Effects of the Primary NbC Elimination on the SSCC Resistance of a HSLA Steel for Oil Country Tubular Goods.

Tianyi Zeng,Ke Yang,Shuzhan Zhang,Yan Tian,Wei Wang,Mingchun Zhao,Xianbo Shi,Wei Yan

doi:10.3390/ma14185301

Abstract

Sulfide stress corrosion cracking (SSCC) has been of particular concern in high strength low alloyed (HSLA) steels used in the oil industry, and the non-metallic inclusions are usually considered as a detrimental factor to the SSCC resistance. In the present work, continuous casting (CC) and electroslag remelting (ESR) were adopted to fabricate a 125 ksi grade steel in order to evaluate the effect of microstructure with and without primary NbC carbides (inclusions) on the SSCC resistance in the steel. It was found that ESR could remove the primary NbC carbides, and hence, slightly increase the strength without deteriorating the SSCC resistance. The elimination of primary NbC carbides caused two opposite effects on the SSCC resistance in the studied steel. On the one hand, the elimination of primary NbC carbides increased the dislocation density and the proportion of high angle boundaries (HABs), which was not good to the SSCC resistance. On the other hand, the elimination of primary NbC carbides also induced more uniform nanosized secondary NbC carbides formed during tempering, providing many irreversible hydrogen traps. These two opposite effects on SSCC resistance due to the elimination of primary NbC carbides were assumed to be offset, and thus, the SSCC resistance was not greatly improved using ESR.

Highlights

With the increasing exploitation of shallow oil and natural gas, some deep wells and ultra-deep wells have recently been developed in some countries [1]
The metallurgical process of Steel continuous casting (CC) was composed of electric arc furnace (EAF) melting → ladle furnace (LF) refining → vacuum degassing (VD) → CC, and the metallurgical process of Steel electroslag remelting (ESR) was composed of EAF → LF → VD → CC → ESR
It can be found that the studied steel melt starts to solidify at about 1784 K, and the content of BCC_A2 (δ) phase gradually increases as the temperature decreases

Summary

Introduction

With the increasing exploitation of shallow oil and natural gas, some deep wells and ultra-deep wells have recently been developed in some countries [1]. In these wells, both a high pressure and a high temperature caused detrimental effects on the drilling and production equipment. SSCC phenomenon will take place when the high strength steels suffer from the joint action of external tensile stress and a specific corrosive environment where the solution pH value is low and the H2S partial pressure is high.

Methods

Results

Conclusion