 kg / mm ² and an impact strength of 7 kg ■ m / cm ² at room temperature.

5. Use of a low-alloy steel according to claim 2 with the proviso that the steel has one or more of the elements molybdenum, vanadium, titanium and zirconium in proportions between 0.1 and 0.5% molybdenum, 0.01 to 0.15% Vanadium, 0.01 to 0.15% titanium and 0.01 to 0.10% zirconium are added for hot-rolled objects which, measured in the transverse direction, require a tensile strength of 79.8 kg / mm ² and an impact energy at 0 ^{° C} of 8.6 kg · m.

6. Use of a low-alloy steel according to claim 4, with the proviso that the steel ^{is heat-treated after hot rolling at 450 to 550 0} C, for objects that have a tensile strength of at least 82.2 kg / mm ² and a notched impact strength of at least 9.5 kg ■ m / cm ² at room temperature.

7. Use of a low-alloy steel according to claim 4, which is heat-treated after hot rolling to a final thickness of 12 mm JO minutes at 450 to 55O ° C, for objects which require a tensile strength of at least 74.0 kg / mm ² and at 0 "C must absorb an impact energy of 10.5 kg · m.

8. Use of a low-alloy steel according to one of the preceding claims with the Provided that the steel used contains 0.3 to 0.5% silicon, for objects according to the claims I -7.

9. Use of a low-alloy steel according to one of the preceding claims with the Provided that the nickel content of the steel used is about half the copper content for the objects according to claims 1 7.

In recent years, low carbon steel that has been hot rolled is one has good toughness and weldability, has been investigated and put into use. Typical examples The pearlite-free steel from GB-PS 10 58 146, the »low carbon steel and high manganese content "from GB-PS 11 91 657 or the" low carbon steel

r> and high manganese content "of DE-OS 19 46 111. It is known, however, that the tensile strength of the steel according to the above-mentioned GB-PS 10 58 146 is at most 60 kg / mm ² , even if it was rolled at low temperature, as this steel except one

ίο contains Si, Mn, Nb or V with low carbon content. Investigations have shown that as a result of the micro-segregation and precipitation at the grain boundaries the addition of more than 2.3% Mn resulted in fine cracking at the break points of a Charpy sample

J ") occurs, resulting in a lowering of the impact strength entails and deteriorates the flexibility. Although the carbon content of the steel according to GB-PS 11 91 657 reduced to less than 0.03% the deficiencies mentioned above are difficult to avoid.

From DE-AS 11 S2 845 u.id 12 98 720 it is known, low-alloy steels for hot-rolled To use objects that have good tensile strength, notched impact strength and low fracture

4 "i transition temperature and its composition overlaps with that of the steel used according to the invention. They contain less than 0.15% Carbon, less than 0.5% silicon, 0.5 to 2% manganese, 0.15 to less than 2% nickel, 0.03 to 0.2%

> i) niobium, 0.2 to 0.5% molybdenum and a total of 0.01 to 0.2% vanadium and / or zirconium (DE-AS 12 98 720) or 0 to 0.2% carbon, 0.01 to 1.0% silicon, 0.2 up to 2.0% manganese, 0.20 to 0.60% copper, 0.05 to 0.5% niobium and 0.027 to 0.5% titanium (DE-AS 11 82 845). Of the

> ") The steel used according to the invention has the following composition:

0.04 to 0.09% carbon,

0.1 to 0.9% silicon,

1.7 to 2.2% manganese,

less than 1.0% each of copper or nickel

0.3 to 1.5% (copper and nickel),

0.01 to 0.10% niobium,

The rest of the unavoidable impurities and iron.

hi The steel according to DK-AS Il 82 845 can be chrome contain. For these chromium-containing steels, a maximum tensile strength of 70.8 kg / mm is given, and the maximum impact strength of 7.8 kg · m / cm- 'becomes

achieved with a composition that provides a tensile strength of 62.2 kg / mm ² . The steel according to DE-AS 12 98 720 is intended for welded objects that should have a high tensile strength and good toughness even after repeated stress relief annealing. The maximum tensile strength given for this is 69.9 kg / mm ² .

The invention consists in using a steel of the composition specified above, particularly with regard to the manganese content, for objects which require a significantly higher tensile strength with at the same time good notched impact strength, namely a tensile strength measured in the transverse direction at a thickness of more than 4 mm of at least 78 kg / mm ^? and an elongation of at least 6.6% and an impact strength of at least 6.0 kg · m / cm ² at room temperature.

For objects that require a final thickness of 12 mm, the hot-rolled steel can have a tensile strength of 81.0 kg / mm and at 0 ^° C. absorb an impact energy of 5.2 kg / mm. Such objects can be produced with a steel of the aforementioned composition, even without subjecting the steel to a further heat treatment after hot rolling. If such a steel after hot rolling, a heat treatment temperature 600-650 ° C, it can be used for articles mm, a minimum tensile strength of 74.3 kg / ² and having at 0 ⁰ C an impact energy of at least 6.5 kg · M have to absorb.

Even higher demands can be made on the mechanical properties of the steel used if the steel has one or more elements molybdenum, vanadium, tilane and zirconium in proportions between 0.1 and 0.5% molybdenum, 0.01-0.15% vanadium , 0.01-0.15% titanium and 0.01-0.10% zirconium are added, which steel can be used for objects which have a tensile strength of 80.1 measured in the transverse direction at a thickness of more than 4 mm kg / mm ² and an impact strength of 7.0 kg · m / cm ² at room temperature.

If the above-mentioned alloy components molybdenum, vanadium, titanium and zirconium are added in the specified proportions to the steel according to the invention for objects in which a final thickness of 12 mm is required, the hot-rolled objects, measured in the transverse direction, can have a tensile strength of 79.8 kg / mm ² and absorb an impact energy of 8.6 kg · m ^{at 0 ° C.}

A steel alloyed with the above-mentioned alloy components molybdenum, vanadium, titanium and zirconium in the corresponding proportions, if it is heat-treated after hot rolling at 450-550 ° C., can be used for objects that have a tensile strength of at least 82.2 kg / mm -, measured on a tensile specimen of (6 25 χ 50 mm) gauge length, and require a notched impact strength of at least 9.5 kg · m / cm ² at room temperature. When this steel, after hot rolling to a final thickness of 12 mm, is heat treated for 30 minutes at 450-550 ° C, it can be used for articles that require a tensile strength of at least 74.0 kg / mm ² and at 0 ° C must absorb an impact energy of 10.5 kg ■ m.

The steel used for these items can contain 0.3-0.5% silicon, and the nickel content of the used steel!.; can hold about half of the copper hold on

Unless otherwise stated, the tensile strength values refer to specimens with the dimensions (4 × 15 × 32 mm) and 1 mm V-notch. Charpy specimens with 2-mni- V-notch for determining the impact energy of steels of objects with a final thickness of 12 mm have the same dimensions as the tensile specimens, while the Charpy specimens for determining the notched impact strength in all cases are half the size of the tensile specimens,
ίο An example of the influence of the heat treatment is given in the attached drawing. Curve A shows the stress-strain diagram for the steel which has not been further heat-treated after hot rolling, and curve B for the steel which has been heat-treated at 500 ° C. for 30 minutes. This steel, which has been heat-treated after hot rolling, has a much sharper yield point.

The reasons for the above limitation of the

The content of each element is as follows:

C: When the carbon content is less than

0.04%, it is difficult to get the steel the

to give the required high tensile strength

and if the content is üL «r 0.09%,

toughness and flexibility become poor.

_n Si: 0.1 to 0.9% Si is used as an auxiliary element

Solidification desirable. More than 1%

Silicon jcuöCh worsens the toughness

of steel.

Mn: When the Mn content is less than 1.7%,

j ,, the strength of the steel becomes quickly

worse, and when this content is more than 2.2%, fine cracks appear at breakage points up and the toughness of the steel becomes bad.

S3 Cu or Ni: High strength is achieved through

the addition of copper or nickel of up to 1% and 0.3 to 1.5% each (Copper + nickel) ensured. If a total content of more than 1.5% (Kup-Ji, fer + nickel) is added, both

Toughness and ductility, poor. Since in the case of a content of more than 0.5% Copper tends to develop hot cracks, should a nicking content, _, -, which is about half of the customer's salary

is to be added.

Nb: 0.01 to 0.10% niobium is necessary for the

Steel high strength and good toughness too

to lend. If the salary is above that

-, ο is the above range, it is difficult to

to give steel these properties.
The other elements mentioned above further promote the required properties if the additive remains in the above-mentioned range.
-, -, {'. However, an addition of chromium must be added because of the increasing hardenability of the steel and because it has a deterioration in the quality of the material. brings itself to be avoided.

In the method for producing the erfindungsge _h ii MAESSEN steel at a steel thickness of more ais 10 mm should be hot rolled at a low finish rolling temperature. The steel can be used for various purposes, such as sheet metal, plates, profile iron, rods and the like.

,,, The exact chemical composition, the manufacturing process and the physical properties of the steel are illustrated by the following examples ii explained earlier.

Example I.

The values given in this example were obtained through laboratory tests. Table I shows the chemical composition of these steels. The steels

Table I.

Al and A2 are comparison steels, each of the steels Bl bi B9 is a steel used in the present invention. Dii steels were 6 mm thick. They were up au I200 "C heated and rolled under the requirements of a conventional hot rolling mill.

C. Si Mn P. S. Cu Ni Nb Other (Gchaltc in A I 0.07 0.41 1.90 0.01H 0.009 0.041 A 2 0.06 0.42 2.80 0.015 0.007 0.043 B I 0.06 0.48 1.92 0.01.S 0.008 - 0.5 I. 0.045 B 3 0.06 0.48 1.92 0.017 0.008 0.43 - 0.044 B 4 0.07 0.25 2.16 0.01 I. 0.009 0.85 0.54 0.044 - B 5 0.06 0.33 1.98 0.008 0.008 0.72 0.52 (1.035 V 0.052 B 6 0.06 0.40 1.91 0.015 0.009 0.35 0.32 0.025 Ti 0.09 B7 0.07 0.42 1.96 0.017 0.008 0.51 0.40 0.035 Zr 0.04 B 8 0.05 0.51 1.93 0.017 (1.009 0.35 0.34 0.046 Mo 0.2 B 9 0.05 0.36 2.08 0.012 0.007 0.34 .- 0.048 V 0.098

Table II shows the mechanical and physical properties in the transverse direction required for the following Test pieces were measured:

Table Il

Sample size:
Charpy sample:

mm χ 15 mm 32 mm

Length

1 mm V 'notch c

Half as big as

the above sample

2mm K notch

0.2% elongation tensile strength, elongation at break, notched impact limit lemperaiur toughness at

Room temperature

kg / mm ² kg / mm ^: % C kg m / cm ²

Fractional structure

Al 59.2 72.0 10.5 -50 9.8 fine crack A2 62.3 83.9 5.0 -40 3.0 education Bl 62.9 78.0 7.5 -70 7.3 B3 68.3 80.0 6.6 -60 7.3 minor crack B4 60.7 84.3 6.9 -35 6.0 education B5 63.2 83.1 7.4 -59 7.0 B6 67.3 83.5 9.6 -48 10.0 B7 66.0 81.6 9.3 -44 9.4 B8 65.5 85.8 7.1 -48 7.0 B9 68.2 85.0 6.8 -55 8.0

The properties, especially the tensile strength, notch elongation and notched impact strength at room temperature of the steel according to the invention show a stable and uniform height, while the properties of the comparative steels are unbalanced, that is, in the case of the Al steel, both of the Notch elongation and impact strength at room temperature are high, while tensile strength is low

and that in the case of A2 steel, both the notch elongation and the notched impact strength at room temperature are low, while the tensile strength is great.

Example I!

In this example, the stability of properties in hot rolling is examined. The hot rolling test

marriage were therefore at an oil temperature of 600 "C and 530" C were carried out on the B9 steel from Table I. The results are shown in the following Table III shown. The values from Table III relate to the transverse direction and were obtained on the same samples as used in Example I.

even if the reel temperature changes. It should therefore be noted that the toughness, ductility and strength can be kept well coordinated.

Example III
This test was carried out at an ordinary warm

Tändle III o, 2% - / llg- Fracture- Killer rolling process carried out. I. The test condition Dchn- lcsligkcit over- / iihigkcit he in were the following: gren / e gangly Room- Ha> pcl- tcmpe- tcmperiitur Material: tenipe- rature Annealing temperature in the furnace: B4 steel from Table I. rntur kg / mnr kg / mm ' ( kg m / cnr Final temperature 1250 ° C ι> for hot rolling: Final thickness: 75O ⁰ C ( 63.0 80.1 -46 8.5 Heat treatment temp. 12 mm 68.2 85.0 -55 8. (1 door after air cooling: Specimen: 600 ⁼ C and 650'C 600 Same size as 530 Charpy sample: that from example I. Same size as the above specimen

This example shows that the relationship between the properties of the invention Steel changes little and good stability The properties in the transverse direction are in the shown in Table IV below:

Tahcllc IN ' Stretch limit tensile strenght Constriction Fracture transition Absorbed temperature energy at 0 C kg / mm ² kg / mm ² % C. kg ■ m / cm ² 59.6 *) 81.0 54 -73 5.2 Hot rolled 66.1 76.7 57 -56 6.5 600 C x 30 min. 61.8 74.3 58 -68 7.0 650 C x 30 min. *) 0.2% elongation.

As shown in Table IV above, the yield strength appears clearer when the steel is subjected to heat treatment. which is beneficial for many uses. However, such a heat treatment above about 680 ^° C should be avoided because the tensile strength decreases as the temperature rises.

Eüe Festigkcitswerie with this example! are mil not directly comparable to those of the other examples insofar as the specimen in the case of Example III has the same thickness of 4 mm as in the case of Example I, but the thickness of the material as the sample is cut out, with 12 mm is twice as high as that in the other examples.

Example IV

The one in this example! The steels tested had the following chemical composition:

C: 0.06% Mn: 2.03% t / i 0.005% Ni: 0.20% V: 0.05%

Solved 0.022% Al: 0.48% Si: 0.01% P: 0.40% Cu: 0.05% Nb: 0.06% Zr:

The above steel is treated in an ordinary hot rolling mill. The final thickness is 6 mm. The tested material cut from the middle part of the above spool in appropriate size, is subjected to heat treatment at different temperatures. The sizes of the specimens are the following:

Specimen:
Charpy sample:

6 mm χ 25 mm χ 50 mm (CL)
Half the size of the above
Specimen

The mechanical and physical properties of these coupons are shown in Table V below shown

9 Measuring direction 21 57 305 10 Notch impact
tenacity at
room
temperature Table V kg ■ m / cm ² L.
Q Pronounced
Stretch limit tensile strenght Fracture transition
temperature 11.8
9.0 L.
Q kg / min kg / mnr C. 12.0
9.5 Hot rolled L.
Q 69.0 *)
75.9 *) 85.5
88.4 -IK)
-87 13.7
10.5 450 C ¹ x 30 min. L. 76.7
81.3 83.0
86.6 -107
76 15.5 500 C x 30 min. Q 76.9
80.9 83.5
85.7 113
84 1 1.1 sill (V 1 (1 min L.
ü 76.6 83.0 117 18.5
11.5 79.2 85.2 ') / 550 C x 30 min. 75.9
80.4 82.6
85.9 -126
-91

*) 0.2% - yield strength. L: rolling direction. Q: cross direction.

The drawing shows the stress-strain diagram, it can be seen that the Slreckgren / e according to the

gram, which on this treatment, namely the heat treatment, is more improved than that of the

Hot rolling and a heat treatment at 500 ⁰ C κ ι hot-rolled steel, the yield strength of which is so good

for 30 minutes based. From Table V and the drawing like that of Example III above.

Example V

In this example, the coil of the steel used in accordance with the invention is ^{heat-treated at 500 °} C. for eight hours in a common insert tempering furnace. Both the chemical composition that

Manufacturing process and measuring conditions are the same as in Example IV. Table VI shows: the Measurement results.

Tabel Vl Tensile strength
speed
kg / mnr fracture
transitional
temperature
C. Notch impact
tenacity at
room
temperature
kg ■ m / cnr MeU
rich
tion Stretch
border
kg / mnr 82.8
84.5 -114
-70 13.0
9.5 L.
O 72.1
79.4

From the above Table VI it can be seen that the steel used properly can therefore have the balanced properties of the steel in spite of excellent properties, regardless of what heat treatment a common tempering furnace for steel treatment it has been subjected to,
can be given by sheet metal dimensions. The inven-

Bc: i game VI

The steel of this example VI has the same chemical composition as that of example IV and is made under the same hot rolling conditions used in Example III. The heat treatment of this steel was carried out at 450''C,

500 ° C and 550 ⁰ C carried out. The Charpy sample was the full size of the specimen. The transverse mechanical and physical properties are shown in Table VIl below.

Table ViI Pronounced
Stretch limit tensile strenght Constriction liruchühergiings-
Icmper.itur Absorbed
Impact
energy at O C kg / nmr kg / mm ' "," ( ng ■ m / cm ' 56.4 *) 79.8 61 -78 8.6 Hot rolled 67.9 76.0 68 -70 10.5 450 C- 30 min. 66.2 74.0 72 -74 11.0 5 (X) C ■ 30 min. 65.9 74.6 71 Th 11.H 550 C 30 min.

*) (U'VDehngretve.

The results from Table VII show excellent toughness and ductility at the various heat treatment temperatures. It is particularly emphasized that the yield strength and that of CfC

absorbed energy by steels, carried on by jas Heat treatment processes treated are far better than those of a hot rolled steel.

I licr / ii I BI.i

Claims (1)

Patent claims: 1. Using a low-alloy steel with 0.04 to 0.09% carbon, 0.1 to 0.9% silicon, 1.7 to 2.2% manganese, less than each 1.0% copper or nickel, 03 to 1.5 (copper and nickel), 0.01 to 0.10% niobium, The rest of the unavoidable impurities and iron