Method for improving welding cold crack resistance of high-strength alloy steel

Abstract

The invention discloses a method for improving welding cold crack resistance of high-strength alloy steel, which comprises the following steps of: feeding uniformly mixed powder to a welding seam, enabling a powder beam and a light beam to intersect at one point, and welding while feeding the powder; the uniformly mixed powder comprises the following elements in percentage by mass: 0 to 0.1 percent of C, 10 to 30 percent of Cr, 0 to 20 percent of Ni, 5 to 10 percent of Mn, 0 to 1 percent of Mo, 0 to 0.5 percent of Sn and the balance of Fe. A proper amount of Sn element powder is added into the deposited metal powder, so that the martensite transformation temperature can be effectively changed, the welding residual stress is reduced by adjusting the martensite transformation temperature, and the cold crack resistance of the high-strength alloy steel can be greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of high-strength alloy steel welding and relates to a method for improving the resistance of high-strength alloy steel to welding cold cracks. Background Art

[0002] There are two main problems with high-strength alloy steel (strength greater than 1300MPa) during welding. First, the weld metal shrinks greatly during solidification, and the stress generated exceeds the crack resistance, causing cracks in the material. Second, due to the uneven heating and cooling of the welding thermal cycle, the mechanical properties of the weld are deteriorated, which indirectly reduces the crack resistance of the weld. Although scholars from various countries have done a lot of work on improving the cold crack resistance of welded joints, the methods used for different materials are different due to the limitations of the material's own characteristics and the working environment. At present, the methods to improve the cold crack resistance of high-strength alloy steel mainly include preheating before welding, stress relief during welding, heat treatment after welding, and changing the welding process.

[0003] After welding, lower residual stress and better mechanical properties in the weld are closely related to the prevention of cold cracks in high-strength alloy steel. Although cold cracks in welding can be effectively prevented by preheating before welding, heat treatment after welding and stress relief during welding, these methods not only have high manufacturing costs, but also seriously affect production efficiency and may even affect product performance. In addition, preventing cold cracks by adjusting the welding process of high-strength alloy steel may cause other irreversible welding defects or other properties of the weld to fail to meet the standards. Due to the different martensitic transformation temperatures of high-strength alloy steels, their volume expansion will be different, resulting in different residual stresses. Therefore, it is very important to design the martensitic transformation temperature corresponding to the minimum residual stress. Undoubtedly, the martensitic transformation temperature of high-strength alloy steel can be changed by reasonably changing the composition of the deposited metal. Summary of the invention

[0004] (I) Purpose of the invention

[0005] The purpose of the present invention is to provide a method for improving the resistance of high-strength alloy steel to welding cold cracks. Under the premise of not reducing its mechanical properties, the martensitic transformation temperature of the high-strength alloy steel is adjusted by adding a trace amount of Sn element to obtain the Sn content corresponding to the minimum welding residual stress, thereby achieving the purpose of controlling the welding cold cracks of the high-strength alloy steel.

[0006] (II) Technical solution

[0007] In order to solve the above technical problems, the present invention provides a method for improving the resistance of high-strength alloy steel to welding cold cracks, the process is: sending mixed powder to the weld, the powder beam and the light beam intersect at one point, and welding while sending powder; in the mixed powder, the mass percentage of each element is: C: 0~0.1%, Cr: 10~30%, Ni: 0~20%, Mn: 5~10%, Mo: 0~1% and Sn: 0~0.5%, and the rest is Fe.

[0008] The raw materials of each element of the mixed powder are all fine powders, and the particle size range of each fine powder is 53μm to 105μm. The physical and chemical performance indicators of the raw materials are as follows: the mass percentage of Fe in iron powder is greater than 99%, the C content in carbon powder is greater than 97%, the Cr content in Cr powder is greater than 99%, the Ni content in Ni powder is greater than 99%, the Mn content in Mn powder is greater than 99%, the Mo content in Mo powder is greater than 99%, and the Sn content in Sn powder is greater than 99%.

[0009] The preparation process of the mixed powder is as follows: C, Cr, Ni, Mn, Mo, Sn and Fe elements are weighed according to the formula ratio, and the weighed elements are put into the mixer for mixing for 30 to 50 minutes. After mixing evenly, a part of the mixed material is randomly taken for chemical composition detection, and the difference between the detection and the formula is accurate to two decimal places; if it exceeds two decimal places, re-mixing is carried out until it is accurate to two decimal places.

[0010] The welded high-strength alloy steel plates are produced by wire cutting according to GB4675.1-84 standard, and the plate size is 200×75×5mm.

[0011] like Figures 1 to 3 As shown, according to GB4675.1-84 standard, at an ambient temperature of -10 to 10°C, fiber laser automatic welding is used to perform double-sided butt welding on the restrained welds of two high-strength alloy steel plates. Fine powder is delivered to the weld, and the powder beam and the light beam intersect at one point, and welding is performed while powder is delivered.

[0012] During welding: powder feeding speed is 0.54~1.50cm 3 / min, the laser welding power is 3~5kW, the welding speed is 150mm / min, the defocus is -4~+4mm, the shielding gas is a mixed gas of Ar and CO2, and the shielding gas flow rate is 5~25L / min.

[0013] The mixed powder must be dried before welding, and there should be no corner deformation or incomplete penetration after welding.

[0014] like Figure 4 As shown, after the two restraint welds are welded, they are placed in an ambient temperature of -10 to 10°C for 12 to 24 hours and then tested. The welding process and ambient temperature are the same as those of the restraint welds, and the start and end positions of the welds are about 2 mm away from the restraint welds.

[0015] After the welded high-strength alloy steel specimens were placed for 48 hours, the crack rate of the specimens was calculated using the coloring method according to GB4675.1-84 standard.

[0016] (III) Beneficial effects

[0017] The above technical solution provides a method for improving the resistance of high-strength alloy steel to cold cracks in welding. When austenite in high-strength alloy steel transforms into martensite, it is accompanied by volume expansion. Different martensite transformation temperatures result in different volume expansions, which further cause different residual stresses. Adding an appropriate amount of Sn element powder to the deposited metal powder can effectively change its martensite transformation temperature. By adjusting the martensite transformation temperature, the welding residual stress can be reduced, which can greatly improve the resistance of high-strength alloy steel to cold cracks. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the shape and size of the test piece in the embodiment of the present invention.

[0019] Figure 2 for Figure 1 AA view of the .

[0020] Figure 3 for Figure 1 BB view.

[0021] Figure 4 Schematic diagram of the weld position in the welding test in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below in conjunction with the drawings and examples.

[0023] Example 1

[0024] Reference Figures 1 to 4 As shown, the method for improving the resistance of high-strength alloy steel to welding cold cracks in this embodiment includes the following process:

[0025] (1) According to the following formula, a comparative test was conducted on Sn-added and Sn-free fine powders. The specific formula is prepared according to the mass percentage of each element as shown in the following table:

[0026]

[0027]

[0028] (2) After the formula is complete, weigh the C, Cr, Ni, Mn, Mo, Sn and Fe elements according to the formula ratio and set aside.

[0029] (3) Put the weighed elements into the mixer and mix them for 30 to 50 minutes. After mixing evenly, randomly take a certain amount of the mixed material for chemical composition testing. The difference between the test and the formula is accurate to two decimal places. If it exceeds two decimal places, re-mix until it is accurate to two decimal places.

[0030] (4) Put the mixed material into the silo for later use.

[0031] (5) According to GB4675.1-84 standard, two high-strength alloy steel plates are made by wire cutting, and the plate size is 200×75×5mm.

[0032] (6) According to GB4675.1-84 standard, at an ambient temperature of -10 to 10°C, fiber laser automatic welding is used to weld the restrained welds of two high-strength alloy steel plates (such as Figure 1 ) for double-sided butt welding, feed fine powder to the weld (where the powder beam and light beam intersect at one point), and weld while feeding powder. The welding process is: the powder feeding speed is 0.54~1.50cm 3 / min, laser welding power is 3~5kW, welding speed is 150mm / min, defocusing is -4~+4mm, and protective gas (Ar and CO2 mixed gas) flow rate is 5~25L / min. The mixed material should be dried before welding, and there should be no angular deformation and incomplete penetration after welding.

[0033] (7) After the two restraint welds are welded, place them in an ambient temperature of -10 to 10°C for 12 to 24 hours. Perform test welding with the same welding process and ambient temperature as the restraint welds. The distance between the start and end of welding is about 2 mm (e.g. Figure 2 ).

[0034] (8) After the welded high-strength steel specimens were placed for 48 hours, the crack rate of the specimens was calculated using the coloring method according to GB4675.1-84 standard.

[0035] Example 2

[0036] In this embodiment, the mass percentage of each element in the mixed powder is changed, and the welding process in Example 1 is repeated. Only the description of process (1) is given below, and the other steps are not repeated.

[0037] (1) According to the following formula, a comparative test was conducted on Sn-added and Sn-free fine powders. The specific formula is prepared according to the mass percentage of each element as shown in the following table:

[0038]

[0039] Example 3

[0040] In this embodiment, the mass percentage of each element in the mixed powder is changed, and the welding process in Example 1 is repeated. Only the description of process (1) is given below, and the other steps are not repeated.

[0041] (1) According to the following formula, a comparative test was conducted on Sn-added and Sn-free fine powders. The specific formula is prepared according to the mass percentage of each element as shown in the following table:

[0042]

[0043] In this embodiment, the three groups of Sn-containing and Sn-free mixed metal powders were not subjected to a deposition test. The results showed that the weld crack rates of the three groups of Sn-containing high-strength alloy steels were all 0, while the weld crack rates of the three groups of Sn-free high-strength alloy steels were 12%, 21% and 24% respectively. This shows that the addition of Sn elements can effectively improve the cold crack resistance of high-strength alloy steels.

[0044] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for improving the resistance of high-strength alloy steel to welding cold cracks, characterized in that: The process is: the mixed powder is sent to the weld, the powder beam and the light beam intersect at one point, and the powder is sent while welding; the mass percentages of each element in the mixed powder are: C: 0~0.1%, Cr: 10~30%, Ni: 0~20%, Mn: 5~10%, Mo: 0~1% and Sn: 0~0.5%, and the rest is Fe.

2. The method for improving the resistance of high-strength alloy steel to welding cold cracks as claimed in claim 1, characterized in that: The raw materials of each element of the mixed powder are all fine powders, and the particle size range of each fine powder is 53μm to 105μm.

3. The method for improving the resistance of high-strength alloy steel to welding cold cracks as claimed in claim 2, characterized in that: The physical and chemical performance indicators of the raw materials of the mixed powder are: the mass percentage of Fe in iron powder is greater than 99%, the C content in carbon powder is greater than 97%, the Cr content in Cr powder is greater than 99%, the Ni content in Ni powder is greater than 99%, the Mn content in Mn powder is greater than 99%, the Mo content in Mo powder is greater than 99%, and the Sn content in Sn powder is greater than 99%.

4. The method for improving the resistance of high-strength alloy steel to welding cold cracks as claimed in claim 3, characterized in that: The preparation process of the mixed powder is as follows: C, Cr, Ni, Mn, Mo, Sn and Fe elements are weighed according to the formula ratio, and the weighed elements are put into the mixer for mixing for 30 to 50 minutes. After mixing evenly, a portion of the mixed material is randomly taken for chemical composition detection, and the difference between the detection and the formula is accurate to two decimal places; If it exceeds two decimal places, remix until it is accurate to two decimal places.

5. The method for improving the resistance of high-strength alloy steel to welding cold cracks as claimed in claim 1, characterized in that: According to GB4675.1-84 standard, at an ambient temperature of -10 to 10°C, fiber laser automatic welding is used to perform double-sided butt welding of the restrained welds of two high-strength alloy steel plates. Fine powder is delivered to the weld, and the powder beam and the light beam intersect at one point, and welding is performed while powder is delivered.

6. The method for improving the resistance of high-strength alloy steel to welding cold cracks as claimed in claim 5, characterized in that: During welding: powder feeding speed is 0.54~1.50cm 3 / min, the laser welding power is 3~5kW, the welding speed is 150mm / min, the defocus is -4~+4mm, the shielding gas is a mixed gas of Ar and CO2, and the shielding gas flow rate is 5~25L / min.

7. The method for improving the resistance of high-strength alloy steel to welding cold cracks as claimed in claim 6, characterized in that: It also includes the test weld welding process. After the two restrained welds are welded, they are placed in an ambient temperature of -10 to 10°C for 12 to 24 hours before test welding. The welding process and welding ambient temperature are the same as those of the restrained welds, and the start and end positions of the welds are 2mm away from the restrained welds. After the welded high-strength alloy steel specimens are placed for 48 hours, the crack rate of the specimens is calculated using the coloring method according to GB4675.1-84 standard.

8. The method for improving the resistance of high-strength alloy steel to welding cold cracking according to any one of claims 1 to 7, characterized in that: The mass percentages of the elements in the mixed powder are: C: 0.05%, Cr: 20%, Ni: 10%, Mn: 7.5%, Mo: 0.5%, Sn: 0.2%, and the rest is Fe.

9. The method for improving the resistance of high-strength alloy steel to welding cold cracking according to any one of claims 1 to 7, characterized in that: The mass percentages of the elements in the mixed powder are: C: 0.01%, Cr: 10%, Ni: 5%, Mn: 5%, Mo: 0.1%, Sn: 0.1%, and the rest is Fe.

10. The method for improving the resistance of high-strength alloy steel to welding cold cracks according to any one of claims 1 to 7, characterized in that: The mass percentages of the elements in the mixed powder are: C: 0.09%, Cr: 30%, Ni: 20%, Mn: 10%, Mo: 0.9%, Sn: 0.5%, and the rest is Fe.

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