JPH05302121A - Production of high strength electric resistance welded steel tube for machine structure - Google Patents

Abstract

(57) [Summary] [Purpose] To increase strength. Prevents deterioration of toughness and workability. It suppresses softening of the HAZ part when arc welding is performed. [Constitution] C: 0.15 to 0.25% by weight, Si: 0.3
0% or less, Mn: 1.00 to 1.50%, P: 0.025% or less, S: 0.005% or less, Nb: 0.020 to 0.050
%, Mo: 0.20 to 0.35%, Sol-Al: 0.005
~ 0.050% and, if necessary, Ca: 0.0040%
Hereinafter, a slab containing one or two or more of Ti: 0.030% or less and V: 0.10% or less and the balance of Fe and unavoidable impurities is hot-rolled. The hot-rolled steel sheet is cold-rolled at a rolling reduction of 10 to 35% and then electric resistance welded to form an electric resistance welded steel pipe. The electric resistance welded steel pipe is heat-treated at a temperature of 400 to 650 ° C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electric resistance welded steel pipe for a high strength mechanical structure which is used for a cylinder, a propeller shaft of an automobile and the like.

[0002]

2. Description of the Related Art With the recent tendency toward weight reduction of automobiles, introduction of high-strength, thin-walled electric resistance welded steel pipes into propeller shafts and the like has been promoted. The electric resistance welded steel pipe for automotive use, the tensile strength at 490 N / mm ² or more, especially in the propeller shaft is required 690n / mm ² or more strength is further also a high degree of toughness and workability requirements.

Such a high-strength electric resistance welded steel pipe is manufactured, for example, by cold rolling a hot-rolled steel strip to increase its strength and then performing electric resistance welding. However, strengthening by cold rolling is
Often accompanied by reduced toughness and workability. Furthermore,
There are problems that the strength is lowered by the post heat treatment, or that the HAZ portion of the manufactured product steel pipe is softened when arc welding is performed. Therefore, a method of increasing the strength of an electric resistance welded steel pipe without using cold working is disclosed in JP-A-2-19752.
It is proposed by Japanese Patent No. 5 publication.

[0004]

However, cold rolling of a hot rolled steel sheet brings about a great advantage for electric resistance welding, although it involves softening of the HAZ portion and the like. That is,
The hot-rolled steel strip is inferior to the cold-rolled steel strip in thickness accuracy in the width direction. If such a hot-rolled steel strip is divided into multiple strips to form an electric resistance welded steel pipe, the thickness of both edge portions is different, so that welding defects occur due to non-uniform welding heat input. Further, when the electric resistance welded steel pipe is used as a rotary shaft of a propeller shaft or the like, vibration occurs due to variation in wall thickness in the circumferential direction, which causes vibration and noise. Therefore, the method for producing a high-strength electric resistance welded steel pipe that does not rely on cold working is effective for softening the HAZ portion, but it cannot be said to be a preferable method when viewed comprehensively.

The object of the present invention is to suppress the softening of the HAZ portion and the like, despite adopting the strengthening by cold rolling,
It is also to provide a method for producing an electric resistance welded steel pipe for a high strength mechanical structure which secures excellent toughness and workability.

[0006]

[Means for Solving the Problems] In the production of high-strength electric resistance welded steel pipes, cold rolling of hot-rolled steel sheets has many positive effects on product quality, so it is considered that high-grade strengthening by cold rolling is essential. .. The present inventors, on the premise of increasing the strength by cold rolling, have conducted research on means for suppressing the adverse effect. As a result, the composition of the hot-rolled steel strip, particularly Mo, effectively functions for HAZ softening, and the heat treatment after electric resistance welding effectively functions for toughness and workability. It was found that there is a region where softening is not a problem in the effective temperature range.

The present invention has been made based on the above findings, and C: 0.15 to 0.25% by weight, Si: 0.30% or less, Mn: 1.00 to 1.50%, P: 0.025% or less,
S: 0.005% or less, Nb: 0.020 to 0.050%, M
o: 0.20 to 0.35%, Sol-Al: 0.005 to 0.0
50% and, if necessary, Ca: 0.0040% or less,
A slab containing Ti: 0.030% or less and V: 0.10% or less, one or two or more, and the balance Fe and unavoidable impurities is hot-rolled, and the hot-rolled steel sheet has a reduction ratio of 10 to 3.
After cold rolling at 5%, ERW welding was performed to form ERW steel pipe,
Furthermore, the gist is a method for producing an electric resistance welded steel pipe for high strength mechanical structure, which is characterized by performing heat treatment at a temperature of 400 to 650 ° C.

[0008]

The reasons for limiting the conditions in the present invention will be described below in the order of the composition of the slab, the cold rolling and the heat treatment.

(A) Slab composition C: The cheapest element for obtaining strength, but 0.15%
If less than 0.25%, a predetermined strength cannot be obtained, and if more than 0.25%, toughness is deteriorated and arc weldability and workability are deteriorated. Therefore, C is set to 0.15 to 0.25%.

Si: Mn-Si, which is added as a deoxidizer at the steel making stage, is called a penetrator during electric resistance welding.
Since it causes the generation of non-metallic inclusions in the system, 0.30
% Or less.

Mn: An element that obtains strength at a relatively low cost, but if it is less than 1.0%, the prescribed strength cannot be obtained. Also, 1.
If it exceeds 50%, the strength becomes too high and segregation in the steel becomes large, resulting in deterioration of workability and the like. Therefore, Mn
Was 1.0 to 1.50%.

P: 0.025% or less since it is an element existing in steel as an impurity and easily segregated.

Like S: P, it exists as an impurity and particularly deteriorates the workability and toughness, so the content was made 0.005% or less.

Nb: An element that improves toughness by making the particles fine while securing strength. If it is less than 0.020%, the effect of addition cannot be obtained, and if it exceeds 0.050%, it has no effect on the strength increase and grain refinement, which causes a cost increase. Therefore, N
b was 0.020 to 0.050%.

Mo: A main element in the present invention. Although this element contributes to strength, it is considered to be an unfavorable element from the viewpoint of toughness. However, it is effective as a softening resistance element in the arc welded HAZ portion of the manufactured electric resistance welded steel pipe.
FIG. 1 is a diagram showing the effect of Mo on the hardness of the HAZ portion and the base material portion when arc welding is performed on the manufactured electric resistance welded steel pipe. The hardness of the base metal part increases as the amount of Mo increases, but the hardness of the HAZ part increases more than that, and Mo becomes H
It can be seen that it effectively functions to prevent softening of the AZ portion.
If the amount of Mo is less than 0.20%, this effect cannot be sufficiently obtained, and arc welding after pipe making causes remarkable HAZ softening. On the other hand, if it exceeds 0.35%, deterioration of toughness becomes a problem. Therefore, Mo is included in a relatively large amount of 0.20 to 0.35%, and the toughness reduction due to this is that Nb is 0.020 to 0.03.
Granulation by adding in the range of 50% and after pipe forming 4
It is compensated by heat treatment at 00 to 650 ° C.

Sol-Al: It is added as a deoxidizing agent in the pipe making stage, but if the amount of addition is too small, deoxidation becomes insufficient, and if it is too large, alumina inclusions increase, and in all cases steel cleaning Therefore, it is set to 0.005 to 0.050%.

Ca: Improves the cleanability and the workability by reducing the sulfide inclusions in the steel and making them spherical. However, if it is too large, it becomes a cause of impairing the cleanability as non-metallic inclusions. Therefore, the upper limit for addition is 0.004
It was set to 0%.

Like Ti: Nb, it increases strength and promotes grain refinement. However, if it is too large, the toughness may be deteriorated, and the upper limit for addition is set to 0.10%.

V: Has the same effect as Nb and Ti,
Since the effect does not increase even if it exceeds 0.10%, the upper limit for addition is set to 0.10%.

(B) Cold Rolling The hot rolled steel strip is cold rolled to increase its strength. Further, by increasing the wall thickness accuracy in the plate width direction, the wall thickness of both edge portions during electric resistance welding is made uniform, and the welding quality is improved. Furthermore, the wall thickness accuracy of the manufactured electric resistance welded steel pipe in the circumferential direction is increased, and the vibration during rotation is suppressed. If the reduction ratio in cold rolling is less than 10%, the effect of increasing the strength is small, and if it exceeds 35%, the toughness and workability are extremely deteriorated, and these properties are satisfied even by the heat treatment described later. I can't improve to the level I go to.

(C) Heat Treatment In the electric resistance welded steel pipe, the electric distortion welded portion is hardened by the processing strain due to forming and the rapid cooling due to the electric resistance welding, and a large hardness difference is generated between the electric resistance welded portion and the base material portion. Therefore, the toughness and workability are essentially not good, and in the present invention, the toughness and the workability are deteriorated due to cold rolling. Therefore, heat treatment is applied to the electric resistance welded steel pipe, but if the temperature is less than 400 ° C, the effect of improving toughness and workability is not sufficient, and if it exceeds 650 ° C, strength is reduced. That is, if the temperature is 650 ° C. or lower, the effect of strengthening by cold rolling is not impaired,
The toughness and workability can be improved.

FIG. 2 is a table showing the relationship between the heat treatment temperature and the tensile strength of the electric resistance welded steel pipe, using the cold reduction rate as a parameter. Although the tensile strength increases as the rolling reduction in cold rolling increases, the effect of increasing the strength by cold rolling is not impaired at any rolling reduction up to 650 ° C. FIG. 3 is a table showing the effects of cold reduction and heat treatment in the flatness test and push-expansion test shown in FIGS. 4 (A) and 4 (B). Cold rolling exacerbates these test data, but heat treatment recovers to a problem-free level.

[0023]

Example A slab having the composition shown in Table 1 was hot-rolled, descaled, and cold-rolled. Further, the steel strip is divided into multiple strips to form an electric resistance welded steel pipe having an outer diameter of 60.5 mm and a wall thickness of 1.6 mm,
This was heat treated. Table 2 shows the results of an examination of the tensile properties and toughness of the electric resistance welded steel pipe after the heat treatment and the hardness reduction amount of the arc welded HAZ part. ERW steel pipe manufactured under the conditions of the present invention,
It has a tensile strength of 800 N / mm ² or more, good toughness and workability, and little softening of the HAZ part. The hot rolling was performed at a heating temperature of 1230 ° C.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

As is apparent from the above description, in the method for manufacturing an electric resistance welded steel pipe for a high strength mechanical structure of the present invention, since the strength is increased by cold working, the high strength can be easily obtained. .. Further, the cold working improves the plate thickness accuracy, improves the quality of the electric resistance welded portion, and improves the dimensional accuracy of the product steel pipe in the circumferential direction. And, despite adopting high strength by cold working, excellent toughness and workability are secured, and HAZ when arc welding is performed on a product steel pipe.
Prevents softening of parts.

[Brief description of drawings]

FIG. 1 is a table showing the effect of Mo on the hardness of a HAZ part and a base metal part when arc welding is performed on a manufactured electric resistance welded steel pipe.

FIG. 2 shows the relationship between the heat treatment temperature and the tensile strength of ERW steel pipe,
It is a chart which shows a cold rolling reduction as a parameter.

FIG. 3 is a chart showing the effects of cold reduction and heat treatment in a flattening test and a spreading test.

FIG. 4 is a schematic diagram for explaining a flatness test and a push-expansion test.

Claims (2)

[Claims] 1. A weight ratio of C: 0.15 to 0.25%, Si:
0.30% or less, Mn: 1.00 to 1.50%, P: 0.025
% Or less, S: 0.005% or less, Nb: 0.020 to 0.05
0%, Mo: 0.20 to 0.35%, Sol-Al: 0.00
A slab containing 5 to 0.050% and the balance Fe and unavoidable impurities is hot-rolled, and the hot-rolled steel sheet has a reduction ratio of 10 to 10%.
A method for producing an electric resistance welded steel pipe for high-strength mechanical structure, comprising cold rolling at 35%, electric resistance welding to form an electric resistance welded steel pipe, and further heat treatment at a temperature of 400 to 650 ° C. 2. C: 0.15 to 0.25% by weight, Si:
0.30% or less, Mn: 1.00 to 1.50%, P: 0.025
% Or less, S: 0.005% or less, Nb: 0.020 to 0.05
0%, Mo: 0.20 to 0.35%, Sol-Al: 0.00
5 to 0.050%, Ca: 0.0040% or less, T
i: 0.030% or less and V: 0.10% or less, and one or more kinds of slabs, and the balance Fe and unavoidable impurities are hot-rolled, and the hot-rolled steel sheet is rolled with a rolling reduction of 10 to 35.
%, Cold-rolled, then electric resistance welded to form an electric resistance welded steel tube, and further heat-treated at a temperature of 400 to 650 ° C., a method for producing an electric resistance welded steel tube for high strength mechanical structure.