Method for identifying and assessing needle-like ferrite pipe line steel tissues

Abstract

The invention relates to a method for identifying and assessing needle-like ferrite pipe line steel tissues, which comprises the following steps: simplifying various ferrite tissues into ferrite and bainite; and by a heat dyeing experiment, enabling the different tissues and crystalline grains in the material to display the different contrast from white to yellow and brown, wherein the assessing of the needle-like ferrite pipe line steel banded tissue is divided into four levels. The measuring method for the ferrite crystalline grains of the needle-like ferrite pipe line steel comprises: a comparative method and a resection method are selected for the judging method of the ferrite crystalline grains; the comparative method is used for production inspection, if dispute exists, the resection method is the arbitration method; the comparative method is as follows: judging the grain size rank by comparing with a standard rating graph; and the resection method is as follows: assessing the grain size rank by counting the measureing segment of given length and number of the points of the grain boundary resection. The invention solves the problem that practical steel rolling tissue is difficult to analyze and identify, improves the contrast difference of phase and grain of components in the tissue, is convenient for tissue identifying and pipe line steel grain size assessing, makes up the defect of the national standard, and has reasonable and feasible quality control, check and evaluation on the line steel tissue.

Description

technical field [0001] The invention relates to a method for structure identification, band structure and grain size evaluation of pipeline steel and steel pipe with acicular ferrite structure of X70 and X80 high steel grades. Background technique [0002] The main microscopic features of acicular ferrite are as follows: (1) lath is the most prominent morphological feature of acicular ferrite. Several laths are arranged in parallel to form a lath bundle, the lath boundary is a small-angle grain boundary, and the lath bundle boundary is a high-angle grain boundary. It is generally believed that the width of the acicular ferrite lath is about 0.6 μm-1 μm; (2) there are granular or film-like M-A components between the ferrites of adjacent laths; (3) there are high-density dislocations in the lath. Compared with ferritic-pearlitic and less pearlitic pipeline steels, acicular ferritic steels have different ways of strengthening and toughening. Observations of the fracture proce...

AI Technical Summary

Problems solved by technology

Due to the complexity of the microstructure of high-grade pipeline steel, especially acicular ferritic pipeline steel, its microstructure identification is different from that of general low-carbon and low-alloy steel. No longer applicable, so it is urgent to propose new methods for tissue identification, banded structure and grain size evaluation to meet the research and development, quality inspection and evaluation and quality control requirements of high-performance pipeline steel and steel pipes, and ensure the smooth progress of major pipeline projects

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