JPS5848277B2 - Welding wire for stainless steel hot coil build-up welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides sufficient elongation, toughness, and cold ductility to the welded part in pill-up welding between bodies of ferritic stainless steel hot coils, which is the most difficult process in pill-up welding of stainless steel hot coils. It can be used not only for pill-up welding of ferritic stainless steel hot coil bodies, but also for welding an austenitic stainless steel leader material to a ferritic stainless steel hot coil, or for pill-up welding of austenitic stainless steel hot coils. This relates to a welding wire for pill-up welding of stainless steel hot coils, which is applicable, and eliminates the trouble of replacing wires for each hot coil material, reducing man-hours for wire replacement, and preventing breakage accidents due to wire misuse. This is to obtain the effect of

When rolling stainless steel hot coils, leader materials are welded to both ends of the hot coil to improve yield, or coil bodies such as end length coils are welded to both ends of the hot coil to improve rolling efficiency by increasing the unit weight of the coil. It is required to perform so-called build-up welding, such as welding the welds together.

However, such pill-up of hot coil is SU
There is no particular problem with austenitic stainless steels such as S304, but ferritic stainless steels such as SUS430 generally have low joint performance, so they are prone to breakage at joints that are build-up welded during the process. This is a concern, especially when welding hot coil bodies together, as the welded area is also rolled.
The risk of breakage is even greater, making it difficult to weld the hot coil bodies together.

As is well known, when a matching metal is used as a welding material in a welded joint of ferritic stainless steel such as SUS 430, both the weld metal and the weld heat affected zone (HAZ) will have poor elongation and toughness if welded as is. However, if subjected to bending deformation or impact stress after welding, it has the disadvantage that it is more likely to break than the welded metal part or the HAZ part.

For this reason, several methods have been used to improve the elongation and toughness of the joint.

The conventional method will be explained below.

(a) The embrittlement of welded joints of ferritic stainless steel occurs due to a combination of the formation of martensite and the so-called high-temperature embrittlement in areas where the crystal grains have coarsened due to heating to high temperatures. The embrittlement is 800~850° after welding.
It is possible to improve this to some extent by performing post-heat treatment at C.

However, the coarse grains cannot be made finer even by the post-heat treatment, and therefore, the post-heat treatment is not sufficient to obtain the elongation and toughness of the weld.

In addition, it is difficult to carry out such processing efficiently online, and the method of annealing the coil in a bell-shaped annealing furnace after winding the coil often causes breakage during coil winding, so this method is not recommended. It's hard to say.

(b) For the purpose of improving the elongation and toughness of the welded joint, A4 Ti, Nb, Ta, Zr, etc. are added singly or in combination to the ferritic welding material to refine grain deformation and fix carbon. There's something I'm aiming for.

When welding ferritic stainless steel using such welding materials, even if weld metal with fine crystal grains is obtained, the crystal growth in the HAZ area adjacent to the pound area is extremely high for SUS430, for example. Due to its large size and the fact that the welding material and base metal are not diluted uniformly, the crystal grains of the weld metal develop greatly near the bond area, and have a greater tendency to fracture than in these large grain areas. A suitable welding material for stainless steel build-up has not yet been found.

(c) When using ferritic stainless steel as welded, an austenitic welding material such as type 309 or type 310 is usually recommended.

However, when pill-up welding is performed using such conventional austenitic welding materials, the work hardening rate of the weld metal is greater than that of the ferritic stainless steel hot coil body, so the weld metal and This creates a difference in thickness between the base metal and the base material, which impedes smooth cold rolling, and especially in t. A thin plate with a thickness of less than OIM has a large tendency to break due to the excessive difference in plate thickness due to impact force when passing through the rolling rolls.

As mentioned above, methods for pill-up welding of ferritic stainless steel hot coils include heat treatment after welding, improving the composition of ferritic welding materials, and using austenitic welding materials. Attempts have been made to do this or in combination, but none of these methods have been satisfactory, and it has been difficult to prevent breakage at the welded portion during winding of the coil after pill-up welding and during the subsequent manufacturing process.

The present inventors have discovered that sufficient elongation and toughness of the welded part can be obtained without post-weld heat treatment in pill-up welding of ferritic stainless steel hot coils, and that the work hardening rate of the weld metal is lower than that of ferritic stainless steel hot coils. The effects of various alloying elements on ferritic and austenitic welding materials were studied in order to find welding materials that are equivalent to the materials used.

As a result, if an austenitic welding material containing 12% Cr, Ni with a coefficient of 12 or more, and Cu with a coefficient of O~ is used as the composition of the weld metal, the work hardening rate can be reduced even if the weld metal composition is austenite. found that it is possible to obtain a welded joint that is equivalent to a ferritic stainless steel hot coil and satisfies the above conditions, and since such a welding material is austenitic, SUS 304 We have found that this method can also be applied to pill-up welding of hot coils of austenitic stainless steel.

That is, the present invention has (1) weight ratio, C; 0.04 or less, si; o. '7 or below, Mn; 2. 0% or less, Cr; 5 to 11%, Ni;
20 to 40 width, balance: Fe and unavoidable impurities, or (2) weight ratio, C: 0.04% or less, Si: 0.7% or less, Mn: 2. 0% or less, Cr; 5 to 12%
, Ni: 20-40%, Cu: 4% or less, remainder: Fe
This is an austenitic welding wire having a composition consisting of sulfur and unavoidable impurities, and is used to fabricate pill-up welded joints of stainless steel hot coils by inert gas arc welding such as TIG welding or MIG welding, and submerged arc welding. .

Next, the reason for limiting the wire components will be explained.

C forms an interstitial solid solution and has the effect of reducing toughness and hardening, as well as forming carbides such as M23C6 and inhibiting deformability. Therefore, it is desirable to keep the value as low as possible, and the upper limit is was set at 0.04%.

Si is a strong deoxidizing element and has the effect of improving the fluidity of molten steel.

However, if it is contained in excess, there is a risk of weld cracking, especially when the composition of the weld metal is an austenite phase. The upper limit was set at 7%.

Mn has the effect of deoxidizing and desulfurizing as well as stabilizing austenite, but when it is contained in a large amount, it increases the work hardening rate, so the upper limit was set at the 2nd factor.

Cr is a main element that provides corrosion resistance and oxidation resistance,
Approximately 12 coefficients is the lowest value that maintains passivity.

Even in pilled up coils, the welded portion undergoes an annealing and pickling process, so the Cr content of the weld metal must be at least 12 scale change.

However, in austenitic stainless steel, as the Cr content increases, the work hardening rate also increases, so in order to obtain low work hardenability, it is desirable that the Cr content be as low as possible.

From the above, in the wire of the present invention, Cr of the weld metal
The target amount was set at 12 parts, and the Cr content was set at 5 to 12 parts in consideration of dilution with the base material.

Ni has the effect of stabilizing austenite and lowering the work hardening rate, thereby improving the ductility and toughness of the weld metal.

In the case of low nickel, austenite becomes unstable,
When the Cr content of the weld metal is 12% and the Ni content is less than 12%, the metal structure becomes a two-phase structure of austenite + martenite, and the elongation and toughness of the weld are significantly impaired, and it is difficult to obtain a completely austenitic structure. The amount of Ni in the wire must be at least 20%.

As mentioned above, it is preferable for the Ni amount to be as large as possible, but
Considering the economical efficiency of the wire, the composition range was set to 20 to 40%.

Like Ni, Cu is an austenite-forming element and is also effective in reducing work hardening.

However, if a large amount is contained, there is a risk of weld cracking, so the upper limit was set at 4.

Next, examples will be given and explained.

Example 1 A SUS430 hot coil (thickness 3.2'mi) was heated using a certain welding wire from the components shown in Table 1 below.
IG welded.

The welding conditions were ■-shaped butt welding with a groove angle of 60°, welding current 140A, welding voltage 15V, and welding speed variable 80 degrees/m.
I n , shielding gas (pure Ar) l O l/m
I made an inbound pass and landed the ball.

In addition, to explain a little about the welding wires in the above table, AF1 to F16 are ferrite wires, and 17C
r or 12Cr steel and Al, Ti, Nb, T
A, Zr, Cu, etc. are added singly or in combination.

In addition, AA1 to A3 are commercially available Y308 type, Y309 type, ¥
310 type austenitic wire, but AA4
~A8 are low Cr austenitic wires, and among these, AA5~A8 are wires of the present invention.

The results of the bending test of the welded part using these wires and the measured values of the hardness of the weld metal are shown in Table 2 below.

As is clear from the table above, even if the hardness of the weld metal is low when using ferrite wire, the bending test results do not yield satisfactory results as cracks occur in the weld metal near the bond.

In addition, in joints using commercially available austenitic wires, the ductility of the weld metal was insufficient and the joints broke at the bonded portion.

On the other hand, in the case of using a low Cr austenitic wire, A. A4 has a low Ni content, so a martensitic structure grows in the weld metal, and it breaks during the bending test, but AA
The hardness of the weld metal using the wire of the present invention of 5 to A8 is SUS.
It showed a lower value than the 430 base material, and also showed good ductility in the bending test with no cracking at 180° bending.

Example 2 SUS 430 hot coil (thickness 3.2 mm
) were MIG welded together using a welding wire (1.2 mm diameter) made of the components shown in Table 3 below, and then cold rolled.

The welding conditions were: 1 groove, groove spacing of 2, welding current 200A, welding voltage 30V. , welding party 4 5 0mi
/min, shielding gas** (pure Ar) 20 l
/min and welded in one pass.

After welding, the bead portion was ground to the thickness of the base metal using a grinder.

The attached drawings show changes in the plate thickness difference between the welded part and the base metal part after each rolling pass by a 20-high Sendzimer rolling mill.

As shown in this figure, when commercially available Y310 wire is used, the cold rollability of the weld is poor, and the difference in plate thickness between the weld and the base metal increases. This indicates that there is a risk of breakage.

On the other hand, in the joint using the wire according to the present invention, 0.57
Even after rolling to 1L71L, there was almost no difference in plate thickness between the welded part and the base metal part, and the cold rollability of the welded part was good.

[Brief explanation of the drawing]

The attached drawings show how the commercially available Y310 and S
This figure shows the change in thickness difference between the welded part and the base metal part after each rolling pass when the US 430 hot coil bodies were pill-up welded together and cold-rolled using a 20-high Sendzimer rolling mill. be.

Claims (1)

[Claims] 1 In weight ratio, C: 0.04 ratio or less, Si: 0.7 ratio or less, Mn: 2.0 or less, Cr: 5 to 12%, N+,
Sections 20 to 40, balance: Welding wire for stainless steel hot coil build-up welding, which is protected from Fe and unavoidable impurities. 2 Weight: C: 0.04% or less, Si: 0.7% or less, Mn: 2.0% or less, Cr: 5 to 1
A welding wire for stainless steel hot coil build-up welding consisting of 2%, Ni: 2C) to 40%, Cu: 4'ly or less, and the balance: Fe and unavoidable impurities.