Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Patent
1998-02-05
1999-08-17
Yee, Deborah
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C21D 810
Patent
active
059388650
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process for producing a seamless steel pipe having high strength and excellent corrosion resistance, especially sulfide stress cracking resistance. More particularly, the invention relates to a process for producing a seamless steel pipe having high strength, good toughness and excellent corrosion resistance, especially sulfide stress cracking resistance, which is characterized by a combination of specified chemical composition of raw materials (steel billet) and specified thermo-mechanical treatment of the material. The process is also characterized by being performed in a continuous line comprising steps of pipe manufacturing and heat treatment thereof.
BACKGROUND ART
In a steel production factory which requires huge facilities, simplification of the process using so-called "on-line processing" has been investigated in order to save energy and to shorten the process. The "on-line processing" means to perform work such as rolling and heat treatment in one continuous manufacturing line. In the on-line processing, a method wherein a hot worked product is immediately quenched for utilizing its heat in the working is called "direct quenching". On the other hand, a method wherein the hot worked product is once cooled, and then subjected to heat treatment in a separate line is called "off-line processing", and quenching which is carried out in the off-line processing is called "reheating and quenching".
Recently, in the field of steel plate making by hot rolling, the off-line processing is diminished and most of the plates are produced in the on-line processing. In manufacturing of seamless steel pipes, however, the heat treatments such as quenching and tempering of the products is still mostly conducted in the off-line processing, because it is considered that quality and reliability of the product are more important. Needless to say, it is necessary for the off-line processing to include hardening facilities (a heating furnace and quenching equipment) and a tempering furnace in a separate line from the pipe manufacturing line.
In the conventional pipe manufacturing process, seamless steel pipes are produced in a consecutive hot working process comprising steps of piercing a steel billet by a pierce, extending and rolling by a plug mill or a mandrel mill, and shape-finishing by a sizer or a reducer. Sometimes, a press machine is used for piercing. Usually, the pipe manufactured in a working line forming is reheated, quenched and then tempered in a line separate from the pipe manufacturing line. In this way, the seamless steel pipes provided with sufficient properties such as strength, toughness and the sulfide stress cracking resistance are supplied to customers. The sulfide stress cracking is a crack which appears in high strength steels exposed to an environment containing sulfide, particularly hydrogen sulfide (H.sub.2 S). The "sulfide stress cracking" is referred to as "SSC" hereafter.
If the above mentioned usual quenching step is replaced by the direct quenching, simplification of the manufacturing facilities and reduction of the production are achieved. As mentioned above, "direct quenching" means the treatment, wherein the product, after hot working, is immediately quenched. In detail, it means a method to obtain a hardened metal structure, consisting of martensite or bainite by direct quenching from an austenite state at a temperature higher than Ar.sub.3 transformation point, in the hot working line.
For example, in Publication of Japanese Patent Application (referred to as PJPA hereafter) Nos. 58-224116, 60-75523 and 6-172859 disclose steel pipe manufacturing processes, including the direct quenching step such as enforced cooling, immediately after hot working. However, the pipes produced in the direct quenching process have coarse grain size in its microstructure and inferior toughness and corrosion resistance (SSC-resistance) in comparison with the pipes produced in the conventional off-line reheating and quenching process.
As mentioned above,
Kondo Kunio
Kushida Takahiro
Osako Hajime
Takabe Hideki
Sumitomo Metal Industries, LTC.
Yee Deborah
LandOfFree
Process for producing high-strength seamless steel pipe having e does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for producing high-strength seamless steel pipe having e, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for producing high-strength seamless steel pipe having e will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-311843