Development of a Mn-Si-Cr-Mo as-rolled dual-phase steel
Development of a Mn-Si-Cr-Mo as-rolled dual-phase steel
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DOI：
10.1007/bf03354351
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发表时间：
1978-04
期刊：
影响因子：
2.6
通讯作者：
A. Coldren;G. Tither
中科院分区：
文献类型：
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作者：
A. Coldren;G. Tither
双相钢的引入标志着新一代高强度低合金（HSLA）钢的开始。双相钢的特征在于：（1）由10%至20%的马氏体 * 岛分散在软的韧性铁素体基体中组成的显微组织，以及（2）在高强度水平下具有异常良好的延展性和可成形性。后一种质量使双相钢在汽车工业目前正在评估的各种新材料名单上名列前茅，以减轻汽车重量，提高汽油里程。迄今为止，用于双相HSLA钢的商业生产的唯一方法涉及连续退火类型的热处理，采用热轧HSLA钢带的卷作为起始材料。如果HSLA双相钢应该被批准作为用于诸如高强度车轮和保险杠表面条的部件的优选汽车钢，那么许多钢铁公司希望能够在不对新的热处理线进行大量资本投资或转移现有设施（诸如不锈钢正火线、镀锌线或用于退火电工钢的线）的情况下生产新的钢。本文介绍了一种生产HSLA双相钢的轧制方法的高潮发展，该方法使钢厂能够生产不需要进一步热处理的热轧双相钢。一种低合金钢，其表现出特殊的连续冷却转变（CCT）特性，高生产率的热带轧机，以在轧制后的卷状板中产生所需的铁素体-马氏体显微组织。CCT图中所需的特殊特性包括（1）伸长的铁素体C曲线，即在输出台上在合理宽的冷却速率范围内形成非常大量的多边形铁素体的能力，（2）抑制（延迟）珠光体鼻以确保在冷却至卷取温度期间避免珠光体形成，（3）高珠光体终轧温度，以避免在高达620 ℃（1150 F）的温度下卷取后形成珠光体，和（4）多边形铁素体和贝氏体铁素体区域之间的间隙，以提供至少75 ℃（135 ° F）的温度范围，在该温度范围内不发生进一步的转变，允许钢以对在工业生产中出现的卷取温度的正常变化很小或不敏感的方式进行卷取。另一个重要的特性是，在多边形铁素体形成后，在缓慢冷却过程中（如在块状线圈中），完全抑制贝氏体铁素体形核，这是所需的，但CCT图上没有显示。这确保了在80%至90%转变为多边形铁素体之后，当钢到达输出台的端部时存在的富碳奥氏体的岛在卷取之后不转变为贝氏体，而是在更低的温度下更晚地转变为马氏体。上述概念导致了
The introduction of dual-phase steels marks the beginning of a new generation of high-strength low-alloy (HSLA) steels. Dual-phase steels are characterized by (1) a microstructure consisting of a dispersion of 10% to 20% martensite* islands in a matrix of soft, ductile ferrite and (2) unusually good ductility and formability at high strength levels. The latter quality puts dual-phase steels high on the list of various new materials that are now being evaluated by the automotive industry in its current move to reduce the weight of automobiles for improved gasoline mileage. To date, the only method used for commercial production of dual-phase HSLA steels has involved a continuous annealing type of heat treatment, employing coils of hot rolled HSLA steel strip as the starting material. If HSLA dual-phase steels should win approval as the preferred automotive steel for parts such as high strength wheels and bumper face bars, many steel companies would like to be able to produce the new steels without making large capital investments in new heat treat lines or diverting existing facilities such as stainless normalizing lines, galvanizing lines or lines for annealing electrical steels. This article presents the Climax development of an as-rolled approach to the production of HSLA dual-phase steels which would enable a steel mill to produce hot-strip dual-phase steel that would not require further heat treatment.CONCEPT The as-rolled dual-phase steel concept is based on a low carbon, low-alloy steel that exhibits special continuous cooling transformation (CCT) characteristics which permit the steel to be processed on a conventional, high production hot-strip mill to produce the desired ferrite-martensite microstructure in the as-rolled coiled sheet. Special characteristics that are needed in the CCT diagram include (1) an elongated ferrite C-curve, ie, the ability to form very large amounts of polygonal ferrite over a reasonably wide range of cooling rates on the runout table,(2) a suppressed (delayed) pearlite nose to ensure avoidance of pearlite formation during cooling to the coiling temperature,(3) a high pearlite finish temperature to avoid pearlite formation after coiling at temperatures up to 620 C (1150 F), and (4) a gap between the polygonal ferrite and the bainitic ferrite regions to provide a temperature range of at least 75 C (135 F) within which no further transformation occurs, permitting the steel to be coiled with little or no sensitivity to the normal variations in coiling temperature that occur in commercial production. Another important characteristic that is needed but which is not shown on a CCT diagram is complete suppression ofbainitic cementite nucleation during slow cooling (as in a massive coil) after the polygonal ferrite has formed. This ensures that the islands of carbon-enriched austenite, which are present when the steel reaches the end of the runout table, after the 80% to 90% transformation to polygonal ferrite, do not transform to bainite after coiling but transform instead to martensite much later at a lower temperature. The above concept led to the development of