In recent years, there has been a sharp increase in global demand for pumping and compressor pipe and oil and gas line pipe with improved corrosion resis tance, capable of operating at low temperatures in environments where hydrogen sulfide is present. The reliability and durability of high pressure pipelines depends on the metal quality of the pipe, which must be characterized by the highest possible strength, high ductility, resistance to brittle and ductile failure at con structional and operational temperatures, good plas ticity, corrosion resistance, and weldability. The vol ume of oil and gas pipe required necessitates a focus on plentiful and inexpensive alloying elements and rela tively simple production technologies.Note that increase in the strength of metal is often accompanied by loss of plasticity or durability. In that content, the potential of two phase ferrite-martensite steel was noted in [1].In the present work, we consider the decomposi tion of supercooled austenite in 13ХФА steel on cool ing from the single phase region and the intercritical temperature range. We also establish that ferrite-mar tensite structure is formed in double quenching (first from the single phase region and then from the inter critical range).We consider economically alloyed 13ХФА struc tural steel obtained by the industrial technology at OAO Severskii Trubnyi Zavod. The chemical compo sition of the steel is as follows: 0.15% C, 0.50% Mn, 0.25% Si, 0.52% Cr, 0.05% V, 0.002% Mo, 0.13% Ni, 0.20% Cu, 0.005% S, and 0.001% P (the remainder is Fe). For the metallographic analysis and mechanical tests, the steel is heated in SNOL laboratory furnaces. An Epiphot 200 microscope (magnification 200-1000) is used for metallographic analysis. The micro structure is photographed using a Nikon digital cam era (on the basis of Nis Elements Basic Research soft ware). The fine structure is studied by means of a Jeol JSM 6490 IV scanning electron microscope, with an attachment for Inca DryCool microanalysis and Inca Feature software. The decomposition kinetics of supercooled austenite in continuous cooling is investi gated on a Linseis L78 R.I.T.A. dilatometer, equipped with a Schaevitz HR 100 (MC) inductive longitudi nal motion sensor.
RESULTSIn selecting the composition and heat treatment conditions for the two phase ferrite-martensite steel, as a rule, the basic goal is to prevent pearlite formation and obtain specific proportions of ferrite and the hard ening phase (martensite) [1]. To that end, holding temperatures in the intercritical temperature range where 40-60% austenite is formed are recommended [2]. That ensures the best distribution of structural components, when the carbon concentration declines from the center of the γ phase grains to the periphery.The quantity of austenite required for an optimal distribution of structural components is formed in the range 790-820°C, according to [3]. That conclusion is based on the dependence of the proportion of auste nite decomposition on the temperature in the inter critical range (A ...
