JPH01108314A - Production of hoop for electric welded tube having excellent cold workability - Google Patents

Abstract

PURPOSE:To produce a hoop for an electric welded tube having excellent cold workability by subjecting steel contg. specific ratios of C, Si, Mn, P, S, N, and SolAl to hot rolling at a specific hot rolling temp. and coiling temp. CONSTITUTION:The steel which contains, by weight 5, 0.003-0.20% C, <=1.0% Si, 0.1-0.8% Mn, <=0.03% P, and <=0.02% S, contains N and SolAl so as to satisfy the range enclosed by OABC [O (0.0), A(0, 0.08), B(0.006, 0.063), C(0.008, 0), where the contents on the lines OA, OC are not included and the contents on the lines AB, BC are included] and consists of the balance Fe and inevitable impurities is prepd. This steel is then hot rolled in such a manner that the hot rolling temp. and the coiling temp. satisfy the range ( deg.C) enclosed by DEFG [D(1050, 300), E(1050, 700), F(1150, 600), G(1210, 300), where the temps. on the lines DE, FE, FG, GD are included]. The hoop for the electric welded pipe having the uniformized hardness in the electric welded part and base material part in a cold drawing stage is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of manufacturing a steel band for electric resistance welded steel pipes used for cold working.

[Conventional technology]

Recently, electric resistance welded steel pipes have been increasingly used as steel pipes for machine structures such as cylinders and automobile parts. For such uses, cold drawing is often performed to improve the dimensional accuracy and surface roughness of the electric resistance welded steel pipe. As shown in Figure 1, the manufacturing of cold-drawn steel pipes made from ERW steel pipes involves heat treatment to soften the hardened structure of the ERW parts as welded, followed by cold drawing. After softening and annealing, cold drawing is performed once or several times. The cold-drawn steel pipe thus produced is subjected to stress relief annealing and then finished into a predetermined shape by secondary forming such as expansion, contraction, and bending to obtain a mechanical structural steel pipe as a product.

Conventionally, steel strips used as raw materials for manufacturing ERW steel pipes have been manufactured by heating m-slabs at 1180 to 1210°C, then hot rolling them, and then rolling them up at 650 to 700°C. .

[Problem that the invention seeks to solve]

However, in the conventional manufacturing method of cold-drawn steel pipes using such ERW steel pipes as raw materials, when softening and annealing is performed after cold drawing, the ease of recrystallization differs between the ERW part and the base metal part. Therefore, depending on the amount of cold drawing and the softening annealing temperature, the respective ferrite grain sizes change, which has the disadvantage of impairing the formability of the cold drawn steel pipe.

In particular, during tube expansion processing, there is a problem in that cracks are likely to occur due to preferential deformation in the electric resistance welded portion where the ferrite grain size locally becomes coarse.

The present invention has been made in view of such conventional problems, and in particular provides a method for manufacturing a steel strip for electric resistance welded steel pipes in which the hardness of the electric resistance welded portion and the base material portion is made uniform during the cold drawing process. That is.

[Means to solve the problem]

Therefore, the present invention provides C: 0.003 to 0.20 wt.
%.

Si: 1. Q wt% or lesse Mn: 0. I
NO, 8wt%, P: 0.03wt% or less, 8:0.0
2wt% or less, and N and So1 person in Figure 2, 0(0,0), A(0,0,08)B(0
,006,0,065),C(0,008,0)However,
The steel contains 0 people, OC is not included on the machine, AB and BC are included in the range surrounded by 0ABC, and the remainder consists of re and unavoidable impurities, and the hot rolling heating temperature and the winding temperature are In Figure 3, D(1050,300), n
(xo5o, woo).

? (1150,600), G(1210,300)
However, the basic feature is that hot rolling is performed so as to satisfy the range surrounded by DFiPG including the lines DB, EF, FG, and GD.

The reasons for limiting the component composition and hot rolling conditions of the present invention will be explained below.

C is an element that can most easily ensure room-temperature strength of steel pipes, but if it is less than 0.003 wt%, the desired strength cannot be ensured, so it is set to 0.003 wt% or more.

Furthermore, when C exceeds 0.20 wt%, the formation of quenched fibers in the ERW becomes noticeable, and heat treatment of the ERW is necessary to equalize the hardness of the ERW and the base material of the cold drawn steel pipe. Since it is necessary, the upper limit was set to 0.20 wt%.

Si is an element that inhibits hot and cold workability.

, the smaller the better, the upper limit is 1.0w1%
And so.

Like C, Mn is an element that increases the room temperature strength of steel pipes,
In order to obtain the desired strength, it is necessary to set the content to 0.1 wt% or more. On the other hand, if Mn exceeds 0.8 wt%, heat treatment of the ERW steel pipe is required to equalize the hardness of the ERW part and the base metal part of the cold drawn steel pipe, so the upper limit is set at 0.8w.
It was set as t%.

P is an element that inhibits the workability of the central segregation zone, and the smaller the amount, the better, and the upper limit was set at 0.03 wt%.

S is also an element that deteriorates the workability of the central segregation zone, and 0.
If it exceeds 0.02 vrt%, the workability of the central segregation zone deteriorates, so this was set as the upper limit.

Figure 2 shows that steel strips with different So1 and N contents are produced under the hot rolling conditions defined in the present invention, and after this is made into an ERW steel pipe, cold drawing is performed, and this steel pipe is expanded. A test was conducted to determine whether or not cracks occurred. According to this, 5olA in the range exceeding straight line λB and straight line BC
Cracks occur within the range of L and N contents, and the workability of the cold-drawn steel pipe deteriorates. On the other hand, 0 (0,0) A (0,0,08) B (0,006, o, oas) C (0,008,0) (unit: wt%) (7
) No cracking was observed in the range surrounded by OABC (excluding straight lines OA and OC, but including straight lines AB and BC). Therefore, in the present invention, Sat and N are defined within the above ranges.

Next, the heating temperature and winding temperature during hot rolling will be explained.

FIG. 3 shows steel strips produced by varying the hot rolling heating temperature and winding temperature for steel having the composition defined in the present invention.
After making this into an ERW steel pipe, it was subjected to cold drawing, and a pipe expansion test was conducted to check for cracks. According to this, the heating temperature and winding temperature during hot rolling are as follows.

D (1050,300), I! ! (1050,
700).

F (1150,800), G (1210,30
0) [Unit: °C] The range surrounded by DEFG (1m in a straight line) D B!
.

(including EF, PG, and DG), no cracking occurs and good cold workability is obtained.

The reason why the lower limit of the winding temperature is set to aOO°C is that if it is less than 300°C, the winding device will be overloaded.

〔Example〕

Steel with the chemical composition shown in Table 1 is heated to 1070°C to 1200°C.
After heating to a temperature of , it was rolled and rolled up at 600 to 700°C. After welding this steel strip into ERW steel pipes (outer diameter 76.3 ms, pipe thickness 7.6 mm), these ERW steel pipes were cold drawn (outer diameter 31.8 mm, pipe thickness 3.0 m111).
L/, then softening annealing (730°C) was performed. Table 1 also shows the expansion in of the cold drawn steel pipes produced in this manner.

The expansion rate is determined by cutting a test piece from a cold-drawn steel pipe (outer diameter: d), pressing the end of the pipe at room temperature into a trumpet shape with a conical tool at an angle of 60', and checking for cracks. When d is the outer diameter of the expanded tube end when this occurs, it is defined by the following formula.

-d Pipe expansion rate (%) w -X 100 As shown in Table 11ζ, by satisfying the compositional conditions of steel and the manufacturing conditions of the raw steel strip specified in the present invention,
Steel pipes with good cold workability can be manufactured.

〔Effect of the invention〕

According to the present invention described above, the AJN of the electric resistance sewing part and the base material part is
A cold-drawn steel pipe with high cold formability can be manufactured by obtaining an ERW steel pipe with an equal amount of precipitation and cold drawing the as-welded ERW steel pipe.

[Brief explanation of the drawing]

FIG. 1 shows the flow of the cold drawing process for using an ERW tube as a material. FIG. 2 shows the relationship between the amount of 5olAl and N-[il and cracking when a cold drawn steel pipe is expanded. FIG. 3 shows the relationship between hot rolling heating temperature, winding temperature, and cracking when a cold drawn steel pipe is expanded. Patent applicant: Nippon Koukan Co., Ltd. Inventor: 1) Dodo Ryu
Toshi Takamura 4 Takeshi Yasutani 1 Figure r-=1 1 ERW steel pipe 1 B: Cold drawing process 1-r-
-J

Claims (1)

[Claims] C: 0.003 to 0.20 wt%, Si: 1.0 wt%
Below, Mn: 0.1-0.8wt%, P: 0.03wt
% or less, S: 0.02wt% or less, and N and SolA_
In Figure 2, l is O (0, 0), A (0, 0.08), B (0.006, 0.065), C (0.008, 0).
However, if the steel contains so as to satisfy the range surrounded by OABC, which does not include the lines of OA and OC but includes the lines of AB and BC, and the remainder consists of Fe and unavoidable impurities, the hot rolling heating temperature and the winding temperature are In Figure 3, D (1050, 300), E (1050, 700), F
(1150, 600), G (1210, 300) However,
A method for producing a steel strip for electric resistance welded steel pipes having excellent cold workability, which comprises hot rolling to satisfy the range surrounded by DEFG, which includes lines DE, EF, FG, and GD.