JPH0776409B2 - High carbon steel and machined steel ERW pipe with excellent hot workability for machine structures - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a high carbon steel material for machine structures, such as an electric resistance welded steel pipe of high carbon steel, which requires hot workability.

[0002]

2. Description of the Related Art A carbon steel material for machine structure is described in JIS standard. As the carbon content of this steel increases, the strength increases, the elongation decreases, and the segregation of C, Mn, P, and S tends to increase. This segregation part is especially 1000 ° C.
The hot workability described above is deteriorated. When manufacturing high carbon steel ERW pipe, the welded part is processed (squeezed) at a temperature within this range, the metal flow rises, and the segregation part undergoes hot cracking.
(2) Causes the hook crack described in P1061. The hot workability increases as the wall thickness increases, and thus the hook crack increases as the wall thickness increases. The hook crack deteriorates the yield of ultrasonic flaw detection,
The workability in the subsequent process is significantly impaired. Therefore, conventional high carbon steel is difficult to weld by electric resistance welding.
Only thin materials with a thickness of 3 mm or less could be made.

[0003]

DISCLOSURE OF THE INVENTION The present invention reduces segregation of high carbon steel and improves hot workability of the segregated portion to facilitate hot working of high carbon steel, and thereby It is an object of the present invention to provide a high carbon steel for machine structure, which has excellent hot workability and enables easy production of ERW steel pipe.

[0004]

The gist of the present invention is, in terms of weight%, C: 0.4 to 0.8%, Si;
0.15-0.35%, Mn; 0.3-2.0%, P;
0.030% or less, S; 0.035% or less, Al;
In a high carbon steel containing 035% or less, the balance being Fe and inevitable impurities, Mo; 0.05 to 0.15% is added, and a high carbon steel for machine structural use having excellent hot workability, and It is a high carbon steel ERW pipe made of high carbon steel for machine structure.

[0005]

The present invention will be described in detail below, and the reason why the composition range of the steel of the present invention is defined as described above will be explained. TECHNICAL FIELD The present invention basically relates to prevention of hot cracking of JIS standard steel for machine structural use. Therefore, Si,
P and S are the same as the JIS standard and are as follows.

Si: 0.15 to 0.35% (weight%, the same applies hereinafter) P; 0.030% or less S; 0.035% or less Al is an element necessary for deoxidation, but if it increases, it becomes an alumina cluster. Since the workability and weldability are deteriorated due to the formation, it is defined as follows.

Al: 0.035% or less

C is necessary for obtaining mechanical strength, but as it increases, the elongation decreases and the workability deteriorates. Actually, the amount of C which is a problem for making ERW steel pipe is 0.4% or more. The upper limit was set to 0.8% or less in consideration of the formability and cutting ability of the electric resistance welded pipe. C; 0.4 to 0.8% Mn is an element generally essential for securing the strength and toughness of steel, and the lower limit was made 0.3% in order to avoid hot embrittlement due to S. However, excessive addition deteriorates workability and weldability, so the content was made 2.0% or less.

Mn: 0.3 to 2.0% The balance consists of Fe and inevitable impurities. In the present invention, a small amount of Mo is added to the steel material having the above basic composition to prevent hot cracking.

FIG. 1 shows a comparison between JIS S50C material and drawing at 1000 ° C., 1100 ° C. and 1200 ° C. in a segregated portion where P of a material containing different amounts of Mo is 0.02%. Show. From this result, high carbon steel 10
The high temperature elongation at a temperature of 00 ° C. or higher is 0.05 to 0.
Since it can be greatly improved by adding 15%, it is defined as follows.

Mo: 0.05 to 0.15%

[0012]

EXAMPLE Steels having the components shown in Table 1 were melted, continuously cast, and hot-rolled, and then an electric resistance welded steel pipe of φ48.6 × t6.0 mm was manufactured. After normalizing and straightening after pipe making, ultrasonic flaw detection (UST) was performed. The results are shown in Table 2. With the steel of the present invention, the yield of ultrasonic flaw detection was significantly improved compared to the comparative steel. As a result of investigating the defective portion for ultrasonic flaw detection, most of them were hook cracks along the rising metal flow. In addition, the ultrasonic flaw passing material of the present invention steel was good in the practical test. Although the embodiments of the present invention have been described with respect to the electric resistance welded steel pipe, the effect is large if the invention is applied to a steel material subjected to severe working at 1000 ° C or higher.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

As described above, according to the present invention, by adding a small amount of Mo to the existing mechanical structural steel,
It is possible to obtain a steel material having greatly improved workability in hot working at 000 ° C. or higher, and to obtain an electric resistance welded steel pipe having good welding quality.

[Brief description of drawings]

FIG. 1 is a diagram showing the influence of Mo on the segregation portion elongation of S50C material.

Claims (2)

[Claims] 1. A C: 0.4 to 0.8% in terms of% by weight,
Si; 0.15 to 0.35%, Mn; 0.3 to 2.0
%, P; 0.030% or less, S; 0.035% or less, A
1; 0.035% or less, the balance being Fe and unavoidable impurities in high carbon steel, Mo: 0.05 to 0.1
A high carbon steel for machine structure with excellent hot workability, characterized by containing 5%. 2. A high carbon steel ERW steel pipe having excellent hot workability, which is made of the high carbon steel for machine structure according to claim 1.