DE2219456A1 - Non-tempered steel with high tensile strength and excellent cold workability - Google Patents

Description

The present invention relates to a non-quenched and tempered steel having high tensile strength, excellent machinability and more particularly has high tensile strength or yield strength along with this machinability.

A high tensile steel with a tensile strength of 60 kg / mm,

2 2

70 kg / mm or 80 kg / mm has already been developed and used in practice. But it is a fact that few Steels were developed with the aim of making Kait machinable ^ · and, in particular, no steel has excellent cold workability along with high

2 2

Tensile strength of 70 kg / mm or 80 kg / mm is shown. But when a steel would be developed that has both this high strength and excellent machinability, there would be innumerable possible uses, e.g.

209845/0885

as a crane boom, as a truck frame, as a container ■ Material or as building material for automobiles and vehicles.

In fact, the most beneficial properties required for the above uses are as follows:

1. high strength, 2. good cold workability,

3. good flat surfaces, 4. good weldability,

5. high impact strength; and 6. low cost.

In order to meet the above conditions, the known quenching and heat treatment has usually been carried out to

2 2 Ί

the high tensile strength of 60 kg / mm, 70 kg / mm or 80 kg / mm ' to obtain. However, such steel generally has a tendency, in spite of good weldability and excellent Impact properties become poor in terms of cold workability and surface flatness. In particular, the cost becomes high. This tendency increases as the strength of the steel decreases. Therefore does not need it should be emphasized that the steels are extremely unsuitable for the purposes mentioned above, i.e. for crane booms, Truck frames, etc. It is well known that cold workability deteriorates as strength increases. A steel which has excellent cold workability has not yet been able to be supplied at a low cost and also has high strength. The investigations carried out with the The aim was mainly to improve weldability and impact properties.

The aim of the invention is to develop a steel which eliminates the difficulties mentioned above. The license plate of the invention resides in the composition of the low C-Nb-Ti-Zr system. That is the chemical composition of the steel according to the invention consists essentially of 0.05 to 0.15% C and a simultaneous presence from 0.01 to 0.1% Nb, 0.03 to 0.15% Ti and 0.05 to 0.15% Zr. Other elements are 0.1 to 1% Si,

209845/0885

~ ³ ~. 22 Ί 9456

0.8 to 1.8% Mn and 0.01 to 0.1% dissolved Al in the steel contain. According to the invention, one or more elements from the group comprising 0.1 to 0.5% Cr, 0.1 to 0.5% Cu, 0.1 to 0.5% Mo, 0.03 to 0.2% V and 0.1 to 0 , Contains 5% Ni, further be added · The steel with the above composition shows excellent mechanical properties that the meet the above requirements, as they are mentioned under 1 to, if he is without any remuneration treatment is rolled.

The invention provides a non-tempered high tensile strength Steel, which at the same time has a high tensile strength has excellent cold workability. In addition, this steel shows a good flat design of the surface, a good weldability and high impact strength.

In the following the invention is illustrated by means of embodiments explained in more detail, reference being made to the accompanying drawing.

Fig. 1 shows the changes in impact properties with the content of Ti or Zr.

Fig. 2 graphically shows the relationship between the content of Ti or Zr and the notch elongation.

Fig. 3 graphically shows the relationship between tensile strength and notch elongation.

In general, the effect of adding Nb, Ti or Zr is well known to steel in terms of quality. Accordingly, a steel containing Nb, Ti or Zr has already been delivered and put into practice used. For example, a typical steel in "Stahl und Eisen" 90 (1970), issue 22, pages 1255 to 1262, as steel of the Nb-Zr system or in "Thyssenforschung", 2 (1970), volume 3, pages 86 to 95, as steel of the Ti-Nb system specified. However, if these references in detail

2 0 9 8 Λ S / 0 S 8 5

are examined, it is clear that the effects are far from the object of the invention. On the contrary that substantial coexistence of the above-mentioned C, Nb, Ti and Zr in the steel is an indispensable requirement. If one of these elements is missing, the steel can achieve the desired mechanical properties in the rolled state not exhibit without a compensation treatment.

According to the invention, such a steel consists of the following composition:

C: 0.05 to 0.15% Si: 0.1 to 1%

Mn: 0.8 to 1.8% Nb: 0.01 to 0.1%

Ti: 0.03 to 0.15% Zr: 0.05 to 0.15%

dissolved Al: 0.01 to 0.1%
Remainder: iron and unavoidable impurities.

The above composition is the basic composition. If necessary, one or more elements from the following group will be added further.

Cr: 0.1 to 0.5% Cu: 0.1 to 0.5%

Mo: 0.1 to 0.5% V: 0.03 to 0.2%.

Ni: 0.1 -I to 0.5%

In this case, the mechanical properties are further improved. As a result, the desired properties for a relatively thick steel can be easily obtained.

The reasons why the levels of each of these elements are limited to the above ranges are mentioned below.

Less than 0.05% C does not give the steel the required strength and more than 0.15% C makes it cold workable bad.

209845/088 $

Si plays a role in adjusting strength other than its deoxidizing effect. However, if the Si content is over 1%, the toughness of the steel becomes poor.

If less than 0.8% Mn; is present, the required Strength cannot be obtained, and if it is more than 1.80%, the crystal structure formed becomes unstable and toughness becomes poor.

Nb is added to achieve the required strength. However, if less than 0.01% is added to I ₁ , the steel cannot be given this strength, and if an Nb content of more than 0.1% is added, the effect of the addition is saturated, so that the addition is useless will.

Ti is added to improve strength while also playing a role in regulating formation of sulfide in the steel »The addition of less than 0.03% Ti shows little effect and the addition of more than 0.15% Ti makes the machinability and impact property suddenly bad ..

Zr is mainly added to control the formation of this sulfide and the chalk workability and impact properties to improve. However, in the case of less than 0.05% Zr, there is improvement in cold workability hardly expected, and in the case of more than 0.15% Zr, on the other hand, the impact properties become inferior, while the Cold workability remains largely as it is.

Dissolved Al is required for deoxidation, and around to obtain a good effectiveness of the added Ti and Zr '. Such effects can occur with less than 0.01% dissolved Al does not occur and more than 0.1% dissolved Al deteriorates the flowability and purity of the filling in the oven.

209845/0885

According to the invention, one or more of the elements Cr, Cu, Mo, V and Ni continues to have the above-mentioned basic composition added when necessary to ensure this strength. If in this case the salary of each of the elements of Cr, Cu, Mo, Ni is lower than 0.1% or that of V is lower than 0.03% can ensure the strength can hardly be expected, and if the content of each of the elements Cr, Cu, Mo and Ni is over 0.5% or that of V is over 0.2%: is, only 'a minor effect is to be expected for the resulting increase in costs.

20984 5/0885

Table I.

Steel C Si Mn PS Nb Ti Zr dissolved. Al Other Cäq ^xx

A ^x 0.09 '0.26 1.03 0.014 0.018 0.027 0.13 - 0.052 - 0.27

B ^x 0.18 0.20 .1.10 0.013 0.008 - 0.10 0.10 0.038 - '0.37

C ^X 0.10 0.21 1.25 0.016 0.010 0.009 0.18 0.08 0.025 - 0.32

D ^x 0.18 0.23 1.27 0.011 0.008 0.035 0.08 0.07 0.038 - '0.40

■ E 0.12 0.26 0.85 0.013 0.020 0.010 0.09 0.10 0.023 - 0.27

F 0.09 0.32 1.24 "0.015 0.017 0.035 0.08 0.06 0.052 - 0.31

G 0.11 0.32 1.26 0.016 0.008 0.035 0.12 0.07 0.064 - 0.33

H 0.10 0.28 1.22 0.016 0.006 0.040 0.06 0.08 0.082 - 0.31

I '0.13 0.27 1.15 0.021 0.017 0.023 0.08 0.07 0.066 - 0.33

NJ J 0.09 0.52 1.35 0.012 0.006 0.043 0.08 0.11 0.042 _Mq - 0.33

S K 0.11 0.48 1.30 0.010 · 0.004 0.038 0.10 0.13 0.029 0.22 0.40

Jj L 0.10 0.63 1.40 0.015 0.008 0.032 0.06 0.07 0.030 ^ ₂₁ q ^U ₂₈ . 0.40

7.7

^ M 0.08 0.50 1.68 0.018 0.005 0.046 0.08 0.12 0.042 J ^0. , S. ^u _or . 0.42

oo N 0.10 0.38 .1.22 0.015 0.010 0.030 0.06 0.08 0.038 Λ _ηΟ {[* J? ¹¹ 0.33

oo υ, Ub υ, ^ j Uj ^ d '

Note: x steel A to D comparative steels

'Steel E to ΪΪ steels according to the invention'

xx Cäq »C + | wn + ₂ ^ Si + ₄ ^ Ni + i Cr + ^ Mo + ^ V

Table II

stole

Tensile properties cold bending
Machinability

Kerchiageigen- ' stocks

Thickness wrapped! - Stretch mm petratur limit ⁰ C kg / mm

Tensile bending

speed _? "180 ° kg / mm 0.5 t notch elongation fracture overtaking transition temperature% ⁰ C

consumed energy at 0 ⁰ C kg - m

A. 6.0 B ' 6.0 C. 6.0 D. 6.0 ro
CD E. 6.0 to F. 6.0 OO G 6.0 cn H 8.0 O I. 8.0 co 7th CO J 8.0 K 8.0 L. 10.0 M. 10.0 N 10.0

610
640
590
510
25th
530
520
560
590
590
40
590
540
560

58.7 52.4 64.2 75.7 58.6 71.3 73.4 64.4 59.4 68.3 72.8 62.3 72.5 59.9

66.6 61.8 74.5 82.9 65.5 80.1 81.3 73.0 65.4 75.4 82.5 72.8 81.6 65.8

If Il ti

Micro crack

Il It It 2.3
3.2
3.5
4.4
10.2
5.7
6.3
8.4
7.3
7.2
6.8
8.7
6.9
8.9

+ 100

+ 40 + 30

- 10

- 70

- 7th

- 20th

- 38

- 32

- 30

- 18th

- 35

- 28

- .65

0.3 0.8

1.1 2.2 4.4 2.2 3.0 4.0 3.5 4.3 3.1 4.0 3.8 4.5

Note: Charpy test piece: 5mm 10mm 55mm

The sulfur content is not restricted according to the invention. However, it has been found that less than 0.01% S is very high is effective for improving cold workability. Especially when a tensile strength greater than

2 70 kg / mm collected agent.

70 kg / mm is required, the S content is one of the suitable

As mentioned above, the substantial coexistence of Nb, Ti and Zr is one of the indispensable requirements. If one of these three elements is not added, the steel can have the required mechanical properties cannot be given in the as-rolled condition without a tempering treatment. These properties are therefore based on the geometric effect of these three elements. The effect of adding Ti or Zr to these three elements is evident in the Figs. 1 and 2 shown. Both figures show the effects of further adding Ti to Nb + Zr, which is in the area of above amount is. The effects of further adding Zr to Nb + Ti are similar in these figures shown.

From Fig. 1 it can be seen that the content of the invention is very effective and the most suitable. That is, when the Ti content is over 0.15%, both the fracture transition temperature will be as well as the energy consumed at OC, which is measured in the direction transverse to the rolling direction, "very bad. When the Zr content is lower than 0.05%, is the fracture transition temperature is very high and the absorbed energy is not improved, and if this content is above 0.15%, the energy consumed is reduced in the same way as it is less than 0.05% shows.

In Fig. 2, the changes in the notch elongation, which corresponds very well to the cold workability, are a function of

209845/0885

shown the Ti or Zr content. The ratio of Nb, Ti and Zr content is the same as that of Fig. 1. When the Ti content is over 0.15%, the notch elongation decreases abruptly. If it is lower than 0.05%, the notch elongation becomes very poor, and if this content is around 0.05% is, the notch elongation is improved and shows little change even if the content increases.

Fig. 3 shows the relationship between tensile strength and. the notch elongation. According to the relationship shown in Fig. 3, it is apparent that the inventive Steel is far superior to the known steel.

The following are examples based on this invention. These examples are compared with known ones Steels shown.

Manufacturing conditions:

Chemical composition: see Table I Steel production:

Furnace used: basic oxygen furnace of 85 t after the usual deoxidizing, one of the alloys: Fe-Nb, Fe-Ti and Fe-Zr or Si-Zr

Hot rolling after the usual casting and slab roughing: Rolling mill used: Tandem hot rolling mill Hot rolling conditions: usual
Final thickness: 6.0 mm to 10.0 mm
Cradle conditions: usual

The mechanical properties of the above steels are in Table II shown.

From the above Tables I and II it is clear that both the strength, i.e. the tensile strength and the yield point, as well as cold workability, i.e. bending properties and the notch elongation, and the notch impact properties, i.e. the fracture transition temperature and the energy consumed

209845/0885

is far better than with the known comparison steels.

ρ That is, the tensile strength shows values of 60 kg / mm,

2 2

70 kg / mm or 80 kg / mm and the yield point is also

2 if without difficulties over 45 kg / mm and shows values

2 2

of 60 kg / mm. and 75 kg / mm. The cold workability is excellent · The carbon equivalent shown in Table I. (C.eq) is low and shows good weldability at. At the same time it can be seen that the strength of the rods, which "contain less than 0.01% S is higher than that of the other steels * The production costs are of course low, because the steel is in the as-rolled condition. It is possible to improve this strength if one or more the elements Cr, Cu, Mo, V or Ni can also be added. It should be noted, however, that the reason that the above-mentioned excellent mechanical properties can be obtained in the as-rolled condition on the is based on the substantially simultaneous presence of Nb, Ti and Zr.

20 9-8 45/0885

Claims (3)

Patent to sayings 1. Non-tempered high tensile steel with excellent Cold workability and a tensile strength of more than 2 60 kg / mm or a yield point greater than 45 kg / now . as rolled, characterized by the following Composition: 0.05 to 0.15% C, 0.1 to 1% Si, 0.8 to 1.8% Mn, 0.01 to 0.1% -Nb, 0.03 to 0.15% Ti , 0.05 to 0.15% Zr, 0.01 to 0.1% dissolved Al, unavoidable impurities and remainder Fe. 2. Non-tempered high-tensile steel according to claim 1, characterized in that one or more of the following elements is further added: 0.1 to 0.5% Cr, 0.1 to 0.5% Cu, 0.1 to 0.5% Mo, 0.03 to 0.2% V and 0.1 to 0.5% Ni. 3. Non-tempered high-tensile steel according to claim 1 or 2, characterized in that the sulfur content is less than 0.01%. 209845/0885