The Study Of Stress Relaxation Of X7CrNiMoBNb16-16 With Thermo-mechanical Treatment

the craft parameter of the thermo-mechanical treatment exerts a tremendous influence to high strength steel X7MoBNb16-16 (are abbreviated as X7 steel, same below).The strength can still maintain above 325MPa from 600 to 650 degrees Centigrade. The material of deformation in 850 degrees Centigrade is higher by 25～30% than in 1000 degrees Centigrade. The test is found, The percentage elongation of X7 steel in 600 degrees Centigrade is lower by 25% than in the room temperature. Analysed by metallography performances, the influence of deformation and temperature is close relations to the change of organization and Nb element.According to relevant stress relaxation definition, elastic strain will be transformedinto plastic strain under the certain total strain, The stress relaxation has appeared like this. In order to improve the properties of stress relaxation, We improve the limit of its elastic stress through the heat strain treatment, Thus the difficulty of its transition is improved. The test indicates, there are direct relations between the stress relaxation of X7 steel and its deformation temperature and deformation. The lower deformation temperature is, it is the better to stress relaxation. Stress relaxation performance in deformation 60% is higher than in deformation 40% and 80%.The results showed that the stress relaxed very fast at the first stage, while slowly at the second stage, and the residual stress approached a limit after a long relaxation time. Stress relaxation was characterized with stress relaxation limit and stress relaxation rate. The higher temperature resulted in higher stress relaxation rate and lower relaxation limit. Different initial stress gave the same relaxation limit at same temperature。To discuss stress relaxation phenomenon of general metal and the importance of studying it. The stress relaxation curve and its characteristic targets are analyzed in text. And the method of stabilizing treatment for improving the anti-stress-relaxation ability are given.In this text, a new expression is proposed, which can be used for fitting the experiment data of stress relaxation of X7 steel and estimating the relaxation behavior under different deformation temperature and deformation. They have initiated the advantage for the research and analysis in the future.