钢静态连续冷却相变研究

钢静态连续冷却相变研究

摘要

随着经济的快速发展，市场对高品质弹簧扁钢的需求量越来越大。50CrMnV A 钢在力学性能、气体含量、夹杂物、脱碳等方面的技术要求均高于常规弹簧钢，是典型的高技术含量和高附加值产品，兼有超高强度和和高塑型，在汽车，化工容器，重工业方面有很大的应用[1,2]。它的自主供应和弹簧钢的极大需求，使得其在国家现有弹簧钢中显得尤为重要，是一种需求量很大的高潜力弹簧钢。

本文以中国第一汽车公司提供的50CrMnV A钢为研究对象，在Formastor-FII型全自动相变膨胀仪上进行了不同冷却速度的静态热模拟实验，采用热膨胀法与金相组织观察和硬度测量法相结合手段，利用orgin软件绘制了实验钢的静态连续冷却转变曲线，即静态CCT曲线，研究了实验钢在静态连续冷却相变过程中的显微组织演变规律。

研究结果表明：

（1）该钢的CCT曲线相变区主要包括高温转变区、中温转变区和低温转变区三部分。相变产物主要是铁素体、珠光体、贝氏体和马氏体。而且随着冷却速度的提高，铁素体、珠光体和贝氏体相变的转变开始温度都降低。

（2）相变产物随冷却速度的改变而改变。当冷却速度小于0.25℃/s时，实验钢的相变组织为珠光体和极少量的铁素体。在0.5℃/s冷却速率下，显微组织为珠光体、贝氏体和极少量的铁素体。当冷却速率达到0.75℃/s时，相变组织为珠光体和贝氏体。当冷却速率为1~2℃/s时，相变组织为贝氏体和马氏体。当冷却速度超过5℃/s时，相变组织为单一的马氏体组织。

（3）随着冷却速度的提高，实验钢的相变组织由铁素体+珠光体，逐渐过渡为珠光体+贝氏体，最后为单相马氏体组织，与此同时，其维氏硬度逐渐升高，数值逐

渐由295升高到728。

关键词：弹簧钢；静态连续冷却相变；热模拟；显微组织

The static thermal simulation analysis on continuous cooling phase transformation of the 50CrMnV A steel

Abstract

With the rapid economic development, market demand for high-quality flat steel spring growing. 50CrMnV A technical requirements in the mechanical properties of steel, gas content, inclusions, and other aspects of decarbonization are higher than conventional spring steel, is typical of high-tech and high value-added products, and both high and ultra high strength plastic, in automotive, chemical containers, heavy industry has a lot of applications [1,2]. It is independent of supply and demand a great spring steel, so that it is particularly important in the existing national spring steel and is a great demand for high potential spring steel.

In this paper, the first Chinese car company provides 50CrMnV A steel for the study, in Formastor-FII-automatic instrument for the expansion phase change on a static thermal simulation experiment with different cooling rates, the use of thermal expansion of the law and observe the microstructure and hardness measurements wears combined means of using software to draw the experimental steel orgin static continuous cooling transformation curve, namely static CCT curves of steel in static experiments studied the continuous cooling transformation process of microstructure evolution.

The results show that:

(1) CCT curve of the steel high-temperature phase transition region including the transition region, the temperature in the transition region and low transition region into three parts. Mainly transformation products of ferrite, pearlite, bainite and martensite. And with the increase of cooling rate, changing the starting temperature of ferrite, pearlite and bainite are reduced.

(2) transformation products with a changed cooling rate is changed. When the cooling rate is less than 0.25 ℃/ s, the steel phase transformation experiments organization very small amount of pearlite and ferrite. At 0.5 ℃/ s cooling rate, the microstructure of pearlite, bainite, and very small amounts of ferrite. When the cooling rate reaches 0.75 ℃/ s, phase change pearlite and bainite. When the cooling rate of 1 ~ 2 ℃/ s, phase change bainite and martensite. When the cooling rate exceeds 5 ℃/ s, organized as a single variable phase martensite.

(3) With the increase of cooling rate, the phase transition from the steel tissue experiments ferrite and pearlite, pearlite and bainite gradual transition to the final phase for the single martensite, while Vickers hardness gradually increased from the value gradually increased from 295 to 728.

Keywords: spring steel; static continuous cooling transformation; thermal simulation; microstructure