Methods for joining two blanks

Abstract

Methods for joining a first blank and a second blank, wherein the first blank and the second blank include a steel substrate with a coating including a layer of aluminum or an aluminum alloy. The method includes selecting a first portion of the first blank to be joined to the second blank, and selecting a second portion of the second blank to be joined to the first portion, and welding the first portion to the second portion. The welding includes using a laser beam and an arc welding torch, wherein the arc welding torch includes a wire electrode, wherein the wire electrode is made of a steel alloy including gammagenic elements, optionally a stainless steel alloy including gammagenic elements and displacing both the laser beam and the arc welding torch in a welding direction, and wherein in the welding direction, the arc welding torch is positioned in front of the laser beam.

Claims

1. A method for joining a first blank and a second blank, the method comprising: selecting a first portion of the first blank to be joined to the second blank, and selecting a second portion of the second blank to be joined to the first portion, wherein the first blank and the second blank comprise a steel substrate with a coating comprising a layer of aluminum or an aluminum alloy, welding the first portion to the second portion with a laser beam and an arc welding torch, wherein the arc welding torch comprises a filler wire electrode, and the filler wire electrode is made of a stainless steel alloy comprising iron, and also comprises, in weight percentages, 0%-0.3% of carbon, 0%-1.3% of silicon, 0.5%-7% of manganese, 5%-22% of chromium, 6%-20% of nickel, 0%-0.4% of molybdenum, and 0%-0.7% of niobium, and displacing both the laser beam and the arc welding torch in a welding direction, the first portion and the second portion of the blanks in a weld zone being melted during the welding, wherein in the welding direction, the arc welding torch is positioned in front of the laser beam.

2. The method according to claim 1, wherein the arc welding torch has an angle of 10-35 with respect to a plane perpendicular to the first portion.

3. The method according to claim 2, wherein the arc welding torch has an angle of 14-30 with respect to a plane perpendicular to the first portion.

4. The method according to claim 1, wherein the laser beam has an angle of 0-15 with respect to a plane perpendicular to the first portion.

5. The method according to claim 4, wherein the laser beam has an angle of 4-10 with respect to a plane perpendicular to the first portion.

6. The method according to claim 1, wherein the first and second blanks are butt-jointed, the first portion being an edge of the first blank and the second portion being an edge of the second blank.

7. The method according to claim 1, wherein the steel substrate is a boron alloyed hardenable steel.

8. A method for forming a product comprising: forming a third blank by joining a first blank and a second blank according to the method of claim 1, heating the third blank, and hot deforming and quenching the heated third blank.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Non-limiting examples of the present disclosure will be described in the following, with reference to the appended drawings, in which:

(2) FIGS. 1a and 1b schematically illustrate a first example of joining two blanks;

(3) FIGS. 2a-2b schematically illustrate an example arrangement for a laser beam and an arc welding torch according to one implementation;

(4) FIGS. 3a and 3b schematically illustrate the effect of a filler material on a resulting microstructure after welding; and

(5) FIGS. 4a and 4b illustrate the distribution of filler material throughout a weld depending on the relative positions of a laser beam and an arc welding torch.

DETAILED DESCRIPTION OF EXAMPLES

(6) FIGS. 1a and 1b schematically illustrate a first example of a method of joining a first blank A with a second blank B. A first portion or region Al of the first blank is to be joined to a second portion or region B2 of the second blank. In this example, the two blanks are to be butt-joined, i.e. an edge-to-edge welding.

(7) In this example, both blanks A and B may be of coated steel, such as e.g. Usibor 1500P. Both blanks comprise a steel substrate 1 upon which a coating 2 is provided. The coating applied is aluminum-silicon (Al87Si10Fe3). Due to the process of application of the coating, the resulting coating has a metal alloy layer 4 and an intermetallic layer 3.

(8) FIG. 1b further illustrates the method of joining according to an example of hybrid laser welding. Schematically illustrated is a laser welder 20 having a laser head 21 from which the laser beam exits. Also schematically illustrated is an arc welding torch 30. An arc welding torch may comprise an electrode wire 32 and a shielding gas may exit the nozzle 31 as schematically illustrated by an arrow.

(9) In the hybrid process, the arc welding torch and laser beam collaborate to form a weld. In the arc welding torch, an electric arc may thus be created between an electrode wire and the portions. This arc melts the electrode wire as well as portions of the blanks. As the electrode wire, sometimes also called a filler wire, melts, any gap between the blanks may be filled and a weld may be created. On the other hand, the laser beam is focused to create a spot with a high energy density. When the laser beam hits the first and the second portion this spot may be heated up to vaporization temperature, creating a vapor cavity in the portions to be welded due to the escaping metal vapor. Such a vapor cavity may be called a keyhole, and may enable a deep welding effect along the entire thickness of portions to be welded.

(10) It may be seen that in this case, there is no need for removing the coating of the steel substrates prior to welding, thus simplifying and speeding up manufacture. This may bring about a substantial cost reduction. At the same time, an electrode wire or filler wire of suitable composition may ensure that good mechanical properties are obtained after the standard heat treatment for Usibor and after hot deformation processes such as hot stamping.

(11) A standard treatment for Usibor blanks would be to heat the obtained blank in e.g. a furnace to bring about (among others) austenization of the base steel. Then the blank may be hot stamped to form e.g. a bumper beam or a pillar. During rapid cooling after a hot deformation, martensite, which gives satisfactory mechanical characteristics, may thus be obtained. The standard treatment is not affected in any manner by the methods of joining proposed herein. In particular, thanks to the elements of the electrode wire that are supplied into the weld zone, a martensite structure can also be obtained in the area of the weld, in spite of the presence of aluminum.

(12) FIG. 2a schematically illustrates a first blank A is to be joined to a second blank B along a weld seam C, wherein the arc welding torch 30 is positioned in front of the laser beam 20 according to the welding direction.

(13) FIG. 2b schematically illustrates a lateral view of the FIG. 2a. The welding torch 30 may have an angle between 10 and 35, optionally between 14 and 30, while the laser beam 20 may have an angle between 0 and 15, optionally between 4 and 10, in relation with a plane perpendicular to the first portion.

(14) In all the examples illustrated herein so far, blanks in the shape of flat plates are joined together. It should be clear that examples of the methods herein disclosed may also be applied to blanks of different shapes.

(15) After initial testing for proof-of-concept of hybrid welding the blanks, extensive testing was performed by the inventors to optimize the welding process with respect to filler materials, position of the welding arch and the laser beam in relation with the welding direction, wire feed rating, welding speed and laser power.

(16) In these tests, two flat Usibor 1500 plates of 1.4 mm thickness were butt-joined and results were compared to two flat 22MnB5 uncoated boron steel plates.

(17) Both hybrid laser welding topologies, the welding arch positioned in front of the laser beam and the laser beam positioned in front of the welding arch in relation with the welding direction, were tested.

(18) Four different fillers were tested, two of them carbon steel filler and two of them austenite stabilizing fillers comprising gammagenic elements. The characteristics and composition of these fillers are summarized below in weight percentages (rest is iron (Fe) and unavoidable impurities):

(19) TABLE-US-00002 TABLE 1 Characteristics and compositions of fillers Filler Sample A B C D Filler Type Carbon Carbon Austenite Austenite steel steel stabilizing stabilizing stainless stainless steel steel Tensile Strength [Mpa] 560 800 640 640 Yield Strength [Mpa] 470 730 450 440 Elongation at break 26% 19% 41% 37% Diameter (mm) 0.9 0.8 0.8 0.8 C 0.1 <0.1 <0.2 0.04 Si 0.9 0.6 <1.2 0.7 Mn 1.5 1.6 6.5 0.7 Cr 0.3 18.5 19 Ni 1.4 8.5 10 Mo 0.3 0.3 Cu <0.4 Nb 0.6

(20) It was found that using an austenite stabilizing stainless steel filler, as in the filler samples C and D, the formation of ferrite may be avoided, because martensite is formed instead of ferrite. Thus, a good weld joint strength can be obtained.

(21) FIG. 3a represents the portion of Austenite and Ferrite phases in a 22MnB5 uncoated boron steel blank in relation with the Aluminum content at a temperature of 920 C. The percentage of ferrite and austenite formation depends on the amount of Aluminum. The ferrite phase first occurs with Aluminum content in mass of at least 1%.

(22) FIG. 3b represents the portion of Austenite and Ferrite phases in relation with the Aluminum content of a mixture (50/50) of 22MnB5 and the austenite stabilizing stainless steel filler OK Autorod 16.95 (commercially available from ESAB) at a temperature of 920 C. The composition in weight percentages of OK Autorod 16.95 is: 0.08% C, 0.9% Si, 7% Mn, 18.7% Cr, 8.1% Ni, 0.2% Mo, 0.1% Cu, 0.04% N and the rest Fe and unavoidable impurities. A ferrite phase now only occurs with Aluminum content in mass of at least 3%. Thus, adding these austenite stabilizing stainless filler materials increases the mass content of Aluminum necessary for establishing a ferrite phase. In other words, thanks to the filler, more aluminum can be allowed in the weld area while still maintaining mechanical properties, i.e. while still ensuring the presence of austenite.

(23) FIGS. 4a and 4b show the distribution and the content of Nickel, Aluminum, Silicon, Chromium and Manganese in a welding line of two flat Usibor 1500 plates of 1.4 mm thickness. In both examples, austenite stabilizing stainless fillers were used. The horizontal axis shows the depth of the welding line in millimeters, wherein 0 corresponds to the top surface of the welding line and 1.9 millimeters to the bottom surface of the welding line. The vertical axis shows the content in weight percentages of the elements in the center of the weld.

(24) In particular, FIG. 4a shows the distribution and content of the above mentioned elements along the depth of the welding line of the two flat plates, in the case of hybrid laser welding with a laser beam and an arc welding torch, positioned in such way that the laser beam is in front of the arc welding torch. In this example, an austenite stabilizing stainless filler was used, in particular a C sample (see Table 1) austenite stabilizing stainless filler.

(25) In particular, FIG. 4b shows the distribution and content of the above mentioned elements along the depth of the welding line of the two flat plates, in the case of hybrid laser welding with a laser beam and an arc welding torch, positioned in such way that the arc welding torch is in front of the laser beam. In this example, an austenite stabilizing stainless filler was used, in particular a D (see Table 1) sample austenite stabilizing stainless filler.

(26) After several tests, in which different fillers were used with the hybrid laser welding with both the laser beam in front of the arch welding torch and the arch welding torch in front of the laser beam, the inventors have found out that the aluminum content and distribution along the welding depth differs when the laser beam is positioned in front of the arch welding torch, compared with the arch welding torch being positioned in front of the laser beam.

(27) When the laser beam is positioned in front of the arc welding torch in the welding direction, the austenite stabilizing stainless filler does not reach the bottom part of the weld. The Aluminum may lead to worse mechanical properties in the welding zone after hot deformation processes such as hot stamping, because of ferrite formation instead of austenite formation.

(28) When the arc welding torch is positioned in front of the laser beam in the welding direction, the austenite stabilizing elements in the filler reaches the bottom part of the weld. Therefore, the Aluminum does not lead to worse mechanical properties in the welding zone after hot deformation processes such as hot stamping. This better distribution of the austenite stabilizing elements is achieved by using a hybrid laser welding wherein the arc welding torch is positioned in front of the laser beam in the welding direction, wherein carbon steel fillers or austenite stabilizing fillers are used. Using austenite stabilizing fillers increases the mass content of Aluminum when the ferrite phase starts as shown in the FIG. 3b. Thus, the influence of the aluminum in the welding area is minimized and a weld joint with good mechanical properties is obtained.

(29) It has also been found that using a hybrid laser welding with the arch welding torch positioned in front of the laser beam increases the welding quality when there is a gap between the two blanks to be welded. Due to a full penetration due to the positioning of the welding torch in front of the laser beam, a gap of up to about 0.7 mm between the two blanks may be welded. On the other hand, when the laser beam is positioned in front of the arch welding torch, the maximum gap between blanks is about 0.2 mm. Providing the arc welding torch in front of the lase beam increases the manufacturability of the welding and may reduce the manufacturing tolerances of the blanks.

(30) Several strength tests have been performed, comparing the welding strength of two flat 22MnB5 uncoated boron steel plates and two flat Usibor 1500P plates of 1.4 mm thickness were butt-jointed. The influence of the fillers and the hybrid laser configuration has also been tested. The following table summarizes the results of these tests.

(31) TABLE-US-00003 TABLE 2 Test results, tensile strength Electrode wire Average Tensile Material Welding Configuration fillers Strength [Mpa] 22MnB5 Pure laser welding 1498 uncoated Laser hybrid welding: Carbon steel 1424 boron Laser beam in front of filler the welding arch torch Laser hybrid welding: Austenite 1527 Welding arch torch in stabilizing front of the laser beam fillers Usibor Pure laser welding 1130 1500P Laser hybrid welding: Carbon steel 1074 Laser beam in front of filler the welding arch torch Austenite 1166 stabilizing fillers Laser hybrid welding: Carbon steel 1210 Welding arch torch in filler front of the laser beam Austenite 1409 stabilizing fillers

(32) Good mechanical properties are obtained, where two Usibor 1500P blanks were welded by laser hybrid welding with the welding arc torch positioned in front of the laser beam according to the welding direction. Particularly, a high tensile strength is obtained when fillers containing austenite stabilizing materials are used. The tensile strength obtained could be compared with an unwelded Usibor products and a welded 22MnB5 uncoated boron products.

(33) These good mechanical properties may be obtained using a relatively high welding speed, improving the manufacturing processes and reducing the welding time. Welding speeds from 5-12 m/min may be achieved in the various examples.

(34) Although only a number of examples have been disclosed herein, other alternatives, modifications, uses and/or equivalents thereof are possible. Furthermore, all possible combinations of the described examples are also covered. Thus, the scope of the present disclosure should not be limited by particular examples, but should be determined only by a fair reading of the claims that follow.