Microstructure and Mechanical Properties of J55ERW Steel Pipe Processed by On-Line Spray Water Cooling
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metals Article Microstructure and Mechanical Properties of J55ERW Steel Pipe Processed by On-Line Spray Water Cooling Zejun Chen 1,2,*, Xin Chen 2 and Tianpeng Zhou 2 1 State Key Laboratory of Mechanical Transmission, College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China 2 College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China; [email protected] (X.C.); [email protected] (T.Z.) * Correspondence: [email protected]; Tel.: +86-23-6511-1547 Academic Editor: Soran Birosca Received: 17 August 2016; Accepted: 4 April 2017; Published: 23 April 2017 Abstract: An on-line spray water cooling (OSWC) process for manufacturing electric resistance welded (ERW) steel pipes is presented to enhance their mechanical properties and performances. This technique reduces the processing needed for the ERW pipe and overcomes the weakness of the conventional manufacturing technique. Industrial tests for J55 ERW steel pipe were carried out to validate the effectiveness of the OSWC process. The microstructure and mechanical properties of the J55 ERW steel pipe processed by the OSWC technology were investigated. The optimized OSWC technical parameters are presented based on the mechanical properties and impact the performance of steel pipes. The industrial tests show that the OSWC process can be used to efficiently control the microstructure, enhance mechanical properties, and improve production flexibility of steel pipes. The comprehensive mechanical properties of steel pipes processed by the OSWC are superior to those of other published J55 grade steels. Keywords: electric resistance welding (ERW); steel pipe; on-line spray water cooling (OSWC); microstructure; mechanical properties 1. Introduction In view of the ever-increasing pipeline and operating pressure, the development of high strength steels makes a significant contribution to pipeline project cost reduction. Increasing the strength of pipeline steel allows for the thickness of the pipeline walls to be significantly reduced, with a consequent reduction in weight and cost. The high strength, in combination with high toughness and formability, are important requirements for the pipeline steels [1]. Many efforts have been made to improve the strength and performance of pipeline steels. The most effective method to improve the welding performance of pipeline steels is microalloying [2–7]. For example, adding Ti [2,3], adding Nb [4–6], adding Mo and Cr [7], etc. Generally, there are four methods to produce steel pipes: fusion welding, electric resistance welding (ERW), seamless hot rolling, and double submerged arc welding (DSAW). The manufacturing procedures of ERW steel pipes begin with a coiled plate of steel of appropriate thickness and specific width to form a pipe that conforms to particular specifications. Steel ribbon is pulled through a series of rollers that gradually form it into a cylindrical tube. As the edges of the cylindrical plate come together, an electric charge is applied at proper points to heat the edges so they can be welded together [8]. The conventional ERW manufacturing procedures of steel pipes and tubes are shown in Figure1. Metals 2017, 7, 150; doi:10.3390/met7040150 www.mdpi.com/journal/metals Metals 2017, 7, 150 2 of 15 Metals 2017, 7, 150 2 of 15 Figure 1. Conventional electric resistance welding (ERW) manufacturing procedures of the steel pipes Figure 1. Conventional electric resistance welding (ERW) manufacturing procedures of the steel pipes and tubes. and tubes. ERW steel pipe production is high-speed and comparatively economical, because most of the ERWprocess steel can pipebe automated. production ERW is steel high-speed pipes have and uniform comparatively wall thickness economical, and outer becausedimensions, most and of the processthey can can be be automated.made with a wide ERW range steel of pipes specifications. have uniform Owing wall to these thickness advantages, and outerthe production dimensions, and and they canapplication be made of withERW asteel wide pipes range have of risen specifications. steadily in recent Owing years. to these The performance advantages, requirements the production of and applicationsteel pipes ofERW have steelcontinuously pipes have increased risen with steadily the development in recent years. of the The oil performanceand gas industry. requirements There is of strong demand to develop steel pipe with both high strength and excellent formability. steel pipes have continuously increased with the development of the oil and gas industry. There is High-performance ERW steel pipes can substitute for seamless steel pipes in some cases, which strongcan demand significantly to develop reduce the steel engineering pipe with costs. both However, high strength it is difficult and excellent to obtain formability. good performance by High-performanceusing the conventional ERW ERW steel process. pipes The can reason substitute is that forERW seamless steel pipes steel are pipes manufactured in some cases,by cold which- can significantlyroll forming of reduce steel bands, the engineering and the ductility costs. of However, steel pipes itis isinevitably difficult inferior to obtain to that good of performancethe steel by usingband thedue conventionalto the work hardening ERW process. of cold roll The forming. reason Furthermore, is that ERW the steel quench pipes hardening are manufactured caused by by cold-rollrapid forming cooling ofafter steel welding bands, has and the the same ductility effect on of the steel mechanical pipes is inevitably properties inferiorof the steel to thatpipe ofin thethe steel bandweld due tojoint the [9]. work Another hardening weakness of coldof the roll conventional forming. ERW Furthermore, process is thethat quench the production hardening flexibi causedlity by rapidof cooling steel pipes after with welding different has specifications the same effect is limited on theby certain mechanical production properties lines. The of themain steel bottleneck pipe in the weldto joint increasing [9]. Another the productivity weakness of of ERW the conventionalsteel pipe is the ERW speed process of the straight is that the seam production welding, which flexibility is of much more notable when manufacturing small-diameter steel pipes. A manufacturing technique that steel pipes with different specifications is limited by certain production lines. The main bottleneck involves reducing diameter of large ERW steel pipe is more efficient and reasonable, and could easily to increasingincrease the the productivity productivity of small of ERW-diameter steel pipeERW issteel the pipes. speed of the straight seam welding, which is much moreTo notableimprove when the mechanical manufacturing properties, small-diameter the Kawasaki steel Steel pipes. Corporation A manufacturing developed technique a tube that involvesproduct reducing called diameterHISTORY of(high large-speed ERW tube steel welding pipe is and more optimum efficient reducing and reasonable, technology) and pipe could [10]. easily increaseThe theHISTORY productivity pipe not of only small-diameter has high strength, ERW steelexcellent pipes. formability, and uniformity of the seam Tohardness improve due the to mechanical the realization properties, of ultrafine the Kawasakimicrostructure Steel Corporationand tiny, dispersed, developed and a spheroid tube product calledcementite HISTORY in (high-speedthe stretch reducer, tube welding but also andfeatures optimum high productivity reducing technology) and flexibility pipe of [ 10production]. The HISTORY by pipeapplying not only a has stretch high-reducing strength, process excellent to pipe formability,-making [11,12]. and uniformity of the seam hardness due to the realizationThe thermo of ultrafine-mechanical microstructure control process and (TMCP) tiny, dispersed, is very important and spheroid to the microstructural cementite in control the stretch of high-performance products [13]. Recently, a new generation of thermo-mechanical controlled reducer, but also features high productivity and flexibility of production by applying a stretch-reducing process (NG-TMCP) for steel production was developed [14], and it has been applied to all kinds of processsteel to products pipe-making (e.g., line [11 ,pipe12]. steels [15]). The NG-TMCP takes the super on-line accelerated cooling The(Super thermo-mechanical-OLAC) and the precise control control process of cooling (TMCP) routes is by very a heat important-treatment to on the-line microstructural process (HOP) controlas of high-performancecore technologies. productsThe NG-TMCP [13]. Recently,consists of aan new advanced generation accelerated of thermo-mechanical cooling device with controlled the processpurpose (NG-TMCP) of reaching for the steel highest production cooling rates, was developedas well as induction [14], and heating it has equipment been applied for HOP to all [16]. kinds of steelThe products steel products (e.g., line can pipe obtain steels high [15 strength]). The NG-TMCPby transformation takes thestrengthening, super on-line high accelerated toughness coolingby (Super-OLAC)refinement andof the the transformed precise control microstructure, of cooling and routes reduce by the a heat-treatment alloying elements on-line [17]. process (HOP) as core technologies.In the conventional The NG-TMCP manufacturing consists technology of an advanced of ERW accelerated steel pipes, cooling off-linedevice heat treatment with the is purpose an essential procedure to enhance the mechanical properties,