All physical, chemical, and biological metabolic reactions that occur in nature are usually accompanied by changes in thermal effects. Advances in materials science also follow this principle.
The progress and development of modern materials science has been supported and helped by thermodynamics, which is the application of classical thermodynamics and statistical thermodynamics theory in the field of materials science, and its formation and development is one of the signs of the maturity of materials science.
1876: The advent of the Gibbs phase law.
1899: HRoozeboom applies phase laws to multi-component systems.
1900: Roberts-Austen constructs the initial form of the Fe-Fe3C phase diagram, which provides theoretical support for the study of iron and steel materials.
Early 20th century: gTamman et al. established a large number of metal phase diagrams through experiments, which strongly promoted the development of alloy materials.
Early 50s: rKikuchi proposed a modern statistical theory on the description of entropy, which created the conditions for the combination of thermodynamic theory and first principles.
Early 60s: mHillert et al.'s research on the thermodynamics of non-equilibrium systems has led to the emergence of the field of unstable decomposition and enriched the understanding of the formation law of material structure.
70s: lThe computational phase diagram (calphad) advocated by experts such as Kaufman has gradually brought materials research into the era of on-demand design.
In June 2011, the U.S. announced a more than $500 million Advanced Manufacturing Partnership, one of the core components of which is the Materials Genome Initiative (MGI), which aims to provide the necessary toolset for the design of new materials, reduce the reliance on physical experiments through powerful computational analysis, and significantly accelerate the development of new materials through advances in high-throughput experiments and characterization methods.
CaseThe problem of surface cracks in Cu-containing steels is solved by thermodynamic calculations - surface cracks occur in Cu-containing steels.
Analyze the scenario. Step 1: Enter the steel containing cuMicrostructure analysis was performed
1) 1000 heating, the oxide layer on the surface of the Cu-containing steel begins to appear white, and the Cu-rich phase is diffusely distributed in the oxide layer close to the interface, and the Cu-rich phase contains 95% of the Cu content.
2) 1100 heating, along the interface between the matrix and the oxide layer to form a Cu-rich phase, and penetrate into the grain boundary on the surface of the matrix, the Cu-rich phase in the Cu-rich phase is 92%.
3) When 1200 is heated, the enrichment degree of Cu is similar to that of 1100, and the thickness of the liquid Cu phase is slightly larger, indicating that the permeability of Cu is stronger at this time.
The above test results show that when the heating temperature is high (1000), the oxide layer on the surface of the steel containing Cu is liquid Cu phase, and the liquid Cu phase is immersed along the austenite grain boundary, resulting in surface cracks.
Through the study of relevant literature,Finding the surface hot cracking problem of Cu-containing steel and improving ideas:
Due to the selective oxidation of Fe on the surface during the heating process, Cu-rich phase is easy to form at the interface between the surface and the oxide layer. Due to the low melting point of Cu, as the oxidation process progresses, the Cu-rich phase forms a liquid Cu phase at heating temperature and penetrates along the grain boundaries, resulting in surface cracks during processing.
The addition of Ni to Cu-containing steels can effectively prevent the formation of liquid Cu phase and thus avoid the formation of cracks.
So,How much ni should be added?
How to control the heating temperature?
Step 2: In order to reduce the cost of the test, take:Soft with thermo-calcpieces
1) Firstly, the fe-cu phase diagram was calculated and verified with the above test information
At 1000, the Cu-rich phase of 95% Cu-Fe is still a solid phase, so it is distributed in a granular form at the interface and in the adjacent oxide layer. Consistent with the test.
In the range of 1100 to 1200, the Cu-rich phase (92%Cu-Fe) formed at the interface enters the liquid phase, aggregates along the interface and penetrates to the grain boundary. Consistent with the test.
2) Apply Thermo-Calc software to perform simulation calculations to solve the problem of how much Ni should be added.
Calculate the isotherm plots of fe-ni-cu ternary system at 1100 and 1200.
1100, Cu-Ni steel (WNI WCU=0..)71) 10% Cu-125% Ni-Fe alloying phase, while in the oxide layer, the position is close to the interface to form 221%cu-23.The alloy phase of 4% Ni-Fe forms 428%cu-23.5% Ni-Fe alloy phase, and all solid phases.
1200 at the interface 71%cu-3.The alloying phase of 4% Ni-Fe forms 96%cu-10.9% Ni-Fe alloy phase and 254%cu-34.8% Ni-Fe alloy phase, and all of them are solid phases.
The calculation results show that the increase of Ni Cu ratio in steel is very effective in preventing the precipitation of liquid phase Cu, and the formation law is shown in Fig. It can be seen that when the addition temperature is below 1250 and the Ni Cu ratio in the steel reaches more than 1, the appearance of phase Cu can be avoided thermodynamically.
3) Test inspection.
According to the results of the simulation calculation study, the Ni Cu ratio of the test steel was 11. Compare. to ni cu than 11. The bending test was carried out, and no cracks were found in the steel plate, and the hot cracking problem of Cu-containing steel was well solved. At present, this technology has been successfully applied on offshore platforms.