The Effect of Microstructure on Stress-Strain Behaviour and Susceptibility to Cracking of Pipeline Steels

Abstract

The effect of microstructure on the stress-strain behaviour of pipeline steels was studied. Slow strain rate (2×10-6 s-1) tests were conducted on grade X65 and X100 steels in silicone oil and hydrogen carbonate/carbonate solution. The as-received grade X100 steel at 75°C showed serrated stress-strain curves. The magnitude of the serrations depended upon the strain rate and test temperature. Annealing at 600°C or above removes the serrations, but this increased the susceptibility to transgranular cracking in hydrogen carbonate/carbonate solution at potentials below −800 mV (sce). The removal and reformation of banding in pipeline steels were also studied. Ferrite/pearlite becomes aligned during the hot rolling stage of pipe manufacture and causes directionality in crack propagation and mechanical properties. Heat treatments were carried out which show that banding in grade X65 and X100 can be removed above 900°C. This depends on homogenisation of carbon which also depends on temperature, time, and cooling rate.

Failure analysis of the pulleys during the press-fit assembling process

“…40% compare to original pulley material (C = 0.07%; S = 0.330%) [8]. The increased carbon content (pearlite) unfavourably affects the toughness and plasticity of steel what can led to cracking [11,12]. Obtained results confirmed negative influence of increased carbon content on toughness and plasticity of material of pulleys.…”

Effect of Temperature and Cooling Rate on the Microstructures of 35MnB and 25Mn Tubes during Heat Treatment

“…Although sufficient heat treatment dwell time is known to be capable of preventing the formation of band structures [4], this study excluded it from the process parameters in order to examine only the factors of cooling rate and heat treatment temperature to prevent band structures. R. P. Todorov et al suggested that band structures can be prevented by Widmanstatten structures, which are created by overheating carbon steel [5].…”

“…A. Mustapha et al found that band structures of carbon steel tubes can be removed or prevented through a heat treatment temperature that is higher than the eutectoid temperature, a cooling rate faster than furnace cooling, and sufficient dwell time for heat treatment [4].…”

Effects of Reduction Pretreatment on the Internal Quality of Casting Billets

“…The central segregation and porosity, occurring inevitably among dendrites during casting, have great effects on the productivity and mechanical properties of casting slabs . For instance, the central segregation is the main reason for the occurrence of longitudinal bands after hot rolling and results in the anisotropy of microstructures and properties. Besides, the porosity derived from solidification shrinkage is responsible for hot cracking and leads to brittleness in the subsequent forming.…”