Effect of Cu Addition in Pipeline Steels on Microstructure, Mechanical Properties and Microbiologically Influenced Corrosion

doi:10.1007/s40195-017-0545-z

Abstract

Abstract:

In the present study, Cu-modified pipeline steels were fabricated to mitigate MIC by the antimicrobial ability of Cu element. The microstructure, mechanical properties and the antimircobial performance of the Cu-modified steel were systematically investigated. The Cu-modified steels showed good antimicrobial performance with remarkable strength enhancement by nanoscale Cu-rich precipitates and good impact toughness without changing the original base microstructures after the optimal aging treatment of 500 °C/1 h.

Key words: Pipeline steel, Cu addition, Mechanical, properties, Microstructure, Antimicrobial performance

Xian-Bo Shi, Wei Yan, Mao-Cheng Yan, Wei Wang, Zhen-Guo Yang, Yi-Yin Shan, Ke Yang. Effect of Cu Addition in Pipeline Steels on Microstructure, Mechanical Properties and Microbiologically Influenced Corrosion[J]. Acta Metallurgica Sinica (English Letters), 2017, 30(7): 601-613.

Figures/Tables 19

Table 1 Chemical compositions of the experimental steels (wt%)

Steel	C	Si	Mn	Mo	Cu	Ni	Nb	S	P	Other
1.0Cu	0.031	0.14	1.09	0.31	1.06	0.32	0.05	0.0011	0.005	0.32Cr
1.5Cu	0.019	0.12	1.03	0.31	1.46	0.31	0.05	0.0011	0.005	0.31Cr
2.0Cu	0.023	0.13	1.06	0.30	2.00	0.30	0.05	0.0010	0.005	0.30Cr
X80	0.028	0.28	1.90	0.22	0.20	0.29	0.08	0.0020	0.012	0.03V

Table 2 Procedure of the thermomechanical control process (TMCP) for the Cu-modified pipeline steels

Steel	Interpass reduction in thickness (mm) and rolling temperature (^oC)							Accelerated cooling
Steel	78 → 62	62 → 45	45 → 30	30 → 24	24 → 16	16 → 11	11 → 9	Water cooling rate (^oC/s)	Finishing temperature (^oC)
1.0Cu	1025	*	*	894	*	*	835	24	420
1.5Cu	1030	*	*	930	*	*	814	20	416
2.0Cu	1019	*	*	923	*	*	830	27	414

Table 3 Compositions of the used soil (μg/kg soil)

pH	Chemical composition								Organic content	Whole nitrogen content	Total salt content
	NO₃^-	Cl^-	SO₄^2-	HCO₃^-	Ca²⁺	Mg²⁺	K⁺	Na⁺
7.75	46	31	48	234	57	32	2	14	2.26 × 10⁴	910	464

Fig. 1 DSC thermograms showing the additional exothermic peak at 546 °C for the 2.0Cu steel compared with the X80 steel

Fig. 2 Hardness of various Cu-modified steels as a function of aging time a X80 for comparison, b 1.0Cu, c 1.5Cu, d 2.0Cu

Fig. 3 Hardness as a function of aging time at different aging temperatures, a 450 °C; b 500 °C; c 550 °C; d 600 °C

Table 4 Increase in hardness (HV) due to peak-aging at different aging temperatures

Steel	450 °C	500 °C	550 °C	600 °C
1.0Cu	58.0	41.0	36.3	24.0
1.5Cu	70.0	54.6	50.3	41.3
2.0Cu	65.3	53.5	44.3	28.0

Table 5 Mechanical properties of the as-rolled steels

Steel	Yield strength (MPa)	Tensile strength (MPa)	Elongation (%)	Impact toughness (-20 °C) (J)
1.0Cu	443	651	30.0	141
1.5Cu	513	645	28.0	82
2.0Cu	608	759	25.0	66
X80	608	677	23.5	140

Fig. 4 Variation of yield strength (YS) and tensile strength (TS) with Cu content for the as-rolled and aged (450 °C/6 h, 500 °C/1 h, 550 °C/1 h) steels. Open and filled symbols represent YS and TS, respectively

Fig. 5 Increment of strength between as-rolled and aged steels with different Cu content

Fig. 6 Variation of impact toughness at -20 °C with Cu content for the as-rolled and aged (450 °C/6 h, 500 °C/1 h, 550 °C/1 h) steels

Fig. 7 SEM microstructures of Cu-modified pipeline steels and the X80 steel, a 1.0Cu steel as-rolled; b 1.5Cu steel as-rolled; c 2.0Cu steel as-rolled; d X80 steel as-rolled; e1.0Cu steel 500 °C/1 h; f 1.5Cu steel 500 °C/1 h; g 2.0Cu steel 500 °C/1 h; h X80 steel 500 °C/1 h

Fig. 8 Bright-field TEM micrographs showing nanoscale copper-rich precipitates in the 2.0Cu steel under different aging conditions, a 450 °C/6 h; b 500 °C/10 min; c 500 °C/5 h; d 550 °C/10 min; e 550 °C/1 h; f 550 °C/5 h

Fig. 9 Average size of Cu-rich precipitates in the 2.0Cu steel under different aging conditions

Fig. 10 Variations of RLPR with exposure time for X80 and 1.0Cu steels in the soil solution with SRB

Fig. 11 Morphologies of 1.0Cu steel a and X80 steel b exposed to soil solution with SRB after removing corrosion products

Fig. 12 Experimental peak-aging time of 1.5Cu steel and its predicted peak-aging time

Fig. 13 Continuous cooling transformation diagrams of a 1.5Cu and b 2.0 Cu steels

Fig. 14 Schematic illustrations of the crack propagation path in quasi-polygonal ferrite (QF) of the 1.5Cu steel a and acicular ferrite (AF) of the 2.0Cu steel b

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