Continuous rolling method for ultralow-temperature-resistant high-strength 316LN bar

Abstract

The invention discloses an ultralow-temperature-resistant high-strength 316LN bar continuous rolling method which comprises the following steps that firstly, a raw material ingot is heated through a heating furnace, the heating furnace is divided into a preheating section, a first heating section, a second heating section, a third heating section and a soaking section, the heating temperature of the preheating section is smaller than or equal to 650 DEG C, the heating temperature of the first heating section is 1120-1150 DEG C, and the heating temperature of the second heating section is 1120-1150 DEG C; the heating temperatures of the heating section 2, the heating section 3 and the soaking section are 1240-1260, so as to obtain a product A; secondly, the product A is roughly rolled and cogged, the rolling pass is 23-25, and a product B is obtained; and thirdly, the product B is subjected to continuous rolling, and finished round steel with the specification being phi 65-160 mm is obtained. The method has the characteristic that the bar with an ultra-fine grain structure and stable low-temperature mechanical performance is obtained.

Description

Technical Field

[0001] The invention relates to a continuous rolling method for a 316LN bar, in particular to a continuous rolling method for a super-low temperature resistant high-strength 316LN bar. Background Art

[0002] Ultra-low temperature resistant austenitic stainless steel is an economical and practical steel grade represented by 316LN, which is characterized by a specific composition system and excellent single-phase ultra-fine austenite structure. The mainstream products on the market are currently used in the form of medium and thick plates, thick-walled tubes, and large-size bars. The main application areas are nuclear power cooling equipment, gas liquefaction equipment, etc. Under the specific composition of the specific steel grade 316LN, the grain size of the product determines the stability of its low temperature strength performance and the effect of resistance to different low temperature strengths.

[0003] At present, the bars of this type of steel are mainly prepared by forging. The grain size control is difficult, and the forging heating temperature and the forging process temperature are not easy to control, which often leads to serious mixed crystal phenomenon on the surface of the round bar. The grain size difference is large, and the surface of the round bar needs to be peeled, resulting in a very low final yield of the bar and unstable low-temperature mechanical properties, which cannot meet the application requirements of low-temperature high-strength. Summary of the invention

[0004] The purpose of the present invention is to provide a method for continuous rolling of ultra-low temperature resistant high-strength 316LN bars. The present invention has the characteristics of obtaining ultra-fine grain structure and low-temperature stable mechanical properties bars.

[0005] The technical solution of the present invention is a method for continuously rolling ultra-low temperature resistant high-strength 316LN bars, comprising the following steps:

[0006] Step 1, heating the raw material ingot in a heating furnace, the heating furnace is divided into a preheating section, a heating section 1, a heating section 2, a heating section 3 and a soaking section, wherein the heating temperature of the preheating section is ≤650°C, the heating temperature of the heating section 1 is 1120-1150°C, the heating temperatures of the heating section 2, the heating section 3 and the soaking section are all 1240-1260°C, and product A is obtained;

[0007] Step 2: Rough rolling of product A, with 23-25 ​​passes, to obtain product B;

[0008] Step 3: Continuously roll product B to obtain finished round steel with a specification of φ65-160mm.

[0009] In the aforementioned method for continuous rolling of ultra-low temperature resistant high-strength 316LN bars, in step 1, heating section 1, heating section 2, heating section 3 and soaking section are all heated by upper and lower burners.

[0010] In the aforementioned method for continuous rolling of ultra-low temperature resistant high-strength 316LN bars, in step 2, during the rough rolling process, the surface thermal deformation temperature of the billet is 1080-1200°C.

[0011] In the aforementioned method for continuous rolling of ultra-low temperature resistant high-strength 316LN bars, in step 2, after the rough rolling is completed, the surface temperature of the billet is not less than 980°C.

[0012] In the aforementioned method for continuous rolling of ultra-low temperature resistant high-strength 316LN bars, in step 2, the average reduction in a single rolling pass is 30-40 mm.

[0013] In the aforementioned method for continuous rolling of ultra-low temperature resistant high-strength 316LN bars, in step three, during the continuous rolling process, the surface thermal deformation temperature of the steel billet is 1000-1050°C.

[0014] In the aforementioned method for continuous rolling of ultra-low temperature resistant high-strength 316LN bars, in step three, eight continuous rolling mills are used for continuous rolling, and the eight continuous rolling mills include four 650 rolling mills and four 550 rolling mills that are alternately distributed horizontally and vertically.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention adopts a special one-fire rolling method, firstly performs rough rolling to open the blank, then performs continuous rolling to form the blank, and the blank is respectively heated at specific temperatures in the preheating section, heating section 1, heating section 2, heating section 3 and soaking section, and is hot processed at a deformation temperature of 1080-1200°C, and the reduction amount is reasonably distributed to ensure that the blank is continuously rolled for 316LN large-size bars (φ65-φ160) after multiple single large deformations (the average single-pass reduction amount is controlled at 30-40mm), and the obtained bars are uniform and ultra-fine grained, the surface structure has no mixed crystal phenomenon, the grain size is ≥8 levels, and the grain size difference is ≤2 levels. The product performance can stably reach a post-fracture yield strength of ≥900MPa at -269°C, a tensile strength of ≥1200MPa, a post-fracture elongation of ≥32%, and a cross-sectional shrinkage of ≥40%, achieving the advantages of low production cost, high yield rate, high production efficiency, and stable mechanical properties at -269°C.

[0017] Therefore, the present invention has the characteristics of obtaining ultrafine grain structure and low temperature stable mechanical property rod. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the metallographic structure diagram of the final finished round steel bar of Example 1.

[0019] Figure 2 This is the metallographic structure diagram of Example 1 with a mixed crystal grain size.

[0020] Figure 3 This is a low temperature physical property test table of 316LN rod in Example 1. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the embodiments, but they are not intended to limit the present invention.

[0022] Embodiment 1:

[0023] Material: 316LN; Raw material ingot dimensions: 460*460*1800mm.

[0024] A method for continuously rolling ultra-low temperature resistant high-strength 316LN bars, comprising the following steps:

[0025] Step 1: Heat the 460*460*1800mm raw material ingot of 316LN material in a pusher-type heating furnace. The furnace body of the pusher-type heating furnace is 35 meters long and 4.5 meters wide. The interior of the heating furnace is divided into 5 heating areas, namely preheating section, heating section 1, heating section 2, heating section 3 and soaking section; the heating temperature of the preheating section is ≤650℃, the heating temperature of heating section 1 is 1120-1150℃, and the temperatures of heating sections 2-3 and soaking section are 1240-1260℃ respectively; and heating section 1, heating section 2, heating section 3 and soaking section are all heated by upper and lower burners; after heating, product A is obtained.

[0026] Step 2: Rough rolling of product A through a 750 reversible rolling mill, with 25 passes. The billet opening mill adopts a 750 reversible 2-roller rolling mill. During the rough rolling process, the surface thermal deformation temperature of the billet is 1080-1200℃, and the average reduction of a single rolling pass is 31mm. During the rough rolling process, the billet is reciprocated to achieve gradual deformation and cooling of the billet, ensuring that the surface temperature of the billet is not lower than 980℃ after the billet opening is completed, preventing the formation of a mixed crystal layer on the surface of the billet before continuous rolling, and obtaining product B.

[0027] Step 3: Product B is continuously rolled through 8 continuous rolling mills. During the continuous rolling process, the surface thermal deformation temperature of the steel billet is 1000-1050°C, and a finished round steel with a specification of φ65-160mm and a compression ratio greater than 10 can be obtained. In this embodiment, a φ100 316LN finished round steel is obtained.

[0028] The 8 continuous rolling mills include 4 650 rolling mills and 4 550 rolling mills which are alternately distributed horizontally and vertically. The motor powers of the 8 continuous rolling mills are 800KW, 800KW, 1000KW, 1000KW, 1000KW, 1000KW, 1250KW, and 1250KW respectively. The speeds of the 8 continuous rolling mills are 520 / 1200RPM, 520 / 1200RPM, 520 / 1200RPM, 520 / 1200RPM, 420 / 1000RPM, 420 / 1000RPM, 420 / 1000RPM, and 420 / 1000RPM respectively.

[0029] After testing, the 316LN finished round steel obtained in this embodiment is an ultrafine grain structure, and the metallographic structure picture is as follows: Figure 1 As shown, Figure 1 The grain size is level 10, there is no mixed crystal, and the grain size difference is level 2.

[0030] Take two sections of the same 316LN finished round steel and make samples for -269℃ tensile performance test. The test standard is GB / T228.4-1010. The test report results are as follows: Figure 3 At -269°C, the average tensile strength of the sample is 1589MPa, the average yield strength is 1091MPa, the average elastic modulus is 204.5GPa, the average elongation after fracture is 43%, and the average section shrinkage is 47%.

[0031] Comparative Example 1:

[0032] This comparative example is basically the same as Example 1, except that the heating temperatures of the heating stage 2, the heating stage 3, and the soaking stage are all 1200-1220°C; the metallographic structure of the finished round steel is shown in FIG. Figure 2 As shown, the grain size is level 7, there is mixed crystal, and the level difference is level 3.

[0033] Comparative Example 2:

[0034] This comparative example is basically the same as Example 1, except that the heating temperatures of heating stage 2, heating stage 3 and soaking stage are all 1280-1300; the grain size of the finished round steel finally obtained is level 4, with mixed crystals and a grade difference of 3 levels.

[0035] According to Example 1 and Comparative Examples 1-2, it can be seen that when the temperature is too high or too low, the product will have large grade differences and mixed crystals. The best heating temperature of heating stage 2, heating stage 3 and soaking stage is 1240-1260°C.

[0036] Comparative Example 3:

[0037] This comparative example is basically the same as Example 1, except that the number of rough rolling passes is 31, the average reduction of a single rolling pass is 26 mm, and the grain size of the final finished round steel is 5 levels, with mixed crystals and a grade difference of 2 levels.

[0038] Comparative Example 4:

[0039] This comparative example is basically the same as Example 1, except that the rough rolling process is 19 times, the average reduction of a single rolling process is 42 mm, and the grain size of the finished round steel is 7, with mixed crystals and large grade difference. Due to the large deformation, the core temperature rises greatly and the grain structure grows.

[0040] According to Example 1 and Comparative Examples 3-4, it can be seen that different reductions in thermal deformation have different effects on the uniformity of the finished product structure. When the reduction is too high or too low, the product will have large grade differences and mixed crystals. Therefore, the best rough rolling pass is 23-25 ​​passes.

[0041] It should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. For those skilled in the art, the technical solutions described in the above embodiments can be modified, or some of the technical features therein can be replaced by equivalents; and all these modifications and replacements should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for continuous rolling of ultra-low temperature resistant high-strength 316LN bars, characterized in that: The following steps are involved: Step 1, heating the raw material ingot in a heating furnace, the heating furnace is divided into a preheating section, a heating section 1, a heating section 2, a heating section 3 and a soaking section, wherein the heating temperature of the preheating section is ≤650°C, the heating temperature of the heating section 1 is 1120-1150°C, the heating temperatures of the heating section 2, the heating section 3 and the soaking section are all 1240-1260°C, and product A is obtained; Step 2: Rough rolling of product A, with 23-25 ​​passes, to obtain product B; Step 3: Continuously roll product B to obtain finished round steel with a specification of φ65-160mm.

2. The method for continuous rolling of ultra-low temperature resistant high-strength 316LN bars according to claim 1, characterized in that: In step 1, heating section 1, heating section 2, heating section 3 and soaking section are all heated by upper and lower burners.

3. The method for continuous rolling of ultra-low temperature resistant high-strength 316LN bars according to claim 1, characterized in that: In step 2, during the rough rolling process, the surface thermal deformation temperature of the steel billet is 1080-1200°C.

4. The method for continuous rolling of ultra-low temperature resistant high-strength 316LN bars according to claim 1, characterized in that: In step 2, after the rough rolling is completed, the surface temperature of the steel billet is not less than 980°C.

5. The method for continuous rolling of ultra-low temperature resistant high-strength 316LN bars according to claim 1, characterized in that: In step 2, the average reduction in a single rolling pass is 30-40 mm.

6. The method for continuous rolling of ultra-low temperature resistant high-strength 316LN bars according to claim 1, characterized in that: In step three, during the continuous rolling process, the surface thermal deformation temperature of the steel billet is 1000-1050°C.

7. The method for continuous rolling of ultra-low temperature resistant high-strength 316LN bars according to claim 1, characterized in that: In step three, eight continuous rolling mills are used for continuous rolling, and the eight continuous rolling mills include four 650 rolling mills and four 550 rolling mills that are alternately distributed horizontally and vertically.

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