New Method of Characterizing and Quantifying Complex Microstructures in Steels
New Method of Characterizing and Quantifying Complex Microstructures in Steels
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表征和量化钢中复杂微观结构的新方法
DOI：
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
M. Hua
中科院分区：
文献类型：
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作者：
A. DeArdo;C. Garcia;K. Cho;M. Hua
从20世纪60年代末到70年代末，热轧成带状和板状的高强度微合金钢表现出铁素体-珠光体组织，屈服强度基本上限制在350-420 MPa范围内。然而，20世纪70年代末能源危机的到来导致了对更高强度钢的需求，同时保持可焊性、韧性和可成形性等其他性能的可接受水平。自20世纪70年代末以来，人们认识到铁素体-珠光体钢的强化机制在晶粒细化和溶质和沉淀硬化方面已经达到了极限；因此，350-420 MPa的障碍是真正的限制。大约在同一时间，人们也认识到，加工钢的高强度只能通过使用较低温度形成的铁素体来实现，即非多边形、针状、贝氏体或马氏体铁素体，无论是作为整体基体组织还是作为组合。这种可实现的微观结构的变化是由间断的加速冷却引起的，要么在带钢轧机的跳动台上，要么在中板轧机的精加工后。因此，高强度热轧或后来的冷作退火（CRA）和/或连续镀锌线（CGL）加工钢，强度超过420兆帕，现在表现出这些复杂的显微组织。如今，对于屈服强度为490mpa的钢来说，表现出由几种微观成分组成的显微组织并不罕见：非多边形铁素体、贝氏体、马氏体，可能还有残留的奥氏体。传统的金相技术已经无法分析这些复杂的微观结构，尤其是在定量方面。无法表征和量化这些复杂的微观结构意味着这些钢的真正强化机制可能被错误地理解和评估。电子库散射衍射（EBSD-IQ）成像质量的定量分析为高强度钢复杂显微组织的定量分析提供了一种创新的方法。本文将介绍该技术，并展示该技术在包括高强度低合金（HSLA）、MA、DP和TRIP钢在内的各种钢的研究中成功应用的地方。
From the late 1960s through the late 1970s, high strength microalloyed steels hot rolled to strip and plate exhibited ferrite-pearlite microstructures with yield strengths essentially limited to the range of 350–420 MPa. However, the advent of the energy crisis of the late 1970s led to the demand for steels of higher strengths, while maintaining acceptable levels of other properties such as weldability, toughness, and formability. Since the late 1970s, it has been recognized that the strengthening mechanisms present in ferrite-pearlite steels had reached their limit in terms of grain refinement and solute and precipitation hardening; hence the barrier of 350–420 MPa was a real restraint. At about the same time, it was also recognized that higher strengths in as-processed steels could only be achieved through the use of ferrite of lower temperature formation, i.e., non-polygonal, acicular, bainitic, or martensitic ferrite, either as a monolithic matrix microstructure or as a combination. This change in achievable microstructures was abetted by interrupted accelerated cooling, either on the runout table of a strip mill or after the finishing pass in a plate mill. Hence, high strength hot rolled or the later cold work and annealing (CRA) and/or continuous galvanizing line (CGL) processed steels, with strengths in excess of 420 MPa, now exhibit these complex microstructures. It is not uncommon today for a 490 MPa yield strength steel to exhibit a microstructure comprised of several types of microsconstituents: non-polygonal ferrite, bainite, martensite, and perhaps retained austenite. Traditional metallographic techniques are no longer capable of analyzing these complex microstructures, especially in a quantitative fashion. The inability to characterize and quantify these complex microstructures means that the true strengthening mechanisms operative in these steels may be incorrectly understood and evaluated. The recent application of the quantitative analysis of the image quality (IQ) of the Kikuchi pattern resulting from the Electron Bank Scattered Diffraction (EBSD-IQ) has led to an innovative way to quantitatively analyze complex microstructures in the higher strength steels. This article will present the technique and show where it has been used successfully in research studies involving a broad range of steels including high strength low alloy (HSLA), MA, DP, and TRIP steels.