JPS5831031A - Production of steel pipe having high strength and toughness - Google Patents

Abstract

PURPOSE:To make the production of a steel pipe having high strength and toughness in the stage of producing the steel pipe of low alloy steel having specific carbon equiv. values and subjecting the pipe to hardening and tempering by effecting the tempering by the heat retained by the pipe itself. CONSTITUTION:An ingot of low carbon low alloy steel contg. 0.26-0.45 carbon equiv. is hot-worked to a steel pipe or after the ingot is hot-rolled to a plate material, the plate material is cold-formed to a steel pipe and the pipe is heated to 880-1,050 deg.C. Immediately, the pipe is quickly cooled and hardened by forced cooling stronger than air cooling down to about 150-500 deg.C, whereby martensite, bainite and fine grain ferrite are deposited from austenite to provide higher strength. Further, the steel pipe is tempered by the heat retained by itself from said temp., whereby yield strength and toughness are improved, and the steel pipe having outstanding properties is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preparing steel pipes with excellent strength and toughness.

Steel pipes used for transporting fluids, AIIS for bridges and high-rise buildings, and structures have excellent strength and toughness! I can ask for it. Until now, many steel pipes with excellent toughness have been used as low-alloy steel pipes to which trace amounts of toughness-improving elements such as steel KNi, Or, and No are added. However, the steel pipe is made by heating the pipe material to a degree of oais above the mcs transformation point, applying a sieve λmM to rapidly cool it to give it strength, and then reheating and cooling it to il& below the AC1 transformation point. Since the material is subjected to L treatment to impart toughness, it is exposed to high temperatures for a long time, and the toughness is excessively improved as the material undergoes heat treatment from a hard structure to a soft structure. 90-strength steel has unbalanced properties of strength and toughness, and because of the back-casting process, it causes a decrease in productivity and increases production costs due to large energy consumption. The problem of deterioration is generally solved by adding large amounts of reinforcing elements.

The purpose of the present invention is to provide a method for manufacturing steel pipes with excellent strength and toughness that does not involve tempering treatment. After being processed into a mature tube or hot rolled and then processed into a cold tube, it is heated to a temperature of 880 to 10,500 and rapidly cooled at a rate higher than air cooling until the middle of cooling.

This is followed by a method of manufacturing steel pipes with excellent strength and toughness, in which the steel pipes are tempered using their own heat.

The present invention will be explained in more detail below.

First, molten steel is melted in a melting furnace such as a converter or an electric furnace, and then converted to OeQ: O by continuous casting method or ingot making method.
- Manufacture of low alloy steel slabs of 26~0.451G.

0-E1+ is calculated by the following blue "#-1'4.-Weldability of steel-5 strength.

It affects toughness, and in the present invention, its range is limited based on yield strength, maximum hardness, and weldability.

Mn Ov Ni Ou M
o VOeq=O+ /6+ I, + I, +
/, + /ten/(qII) That is, as shown in the example in Table 2, if @Oe噸 is less than 0.269G, the yield strength of the as-quenched material cannot be obtained, and if it exceeds 0.4516e, the steel pipe O maximum hardness However, disadvantages occur that result in a decrease in the weldability and weldability.

Further, in the present invention, the composition IIt of the low-alloy steel slab is not particularly limited, but it is preferably FiO: 0.04 to 0-18 because the desired properties can be stably obtained.
5b s St: 0-01~low 5 ref #him
: 04-2.0%, P: 0.025 or less,
S: 0.020 inch or less.

N: 0.010% or less, Ht: O, Oe: 0-0010 or more as required.
0-070 Regret + 0 Admiration: 0.007~0.070
Sorry, Nb: 0.01~0.1011
, Cu: 0.05~0-50,
Nl: 0.0 5-3.0%, Or: 0
．． 05~! -01, Mo: +1-05~o, sl.

Tt! 0.005~0. (150%, V
: Two or more types of 0-010 to 0-10 types can be added.

A steel billet processed into a thermofunction tube or hot rolled into a plate shape! ,
Formed into a tubular shape by cold-opening by bending or twisting 4! , Heat to 11 degrees 880-1050℃. This heating was carried out at a quenching temperature that imparts strength to the tube-forming material, and was set at 880°C or higher because if it was lower than 880°C, the austenite crystal grains would not be sufficiently sized and homogeneous material properties could not be obtained. In this heating, after heating or after cooling to a temperature below the Ar & transformation point.

Cannot be pulled even if heated immediately. However, the Ar1 transformation point in this case is a temperature at which the amount of α transformation is 6016 or more.

(If the temperature exceeds 150C, the austenite crystal grains become coarse, forming coarse martensite, bainite, and ferrite structures, resulting in aem properties after quenching.

The pipe material heated to such a quenching temperature is immediately cooled by air-cooling or more at a cooling rate that is shielded with O to give it strength, and then tempered using the heat possessed by the steel pipe itself, that is, the heat possessed by the steel pipe itself. and imparts yield strength and toughness.

The stop temperature of rapid cooling, i.e., the return temperature due to the steel pipe's own heat, is determined by various conditions such as the content of reinforcing elements, the wall thickness of the steel pipe, the temperature before rapid cooling, and the rapid cooling rate. It is preferable to carry out the process at a temperature of 150 to 500°C, where the p-yield strength increases due to the disappearance of the generated dislocations or p-fixation by precipitated carbides. In the rapid cooling process, martensite, 4-nite, and fine-grained 7-erite appear from austenite, imparting strength, and further, yield strength and toughness are imparted by tempering.

Examples of the present invention will be described below.

Table 1 shows the chemical composition of the sample steel of the example, and the sample steel has a tt symbol A-z 6 people 1 to 31 charges.

The component system that is essential to the present invention is 20 charges. A-Z is a test material made by compressing laboratory melted material into a plate, and O, Mn,
By changing the C@ basket in various ways depending on the pot type combination of Nl, Or, V, for nine people 0 person 1 to person 5, -Q, O based on 18i -Mu -Nb $ t'
u.

It is manufactured as a seamless steel pipe material using a combination of Ni, Mo, V, and 4D wood.

Table 2 shows the processing conditions and mechanical properties.

The tensile strength of quenched materials increases with the increase in C and S, but the yield strength decreases rapidly when the Oeq reaches 0.26 or more, or the poor LOe increases. Even if it is strong [F! It was found that it is difficult to produce high-strength timber without increasing yield strength.

Furthermore, when 0@q becomes 0.3496 or more, the yield strength r increases again, but it was found that this increase in yield strength 0. It is clear that the quenched material is inferior in toughness and yield strength to the treated material and the material tempered by self-retained heat of the steel pipe according to the present invention; it is clear that t≧.

According to the heat treatment method described in the present invention, both tensile strength and #deflection strength increase as the Oeq increases, and the strength is higher than that of the current quenched-tempered material, and the toughness level is also the same as that of P1y. have.

In sample material 2 with an Oeq of 0.31, the austenitization temperature is high and the WilK produced by the present invention does not correspond to #, but the toughness seems to deteriorate.

As explained above, in the present invention, after processing the thermofunction tube or hot rolling and cold tube forming,
It is heated to osoc and rapidly cooled faster than air cooling until halfway through the cooling process, and then tempered using the heat possessed by the steel pipe, resulting in a product with a width of 1 compared to normal mature coral (quenched-tempered). At the same time, it does not require energy due to tempering process, and #! It is a novel method that could not be predicted by conventional methods, as it makes it possible to measure a significant reduction in the structural and industrial stress O.

Commissioner of the Patent Office, 1. Indication of the case Japanese Patent Application No. 128409 No. 128409 2, Name of the invention 3. Process for manufacturing steel pipes with excellent strength and toughness 3. Person making the amendment Relationship to the case Applicant's address (residence) ) 2-6-3-8 Otemachi, Chiyoda-ku, Tokyo
6. Contents of the amendments The contents of the amendments are as per the attached sheet.il+ Corrections are made as per T1 in 11B5 of the patent claim of the present application.

r(11Cep O, 26~0.45%) A low alloy steel billet is subjected to hot tube forming or after hot rolling and cold tube forming process, the temperature is 880℃. A method for manufacturing steel pipes with excellent strength and toughness, which is characterized by heating the pipe to ~1050°C, performing rapid cooling faster than air cooling until halfway through the cooling process, and then tempering the pipe using the tube's own heat.'' (2) Specification page 1N, line 20, page 2, lines 16 and 17.

Off page 4 lines 6, 7, 9, 13 lines #Off page 9 lines, 10
Correct "pipe making" in the lines to "pipe making" respectively.

(3) Corrected as 1'3'liS line, O8 end of Qin line.

(4) Correct "transfer" to "transposition" in line 5119.

Claims (1)

[Claims] (1) A low alloy steel billet with an Oeq of O-26 to 0.4511 is hot-formed or hot-rolled and then cold-formed, then heated to an iI degree of 880 to 10,501C and rapidly cooled more than air-cooled. Cooling is performed halfway through the cooling process. A method for producing steel #g with excellent strength and toughness, which is characterized by subsequently tempering the steel pipe using its own heat.