JPS6054122B2 - Cold rolling method of metastable austenitic stainless steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cold rolling metastable austenitic stainless steel, which reduces variations in product hardness values and increases rolling speed to improve rolling efficiency.

In order to obtain high-grade stainless steel spring materials, metastable austenitic stainless steel is cold rolled.

SUS30l is austenitic stainless steel SUS3
It is a metastable austenitic steel with lower austenite stability than 04, and has an increased amount of martensite produced by strain deformation, but when shipped as a high-grade spring material, it is required to have excellent spring properties , high hardness must be achieved by high-grade cold rolling. Conventionally, in cold rolling of this type of material, the cold rolling rate must be high and the rolling line speed must be set extremely low to obtain a material with the specified high hardness, so the rolling efficiency is extremely low. The price was low and the cost was high.

In addition, variations in the composition of the materials used cause significant variations in the work hardening properties, which tends to cause large variations in the target product hardness value, and so-called hardness abnormalities that are outside the target product hardness range. material is generated, and the waste must be disposed of each time, resulting in a decrease in yield.
This was contributing to higher costs. The present invention was made to solve this problem.

As a result of various studies for this purpose, the inventors found that the first
The temperature of rolling oil during cold rolling is lower than the conventional 30~40℃.
Second, we select a material that matches the hardness value of the product by using the relational expression between the Ms point and the component composition that we have independently studied and proposed, and we also select the material that matches the hardness value of the product. If the optimal rolling rate is determined and rolled at an increased rolling speed based on the correlation between the cold rolling rate and the Ms point and the rolling speed, a product of constant quality (constant hardness) can be obtained with high efficiency. We were able to establish a cold rolling method for metastable austenitic stainless steel that can produce products with a target hardness at a high yield and at low cost. That is, in cold rolling metastable austenitic stainless steel, the present invention supplies the rolling oil to a mill at a low temperature of less than 30°C, and creates a relational expression between the Ms point and the component composition that essentially follows the upper and lower equation (1). The target product hardness is determined from The object of the present invention is to provide a method for cold rolling metastable austenitic stainless steel, which is characterized in that cold rolling is carried out by determining the component composition, cold rolling rate, and rolling speed of the material depending on the conditions. −
- All Hereinafter, each requirement of the present invention will be specifically explained using experimental examples. Equation (1) is SUS3Ol
The fluctuation in the content of the component elements gradually changes to the Ms point, that is, the temperature at which martensite begins to precipitate in the metal structure when stainless steel, which exhibits an austenitic metal structure at room temperature, is brought to a low temperature. This is an empirical formula derived from the results of investigating the influence of stainless steel, and this formula is the content percentage value of the component element determined by analyzing a sample extracted during the steelmaking process of the stainless steel copper manufacturing process! The Ms point can be calculated by substituting it as it is.

Next, Figure 1 shows part of the results of investigating the relationship between the Ms point calculated by equation (1) and the cold rolling rate on the hardness of stainless steel.・Even for stainless steel, the lower the temperature at the MS point calculated using equation (1), the lower the hardness.

In other words, if you want to obtain a product with the same hardness, M
It can be seen that the higher the temperature at the S point, the lower the cold rolling rate. Furthermore, Figure 2 shows the relationship between the temperature at the Ms point calculated by equation (1) and the temperature of rolling oil supplied to the mill, and Figure 3 shows the effect of rolling on the hardness of the product. This study investigated the relationship between speed.

Figure 2 shows that even if cold rolling is performed at the same cold rolling rate and rolling speed, the lower the rolling oil temperature, the higher the hardness of the stainless steel after cold rolling. It can be seen that even if cold rolling is performed at the same rolling oil temperature, the lower the rolling speed, the higher the hardness of the stainless steel after cold rolling.

The present invention is based on such a correlation to determine optimal conditions according to the target product hardness of stainless steel.
In other words, in order to efficiently cold-roll stainless steel with a preset product hardness, conditions must be set so that the rolling speed is as high as possible, close to the limit of the mill's capacity, but can be cold-rolled at a smaller cold rolling rate. However, the present invention is a method that can set the rolling speed high, mainly by keeping the temperature of the rolling oil at a low temperature of less than 30°C, and by obtaining the target product hardness even if the cold rolling rate is small. The conditions under which this can be done include determining the content of the constituent elements of the stainless steel material analyzed during the steelmaking process before the cold rolling process.
), a material with a high Ms point temperature is selected for a product with high product hardness, and a material with a low Ms point temperature is selected for a product with low product hardness. The present invention provides a method of determining cold rolling conditions using a predetermined correlation between the Ms point, cold rolling rate, and cold rolling speed while efficiently operating a cold rolled material. For example, if you want to find the target hardness value of the product Hv53O, use MS in the range of -120℃ to -5℃ in Figure 1.
The work hardening characteristic curves shown point by point are drawn, and the Ms point range of the curve where each of these curves intersects with the horizontal axis of the target hardness value HV53O is from -20°C to -5°C. A material having a Ms point of -5°C to 20°C may be selected.

If a material with a Ms point of, for example, -20°C is selected, the finish cold rolling rate is set to 65% as shown in Figure 1, the temperature of the rolling oil is set to 20°C as shown in Figure 2, and the third cold rolling rate is set to 65%. As shown in the figure, the manufacturing routing is determined at a rolling speed of 120 m/min. In the case of the conventional example, it was not possible to utilize such an established correlation, so, for example, in Fig. 2, the temperature of the rolling oil was used at about 35°C as in the past, and the finishing cold rolling rate was changed. It is clear that when the hardness is set to 65%, the target hardness of HV53O cannot be obtained, and a product with a hardness of HV5O4 lower than this is obtained.

In order to obtain the target hardness of H■530 by using the rolling oil at a temperature of about 35°C as before, and by setting the finish cold rolling rate to 65%, the rolling speed should be set to 120rr as shown in Figure 3.
It has to be reduced from 1/Min to about 80rr1/Min, which is extremely inefficient.

Also, if you try to increase the rolling speed to 120rn/min, the Hv
This means that the target hardness value of 3O cannot be obtained. Therefore, due to the lack of information regarding the selection of materials based on the Ms point and the temperature control of rolling oil, when using the conventional method, the cold rolling rate and rolling speed are changed, especially by slowing down the cold rolling speed. It was difficult to efficiently manufacture products with uniform hardness because each product was manufactured at different times. In the present invention, after selecting the material based on the Ms point according to the above formula (1), and using the correlations shown in Figs. Since a high-hardness product is obtained by rolling, a constant-hardness product can be obtained with high efficiency.

In carrying out the method of the present invention, the operating temperature of the rolling oil is 3.
Even if the temperature is lower than 0℃, there is no particular adverse effect on rolling performance or the material to be rolled, but consider the refrigeration function of rolling oil and the increase in load on pumps and filters due to the increase in viscosity of rolling oil. Then, it is better to set the lower limit to 17°C. FIG. 4 is a process diagram of a preferred embodiment for supplying rolling oil to the mill 20 with the oil level at a low temperature of less than 30°C, in which the recovered oil collected in the oil pan 1 below the mill 20 is Normal oil spray circulation in which the oil is sprayed between the work roll 8 and the rolled material 9 from the rolling oil spray device 7 through the dirty oil tank 2, pressure pump 3, filter 4, clean oil tank 5 and pressure pump 6. A cooler 10 is interposed in the route. This cooler 10 is equipped with a coil 13 to which cold water in a cold water tank 11 is circulated and supplied, and heat exchange is performed between the cold water and rolling oil. Refrigerant from the refrigerator 12 circulates in the coil 14 in the cold water tank 11, and the coil 1
4 serves as an evaporator to cool the cooling water. In carrying out the method of the present invention, temperature control of this rolling oil plays an important role in the hardness of the product as described above, and this temperature control is achieved by keeping the temperature of the cold water in the cold water tank 11 at a predetermined value. This can be carried out suitably. As described above, the present invention improves the relationship between the Ms point and the component composition, the correlation between the Ms point and the cold rolling rate, and the correlation between the cold rolling rate and the cold rolling rate based on equation (1) when the rolling oil temperature is lower than 30°C. Since the cold rolling of metastable austenitic stainless steel is carried out by effectively utilizing the low temperature, the target hardness value can be obtained without variation across each coil, and the rolling efficiency can be greatly improved. Mukodo can be achieved.

Taking the average of the implementation results, the rolling efficiency is 50% higher than conventional
% has also improved, and the hardness abnormality rate is 10 to 15% compared to the conventional method.
was also able to be reduced.

[Brief explanation of the drawing]

Figure 1 shows the relationship between Ms point and cold rolling rate on product hardness, Figure 2 shows the relationship between Ms point and rolling oil temperature on product hardness, and Figure 3 shows the effect on product hardness. FIG. 4, which is a diagram showing the relationship between the Ms point and the rolling speed, is a diagram of a rolling oil cooling system suitable for cooling the rolling oil to below 30°C. 10... Cooler, 11... Cold water tank, 12... Freezer, 13... Coil, 14
...Coil, 20...mil.

Claims (1)

[Claims] 1. The correlation between the Ms point and the cold rolling rate according to the following formula (1) on the product hardness is determined in advance, and from this predetermined correlation, a material having the Ms point that provides the target product hardness is selected. At the same time, the cold rolling rate of this material is determined from the correlation, and further the rolling speed of the material is determined from the predetermined correlation between the Ms point and the rolling speed according to the following formula (1) on the product hardness, and this determination A method for cold rolling metastable austenitic stainless steel, characterized in that cold rolling is carried out while supplying rolling oil to a mill at a low temperature of less than 30 ° C. Ms(℃)=0.56(2730.00-20
94.00C%-2915.00N%-117.30M
n%-101.10Ni%-99.75Cr%-195
．． 00Mo%-32.00). ...(1)