METHOD FOR WELDING COATED STEEL PLATES

Abstract

The disclosure relates to a method for welding steel sheets made of steel materials coated with an aluminum silicon anti-corrosion layer, in particular CMnB and CMn steel materials that can be hardened using the quench hardening method, wherein a welding filler rod is used in the welding of the sheets and the welding filler rod has the composition: C=0.80-2.28% C base material, Cr=8-20, Ni<5, Si=0.2-1, Mn=0.2-1, Mo<2, with the rest being composed of iron and unavoidable smelting-related impurities and with all indications expressed in % by mass.

Claims

1. A method for welding steel sheets made of steel materials coated with an aluminum silicon anti-corrosion layer, in particular CMnB and CMn steel materials that can be hardened using the quench hardening method, wherein a welding filler rod is used in the welding of the sheets and the welding filler rod is of the following composition: C=0.80 -2.28% C base material Cr=8-20% Ni<5% Si=0.2-3% Mn=0.2-1% optionally Mo<2% optionally V and/or W totaling <1% residual iron and unavoidable smelting-related impurities, with all indications expressed in % by mass.

2. The method according to claim 1, wherein a welding wire is used having a nickel content below 1% by mass.

3. The method according to claim 1, wherein the welding wire has a molybdenum content of 0.5 to 2% by mass.

4. The method according to claim 1, wherein the sheets are laser butt welded.

5. The method according to claim 1, wherein the weld advancing speed is 4 to 15 m/min.

6. The method according to claim 1, wherein gap widths of 0 to 0.3 mm, in particular 0 to 0.1 mm, are set.

7. The method according to claim 1, wherein the carbon content of the filler rod is set to C=0.88 to 1.51C base material, preferably C=0.90 to 1.26C base material, and particularly preferably C0.90 to 1.17C base material.

8. The method according to claim 1, wherein for the base material, a steel is used, which is a boron manganese steel that can be hardened by means of an austenitization and quench hardening process, particularly preferably to a tensile strength of greater than 900 MPa, and in particular, a steel from the group of CMnB steels is used, for example 22MnB5 or 20MnB8.

9. The method according to claim 1, wherein a steel of the general alloy composition (in % by mass) is: TABLE-US-00004 carbon (C) 0.03-0.6 manganese (Mn) 0.3-3.0 aluminum (Al) 0.01-0.07 silicon (Si) 0.01-0.8 chromium (Cr) 0.02-0.6 nickel (Ni) <0.5 titanium (Ti) 0.01-0.08 niobium (Nb) <0.1 nitrogen (N) <0.02 boron (B) <0.02 phosphorus (P) <0.01 sulfur (S) <0.01 molybdenum (Mo) <1; and residual iron and smelting-related impurities is used as the base material.

10. The method according to claim 9, wherein a steel of the general alloy composition (in % by mass) is: TABLE-US-00005 carbon (C) 0.03-0.36 manganese (Mn) 0.3-2.00 aluminum (Al) 0.03-0.06 silicon (Si) 0.01-0.20 chromium (Cr) 0.02-0.4 nickel (Ni) <0.5 titanium (Ti) 0.03-0.04 niobium (Nb) <0.1 nitrogen (N) <0.007 boron (B) <0.006 phosphorus (P) <0.01 sulfur (S) <0.01 molybdenum (Mo) <1; and residual iron and smelting-related impurities is used as the base material.

11. The method according to claim 9, wherein a steel of the alloy composition C=0.22, Si=0.19, Mn=1.22, P=0.0066, S=0.001, Al=0.053, Cr=0.26, Ti=0.031, B=0.0025, N=0.0042, residual iron, and smelting-related impurities is used as the base material, with all of the above indications expressed in % by mass.

12. The method according to claim 9, wherein the filler rod has a carbon content in the range from 0.024 to 1.086% by mass, particularly preferably 0.186 to 0.5082% by mass, and more particularly preferably between 0.20 and 0.257% by mass.

13. A sheet bar comprising a first steel sheet and a second steel sheet, which are welded to each other using a method according to one of the preceding claims.

14. The sheet bar according to claim 13, wherein the steel sheets have different alloy compositions.

15. A press hardened component, wherein a sheet bar according to claim 13 is subjected to a hot forming or cold forming and a subsequent press hardening.

Description

[0034] The disclosure will be explained below by way of example based on the drawings. In the drawings:

[0035] FIG. 1 shows a cross-section through a welding seam between two sheets of different thicknesses; a welding method according to the prior art has been used and a welding seam with scale formation and decarburization is visible;

[0036] FIG. 2 shows a polished cross-section of the decarburized zone in a welding seam according to the prior art and a welding seam according to the disclosure;

[0037] FIG. 3 shows the hardness curve within a welding seam; the welding seam is shown in a micrograph with the hardness sample points;

[0038] FIG. 4 shows an overview of the strength levels of welding seams with different gap widths and different wire materialsboth according to the disclosure and not according to the disclosureand different weld advancing speeds;

[0039] FIG. 5 shows an overview of the compositions of the filler rods composed of the wire materials according to the disclosure and not according to the disclosure that are shown in FIG. 4.

[0040] According to the disclosure, the welding of two sheets of different thicknesses, preferably CMn steels, particularly of a hardenable CMnB steel, in particular 22MnB5 steel materials, is carried out using a welding filler rod. In particular according to the disclosure, aluminum silicon-coated steel sheets with >900 MPa tensile strength after hardening are joined in an ablation-free way by welding.

[0041] The preferred chemical alloy of the filler rod or filler wire consists of the following elements:

C=0.80-2.28C base material
Cr=8-20% by mass
Ni5, preferably 1% by mass
Si=0.2-3% by mass
Mn=0.2-1% by mass
optionally Mo=<2, preferably 0.5-2.5% by mass
optionally V and/or W totaling <1% by mass
residual iron and unavoidable smelting-related impurities

[0042] Preferably, the carbon of the filler rod or filler wire is adjusted as follows or more precisely, the filler rod has the following composition:

C=0.88 to 1.51C base material
Cr=10-18% by mass
Ni=1% by mass
Si=0.3-1% by mass
Mn=0.4-1% by mass
Mo=0.5-1.3% by mass
V=0.1-0.5% by mass
W=0.1-0.5% by mass
residual iron and unavoidable smelting-related impurities
Particularly preferably:
C=0.90 to 1.26C base material
Even more particularly preferably:
C=0.90 to 1.17C base material

[0043] As has already been explained above, aluminum silicon-coated sheets with a layer of 60 g/m.sup.2 per side composed of a 22MnB5 are joined, wherein for purposes of the tensile specimens, 1.5 mm sheets were joined. Such sheets were provided with welded edges and were welded with a Trumpf 4006 welding laser (4.4 kW) with a focal length diameter of 0.6 mm.

[0044] The base material is a steel of the following general alloy composition (in % by mass):

TABLE-US-00001 carbon (C) 0.03-0.6 manganese (Mn) 0.8-3.0 aluminum (Al) 0.01-0.07 silicon (Si) 0.01-0.8 chromium (Cr) 0.02-0.6 nickel (Ni) <0.5 titanium (Ti) 0.01-0.08 niobium (Nb) <0.1 nitrogen (N) <0.02 boron (B) 0.002-0.02 phosphorus (P) <0.01 sulfur (S) <0.01 molybdenum (Mo) <1 residual iron and smelting-related impurities.

[0045] This means that the carbon content of the filler rod can be in the range from 0.024 to 1,086% by mass.

[0046] Naturally, the carbon content of the filler rod is selected specifically based on the carbon content of the base material that is present in production.

[0047] Preferably, the base material can have the following alloy composition:

TABLE-US-00002 carbon (C) 0.03-0.36 manganese (Mn) 0.3-2.00 aluminum (Al) 0.03-0.06 silicon (Si) 0.01-0.20 chromium (Cr) 0.02-0.4 nickel (Ni) <0.5 titanium (Ti) 0.03-0.04 niobium (Nb) <0.1 nitrogen (N) <0.007 boron (B) 0.002-0.006 phosphorus (P) <0.01 sulfur (S) <0.01 molybdenum (Mo) <1 residual iron and smelting-related impurities.

[0048] Specifically, for example, the 22MnB5 can have the following composition:

C=0.22

Si=0.19

Mn=1.22

P=0.0066

S=0.001

Al=0.053

Cr=0.26

Ti=0.031

B=0.0025

N=0.0042,

[0049] residual iron and smelting-related impurities, with all indications expressed in % by mass.

[0050] With this specific composition of the base material, the carbon content of the filler rod can lie in the range from 0.186 to 0.5082% by mass, particularly preferably between 0.216 and 0.257% by mass.

[0051] In the course of the trials the process parameters were varied as follows: [0052] Trumpf 4006 welding laser 4.4 kW (focal length =0.6 mm) [0053] Variation of process parameters: [0054] v.sub.w=4-7.5 m/min [0055] V.sub.d=2.3-6.4 m/min [0056] gap=0/0.1 mm [0057] hardening [0058] furnace temperature: 930 C. [0059] furnace dwell time: 310 sec [0060] transfer time: approx. 6 sec [0061] water-cooled sheet die
where v.sub.w is the weld advancing speed and V.sub.d is the rod feed speed.

[0062] Then the hardening of the samples was carried out at 930 C. furnace temperature and with a furnace dwell time of 310 seconds. The transfer time between removal from furnace and insertion into a water-cooled sheet die was 6 seconds. The welding with welding wires according to the disclosure resulted in welding seams shown at the bottom in FIG. 2. A homogeneous structure is apparent, without a decarburized zone as shown at the top in FIG. 2, which shows a welding seam according to the prior art. Such a welding seam according to the prior art is also shown in FIG. 1 in which a clear scale formation and an underlying decarburized zone are visible. The scale formation on the welding seam reduces the load-bearing cross-section and the decarburization of the welding seam likewise reduces the load-bearing cross-section so that in this case, the tensile specimens tear in the vicinity of the welding seam. The goal, however, must be for the tensile specimens to not tear at the welding seam, but rather in the base material, thus ensuring that it is the base material that determines the mechanical properties.

[0063] FIG. 3 shows the hardness curve in a welding seam that is welded with a filler wire according to the disclosure; the hardness recording points are visible on the right in FIG. 3 and the corresponding hardness curve is shown on the left in FIG. 3. It is clear that there are indeed slight fluctuations in the hardness curve, but these have values in the upper range and in no way decrease compared to the edge zones or the base material. FIG. 4 shows the averages of tensile specimens; different wire materials and different advancing speeds as well as different gap widths were used.

[0064] The wire materials 1 and 7 in this case were assessed to be unsuitable whereas the wire materials 3, 6, and 8 have the composition according to the disclosure and have the lowest range of fluctuation throughout the entire process and all of the processing possibilities. It is noteworthy that the samples welded with the wire materials according to the disclosure greatly exceed the minimum strength specified by most users. The wire compositions are summarized in FIG. 5.

[0065] The following compositions of wire material were tested (see FIG. 5)

TABLE-US-00003 Wire no. [mm] C Si Mn Cr Mo Ni W V 1 1.2 0.12 0.8 1.9 0.45 0.55 2.35 not according to disclosure 3 1.2 0.2 0.65 0.55 17 1.1 0.4 according to disclosure 6 1.2 0.5 3 0.5 9.5 according to disclosure 7 0.7 0.25 0.3 0.5 1.45 0.4 3.6 0.2 not according to disclosure 8 0.8 0.2 0.5 0.5 12 1 0.1 0.5 0.35 according to disclosure
All values in % by mass, residual iron and unavoidable smelting-related impurities.

[0066] The wires with the numbers 3, 6, and 8 in this case exhibited particularly advantageous properties, but wire number 6 exhibited the fracture pattern shown and a possible susceptibility to brittle fracture due to the somewhat elevated carbon and silicon content. All in all, however, the results achieved with all of these wires were assessed as satisfactory.

[0067] As mentioned previously, these strength value results are shown in FIG. 4

[0068] With the disclosure, it is advantageous that without a costly ablation step that cannot be reliably controlled, aluminum silicon-coated hardenable steel sheets, particularly composed of a hardenable boron manganese steel, especially a steel from the family of MnB steels, preferably a 22MnB5 or 20MnB8, can be welded to each other without the welding seam constituting a weak point.

[0069] Naturally, however, the disclosure can also be used for less high-strength steel alloys like so-called soft partner materials such as 6Mn6, 6Mn3, or 8MnB7.