DE2157305A1 - Low alloy steel with high tensile strength - Google Patents

Description

CHECK ACCOUNT: MUNICH 91139

BANK ACCOUNT: BANK H. HOUSES

Case P-816-41
3 / th

NIPPON KOKAE KABUSHIKI KAISHA, Tokyo / Japan

Low alloy steel with high tensile strength

The invention "relates to a low-alloy steel of high tensile strength with excellent toughness, good impact strength and high strength.

In recent years, steel with a low carbon content, which has been hot rolled and has good toughness and weldability, examined and put into use · Typical examples of these investigations are the »Reduced Perlite Steel» from GB-PS No. 1 058 146, the "Low carbon and high manganese steel" from GB-PS No. 1,191,657 or the "low carbon steel content and high manganese content "of DOS No. 1 946 111. It is a fact, however, that all of these steels have certain Show weaknesses. It is well known that the tensile strength of the steel according to the above-mentioned GB-PS 1,058,146 is at most 60 kg / mm even if it was rolled at a low temperature because this steel is made of a low carbon content and a Si-Mn-Nb or V system. Studies have shown that as a result of microsegregation and excretion

2 0 9 & 27 / .Q5 3

at the grain boundaries due to the addition of more than 2.3 ° 1 "In a fine formation occurs at the fracture points of a Charpy-Iest piece, which brings a reduction in the notch toughness with it and deteriorates the bendability. Although the carbon content in the Steel according to GB-PS 1 191 657 has been reduced to less than 0.03 ° , it is difficult to avoid the above-mentioned deficiencies strength, i.e. a low fracture transition temperature, good notched impact strength and high strength, has not yet become known.

The steel of the present invention has been developed to solve the above problems. The merlanals of the steel according to the invention are that 1.7 to 2.2 $> Mn, less than 1.0 io in each case Cu or Ui and 0.3 to 1.5 # (Cu + iTi) and 0.01 to 0 , 10 io Nb are simultaneously present as a basic composition. If the steel has the above-mentioned composition, it can easily be given the required properties.

It is therefore the object of the invention to develop a low-alloy steel of high tensile strength which is excellent Has toughness, good ductility and high strength, and can be manufactured at low cost.

An exemplary embodiment of the invention is described below explained in more detail using the accompanying drawing:

Fig. 1 shows an example of a stress-strain diagram of the steel according to the invention,

Fig. 2 is a photograph comparing the fracture nature of a Charpy test piece made from the steel of the present invention shows with that of a comparison steel.

The steel according to the invention consists in its basic composition from the following elements:

C: 0.04 Ms 0.09 #

Si: 0.1 "to 0.9 #

Mh: $ 1.7 to $ 2.2, preferably

1.8 Ms 2.0 #

Cu or Ni: less than {each $ 1.0 and (öu + Ni) 0.3 Ms 1.5 #

Fb: _x . 0.01 to 0.10 %

If necessary, one or more of the following items can be used Group selected and the above-mentioned basic composition to be added:

Mo: 0.1 Ms 0.5 fo

V: 0.01 Ms $ 0.15>

Ti: 0.01 Ms $ 0.15

Zr: 0.01 Ms $ 0.10

The reason for the above limitation on the salary of each Element is the following:

C: When the carbon content is less than 0.04 % , it is difficult to give the steel the required high tensile strength, and when the content is over $ 0.09, toughness and ductility become poor.

Si: 0.1 to 0.9 # Si (preferably 0.3 to 0.5 $>) is desirable as an auxiliary element for solidification. More than 1 $ silicon, however, worsens the toughness of the steel

Mn: When the Mn content is less than 1.7 $, the strength of the steel quickly deteriorates, and when this content is more than 2.2 ia , fine cracks occur and the toughness of the steel becomes poor.

Cu or Ni: A strength of at least 70 kg / mm is achieved by adding copper or nickel of 0.3 to 1 # and 0.3 to 1.5 #, preferably 0.5 to 1 % (copper + nickel) ensured. If a total content of more than 1.5 % (copper + nickel) is added, both toughness and ductility,

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bad. As in the case of a copper salary of more than $ 0.5 the tendency to the occurrence of hot cracks "exists, should a nickel content, which is about half of the copper content, be added.

Nb: $ 0.01 to $ 0.10 Niobium is necessary to make the steel the high To give strength and good toughness. If the content is above the above range, it is difficult for the steel to obtain this To give properties.

The other elements mentioned above promote the required properties more and more when the addition in the above mentioned Area remains.

However, chromium must be added because of the increasing hardenability of the steel and because it dilutes the Material quality brings with it, should be avoided.

The steel according to the invention can therefore exhibit the required toughness, ductility and high strength, that is to say a low Bruohum transformation temperature, good notched impact strength and high tensile strength, even when it is hot-rolled. If necessary, the hot-rolled steel may be a hot treatment at .Less than be subjected to approximately 680 ⁰ C, thereby imparting the steel even better properties.

In the method for producing the steel according to the invention should be a steel thickness of more than 10 mm at a low Fe in rolling temperature are hot rolled. The steel according to the invention can be used for various purposes, such as for Sheets, plates, profile iron, rods and the like can be used.

The exact chemical composition, the manufacturing process and the physical properties of the steel according to the invention are explained in more detail using the following examples.

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Example I.

The values given in this example were obtained through laboratory tests. Table I shows the chemical composition of these steels. Steels A1 and A2 are comparative steels; each of steels B1 to B9 is a steel according to the invention. These steels were ^{heated to 120O 0} O and rolled under the requirements of a conventional hot rolling mill.

Table I.

0 Si Mn P. S. Gu Ni Nb Other V - 0. 052 A1 0.07 0.41 1.90 0.018 0.009 mm 0.041 Ii - 9 · 09 A2 0.06 0.42 2.80 0.015 0.007 - 0.043 Zr 0. 04 B1 0.06 0.48 1.92 0.018 0.008 - 0.51 0.045 Mon - O. 2 B2 0.06 0.49 1.95 0.019 0.008 - 1.01 0.044 V - O. 098 B3 0.06 0.48 1.92 0.017 0.008 0.43 - 0.044 B4 0.07 0.25 2.16 0.011 0.009 0.85 0.54 0.044 B5 0.06 0.33 1.98 0.008 0.008 0.72 0.52 0.035 B6 0.06 0.40 1.91 0.015 0.009 0.35 0.32 0.025 B7 0.07 0.42 1.96 0.017 0.008 0 51 0.40 0.035 B8 0.05 0.51 1.93 0.017 0.009 0.35 0.34 0.046 B9 0.05 0.36 2.08 0.012 0.007 0.34 - 0.048

Table II shows the mechanical and physical properties in i iiiii ^ i ^ transversal direction ^ that goes to the following Test pieces were measured:

Test piece:

Charpy test piece k:

4 M χ 15 mm χ 32 mn (stretched length)

1 mm V-notch

Half the size of the test piece above

2 mm V-notch

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Table II

0.2 ° / o trial tensile breaking notch. Notched impact tensile strength elongation transition toughness be-Kg / mm ^ Kg / mnr ^c / o temperature at carpentry

Oq temperature fen-Kg-m / cm ^{2 unit}

A1 59.2 72.0 10.5 - 50 9.8 fine A2 62.3 83.9 5.0 - 40 3.0 manure B1 62.9 78.0. 7.5 - 70 7.3 B2 66.8 84.0 6.3 - 64 7.8 B3 68.3 80.0 6.6 - 60 7.3 Low B4 60.7 84.3 6.9 - 35 6.0
JE manure 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

2 is a photograph showing the Bruohbeschaffendeit the steels of Eabelle I at +20 ⁰ C. Photograph a or b is that of the comparison steels A1 or A2. Photograph c is that of another comparative steel consisting of 0.05 ° / ° C, 3.2 $ Mn and 0.08 $ Fb. Photograph d shows the fracture properties of the steel B5 according to the invention in Table I. From these photographs it can be seen that photographs a and d show no fluff formation, while fine tarring can be observed at b and c. 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 level, while the properties of the comparison steels are unbalanced, that is, in the case of the A1 steel, both the notch elongation and the notched impact strength at room temperature are high are while the tensile strength is low and that im

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

Example II

In this example, the stability of the properties in hot rolling is examined. The hot rolling tests were therefore carried out at a coiling temperature of 60O ⁰ G and 55O ⁰ C for the B9 steel from Table I. The results are shown in Table III below. The values from Table III relate to the transverse direction and were obtained under the same requirements for the test piece as were used in Example I.

Table III

Winding 0.2 # ^ <M · fracture transition- notched impact strength tempera- test- dukHJUüt, temperature at room temperature for chip- Kg / minr o «Kg-m / cm ^ o ₀
Kg / mar

600 63.0 80.1 - 46 8.5

530 68.2 85.0 - 55 8.0

This example shows that the relationship between the properties of the steel according to the invention changes little and has good stability, even if the winding temperature changes changes. It can therefore be stated that the toughness, ductility and strength are kept well coordinated can be.

Example III

This test was carried out in an ordinary hot rolling process. The requirements were as follows:

Tested material: B4 steel from Table I the annealing temperature in the oven: 1,250 ⁰ C
Final temperature in the hot rolling: 75O ⁰ C

209827/0537 : ν ORfOINAL-INSPECTED

Final thickness: 12 ram ■

Heat treatment temperature after air cooling: 600 0

and 650 ⁰ C

Sample: Same size as that from Example I. Charpy test piece: Same size as the above test piece

The transverse properties are shown in Table 17 below:

Table IV

Stretching tensile ~ ΐ $ ^ · Bruchüber- Absorbed border ness _o would take Gangst egg bi Kg / ^mm2 Kg / mm ^'1% temperature

limit kei Kg / mm ² Kg / mm

would take gear temperature energy at % t 0 ^ü ö E ^

0 ^ü ö

Hot rolled
6OO ° Cx3OMin

59.6 ^X
66.1

65O ° Cx3OMln. 61.8

31.0 76.7 74.3

54 - 73 57 - 56 58 - 68

5.2

6.5 7.0

As shown in Table 17 above, the yield strength appears clearer when the steel is subjected to heat treatment, which is advantageous for many uses. However, such a heat treatment at more than about 680 ⁰ C should be avoided because the tensile strength with the increase in temperature is lower.

Example IV

The steels tested in this example consisted of the following chemical composition.

C: 0.06 fo Si: / 0537 0.48 % Mh: 2.03 f P: $ 0.01 Si: $ 0.005> Cu: $ 0.40> Ki: 0.20 <? O Nb: 0.05 % Vi 0.05 % Zr: $ 0.06> Solved Al: 0.022 # 209827

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 coil in the appropriate size is subjected to a heat treatment at different temperatures. The sizes of the specimens are as follows:

Specimen:
Charpy test piece:

6 mm 25 mm 50 mm

Half the size of the sample above

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

Table V

Messrich
tion

pronounced yield point Kg / mm ²

Tensile strength at break transition temperature ρ rature Kg / mm Oq

Notched impact strength at Zimmert empe> rai

Hot rolled

L.
C.

69.0:

75.9

, x

85.5
88.4

- 110

- 87

11.8 9.0

45O ° Ox3OMin

L.
C.

76.7 81.3

83.0
86.6

107 76

12.0 9 5

5OO "Ox3OMin

L.
C.

76.9 80.9

83.5
85.7

113 84

13.7 10.5

55O ° Cx1OMin

L.
C.

76.6 79.2

83.0
85.2

- 117

- 97

15.5 11.1

55O ^u Cx3OMin

L.
G

75.9 80.4

82.6
85.9

- 126

- 91

18.5 11.5

x: 0.2 fo test tension 1: rolling direction 0: transverse direction

Fig. 1 is a stress-strain diagram based on this treatment development, namely hot rolling and heat treatment bai

ORIGINAL INSPECTED

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500 ⁰ C for 30 minutes "is based. From Table V and Pig. 1 it can be seen that the yield strength after the heat treatment is improved more than that of the hot-rolled steel, the yield strength is as good as that of the above Example III.

Example V

In this example, the coil of the steel according to the invention is ^{heat-treated at 500 °} C. for eight hours in a customary insert tempering furnace. Both the chemical composition, the manufacturing process and the measurement conditions are the same as those from Example IV. Table VI shows the measurement results.

Table VI

Measuring direction, stretching, tensile strength, fracture transition, notched impact strength limit ₂ temperature at room Kg / mm ^ Kg / mm o «temperature

^ ²

L 72.1 82.8 - 114 13.0 C 79.4 84.5 - 70 9.5

From Table VI above it can be seen that the well balanced Properties of the steel despite a treatment in. an ordinary tempering furnace for steel of sheet metal dimensions be awarded. The steel of the present invention can therefore exhibit the excellent properties regardless of the heat treatment he was subjected to exhibit.

Example VI

The steel of this example VI consists of the same chemical composition as that of example IV and has been produced under the same hot rolling conditions that were used in example III. The heat treatment of this steel was carried out at 45O ⁰ C, 500 ⁰ C and 55O ⁰ C. The Charpy test piece was the full size of the test piece. The mechanical and physical properties in the transverse direction are λ-zeroed in the following

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ORIGINAL INSPECTED

Table TII shown

Tabel. VII

Hot rolled 56.4 ^X 79.8 61 - 78 45O ° Cx30MiM 67.9 76.0 68 - 70 5OO ° Cx3OMin 66.2 74.0 72 - 74 55O ° Cx3OMin 65.9 74.6 71 - 76

excellent- tensile- -ab- breakage over- absorbed Ire it _{9 took} initial temperature- energy at stretch- Eg / mnT # temperature O ° -C limit o «Kg-m

Kg / mm ² ■

8.6

10.5 11.0 11.8

x: 0.2 ^c / o test tension

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 the ^{energy absorbed at 0} ° C. of steels which have been further treated by the hot treatment process are far better than those of a hot-rolled steel.

The steel of the present invention can have well-balanced properties, that is, high strength, excellent toughness and have good extensibility. Until this ■ With the steel according to the invention, it had been difficult to impart these properties to the same level in a steel. Of the As noted above, steel according to the invention can be used for many purposes to be used.

The steel of the present invention has excellent toughness, ductility, particularly a low fracture transition temperature and good impact strength, as well as high strength, based on the coexistence of 1.7 to 2.2 i> Mn, less than 1.0 # Cu or each Ui, 0.3 to 1.5 $> (Cu + Ni) and 0.01 to 0.10 $ Nb as the basic composition

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is. Such properties can be given to the steel not only by heat treatment at less than 680 ^° C., but also by hot rolling.

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Claims (1)

1 Claims Low-alloy steel of high tensile strength, which has excellent toughness, good ductility and high strength, characterized in that its chemical composition consists of 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 niocel, $ 0.3 to $ 1.5 (copper + nickel), $ 0.01 to $ 0.10 niobium, inevitable impurities and the balance Iron is made. ORIGINAL INSPECTED 209827/0537 Patent to s.p r ü c heinische Zusamm 1. Low excellent
height or until 0.10? Δ. ITiob exists. Steel according to claim 1, characterized in that one or more of the elements molybdenum, vanadium, titanium and zirconium in proportions between 0.1 to 0.5 $> molybdenum, 0.01 to 0.15 $> vanadium, 0.01 to 0.15 ^ 5 titanium and 0.01 to 0.10 ° / o zirconium in the chemical composition are additionally added. 3 » Steel according to claims 1 and 2, characterized in that it is hot-rolled. know 4 · A steel according to claim 1 and 2, characterized in that it is subjected to a heat treatment at less than about 680 ⁰ C, preferably about 65O ⁰ O to 45O ⁰ C after hot rolling. ORIGINAL INSPECTED 209827/0537