JPS6225746B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a tool material for pipe making, and is particularly advantageous for producing plugs for plug mill rolling among tool materials used in the production of seamless steel pipes, and has high wear resistance at high temperatures. The aim is to achieve advantageous improvements. Seamless steel pipes are manufactured by drilling round or square steel pieces using the Mannesmann method or press method to create a hollow material, and then elongating this hollow material using a rolling mill such as an elongator, plug mill, or mandrel mill. The most common method is to In each step of manufacturing such seamless steel pipes, tool materials such as forming plugs and guide shoes are exposed to severe abrasive environments at high temperatures. Among these, in the plug mill rolling process, the temperature of the raw tube is usually as high as 950 to 1150°C, and rolling is performed in such a high temperature atmosphere at a rolling load of about 100 to 250 tons and a rolling speed of about 3 m/s. As a result, plugs for plug mill rolling are forced to come into contact with the inner surface of the raw tube under high temperature and pressure, and the plugs themselves do not rotate, so they are subject to complete sliding wear, making them subject to especially severe conditions. It's below. Therefore, improving the wear resistance of such tool materials at high temperatures and extending their service life is one of the most important issues in the production of seamless steel pipes using the process described above, especially in oil wells. In recent years, the importance of seamless steel pipes has become even greater, as increased productivity and higher alloying of seamless steel pipes are desired. The present invention advantageously satisfies the above-mentioned demands, and aims to propose an advantageous method for manufacturing a pipe-making tool material that has excellent wear resistance even at high temperatures. By the way, the most common means of improving the wear resistance of materials at high temperatures is to increase the high temperature strength of the materials, and for that purpose C,
It is known that the addition of alloying elements such as Cr, Mo, W, Ni, Co, Nb, and V is effective, and such alloying elements are also added to plug materials for plug mill rolling (1.3 to 1.5). %C-17%Cr-2%
High carbon, high Cr cast steels such as W steel and (1.3-1.8)%C-24%Cr-3%Ni steel are mainly used. However, plugs made of such materials are no longer able to cope with the shortening of rolling intervals due to the recent increase in production of seamless steel pipes for oil wells, as well as the increase in rolling load due to the high alloying of such steel pipes.
Plug wear has become a major manufacturing problem. In this regard, as a means to increase the high-temperature strength of the plug, increasing the amount of Ni, W, Co, and Mo added, adding Al and Ti and using precipitation hardening by Ni-Al and Ni-Ti intermetallic compounds, Furthermore, the use of Ni-based alloys may be considered. However, the addition of large amounts of such elements causes a significant decrease in thermal conductivity.
Therefore, when plug mill rolling is performed using this type of plug, even if the heat of the raw tube itself or the heat generated by rolling tries to flow into the plug, this heat is difficult to transfer into the inside of the plug. This causes a temperature rise only in the surface layer, which ultimately leads to a decrease in strength. In addition, in highly alloyed iron-based alloys and Ni-based alloys, the oxidized scale on the plug surface, which effectively contributes to cutting off the flow of heat from the raw pipe, remains satisfactory even when heated at high temperatures in an oxidizing atmosphere. There is also the added disadvantage of not being generated to a certain extent. For this reason, even if the above-mentioned measures were taken, the degree of wear and tear on the plug would be greater than in the past. Therefore, the inventors conducted intensive research to solve the above problem, and found that a predetermined amount of C, Si, Mn, Cr,
In addition to Ni and Nb, a suitable amount of at least one selected from Mo, W, and Co is added to the cast steel, which is then finished into a predetermined shape and then subjected to nitriding, oxidation, and hardening. It was newly discovered that it was possible to obtain a tool material that has higher high-temperature strength than other materials, and also has an oxide scale that is dense and has excellent adhesion, and thus completed this invention. That is, this invention includes: C: 0.60 to 2.0% by weight, Si: 0.10 to 2.0% by weight, Mn: 0.30 to 2.0% by weight, Cr: 9.0 to 22.0% by weight, Ni: 0.60 to 8.0% by weight, and Nb: 0.020 to 2.0% by weight. Molten steel containing 2.0% by weight and at least one selected from Mo: 0.20 to 5.0% by weight, W: 0.20 to 5.0% by weight, and Co: 0.20 to 5.0% by weight is cast, and then cast into a predetermined shape. After finishing it, 500
Surface nitriding treatment with a nitriding depth of 10 μm or more in the temperature range of ~1100℃, followed by 1000 ~ 1250℃
Oxidation treatment is performed at a temperature range of 800 °C to form oxide scale on the finished surface, and then the heating temperature is 800 °C.
This is a method for manufacturing a pipe-making tool material, which is characterized by performing a hardening treatment at a temperature in the range of ~1000°C. This invention will be explained in detail below. First, the reason why the basic components are limited to the above range in this invention will be explained. C: 0.60 to 2.0% by weight (hereinafter simply expressed as %) C is useful as an element that forms carbides and improves high-temperature wear resistance, but if it is less than 0.60%, its effect is small, while if it exceeds 2.0% Since cracking is likely to occur due to thermal shock, the content was set in the range of 0.60 to 2.0%. Si: 0.10-2.0% Si is a useful element for creating scale with good adhesion to the base alloy, but if it is less than 0.10%, its effect is small, while if it exceeds 2.0%, it reduces high-temperature strength. Therefore, it was set in the range of 0.10 to 2.0%. Mn: 0.30-2.0% Mn effectively contributes to increasing high-temperature strength, but below 0.30%, the effect is small;
%, the thermal conductivity deteriorates and high temperature wear resistance deteriorates, so the range was set to 0.30 to 2.0%. Cr: 9.0-22% Cr is a useful element that increases high-temperature strength by forming scales on the surface that have good adhesion to the base alloy and good heat insulation properties, as well as forming Cr carbides. If the content is less than 9.0%, the effect will be small, while if it exceeds 22%, the amount of scale deposited will decrease, the high temperature strength will decrease, and the high temperature wear resistance will deteriorate, so the content was set in the range of 9.0 to 22%. Ni: 0.60-8.0% Ni is a useful element that generates Ni-enriched alloy grains at the boundary between scale and base alloy during scale adhesion heat treatment, increases the adhesion between scale and base alloy, and increases high-temperature strength. It is. If it is less than 0.60%, the effect will be poor, while if it exceeds 8.0%, the amount of scale produced will decrease, thermal conductivity will deteriorate, and high-temperature wear resistance will deteriorate. Nb: 0.020-2.0% Nb is a particularly important element in this invention because it forms carbides and increases high-temperature strength, increases the amount of oxide scale produced, and improves its adhesion and high-temperature wear resistance. However, if it is less than 0.020%, the effect is small, so the lower limit is set to 0.020%, while if it exceeds 2.0%, the effect reaches saturation and is also expensive, so the upper limit is set to 2.0%. Mo, W, or Co: 0.20-5.0% Mo, W, or Co increases high-temperature strength and increases scale compactness and adhesion to improve high-temperature wear resistance, so Mo, W, or Co is one of these. 1
It is particularly important in this invention to add a species or two or more species, but the effect is small if each species is less than 0.20%, so the lower limit is set at 0.20%.
If it exceeds 5.0%, the effect reaches saturation and it is also expensive, so the upper limit was set at 2.0%. In addition to the above-mentioned basic components of C, Si, Mn, Cr, Ni, Nb, and one or more of Mo, W, and Co, in this invention, Zr, Ca, Mg , Y, or one or more selected from V, Cu, Al, B, and S within the following range. The reasons for limiting these additive elements are as follows. Zr: 0.050-5.0% Zr has good adhesion to the steel base, heat insulation, and wear resistance due to the combined addition of one or more selected from the following Ca, Mg, and Y. It is useful as an element that generates oxide scale containing stabilized zirconia, which has excellent stability, but the amount added is
If it is less than 0.050%, the effect will be small, while if it exceeds 5.0%, the amount of scale produced will be extremely small and the high-temperature wear resistance will deteriorate, so it was limited to a range of 0.050 to 5.0%. Ca, Mg, Y: 0.003Ca/Zr0.06, 0.002Mg/Zr0.04 0.005Y/Zr0.10 As mentioned above, Ca, Mg, and Y improve their adhesion to the base steel due to their combined addition with Zr. It is useful as an element that generates oxide scale with good heat insulation and wear resistance, but the amount of these additions is in the ratio of Ca/Zr<0.003 and Mg/Zr<0.003 to Zr content, respectively.
0.002, when Y/Zr<0.005, it is difficult to obtain a scale with good adhesion to the base metal, while on the other hand, when Ca/Zr>0.06,
Adhesion tends to decrease when Mg/Zr>0.04 and Y/Zr>0.10, and these are also expensive, so 0.003≦Ca/Zr≦0.006 and 0.002≦, respectively.
The range was limited to Mg/Zr≦0.04 and 0.005≦Y/Zr≦0.10. V: 0.020-2.0% V effectively contributes to forming carbides and increasing high-temperature strength, but if it is less than 0.20%, the effect is small, while if it exceeds 2.0%, the effect reaches saturation and is expensive. Therefore, it was limited to the range of 0.020 to 2.0%. Cu: 0.10-3.0% Cu effectively contributes to improving the adhesion between scale and steel base, but less than 0.10% the effect is poor, while more than 3.0% a Cu-enriched layer forms on the surface. The content was limited to 0.10 to 3.0% because the melting point of this part decreases and the high-temperature wear resistance deteriorates. Al: 0.020-2.0% Al contributes effectively to the generation of scale that has good adhesion to the steel base and has excellent heat insulation properties, but if it is less than 0.020%, the effect is small;
%, the amount of scale formed will significantly decrease and high temperature wear resistance will deteriorate, so it was limited to a range of 0.020 to 2.0%. B: 0.0020-0.50% B is a useful element that increases high-temperature strength and improves surface lubricity by forming BN in the nitriding treatment after final forming, but if it is less than 0.0020%, the effect is small; %, thermal shock cracking will occur, so it was limited to a range of 0.0020 to 0.50%. S: 0.020-0.30% S effectively contributes to increasing surface lubricity through the formation of sulfides, but if it is less than 0.020%, the effect is small, while if it exceeds 0.30%, thermal shock cracking is likely to occur. Therefore, it was limited to the range of 0.020 to 0.30%. Next, a description will be given of the heat treatment that is applied to cast steel that has been adjusted to have an appropriate composition and is finished into a predetermined shape. First, in this invention, surface nitriding treatment is performed. This is because such nitriding treatment further increases the high-temperature strength of the surface layer due to solid solution hardening of N and the formation of nitrides such as Cr and Nb, and especially in materials containing B, the formation of BN results in surface lubrication. This is because, together with the increased properties, the high-temperature wear resistance is significantly improved. However, if the nitriding layer thickness obtained by nitriding treatment, that is, the nitriding depth, is less than 10 μm, the improvement effect is poor, so the nitriding depth is limited to 10 μm.
In order to achieve this, nitriding treatment is necessary.
It is necessary to carry out in the temperature range of 500-1100℃. Note that as the nitriding method, any of gas nitriding, gas soft nitriding, liquid nitriding, and ion nitriding can be used. Then, following the nitriding treatment, an oxidation treatment is performed. The purpose of oxidation treatment is to form an oxide scale on the finished surface of the tool material to effectively cut off heat input from the high-temperature material to be treated, but heating temperatures below 1000℃ are sufficient. It is difficult to obtain an oxide scale layer with a thickness (20 μm or more) that exhibits good thermal insulation properties, contains Cr, and has good adhesion to the base steel.On the other hand, when the temperature exceeds 1250℃, many voids occur in the scale layer, causing the scale layer to deteriorate. The oxidation treatment must be carried out in a temperature range of 1000 to 1250°C, since the adhesion with the iron alloy decreases and both deteriorate the high temperature wear resistance. The hardening treatment that is performed following or after the above oxidation treatment is performed to reduce the amount of retained austenite and convert it to martensite, and to increase the amount of solid solution of C in austenite to increase high-temperature hardness. However, if the treatment temperature is less than 800℃, the amount of solid solution of C in austenite is small, making it difficult to obtain satisfactory high-temperature hardness.On the other hand, if the treatment temperature exceeds 1000℃, the amount of retained austenite increases and the high-temperature hardness decreases. The treatment temperature was limited to a temperature range of 800 to 1000°C. The cooling rate from the above heating temperature range has almost no effect on the hardness at high temperatures, so if you heat it to a predetermined temperature and hold it for about 0.5 to 5 hours, then cool it in the usual manner, for example by air. good. By performing such nitriding, oxidation, and hardening treatments in sequence, not only high-temperature hardness but also high-temperature wear resistance is significantly improved, thus further extending tool life. . Examples of the present invention will be described below. After forming each cast steel having the chemical compositions shown by symbols A to P in Table 1 into plugs for plug mills,
Nitriding treatment (in _NH3 atmosphere), oxidation treatment (atmosphere) under the treatment conditions shown in
CO: 3%, _CO2 : 10%, _O2 : 4%, remaining _N2 ),
Subsequently, a hardening treatment was performed. The nitriding depth of the nitrided material is 40 to 160 μm, and the thickness of the oxide scale layer, which has good adhesion to the Cr-containing steel, is 200 to 250 μm.
It was μm. Then, using each plug obtained, C: 0.23
%, Si: 0.24%, Mn: 1.33%, Ti: 0.017%,
B: 0.0018%, balance 249mm in diameter, with a composition of Fe;
The perforation life of each plug was investigated when a raw carbon steel pipe with a wall thickness of 12.9 mm was continuously rolled in a plug mill to a diameter of 244 mm and a wall thickness of 9.9 mm. The results are also shown in Table 2 as a lifespan ratio when the lifespan of the comparative example (symbol P) is set to 1.

【table】

[Table] As is clear from the results shown in Table 2, the plugs for plug mills (symbols A to
All of O) had a piercing life 2.3 to 3.5 times longer than the conventional plug shown as a comparative example (symbol P). In the above embodiments, the present invention was mainly explained in the case where it was applied to the production of plugs for plug mills, but it can also be widely applied to the production of other piercers, elongator guide shoes, elongator plugs, etc., and the same effects can be obtained. Needless to say, it is possible. Thus, according to the present invention, the high-temperature wear resistance and high-temperature strength of the pipe-making tool material can be significantly improved without deteriorating the thermal conductivity, and the useful life of the tool material can therefore be significantly extended. It is possible and advantageous.

Claims (1)

[Claims] 1 C: 0.60 to 2.0% by weight, Si: 0.10 to 2.0% by weight, Mn: 0.30 to 2.0% by weight, Cr: 9.0 to 22.0% by weight, Ni: 0.60 to 8.0% by weight, and Nb: Molten steel containing 0.020 to 2.0% by weight and at least one selected from Mo: 0.20 to 5.0% by weight, W: 0.20 to 5.0% by weight, and Co: 0.20 to 5.0% by weight is cast, and then After finishing the specified shape, 500
Surface nitriding treatment with a nitriding depth of 10 μm or more in the temperature range of ~1100℃, followed by 1000 ~ 1250℃
Oxidation treatment is performed at a temperature range of 800 °C to form oxide scale on the finished surface, and then the heating temperature is 800 °C.
A method for manufacturing a pipe-making tool material, which comprises performing a hardening treatment at a temperature in the range of ~1000°C.