High-toughness medium-carbon ferrite-pearlite type non-quenched and tempered steel and method for manufacturing the same

Abstract

The application discloses a high-strength and high-toughness medium-carbon ferrite-pearlite type non-quenched and tempered steel and a preparation method thereof. The chemical component of the steel is as follows: C: 0.40-0.48%; Si: 0.20-0.60%; Mn: 1.20-1.60%; Ti: 0.010-0.020%; Zr: 0.005-0.020%; P: less than or equal to 0.025%; S: less than or equal to 0.015%; N: 0.010-0.025%, and the rest is Fe and inevitable impurities. The preparation method comprises the following steps: continuous casting of a large square billet, heating in a heating furnace, rough rolling, finish rolling, air cooling on a cooling bed, sawing and bundling. The non-quenched and tempered steel can improve the strength and toughness matching while reducing the cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of non-quenched and tempered steel, and particularly relates to a high-strength and high-toughness medium-carbon ferrite-pearlite type non-quenched and tempered steel and a preparation method thereof. BACKGROUND

[0002] Non-quenched and tempered steel is a kind of steel grade that is added with a certain amount of micro-alloying elements on the basis of medium and high carbon steel, and is controlled by rolling (forging) and controlled cooling, so that the mechanical properties of the steel grade can be equivalent to those of quenched and tempered steel after rolling (forging) without quenching and tempering process. Under the background of double-carbon, using non-quenched and tempered steel which is energy-saving, emission-reducing and lower in cost to replace quenched and tempered steel has become an important trend of the current steel industry. The research and use of non-quenched and tempered steel can further develop the energy utilization and pollution control technology in the steel production process, and have important guiding significance for promoting the transformation and upgrading of the steel industry, and will certainly set off a trend of energy saving and emission reduction.

[0003] In medium-carbon non-quenched and tempered steel, the addition of Ti element can further reduce the cost and has a very broad market prospect, but Ti has a relatively active chemical property and can generate liquid-precipitated TiN and some relatively coarse Ti-containing inclusions at high temperature, which has an adverse effect on the performance of the steel. Zr, as an element adjacent to Ti and having similar physical and chemical properties to Ti, can refine and modify the inclusions in Ti steel. Zr element is initially used for deoxidation and modified sulfide in the steelmaking process, and in modern steelmaking technology, more attention is paid to its addition as a micro-alloying element to form carbonitride and perform precipitation and deposition. The application of Ti and Zr composite micro-alloying provides a new idea for realizing the matching of strength and toughness of non-quenched and tempered steel.

[0004] Current relevant patents focus on the micro-alloying design of non-quenched and tempered steel. For example, the patent with publication number CN106119711A discloses a V-Ti micro-alloyed non-quenched and tempered steel bar and a manufacturing method thereof. By adding V: 0.05-0.30%, Ti: 0.010-0.060%, and controlling N: 0.010-0.035%, the tensile strength is ≥900 MPa, and the yield strength is ≥640 MPa. The patent with publication number CN111748751A discloses a non-quenched and tempered steel with multiple elements added, including V, Nb, Ti, Ni, Mo, N and the like. The tensile strength is 900-1150 MPa, the yield strength is ≥600 MPa, and the impact energy A Ku≥30J. The above patents solve the problem of matching strength and toughness to some extent, but the composition is complex and the cost is high due to the addition of micro-alloying elements. The publication number CN107312908A adopts the method of adding Zr element to the steel to control the morphology of MnS, adopts Zr deoxidization, and utilizes ZrO2 as a heterogeneous nucleation core of MnS in the solidification process to achieve the purpose of refining MnS, but zirconium dioxide is easy to gather and form brittle inclusions, which will cause certain harm to the performance of the steel, and it does not involve the beneficial effect of Zr element as a micro-alloying element. SUMMARY

[0005] The present application provides a high-strength and high-toughness medium-carbon ferrite-pearlite type non-quenched and tempered steel and a preparation method thereof, which can improve the matching of strength and toughness while reducing the cost.

[0006] To solve the above technical problems, the technical scheme provided by the present application is as follows:

[0007] A high-strength and high-toughness medium-carbon ferrite-pearlite type non-quenched and tempered steel, comprising the following components: C: 0.40-0.48%; Si: 0.20-0.60%; Mn: 1.20-1.60%; Ti: 0.010-0.020%; Zr: 0.005-0.020%; P≤0.025%; S≤0.015%; N: 0.010-0.025%, and the remainder being Fe and unavoidable impurities.

[0008] Preferably, the high-strength and high-toughness medium-carbon ferrite-pearlite type non-quenched and tempered steel according to the present application has the following chemical components: C: 0.43-0.46%; Si: 0.30-0.45%; Mn: 1.20-1.30%; Ti: 0.015-0.018%; Zr: 0.008-0.012%; P≤0.010%; S≤0.005%; N: 0.013-0.018%, and the remainder being Fe and unavoidable impurities.

[0009] The production method of the high-strength and high-toughness medium-carbon ferrite-pearlite type non-quenched and tempered steel according to the present application is as follows: continuous casting large square billet→heating furnace heating→rough rolling→finish rolling→cold bed air cooling→saw cutting→bundling; wherein the heating time of the continuous casting billet is 3-4h, and the soaking temperature is 1150-1200℃; the rough rolling opening temperature is 1150-1200℃, and the finish rolling opening temperature is 900-1000℃.

[0010] The effects of each alloying element and the specific content in the high-strength and high-toughness medium-carbon ferrite-pearlite type non-quenched and tempered steel according to the present application are as follows:

[0011] C: the most important element for the strength and hardness of the steel, but the content should be controlled, otherwise the plasticity and toughness of the steel will be seriously affected, the content of C in the medium carbon non-quenched and tempered steel is generally not allowed to exceed 0.5%, the content of C in the ferrite-pearlite non-quenched and tempered steel in the application is 0.40%-0.48%, wherein the content of C can be 0.40%, 0.41%, 0.42%, 0.43%, 0.44%, 0.45%, 0.46%, 0.47% or 0.48%.

[0012] Mn is one of the most important elements of the medium carbon non-quenched and tempered steel, and the addition of an appropriate amount of Mn in the steel is beneficial to the strength and toughness of the non-quenched and tempered steel. However, it should be noted that the content of Mn should not be too high, otherwise the plasticity and toughness of the steel will be deteriorated due to the generation of bainite in the quenched structure, and the content of Mn in the medium carbon non-quenched and tempered steel is generally not more than 1.5%, and the content of Mn in the designed steel is 1.20%-1.60%.

[0013] Si exists in the form of solid solution in the steel, and is an important ferrite strengthening element, and like C element, excessive Si will seriously reduce the toughness of the steel, and the content of Si in the designed steel should be 0.20%-0.60%.

[0014] Ti has a low solid solubility in the steel, is easy to precipitate in austenite, is pinned at the grain boundary, prevents grain growth and recrystallization, and can play a role in refining the grain, Ti is also a strong deoxidizer in the steel, can make the internal structure of the steel dense, reduce the aging sensitivity and cold brittleness, and improve the welding performance, in addition, due to the low solid solubility, Ti is easy to appear in the form of interphase precipitation in the process of austenite to ferrite transformation, and improves the high temperature strength, and the content of Ti in the designed steel is 0.010%-0.020%.

[0015] Zr has a stronger binding force with S and N than Ti, can reduce the loss of Ti at the high temperature stage, reduce the activity of Ti and C in ferrite, and improve the solid solubility of Ti in austenite, and Zr can be used as an auxiliary element of the steel, and the effect of Ti can be fully utilized, and the content of Zr in the designed steel is 0.005%-0.020%.

[0016] For the medium carbon non-quenched and tempered steel, S is easy to segregate in the steel, and deteriorates the quality of the steel, and for the shaft rod type parts, the high content of S will affect the quality of the later plating process, therefore, the content of S in the designed steel is controlled to be ≤0.015%.

[0017] P element can form micro-segregation when the steel liquid solidifies, and then is aggregated at the grain boundary when heated at high temperature, so that the brittleness of the steel is significantly increased, therefore, the content of P in the designed steel is controlled to be ≤0.025%.

[0018] The technical scheme of the application has the following beneficial technical effects:

[0019] 1. The chemical composition of the present application is designed to improve the strength and toughness level by adding basic elements and micro-alloying elements Ti and Zr without using V micro-alloying element. Similar to Ti, Zr can also form fine ZrN at high temperature stage, and the particle size of ZrN is not greater than 100 nm. The addition of Zr reduces the loss of Ti element at high temperature stage, avoids the generation of large size TiN, and the rolling process can increase dislocation and refine grains. Most of the remaining Ti and part of Zr precipitate to strengthen soft ferrite after phase transformation and phase change. The production method has the advantages of simple control, low manufacturing cost and strong operability.

[0020] 2. The non-quenched and tempered steel provided by the present application has excellent mechanical properties, the tensile strength is 900-950 MPa, the reduction of area is 55-60%, and the U-shaped notch impact value is 60-70 J; the microstructure is ferrite + pearlite, the structure is uniform and fine, and the uniformity is good, the austenite grain size at the 1 / 2 radius position of the bar can reach 8.5 grade, and the grain size difference between the core and the surface can be as low as 0.5 grade. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is the optical microstructure picture of the non-quenched and tempered steel of example 1 of the present application.

[0022] Figure 2 It is the grain size statistical diagram of the non-quenched and tempered steel of example 1 of the present application.

[0023] Figure 3 It is the optical microstructure picture of the non-quenched and tempered steel of example 2 of the present application.

[0024] Figure 4 It is the grain size statistical diagram of the non-quenched and tempered steel of example 2 of the present application.

[0025] Figure 5 It is the optical microstructure picture of the non-quenched and tempered steel of example 3 of the present application.

[0026] Figure 6 It is the grain size statistical diagram of the non-quenched and tempered steel of example 3 of the present application.

[0027] Figure 7 It is the sulfide and carbonitride particle size distribution diagram of the non-quenched and tempered steel of example 1 of the present application.

[0028] Figure 8 It is the inclusion distribution diagram of the non-quenched and tempered steel of example 1 of the present application. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Embodiment 1

[0030] The element composition of the non-modified steel in this embodiment is as follows in terms of mass percentage: C: 0.44%; Si: 0.24%; Mn: 1.28%; Ti: 0.016%; Zr: 0.009%; P: 0.006%; S: 0.002%; N: 0.0146%, and the remainder is Fe and unavoidable impurities.

[0031] The production method of the non-modified steel in this embodiment is as follows: continuous casting of large square billets, heating in a heating furnace, rough rolling, finish rolling, air cooling on a cooling bed, sawing and bundling; wherein the heating time of the continuous casting billets is 3.5 h, the soaking temperature is 1200℃, the rough rolling starting temperature is 1200℃, and the finish rolling starting temperature is 950℃.

[0032] The mechanical properties of the non-modified steel in this embodiment are shown in Table 1.

[0033] The non-modified steel in this embodiment is cut into small test blocks of 10mmx10mmx10mm, the surface of the small test blocks is polished and polished, and then etched with nitric acid alcohol, and the microstructure is observed by optical microscope (OM), the metallographic structure is ferrite + pearlite, the proportion of pearlite is 85%, and the proportion of ferrite is 15%; the structure is uniform and small, and the reticular ferrite is surrounded around the uniform-sized pearlite, as shown in Figure 1 .

[0034] The grain size of the non-modified steel in this embodiment is counted, and the results are shown in Figure 2 , it can be seen that the austenite grain size at the 1 / 2 radius position of the bar can reach 8.5 grade, and the grain size difference between the core and the surface can be as low as 0.5 grade.

[0035] The inclusions in 100 fields of view of the non-modified steel in this embodiment are photographed by scanning electron microscope, and the particle size distribution of sulfides and carbonitrides is counted, and the results are shown in Figure 7 and Figure 8 , it can be seen that the inclusions are uniform in size and shape, and the smaller size sulfides and carbonitrides are uniformly distributed in the non-modified steel; the number and shape of the inclusions in the steel are counted, the A-type inclusions are ≤0 grade, the B-type inclusions are ≤0.5 grade; the C-type inclusions are ≤0.5, the D-type inclusions are ≤1, and the Ds-type inclusions are ≤0.5. Embodiment 2

[0036] The element composition of the non-modified steel in the embodiment is as follows in terms of mass percentage: C: 0.46%; Si: 0.24%; Mn: 1.32%; Ti: 0.017%; Zr: 0.009%; P: 0.005%; S: 0.002%; N: 0.0152%, and the remainder is Fe and inevitable impurities.

[0037] The production method of the non-modified steel in the embodiment is as follows: continuous casting of a large square billet, heating in a heating furnace, rough rolling, finish rolling, air cooling on a cooling bed, sawing, and bundling; wherein the heating time of the continuous casting billet is 3.5 h, the soaking temperature is 1160℃, the rough rolling starting temperature is 1170℃, and the finish rolling starting temperature is 930℃.

[0038] The mechanical properties of the non-modified steel in the embodiment are shown in Table 1.

[0039] The non-modified steel in the embodiment is cut into small test blocks of 10mmx10mmx10mm, the surface of the small test blocks is polished and polished, and then etched with nitric acid alcohol, and the microstructure is observed by optical microscope (OM), the metallographic structure is ferrite + pearlite, the proportion of pearlite is 83%, and the proportion of ferrite is 17%; the structure is uniform and small, and the reticular ferrite is surrounded around the uniform size pearlite, as shown in Figure 3 .

[0040] The grain size of the non-modified steel in the embodiment is counted, and the results are shown in Figure 4 It can be seen that the austenite grain size at the 1 / 2 radius position of the bar can reach 8.5 level, and the grain size range of the core and surface can be as low as 0.5 level.

[0041] The A-type inclusions in the steel are ≤0 level, the B-type inclusions are ≤0.5 level, the C-type inclusions are ≤0.5, the D-type inclusions are ≤1, and the Ds-type inclusions are ≤0.5; the sulfide and carbonitride inclusions are small in size and uniformly distributed in the non-modified steel. Example 3

[0042] The element composition of the non-modified steel in the embodiment is as follows in terms of mass percentage: C: 0.46%; Si: 0.30%; Mn: 1.32%; Ti: 0.017%; Zr: 0.005%; P: 0.006%; S: 0.002%; N: 0.0141%, and the remainder is Fe and inevitable impurities.

[0043] The production method of the non-modified steel in the embodiment is as follows: continuous casting of a large square billet, heating in a heating furnace, rough rolling, finish rolling, air cooling on a cooling bed, sawing, and bundling; wherein the heating time of the continuous casting billet is 3.5 h, the soaking temperature is 1200℃, the rough rolling starting temperature is 1200℃, and the finish rolling starting temperature is 950℃.

[0044] The mechanical properties of the non-modified steel in the embodiment are shown in Table 1.

[0045] The non-quenched and tempered steel of the present example is cut into small test blocks of 10 mm x 10 mm x 10 mm, and after polishing and polishing treatment on the surface of the small test blocks, nitric acid alcohol is used for etching, and the microstructure thereof is observed by optical microscope (OM), the metallographic structure of which is ferrite + pearlite, the proportion of pearlite is 85%, and the proportion of ferrite is 15%; the structure is uniform and fine, and the reticular ferrite is surrounded around the uniformly sized pearlite, as shown in Figure 5 .

[0046] The grain size of the non-quenched and tempered steel of the present example is counted, and the result is shown in Figure 6 , it can be seen that the austenite grain size at the 1 / 2 radius position of the bar can reach 8.5 grade, and the grain size difference of the core and surface can be as low as 0.5 grade.

[0047] The A-type inclusions in the steel are ≤0 grade, the B-type inclusions are ≤0.5 grade; the C-type inclusions are ≤0.5, the D-type inclusions are ≤1, and the Ds-type inclusions are ≤0.5; the sulfide and carbonitride inclusions are small in size and uniformly distributed in the non-quenched and tempered steel. Example 4

[0048] The element composition of the non-quenched and tempered steel of the present example is as follows in mass percentage: C: 0.43%; Si: 0.36%; Mn: 1.44%; Ti: 0.019%; Zr: 0.008%; P: 0.008%; S: 0.003%; N: 0.0179%, and the rest is Fe and unavoidable impurities.

[0049] The production method of the non-quenched and tempered steel of the present example is as follows: continuous casting large square billet→heating furnace heating→rough rolling→finish rolling→cold bed air cooling→sawing→bundling; wherein, the heating time of the continuous casting billet is 4h, the soaking temperature is 1150℃, the rough rolling opening temperature is 1150℃, and the finish rolling opening temperature is 900℃.

[0050] The mechanical properties of the non-quenched and tempered steel of the present example are shown in Table 1.

[0051] The metallographic structure of the non-quenched and tempered steel of the present example is ferrite + pearlite, the proportion of pearlite is 84%, and the proportion of ferrite is 16%; the structure is uniform and fine, and the reticular ferrite is surrounded around the uniformly sized pearlite; the austenite grain size at the 1 / 2 radius position of the bar can reach 8.0 grade, and the grain size difference of the core and surface can be as low as 0.5 grade. The A-type inclusions in the steel are ≤0 grade, the B-type inclusions are ≤0.5 grade; the C-type inclusions are ≤0.5, the D-type inclusions are ≤1, and the Ds-type inclusions are ≤0.5; the sulfide and carbonitride inclusions are small in size and uniformly distributed in the non-quenched and tempered steel. Example 5

[0052] The element composition of the non-modified steel in this embodiment is as follows in terms of mass percentage: C: 0.40%; Si: 0.42%; Mn: 1.60%; Ti: 0.020%; Zr: 0.017%; P: 0.022%; S: 0.008%; N: 0.0211%, and the remainder is Fe and inevitable impurities.

[0053] The production method of the non-modified steel in this embodiment is as follows: continuous casting of a large square billet, heating in a heating furnace, rough rolling, finish rolling, air cooling on a cooling bed, sawing and bundling; wherein the heating time of the continuous casting billet is 3 h, the soaking temperature is 1200℃, the rough rolling starting temperature is 1200℃, and the finish rolling starting temperature is 1000℃.

[0054] The mechanical properties of the non-modified steel in this embodiment are shown in Table 1.

[0055] The metallographic structure of the non-modified steel in this embodiment is ferrite + pearlite, with the proportion of pearlite being 85% and the proportion of ferrite being 15%; the structure is uniform and fine, with reticular ferrite surrounding the uniformly sized pearlite; the austenite grain size at the 1 / 2 radius position of the bar can reach level 8.5, and the grain size difference between the core and the surface can be as low as level 0.5; the A-type inclusions in the steel are ≤ level 0, the B-type inclusions are ≤ level 0.5, the C-type inclusions are ≤ 0.5, the D-type inclusions are ≤ 1, and the Ds-type inclusions are ≤ 0.5; the sulfide and carbonitride inclusions are small in size and uniformly distributed in the non-modified steel. Example 6

[0056] The element composition of the non-modified steel in this embodiment is as follows in terms of mass percentage: C: 0.42%; Si: 0.45%; Mn: 1.30%; Ti: 0.018%; Zr: 0.012%; P: 0.010%; S: 0.004%; N: 0.0132%, and the remainder is Fe and inevitable impurities.

[0057] The production method of the non-modified steel in this embodiment is as follows: continuous casting of a large square billet, heating in a heating furnace, rough rolling, finish rolling, air cooling on a cooling bed, sawing and bundling; wherein the heating time of the continuous casting billet is 3 h, the soaking temperature is 1180℃, the rough rolling starting temperature is 1180℃, and the finish rolling starting temperature is 900℃.

[0058] The mechanical properties of the non-modified steel in this embodiment are shown in Table 1.

[0059] The metallographic structure of the non-quenched and tempered steel of the embodiment is ferrite + pearlite, the proportion of pearlite is 83%, and the proportion of ferrite is 17%; the structure is uniform and fine, and the reticular ferrite is surrounded around the uniformly sized pearlite; the austenite grain size at the 1 / 2 radius position of the bar can reach 8.5 level, and the core-surface grain size difference can be as low as 0.5 level. The A type inclusions in the steel are ≤0 level, the B type inclusions are ≤0.5 level, the C type inclusions are ≤0.5, the D type inclusions are ≤1, and the Ds type inclusions are ≤0.5; the sulfide and carbonitride inclusions are small in size and uniformly distributed in the non-quenched and tempered steel. Embodiment 7

[0060] The element composition of the non-quenched and tempered steel of the embodiment is as follows in terms of mass percentage: C: 0.48%; Si: 0.60%; Mn: 1.51%; Ti: 0.015%; Zr: 0.020%; P: 0.017%; S: 0.011%; N: 0.0248%, and the rest is Fe and inevitable impurities.

[0061] The production method of the non-quenched and tempered steel of the embodiment is as follows: continuous casting large square billet → heating furnace heating → rough rolling → finish rolling → cold bed air cooling → sawing → baling; wherein, the heating time of the continuous casting billet is 4 h, the soaking temperature is 1150℃, the rough rolling starting temperature is 1150℃, and the finish rolling starting temperature is 1000℃.

[0062] The mechanical properties of the non-quenched and tempered steel of the embodiment are shown in Table 1.

[0063] The metallographic structure of the non-quenched and tempered steel of the embodiment is ferrite + pearlite, the proportion of pearlite is 82%, and the proportion of ferrite is 18%; the structure is uniform and fine, and the reticular ferrite is surrounded around the uniformly sized pearlite; the austenite grain size at the 1 / 2 radius position of the bar can reach 8.5 level, and the core-surface grain size difference can be as low as 0.5 level. The A type inclusions in the steel are ≤0 level, the B type inclusions are ≤0.5 level, the C type inclusions are ≤0.5, the D type inclusions are ≤1, and the Ds type inclusions are ≤0.5; the sulfide and carbonitride inclusions are small in size and uniformly distributed in the non-quenched and tempered steel. Embodiment 8

[0064] The element composition of the non-quenched and tempered steel of the embodiment is as follows in terms of mass percentage: C: 0.45%; Si: 0.20%; Mn: 1.56%; Ti: 0.010%; Zr: 0.010%; P: 0.011%; S: 0.006%; N: 0.0128%, and the rest is Fe and inevitable impurities.

[0065] The production method of the non-quenched and tempered steel of the embodiment is as follows: continuous casting large square billet → heating furnace heating → rough rolling → finish rolling → cold bed air cooling → sawing → baling; wherein, the heating time of the continuous casting billet is 3.5 h, the soaking temperature is 1200℃, the rough rolling starting temperature is 1200℃, and the finish rolling starting temperature is 950℃.

[0066] The mechanical properties of the non-quenched and tempered steel of the embodiment are shown in Table 1.

[0067] The metallographic structure of the non-quenched and tempered steel of the embodiment is ferrite + pearlite, the proportion of pearlite is 84%, and the proportion of ferrite is 16%; the structure is uniform and fine, and the network ferrite is surrounded around the uniformly sized pearlite; the austenite grain size at the 1 / 2 radius position of the bar can reach 8.5 grade, and the grain size difference between the core and the surface can be as low as 0.5 grade; the A type inclusions in the steel are ≤0 grade, the B type inclusions are ≤0.5 grade; the C type inclusions are ≤0.5, the D type inclusions are ≤1, and the Ds type inclusions are ≤0.5; the sulfide and carbonitride inclusions are small in size and uniformly distributed in the non-quenched and tempered steel.

[0068] Table 1: Mechanical property test results of non-quenched and tempered steel of each embodiment

[0069]

[0070] The above embodiments are only used to illustrate the present application and not to limit the technical solutions described in the present application; therefore, although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present application can still be modified or replaced equivalently; and all technical solutions and improvements that do not deviate from the spirit and scope of the present application should be covered within the scope of the claims of the present application.

Claims

1. A high-toughness medium-carbon ferrite-pearlite type non-quenched and tempered steel, characterized in that: By mass percent, the following components are included: C: 0.40-0.48%; Si: 0.20-0.60%; Mn: 1.20-1.60%; Ti: 0.010-0.020%; Zr: 0.005-0.020%; P≤0.025%; S≤0.015%; N: 0.010-0.025%, the rest being Fe and inevitable impurities; The microstructure of the non-quenched and tempered steel is ferrite + pearlite, the pearlite accounts for 80-85%, the ferrite accounts for 15-20%, the austenite grain size at the 1 / 2 radius position of the bar reaches 8.5 grade, and the heart-surface grain size difference is as low as 0.5 grade; The non-quenched and tempered steel has a tensile strength of 900-950 MPa, a reduction of area of 55-60%, and a U-shaped notch impact value of 60-70 J; The production method of the non-quenched and tempered steel comprises the following steps: continuous casting of a large square billet, heating in a heating furnace, rough rolling, finish rolling, air cooling on a cooling bed, sawing, and bundling; wherein the heating time of the continuous casting large square billet is 3-4 h, and the soaking temperature is 1150-1200℃.

2. A high tough medium carbon ferrite-pearlite type non-quenched and tempered steel according to claim 1, characterized in that: The chemical components by mass percent are: C: 0.43-0.46%; Si: 0.30-0.45%; Mn: 1.20-1.30%; Ti: 0.015-0.018%; Zr: 0.008-0.012%; P≤0.010%; S≤0.005%; N: 0.013-0.018%, the rest being Fe and inevitable impurities.

3. The high tough medium carbon ferrite-pearlite type non-quenched tempered steel according to claim 1, characterized in that, The rough rolling opening rolling temperature is 1150-1200℃.

4. The high tough medium carbon ferrite-pearlite type non-quenched tempered steel according to claim 1, characterized in that, The finish rolling opening rolling temperature is 900-1000℃.

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