DE1533435C - Use of low-carbon, manganese and tungsten-containing sheet steel for deep-drawing purposes - Google Patents

Description

I 533 435

Sheet steel, which is used for automobiles and for other pressing work, must have good deep-drawing properties, Have stretchability and stretch-aging properties.

It is generally accepted that deep drawability is determined by the anisotropy value? is determined who represented by the ratio of a change in shape in width and in thickness by a tensile test will. 7 is usually represented by the following formula:

_
■

r ₉₀

where r _{0 is} the value of r in the rolling direction, r _{45 is} the value of r in the 45 ° direction to the rolling direction, and r _{90 is} the value of r in the 90 ° direction to the rolling direction. The deep-drawability is better if the value is larger, and in an ordinary unskilled steel is? about 1.3.

The stretchability indicates the degree of extensibility of a material when the material is deformed under a biaxial state of stress, and it is generally determined by the solidification ^: exponent η . The value η shows the degree of solidification, and it is practically obtained by tensile test of a material. The value corresponds to an index η approximating a stress (ff) -strain (f) curve σ = Cf "(C is a constant), and it is in a strain range of by the mean slope of a log fT-logf curve The stretchability is better when the value is larger, and in an ordinary non-killed steel the η value is about 0.33. As a standard, an Erichsen test is usually used in which a punch is inserted into a test plate on the condition that the flow of material from an outer edge portion into the deformation portion is cut off and the punch path is measured until the sample is torn off, the stretchability is better when the value is larger and in an ordinary one unkilled steel, the value is around 10 to 11.

A cone bowl test is also used to demonstrate the combined effect of the deep-drawing and to show stretching ability. The effect is better when the value is smaller, and in an ordinary unkilled steel, the value is about 38 mm.

The stretching aging property is to be understood as follows: When steel sheet is subjected to plastic deformation, an uneven pattern, called "flow figures", sometimes occurs on the sheet surface, which deteriorates the appearance of the object, and therefore a slight skin pass is usually carried out, to avoid the formation of hot characters. However, some time after the skin pass is applied, its effect is lost and the flow steps occur again when the steel sheet is deformed. This phenomenon is called stretching aging. The extent of stretching is determined z. B. by developing a pre-tension of 8% on a sample, the test piece being held at 100 ° C for 1 hour and the changed amount of the yield stress measured before and after the test (\ α ·>) . In the case of ordinary unkilled steel if the value, \ αγ is about 5 kg / mm ² , and if the value is less than 1.5 kg / mm ² , the steel is considered non-aging.

According to the present invention, a steel composed of less than 0.1% carbon, 0.01 to 0.50% Manganese, 0.002 to 0.30% tungsten and the rest of iron and impurities from the melting process consists,. for the production of cold-deformable, ductile, cold-rolled steel sheets, in particular deep-drawable cold-rolled steel sheet is used. Steels are preferred for this purpose the aforementioned composition is used, the additional 0.002 to 0.30% chromium and / or vanadium contain.

The invention is explained in more detail below with reference to the drawings, in which

Figure 1 is a graph of the relationship ■ between the tungsten content of the tungsten containing Steel sheet and the mean r-value is; B i 1 d 2 is a graph of tungsten content of the steel sheet and the hardening exponent n;

Figure 3 is a graph of the? Value of the steel sheet in the cold rolling direction in which. 45 ° direction to the cold rolling direction and in the 90 ° direction to the cold rolling direction;

Figure 4 is a graph of the relationship between the chromium and vanadium content of the steel sheet containing these components and of the? value.

In general, engineering steel and the like are used to improve wear and heat resistance of the steel added to this tungsten. However, up to now, sheet steel was used for pressing or Form punching not known, to improve the press deformability, especially the deep-drawing and Stretching ability to add tungsten to the steel.

The steel to be used according to the invention can be in a converter, a Siemens-Martin furnace or made in an electric furnace, hot and cold rolled and then annealed at a temperature which is higher than the recrystallization temperature, but lower than the Ac3 transition temperature.

It is known - that the stretching aging property. is influenced by carbon and that nitrogen in particular is present as a solid solution in the steel sheet. Accordingly, the stretching aging property of the steel can be reduced or eliminated when the nitrogen present as a solid solution is bound as a nitrite. In tungsten-steel sheet, the addition of only tungsten 'is not effective to produce the aging resistance of the steel sheet ^v, since tungsten has a weak affinity for nitrogen. Therefore, the addition of aluminum, titanium, zirconium, chromium, vanadium, boron, etc., which have a high affinity for nitrogen, can be considered.

A steel sheet with good aging resistance together with an excellent deep-drawing and Stretchability can be increased by adding 0.002 to 0.3 percent by weight of chromium (and / or vanadium) can be obtained.

The chemical compositions of the test steels, which contain various amounts of tungsten, are shown in Table I along with the chemical composition of a non-killed test steel.

Table I.

sample . C. Chemical composition ("/ Mn P. S. W. No. 0.05 Si 0.32 0.014 0.013 default *· 1 0.04 0.010 0.32 0.010 0.009 0.002 * 2 0.05 0.008 0.30 0.011 0.010 0.005 3 0.04 0.010 0.33 0.009 0.012 0.010 4th 0.06 0.010 0.39 0.010 0.008 0.014 5 0.05 0.009 0.36 0.010 0.010 0.021 6th 0.04 0.010 0.28 0.009 0.010 0.032 7th 0.05 0.008 0.35 0.010 0.009 0.051 8th 0.04 0.010 0.28 0.011 0.010 0.083 9 0.04 0.009 0.38 0.008 0.011 0.110 10 0.05 0.009 0.29 0.010 0.007 0.312 * 11 0.06 0.010 0.31 0.008 0.010 0.520 * 12 0.05 0.010 0.28 0.010 0.009 0.823 * 13 0.002 0.009 0.30 0.008 0.010 0.015 14th 0.005 0.009 0.37 0.010 0.011 0.017 15th 0.005 0.010 0.38 0.008 0.009 0.031 16 0.006 0.010 0.27 0.009 0.010 ". 0.050 17th 0.005 0.008 0.34 0.011 0.007 0.112 18th 0.004 0.010 0.29 0.009 0.008 0.323 * 19th 0.007 0.011 0.28 0.010 0.008 0.524 * 20 0.018

sample 5 • 12 15th ASTM
Grain- Anisotropic cone Ver
strengthening Erichsen- No. • 13 16 size
No. piewert T cup value exponent H worth ■ 14
[Π 17th 10 1.42 38.2 0.24 10.7 I U 5 18 10 1.17 38.5 0.22 10.5 • 19th 10 1.08 39.0 0.20 10.2 * 20 7th 1.99 one 0.31 11.3 drawn 7th 2.13 the same 0.33 11.4 7th 2.17 the same 0.32 11.3 8th 2.05 36.2 0.28 10.9 8th 1.81 36.6 0.27 10.9 8th 1.32 37.1 0.26 10.6 9 1.31 38.1 0.22 10.4

20th

Comment: (
finding.

") outside the scope of the present

The sample was melted in a vacuum or in the atmosphere, poured into an ingot and then hot-rolled at an annealing temperature or low oven temperature of 1200 ⁰ C and a final temperature of 850 or Schlußglühtemperatur ⁰ C to a 2.3 mm thick sheet. The sheet metal was then cold-rolled with a reduction in thickness of 70% and ^{annealed for 4 hours at 700 °} C. in a decarburizing and reducing atmosphere or an inert atmosphere. After these treatments, a pulling test (r value, cone cup value) and a stretching test (value, Erichsen test) were carried out on the steel sheet, the results of which are shown in Table 11. The relationships of the content of tungsten to the 7 value and the «value in the results are shown in B i 1 d 1 and 2, respectively. In the case of the "cone cup value", "withdrawn" indicates the case in which the measurement of the cone cup value is impracticable because such a good value occurs that it is below 36.

As is clear from the results, by adding 0.002 to 0.30 percent by weight Tungsten according to the present invention has the r value, the value, the cone cup value and the Erichsen value extremely improved compared with those of the standard samples. In particular, those improvements are noteworthy where the amount of tungsten addition Is 0.005 to 0.15%.

In B i 1 d 3, the r value is shown over r ₀ , r ₄₅ or r _g0 and, as can be clearly seen from the figures, the sequence r ₉₀ > r ₀ > r _{45 for the comparison material (dashed line 1)} , but in the materials (continuous lines 5 and 17) the order approximately r _go = r ₄₅ > r ₀ , although there may be a difference here in a certain range. The digits iri B i 1 d 3 denote the sample no. in table I.

As is clear from the example in B i 1 d 3, the formation of so-called "ears" is involved Pulling is extremely reduced, since the difference in the r-value in the steel used according to the invention between the maximum and minimum guideline values is not as remarkable as with the reference material!

The extent of the formation of "ears" (Jr) can be approximated by

ASTM
Grain- Tables cone -
strengthening Erichsen- sample size
No. Anisotropic cup value exponent η worth No. 8th piewert F 38.2 0.22 10.5 *1 8th 1.30 37.6 0.28 10.8. .2 8th 1.38 37.3 0.29 11.0 3 8 _t 1.51 36.6 0.30 11.0 4th 8th 1.98 one 0.32 11.4 5 2.12 drawn 8th the same , 0.31 11.2 6th 8th 2.18 the same 0.32 11.3 7th 9 2.02 37.0 0.28 10.9 8th 9 1.90 37.1 0.27 10.9 9 9 1.76 37.5 0.25 10.9 10 1.58

Ir =

^r 0

- »45

55

60 can be played back.

The difference (Ir) at an ordinary unquantified Steel is approximately 0.6, with the difference in the steel used according to the invention being 0.1 to 0.2 in the best case and even less than 0.4 in the worst case. There are several examples of this shown in Table III. ,:, -,

: - ■ Table III _; . —R ^!

Sample

No.

1
3

Anisotropy values

1.20
1.11

»45

0.99
1.61

2.00
1.72

1.30 1.51

0.61-0.20

continuation

sample ^r o. »43 Anisotropy values r Ar ' No. 1.72 2.30 2.12 -0.24 5 ■ 1.22 1.70 1.58 -0.24 10 1.61 2.13 2.05 -0.16 17th »90 2.40 1.70 2.34

It is clear that the r-value of the steel sheet in a is firmly interrelated with the structure (compare e.g. W; J. Lankford et al, »Transaction of the A. S. Μ. ", Vol. 42, [1950], p. 1197, R. L. W h i t e 1 e y et al," Sheet Metal Ind. ", Vol. 38, [1961], P. 349, etc.), and it is known that the anisotropy value r becomes larger and the steel becomes excellent . Has deep drawability if the number of crystals with the (III) plane parallel to the sample surface larger and the number of crystals with the (100) plane parallel to the surface is smaller (cf. Miller-Index C. S. Barrett "Structure of Metals" 8 [1952], Mc Graw-Hill).

Table IV shows the results of the measurement of the values for the crystal orientation in the (111) direction and in the (100) direction of the steel used according to the invention parallel to the rolling plane, expressed by the integral intensity of the X-ray diffraction reflections, from which it can be seen that the reflection of the crystals aligned in the (III) direction to the rolling plane is about 2 or 3 times stronger than that of the comparison material and that the reflection of the crystals aligned in the (100) direction of the approximately " ¹ I ₁ - to V ₃ of that of the Comparative material is, which shows the excellent mechanical properties of the steel, ... ·., · ■■

Table IV

Crystalline direction the rolling plane . Sample no. (ΠΙ) (100) ■■■ '· ι; 5.2 1.0 6th 16.2 0.3 to 10.4 0.5 ... 18.:. 14.8 0.4

As shown in the example, the range of tungsten content is in that to be used in the present invention Steel 0.002 to 0.30%, preferably 0.005 to 0.15%. When the tungsten content is less than the lower limit, the properties of the steel are almost the same as those of an ordinary one unskilled steel that does not contain tungsten, and the accuracy of the analysis becomes too great to have the effect • to be able to judge its addition. Furthermore, if the content is larger than the above Limit, whose bad influences on the mechanical properties are noticeable. So z. B. the The tensile strength is greater and the elongation less, "which is not desirable. Accordingly, the am most preferred range of tungsten content from 0.005 to 0.15%. . ,. ;

In the case of ordinary mild steel with 0.03 to 0.1% carbon, the carbon content can be reduced by treating the steel in a known manner in a vacuum. It is confirmed that a remarkable amount of carbon is bound by tungsten.

However, the mechanical properties of the steel for machinability are deteriorated, when the carbon content is greater than 0.1%.

The carbon content can also be reduced or controlled by adjusting the steel sheet after the Rolls for decarburization is annealed.

Furthermore, the content of manganese in steel has a close relationship with the content of sulfur in the case the "red brittleness", and usually the

An additional amount of manganese about ten times greater than that of sulfur taking into account the segregation. On the other hand, because manganese hardens the material and its mechanical properties deteriorate, there is an upper limit for its addition amount, and its amount is 0.25 to 0.50% in ordinary mild steel.

However, as shown in Table V, appears even in the sample where the sulfur content is low and the additional amount of manganese is less than that in the ordinary mild steel mentioned above, the effect of tungsten is evident, and the success of the present invention can be seen. That is, the effect of tungsten is not decreased even in the case of 0.01 to It contains 0.50% manganese.

Table V

sample
No. -C- ■ -. ' Chen
Si niche combination
Mn mmensetzui
P. lg (%)
S. - 'ASTM
Grain-
size
No. 7 value Mechanical E.
Cone-
cup value properties
Ver
strengthening
exponent Erichsen-
worth vioi 0.05; 0.008 0.05 0.008 0.005 0.020 7th 1.40 37.9 • 0.23 10.9 102 0.04 0.008 0.04 0.009 0.005 0.031 7th 2.20 moved in 0.32 11.4 103 0.003 0.009 0.04 0.009 0.004 0.083 6th 2.15 .. moved in 0.31 11.5. 104 0.006 0.008 0.05 0.010 0.006 8th 1.80 36.8 0.27 11.1.

The chemical compositions and the results in the case of the. Adding tungsten along with Chromium and / or vanadium to improve the stretch aging property are shown in Table VI.

Table VI

C. Si ' Chemical composition (%) Mn P. S. W. _# Cr V Mechanical properties "r-value Ver sample strengthening No. 0.04 0.008 0.03 0.011 0.008 0.030 0.025 I σ μ kg / mm ² 1.82 exponent 0.03 0.010 0.03 0.008 . 0.007 0.032 0.112 - 1.54 0.30 201 0.03 0.011 0.03 0.010 0.008 0.028 0.230 - 1.0 1.46 0.32 202 0.04 0.009 0.03 0.009 0.006 0.030 - 0.026 0.5 1.88 0.33 203 0.03 1.008 0.04 0.011 0.005 0.031 - 0.132 0.2 1.60 0.31 204 0.04 0.010 0.03 0.010 0.008 0.029 - 0.225 0.4 1.45 0.31 205 0.0 0.32 206 0.0

The methods of treating the specimens in the above case are the same as those described above Process except that the melting under atmospheric pressure and the final tempering was carried out in an argon atmosphere.

The results confirmed that the stretching aging property of the steel was remarkably improved, although the? Value and the solidification exponent η of the steel were decreased by adding chromium and vanadium together with tungsten. However, although even the 7 value and the solidification exponent η can be reduced by adding them, it is clear that they are considerably better than those of an ordinary unkilled steel sheet.

On the contrary, it was observed that the "r value changed as in B i 1 d 4 when the content of chromium or vanadium was kept constant (about 0.20%) and the content of tungsten was changed. The tendency is similar to the case in which tungsten was added alone in Figure 1. The r-value is lower than that of the case of the sole addition of tungsten, but the value is considerably better than that of an ordinary unskilled steel.

Mild steel is usually hot rolled, cold rolled, and then tempered on a strip mill to be deformed into an article. In the case where the steel of the present invention was subjected to similar treatments, it was found that the following progress was made. In general, in order to obtain excellent deep drawability of the final product, it is desirable that the finishing temperature of rolling in ordinary hot rolling is higher than the transition temperature (Ac ₃ ). However, this is not necessary in the case of the steel to be used according to the invention.

Furthermore, the degree of cold-rolling deformation of the steel to be used according to the invention is preferably 40 to 85% and particularly preferably 60 to 80%. The tempering after cold rolling is carried out at a temperature higher than the recrystallization temperature but lower than the transformation temperature (Ac ₃ ), and it is effectively carried out in an inert atmosphere or in a decarburizing atmosphere. The above facts show that the steel used in the present invention gives a steel sheet excellent in deep drawability.

Claims (3)

Patent claims: 1. Use of steels consisting of less than 0.1% carbon, 0.01 to 0.5% manganese, 0.002 to 0.3% tungsten, the remainder iron and impurities from the melting process cold-deformable, stretchable cold-rolled steel sheets, especially deep-drawable, cold-rolled steel sheet. 2. Use of steels with a composition according to claim 1, which additionally Containing 0.002 to 0.3% chromium and / or vanadium for the purpose according to claim 1. 3. Use of steels according to claim 1, which contain 0.005 to 0.15% tungsten, for the Purpose according to claim 1. 1 sheet of drawings 20V 609/103