Research On The Mechanism Of Hydrogen Brittleness Damage In Heavy Forgings

Large forgings manufacturing is one of the key technologies of major equipment manufacturing, its quality directly affects the overall level and operation reliability of major equipment. Large forgings manufacturing is the basis for the development of electric power, shipbuilding, metallurgy, petrochemical, heavy machinery and defense industry, is also the prerequisite of the development of advanced equipment manufacturing industry. When heavy forgings in high-temperature forming and cooling process, the hydrogen will be separated out and aggregated in forgings internal micro defects and lead to cracks initiation because of high hydrogen pressure, which called hydrogen embrittlement that are the most knotty and dangerous defects in heavy forgings. The research achievements in recent years although in terms of coupled thermal-stress-microstructure has made some new progress, but for hydrogen embrittlement problems of large forgings has not been solved very well. To study the mechanism of forming hydrogen embrittlement damage, in this paper, we use high hydrogen embrittlement sensitivity alloy steel as the research object. By adopting the combination of physical simulation and finite element analysis method has carried on the comprehensive research on the concentration of hydrogen, hydrogen diffusion, and the mechanism of hydrogen embrittlement damage of the large forgings.Hydrogen atom has the lightest quality and minimum radius in nature, thus how to measure hydrogen content in steel accurately besetting industrial circles and the scientific community. In this paper, in order to study the hydrogen content and hydrogen concentration distribution in the forgings, finite element method is used to establish the hydrogen diffusion model of the heat treatment process after forging. Hydrogen diffusion laws in materials can be provided by the analysesof the experiment.For large forgings, the whole process of heat treatment is in the process of hydrogen diffusion. In order to detect the content of hydrogen in steel at any time, it is necessary to know the permeation rate of hydrogen in steel. This paper is based on Fick’s second law, hydrogen diffusion coefficient of alloy steel which has different components was determined by the electrochemical workstation and its matching test software. A new method for determination of hydrogen diffusion coefficient in metal materials is presented.In order to study the damage mechanism of materials caused by hydrogen embrittlement.Through the hydrogen charging experiment, the hydrogen atoms in the outer part of the forgings are continuously diffused into the inner part,record the specimen experiment data of the slow tension test process,and the characteristics of fracture morphology, tensile strength, elongation rate and other mechanical properties of 40 Cr and 45# steel under different hydrogen charging current and hydrogen charging time were analyzed.Measurement the hydrogen embrittlement degree by using the changes of elongation rate as a standard,through the experiment of hydrogen charging-tensile test and hydrogen charging-staying in static state-tensile test,the experimental results verify the non reversibility of hydrogen induced damage.In order to make a quantitative analysis of the hydrogen pressure and hydrogen content in the inner micro hole of the forging,hydrogen pressure inside the hydrogen drum package was reverse calculation researched by means of the finite element method on the basis of electrochemical hydrogen charging experiment,established the relationship between hydrogen concentration and hydrogen pressure in the micro hole.Study on the growth law of the hydrogen drum package and the calculation of the hydrogen pressure in the drum package,it can solve the problem that the micro hole or hydrogen segregation in the metal material is often located in the centre part and is difficult to be directly measured.In order to study the change of microporosity hydrogen pressure strength in forming process of large forgings, based on the principle of hydrogen pressure, established the finite element model of hydrogen temperature-pressure field analysis of the large forgings, got the change rule under the different condition of hydrogen pressure intensity and the hydrogen concentration of the micro pore in the forging. And studied the distribution of hydrogen pressure stress field under different concentration of hydrogen and the coupling effect between adjacent micro holes.