JPS5819432A - Manufacture of steel for line pipe with superior characteristic of stopping propagation of brittle crack - Google Patents

Abstract

PURPOSE:To manufacture steel products with high strength and superior characteristics of stopping the propagation of brittle cracks by subjecting a steel contg. specified amounts of C, Si, Mn, Nb, Al, N, V, Cu, Cr, etc. to rolling, hardening and tempering under specified conditions. CONSTITUTION:A steel contg. 0.04-0.18% C, 0.01-0.90% Si, 0.30-2.00% Mn, 0.008-0.060% Nb, 0.03-0.10% Al, 0.0080-0.0200% N, 1 or >=2 kinds of metals selected from 0.01-0.10% V, 0.05-0.50% Cu, 0.05-1.0% Cr, 0.05-0.50% Mo, 0.005-0.050% Ti, 0.007-0.070% Ce and 0.0010-0.070% Ca, and inevitable impurities is heated to >=1,200 deg.C and hot worked. The hot worked steel is cooled to a temp. below the Ar1 transformation point, austenitized again, cooled to a temp. close to ordinary temp. at a higher rate than air cooling rate, and tempered by heating to 400 deg.C- the Ac1 transformation point to convert most of the structure into a fine ferrite structure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a nine-line stainless steel steel having excellent brittle crack propagation arresting properties.

tI steel welding, θ and seamless steel pipe materials have been on the rise in recent years. With the increase in the number of Vegas pipe fins, the propagation arresting characteristics of brittle fractures and unstable ductile fractures are attracting particular attention. 14-DWT T (Drop W
eigbt Tear Te5t) is the actual /I? As a method for improving this magical crack propagation stopping property, which has been recognized as having a good correspondence with the fracture properties of carbon steel and has been incorporated into the API standard, so-called control trolling using Nb or ■added steel has been used. By heating the slab at a low temperature and rolling it in the non-recrystallization temperature range 1, the nodules are made finer, and further, during cooling after compaction, Nl), V! A rolling method that precipitates positive carbonization is widely used. However, this method significantly reduces the rounding productivity, which requires active control of rolling conditions, and is difficult to apply to seamless steel pipes and the like because the processing temperature is low.

The present invention provides a method for producing copper for nine-day use with excellent brittle crack propagation stopping properties by quenching and tempering heat treatment after rolling without using an unfavorable processing method such as controlled trawling. With the aim of making the microstructure after the main heat treatment mainly composed of fine-grained ferrite, Minami et al. ( The use of Nb, AtH and the combination with Ni, which is stimulated as a fine grain effect during α transformation, and S, which further improves arrest performance, results in high strength and brittle crack propagation stopping properties.
It is a method of manufacturing steel materials with excellent rFI properties, and involves rolling processing that is suitable for producing steel pipes without forming A plates.1.
1 r; is also easily applicable.

The Charpy impact test has traditionally been used as a method to measure the toughness of a material due to its simplicity. Evaluation 11: 7'L is low, so if the rough texture of the portion excluding the quenched six-layered portion is made finer on average, the toughness value in this trial method will be improved.

Therefore, elements (such as Nb) that are effective in refining the structure.
Although the effect of improving toughness in the Charpy impact test is exhibited even with single or I insects, it is not always possible to improve the structure of the quenched surface layer. In other words, even in the range of constituent elements where the structure after quenching is mainly ferrite, the cooling rate of the quenched surface layer is fast, resulting in an intermediate stage structure (hereinafter referred to as Bt41 weave).
Or this B, which is easy to form an island-like martensitic structure.
U (upper bainite) and island martensitic structures increase strength but are detrimental to toughness. In the present invention, in addition to Nb, At-
The present invention relates to a method for producing copper for isolating, which has high strength and excellent brittle crack propagation arresting properties due to the combined addition of N and Ni and the effect of the addition of 8.

The components of the steel that is the object of the present invention and reasons for manufacturing limitations will be described below.

The lower limit of rounding required for strengthening the steel and refining the structure after quenching is 0.04%, but if it is too large, the toughness will deteriorate due to the appearance of Bu and island martensite structure, and The upper limit is set to 0.1 because it has a negative effect on weldability.
8i with 8
．． 0.01 N, but since too much will deteriorate the toughness, the upper limit was set to 0.90.

The lower limit is set to 0 because it is necessary to increase M1 strength and toughness.
．． The upper limit was set to 30 N, but since too much N increases the hardenability and causes the appearance of Bu or island martensite structure, which causes toughness deterioration, the upper limit was set as ZOOX.

Carbonitrides precipitated during Nb1j hot-open forming processing and reheating prevent the coarsening of Ju-stenite crystal grains during re-austenitization, and also act as α-transformation nuclei during rapid cooling. The lower limit was set to 0.008 N because it was necessary to smooth the structure, but the effect would be saturated if it was too much, so the upper limit was set to 0.060.

^1. N mainly precipitates as AtN during reheating during quenching heat treatment, prevents coarsening of austenite grains, and also acts as alpha transformation nuclei in quenching sowing, refining grains of hepatite and improving the quenched surface layer. By suppressing the appearance of Bu or island-like martensitic structure in the area, the brittle crack propagation arresting property is improved by K. If At and N are too small, it will not be possible to obtain the ml precipitation amount that brings about the above effect, so the lower limit is set to 0.0 for each.
30N and α0080%, but if too much At will cause an increase in non-metallic inclusions, and N will cause an increase in 717-N, both of which will cause deterioration of toughness, so the upper limit was set at 0.1ON for each.

It was set to 0.0200%.

By lowering the α transformation temperature during quenching,
It is possible to refine the ferrite grains after quenching. If the amount is too small, the effect will not be achieved, and if it is too large, the effect will be saturated, and it will be expensive.
It was set to 00X.

No. 8 has the effect of improving brittle crack propagation arresting properties due to formation of Nakaaki A-based inclusions during rolling. The lower limit of rounding is set at α008N, where the effect cannot be seen if the rounding is too small, but the effect is weakened if it is too large, so the upper limit was set at 9,020N.

In addition, two or more of the following elements should be added beforehand.V is mainly precipitated as a carbide during tempering heat treatment and is intended to increase strength, but if it is too small, it will not be effective, and if it is too large, the effect will be saturated, so Oo1 ~()1°9'.

() The purpose of horses is to increase their strength, but too little will have no effect, and too much will increase strength and deteriorate toughness, so 0.05 to 1.0% and 0.05 to 0.50%, respectively. And so.

The purpose of 0 to On is to reduce the directionality of toughness and improve the toughness of the welded joint by controlling the form of sulfides, but if it is too little, it is ineffective, and if it is too much, it will cause an increase in inclusions and deteriorate the toughness. 0.007 to 0.070 X, respectively.
O, IJ 010~0.070 N 3, Ti increases the coercion by precipitation of l'i carbide, but if it is too little, it is ineffective, and if it is too much, huge nitrides are generated and the toughness is reduced, so 0005~0 .05% and circle.

The purpose of Ou is to increase strength as well as provide weather resistance, corrosion resistance, and -1 hydrogen-induced cracking resistance, but if there is too little, the effect will be ineffective, and if there is too much, the effect will be saturated, so 005 to 05ON
And so.

Among the hot working conditions for forming steel plate% seamless steel pipes, etc., the heating temperature is #1 most of Nb, I\V before hot forming.
This temperature must be kept high enough to form a solid solution. This temperature is controlled by the solubility products of O, N, Nb, At, and V, but is within the range of the present invention. The heating temperature is 1200°C because N, Nb, and the amount of V all form a solid solution at a temperature of 1200°C or higher and do not cause any problems in terms of hot forming processing efficiency.
℃ or higher.

Furthermore, the present invention does not involve rolling at a low temperature as in controlled P rolling, but rather uses quenching and tempering heat treatment. The rolling conditions are not particularly limited. In this case, rolling, extrusion, etc. are used, but the processing method is not limited in the present invention. In order to perform heat treatment after the hot forming process is completed, it is necessary to cool the product to a temperature below the −IJjArs point. However, the cooling rate is not particularly limited.Also, the Ar1 point in this case is the temperature at which all austenite completes the K transformation of low-temperature transformed structures (7-elite, barite, bainite, martensite).Then, the Ar1 point or lower When austenitizing is performed by reheating from a temperature of In addition, N1 acts as α-transformation nuclei, and the fine-grained effect of N1 forms a fine-grained ferrite structure from the quenched surface layer to the center of the wall thickness, improving brittle crack propagation arresting properties. It is desirable to keep the holding time at the austenitizing temperature to a minimum necessary *Jl! to prevent coarsening of austenite crystal grains.Also, the cooling rate during rapid cooling varies depending on the name of the additive, but the structure after cooling It is essential that the cooling speed be such that most of the ferrite becomes fine-grained ferrite.Therefore, in the present invention, the cooling speed is not limited, but it is preferably faster than air cooling. 4 to stabilize the toughness of
00m'C or more is necessary, but Sc1. If it exceeds + shellfish, the original meaning of tempering will be lost, so the upper limit should be set to less than 1 Ac point.

- Furthermore, the apparatus used for the quenching and tempering heat treatment includes furnace heating, induction heating, flame radiation, salt bath, gold maple bath, etc., but is not particularly limited in the present invention. However, the induction heating device 1
The shorter heating time, which facilitates homo-austenitization, is more advantageous for the steel of the present invention.The steel plates and seamed steel pipes manufactured by the method of the present invention with excellent brittle crack propagation arresting properties are particularly suitable for thick-walled materials. It is effective for line and guide use.

Embodiment -J of the present invention will be described below.

Table 1 shows the chemical components of the example test materials, and Table 2 shows the hot forming and rolling conditions and heat treatment conditions. Furnace heating, JL bath, and induction heating equipment were used for heat-treated skin.

As a monovalent means of brittle crack propagation arresting property, B-1)
W'r i'' was carried out, and in addition, 2 V notched sharpy impact, which has been commonly used as a toughness evaluation method since JlE, was also carried out.The sample location of the test piece was B-■
'r'rit full thickness, Charpy test was at the center of the thickness. For Naori-D'wV'r'r, in order to more accurately evaluate the brittle crack propagation arresting characteristics, the notch portion of the test piece was previously treated with TlG11i Be 1 treatment and then press notched. With this method, the reverse fracture surface that often appears in the case of only press notches (a ductile crack once starts from the bottom of the notch and then transforms into a brittle crack) did not appear round.

2.3 shows the Charpy test, B-DWTT, and tensile test results. It is clear from the same table that the quenching table B-DWT'l
', it can be seen that the steel of the present invention is significantly improved compared to the comparative steel.

In other words, according to the present invention, in addition to the fine grain effect of Nh, AI-N and Ni, the structure of the quenched surface layer can be improved, which was not possible with conventional methods. By combining the improvement effects of S, it is possible to create a line/l (plate) with excellent brittle crack propagation arresting properties using the usual quenching and tempering heat treatment method without using severe compaction methods in low temperature ranges such as control rolling. It becomes possible to produce copper for industrial use.

[Brief explanation of drawings]

Figure 1 shows the steel N E-Yuri and Charpy properties, DW'
It is a figure which shows the relationship of l'T characteristics.

Claims (3)

[Claims] (1) O: α04-0.18%, 8i: 0.01-0.
90%, Me: 0.30-200%, Nb: αOOS
~0.0609, At:o, os~α10%, N:0.
0080~α0200%, ■: α01~0.10X,
Ou: 0.0 0.50X, Or: α05~1.0
X% MO: α05~part O%, Tl: αO05~0.05
0X%O@:0.0G7~α070%, 01:α00
Steel containing 10 to 0.070% of one or more types depending on the purpose and other unavoidable impurities is heated to a temperature of 1200°C or higher and subsequently hot worked, and then undergoes Art transformation. The material is cooled to a temperature below the point, becomes austenite again, and then is cooled to near room temperature at a faster rate than the air cooling rate, and then heat-treated to a temperature of 400°C to the ACl transformation point to form a mostly fine-grained ferrite structure. 1. A method for producing a steel for line production with excellent brittle crack propagation arresting properties. (2) O: Q, 04-1118N, 8i:
α01~0.9ON, Mn: 0.30-2-008,
Nb: aO08-a06G%, M: 0.03-0.
10X, N: 0.008 G-0,0200x, V: (101~al OX%Ou: 0.05~
0.50X, Or: α05~1. ON, Mo: α0
5-0.50-, Tl: 0. O05~a050X, O
e: 0.007~0,070k, Oa: 0.00
1G-0,070
A method for producing a steel for an inno-zoobe having excellent brittle crack propagation arresting properties, which is characterized by subjecting the steel to a heating and tempering heat treatment at a temperature of the Ac1 transformation point to form a fine-grained heptite structure. (3) 0: 0.04-0.18X, Sl: 0
．． 01~0.90X, Mn: 0.30~2.0
ON, Nb: 0.008~O,060% 1M:
α03~αl0XN: 0.0080~00200X,
v:α01-0.10X%Ou: 0.05-0.50
X, Or: α05~1.0 X, Mo:
0.05'-0, 50X, Tl:α0G5~α
Contains 050% of one or two or more E depending on the purpose,
Furthermore, Ni: 0.20~ZOOX%S: αOOS~0.
Steel containing 020 N and other unavoidable impurities is heated to a temperature of 1,200°C or higher, followed by hot working, then cooled to a temperature below the Arl transition point to austenitize again, and then air cooled and hardened. A line pipe with excellent brittle crack propagation stopping properties characterized by being cooled at a faster rate to near room temperature and then subjected to WILK heating and tempering heat treatment at a temperature of 400°C to AC1 transformation point to form most of the fine-grained ferrite grains. Manufacturing method for industrial steel.