Hardness prediction for sub-critically and inter-critically reheated HAZs of low alloy steels

In order to predict HAZ hardness of multi-pass welding, a hardness prediction method for sub-critically and inter-critically reheated HAZs of steels was developed. The dilatometry experiments were conducted to measure the Ac-1 and Ac-3 temperatures and austenite volume fraction. The experimental results were used to develop empirical equations to predict these properties. Next, hardness measurements were conducted. Specimens were heated to 1400 & DEG;C, cooled to room temperature, sub-critically or inter-critically heated again, and then cooled to room temperature. For sub-critically reheated HAZ, a parameter to integrate the tempering effect was introduced. Using the parameter, an empirical equation to predict hardness reduction by tempering and hardness change by precipitation was developed. For inter-critically reheated HAZ that consists of tempered and re-austenitized HAZs, the equation for sub-critically reheated HAZ was applied to the tempered HAZ, while a previous HAZ hardness prediction equation for single-pass welding was applied to the re-austenitized HAZ. The differences between the experiments and predictions were under 50 (Vickers hardness) and the average error was 23.0, which is considered good agreement. The present method was also applied to predict stress-strain curves and compared with the experiments, resulting in good agreement.