CN107818211A - A kind of method of evaluation TWIP steel platabilitys - Google Patents

Abstract

The invention belongs to the technical field of advanced high-strength steel coating, and in particular relates to a method for evaluating the platability of TWIP steel. The data used can be calculated according to the annealing parameters, such as: annealing temperature, annealing dew point, hydrogen ratio, relatively complete experimental parameters are conducive to the acquisition of the required data, and provide theoretical data basis for the subsequent evaluation of the plateability of the steel plate; Establishing the equation of the experimental parameters can quickly evaluate the platability of TWIP steel. This evaluation method is less affected by the outside world, which can save a lot of time and workload, and eliminate the analysis and detection of the experimental process, making the evaluation method more accurate. For simplicity, less time is required.

Description

A Method for Evaluating Platability of TWIP Steel

technical field

The invention belongs to the technical field of advanced high-strength steel coating, and in particular relates to a method for evaluating the platability of TWIP steel.

Background technique

With the increasing global energy crisis and environmental deterioration, safety, energy saving and environmental protection have become the development trend of the automobile manufacturing industry. Compared with traditional high-strength steel, advanced high-strength steel has both strength and toughness, and has a higher collision energy absorption capacity. It can still meet safety requirements while ensuring vehicle weight reduction. It is the best material for automotive steel. Twin-induced plasticity (TWIP) steel mainly obtains superior mechanical properties by adding alloy elements. When there is no external load, the structure of this type of steel at room temperature is stable retained austenite; but under external load, due to the strain The induction of mechanical twins will produce large neck-free extensions, showing very excellent mechanical properties, mainly manifested in high strain hardening rate and strong plasticity.

Corrosion of steel is a kind of uneven damage. Corrosion reduces the cold brittleness resistance and fatigue strength of steel. Metal corrosion is extremely harmful to modern industry. It not only causes waste of resources, but even endangers people's lives and property. The methods to prevent corrosion include: cathodic protection, anodic protection, and adding inhibitors, protective coatings and metal coatings. The galvanized layer not only acts as a physical shield for the steel plate, but also electrochemically protects the base steel. After using galvanized steel for the body and other components, the corrosion resistance and the service life of the car are greatly improved.

TWIP steel contains a large amount of alloying elements such as Al, Si, Mn and Cr. During the annealing process of the continuous hot-dip galvanizing production line, although the annealing atmosphere in the furnace is reducing and can reduce the iron oxide on the surface of the steel plate, it is Advanced high-strength steel contains a large amount of alloying elements such as Al, Si, and Mn, but they are thermodynamically oxidizable. These alloying elements are selectively oxidized on the surface of the steel plate to form oxides that cannot be reduced, such as: MnO, SiO ₂ , Al ₂ O ₃ , Mn ₂ SiO ₄ . Subsequently, when the steel plate enters the zinc pool, these oxides will reduce the wettability between the molten zinc and the steel plate, causing the galvanized layer between the zinc liquid and the surface of the steel plate to peel off or cause missing plating.

At present, in view of the problem of poor plateability caused by the selective oxidation of alloying elements such as Mn and Si in advanced high-strength steels such as TWIP, many scholars have carried out specific research work on the influence of alloying element oxides on the coating, but there is still a lack of A specific method can be used to evaluate TWIP steel's excellent plating ability.

Contents of the invention

In order to overcome the above disadvantages, the object of the present invention is to provide a method for evaluating the galvanization of TWIP steel, which can conveniently and efficiently evaluate the galvanized layer on the surface of TWIP steel.

In order to achieve the above object, technical scheme of the present invention is:

A method for evaluating TWIP steel platability, comprising the steps of:

Step 1: Calculate the saturated vapor pressure of water from the annealing dew point through formula calculation;

Step 2: Obtain the oxygen partial pressure value in the annealing atmosphere at any given temperature through the relationship between the saturated vapor pressure of water and the hydrogen partial pressure;

Step 3: Characterize the excellent and good platability of TWIP steel by oxygen partial pressure.

Step 4: Through the galvanizing experimental research, the relationship between the oxygen partial pressure and the surface oxide morphology after annealing and the density of the inhibition layer is obtained, so as to verify the feasibility of the characterization method.

In the step one, the calculation method of the saturated vapor pressure of the water is:

When the annealing dew point is less than 0°C,

When the annealing dew point is greater than 0°C,

P(H ₂ O) _sat - saturated vapor pressure of water, in atm;

T _DP ——annealing dew point, unit is ℃.

In said step 2, the relationship between the saturated vapor pressure of water and the partial pressure of hydrogen is as follows: And thus obtain the oxygen partial pressure value in the annealing atmosphere at any given temperature.

P(H ₂ O) _sat - saturated vapor pressure of water, in atm;

P(H ₂ )——hydrogen partial pressure, the unit is atm;

log ₁₀ P(O ₂ )——Oxygen partial pressure, the unit is atm;

T——Temperature, the unit is ℃.

In the third step, the oxygen partial pressure is used to characterize the galvanization of TWIP steel. The effect of the oxygen partial pressure on the galvanizing effect is direct: when the oxygen partial pressure increases from low to high, the hot-dip galvanizing effect first deteriorates and then improves.

If the oxygen partial pressure is 1×10 ^-31 to 1×10 ^-28 atm, it is a low oxygen partial pressure, and the galvanized surface quality of TWIP steel is good, and there is almost no missing plating defect.

If the oxygen partial pressure is 1×10 ^-26 to 1×10 ^-23 atm, it is a medium oxygen partial pressure, and the galvanized surface quality of TWIP steel is poor, the surface is not smooth, and there are many missing plating defects.

If the oxygen partial pressure is 1×10 ^-22 to 1×10 ^-19 atm, it is a high oxygen partial pressure, and the galvanized surface quality of the TWIP steel is very good without missing plating defects.

When the oxygen partial pressure is low, there are not enough oxygen atoms near the surface to provide Mn and other alloying elements, so the surface oxide of TWIP steel after annealing is very thin, Mn and Al basically have no external oxidation phenomenon, and Al oxides that undergo external oxidation are very small. Obviously, the plating quality is good.

When the oxygen partial pressure is medium, the oxide on the surface of TWIP steel after annealing is much thicker than that at low oxygen partial pressure, with obvious delamination, and obvious external oxidation of Mn and Al, and the quality of the coating is poor.

When the oxygen partial pressure is high, a thicker oxide layer is formed on the surface of the annealed TWIP steel than when the oxygen partial pressure is low. is excellent.

Advantage of the present invention and beneficial effect are:

1. Compared with the prior art, the method for evaluating the platability of TWIP steel in the present invention can use data calculated according to annealing parameters, such as: annealing temperature, annealing dew point, hydrogen ratio, relatively complete experimental parameters are conducive to the required The acquisition of data provides a theoretical data basis for the subsequent evaluation of the plateability of the steel plate.

2. The value of oxygen partial pressure in the present invention can reasonably evaluate the excellent platability of TWIP steel sheet.

3, the present invention evaluates the method for TWIP steel platability, sets up the equation of experimental parameter, by the calculated value of experimental parameter equation, can evaluate the platability of TWIP steel fast, this evaluation method is less affected by the outside world, can It saves a lot of time and workload, eliminates the analysis and detection of the experimental process, makes the evaluation method more convenient and requires less time.

4, the present invention is by providing the excellent method means of evaluation TWIP steel platability, judges the excellent platability of TWIP steel by the size of oxygen partial pressure value, when platability is poor, can optimize annealing dew point, annealing temperature and hydrogen ratio, In order to obtain the annealing parameters with good galvanizing effect, thereby improving the platability of TWIP steel.

Description of drawings

Figure 1 is a schematic diagram of the continuous hot-dip galvanizing annealing process.

Fig. 2 is an embodiment of the present invention, the metallographic structure diagram (a) (c) (e) of the advanced high-strength steel TWIP steel and the macroscopic diagram (b) (d) (f) of the experimental steel plate coating.

Detailed ways

The present invention will be further described below through the embodiments and the accompanying drawings.

Example

The method for evaluating TWIP steel platability in the present embodiment may further comprise the steps:

Step 1: Calculate the saturated vapor pressure of water from the annealing dew point through formula calculation;

The formula for calculating the saturated vapor pressure of water is:

When the annealing dew point is less than 0°C,

When the annealing dew point is greater than 0°C,

In the formula: P(H ₂ O) _sat —— saturated vapor pressure of water, the unit is atm;

T _DP ——annealing dew point, unit is ℃.

Step 2: Obtain the oxygen partial pressure value in the annealing atmosphere at any given temperature through the relationship between the saturated vapor pressure of water and the hydrogen partial pressure;

The relationship between the saturated vapor pressure of water and the partial pressure of hydrogen is:

And thus obtain the oxygen partial pressure value in the annealing atmosphere at any given temperature.

In the formula: P(H ₂ O) _sat —— the saturated vapor pressure of water, the unit is atm;

P(H ₂ )——hydrogen partial pressure, the unit is atm;

log ₁₀ P(O ₂ )——Oxygen partial pressure, the unit is atm;

T——Temperature, the unit is ℃.

Step 3: Characterize the excellent and good plating properties of TWIP steel by oxygen partial pressure;

The method of oxygen partial pressure to characterize the platability of TWIP steel is that the effect of oxygen partial pressure on the galvanizing effect is direct: from low to high oxygen partial pressure, the hot-dip galvanizing effect first deteriorates and then improves.

When the oxygen partial pressure is 1×10 ^-31 ～1×10 ^-28 atm, it is a low oxygen partial pressure, and the galvanized surface quality of TWIP steel is good, and there is almost no missing plating defect.

When the oxygen partial pressure is 1×10 ^-26 ～1×10 ^-23 atm, it is a medium oxygen partial pressure, and the galvanized surface quality of TWIP steel is poor, the surface is not smooth, and there are many missing plating defects.

When the oxygen partial pressure is 1×10 ^-22 ～1×10 ^-19 atm, it is a high oxygen partial pressure, and the galvanized surface quality of TWIP steel is very good, and there is no missing plating defect.

Step 4: Through the galvanizing experiment research, the relationship between the oxygen partial pressure and the surface oxide morphology after annealing and the density of the inhibition layer is obtained, and the feasibility of the characterization method of the present invention is verified.

As shown in Figure 1, in this embodiment, the continuous hot-dip galvanizing annealing process is as follows: first, the temperature is raised to the annealing temperature at 10°C/s, and kept for 120s; then, the temperature is lowered to 480°C at 30°C/s, and naturally cooled to 460 °C and keep it warm for 4s; finally cool down to room temperature at 10°C/s.

When the annealing temperature is 700°C, the dew point DP is -50°C, and the hydrogen volume ratio is 15% _H2 , the oxygen partial pressure of the atmosphere is 8.28×10 ^-29 atm, and there are not enough oxygen atoms near the surface to provide Mn and other Alloying elements, so the surface oxide of TWIP steel after annealing is very thin, Mn and Al basically have no external oxidation phenomenon, Al oxides that have external oxidation are obvious, and the coating quality is good.

When the annealing temperature is 700°C, the dew point DP is -15°C, and the hydrogen volume ratio is 15% H ₂ , the oxygen partial pressure of the atmosphere is 1.48×10 ^-25 atm. Compared with the low oxygen partial pressure, the annealed The oxide phase on the surface of TWIP steel is very thick, with obvious layering, and obvious external oxidation of Mn and Al, and the quality of the coating is poor.

When the annealing temperature is 800°C, the dew point DP is 0°C, and the hydrogen volume ratio is 5% H ₂ , the oxygen partial pressure in the atmosphere is 5.89×10 ^-21 atm, and the surface of the TWIP steel after annealing is formed at a lower oxygen partial pressure than Thick oxide layer, the delamination between the oxide layer and the substrate is not obvious, the internal oxidation of Mn and Al is obvious, the surface oxide is reduced, and the coating quality is excellent.

As shown in Figure 2, it can be seen from the metallographic structure diagram (a)(c)(e) of the advanced high-strength steel TWIP steel and the macroscopic diagram (b)(d)(f) of the experimental steel plate coating: when the oxygen partial pressure is higher When it is low, as shown in Figures (a) and (b), the coating on the TWIP steel section is relatively continuous, but the thickness is thin and uneven, and there are almost no missed plating spots on the surface of the galvanized layer; when the oxygen partial pressure is medium, as shown in Figure As shown in (c) and (d), the thickness of the coating on the TWIP steel section is very thin and quite uneven, and even there is almost no coating in some positions, the surface of the galvanized layer is rough and not smooth, and there are many missing plating defects; when the oxygen partial pressure When it is higher, as shown in Figures (e) and (f), the coating of the TWIP steel section is thicker, continuous and evenly distributed, and there is no missing plating defect on the surface of the galvanized layer.

Claims (6)

1. a method for evaluating TWIP steel platability, is characterized in that: comprise the following steps: Step 1: Calculate the saturated vapor pressure of water from the annealing dew point through formula calculation; Step 2: Obtain the oxygen partial pressure value in the annealing atmosphere at any given temperature through the relationship between the saturated vapor pressure of water and the hydrogen partial pressure; Step 3: Characterize the excellent and good plating properties of TWIP steel by oxygen partial pressure; Step 4: Through the galvanizing experimental research, the relationship between the oxygen partial pressure and the surface oxide morphology after annealing and the density of the inhibition layer is obtained, so as to verify the feasibility of the characterization method. 2. the method for evaluating TWIP steel platability according to claim 1, is characterized in that: in described step 1, the size calculation method of the saturated vapor pressure of water is: When the annealing dew point is less than 0°C, When the annealing dew point is greater than 0°C, P(H ₂ O) _sat - saturated vapor pressure of water, in atm; T _DP ——annealing dew point, unit is ℃. 3. the method for evaluating TWIP steel platability according to claim 1, is characterized in that: in described step 2, the relational expression between the saturated vapor pressure of water and hydrogen partial pressure is as follows: And thus obtain the oxygen partial pressure value in the annealing atmosphere at any given temperature; P(H ₂ O) _sat - saturated vapor pressure of water, in atm; P(H ₂ )——hydrogen partial pressure, the unit is atm; log ₁₀ P(O ₂ )——Oxygen partial pressure, the unit is atm; T——Temperature, the unit is ℃. 4. the method for evaluating TWIP steel platability according to claim 1, is characterized in that: in described step 3, the method that oxygen partial pressure characterizes TWIP steel platability is, the influence of oxygen partial pressure on galvanizing effect It is direct: from low to high oxygen partial pressure, the effect of hot-dip galvanizing first deteriorates and then improves. 5. the method for evaluating TWIP steel platability according to claim 1, is characterized in that: If the oxygen partial pressure is 1×10 ^-31 ～1×10 ^-28 atm, it is a low oxygen partial pressure, and the galvanized surface quality of TWIP steel is good, and there are almost no missing plating defects; If the oxygen partial pressure is 1×10 ^-26 to 1×10 ^-23 atm, it is a medium oxygen partial pressure, and the galvanized surface quality of TWIP steel is poor, the surface is not smooth, and there are many missing plating defects; If the oxygen partial pressure is 1×10 ^-22 to 1×10 ^-19 atm, it is a high oxygen partial pressure, and the galvanized surface quality of the TWIP steel is very good without missing plating defects. 6. the method for evaluating TWIP steel platability according to claim 1 or 5, is characterized in that: When the oxygen partial pressure is low, there are not enough oxygen atoms near the surface to provide Mn and other alloying elements, so the surface oxide of TWIP steel after annealing is very thin, Mn and Al basically have no external oxidation phenomenon, and Al oxides that undergo external oxidation are very small. Obviously, the coating quality is good; When the oxygen partial pressure is medium, compared with the oxide on the surface of TWIP steel after annealing, it is much thicker when the oxygen partial pressure is low, the layering is obvious, and there are obvious external oxidation phenomena of Mn and Al, and the quality of the coating is poor; When the oxygen partial pressure is high, a thicker oxide layer is formed on the surface of the annealed TWIP steel than when the oxygen partial pressure is low. is excellent.