JPS5852758B2 - Low hydrogen coated arc welding rod for high tensile strength steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coating agent formulation for a low hydrogen-based coated arc welding rod, and the tensile strength of the weld metal is 88 to 100 kg/m.
An object of the present invention is to provide a low hydrogen-based coated arc welding rod that has a high strength of m2 and excellent durability.

Currently commercially available coated arc welding rods for high-strength steel with a tensile strength of 88 kg/mm" or higher tend to cause cracks in the welded area, and weld cracks cannot be prevented unless preheated to 150°C or higher before welding. There is.

For this reason, there is a strong demand for a coated arc welding rod for high-strength steel that can be used at a lower preheating temperature without causing weld cracks.

The present invention is a completely new coated arc welding rod obtained as a result of various studies aimed at improving this drawback.

The gist is CaCO340-60%, CaF210-2
5%, Mn2-5%, Ni6-9%, Cr1-3%, M
o A low hydrogen-based coated arc welding rod in which a mild steel core wire is coated with a coating material containing 0.5 to 1.5%, the balance being a deoxidizer, an arc stabilizer, etc., and the tensile strength of the weld metal is 88 to 100 kg. /
When welding high-strength steel, which has a tensile strength in the range of 1.0 mm'' and comparable to the tensile strength of the weld metal, it has the advantage that weld cracks do not occur even when preheated to 100°C.

The effects and reasons for limitations of the coating components of the coated arc welding rod used in the present invention will be described below.

First, let's talk about Ca CO3 and Ca F2.C
aCO3 acts as a slag generation agent and a CO2 gas generator.

When CaCO3 is less than 40%, the amount of CO2 gas generated is insufficient and the shielding of the atmosphere is insufficient, making it easy to generate blowholes, and the amount of hydrogen in the weld metal increases, making it easy to cause weld cracks.

Moreover, if it exceeds 60%, the viscosity of the slag becomes excessive, and the shape of the weld bead becomes poor in the vertical position.

CaF2 is necessary to adjust the viscosity and fluidity of the slag to an appropriate state and to improve the bead shape, but if it is less than 10%, the viscosity of the slag is too high and the bead does not fit well with the base material.

If it is used in excess of 25%, the slag will drip down in an upright position, resulting in poor repeat shape.

Next, the range of Mn, NisCr)Mo components is the most important part of the present invention, and will be explained in detail below.

CaCO350%, CaF218%, Ni8%, Cr2
%, Mo contains 1.2%, and Mn is 1.6%, respectively.
, 2.4, 3.2, 4.8, 5 containing 6.1%
C0.0 types of coating materials (Mn-5, 4, 3, 2, 1)
2%, Si0.01%, Mn0.48% Diameter 4.011
Lm A low-hydrogen welding rod was made by coating a mild steel core wire with a length of 400 mm, and a weld metal was made under the conditions of a welding current of 170 A and a preheating pass temperature of 100°C, and a tensile test was performed on the weld metal. Using a high-tensile steel plate with a strength of 90 kg/mrn'' class and a plate thickness of 257 ILm, a window type restraint test was conducted to investigate the presence or absence of cracks in the weld metal.

The window type restraint test is a test method devised as a method for determining the resistance of welded metal.As shown in Figure 1 a and b, the window type restraint test is a test method that was designed to determine the fracture resistance of weld metal.
80kg/mTrL2 high tensile strength steel plate with a vertical length of 460mm,
A window with a width of 310 mm is attached, and several 90 kg/mm tensile steel plates having a groove shape as shown in Fig. 2 are attached to this part (surroundings are restrained by restraint welding W) and welded to the groove part. This is a method to investigate cracks that occur in the weld metal after welding.

Next, in the same manner as in the case of Mn, Ni was
, 5.1, 6.4, 8.6, 10.6% welding rods (Ni-5,4,3,2,1), and similarly Cr
Welding rods (Cr-4, 3, 2, 1) containing 0.7, 1.4, 2.7, and 3.8%, respectively, and 0.2% Mo
Welding rods (Mo
-4°3.2.1) was prepared to investigate the relationship between the tensile strength of the weld metal and the occurrence of cracking in the weld metal by a window type restraint test. Table 1 shows the results.

As is clear from this, when 6.1% Mn is added, cracks occur in the weld metal, and when 1.6% or less of Mn is added, the tensile strength of the weld metal is less than 88 kg/rrart2, resulting in insufficient strength. .

From this, the Mn component range was determined to be 2 to 5%.

Next, when Ni is added at 10.6%, cracks occur in the weld metal, and when Ni is added at 4.1%, the tensile strength is 88 kg/
If it is less than my2, the strength will be insufficient.

Furthermore, if Ni is less than 5%, the notch toughness of the weld metal is poor.

From this, the Ni component range was determined to be 5 to 9%.

Next, for C, when 3.8% is added, cracks occur in the weld metal, and when 0.7% is added, the tensile strength is 88 kg/mr.
If it is less than ft2, the strength will be insufficient.

From this, the range of Cr content was determined to be 1 to 3%.

Next, regarding Mo, when 2.0% is added, cracks occur in the weld metal, and when 0.2% is added, the tensile strength of the weld metal is 88%.
If it is less than kg/mu2, the strength is insufficient.

From this, the Mo component range was determined to be 0.5 to 1.5%.

Next, the present invention will be explained in more detail with reference to Examples.

Table 2 of Examples shows the results of investigating the strength and fragility of weld metal using a coated arc welding rod in which a 4x400 mm mild steel core wire was coated with the coating material of the present invention.

The steel plate used in the window type restraint test to investigate the fragility was 90 kg/xi class high tensile strength steel with the chemical composition shown in Table 3.

(1) Symbol S1 is an example of a conventional welding rod with a tensile strength of 100 kg/mm2 class, and the Mo content in the coating material is out of the range of the present invention, resulting in poor durability.

(2) Symbol T1 is a welding rod in which Mn and Ni are outside the scope of the present invention and has poor resistance to fragility.

(3) Symbols T2 to T6 are welding rods within the scope of the present invention, and 88 to
It has a tensile strength of 100 kg/rntn2 and good resistance to wear.

(4) Symbol T7 is a welding rod with Mn outside the range of the present invention and has poor durability.

(5) Symbol T8 is a welding rod in which Mn and Ni are outside the range of the present invention, and the strength of the weld metal is low.

(6) Symbol T9 is a welding rod in which Ni and Cr are outside the scope of the present invention and has poor resistance to fragility.

(7) Symbol TIO is a welding rod in which Ni and Cr are outside the scope of the present invention, and the strength of the weld metal is low.

(8) Symbol Tll is a welding rod in which Mn and Cr are outside the range of the present invention and has poor durability.

(9) Symbol T12 is a welding rod in which Mo is outside the scope of the present invention and has poor durability.

00) Symbol T13 is a welding rod in which Mn, Ni, Cr, and Mo are outside the range of the present invention and has poor resistance to fragility.

As is clear from the above results, when the welding rod of the present invention is used, a weld metal having high strength of 88 to 100 kg/mw2 and good fracture resistance can be obtained.

[Brief explanation of drawings]

Figure 1 is a front view of an example of a window-type restraint plate for testing;
B side view and FIG. 2 respectively show the groove shapes used in the test.

Claims (1)

[Claims] 1 CaCO340-60%, CaF210-25%,
Mn 2-5%, Ni 6-9%, Cr 1-3%,
A low-hydrogen-based coated arc welding rod for high-strength steel, which is made by coating a mild steel core wire with a coating agent containing 0.5 to 1.5% Mo, the remainder a deoxidizing agent, an arc stabilizer, etc.