中国微合金化技术与含铌钢发展30周-of Evolution

中国微合金化技术与含铌钢发展30周-of Evolution

High Strength Microalloyed Linepipe: Half a Century

of Evolution

J. Malcolm Gray, F. Siciliano

Microalloyed Steel Institute

5100 Westheimer, Suite 540, Houston, TX 77056 USA

INTRODUCTION

Microalloyed low carbon steels, originally termed High Strength Low Alloy (HSLA) steels, were first introduced in the late 1930’s. The elements niobium vanadium and titanium were added singly, in amounts as low as 0.005 to 0.010 percent in early steels, but later in combination as strengths increased and the metallurgical approach became more refined. The predominant melting method at that time was the Siemens - Martin Open Hearth Process, the steels were ingot cast, usually semi-killed, and in many cases were normalized. Over time this manufacturing approach has dramatically changed. Very low carbon, fully killed, steels are now continuously cast than converted to plate and coil using complex thermomechanical controlled processing (TMCP) regimes. Via this revolution the rolling mill has emerged as a sophisticated metallurgical tool, not simply a means of achieving the final product shape.

Microalloying was first introduced in ship plate, beams, bridge steels, reinforcing bar and heat treated forgings and was not introduced into linepipe steels until 1959 [1]. However, the escalating technological demands of high pressure pipeline systems can be credited with the rapid evolution of HSLA technology since then.

Today’s pipeline designs consider all aspects of a steel’s performance, including strength, toughness, weldability, fatigue and collapse resistance, strain tolerance, as well as environmental degradation such as stress corrosion cracking, and resistance to sour hydrocarbons containing H2S and CO2, which combination of properties must be achieved at affordable prices.

Some of the technological gains and escalating end user expectations have evolved naturally, as competitive producers applied technology developed primarily for other steel products, whereas other requirements may have been provoked by catastrophic and costly failures. The time period of interest involves the last 50 years during which dramatic changes have taken place in steel manufacturing, plate rolling and pipe making technology. Nowadays the melt shop is concerned with ultra purification (impurities measured in ppm), rather than with